ENVIRONMENTAL IMPACT ASSESSMENT REPORT ETALIN H. E

ENVIRONMENTAL IMPACT ASSESSMENT REPORT

ETALIN H. E. PROJECT (3097 MW)

JANUARY 2015

Prepared by

R. S. Envirolink Technologies Pvt. Ltd. 402, Radisson Suites Commercial Plaza,

B-Block, Sushant Lok-I, Gurgaon

Ph. +91-124-4295383 : www.rstechnologies.co.in

for

Etalin Hydro Electric Power Company Limited (EHEPCL)

http://www.rstechnologies.co.in/

Scheme for Accreditation of EIA Consultant Organizations

List of Accredited Consultant Organizations (Alphabetically

*denotes Provisionally Accredited Consultants

List of Accredited

S. No.

Consultant Organization

1

Aarvee Associates Architects Engineers & Consultants Pvt. Ltd. * Address: 8-2-5, Ravula Residency

Srinagar Colony, Hyderabad

E.mail: [email protected], [email protected]

[email protected]

Tel.: 040-23737633

Conditions apply

2

ABC Techno Labs India Private Limited known as ABC Environ Solutions Pvt. Ltd.) Address: No. 2, 2

nd Street, Thangam Colony, Anna

Nagar West, Chennai – 600040

E-mail:[email protected],

[email protected]


Alphabetically)/ Rev. 26/ Jan. 08, 2015

List of Accredited EIA Consultant Organizations – 1

(as on January 08, 2015)

Scope of Accreditation

As per NABET Scheme

Sector Number

Name of Sector

Architects Engineers & Consultants

[email protected], 34

Highways, Railways, transport

terminals, mass rapid transport

system

(formerly

Street, Thangam Colony, Anna

1 Mining of minerals (Opencast only)

Mining (Open cast and Underground)

3 Irrigation projects only

4 Thermal Power Plant

8 Metallurgical industries (sec. ferrous

only)

9 Cement Plants

10 Petroleum refining industry

15 Leather/skin/hide processing

Page 1

166

Accreditation

Project or Activity as per Schedule of MoEF Notification dated

September 14, 2006 and subsequent amendments

Category

Highways, Railways, transport

terminals, mass rapid transport A 7 (f)

A 1 (a) (i)

B

A 1 (c )

A 1 (d)

ferrous B 3 (a)

A 3 (b)

A 4 (a)

processing A 4 (f)


List of Accredited Consultant Organizations (Alphabetically

*denotes Provisionally Accredited Consultants

S. No.

Consultant Organization

E.mail:[email protected],

[email protected]

Tel.: 0291- 2706098, 09829021098

** Though the EIA Coordinator for this sector was

found suitable for Cat. A, however, the organization as

a whole was accredited for Cat. B, in view of their

having scored less than 60% marks in Office

Assessment. They can take up projects in this sector

only for Cat. B as an organization.

Conditions apply

120

R. S. Envirolinks Technologies Pvt. Ltd. * Address: 402, Radisson Suites Commercial Plaza, B

Block, Sushant Lok 1, Gurgaon – 122009

e. mail: [email protected] Tel.: 0124 – 4295383

09810136853

Conditions apply


Alphabetically)/ Rev. 26/ Jan. 08, 2015

Scope of Accreditation

As per NABET Scheme

Sector Number

Name of Sector

this sector was

found suitable for Cat. A, however, the organization as

a whole was accredited for Cat. B, in view of their

having scored less than 60% marks in Office

Assessment. They can take up projects in this sector

402, Radisson Suites Commercial Plaza, B

1 Mining of minerals (Open cast only)

3 River Valley, Hydel, Drainage and

Irrigation projects

27

Oil & gas transportation pipeline

(crude and refinery/ petrochemical

products), passing through national

parks/ sanctuaries/coral reefs

/ecologically sensitive Areas including

LNG terminal

33 Jetties only

34 Railways only

40 (i) Automobile and Auto Components

Page 92

Accreditation

Project or Activity as per Schedule of MoEF Notification dated

September 14, 2006 and subsequent amendments

Category

A 1 (a) (i)

River Valley, Hydel, Drainage and A 1 (c)

Oil & gas transportation pipeline

(crude and refinery/ petrochemical

passing through national

parks/ sanctuaries/coral reefs

/ecologically sensitive Areas including

A 6 (a)

B 7 (e)

A 7 (f)

- -

CONTENTS

CHAPTER 1: INTRODUCTION

1.1 GENERAL 1.1

1.2 ETALIN H.E. PROJECT 1.1

1.2.1 Purpose of the Study 1.1

1.2.2 Scope of the Study 1.1

1.3 CASCADE DEVELOPMENT PLAN 1.3

1.4 STUDY OF ALTERNATIVES 1.3

1.4.1 Alternative Layouts 1.3

1.4.1.1 Layout by CEA 1.4

1.4.1.2 Layout by NHPC 1.5

1.4.1.3 Alternatives Studies in the Present DPR 1.7

1.5 POLICY, LEGAL & ADMINISTRATIVEE FRAMEWORK 1.10

1.6 EIA NOTIFICATION, 2006 1.12

1.7 FOREST CLEARANCE 1.13

1.8 STATE R&R POLICY 1.13

1.9 DISCLOSURE BY THE CONSULTANT 1.13

1.10 OUTLINE OF THE REPORT 1.13

CHAPTER 2: PROJECT DESCRIPTION & INFRASTRUCTURE

2.1 PROJECT LOCATION & ACCESSIBILITY 2.1

2.2 SALIENT FEATURES OF THE PROJECT 2.1

2.3 PROJECT COMPONENTS 2.2

2.3.1 Dri Limb 2.2

2.3.1.1 Dam Complex 2.2

2.3.1.2 Head Race Tunnel 2.2

2.3.1.3 Surge Shaft & Pressure Shafts 2.2

2.3.2 Talo (Tangon) Limb 2.3

2.3.2.1 Dam Complex 2.3

2.3.2.2 Head Race Tunnel 2.3

2.3.3 Components at Power House 2.4

2.3.3.1 Dri Dam-toe Power House 2.4

2.3.3.2 Talo (Tangon) Dam-toe Power House 2.4

2.4 INFRASTRUCTURE FACILITIES 2.14

2.4.1 Approach to the Project 2.14

2.4.1.1 Transportation by Railway 2.14

2.4.1.2 Transportation by Waterway 2.14

2.4.1.3 Transportation by air 2.14

2.4.1.4 Transportation by road 2.15

2.4.2 Project Roads 2.15

2.4.3 Project Bridges 2.15

2.4.4 Construction of new bridges 2.17

2.4.5 Project Colonies 2.17

2.4.5.1 Owner’s building and colonies 2.18

2.4.5.2 Contractors colonies and buildings 2.19

2.4.6 Workshops and Parking Space 2.19

2.4.7 Stores and Warehouses 2.19

2.4.8 Penstock Fabrication Yard 2.19

2.4.9 Aggregate Processing Plants/Batching and Mixing Plants 2.20

2.4.10 Quarries/Borrow Areas 2.20

2.4.11 Muck Disposal Areas 2.21

2.4.12 Explosive Magazine 2.21

2.4.13 Land Requirement 2.21

2.4.13.1 Land Required Permanently 2.23

2.4.13.2 Land Required on Lease or Temporary Basis 2.23

2.4.14 Construction Power 2.24

2.4.15 Tele-Communication and Other Facilities 2.24

2.4.16 Security and Safety 2.24

CHAPTER 3: METHODOLOGY

3.1 INTRODUCTION 3.1

3.2 METHODOLOGY 3.1

3.2.1 Study Area 3.3

3.2.2 Scoping Matrix 3.3

3.2.3 Baseline Status Primary Data Collection 3.3

3.2.4 Secondary Data 3.3

3.2.4.1 Physiography 3.3

3.2.4.2 Geology 3.5

3.2.4.3 Meteorology 3.5

3.2.4.4 Hydrology 3.6

3.2.4.5 Forest Types & Forest Cover 3.6

3.2.4.6 Infrastructure Facilities 3.6

3.2.5 Primary Data Collection –Field Surveys 3.6

3.2.5.1 Soil 3.7

3.2.5.2 Ambient Air Quality 3.8

3.2.5.3 Ambient Noise levels & Traffic Density 3.9

3.2.5.4 Land use / land cover 3.10

3.2.5.5 Vegetation Community Structure/ Floristic Surveys 3.11

3.2.5.6 Faunal Elements 3.13

3.2.5.7 Water Quality 3.15

3.2.5.8 Aquatic Ecology 3.16

3.2.5.9 Socio-economic Surveys 3.18

3.3 IMPACT ASSESSMENT & MITIGATION MEASURES 3.20

3.4 ENVIRONMENTAL MANAGEMENT PLAN 3.20

3.5 ENVIRONMENTAL MONITORIG PROGRAMME 3.21

CHAPTER 4: HYDROLOGY

4.1 GENERAL 4.1

CHAPTER 5: GEOLOGY

5.1 GENERAL 5.1

CHAPTER 6: ENVIRONMENTAL BASELINE STATUS: PHYSICO-CHEMICAL

PARAMETERS


6.2 DRAINAGE 6.1

6.3 PHYSIOGRAPHY 6.1

6.4 SOIL 6.2

6.4.1 Soil Taxonomic Classification 6.2

6.4.2 Soil Fertility Status 6.6

6.5 AIR ENVIRONMENT 6.6

6.5.1 Ambient Air Quality 6.11

6.6 NOISE & TRAFFIC 6.12

6.6.1 Noise Level 6.12

6.6.2 Traffic Density 6.13

CHAPTER 7: ENVIRONMENTAL BASELINE STATUS: BIOLOGICAL

RESOURCES


7.2 LAND USE/ LAND COVER 7.1

7.3 FOREST TYPES 7.4

7.3.1 Tropical Vegetation 7.4

7.3.1.1 Upper Assam Valley Tropical Evergreen Forest (Tropical

Evergreen Forest) (1B/C2) 7.4

7.3.1.2 Eastern sub-montane Semi-evergreen Forest (Tropical

Semi-evergreen forest) – (2B/C1b) 7.4

7.3.2 East Himalayan moist mixed deciduous forests (Sub tropical

Broadleaved Forests) – (3/C3b) 7.5

7.3.3 Assam Sub-tropical Pine Forests – (9/C2) 7.5

7.3.4 East Himalayan Wet Temperate Forests (Temperate Broadleaved

Forests) – (11B/C1) 7.5

7.3.5 East Himalayan Mixed Coniferous Forest (Temperate Conifer

Forests) – (12/C3a) 7.6

7.3.6 Alpine Pastures (Alpine Forests) – 15/C3) 7.6

7.3.7 Secondary Forests (1B/2S) 7.6

7.3.7.1 Degraded Forests 7.6

7.3.7.2 Bamboo and Musa Forests 7.6

7.3.7.3 Grasslands 7.6

7.4 FLORISTICS 7.7

7.4.1 Objectives 7.7

7.4.2 Taxonomic Diversity 7.7

7.4.3 Community Structure 7.8

7.4.3.1 Catchment of Dri River (V1) 7.8

7.4.3.2 Dam Site Dri River (V2) 7.12

7.4.3.3 Downstream of Dri Dam near Ru Pani (V3) 7.15

7.4.3.4 Catchment Area Talo (Tangon) River (V4) 7.18

7.4.3.5 Talo (Tangon) Dam Site Talo (Tangon) River (V5) 7.20

7.4.3.6 Downstream of Talo (Tangon) Dam near Anon Pani (V6) 7.23

7.4.3.7 Power House Site (V7) 7.25

7.4.3.8 Downstream of Power House Site (V8) 7.28

7.4.4 Density & Dominance 7.31

7.4.5 Diversity 7.34

7.4.6 Economically Important Plant Species 7.36

7.4.7 Rare & Endangered Flora 7.38

7.5 TERRESTRIAL FAUNA 7.38

7.5.1 Mammals 7.38

7.5.2 Avifauna 7.40

7.5.3 Herpetofauna 7.42

7.5.4 Insects 7.42

7.5.5 Threatened and Endangered Fauna 7.45

7.6 WATER QUALITY 7.45

7.6.1 Physico–chemical Characteristics 7.46

7.6.2 Biological Characteristics 7.46

7.6.2.1 Periphyton 7.46

7.6.2.2 Phytoplankton 7.53

7.6.2.3 Zooplankton 7.55

7.6.2.4 Macro-Invertebrates 7.56

7.6.2.5 Water Quality Assessment 7.57

7.7 FISH AND FISHERIES 7.62

CHAPTER 8: ASSESSMENT OF IMPACTS

8.1 GENERAL 8.1

8.2 IMPACTS DURING CONSTRUCTION 8.2

8.2.1 Impacts due to immigration of Construction Workers 8.2

8.2.2 Construction of Main Project Components 8.3

8.2.3 Quarrying Operations 8.4

8.2.4 Operation of Construction Plant and Equipment 8.5

8.2.5 Muck Disposal 8.9

8.2.6 Road Construction 8.10

8.2.7 Flora and Fauna 8.13

8.2.8 Impacts Summary during Construction Phase 8.13

8.3 IMPACTS DURING OPERATION PHASE 8.18

8.3.1 Downstream Impacts 8.18

8.3.2 Impact on Migratory Fishes 8.19

8.3.3 Impact on Downstream Users 8.19

8.3.4 Impact on Reservoir Water Quality 8.20

8.3.5 Minimum Environmental Flow Requirement 8.20

LIST OF TABLES

Table 1.1: Key Environmental Legislations in India 1.10

Table 2.1: Salient Features of Etalin HE Project 2.4

Table 2.2: Existing Bridges in Project area 2.15

Table 2.3: Land requirement of Etalin HE Project 2.21

Table 3.1: Scoping matrix for EIA study of Etalin H.E. Project 3.4

Table 3.2: Sampling schedule for various Environmental Parameters 3.6

Table 3.3: Sampling locations 3.7

Table 3.4: Ambient air quality, noise and traffic density monitoring locations 3.10

Table 3.5: Sampling Locations for terrestrial ecology 3.12

Table 3.6: Number of quadrats studied during field surveys for trees, shrubs

and herbs 3.13

Table 3.7: Transects and trails for faunal elements 3.14

Table 3.8: Water sampling locations 3.15

Table 3.9: Source of data for various Environmental Parameters 3.19

Table 6.1: Areas falling under different slope categories in the study area 6.2

Table 6.2: Description and Area under different Soil Classes 6.8

Table 6.3: Physico-chemical Composition of Soil in the Study Area 6.10

Table 6.4: National Ambient Air Quality Standard by (MOEF&CC) 6.11

Table 6.5: Air Quality Monitoring of the Study Area (unit: µg/m3) 6.11

Table 6.6: Ambient Noise Standards 6.12

Table 6.7: Equivalent Noise levels in study area during day time [dB(A)] 6.13

Table 6.8: Traffic density (per hr) in the study area 6.13

Table 7.1: Area under different land use/ land cover categories in the study area 7.1

Table 7.2: Community structure –Site: V1 (Trees & Shrubs) 7.9

Table 7.3: Community structure –Site: V1 (Herbs) 7.11















Table 7.18: Density (per ha) of Trees, Shrubs and Herbs 7.31

Table 7.19: Shannon Weiner Diversity Index (H) 7.34

Table 7.20: Evenness Index (E) 7.35

Table 7.21: Plant Species used as timber, fodder and fuel wood 7.36

Table 7.22: Commonly used plants species for medicinal purposes in the area 7.36

Table 7.23: Commonly used wild plants species as food 7.37

Table 7.24: Mammalian species sighted in the study area 7.39

Table 7.25: Mammalian species reported from the study area 7.39

Table 7.26: List of birds recorded from the study area and their

conservation status 7.40

Table 7.27: Herpetofaunal composition of the Study area 7.42

Table 7.28: List of commonly found amphibians in the area 7.42

Table 7.29: Insects found in the Study Area 7.43

Table 7.30: List of butterflies/insects recorded from the study area 7.43

Table 7.31: Physico-Chemical Characteristics of Water at Different Sampling

Sites in the Study Area: Winter (Lean) 7.48


Sites in the Study Area (Pre-Monsoon: Summer) 7.49


Sites in the Study Area (Monsoon) 7.50

Table 7.34: List of periphyton found in Study Area 7.51

Table 7.35: Density, Species Diversity (H) and Evenness Index (E) of periphyton

7.52

Table 7.36: List of phytoplankton species found in Study Area 7.54

Table 7.37: Density, Species Diversity (H) and Evenness Index (E)

of phytoplankton 7.55

Table 7.38: Zooplankton density and Shannon-Weiner Diversity index in

study area 7.56

Table 7.39: Macro-invertebrates density (individuals/m2) in study area 7.57

Table 7.40: Percent composition of macro-invertebrates at different sampling

locations (Winter Season) 7.59


locations (Pre-Monsoon) 7.60


locations (Monsoon) 7.61

Table 7.43: Fish composition and their status in the Dri and Talo (Tangon) Rivers7.62

Table 8.1: Calculation of Total Migratory Population 8.2

Table 8.2: Details of the quarry sites proposed in the Etalin H.E. Project 8.4

Table 8.3: List of Construction Equipment 8.5

Table 8.4: Details of Excavation work in Etalin Hydroelectric Project 8.9

Table 8.5: Details of Road Construction 8.11

Table 8.6: Summary of Impacts during Construction Phase 8.14

Table 8.7: Summary of Impacts during Operation Phase 8.21

LIST OF FIGURES

Figure 1.1: Map of Arunachal Pradesh showing location of Etalin H.E. project 1.2

Figure 1.2: L-section of Dri river showing cascade of projects 1.4

Figure 1.3: L-section of Talo (Tangon) river showing cascade of projects 1.4

Figure 1.4: Alternatives studied in Etalin HE project 1.5

Figure 2.1: Accessibility of Etalin HE project 2.2

Figure 2.2: Layout map of Etalin H.E. Project showing infrastructural facilities 2.16

Figure 3.1: Study area map delineated as per approved TOR of Etalin H.E. Project 3.2

Figure 6.1: Drainage Catchment areas of two limbs of Etalin HE project 6.3

Figure 6.2: Digital Terrain Model (DTM) of the study area generated from ASTER

G-DEM data 6.4

Figure 6.3: Slope map of the study area generated from DEM 6.5

Figure 6.4: Soil Series and their description in the Study Area 6.7

Figure 6.5: Map showing sampling sites for soil sampling, air and

noise monitoring stations in the study area 6.9

Figure 7.1: FCC generated from satellite data showing study area 7.2

Figure 7.2: Land Use/ Land Cover Map of the project Study Area 7.3

Figure 7.3: Location of terrestrial biodiversity sampling sites in the study area 7.10

Figure 7.4: Variation in Tree Density at different Sampling Locations 7.32

Figure 7.5: Variation in Shrub Density at different Sampling Locations 7.32

Figure 7.6: Seasonal variation in density of herbs 7.33

Figure 7.7: Importance Value Index of dominant tree species at

different sampling locations 7.33

Figure 7.8: Importance Value Index of dominant shrub species at

different sampling locations 7.34

Figure 7.9: Species Diversity Index (H) of Trees and Shrubs 7.35

Figure 7.10: Species Diversity Index (H) of Herbs 7.35

Figure 7.11: Location of sites for water sampling 7.47

Figure 7.12: Seasonal Variation in density of periphyton 7.53

Figure 7.13: Seasonal variation in Species Diversity Index (H) of periphyton 7.53

Figure 7.14: Seasonal Fluctuation in Evenness Index (E) of periphyton 7.53

Figure 7.15: Macro-invertebrates density (individuals/m2) 7.56

Figure 7.16: BMWP scores a different sites in different seasons 7.58

Figure 7.17: ASPT scores a different sites in different seasons 7.58

Figure 8.1: Drainage downstream of Dri and Talo (Tangon) dam sites 8.24

LIST OF PLATES

Plate 7.1: Blue green algae recorded from Dri and Talo (Tangon) rivers 7.63

Plate 7.2: Diatoms recorded from Dri and Talo (Tangon) rivers 7.64

LIST OF ANNEXURES

Annexure I: Approved Scoping and TOR by MoEF, GOI vide its letter No. J-

12011/61/2006-IA.I dated November 30, 2009

Annexure II: Revised TOR by MOEF, letter No. J-12011/60/2006-IA-I dated April

26, 2013

Annexure III: ToR Compliance

Annexure IV: Hydrology

Annexure V: Geology

Annexure VI: Inventory of Plants

References

Photographs

Environmental Impact Assessment (EIA) Report of Etalin HE Project

Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) 1.1

Consultant: RS Envirolink Technologies Pvt. Ltd.

1.1 GENERAL

The state of Arunachal Pradesh has vast Hydro Power potential. The main rivers that flow

through Arunachal Pradesh region are Dibang, Lohit and Siang. Dibang River, also known as Dri

at its origin, is the major tributary of Brahmaputra River. Dri and Talo (Tangon) rivers meet

near Etalin village; downstream of the confluence of Dri and Talo (Tangon) rivers, the river is

named Dibang.

1.2 ETALIN H.E. PROJECT

Etalin HEP is a run-of-the-river project that will be using the waters of Dri and Talo (Tangon)rivers

in Dibang Valley district of Arunachal Pradesh. The diversion structure on Dri limb is located near

Eron village, around 22 km from Etalin village while the diversion structure on Talo (Tangon)

limb is located near Avonli village, around 17 km from Etalin village. The powerhouse site is

located near Etalin village, around 185 km from Roing, the district headquarter of Lower Dibang

Valley district. Anini, the district headquarter of Dibang Valley district, is around 240 km north of

Roing. The nearest railhead is at Tinsukia, about 110km from Roing. Roing and Tinsukia are

connected by means of NH-37 and a district road, which includes crossing river Lohit at Dhola.

The project site is about 300km from Tinsukia. The location of the project is shown in Figure 1.1.

1.2.1 Purpose of the Study

The purpose of Environmental Impact Assessment (EIA) is to assist in the decision making

process and to ensure that the project options under consideration are environmentally sound

and sustainable. This Environmental Impact Assessment (EIA) study has been conducted to

identify possible environmental impacts and to suggest ways for mitigating or minimizing them.

The EIA also identifies the possible benefits and adverse impacts on the environment as a result

of construction and operation of the project. The Environment Management Plan (EMP) provides a

plan which, upon implementation, will reduce impacts of the project and minimize environmental

degradation. This minimization may be a result of implementation of a project alternative or

project modifications or environmental protection measures which simply reduces the severity or

magnitude of impacts.

1.2.2 Scope of the Study

The general scope of this EIA study is as follows:

Assessment of the existing condition of physico-chemical, ecological and socio-economic

aspects of environment;

Identification of potential impacts on various environmental components due to activities

envisaged during construction and operational phases of the proposed hydro-electric project.

Prediction of significant impacts on major environmental components;

Preparation of Environmental Management Plan (EMP) outlining measures to minimize adverse

impacts during construction and operational phases of the proposed project. This includes

components like Catchment Area Treatment Plan (CAT), Green Belt Development

Chapter INTRODUCTION

1




Figure 1.1: Map of Arunachal Pradesh showing location of Etalin H.E. Project




Plan, Fisheries development, conservation/management plan, Muck Disposal Plan, Dam Break

Analysis etc;

Formulation of Rehabilitation and Resettlement Plan as per ‘The Right to Fair Compensation and

Transparency in Land Acquisition, Rehabilitation and Resettlement Act, 2013 (RFCT_LARR)’, The

National Rehabilitation and Resettlement Policy (NRRP), 2007 and State Rehabilitation and

Resettlement Policy (SRRP), 2008 of Arunachal Pradesh;

Formulation of environmental monitoring plan for construction and operation phases;

Estimation of Cost for implementation of Environmental Management Plan, Resettlement &

Rehabilitation Plan, Catchment Area Treatment Plan and Environmental Monitoring Programme.

1.3 CASCADE DEVELOPENT PLAN

Dri and Talo (Tangon) rivers are two major rivers in Dibang Valley district. There are seven

projects planned on Dri river which is main limb of Dibang river. Similarly there are two projects

planned on Talo (Tangon) river. These are:

On Dri Limb (Dibang river)

Upstream Projects

Etalin (3097 MW) on Dri river limb (Dri Dam)

Agoline (375 MW) on Dri river

Mithundon (400MW) on Dri river

Etabue on Ange Pani river, a tributary of Dri river

Amuliin (420 MW) Mathun river, tributary of Dri river

Emini (500 MW) Mathun river, tributary of Dri river

Downstream Projects

Dibang Multipurpose (3000 MW) project on Dibang river

On Talo (Tangon) Limb

Upstream Projects

Etalin (3097 MW) on Talo (Tangon) river limb (Tangon Dam)

Attunli (680 MW) on Talo (Tangon) river

Malinye (335 MW) on Talo (Tangon) river

Downstream Projects

Dibang Multipurpose (3000 MW) project on Dibang river

Out of about 79 km long river stretch of Dri river from origin to its confluence with Talo

(Tangon) river, these projects will use up about 33.6 km (42%) of main Dri river stretch. Major

free riverine stretch of 18.93 Km is between Amulin and Emini HEPs. Free flowing river stretch

in adjacent projects can be seen from L-sections given at Figures 1.2 & 1.3. There are 3

projects upstream of Dri limb of Etalin HEP on main Dri river and 3 projects on its tributaries

i.e. Mathun and Ange Pani whereas there are 2 projects upstream of Talo (Tangon) river limb.

There is one downstream project which is Dibang Multipurpose Project whose FRL is at a

distance of 2 Km along the river from the TWL of Etalin HEP.

1.4 STUDY OF ALTERNATIVES

1.4.1 Alternative Layouts

Since the conception of the project, several alternative layouts were developed and analyzed.

The merits and demerits of the selected layout as discussed in DPR of the project have been

being been described in the following paragraphs.




Figure 1.2: L-section of Dri river showing cascade of projects

Figure 1.3: L-section of Talo (Tangon) river showing cascade of projects

1.4.1.1 Layout by CEA

The project, as originally conceived by Central Electricity Authority (CEA) at the pre-feasibility

stage, envisaged construction of two diversion structures, one each on Dri and Talo (Tangon)

rivers with the underground powerhouse located at their confluence. The riverbed level at the

selected diversion sites on both rivers was at El 1040m and the level at the location of tailrace

discharge was El 600m. Water conductor systems along both rivers were proposed underground

and culminated in a common underground powerhouse located in the hill mass at the

confluence of the two rivers near Etalin village. The water conductor system of Dri limb of the

project followed the left bank of Dri and that of the Talo (Tangon) limb followed the right bank

of Talo (Tangon). The total length of the two water conductor systems aggregated to 26km. The

installed capacity was estimated as 3045MW. The line layout of the scheme is shown in Figure

1.4.




Figure 1.4: Alternatives studied in Etalin HE Project

1.4.1.2 Layout by NHPC

The project was subsequently studied by National Hydroelectric Power Corporation Ltd. (NHPC)

as part of preparation of the Pre-Feasibility Report (under Government of India’s 50,000 MW

Hydro Initiative). Based on their study of the topography and geology of the area, NHPC

proposed some modifications to the project layout conceived by CEA. The main changes

comprised:

Downstream relocation of dam site on Dri river to about 1.5 km downstream of the

confluence with Ayo Pani nala. The proposed dam site is near Yuon Village. Riverbed at this

location is about El 980 m.

It was observed that by keeping the diversion structure at the same location as proposed by

CEA, the HRT had to negotiate Ayopani, a deeply dissected nala with presence of thick

fluvio-glacial deposits. It was apprehended that adequate rock cover over the tunnel may

not be available without a very long detour. Keeping this in view, an alternative diversion

site located about 1.5km downstream of confluence of Ayo Pani with Dri river was identified.

Downstream relocation of dam site on Talo (Tangon) river to about 800 m downstream of

confluence with Anon Pani nala. The proposed dam site is near Avonli Village. The riverbed

at the proposed location is El 920 m.

In this case, the diversion site proposed by CEA was not found suitable due to non-

availability of rock on the left bank of the river within 1km from the dam axis identified by

CEA. Keeping this in view, a site located about 800m downstream was proposed. Another

advantage of this site was utilization of the discharge of Anon Pani and Kun Pani joining the

river Talo (Tangon) downstream of the axis proposed by CEA. Reaches further downstream

were also examined and were not found suitable due to increase in width of valley and




presence of thick overburden on the right bank of the river. In addition, further shifting of

the dam towards downstream would have resulted in increase in the height of diversion

structure for maintaining same FRL and gross head.

Splitting the single powerhouse into two independent underground powerhouses one for Dri

limb and the other for Talo (Tangon) limb. The two powerhouses were however kept in the

same general location as proposed by CEA, with tailrace outfall level retained at El 600 m.

The water conductor system was changed and two HRTs and two surge shafts were

proposed for each limb.

The total installed capacity of the project was increased to 4000 MW. The scheme on Talo

(Tangon) envisaged diversion of 426 cumec of water to utilize a gross head of about 466.5m to

generate 1500MW (6x250 MW) of power. Dri limb of the project was envisaged to generate 2500

MW (10x250 MW) of power through a design discharge of 720cumec and a gross head of 461.5m.

Other alternatives were also studied. One of them comprised locating the waterway system for Dri

limb on the right bank of Dri and that of Talo (Tangon) limb on the left bank of Talo (Tangon).

Two separate powerhouses were accordingly planned with the tailrace levels still kept at around El

600m. In other words, two independent schemes were formulated with Talo (Tangon) limb

scheme on left bank of Talo (Tangon) and Dri limb scheme on right bank of Dri river. As the

alternatives were developed, it was found that the tunnel alignments in both limbs were to

negotiate several deep nalas and, consequently, the tunnel lengths were found to increase by

6.6km on Dri limb and 4km on Talo (Tangon) limb. The areas identified for locating the

powerhouses also did not provide adequate space for working. Moreover, it was also noted that

substantial additional infrastructure facilities would be required, particularly on Dri limb where the

existing road is on the left bank and the valley is quite steep. Clearly, the overall cost of the

project would increase considerably without any benefit of additional generation. Consequently,

the proposal for laying out the schemes on left bank for Talo (Tangon) and right bank for Dri was

rejected at the initial stage itself. Figure 1.4 shows the schemes studied by NHPC.

Project components as envisaged by NHPC are briefly described in the following

paragraphs:

The diversion structure on Talo (Tangon) comprised a 135m high concrete gravity dam having a

gross storage capacity of 50.61MCM. The proposed MWL / FRL was kept at El 1050m, and MDDL

was proposed at El 1030m. Eight spillway bays (7.0mX9m), were conceived, out of which six

are provided as lower spillways and remaining two as upper spillways. The invert levels of the

lower and upper spillway bays were fixed at elevation 1000m and 1040m, respectively.

The diversion structure on Dri was a 70m high concrete gravity dam having a gross storage

capacity of 28.16MCM. The proposed MWL / FRL for the scheme was El 1045m with MDDL

at El 1025m. Ten spillway bays (7.5mX9m) were provided, with eight bays as lower

spillways and remaining two as upper spillways. The invert levels of the lower spillway bays

and upper spillway bays were fixed at elevation 998m and elevation 1036m, respectively.

Two numbers intakes of 8.0 x 9.0m were envisaged for drawl of 255.6 cumec of water

through each opening for Talo (Tangon) limb to feed the desanding chambers. For Dri limb,

four nos. of intakes of size 7.3 x 8.3m were considered for drawl of 216.0 cumec of water

through each opening.

Four desanding chambers (350mx17mx23m, each) were proposed on Talo (Tangon) limb

and eight chambers (8-300mx16mx23m, each) were proposed on the Dri limb.




Two circular headrace tunnels were proposed on each limb. The tunnel on Dri limb were

10.5m diameter and 9.7km and 9.9km long while those on the Talo (Tangon) limb were 8m

in diameter and 12km and 12.5km long.

Two 15.0m diameter, 125m high restricted orifice surge shafts were proposed in the Talo

(Tangon) limb. Water from each surge shaft was to be carried through a 6.7m diameter

steel lined pressure shaft with vertical drop of 361m. Surge shafts in the Dri limb were

23.0m in diameter and 125m high. The steel lined pressure shafts were of diameter 5.5m

and 6.7m and negotiated a vertical drop of 379m.

Surge shafts in the Dri limb were 23.0m in diameter and 125m high. The steel lined

pressure shafts were of diameter 5.5m and 6.7m and negotiated a vertical drop of 379m.

Two separate caverns having dimension 180 m X 24.0 m X 48.0 m for Talo (Tangon) limb

and 270m x 24.0m x 48.0m for Dri limb were proposed to accommodate six numbers of

250MW and 10 nos. of 250 MW turbines, respectively. Orientation of the cavity was

considered in E-W direction.

1.4.1.3 Alternatives Studies in the Present DPR

At the start of work on the present DPR, a detailed study of the reports prepared by CEA and

NHPC was carried out along with on-site assessment of the proposals contained therein.

Specialists from diversified fields such as hydrology, geology, planning and design were

involved and they came up with the following observations.

The dam site proposed in PFR for the Dri limb of the project appears in general suitable.

However, an alternative site that offers a superior location exists downstream of this axis.

On the Talo (Tangon) limb, the left bank at the proposed dam axis does not appear to be

very attractive due to the existence of a large terrace. Upstream and downstream of this

axis, the river flows along the right bank in a width of 20m while the left bank shoal

formation extends up to 50m (width) at places and is covered by large boulders as big as 5

cubic meter in size. In this case too, an alternative dam axis, about 2.3km upstream, was

identified for further study. Riverbed level at this new location is of the order of El 1000m.

The intake structures, as proposed in the PFR, are suitably located vis-à-vis the proposed

dam axis. The intakes also appear to be sized appropriately.

Based on preliminary observation of surface geology, orientation of desilting chambers on

Talo (Tangon) limb is considered suitable from rock mass structural stability point of view.

Construction of eight large underground desanding chambers will be a major challenge that

will be fraught with significant geological and construction risks. Attempt should be made to

find other ways of minimizing sediment entry into the water conductor system. Even the

proposed desanding arrangement on the Talo (Tangon) side, comprising of four large

underground chambers, will also involve substantial effort.

The proposed 6.7m diameter pressure shafts would require a very thick steel liner at the

lower portion of the pressure shafts, and is considered not preferable from fabrication and

erection point of view. Also providing a trifurcation in such a thick steel plate shall be

extremely difficult from design (particularly, weld design) and fabrication point of view.

The powerhouse is proposed to be accommodated within the ridge; in-situ stresses across

the gable walls would require careful assessment. Moreover, provision of two separate

powerhouses will leave a rock wall between the two caverns which are not desirable from

construction and operational point of view.

Keeping the above observations in view, the detailed assessment of different appurtenant of




both limbs of the project was made in the initial stages based on the data available on

topography, geology and hydrology etc. The summary of the studies and conclusions drawn

from these are discussed in the following paragraphs. Alternatives considered for each

component of the project are described as applicable.

a) Diversion Site on Dri River

As per PFR, the diversion site on Dri river was located near Yuron village, about 1500m

downstream of confluence of Ayo Pani nala with Dri river. During the site reconnaissance in the

initial DPR stage, an alternative diversion site located about 250m downstream of the PFR site

was identified. The PFR stage dam axis is termed as Alternative-I and the downstream dam axis

as Alternative-II.

At the Alternative-I dam site Dri river flows in a meandering course through a narrow to

moderately wide modified V-shaped valley. The river exhibits a westerly bend with convexity

towards the left bank; the proposed axis is located at the curvature. The water flow is

approximately 60m wide and a shoal exists on the right bank which is covered with boulders of

various sizes (even up to 3m in diameter). The valley width at this site is around 90m (Figure

1.4). Massive gneissic bedrock has been observed protruding in the river on the left bank. The

bank rises with a slope of about 50º up to about 80m above the riverbed and, beyond that, at

70° up to the road level. Vegetation is rather sparse on this bank. The right bank of the river is

covered by a shoal at the foot of the hill slope which then rises up at an angle of around 45º

and is covered by dense forest. The bedrock comprising granodiorite gneiss is medium strong to

strong with four major joint sets. The foliation joint is oblique to the river, dipping towards

upstream at 247º/55º to 75º. The riverbed is covered with pebbles, cobbles, boulders and sand.

Boulders are as big as 3m3 to 5m3.

While the site generally appears suitable for locating a dam-spillway structure, the width of the

valley is somewhat inadequate. Substantial excavation would be required on the abutments to

accommodate the dam-spillway structure. Presence of the bend in the river course would also

make it difficult to locate and design proper energy dissipation arrangement. Presence of a nala

on the left bank of the river would pose further constraints for locating the diversion structure

at this site.

Keeping in view the above factors, another site located about 250m downstream was identified

and designated as Alternative-II site.

The river at this site flows along almost straight course for length of about 500m. The river

valley is about 110m wide with the water way taking up approximately 60m. A 50m wide shoal

exists on the left bank which is covered with boulders of various sizes (up to 3m in diameter).

The riverbed is generally covered by large boulders, up to 3 to 5m in size. The bedrock is

exposed along river edge on both the banks. The left bank has uniform, moderate to steep

slopes and exposes granodiorite gneiss all through the slope with occasional occurrence of

superficial overburden over the rock mass. The area in general is covered by thick vegetation.

One nala has been observed on the upstream of the proposed dam axis. The right bank initially

rises in a steep slope (700) followed by moderate to gentle upward slopes. The rock exposures

have been observed just at the riverbed level. These are followed upslope by vegetation cover

and grass cover at higher altitude. The bedrock on the right bank appears to be massive gneiss




with some local folds.

Alternative-II diversion site on Dri was thus found to offer better conditions to locate the dam-

spillway and was selected for further studies during the DPR preparation. Subsequent detailed

assessment of topographic, geologic, design and planning aspects have confirmed that this site

is indeed suitable for locating the diversion structure.

b) Diversion site on Talo (Tangon) River

On the Talo (Tangon) limb also, two alternative diversion sites have been studied. The diversion

site selected by NHPC is called Alternative-I. As discussed above, this site is located about

600m downstream of the confluence of Anon Pani nala with Talo (Tangon).

River Talo (Tangon) at this site flows along a meandering course through a flat and wide valley.

Upstream of the proposed axis, the river takes a right angled bend. The riverbed is covered by

large boulders, gravels, pebbles admixed with sand. Extensive terrace deposits occupy the left

bank, even at the road level and above. The terrace extends upstream and downstream of the

proposed axis. Toe erosion of the terrace is quite prominent in the upstream area where the

river takes the right-angled bend. Beyond the terrace, the slope of the left bank is moderate to

steep and is covered by thick forest. Upstream and downstream of the terrace, granodiorite

rock is exposed along the river water edge. The right bank has a steep slope covered by thick

vegetation but patches of rock exposures can be seen through the vegetation cover all along

the slope. The width of the valley, approximately 20m above riverbed level, is estimated to be

170m. The rock at the proposed dam site is slightly to moderately weathered, jointed and

medium strong to strong granodiorite/diorite gneiss, massive in nature.

Visual examination of the site indicated that the bedrock in the riverbed could be at a

considerable depth. In order to assess the depth of overburden, exploratory drilling and

geophysical investigations through seismic profiling were commissioned immediately after the

start of the DPR preparation work. Exploration of riverbed through two drill holes indicated the

presence of thick terrace deposits extending to a considerable height on the left abutment and

existence of more than 70m thick overburden in the riverbed. With the riverbed elevation at

this location being around El 945m, the height of dam for an FRL of El 1050m would be around

110m above the existing riverbed level. A wide valley with deep bedrock was not considered

amenable to locate a concrete gravity structure.

Keeping the above aspects in view another alternative site (Alternative-II) located about 2.3km

upstream was identified. The river at this dam site flows through a flat and narrow valley. The

river Talo (Tangon) at the site flows along more or less straight course for a considerable

length. The right abutment is in general covered by thick overburden that supports dense

vegetation and occasional exposures of bedrock are observed at higher elevations. The left

abutment has very steep slope and the bedrock is exposed right from riverbed level and

extends all along up to road and above. The riverbed level at the site is around El 1000m and

the dam height for an FRL of El 1050m would be about 50m above the riverbed. This site was

therefore selected for locating the dam and further investigations were focused on this site.

c) Water Conductor Systems

Alternative studies related to the water conductor systems comprised the alignment of the




tunnels, the size and number of tunnels as well as requirement, and subsequently alignment

of the desilting chambers. Alternative locations of surge shafts also formed part of the initial

studies. The selected tunnel alignments have considered such factors as the optimal overall

cover, optimal length of adits etc. A single tunnel is proposed for each limb based on the study

of construction logistics and cost. Geologically also, a single large diameter tunnel is considered

acceptable. The HRT on Dri limb is proposed as a 11.3m diameter circular tunnel while the HRT

on Talo (Tangon) limb is 9.7m in diameter. Studies have indicated that desilting chambers could

be eliminated in case of Dri limb, no such arrangement is therefore provided. Three

underground desilting chambers are however provided in Talo (Tangon) limb. Each HRT

culminates in a surge shaft from where pressure shafts emanate. The layout of the water

conductor system adopted at DPR stage is shown in Figure 1.4.

d) Powerhouse Complex

In case of the powerhouse, two separate caverns (having dimension 180m x 24.0m x 48.0m for

Talo (Tangon) limb and 270m x 24.0m x 48.0m for Dri limb) were to be located within ridge at

the confluence of Dri and Talo (Tangon) rivers as proposed by NHPC during PFR stage. In the

CEA study, a single powerhouse was proposed with an installed capacity of 3045 MW. The

provision of two separate powerhouse caverns is not desirable from construction and

operational point of view. Moreover, such an arrangement would leave a rock wall in between

the two caverns. Stability of this wall located in a ridge open on two sides could be of concern.

A single powerhouse cavern is therefore retained to accommodate the power plant for both the

limbs of the project.

1.5 POLICY, LEGAL & ADMINISTRATIVE FRAMEWORK

In the emerging scenario of rapid economic growth, sustainability of existing resources for the

present and future generations requires an integrated approach so that, the existing resources

are optimally utilized without causing undue damage to the environment. To achieve this

objective, the Ministry of Environment, Forests & Climate Change (MoEF&CC), Government of

India has enacted Acts, Legislations, Guidelines and Standards to ensure sustainable

development and conserve the environment. These are required to be compiled by the Project

proponents while executing the development of Project. The Project proponent thus prepares

the EIA report, incorporating management plans to mitigate the adverse impacts (if any) for

perusal of the MoEF&CC. The MoEF&CC in turn evaluates the proposal and suggests stipulations

for mitigation of adverse impacts while granting the clearance for execution of the Project. The

important Environmental legislations laid down for conservation of environment are presented

in Table 1.1.

Table 1.1: Key Environmental Legislations in India

Name Scope and Objective Key Areas Operational Agencies/

Key Players

Water (Prevention

and Control of

Pollution) Act, 1974,

Amendment 1988

To provide for the

prevention and control

of water pollution and

enhancing the quality of

water

Controls sewage and

industrial effluent

discharges

Central and State

Pollution Control Boards

Air (Prevention and

Control of Pollution)

Act 1981 Amendment

1987

To provide for the

prevention and control

of air pollution

Controls emissions

of air pollutants

Central and State

Pollution Control Boards

Forest (Conservation)

Act,1980 Amendment

To consolidate

acquisition of common

Regulates access to

natural resources,

State Government and

Central Government




Name Scope and Objective Key Areas Operational Agencies/

Key Players

1988 property such as

forests; halt India’s

rapid deforestation and

resulting Environmental

degradation

state has a

monopoly right over

land; Restriction on

de-reservation and

using forest for non-

forest purpose

Wildlife (Protection)

Act, 1972,

Amendment 1993

To protect wildlife Creates protected

areas (National

parks/ sanctuaries)

categories of wildlife

which are protected

Wildlife Advisory Boards;

Central Zoo Authorities

Environment

(Protection) Act,

1986

To provide for the

protection and

improvement of

Environment

An umbrella

legislation;

supplements

pollution laws

Central Government

nodal agency MoEF, can

delegate powers to state

departments of

Environments

National Policy on

R&R 2007, The Right

to Fair Compensation

& Transparency in

Land Acquisition,

Rehabilitation and

Resettlement Act,

2013 and Arunachal

Pradesh State R&R

Policy 2008

Resettlement and

Rehabilitation of Project

affected people and

Social Impact

Assessment

Social issues Central Government

EIA Notification 2006

with subsequent

amendment (2009 &

2011)

Environmental Impact

Assessment

Environmental

Protection

Project Developer,

State and Central

government

(Source: Government of India Publications)

Like many other developmental activities, the proposed Project, while providing planned power

generation could also lead to a variety of adverse environmental impacts. However, by proper

planning at the inception stage and by incorporating appropriate mitigation measures in the

planning, design, construction and operation phases, the adverse impacts can be minimized to a

large extent, whereas the beneficial impacts could be maximized. The main objective of the EIA

study is to assess the positive and negative impacts likely to accrue as a result of the

construction and operation of the proposed Project and to suggest suitable Environmental

Management Plans (EMP) to ameliorate the adverse impacts, if any. A well-designed

environmental monitoring programme covering various critical parameters to be covered in the

Project construction and operation phase would also be required. The present EIA for Etalin HEP

has been prepared based on the analysis of baseline data and accordingly Environment

Management Plan has been prepared for seeking Environment Clearance.

The principal Environmental Regulatory Agency in India is the Ministry of Environment, Forests

and Climate Change (MoEF&CC). MoEF&CC formulates environmental policies and accords

environmental and Forest clearance for the projects. The State Pollution Control Board (SPCB)

conducts Public hearing and accords Consent to Establish and Consent to Operate for the

project.

The project would need the following clearances before starting construction:

Public hearing as per EIA notification 2006 (and addendum thereafter)




Prior Environmental Clearance from the MoEF&CC, GoI;

Forest Clearance from MoEF&CC;

Consent to Establish from the Arunachal Pradesh State Pollution Control Board;

1.6 EIA NOTIFICATION, 2006

Etalin (3097 MW) HEP is a Category ‘A’ project (>50 MW), as per item 1 (c) of Schedule

attached to EIA notification of September 2006 and require environmental appraisal from the

Ministry of Environment, Forests and Climate Change (MoEF&CC), Government of India. The

environmental clearance process involves three stages:

Scoping

Public Consultation

Appraisal

As per MoEF&CC EIA Notification, dated 14th September 2006 (and amendments

thereafter), under Activity 1(c) - River Valley projects; if, the capacity of power generation for

any HEP will more than 50 MW, the project falls under Category A. Comprehensive EIA study

needs to be undertaken and environmental clearance to be obtained from MoEF&CC before start

of any construction activity.

The Etalin HEP (3097 MW) is a Category A project (> 50 MW), as per item 1 (c) of Schedule

attached to EIA notification of September 2006 and requires environmental appraisal from the

Ministry of Environment, Forests & Climate Change (MoEF&CC), Government of India.

Scoping: The scoping and Terms of Reference (TOR) for EIA studies was earlier accorded to

this project on 15.1.2007 under the provisions of EIA Notification of September 14, 2006 to

NTPC Ltd. Later on the project was allotted to joint venture Company Etalin Hydro Electric

Power Company Limited a subsidiary of Jindal Power Ltd. and Hydro Development Corporation

of Arunachal Pradesh vide letter no. Sectt/Power/03/Jindal/2009 dt. 29.8.2009. A fresh Form 1

including proposed Terms of Reference (TOR) for the EIA study along with Pre Feasibility Report

(PFR) in prescribed format was submitted to MoEF&CC for determining TOR by Expert Appraisal

Committee under the category of River Valley Projects of Ministry of Environment & Forests,

Government of India. The TOR for 4000 MW was conveyed by MoEF&CC vide letter no. J-

12011/61/2006-IA-I dt. 30.11.2009 (Refer Annexure I).

On approval of Scoping, EIA study was undertaken with extensive field data collection during

three different seasons, data generation and analysis, impact assessment and preparation of

Environmental Management Plan (EMP) as per the TOR. After the downward revision of capacity

of Etalin HEP from 4000 MW to 3097 MW with slight changes in project features, MoEF&CC vide

letter no. J-12011/61/2006-IA-I dt. 26.04.2013 issued revised TOR valid for 2 years from the

date of issue of letter (Refer Annexure-II). A draft report was prepared incorporating all the

above required for submission for other two stages viz. Public Consultation and Appraisal.

Public Consultation:

After the preparation of Draft EIA report along with Executive Summary, Public consultation

process was initiated as per stipulated public consultation process by Arunachal Pradesh State

Pollution Control Board (APSPCB). Public hearing was held on 12 December, 2014 at Etalin

Head Quarter, under Etalin Circle, Dibang Valley District of Arunachal Pradesh. After the

completion of the Public Consultation minutes of the same have been appended as a separate




document in the form of report detailing the proceedings and video of the entire event has

been submitted to MoEF&CC by APSPCB. Major issues raised during Public Consultation process

and responses addressed in the Final EIA/EMP report are given in a separate chapter i.e. in

Chapter 14 of EMP

Appraisal: After completion of Public Consultation process, the final EIA report has been

prepared for submission to MoEF&CC for appraisal and environment clearance.

Environmental Clearance:

The final EIA report prepared as per the approved TOR after incorporating the concerns and

suggestions made during the Public Hearing, is now submitted to MoEF&CC for appraisal and

grant of Environment Clearance.

1.7 FOREST CLEARANCE

Forest Clearance under the Forest (Conservation) Act 1980 from Ministry of Environment,

Forests & Climate Change, Government of India is one of major step in project development as

the project is required to divert 1155.11 ha of forest land for non-forestry purposes i.e. for the

purpose of construction of various project components. Application for diversion of forest land

has already been moved and proposal is under examination by the regional office of MoEF & CC,

Shillong.

1.8 STATE R&R POLICY

In addition to the National Rehabilitation and Resettlement Policy 2007 by Ministry of Rural

Development (Department of Land Resources, Land Reforms Division), Government of India in

2007, and recently notified The Right to Fair Compensation and Transparency in Land

Acquisition, Rehabilitation and Resettlement Act, 2013, the Government of Arunachal Pradesh

has come out with a policy in September 2008 as State Rehabilitation & Resettlement Policy

2008 to address specific concerns of the state. R&R plan has been prepared as per state policy

and recent 2013 Act.

1.9 DISCLOSURE BY THE CONSULTANT

Final EIA/EMP reports have been prepared by M/s RS Envirolink Technologies Pvt. Ltd., (RSET)

Gurgaon which is a QCI-NABET accredited company to undertake River Valley, Hydroelectric,

Drainage and Irrigation Projects (Category ‘A’) according to the TOR approved by MoEF&CC. A

copy of the Accreditation certificate along with the list of experts involved is appended at the

beginning of the report.

1.10 OUTLINE OF THE REPORT

The Comprehensive EIA for the proposed Etalin hydroelectric project has been presented in two

parts - First part presents the findings of EIA study and the second part includes various

mitigation as well as management measures under the Environmental Management Plan. The

report has been prepared according to approved TOR of the project and the compliance to the

TOR is given at Annexure III.

The contents of Part - I of the document are organized as follows:




PART – I: Environmental Impact Assessment (EIA) Report Chapter-1: Introduction: The Chapter gives brief of the project. The Environmental Clearance

procedure and the related policies, legal and administrative framework for the same have been

summarized in this chapter. The objectives and need for EIA study too have been covered. Brief

description of the proposed hydroelectric project is also given.

Chapter-2: Project Description & Infrastructure: It gives the salient features of the project

and also the brief of major components of the project. In addition, the details of various

infrastructural facilities including land requirement for different components of the project and

equipment to be deployed for construction has been covered.

Chapter-3: Methodology: It includes the methodology adopted for conducting the

Comprehensive EIA study. The details of selected sampling sites and specific methodology

adopted for each environmental parameter have been given.

Chapter-4: Hydrology: It covers aspects like river system, drainage, basin characteristics,

hydro-meteorology, water availability, flow series, design flood, etc. It is being appended as

Annexure –IV.

Chapter-5: Geology & Seismicity: It includes details on regional geology of the area,

geomorphology, and geological details of various project components along with their

geotechnical appraisal. In also covers seismo-tectonic environment of the project area. It is

being attached as Annexure-V.

Chapter-6: Environmental Baseline Status: Physico-chemical Aspects: Presents physic-

chemical aspects of environment. The study is based on collection of data from various

secondary data sources. As a part of the Comprehensive EIA study, detailed ecological survey

was conducted for various seasons. The findings of the study were analyzed and ecological

characteristics of the study area have been described in this Chapter.

Chapter-7: Environmental Baseline Status: Biological Resources: Presents biological

aspects of environment. The study is based on collection of data from various secondary data

sources. As a part of the Comprehensive EIA study, detailed ecological survey was conducted

for various seasons. The findings of the study were analyzed and ecological characteristics of

the study area have been described in this Chapter.

Chapter-8: Assessment of Impacts: It describes the anticipated positive and negative

impacts as a result of the construction and operation of the proposed Etalin hydro-power

project. It is essentially a process to forecast the future environmental conditions of the project

area that might be expected to occur as a result of the construction and operation of the

proposed project. An attempt was made to forecast future environmental conditions

quantitatively to the extent possible. But for certain parameters, which cannot be quantified,

the general approach has been to discuss such intangible impacts in qualitative terms so that

planners and decision makers are aware of their existence as well as their possible implications.

PART – II: Environmental Management Plan (EMP)

The Part-II of the report deals with different Environmental Management Plans prepared to




mitigate the adverse environmental impacts. The contents of the Part-II are organized as

follows:

Chapter-1: Biodiversity Conservation & Management Plan: It delineates the plan for

mitigation of anticipated adverse impacts likely to accrue as a result of the proposed project on

the biodiversity of the area. The approach for formulation of Biodiversity Conservation Plan is to

maximize the positive environmental impacts and minimize the negative ones. After suggesting

environmental mitigation measures, the cost required for implementation of various measures

is also estimated.

Chapter-2: Catchment Area Treatment (CAT) plan: CAT plan methodology suggested by

SLUSOI has been used and Silt yield Index (SYI) method has been used for categorization of

sub-watersheds into priority classes. Treatment measures for very severe and severe categories

of sub-watersheds have been formulated. Cost required for implementation of CAT Plan too has

been estimated.

Chapter-3: Fisheries Conservation & Management Plan: It describes the various measures

to be undertaken for the Conservation & Management of the fish fauna.

Chapter-4: Solid Waste Disposal Plan: This chapter describes issues related to solid waste

disposal that are likely to accrue during the construction period and also the formulation of

management plan for the same.

Chapter-5: Public Health Delivery System: This chapter deals with the basic health care

facilities available in the area and setting up of new infrastructure as well as improvement of

existing infrastructure along with the cost estimates.

Chapter-6: Energy Conservation Measures: It deals with the provisions being made for the

reduction of pressure on the adjoining forest of the project area during the construction period

energy conservation measures like subsidy for fuel wood, etc. along with the cost of these

measures.

Chapter-7: Muck Disposal Plan: It deals with the rehabilitation of muck that is likely to be

generated during the construction of various project components and also suggests measures

for both engineering and biological measures for restoration of muck disposal sites in

environmentally sustainable manner.

Chapter-8: Landscaping & Restoration of Quarry & Working Areas: This chapter covers

adverse impact of construction activities on the landscape and suggests measures for

restoration of the disturbed area back to their similar or near-similar pre-construction conditions

and land use. It also includes green belt to be created along reservoir periphery and around the

colony areas.

Chapter-9: Reservoir Rim Treatment Plan: This Chapter describes the possibility of slope

failures, land slips, etc. due to fluctuation in water level along the reservoir periphery. In order

to mitigate the same, Reservoir Rim Treatment Plan and measures for treatment of existing

landslides/ slips, and prevention of further slides by undertaking engineering as well as




biological measures have been suggested. The cost estimation for various activities involved has

also been made.

Chapter-10: Air and Water Environment Management Plan: This chapter covers various

environmental risks that are foreseen during the construction on air, water and noise

environment in the project area and also deals with mitigation measures during the construction

and operational phase.

Chapter-11: Dam Break Modeling & Disaster Management plan: Dam Break Modeling

using MIKE11 model has been conducted. The results of the modeling exercise are outlined in

this Chapter. Disaster Management Plan (DMP) too has been outlined for implementation in

case of Dam Break.

Chapter-12: Compensatory Afforestation Programme: This Chapter discusses various

aspects of Compensatory Afforestation Programme to be implemented by the State Forest

Department.

Chapter-13: Environmental Monitoring Plan: This chapter deals with the issues of

implementation of various mitigation measures and environmental management plans during

project construction and operation phases. The environmental monitoring plan has been

suggested to assess the adequacy of various environmental safeguards and to compare the

predicted and actual scenario during construction and operation phases. This will help the

project proponents to formulate remedial measures not foreseen during the planning stage but

arising during these phases and to generate data for further use.

Chapter-14: Cost Estimates: It summarizes the cost to be incurred for implementation of the

Environmental Management Plan (EMP) and the Environmental Monitoring Programme.

Chapter-15: Public Consultation – Concerns and Responses: This chapter covers the

major issues raised during Public Consultation process and response given by

developer/consultant and where EIA related issues have been addressed in the EIA report.

Social Impact Assessment (SIA) and Rehabilitation & Resettlement Plan:

As the project involves displacement of more than 20 families, therefore as mandated by SRRP,

2008 of Arunachal Pradesh, a Social Impact Assessment report was prepared in addition to EIA

report. In addition based upon the SIA report findings an elaborate Rehabilitation &

Resettlement Plan for Project Affected Families has been prepared which deals with the

resettlement issues, rehabilitation measures, economic development package and benefits to be

given to the project affected families. These two reports have been appended as a separate

volume with the EIA volumes covering both the SIA report and R&R plan.

Environmental Flow Assessment Report

As mandated in the approved TOR for the project, a detailed Environmental Flow assessment

study was undertaken by Central Inland Fisheries Research Institute (CIFRI), Barrackpore and

findings of the same have been appended as a separate report along with the EIA volumes.


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL 2.1


2.1 PROJECT LOCATION & ACCESSIBILITY

The project is located in Dibang Valley district of Arunachal Pradesh, which is almost entirely hilly and

covered mostly by forests. The project area falls in the Lower Himalayan region and is located in a

remote area with limited local infrastructure. It envisages diversion of two rivers - Dri / Dibang (called

Dri limb) and Talo (Tangon) (called Talo (Tangon) limb). The dam site of the Dibang limb of the

project is located across Dri River near Yuron village about 22 km from Etalin. The Talo (Tangon) limb

consists of construction of dam about 800m upstream of Anon Pani confluence with Talo (Tangon)

river. The installed capacity for the scheme proposed on Dri limb is 1861.6MW, comprising of a small

hydro scheme of 19.6MW at the toe of the dam on Dri river and six (6) units of 307MW each in the

common underground powerhouse near Etalin village. The installed capacity for the scheme proposed

on Talo (Tangon) limb is 1235.4MW, including a small hydro scheme of 7.4MW envisaged at the toe of

the dam on Tangon river and four (4) units of 307MW each in the common underground powerhouse.

The total installed capacity of the project consequently is 3097MW. The Etalin Hydroelectric Project is

proposed upstream of the 3000MW Dibang Multipurpose Project being developed by NHPC.

The diversion structure on Dri limb is located near Yuron village, around 22km from Etalin village, and

can be approached via Etalin-Anini road. The diversion structure on Talo (Tangon) limb is located on

near Avonli village, 17 km from Etalin village and approachable by Etalin-Maliney road.

The powerhouse site is located near Etalin village, around 185 km from Roing, the district headquarter

of Lower Dibang Valley district. Anini, the district headquarter of Dibang Valley district, is around 240

km north of Roing. The nearest railhead is at Tinsukia, about 110 km from Roing. Roing and Tinsukia

are connected by means of NH-37 and a district road, which includes crossing river Lohit at Dhola.

The project site is about 300 km from Tinsukia. The nearest airport is at Dibrugarh, about 350km

from the project site via Dhola/Sadiya Ghat.

Etalin village can be reached by a single lane road which connects Roing to Anini via Hunli (see

Figure 2.1). The road crosses a high altitude pass between Roing and Hunli and is frequently blocked

by ice and snow during peak winter months.

2.2 SALIENT FEATURES OF THE PROJECT

Etalin HEP (6 X 307 MW at Dri Limb + 4 X 307 MW at Talo (Tangon) Limb + 19.6 MW + 7.4 MW) is a

run-of-the-river project that will be using the waters of Dri and Talo (Tangon) rivers in Dibang Valley

district of Arunachal Pradesh. Dri and Talo (Tangon) rivers meet near Etalin village; downstream of

the confluence the river is named Dibang. The project is proposed to be developed as a run-of-the-

river scheme by constructing concrete gravity dams on Talo (Tangon) and Dri rivers and diverting the

water through two (2) separate waterway systems to utilize the available head in a common

underground powerhouse located just upstream of the confluence of Dri and Talo (Tangon) rivers.

Height of dams as envisaged for diversion of Dri and Talo (Tangon) rivers, are 101.5m and 80m,

respectively. The salient features of the project are given at Table 2.1. The layout map of the Etalin

HE project is given at Figure 2.2.

Chapter PROJECT DESCRIPTION & INFRASTRUCTURE 2




Figure 2.1: Accessibility of Etalin HE project

2.3 PROJECT COMPONENTS

2.3.1 Dri Limb

2.3.1.1 Dam Complex

A 101.5m high concrete gravity dam is proposed at this location to divert water of Dri river into the

water conductor system. The top level of the dam is at El 1047m. The total length of the dam at top is

213.7m, with fourteen (14) concrete gravity blocks. The average riverbed level at the dam site is

around El 968m. The Full Reservoir Level (FRL) and Minimum Draw Down Level (MDDL) of the

reservoir are El 1045m and El 1039m, respectively, with a live storage of 4.6 MCM for diurnal peaking

capabilities. The total area of submergence is 83.32 ha.

The intake is located on the left bank of Dri River, upstream of the dam axis. The left bank is steeply

sloping with exposed rock mostly along the slope and is covered by thin overburden at lower

elevations. The intake system consists of two (2) inlet tunnels, which later combine to form the

headrace tunnel. The intake system is provided with a trash rack and four (4) vertical fixed wheel

gates – two for service and two for emergency.

2.3.1.2 Head Race Tunnel

The headrace tunnel is a circular shaped tunnel of 11.3m finished diameter having length of 10722m.

The headrace tunnel culminates in a vertical surge shaft of 26m internal diameter having restricted

orifice of diameter 5.5m.

2.3.1.3 Surge Shaft & Pressure Shafts

The surge shaft is envisaged as a 132m high structure, with the top at El 1102m. Three (3) main

pressure shafts, each of 5.6m diameters, originate from the bottom of the surge shaft. Each pressure

shaft bifurcates into two (2) unit pressure shafts of 4m diameter each to feed the six (6) units of Dri

limb. Main pressure shafts are 49.2, 26.6, 49.2m long and each unit pressure shaft is 512m long. Six

(6) butterfly valves are proposed for emergency closure of the underground penstock. A separate

underground cavern of dimensions 131m (L) x 10m (W) x 20m (H) is foreseen to accommodate

butterfly valves of 4m diameter each.

Talo Dam

Site




2.3.2 Talo (Tangon) Limb

2.3.2.1 Dam Complex

The proposed Talo (Tangon) dam is a 80m high concrete gravity structure with top level at El 1052m.

The total length of the dam at top is 184.1m, with twelve (12) concrete gravity blocks. The average

riverbed level at the dam site is around El 1003m. The Full Reservoir Level (FRL) and Minimum Draw

Down Level (MDDL) of the reservoir are El 1050m and El 1040m, respectively with a live storage of

2.94 MCM for diurnal peaking capabilities. The total area of submergence is 36.12 ha.

The intake is located on the right bank of Talo (Tangon) river, upstream of the dam axis. The right

bank is moderately sloping with thick overburden above the riverbed level. The intake consists of

three (3) 6m diameter modified horseshoe shaped tunnels of lengths 925m, 851m and 777m. The

intake would also consist of three (3) service gates, operated by rope drum hoist of 55MT capacity

and three (3) emergency gates, operated by rope drum hoist of 30MT capacity.

The water from the intake is conveyed to three (3) Duffore type underground desilting basins of

dimensions 350m (L) x 18.5m (W) x 26.5m (H) each. The layout of the desilting basins would help in

isolating each basin during flushing and other maintenance operations. Gates are proposed at the end

of each desilting basin. The gates, each 4.5m (W) x 5.5 m (H) would be operated from an

underground gate operating chamber, access to which will be provided through an access tunnel. The

settling silt would be collected in the flushing ducts running under each of the desilting basins. Gates

are provided at the end of each flushing duct. Individual flushing ducts merge downstream of the

gates to form a single silt flushing tunnel which would discharge the sediments back into the Talo

(Tangon) river.

2.3.2.2 Head Race Tunnel

Water from the desilting basins would then be led to the headrace tunnel, a 13045m long, 9.7m

diameter circular shaped structure. The tunnel, with a design discharge of 320.2 cumec, will also

contain five (5) intermediate adits of lengths 555m, 370m, 530m, 417m and 366m.

Surge Shaft & Pressure Shafts

The headrace tunnel culminates in a 137m high restricted orifice type surge shaft. The internal

diameter of the surge shaft is proposed to be 21m, while the orifice diameter would be 4.25m. The

top of the surge shaft is envisaged at El 1107m. Two (2) main pressure shafts, each of diameter

5.6m, originate from the bottom of the surge shaft. The 46m (each) long pressure shafts envisage a

design discharge of 160.1 cumec . Each main pressure shaft bifurcates into two (2) unit pressure

shafts of 4m diameter each, to feed the four (4) units of Talo (Tangon) limb. The unit pressure shafts

have a design discharge of 80.05 cumec each and the length of each unit pressure shaft is 512m.

Four (4) butterfly valves are proposed for emergency closure of the underground penstock.

A separate underground cavern is foreseen to accommodate the butterfly valves. The dimensions of

the cavern are 85.6m (L) x 10m (W) x 20m (H) to house the butterfly valves of 4m diameter each.




2.3.3 Components at Power House

A common underground power house of size 352m (L) x 23.5m (W) x 59.73m (H) with six units of

307 MW at Dri Limb and four units of 307 MW at Talo (Tangon) Limb and two tail race channel

discharging into the river is envisaged.

2.3.3.1 Dri Dam-toe Power House

An intake structure for a design discharge of 30.64 cumecs, near left abutment

A surface power house with 19.6 MW capacity

a 39.7m long rectangular tailrace duct of size 5.5m (W) x 3.5m (H)

2.3.3.2 Talo (Tangon) Dam-toe Power House

An intake structure for a design discharge of 19.52 cumecs, near left abutment

A surface power house with 7.4 MW capacity

a 27.9 m long rectangular tailrace duct of size 4.0 m (W) x 3.0 m (H)

The reservoir to be created by the dam at Dri and Talo (Tangon) Rivers will operate between FRL

1045 m & MDDL 1039 m and FRL 1050 m & MDDL 1040 m, respectively. The installed capacity of the

main power house will be 3070 MW (6 X 307 MW + 4 X 307 MW) while that of the Two Dam Toe

Powerhouses will be 27 MW (19.6 MW+ 7.4MW) totaling to 3097 MW (3070 MW + 27 MW). The rated

head for the Dri and Talo (Tangon) limb is 420 m. The design energy at 95% plant availability is

12,766.8 MU.

Table 2.1: Salient features of the Etalin HE project

State Arunachal Pradesh

District Dibang Valley

Dam Complex & Water Conductor –

Dri Limb

Location of Dam Site

Latitude 28° 42’ 24”N

Longitude 95° 51’ 52”E

Location of Power House

Latitude 28°36’ 40”N


HYDROLOGY

Catchment Area 3685 sq km

Design Flood (PMF) 11,811 m3/s

Glacial Lake Outburst Flood (GLOF) 1,170 m3/s

River Diversion Flood 4,805 m3/s

RESERVOIR

Full Reservoir Level (FRL) El 1045m

Minimum Draw Down Level (MDDL) El 1039m

Gross Storage at FRL 21.97 MCM

Gross Storage at MDDL 17.37 MCM

Live Storage 4.6 MCM

Submergence Area 83.32 Ha

Diversion Tunnel

Number 3 on Right bank & 1 on Left bank

Diameter 10.9m Circular shape




Inlet Invert / Outlet Invert El 975.0 m / El 964.0m

Length 338m, 461m, 594m & 692m

Slopes

Number and size of Gates in each tunnel

1 in 30.73, 1 in 41.91, 1 in 53.96 and 1 in

62.92,

2 Nos, 4.45m (W) x 10.9m (H)

Hoist Arrangement and Capacity 110MT, Electrically operated Rope Drum Hoist

COFFER DAM (UPSTREAM)

Type Concrete face with plum core

Top level 993m

Average river bed elevation 973m

Top width 6.5m

Length at top 140m

COFFER DAM (DOWNSTREAM

Type Random fill with downstream sealing layers

Top level El 975m

Average river bed elevation El 966m

Top width 5.0m

Length at top 70m

Upstream / downstream slope 1 in 1.5

GRAVITY DAM

Average river bed level around 968m

Top of Dam El 1047m

Length at top 213.7m

Foundation level (Deepest) El 945.5m

Height above deepest foundation 101.5m

Number of Blocks 14 Nos.

LOWER SPILLWAY

Number 7 Nos.

Crest elevation El 990m

Gate Type and Size Radial gates; 6.1m (W) x 12.6m (H)

Hoist Type and Capacity Twin Hydraulic cylinders, 2 x 175 MT

Stop Log Gates 1 No., 7 units, 6.1m (W) x 2.585m (H)

Hoist Type and Capacity Gantry Crane, 35 MT

ENERGY DISSIPATION ARRANGEMENT

Type Trajectory Bucket

Bucket radius 49.0 m

Lip angle 30o

Bucket Invert level EL 973.0 m

AUXILIARY SPILLWAYS

Number 2 Nos.


Size (including free board of 200mm) 5.0 x 4.2m

No. of Gates 3 (2 Service & 1 Emergency)

Hoist Type and Capacity Gantry Crane operating Stoplog units

INTAKE

Number 2 Nos.

Invert elevation El 1021m

Gate opening size 7.0m x 7.5m

Total width of trash rack arrangement 49m

Length of trash rack arrangement 16.24m

Length of inlet tunnel (including transition) 41.1m

Number of Gates 2 Nos. – Service Gate




2 Nos. – Emergency Gate (Bulk Head)

Hoist Arrangement and Capacity Rope Drum Hoist, 45 MT for bulk head Rope Drum Hoist, 80 MT for Intake Gate Rope Drum Hoist, 45 MT for bulk head

Rope Drum Hoist, 80 MT for Intake Gate

HEAD RACE TUNNEL

Number 1No.

Diameter & Shape 11.3m Circular shape

Length 10722m

Slope 1 in 227.16

Design discharge 480.3 m3/s

Velocity 4.79m/s

Number of intermediate Adits 4 Nos.

Length of intermediate Adits 301m, 740m, 355 and 267m

SURGE SHAFT

Number and type 1 No., Restricted orifice type

Diameter 26.0m

Orifice Dia 5.5m

Height 132 m

HRT invert at Surge shaft El 970.0 m

Top of Surge shaft 1102 m

Maximum surge level El 1100.5 m

Minimum surge level El 990.9 m

Length of Surge shaft bottom tunnel

(including transitions) 51 m

PRESSURE SHAFT

Number 3 Nos.

Diameter 5.6m

Length 49.2m, 26.6m, 49.2m

Design discharge 160.1 m3/s each

Steel Liner 28mm, ASTM 537 Class II

UNIT PRESSURE SHAFT

Number 6 Nos.

Diameter 4.0m

Length 512m each

Height of vertical drop 195m and 182m


Steel Liner 22mm to 40mm, ASTM 537 Class II

40mm to 44mm, ASTM 517 Grade F

Intermediate Adit level & length El 775.0m; 313m

BUTTERFLY VALVE (BFV) CHAMBER

Dimension 131m (L) x 10m (W) x 20m (H)

Number of BF Valves 6 Nos

BFV diameter 4.0m

BFV Centerline elevation El 972.0m

Floor Invert elevation El 968.0m

DRAFT TUBE

Invert level El 578.47 m

Size (Start / End) 1 No. – 11.53m (w) x 3.04m (h) /

2 No. - 6.5m (w) x 5.5m (h)

Length 22.82 m

Slope 1 in 10

DRAFT TUBE TUNNEL

Numbers 6 Nos.




Size and type D-Shape, 6.6m

Length (including transition) 99m

Slope 1 in 12

DOWNSTREAM SURGE CHAMBER


Invert level El 589.0m

Gate operation level El 621.0m

Maximum Surge level EL 619.7m

Minimum Surge level EL 597.4 m

Draft Tube Gate – Number and Size 6m, 6.2m x 6.2m

Hoist Arrangement and Capacity Rope Drum Hoist, 40 MT

TAILRACE TUNNEL

LINK TRT (s)

Number 3 / 1

Diameter 6.6m / 9.5m Modified Horse shoe

Length 85m, 60m, 86m / 52m

Invert at downstream surge chamber El 589.0m

MAIN TRT

Number 1 No.

Diameter 11.3m circular shape

Length (including transition) 555m

Invert level (Start / End) El 589.83 m / El 595.18 m

Slope 1 in 102

TRT DOWNSTREAM TRANSITION

Size - Start / End 11.3m D-shape /

11.3m (w) x 8.0m (h) D-shape

Length 50m

Bottom slope 1 in 8

TRT OUTFALL


Transition - size 1 No - 11.3m (w) x 8.0m (h) D-shape to 3 No –

6.0m (w) x 8.0 (h) Rectangle

Transition - length 9m

Minimum TWL El 603.0m

Normal TWL El 605.6m

Maximum TWL El 613.3m

TRT Outfall Gates 3 Nos, 6.0m (W) x 8.0m (H)

Gate Operating platform El 615.0 m


DAM COMPLEX & WATER CONDUCTOR

– TALO (TANGON) LIMB

Location of Dam Site

Latitude 28°39’18”N

Longitude 96°00’07”E

Location of Power House

Latitude 28°36’ 40”N


HYDROLOGY

Catchment Area 2573 sq km

Design Flood (PMF) 10,218 m3/s

River Diversion Flood 3,670 m3/s

Glacial Lake Induced Flood (GLOF) 2143 m3/s




RESERVOIR

Full Reservoir Level (FRL) El 1050m

Minimum Draw Down Level (MDDL) El. 1040m

Gross Storage at FRL 6.15 MCM

Gross Storage at MDDL 3.21 MCM

Live Storage 2.94 MCM

Submergence Area 36.12 ha

DIVERSION TUNNEL

Number 3 (on Left bank)

Diameter 11.5m Circular shape

Inlet Invert / Outlet Invert El 1010.0 m / El 1002.0m

Length 368m, 490m and 631m

Slopes 1 in 46.05, 1 in 61.27, 1 in 78.87

Number and size of Gates in each tunnel 2 Nos, 5.0m (W) x 11.5m (H)

Hoist Arrangement and Capacity 90 MT, Electrically operated Rope

Drum Hoist

COFFER DAM (UPSTREAM)

Type Concrete face with plum core

Top level El 1028.5m


Top width 6.5m

Length at top 93m

Upstream / downstream slope Vertical; 1 in 0.9 Stepped

COFFER DAM (DOWNSTREAM)

Type Random fill with downstream sealing layers

Top level El 1010m


Top width 5.0m

Length at top 75m

Upstream / downstream slope 1 in 1.5

GRAVITY DAM

Average river bed level El 1003m

Top of dam El 1052m

Length at top 184.1m

Foundation level (Deepest) El 972m

Height above deepest foundation 80m

Number of blocks 12

LOWER SPILLWAY

Number 6


Gate Type and Size Radial gates; 7.9m (W) x 13.37m (H)

Hoist Type and Capacity

Twin Hydraulic cylinders,

2 x 150 MT

Stop Log Gates 1 No., 8 units, 7.9m (W) x 2.44m (H)

Hoist Type and Capacity Gantry Crane, 35 MT

AUXILIARY SPILLWAY

Number 1 1 No.


Size (including free board of 200mm) 5.0m x 4.2m

Hoist Type and Capacity Gantry Crane operating Stoplog units

ENERGY DISSIPATION ARRANGEMENT

Type Trajectory Bucket




Bucket Radius 30.0 m

Lip Angle 30O

Bucket Invert Level EL 1001.5 m

INTAKE

Number 3 Nos.

Invert elevation El 1027.5m

Gate opening size 6.0m x 5.75m (H)

Total width of trash rack arrangement 74.0m

Diameter of Inlet tunnel 6.0m Modified horse shoe

Length of inlet tunnel 925m, 851m & 777m

Number of Gates 3 – Service Gate 3 – Emergency Gate

Hoist Arrangement and Capacity Rope Drum Hoist, 30 MT for Emergency Gate;

Rope Drum Hoist 50 MT for Intake Gate

DESILTING BASIN

Number and Type 3, Underground Duffore type

Size 18.5m (W) x 26.5m (H)

Length 350 m

Particle size removal 0.2 mm

Design discharge per basin 128.08 m3/s

Outlet gate, Number and size 3 Nos., 4.5m (W) x 5.5m (H)

Hoist arrangement and capacity Rope Drum Hoist, 45 MT

Design discharge per flushing duct 21.34 m3/s

Flushing duct size (upto SFT Gate

chamber) 3 Nos. - 2.0m (W) x 2.7m (H)

Flushing duct size (SFT Gate chamber to

Main SFT) 3 Nos. - 2.0m (W) x 3.55m (H)

Silt Flushing Tunnel (SFT) size 5.0m (W) x 5.7m (H)

Length of flushing tunnel 515m

Outlet level of flushing tunnel El 999.55m

Flushing Duct Gate, Number & Size 6 Nos., 2.0m (W) X 2.7m (H) (2 Gates in Each

Tunnel)

Gate Hoist arrangement and capacity Hydraulic Hoist, 190 MT

HEADRACE TUNNEL

Number 1 No.

Diameter & Shape 9.7m Circular shape

Length 13045 m

Slope 1 in 235.13


Velocity 4.34 m/s

Number of intermediate adits 5 Nos.

Length of Adits 555m, 370m, 530m, 417m & 366m

SURGE SHAFT

Number and type 1 No., Restricted orifice type

Diameter 21.0 m

Orifice diameter 4.25 m

Height 137 m

HRT invert at Surge shaft El 970.0 m

Top of Surge shaft El 1107.0 m

Maximum surge level El 1104.9 m

Minimum surge level El 984.0 m

Length of Surge shaft bottom tunnel

(including transitions) 46 m




PRESSURE SHAFT

Number 2 Nos.

Diameter 5.6 m

Length 46m (each)

Design discharge 160.1 m3/s each

Steel Liner 28mm, ASTM 537 Class II

UNIT PRESSURE SHAFT

Number 4

Diameter 4.0 m

Length 512 m each

Height of vertical drop 377 m


Steel Liner 25 to 40mm, ASTM 537 Class II

40 to 46mm, ASTM 517 Grade F

Intermediate Adit (Level, Length) El 775m, 422m

BUTTERFLY VALVE (BFV) CHAMBER

Dimension 85.6m (L) x 10m (W) x 20m (H)

No. of BF Valves 4 Nos.

BFV diameter 4.0 m

BFV Centerline elevation El 972.0 m

Floor Invert elevation El 968.0 m

DOWNSTREAM SURGE CHAMBER



Gate operation platform level El 621.0m

Maximum Surge level EL 619.6 m

Minimum Surge level EL 597.6 m

Draft Tube Gate – Number and Size 4 Nos, 6.2m x 6.2m

Hoist Arrangement and Capacity Rope Drum Hoist, 40T

TAILRACE TUNNEL

LINK TRT (s)

Number 2 Nos.

Diameter 6.7 m Modified Horse shoe

Length 81 m and 99m

Invert at downstream surge chamber El 589.0m

MAIN TRT

Number 1 No.

Diameter 9.5 m circular shape

Length (including transition) 544 m

Invert level (Start / End) El 589.83 m / El 595.18 m

Slope 1 in 99.45

TRT DOWNSTREAM TRANSITION

Size - Start / End 9.5 m D-shape /

9.5m (w) x 8.0m (h) D-shape

Length 50 m

Bottom slope 1 in 8

TRT OUTFALL


Transition - size 1 No. – 9.5m (w) x 8.0m (h) D-shape to

2 Nos. – 6.0m (w) x 8.0m (h) Rectangle

Transition - length 9 m

Minimum TWL El 603.0 m




Normal TWL El 605.6 m

Maximum TWL El 613.3 m

Gate Operating platform El 615.0 m

TRT Outfall Gates 2 Nos., 6.0m (W) x 8.0m (H)


POWER HOUSE COMPLEX

UNDERGROUND POWER HOUSE

Dimensions 352m (L) x 23.5m (W) x 59.73m (H)

Installed Capacity 3070 MW

Number of Units 6 x 307 MW (Dri) + 4 x 307 MW (Talo)

Turbine centerline elevation El 595.0m

Maximum gross head 447.0m (Dri) / 442.0m (Talo)

Maximum net head 446.9m (Dri) / 441.9m (Talo)

Minimum net head 413.40m (Dri) / 415.9m (Talo)

Rated Net Head 420.0 m

Service Bay Level El 610.0m

MAIN ACCESS TUNNEL (MAT)

Size and type D-Shape, 8.0m (W) x 8.0m (H)

Length (Dri / Talo (Tangon) Limb) 474m / 779m

TRANSFORMER HALL

Dimension 349.6(L) x 16.5(w) x 24.3 (H)

Transformer floor level El 610.0m

GIS floor level El 622.0 m

TURBINE

Numbers & Type 10 Nos., Vertical Axis Francis

Rated Turbine Output 311.68 MW

Rated head 420.0m

Speed 250 rpm

Rate discharge 80.05 m3/s

GENERATOR

Number & Type 10 Nos., Semi Umbrella Type

Output 341.11 MVA

Nominal speed 250 rpm

Voltage/Frequency 17.5 kV, 50 Hz

Power factor 0.9

TRANFORMER

Type ODWF

Rating 17.5 kV, 400/√3 kV, 125 MVA

Phase Single

SWITCHYARD

Type Gas Insulated Switchyard (GIS)

Location Above transformer hall

POTHEAD YARD

Size 234m (L) x 60m (W) & 120m (L) x 45 m (w)

Bench Elevation El 725m

Nominal Voltage Class 400kV

POWER BENFITS

50% Dependable Energy 13, 694.3 MU

90% Dependable Energy 12, 846.8 MU

Design Energy (@ 95% Plant availability) 12, 766.8 MU

DRI DAM-TOE POWER HOUSE

OPERATING LEVELS




Full Reservoir Level El 1045m

Minimum Draw Down Level El 1039m

INTAKE STRUCTURE

Number of Intakes 1 No.

Block Number 4 Nos.

Nearest Abutment Left

Invert level of intake El. 1030m

Size of Trash Rack Opening 17.00m (H) x 6.0m (W)

Size of Gate 4.675m (H) x 2.8m (W)

Hoist Capacity Rope Drum Hoist Capacity 18T

Design Discharge 30.64 m3/s

PENSTOCK

Number and Diameter 1 No., 2.8m

Thickness of Liner 10mm

Type of Steel ASTM A537 Cl-2

Length of Penstock 108.6m

Design Discharge through Penstock 30.64 m3/s

SURFACE POWER HOUSE

Dimensions 20m (L) x 20m (W) x 40.7m (H)

Installed Capacity 19.6 MW

Number of Units 1 x 19.6 MW

Elevation of Turbine Runner Center Line 964.8m


Maximum Gross Head 77.8m

Min. Gross Head 71.0m

EOT Crane capacity (Powerhouse) 80 MT

TURBINE

Number and Turbine Type 1 Nos., Vertical Axis Francis

Turbine Rated Output 20 MW

Rated Head 72.5m

Rated Speed 300 rpm

GENERATOR

Number & Type 1 Nos., Suspended Type

Rated Capacity 21.8 MVA

Generation voltage 11 kV

Power factor 0.9

TRANFORMER

Type ONAN

Rating 11/66 kV, 24 MVA

Phase 3 –phase

SWITCHYARD

Max. voltage 72.5 kV

Rated Voltage Class 66 kV

Rated Continuous Current 191 A

DRAFT TUBE GATE

Type of Gate Vertical Lift Slide Type

Gate Size 5.5m (W) x 3.1m (H)

Hoist Type Rope drum hoist, Capacity 15T

TAILRACE DUCT

Length 39.7m

Duct shape Rectangular

Duct size 5.5m (W) x 3.5m (H)




Outlet sill elevation El 965.8m

Normal Tailwater Level 968.0m

Maximum Tailwater Level 980.7m

Minimum Tailwater Level 967.2m

POWER BENEFITS

90% Dependable Energy 172 MU

Design Energy (@ 95% Plant availability) 163 MU

TALO (TANGON) DAM-TOE POWER

HOUSE

OPERATING LEVELS

Full Reservoir Level El 1050 m

Minimum Draw Down Level El 1040 m

INTAKE STRUCTURE

Number of Intake 1 No.

Block Number 2 Nos.

Nearest Abutment Left

Invert level of intake El. 1034 m

Size of Trash Rack Opening 18.00 m (H) x 5.38 m (W)

Size of Gate 4.01 m (H) x 2.4m (W)


PENSTOCK

Number and Diameter 1 No., 2.4m

Thickness of Liner 10mm

Type of Steel ASTM A537 Cl-2

Length of Penstock 68.50m

Design Discharge through Penstock 19.52 m3/s

SURFACE POWER HOUSE

Dimensions 19m (L) x 32m (W) x 36.35m (H)

Installed Capacity 7.4 MW

Number of Units 1 x 7.4 MW

Elevation of Turbine Runner Center Line 998.3 m


Maximum Gross Head 49.0m

Min. Gross Head 38.5m

EOT Crane capacity (Powerhouse) 32 MT

TURBINE

Number and Turbine Type 1 Nos., Vertical Axis Francis

Turbine Rated Output 7.55 MW

Rated Head 43m

Rated Speed 375 rpm

GENERATOR

Number & Type 1 No., Suspended Type

Rated Capacity 8.22 MVA

Generation voltage 11 kV

Power factor 0.9

TRANFORMER

Type ONAN

Rating 11/66 kV, 9 MVA

Phase 3 –phase

SWITCHYARD

Max. voltage 72.5 kV

Rated Voltage Class 66 kV




Rated Continuous Current 72 A

DRAFT TUBE GATE

Type of Gate Vertical Lift Slide Type

Gate Size 4.0m (W) x 2.5m (H)

Hoist Type Rope drum hoist, Capacity 10T

TAILRACE DUCT

Length 27.9m

Duct shape Rectangular

Duct size 4m (W) x 3m (H)

Outlet sill elevation El 999.85m

Normal Tailwater Level 1001.5m

Maximum Tailwater Level 1013.5m

Minimum Tailwater Level 1001.0m

POWER BENEFITS

90% Dependable Energy 65 MU

Design Energy (@ 95% Plant availability) 62 MU

PROJECT ECONOMICS (FOR 3097 MW)

Base cost of Civil Works (Dec.2011 Price

Level) Rs.9865.34 Crore

Base cost of E&M Works (Dec.2011 Price

Level) Rs.3,566.65 Crore

Miscellaneous Cost Rs. 52.00 Crores

Total Base Cost (Dec.2011 Price Level) Rs.13,483.99 Crore

Construction period (including

commissioning of all units)

84 months (after 43 months of preconstruction

activities)

Escalation in Cost (Civil & HM) Rs. 3,903.32 Crores

Escalation in Cost (E&M) Rs. 1,418.72 Crores

IDC & Financing Cost Rs. 6,464.19

Total completion cost of the project Rs.25,296.95 Crores

2.4 INFRASTRUCTURE FACILITIES

This part outlines the preliminary planning of infrastructure facilities.

2.4.1 Approach to the Project

The project can be approached through various routes and modes of transportation like railways,

airways, waterways and roadway.

2.4.1.1 Transportation by Railway

Project site is accessible by railway up to Dangari railway station on the south bank (Assam side) of

Lohit River which is connected with broad-gauge rail line. The transportation of project cargo by

railway is possible up to Tinsukia. Tinsukia is the nearest rail yard from this head.

2.4.1.2 Transportation by Waterway

The nearest sea port is Haldia port at Kolkata. The Haldia port is connected to nearest waterway head at

Sadiya Ghat through India-Bangladesh protocol route from Haldia port to Bangladesh border and from

Bangladesh border to Sadiya Ghat by national waterway number 2.

2.4.1.3 Transportation by air

The nearest airport is at Dibrugrah which is about 350km from Etalin village, the power house

location. The distance from Dibrugarh to Tinsukia is 60km. The nearest operational helipad is at Anini




which is 60 km from Etalin village.

2.4.1.4 Transportation by road

There are various alternative road routes connecting Kolkata port to Guwahati and then Guwahati to

Roing. A detailed study has been conducted by ABC India Ltd, Kolkata to explore all the possible

alternative routes connecting Kolkata to Roing and Roing to Etalin.

2.4.2 Project Roads

A network of roads is required to approach various locations of project site such as Dam sites, Adits,

surge shaft, powerhouse, pothead yard, Main Access Tunnel (MAT) and Tailrace Tunnel (TRT) portal,

Dumping yards, quarry locations etc. It has been assessed that about 50km length of new road is

required to be constructed to facilitate construction of various components. Average gradient of 1(V)

to 15(H) has been considered for proposed roads from the construction point of view. Apart from the

construction of new project roads 35km stretch of existing roads with in project area needs to be

widened and strengthened for the movement of heavy equipment and machinery in all weathers and

round the year. All the major roads have been proposed for 40R loading class as per IRC standards

and allowing clearances on the sides, drains and parapets, the required formation width of the road

works out to be 7.5m for the free flow of traffic mostly comprising of rear end dumpers, tippers,

transit mixers and loading equipment like loaders, excavators, backhoes.

2.4.3 Project Bridges

Keeping in view the access to various project components and approaches it has emerged that 2nos.

of temporary and 2nos. of permanent new bridges and culverts at various locations would be required

during and after the construction phase of the project. It is also required to strengthen or recast the

existing bridges in the project area.

The details of bridges and culverts in the project area which are required to be strengthened or

recasting are given in Table 2.2.

Table 2.2: Existing Bridges in Project Area

S.

No.

Location (distance

measured from

Etalin)

Type of

bridges Class Sector

Road

maintained

by

Bridge

characteristics

1 Talo (Tangon) , 3.4

km

DTBB

DDBB 24 R

Etalin-Talo (Tangon)

Dam site BRO

Span-1 X 67m,

CW-3.8m, VC-3.2m

2 3.9 km RCC

Slab

Etalin-Talo (Tangon)

Dam site BRO

Span-1 X 6.5m,

CW-7m

3 Noh Nallah, 7 km DSR BB 18 R Etalin-Talo (Tangon)

Dam site BRO

Span- 1 X 42.6m

CW-3.7m, PH-1.1m

4 Makri Pani, 11 km DLR 24 R Etalin-Talo (Tangon)

Dam site BRO

Span-1 X 36.5m,

CW-3.7m, PH-1.1m

5 Chambopani, 9.5

km Bailey 24 R Etalin-Dri Dam site BRO

Span-1 X 33m,

CW-3.8m, PH-1.1m

7 Rupani, 14 km Bailey 24 R Etalin-Dri Dam site BRO Span-1 X 43m, Cw-

3.8m, PH-2.2m

8 17.4 km Bailey 24 R Etalin-Dri Dam site BRO Span-1 X 27.3m,

CW-3.8m, PH-1.1m

9 24 km Bailey 24 R Etalin-Dri Dam site BRO Span-1 X 30.4m,

CW-3.8m, PH-1.1m




Figure 2.2: Layout map of Etalin H.E. Project showing infrastructural facilities




2.4.4 Construction of new bridges

Permanent bridge at Etalin village (PPB1)

Permanent bridge no.1 (PPB1) has been proposed to cross left bank of the Talo (Tangon) river to

the right bank at the powerhouse location. This bridge is envisaged to serve and facilitate

construction of powerhouse located at the right bank of the Talo (Tangon) river. The existing road

is aligned along left bank. The approximate span of bridge will be 145m.

Permanent bridge at Punli village (PPB2)

Bridge PPB2 has been proposed near Punli village to provide access to adit-T1, T2 and T3 on the

right bank of Talo (Tangon) river from existing road which is on the left bank of Talo (Tangon)

river. The bridge is envisaged to serve and facilitate Talo (Tangon) -HRT and desilting basins. The

approximate span of bridge will be 130m.

Temporary Bridge at Talo (Tangon) Dam site (PTB1)

Temporary bridge No.1 (PTB1) is proposed just at the downstream of dam axis of Talo (Tangon).

This bridge is required solely for the construction of upstream works of Talo (Tangon) limb viz.

Diversion tunnel, Dam and Intake as the extent of construction will be carried out on both the

banks simultaneously and hence, needed to be connected. The approximate span of bridge will be

125m.

Temporary Bridge at Dri Dam site (PTB2)

Temporary bridge at Dri Dam site is proposed as PTB2 at the downstream of dam axis. The

approximate span of bridge will be 100m. This bridge is required solely for the construction of

upstream works of Dri limb viz. Diversion tunnel, Dam as the extent of construction will be carried

out on both the banks simultaneously and hence, needed to be connected.

Brief summary of proposed bridges has been presented in table as follows:

S. No. Notation Description Nature Length (m) Elevation

1 PPB1 Bridge at Etalin Village Permanent 145 650

2 PPB2 Bridge at Punli Village Permanent 130 950

3 PTB1 Bridge at Talo (Tangon) Dam

Temporary 125 1000

4 PTB2 Bridge at Dri Dam Temporary 100 1000

2.4.5 Project Colonies

In order to execute the project, it has been envisaged that proper infrastructure works are

required as permanent and temporary staff residential buildings, office complex, field hostel,

school, hospital, shops, canteen or mess, places for worship etc.

These Buildings and Colonies (see Figure 2.2) will have the following basic facilities:

Potable water supply arrangements.

Sanitation and sewage disposal arrangements.

Drainage arrangements.

Internal roads and their drainage works.

Electrification.

Fencing and security.

The Project construction is likely to last for 7 years. The peak manpower strength likely to be

employed during project construction stage is estimated about 3000 Nos.

The following assumptions have been made for assessing the emigrating population in the area:




80% of workers and technical staff immigrating into the area are married.

In 80% of the family of workers both the husband and wife will work.

In 100% of the family of technical staff, only husband will work.

2% of total migrating population has been assumed as service providers.

50% of service providers will have families.

Family size has been assumed as 5.

Based on experience of similar projects and above referred assumptions, the increase in the

population as a result of migration may be of the order of 12000.

The water requirement during construction phase is proposed to be met from the flow of nearby

Nala/Streams by gravity flow and providing water treatment plant and overhead storage tanks.

The domestic water requirement has been estimated as 70 lpcd (Liters Per capita per day). Thus,

total water requirements work out to 0.84 Mld (Million Liters per day). It is assumed that about

80% of the water supplied will be generated as sewage. Thus, total quantum of sewage generated

is expected to be of the order of 0.67 Mld. The sewage shall be collected in anaerobic septic tanks.

The details are discussed in Chapter 4 on Solid Waste Management in EMP report.

During the operation phase the cause and source of water will be much different. Since, only a

small number of staff, about 300 persons will be residing in the project colony proposed to be

developed. About 0.20 to 0.30 Mld of sewage will be generated.

It is proposed to provide biological treatment facilities including secondary treatment units for

sewage so generated. The BOD load after treatment shall reduce to 10 to 12 kg/day. It shall be

ensured that sewage from the project colony be treated in a sewage treatment plant so as to meet

the disposal standards for effluent. Thus, with commissioning of facilities for sewage treatment, no

impacts are anticipated as a result of disposal of effluents from the project colony. Each building is

proposed to be provided with septic tanks of required capacity and maintained on regular basis for

the collection of anaerobic sewage.

2.4.5.1 Owner’s building and colonies

The owner’s colony would provide for residential as well as office accommodation to its staff, both

for pre and post construction stages. In addition to residential complex, the colony would also

have facilities for medical aid, places of worship, fire fighting, educational and vocational facilities,

banking and telecom facilities, shopping, sports and recreational activities including community

functions, fuel dispensing outlet, material testing laboratory, etc. A small workshop or auto shop

for up keep of automobiles in the post construction period would also be located in the colony. One

project colony has been proposed on the left bank of the Talo (Tangon) river, about 9km upstream

of Etalin village on Etalin-Maliney road. This colony is proposed to have Main building for Project

office and a residential campus for high rank officers. One field hostel has also been envisaged for

engineers and equivalent staff, one school for residential staff and a hospital.

One building at each dam site (Dri and Talo (Tangon)) has been envisaged for operation and

maintenance. The total number of permanent O&M Staff required for the project is estimated to be

about 702 for which 3,000 Sq m flat area will be required.




2.4.5.2 Contractors colonies and buildings

Temporary buildings will include contactors colonies which would serve the purpose of residence

and offices, facilities for social activities like shopping, social gatherings, worship, etc. for the

contractors and their families engaged in project. Ample space for colonies of Civil, H&M and E&M

contractors has been marked near powerhouse location the same location shall be partially shared

by a proposed permanent hospital building and first aid center during project execution phase. Five

locations for laborers camps have been earmarked as 1 on each dam site, 1 at Chanal village near

Ron pani, 1 at Punli village and 1 at powerhouse location.

2.4.6 Workshops and Parking Space

Given the layout of civil components, both the dam site and powerhouse areas would be major

hubs of construction activities throughout the implementation period of the project. Moreover, as

they are not close to each other, it would be practical and efficient that separate job facilities of

major nature are created near each of these work zones. Three (3) separate base workshops have

been proposed for earth moving, concreting and drilling equipments one each at both the dam

locations and one near to the powerhouse area.

Every workshop would have partly covered area in addition to open area. Equipment requiring

major overhaul/repairs would normally be parked under cover. The open areas would provide

parking space for the equipment under minor repair. A store to stock the spares for the

equipment, an office and toilet facilities would be provided under the covered space.

One first aid post would be provided at each work site which would also cater to the requirements

of the workshop crew.

2.4.7 Stores and Warehouses

The storage of material and spares required for various activities of the project would be efficiently

managed. Adequate material supply is the backbone of any job.

Three central warehouses have been planned; one would be established for the powerhouse

complex and the other two for the dam complexes on each limb, which would receive all incoming

supplies. Cement, reinforcement steel, explosives, and other job specific items of material could

also be sent directly to the respective sites as per their demand. The ware houses would stock

electrical items separately.

2.4.8 Penstock Fabrication Yard

A penstock fabrication yard equipped with two plate bending rolls, a battery of welding and gas

cutting sets, hydro-testing and radiography facility, sand-blasting and painting equipment and

sufficient space to stock the raw plates as well as the finished ferrules awaiting dispatch, would be

provided near the powerhouse complex. An E.O.T crane of 40 MT capacities traveling over the yard

would be deployed for handling the ferrules during different stages of fabrication. A separate

mobile crane of 40 MT would be deployed to handle the plates/ferrules in the stock yard. The

fabrication yard would be partly covered to allow welding and other activities to go on unhindered

under the covered area.




2.4.9 Aggregate Processing Plants/Batching and Mixing Plants

The overall demand of concreting for various structures has been computed as 31.68 lakhs cum.

The quantities involved in the construction of the civil works, both in the dam and powerhouse

areas, are large. The concentration of construction activity would be confined mainly to three areas

i.e. the dam areas (one on each limb) and the powerhouse area. These three working zones are

about 25km apart from each other. Due to this large distance, it would be more efficient and

pragmatic to set up independent services on all three major working zones.

Based on the construction planning, methodology & schedule the peak requirement of concrete

and raw aggregates has been estimated to decide the plant capacities for Aggregate processing

(APP) and Batching & Mixing (BM). The following table shows the capacities of aggregate

processing and concrete batching & mixing plants.

Size and location of aggregate processing and batching plants

S.No. Location Components Capacity, T/Hr (Aggt. Processing

Plant)

Capacity, Cum/Hr (Batching Plant)

1 Talo (Tangon) -Dam Talo (Tangon) -Dam 500(TAPP1) 160(BM1)

2 Talo (Tangon) -Intake

Intake and Desilting

500(TAPP2)

160(BM2)

3 Adit-T2 Talo (Tangon) -HRT 45(BM3)

4 Adit-T3 Talo (Tangon) -HRT 45(BM4)

5 Adit-T4 Talo (Tangon) -HRT

2x500(PAPP)

45(BM5)

6 Surge Shaft(Top) Talo (Tangon) -HRT 45(BM6)

7 Surge Shaft(Top) Surge shafts

8 Surge Shaft (Bottom) Surge Shaft/ Pressure Shaft 120(BM7)

9 Powerhouse Powerhouse Complex 120(BM8)

10 Adit-D3 Dri-HRT 45(BM9)

11 Dri-Dam & Intake Dri-Dam

750(DAPP2)

45(BM10)



2.4.10 Quarries/Borrow Areas

The total requirement of coarse and fine aggregates has been estimated as 32.82 Lakh m3 and

18.92 Lakh m3, respectively, to fulfill the requirement of construction material. Most of the

requirement of coarse aggregate will be met from the rock excavated from tunnels and

underground works and the remaining will be quarried from identified quarries. About 10.75 Lakh

m3 has been anticipated from 2 Nos. of identified Rock Quarries (RQ). Similarly, the requirements

of fine aggregates will be met from the 4Nos. of identified Shoal & Sand quarries (PQ). About 9.43

lakh m3 is anticipated from the various identified quarries for fine aggregates and the rest will be

obtained by crushing the potential muck generated from underground excavation muck.

Total Concrete = 31,68,400 m3

Total Coarse Aggregates = 32,82,200 m3

Total Fine Aggregates = 18,92,300 m3

Total Cement = 10,83,800 MT

To meet the requirement of coarse and fine aggregates for all components of the project, 2 nos. of

rock quarries and 4 nos. of Shoal quarries have been identified in the vicinity of the project and

are located above the Etalin-Anini Road upstream of dam site, near Powerhouse location at Etalin.




2.4.11 Muck Disposal Areas

The project would generate substantial quantity of muck from excavation of various structures.

The total quantity of muck likely to be generated from open excavation including construction and

widening of the roads, etc. including swell factor is about 165.65 lakh cum. However after the

utilization of muck for different project components and also considering the swell factor total

estimated quantity to be disposed of is about 117.35 lakh cum. Most of the excavated material is

proposed to be dumped at 12 suitable locations identified specifically for this purpose with 7 sites

along Dri limb, 1 site near powerhouse location and 4 sites along Talo (Tangon) limb.

2.4.12 Explosive Magazine

For the storage and handling of explosives required for the drilling and blasting operations,

permanent and portable magazines will be constructed for which necessary approvals will be taken

from the concerned authorities. Explosive vans will be used for the transport of explosives from

the magazine to the work sites. All safety codes and regulations prescribed by the central and

state government in this respect will be followed and magazines will be suitably guarded round the

clock. It has been assessed that 2 no. of magazines of 20MT capacities would be required. The

explosive magazine complex has been planned to keep the distance traveled by the explosive van

to the minimum.

As laid down in the Explosive Rules of 1983, a safe distance of 300m is required to be maintained

from public roads, etc. The location of the magazines has been indicated in the Infrastructure

layout plan keeping the above in mind.

2.4.13 Land Requirement

For the development of Etalin Hydroelectric Project, land would be acquired for construction of

project components, submergence area, muck dumping, quarrying, construction camps and

colony, etc. Based on the final project layout, land requirement has been finalized as 1155.11 ha

(Table 2.3).

Table 2.3: Land Requirement of Etalin H.E. Project

(For Legends (LA-1 to LA-21A refer to Figure 2.2)

LA Name of the Component Area

(Ha)

LA-1

RQ1 (Rock Quarry)

58.02

RQ2 (Rock Quarry)

Contractor / Owner site office and store

Dumping Yard, DMD-4 (a)

Dumping Yard, DMD-4 (b)

Labour Camp-5

DT -RB(Diversion Tunnel- Right Bank); 3 Nos. (DRI LIMB)

DT -LB(Diversion Tunnel- Left Bank); 1 No. (DRI LIMB)

Dam/ Dam Toe Power House & Coffer Dam D/S

Intake Structure

Project Roads

LA -2

Explosive magazine/construction facility areas and labour camps (Right Bank)

56.53 Work Shop, Warehouse, Store &

Parking Space-3 (Left Bank)

Dumping area DMD 5 (Left bank)

Project Roads

LA-3

Dumping Yard, DMD-3

20.05 Dumping Yard, DMD-2

Total Road Area in LA -3




LA Name of the Component Area (Ha)

LA-4 Labour camps

23.98 Total Road Area in LA -4

LA-4A

Store/ work shop for package- B

67.74 Batching plant / main work shop

Contractors camp and owners camp office/residences

Provision for Priority Road (Dri Limb)

LA-5 Road Area 2

LA-6

Batching Plant/ work shop

39.79 Labour Camp-4

Dumping Yard, DMD-6


LA-6A Provision of facility area/explosive magazine and change in road alignment 12.33

LA-7

Batching Plant

80.56

Dumping site

Aggregate crushing plant

Batching plant and aggregate stock piling

Batching plant and work shop


LA-7A Provision of change in portal & alignment of road 6.38

LA-8

Batching Plant BM-6

120.65

Batching Plant BM-7

Contractor & Departmental Office-2

PQ-01 (Shoal Quarry)

Labour Camps

Power House

Main store/workshop and facility areas

Total Road & Bridge (PPB1) Area in LA -8

LA-9 Dumping yard EM & HM Storage Workshop, Warehouse, store, Parking 20.81

Total Road & Bridge (PPB1) Area in LA -9

LA-10

Owners temporary colony and office

11.31 Dumping Yard, PMD-2


LA-10A Provision of Shoal Quarry PQ-02 9.77

LA-11 Road Area 41.38

LA-11A Provision of Shoal Quarry PQ-03

17.2 Contractors colony and office and facility areas

LA-12

Batching Plant and aggregate processing plant

52.79

Labour camps for Contractors Colony-EM, HM &

Civil PH Works

Penstock fabrication yard

Dumping Yard, TMD-7 / PQ-02


LA-13 Site office and work shop

8.33 Total Road Area in LA -13

LA-13A Provision of facility Area 1.5

LA-14

Main Project Office and Residential Campus including school and hospital (Left Bank) 67.78

Road & Labour Camp

LA-14A

Main work shop and batching plants

31.49 Labour camps for contractor (Right Bank)

Road Area

LA-14B Additional Bridge to access Adit T2 & T3

6.99 Contractors colony

LA-15

Dumping Yard, TMD-5

79.18

Dumping Yard, TMD-4

Batching Plant BM-3

Labour Camp -2

Dumping Yard, TMD-6

Dumping Yard, TMD-7

Aggregate crushing plant





LA Name of the Component Area (Ha)

LA-15A Access to Adit T3 and explosive magazine 14.3

LA-16

Adit T-1 portal re-located (Right Bank)

23.27 Workshop and construction facility areas (Right Bank)


LA-17 Shoal deposit

16.24 Additional In-situ rock quarry

LA-18

Stone Crucher TAPP-2

57.65

Batching Plant BM-2

Contractor & Departmental Office Space-1

Store / workshop and construction facility areas

Dam/ Dam Toe Power House & D/S Coffer Dam

Total Road & Bridge (PTB1) Area in LA -18

LA-19

Batching plant

32.82

Dumping Yard, TMD-2 and batching plant

Workshop, Warehouse, Store & Parking Space-1

Diversion Tunnel (Tangon) 3 Nos.

DAM/ DAM Toe Power House


LA-20

Dri Reservoir, U/S Coffer Dam

83.32 & Project Roads

PQ-04 (shoal quarry)

LA-20A Realignment of existing road to be submerged & provision of dumping yard u/s of dam

20.44

LA-20B Provision of foot track along Dri reservoir

9.32 Additional land for road to Dam top

LA-20C Provision of priority road (Dri area) 6.16

LA-21 Tangon Reservoir, U/S Coffer Dam

36.12 & Project Roads

LA-21A Provision of foot track along Tangon reservoir 6.89

EBP Project Colony & Office establishment 12.02

Total 1155.11

Surface Land 1063.78 ha + Underground Area 91.33 ha

Land would be required for locating the permanent works as well as for setting up the

infrastructural and job facilities necessary for constructing the project in an expeditious and

optimal manner. Of the total extent of area of land required, some areas would be acquired

permanently while the balance can be obtained on lease from the owners for a definite time period

and returned to them after the project is completed. In the latter case, it would be restored to its

original condition as far as possible.

2.4.13.1 Land Required Permanently

Land would be acquired on permanent basis for:

Project Components, Tunnels and Adit Portals

Submergence Area

Area required for Project office and O&M Buildings

Area required for Permanent Residential colonies

Muck Dumping yards

Quarry or Borrow Areas

Area required for Access Roads, Approach paths and Bridges

Land required for permanent works, and

Owner’s colony and offices.

2.4.13.2 Land Required on Lease or Temporary Basis

The following land will be taken on lease basis for a few years during the construction period:




Temporary buildings and residential colonies includes labour camps

Temporary site offices testing laboratories

Workshops and Equipment parking

Stores and warehouses

Pre-Fabrication yards

Construction plants (APP and BM)

Temporary bridges

Areas near construction of roads or project components where disturbance is expected due

to be loose muck, noise etc.

2.4.14 Construction Power

Dibang valley district has about 1.85MW of power supply through mini/micro projects, which is not

even sufficient to meet to their local domestic demands and thus the state Government has kept

D.G. sets to meet the shortfall in demand.

There is no grid power available in the region. Therefore the project has to make its own

arrangements of power supply for its construction activities as well as domestic need and thus

27MW of power supply through D.G sets has to be arranged. 7 DG-Houses have been envisaged

with different capacities of DG sets to meet the project demand.

2.4.15 Tele-Communication and Other Facilities

Mobile network or any other telecommunication facilities in the project area are not available. The

nearest mobile network is available at Hunli and is served only by BSNL. It is proposed that the

project area will be connected by the mobile network, fixed line and WLL services from BSNL as

available in other parts of the state. For effective coordination among various work sites,

workshop, colonies, stores, design office, head office, etc. and a reliable tele-communication

network is necessary. An electronic automatic telephone exchange with a capacity of about 100

lines is proposed at project head quarters. The internal telephone or EPBAX system would be

maintained by the project authority. Telecommunication link outside the project area would be

provided by upgrading the existing BSNL network. A wireless V-SAT system is also proposed for

linking the project site with Dri-Dam site, Talo (Tangon) -Dam site, Etalin Powerhouse Site, Hunli,

Roing, Tinsukia, Guwahati and Delhi. After completion of construction activities, the

telecommunication network is proposed to be continued so as to serve during operation and

maintenance stage.

A VHF wireless network is also proposed to be established to connect various project sites,

Guwahati and Tinsukia, Roing Etalin. This will be mainly utilized for the construction purpose and

will be scaled down after commissioning.

2.4.16 Security and Safety

Safety being an essential job requirement, adequate arrangement for lighting and security will be

made in the project area. Adequate preventive measures against accidents will be taken as

prescribed in various IS codes. The project work site will have restricted entry and visitors will only

be allowed on permits issued by the relevant competent authority. All work force and other

personnel will be required to carry identity cards and passes issued by the project authority which

will be checked at the entry check posts provided at suitable places.




3.1 INTRODUCTION

The importance given to environmental considerations in order to achieve sustainable and

successful development is increasingly gaining acceptance among various developmental

experts and institutions. Understanding the consequences of development and forecasting its

impact on the basic life support system - land, water and air - is referred to as the

Environmental Impact Assessment or EIA. New dimensions have also been added to the EIA

studies encompassing impacts on the ethnic diversity, socio-cultural and socio-economic

aspects including displacement, resettlement and rehabilitation of human societies where

developmental activities are undertaken.

EIA is a location specific study; with a common basic structure of understanding the baseline

status of relevant environmental components and impact prediction due to proposed

development. However, the process varies from project to project based on location, type and

magnitude of the operations. EIA studies give emphasis on the assessment and prediction of

impacts of development on natural ecosystems and their species along with concentrating on

geophysical features, which mostly cover reversible impacts. The main aim of having EIA

studies carried out is to understand and prioritize the impact of development activity on the

natural life support systems and processes with main emphasis on the continuation of

ecosystem processes and functions, so that adequate remedial/mitigating measures are taken

right from the design stage.

Typically in a hydro-power scheme, whose sustenance and continuity largely depends on the

quality of ecosystems in the catchment of its river and reservoir, biological health of the

catchment will control not only the quality and quantity of water in the river but also the life of

reservoir. There is only one way to generate hydro-power on sustainable basis and that is by

maintaining the natural ecosystems in the catchment. Hydro-power is a direct benefit of

natural ecosystem functions, which are controlled by the biodiversity.

3.2 METHODOLOGY

Standard methodologies of EIA were followed for conducting the CEIA study for the proposed

Etalin HE Project. A brief account of the methodologies and matrices followed in the present

study is given below under different headings. All the methods were structured for the

identification, collection and organization of baseline environmental data, assessment of

developmental component and their impacts on the baseline environment. The information

thus gathered has been analyzed and presented in the form of a number of visual formats for

easy interpretation and decision-making.

Chapter METHODOLOGY

3




Figure 3.1: Study area map delineated as per approved TOR of Etalin H.E. Project




3.2.1 Study Area

Study area for environmental study has been delineated as:

Project area or the direct impact area within 10 km radius of the main project

components like barrage and also area within 10 km upstream of reservoir tail.

Submergence Area

Catchment area up to the dam sites

A map of the study area prepared based on the above criteria is given at Error! Reference

source not found..

3.2.2 Scoping Matrix

Scoping is a tool which gives direction for selection of impacts due to the project activities on

the environment. As part of the study, scoping exercise was conducted selecting various types

of impacts which can accrue due to hydroelectric project. Based on the project features, site

conditions, the scope of studies were approved by MoEF&CC (Refer Annexures – I & II).

The approved Terms of Reference (TOR) specified for various parameters were covered during

the EIA study.

Based on the Scoping matrix (Table 3.1), the environmental baseline data have been

collected and the project details superimposed on environmental baseline conditions to

understand the beneficial and deleterious impacts due to the construction and operation of the

proposed project.

3.2.3 Baseline Status Primary Data Collection

The data on baseline status of various environmental parameters in the study area was

collected through primary surveys for three seasons as specified in the approved TOR for the

Etalin HEP.

3.2.4 Secondary Data

The data for various environmental baseline parameters like forest types, flora, wildlife, fishes,

and also socio-cultural aspects was collected from secondary sources like published reports of

Government departments like State Forest Department, State Fisheries Department

educational and research institutions like State Forest Research Institute, Itanagar, Regional

Centers of Botanical Survey of India and Zoological Survey of India, Itanagar, Rajiv Gandhi

University and Census of India. The secondary data was duly supplemented, wherever

applicable, with primary field surveys conducted in different seasons.

3.2.4.1 Physiography

The spatial database on physiographic features like drainage, roads, settlements and villages,

etc. was created from maps of topographic sheets and satellite data followed by ground truth

verification and data analysis with Geographic Information System (GIS) tools. The contours

of study area including that of catchment area were digitized from Survey of India 1:50,000

scale toposheets to calculate slope category for the entire catchment. Percent area under

various slope categories namely gently sloping, moderately sloping, strongly sloping,

moderately steep to steep, steep, very steep and escarpments were also calculated for the

entire catchment.




GIS based maps have been provided for the following themes:

General Features (Villages, roads, tributaries)

Hydrology: Drainage of Dri and Talo (Tangon) river along with their tributaries

Geology

Erosion

Elevation profile

Slope

Land use in study area

Villages in Impact Zone

Table 3.1: Scoping matrix for EIA study of Etalin H.E. Project

Environmental Parameter Likely Impacts

Land Environment

Construction phase

Increase in soil erosion

Pollution by construction spoils

Acquisition of land for construction works colonies

Solid waste from construction works colonies

Acquisition of land for various project appurtenances

Change of land use

Water Resources and Water Quality

Construction phase

Increase in turbidity of nearby receiving water bodies

Degradation of water quality due to disposal of wastes from

construction works colony and construction sites

Operation phase

Disruption of hydrologic regime

Sedimentation and siltation risks

Impacts on D.O. due to reservoir stratification

Risk of eutrophication

Reduced flow impacting downstream users

Aquatic Ecology

Construction phase

Increased pressure on aquatic ecology as a result of

indiscriminate fishing.

Reduced productivity due to increase in turbidity and

pollution of the river body

Operation phase

Impacts on migratory fish species

Impacts on spawning and breeding grounds

Degradation of riverine ecology

Shift in species density and diversity due to change in

aquatic ecosystem from lotic to lentic.

Increased potential for reservoir fisheries

Terrestrial Ecology

Construction phase

Increased pressure from construction works to meet their

fuel wood and timber requirements

Adverse impacts due to increased accessibility of the area

Loss of vegetation and forest area

Operation phase Impacts on wildlife movement




Environmental Parameter Likely Impacts

Loss of forest area due to submergence

Impact on Rare, Endangered and Threatened (RET) species,

if any

Socio-Economic Aspects

Construction phase

Improved employment potential during the project

construction phase

Development of allied sectors leading to greater

employment

Pressure on existing infrastructure facilities

Friction between the construction works and the native

population

Operation phase

Loss of land

Loss of private properties

Increased revenue from power generation

Increase in employment opportunities and standard of living

Public Health

Construction phase

Impacts due to disposal of untreated sewage from

construction works camps

Increase in incidence of communicable diseases

Operation phase Increased incidence of vector borne disease due to increase

in water spread area

Air Environment

Construction phase

Emissions due to fuel combustion in construction equipment

Increased vehicular movement

Entrainment of fugitive emissions

Noise Environment

Construction phase Increased noise level due to operation of various equipment

Increased vehicular movement

3.2.4.2 Geology

The regional geology around the project area highlighting geology, stratigraphy and structural

features, based on the existing information on these aspects contained in Detailed Project

Report (DPR) of the project. In addition the important parameters of seismicity were assessed

using published literature on seismic history and seismo-tectonic nature of the regional rock

types in the area.

3.2.4.3 Meteorology

Meteorological factors like precipitation, temperature and evapo-transpiration are important,

as they have a profound impact on the water availability, cropping pattern, irrigation and

drainage practices, soil erosion, public health, etc. Meteorological data have been collected

and analyzed as part of the DPR preparation by DPR consultants and the same has been used

in preparation of the EIA study.




3.2.4.4 Hydrology

Hydrological data for Dibang river available as Hydrology Volume in the DPR of Etalin HE

project has been appropriately compressed and duly incorporated in the EIA report as a

separate Chapter on Hydrology. The discharge data given in this Chapter has been used for

deriving minimum environmental flows and the discharge pattern in the river. As mandated in

the approved TOR for the project, a detailed Environmental Flow assessment study was

undertaken by Central Inland Fisheries Research Institute (CIFRI), Barrackpore and findings of

the same have been appended as a separate report along with the EIA volumes.

3.2.4.5 Forest Types & Forest Cover

The details on forest types and forest cover in the catchment area were based on field surveys

in the area supplemented with the working plans of the forest divisions of the study area.

Major forest types in the study area have been described based upon the classification of

Champion and Seth (1968).

3.2.4.6 Infrastructure Facilities

The present status of infrastructure facilities, status and availability of electricity, drinking

water, communication and mode of transportation, commercial, educational and health

facilities, veterinary services, etc. were collected using secondary data from Census of India

2011, District Statistical Handbook and interactions with the locals.

3.2.5 Primary Data Collection –Field Surveys

The field surveys for the collection of primary data commenced from April 2010 up to

November 2013 and were conducted in different seasons of the year i.e. winter/lean season,

pre-monsoon/summer and monsoon to collect data/ information on flora, fauna, forest types

and ecological parameters as well as sociological aspects. In addition, surveys and studies

were also conducted for understanding aquatic ecology and fish diversity of Dri and Talo

(Tangon) Rivers. The details of sampling are given in Table 3.2.

Field surveys in the study area were also conducted for the purpose of ground truthing and

augmenting the remote sensing data. For this purpose various attributes such as land

features, rivers, forests and vegetation types were recorded on the ground.

Table 3.2: Sampling schedule for various Environmental Parameters

Parameters Winter Pre-monsoon/

Summer Monsoon

Soil sampling December 2009 & Dec

2012

March-April 2010 &

March-April 2012

July-August 2010 &

July-August 2012

Air environment December 2009 & Dec

2012

March-April 2010 &

March-April 2012

July-August 2010 &

July-August 2012

Noise & Traffic December 2009 & Dec

2012

March-April 2010 &

March-April 2012

July-August 2010 &

July-August 2012

Vegetation

sampling

December 2009 & Dec

2012

March-April 2010 &

March-April 2012

July-August 2010 &

July-August 2012

Faunal surveys December 2009 & Dec

2012

March-April 2010 &

March-April 2012

July-August 2010 &

July-August 2012

Water sampling

and Aquatic

Ecology

December 2009 & Dec

2012

March-April 2010 &

March-April 2012

July-August 2010 &

July-August 2012




Parameters Winter Pre-monsoon/

Summer Monsoon

Socio-economic

survey of study

area villages

December 2009 & Dec

2012

March-April 2010 &

March-April 2012

July-August 2010 &

July-August 2012

Socio-economic

survey of project

affected families

- July-August 2010, June 2012 and

November 2013

3.2.5.1 Soil

The soil taxonomic (family) classification map of Etalin H.E. Project area was prepared as per

the Soil Atlas of Arunachal Pradesh procured from National Bureau of Soil Survey & Land Use

Planning (NBSS & LUP). Soil resource map of the study area was prepared and the area under

each soil taxonomic class was calculated using GIS.

In order to assess the nutrient and fertility status of the soil in the study area the samples

were collected from five different locations (Table 3.3 & Figure 3.1). The sampling for soil

was done at locations where major components of the projects are planned. Soil samples were

collected with help of khurpi from a depth of 15-30 cm (deep soil) and from surface (top soil)

after removing the debris material and were stored in cotton bags and brought to laboratory

for further physico-chemical analysis. The soil analysis was carried out at the Hitech Labs

Limited (CPCB accredited Lab.), Okhla, New Delhi. The soil samples were collected during all

the three seasons.

Table 3.3: Sampling locations

Sampling Site Location in Study Area

Site S1 Near Dri dam site

Site S2 Punli village on Dri limb

Site S3 Near Talo (Tangon) dam site

Site S4 Chanli village on Talo (Tangon) limb

Site S5 Powerhouse near Etalin village

The following parameters were analysed.

Physical parameters included:

Bulk density (gm/cc)

Water holding capacity (%w/w)

Porosity (%w/w)

Soil texture

Electrical conductivity (mhos/cm)

Chemical Parameters included:

pH

Organic matter (%w/w)

Nitrogen as N (% w/w)

Phosphorus as P (mg/kg)

Potassium as K (mg/kg)




Magnesium as Mg (mg/kg)

Chloride as Cl (mg/kg)

Sodium as Na (mg/kg)

Calcium as Ca (mg/kg)

Total alkalinity (mg/kg)

Salinity, ppt

Exchangeable Sodium Percentage (ESP)

3.2.5.2 Ambient Air Quality

Instruments such as Respirable Dust Samplers APM-460 and APM-411 (Envirotech make) was

used for monitoring Particulate Matter (PM10 and PM2.5 and gaseous pollution like SO2 and NOx.

Monitoring was carried out twice a week for 4 weeks at each location. Following parameters

were measured to understand the baseline condition:

i) Particulate Matter (PM10)

ii) Particulate Matter (PM2.5)

iii) Sulphur dioxide (SO2)

iv) Nitrogen oxide (NOx)

Identification of Sampling Location

Sampling locations are identified keeping in view the following:

Potential source of pollution - location of construction machinery and equipment, DG

sets, material storage and handling areas

Receptors - populated area or habitation, typically villages in the vicinity

Predominant wind direction – typically winds in mountainous regions that change

direction twice daily: - In the daytime the air over the mountain ridges and valleys

becomes warmer than the air at the same levels over the plains and expands more.

Consequently, at the higher levels the downward pressure from the mountains to the

valleys is reduced and air travels in that direction. At night the temperature and

pressure factors are reversed, so that mountain winds result. In addition to this

circulation of air between the valleys and mountains, there is a down flow of cooled air

along the mountain slopes at night and an upward flow of warmed air along the slopes

during the day.

Accessibility – Based on the above analysis sampling locations are identified, however,

they are finalized keeping in the view the accessibility of the identified sites;

acceptance of the locals to monitoring, safety of equipment and source of power

supply.

Sampling and Analysis

Sulphur dioxide (Modified West and Gaeke method (IS-5182 Part-II, 1969))

Placed 30 ml of absorbing solution in an impinger and sample for four hours at the flow rate of

1 L/min in High Volume Sampler. After sampling measured the volume of sample and

transferred to a sample storage bottle.

Sulphur dioxide from air is absorbed in a solution of potassium tetrachloromercurate (TCM). A

dichlorosulphitomercurate complex, which resists oxidation by the oxygen in the air, is




formed, which is stable to strong oxidants such as ozone and oxides of nitrogen and therefore,

the absorber solution was stored for some time prior to analysis. The complex was made to

react with para-rosaniline and formaldehyde to form the intensely coloured pararosaniline

methylsulphonic acid. The absorbance of the solution was measured by means of a suitable

spectrophotometer and SO2 concentration was calculated using the standard calibration graph.

Nitrogen dioxide (Jacobs Hochheiser method (IS 5182 Part-IV, 1975))

Place 30 ml of absorbing solution in an impinger and sample for four hour at the flow rate of

0.2 to 1 L/min in High Volume Sampler. After sampling measure the volume of sample and

transfer to a sample storage bottle.

Ambient nitrogen dioxide (NO2) is collected by bubbling air through a solution of sodium

hydroxide and sodium arsenite. The concentration of nitrite ion (NO2-) produced during

sampling is determined colorimetrically by reacting the nitrite ion with phosphoric acid,

sulfanilamide, and N-(1-naphthyl)-ethylenediamine di-hydrochloride (NEDA) and measuring

the absorbance of the highly coloured azo-dye at 540 nm using spectrophotometer and

concentration is calculated using the standard calibration graph.

Particulate Matter (PM10) - Gravimetric Method

Air is drawn through a size-selective inlet and through a 8” X 10” filter at a flow rate, which is

typically 1132 L/min using High Volume Sampler for 8 hours. Particles with aerodynamic

diameter less than the cut-point of the inlet are collected, by the filter. The mass of these

particles was determined by the difference in filter weights prior to and after sampling. The

concentration of PM10 in the designated size range was calculated by dividing the weight gain

of the filter by the volume of air sampled.

Particulate Matter (PM2.5) - Gravimetric Method

An electrically powered air sampler draws ambient air at a constant volumetric flow rate (16.7

lpm) maintained by a mass flow / volumetric flow controller coupled to a microprocessor into

specially designed inertial particle-size separator (i.e. cyclones or impactors) where the

suspended particulate matter in the PM2.5 size ranges is separated for collection on a 47 mm

polytetrafluoroethylene (PTFE) filter over a specified sampling period. Each filter is weighed

before and after sample collection to determine the net gain due to the particulate matter. The

mass concentration in the ambient air is computed as the total mass of collected particles in

the PM2.5 size ranges divided by the actual volume of air sampled, and is expressed in μg/m3.

The microprocessor reads averages and stores five-minute averages of ambient temperature,

ambient pressure, filter temperature and volumetric flow rate.

In order to build data base on the existing air quality of the study area, ambient air monitoring

at three locations at nearby villages viz. Etalin, Punli on Dri Limb and Punli on Talo (Tangon)

Limb were undertaken.

3.2.5.3 Ambient Noise levels & Traffic Density

Unwanted sound that is loud and unpleasant or unexpected is termed as noise pollution. It has

adverse impact on the daily activities of the human being and animals. The adverse impact of

the noise on human and animals also depends upon time, season and the quality of sound.




Sound Levels monitoring was carried out by digital sound level meter in terms of dB(A) levels

along with time of the day and source of sound, if any, to establish baseline data.

Monitoring locations are selected keeping in view the project activity area which are likely to

be potential source of noise in the area during the construction phase; location of receptors

i.e. habitation for human population and nearby forest areas to assess the impact on fauna

due to increased sound levels in the region. Existing sources of noise such as river flow and

accessibility of the identified location are also considered during the finalization of sound level

monitoring location.

Hourly monitoring is carried out where levels are recorded using hand held digital sound level

meter for 6-8 hours during the daytime. Night time readings are not practical as the

accessibility and security at nighttime is always a cause of concern in remote areas. Data

collected is compiled and analyzed to establish baseline equivalent levels.

Noise levels were monitored during the studies at locations in the Direct Impact Area of the

project is given in Table 3.4.

Table 3.4: Ambient air quality, noise and traffic density monitoring locations

Sl. No. Monitoring location

1 Dam Site Dri River

2 Punli Village on Dri Limb

3 Dam Site Talo (Tangon) River

4 Avonli village

5 Punli Village on Talo (Tangon) Limb

6 Etalin Village

7 Power house Area

8 Near Etalin School

Traffic density data was recorded by physically counting the number of different types of

vehicles passing through a particular point in a fixed time interval. Some major villages along

the road were considered as nodes for monitoring movement of traffic.

3.2.5.4 Land use / land cover

The objective of the study was to produce a detailed vegetation/ land use map using hybrid

digital classification technique. The study also aims to produce land cover data set appropriate

for applications like erosion mapping, etc. Land use and land cover mapping of the study area

was prepared from the data procured from Forest Survey of India (FSI). It was further refined

by ground checks carried out during the field surveys. For this purpose FCC of the entire study

area was generated from digital satellite data of IRS-1D LISS-III, Path/Row - 94/47 with

Bands 2, 3 and 4. In addition Landsat ETM+ data was also downloaded from Global Land

Cover Facility web site.

The data procured from FSI was downloaded and further processed to generate mosaic of

study area. In order to understand the extent of forest cover in particular, the classification

scheme suggested by Forest Survey of India was adopted for the preparation of land use/land

cover maps. Three forest density classes were interpreted for the forest cover mapping. The




forests with <70% canopy cover has been demarcated as Very Dense forest, between 40%

and 70% canopy cover was delineated as Moderately Dense forest and between 10% and 40%

crown density as Open forest. Furthermore, degraded forests, grass covered slopes with

canopy density <10% were delineated as scrubs. The area not included in any of the above

classes has been delineated as non-forest land cover.

Data Set Used

Survey of India (SoI) : 82/P-14, 82/P-15, 83D/2 & 82/D-3

(Scale: 1:50000)

Projection and Datum : UTM and WGS 84 North

Satellite Data : IRS P6 LISS 3 and LANDSAT ETM+

3.2.5.5 Vegetation Community Structure/ Floristic Surveys

The objectives of the present floristic study are as follows:

To prepare an inventory of various groups plants (Angiosperms, Gymnosperms,

Pteridophytes, Bryophytes, and Lichens) in the study area

To assess the community structure in the study area

To Determine Importance Value Index and

Shannon Wiener Diversity Index for trees, shrubs and herbs present in the study area.

The detailed account of floristic diversity and ecology has been described based on the primary

surveys in the catchment area and study area of the proposed project. These surveys were

undertaken during different seasons of the year to assess the vegetation structure and to

prepare inventory of plant species belonging to different plant groups like angiosperms,

gymnosperms, pteridophytes, bryophytes and lichens found in the study area.

The community structure of the study area was studies by Quadrat method. The size and

number of quadrats needed were determined using the species- area curve (Misra, 1968). The

data on vegetation were quantitatively analyzed for abundance, density, frequency as per the

methodology given in Curtis & McIntosh (1950). The Importance Value Index (IVI) for trees

was determined as the sum of relative density, relative frequency and relative dominance

(Curtis, 1959).

Sampling Site Selection

The sampling locations were selected on the basis of the area located in the vicinity of

proposed projects and its components. Sampling was undertaken to assess the composition of

particular forest type/s in that area. Eight sampling locations were selected for carrying out

phytosociological surveys of the vegetation and in addition an inventory of various floristic

elements was also prepared by walking along different transects around these sampling sites.

The location of sampling sites has already been described earlier in the document. In order to

understand the composition of the vegetation, most of the plant species were identified in the

field itself whereas the species that could not be identified a herbarium specimen was made

along with their photographs for identification later with the help of available published

literature and floras of the region.




Detailed list of sampling locations along with their coordinates is given at Table 3.5 and their

location on the study area map of Etalin HE project has marked as shown in Figure 3.1.

Sampling Methodology

Standard methodology of vegetation sampling was used for community structure. Nested

quadrat sampling method was used for the study of community structure of the vegetation.

For arriving at the requisite size of the quadrats, species area curve was plotted. Though the

requisite size of the quadrats varied from 8x8 m2 for trees and 4x4m2 for shrubs, however in

order to make calculations easier, the quadrat sizes for trees and shrubs adopted was 10 x 10

m2 for trees and 5 x 5m2 for shrubs. In case of herbs the requisite size was 1 x 1m2 and the

same was adopted for sampling (Table 3.6). The number of quadrats laid for each stratum

varied from minimum of 14 quadrats to 25 quadrats during seasonal surveys at a particular

sampling site/ area depending upon the heterogeneity/ homogeneity of the vegetation

encountered in a particular site/ area (see Table 3.6). At each site the quadrats were laid

along the altitudinal gradient beginning from the vegetation along the river bank/riverine

vegetation and further up along the slope ensuring maximum possible representative coverage

of the vegetation of a particular sampling location. Each sampling location/ area was divided

into grids vertically as well as horizontally along the slopes thereby capturing the maximum

diversity of vegetation. In case of trees total basal area/cover per unit area was calculated by

measuring the cbh (circumference at breast height) of each individual tree belonging to

different species which was then converted into basal area using the formula given in the

following paragraph. However in case of herbs and shrubs the circumference of at least 10-20

individuals was measured by bunching them together which was then converted into

circumference of total number of individuals which was then further used to calculate basal

area of herbs and shrubs per unit area as per the formula given below. As already mentioned

the number of individuals of herbs and shrubs to be bunched together depends upon the

thickness of their stems.

Calculation of Dominance & Diversity Indices

Based on the quadrat data, frequency, density and cover (basal area) of each species were

calculated. The data on density and basal cover are presented on per ha basis.

The Importance Value Index (IVI) for different tree species was determined by adding up

the Relative Density, Relative Frequency and Relative Dominance/ Cover values. The Relative

Density and Relative Frequency values were used to calculate the IVI of shrubs and herbs.

Table 3.5: Sampling Locations for terrestrial ecology

Site

ID Sampling Location

Forest Type Coordinates

Dri Limb

V1 Catchment Area Dri River Pine and Temperate

broad leaved forest

95O 53’ 16”E, 28O 46’

30”N

V2 Dam Site Dri River Sub-tropical forest 95O 52’ 11”E 28O 43’

57”N

V3 Downstream of Dam Near Ru Pani Sub-tropical forest 95O 50’ 38”E 28O 39’

21”N




Talo (Tangon) Limb

V4 Catchment Area Talo (Tangon)

River

Pine and Temperate

broad leaved forest

96O 3’ 20”E 28O 39’ 16”N

V5 Dam Site Talo (Tangon) River Sub-tropical forest 96O 0’ 55”E 28O 38’ 36”N

V6 Downstream Near Anon Pani Sub-tropical forest 96O 56’ 59”E 28O 37’

32”N

Power House Area

V7 Power House Site Sub-tropical forest 95O 51’ 55”E 28O 37’ 7”N

V8 Downstream of Power House Site Sub-tropical forest 95O 50’ 58”E 28O 35’

26”N

Table 3.6: Number of quadrats studied during field surveys for trees, shrubs and

herbs

Sampling Site Trees

(10x10) m2

Shrubs

(5x5) m2

Herbs (1x1)

m2

V1 14 20 15

V2 14 20 24

V3 14 20 25

V4 14 20 15

V5 14 20 15

V6 14 20 22

V7 14 20 15

V8 14 20 20

For the calculation of dominance, the basal area was determined by using following formula.

Basal area = π r2

Species diversity and evenness index were calculated by using the Shannon-Wiener Diversity

Index (1963) and Evenness Index, respectively.

The index of diversity was computed by using Shannon Wiener Diversity Index (Shannon

Wiener, 1963) as:

H = - Σ (ni/n) x ln (ni/n)

Where, ni is individual density of a species and n is total density of all the species

The Evenness Index (E) is calculated by using Shannon's Evenness formula (Magurran, 2004).

Evenness Index (E) = H / ln(S)

Where, H is Shannon Wiener Diversity index; S is number of species

3.2.5.6 Faunal Elements

The fauna of the study area has been compiled with the help of secondary sources

supplemented with information provided by local people during field surveys in the study area.

For the preparation of checklist of animals, Forest Working Plan of Anini Social Forestry

Division and Dibang Valley Forest Divisions, as well as State Biodiversity Management Action

Plan prepared by SFRI, Itanagar were consulted. In addition data was compiled from published

literature like Chetri & Chetri (2007), De et al. (2006), Sanyal & Gayen (2006), Sarkar & Ray




(2006), Ali & Ripley (1983), Grewal et al. (2002), Grimmett et al. (1998), Fleming et al.

(1984), Sumit Sen (2007).

Sampling Methodology & Constraints

Since observations of fauna and wildlife take long time, primary surveys were limited to

indirect sightings of animals during the field surveys as direct sightings are very rare. The

presence of wildlife was also confirmed from the local inhabitants depending on the animal

sightings and the frequency of their visits in the catchment area.

Table 3.7: Transects and trails for faunal elements

Transect Location

Tr1 Catchment Area Dri River (Dri Limb)

Tr2 Catchment Area Talo (Tangon) River (Talo Limb)

Tr3 Near Dri Dam site

Tr4 Near Talo (Tangon) Dam site

Tr5 Power House Site

Tr6 Downstream of Power House Site

The study area was divided into different strata based on vegetation and topography.

Sampling for habitat and animals was done in different strata. As the normal systematic

transects for mammals and birds were not possible in this study area due to difficult terrain,

therefore mostly trails were used for faunal sampling. In addition to the field sampling the

data/ information was also collected as follows:

Direct sighting and indirect evidences such as calls, signs and trophies of mammals were

recorded along the survey routes taking aid from Prater (1980).

The interviews with local villagers were conducted for the presence and relative abundance of various

animal species within each locality. In addition, the data was also collected on habitat condition,

animal presence by direct sighting and indirect evidences by forest personnel and villagers.

Transects were walked along the forest trail in the study area (as shown in Figure 3.1) to

make observations on the wildlife in each forest areas that fall within study area of the

proposed hydropower project. To study the wild mammalian fauna of the study area, 2 - 5 km

long transects and trails were walked during early morning and evening hours. Direct sighting

of animals as well as indirect signs like scat, pellets, pugmarks, scraps, vocalizations, horns

etc. were also recorded during the survey trails. On each transect, the locations were marked

with the help of a hand held GPS. Animals and birds observed along the route were recorded,

together with information on their habitat. This method of continuous recording (Martin &

Batson, 1993, Chalise, 2003) was adopted for the collection of general information on species

presence and absence. It also reveals diversity and population by direct observation. This

method is also known as Visual Encountered Sampling to reflect wildlife population and

diversity (Mukherjee, 2007). Four to five separate walks were done along both the banks of

Dri and Talo (Tangon) rivers and their tributaries to collect information on riverine tract.

Secondary data as well as information gathered from the locals were also noted for the

presence or absence of wild animals in the area. These indirect evidences and information

have to be analyzed and ascertained with the help of literature available.




The birds were also sighted on the same transect and trails marked for mammals. Sampling

was carried out on a fixed width trails of 2 km wherever the terrain permitted and point counts

were carried out at a fixed distances at more or less regular intervals. A prismatic field

binocular (10 × 50) was used for bird watching during transect survey and nearby the human

habitation of study area. Birds were identified as per the field guide of Ali & Ripley (1983),

Grimmett and Flaming et al. (1984), Krys Kazmierczak (2006) and Grimmett (2007).

The herpetofauna was also sampled along the same transects marked for mammals.

3.2.5.7 Water Quality

The data on water quality has been collected to:

Assess the quantitative and qualitative nature of effluent discharges to the river and its

tributaries.

Evaluate river water quality on upstream and downstream of the project site and also in

the stretch between barrage and powerhouse.

Selection of Sampling Sites

The sampling was carried out at 11 different locations during three seasons as described below

in the table to study various physico-chemical and biological characteristics of Dri and Talo

(Tangon) rivers (Table 3.8 & Figure 3.1). Water samples were collected during each

sampling season for physico-chemical as well as biological parameters. The sampling sites in

the Dri and Talo (Tangon) rivers were located near the area where major project components

are proposed like dam site, powerhouse, muck dumping sites, working area, near the

confluence of major tributaries of Dri and Talo (Tangon) rivers and near settlements.

Sampling Parameters

Analysis of physico-chemical parameters included temperature, turbidity, total dissolved

solids, pH, dissolved oxygen, total alkalinity, total hardness, electrical conductivity, chloride,

nitrate, phosphate and silicates in the water samples collected during the field visit of the

proposed project site. The samples were taken in the replicates at each site of the river and

the average value was calculated for the result. The sites at which sampling was done are as

listed in Table 3.8 and also shown in Figure 3.1.

Table 3.8: Water sampling locations

Sites Location

W1 Catchment Area (Dri River)

W2 Dam Site (Dri River)

W3 Ayo Pani

W4 Ru Pani

W5 Catchment Area (Talo River)

W6 Dam Site (Talo River)

W7 Non Pani

W8 Makri Pani

W9 Noh Pani

W10 Power house Site (near Etalin village)

W11 After confluence of Dri and Talo rivers




Some of the physico-chemical parameters of water necessary for the ecological studies were

measured in the field with the help of different instruments. The water temperature was

measured with the help of graduated mercury thermometer. The hydrogen ion concentration

(pH), electrical conductivity and total dissolved solids were recorded with the help of a pH, EC

and TDS probes of Hanna instruments (Model HI 98130) in the field. Dissolved oxygen was

measured with the help of Digital Dissolved Oxygen meter (Eutech ECDO 602K). The water

samples were collected in polypropylene bottles from the different sampling sites and brought

to the laboratory for further analysis after adding formalin as preservative. The turbidity was

measured with the help of Digital Turbidity meter and other parameters such as total

alkalinity, total hardness, chloride, nitrate, phosphate, and silicates were analyzed at the

Hitech Labs Limited, Okhla, New Delhi. These parameters were analysed as per the standard

procedures given by Adoni (1980) and APHA (1992).

Presence/ Absence (P/A) test was performed in the field for Total coliform using P/A broth

ampules without MUG reagent (4-methylumbelliferyl-ß-Dglucuronide). The colour change from

reddish purple to yellow or yellow brown indicates positive for Total coliform presence whereas

no colour change after incubation for more than 48 h indicates negative for Total coliform.

3.2.5.8 Aquatic Ecology

Sampling of Phytoplankton & Periphyton -Benthic (Epilithic) Diatoms and

Zooplankton

For the quantification of phytoplankton and zooplankton 50 liters of water for each community

was filtered at each site by using plankton net made up of fine silk cloth (mesh size 25 m).

The study was repeated three times at each site and samples were pooled. The filtrate

collected for phytoplankton was preserved in1% Lugol’s Iodine solution.

For periphyton sampling was performed across the width of the river at the depth of 15 - 30

cm. The samples were taken from the accessible banks only. The pebbles (64 - 128 mm size)

usually 4 - 5 in number, were picked from the riffle and pools, in apparently different flows

such as stones above and below gushing waters, swift flow and slow flow conditions so as to

obtain a representative sample. Benthic diatom samples were collected by scratching the

pebbles with a brush of hard bristles in order to dislodge benthos from crevices and minute

cavities on the boulder surface from an area of 3 x 3 cm2, using a sharp edged razor. The

scrapings from each cobble were collected in 25µ mesh and transferred to storage vials. The

samples were preserved in 1% Lugol’s iodine solution.

For preparing permanent mounts from the treated samples, the slide was first smeared with

Mayer’s albumen. The sample was then agitated to render it homogeneous. Quickly a drop of

known volume (0.04 ml) of processed material was placed on the slide and heated gently till it

dried. It was dehydrated using 95% and 100% alcohol, consecutively. The dehydrated

material was transferred to Xylol twice before finally mounting in Euparol.

Identification of Benthic algae & Zooplankton

The permanent mounts were then subjected to analysis under a phase contrast binocular

microscope using an oil immersion lens of x 100 magnification. For identifying the various

diatom species, varieties and forms, the morphological characteristics used included length,




width (µm), number of striae, raphe, axial area, central area, terminal and central nodules.

Identifications were made according to standard literature (Schmidt 1914 - 1954, Hustedt

1943, Hustedt 1985, Krammer & Lange - Bertalot 1986, 1991, 1999, 2000 a & b, Lange -

Bertalot, H. Krammer, K. 2002, Metzeltin & Lange - Bertalot 2002, Krammer 2000, 2003,

Lange Bertalot et al. 2003, Werum & Lange - Bertalot 2004., Metzeltin et al. 2005). Sarode &

Kamat (1984), Prasad (1992) and Gandhi (1998) were also consulted for the Oriental species.

The slide preparation and identification of benthos was done at Ecology Lab., Department of

Zoology, HNB Garhwal University, Srinagar and the permanent mounts have been adequately

stored there.

The supernatant plankton free water was removed and the settled zooplankton were

enumerated by ‘Sedgwick-Rafter Cell’ method. Identification of zooplanktons species was

performed under microscope by using keys and monographs of standard references like Ward

and Whipple (1959) and Battish (1992).

For samples were preserved in 1% Lugol’s iodine solution acid treatment was done according

to Reimer (1962) method adopted earlier by (Nautiyal & Nautiyal 1999, 2002) to process the

samples for light microscopy. The treated samples were washed repeatedly to remove traces

of acid. Samples were treated with hydrogen peroxide with high organic content to clean the

diatom frustules. The permanent mounts were prepared in Naphrax for further analysis. They

were examined using a BX-40 Trinocular Olympus microscope (x10 and x15 wide field

eyepiece) fitted with Universal condenser and PLANAPO x 100 oil immersion objective under

bright field using appropriate filters to identify the species.

Sampling & Identification of Macro-invertebrates

The Macro-invertebrate samples were collected from 1 sq ft area by lifting of stones and

sieving of substratum from the wide able portion of the river. The material was sieved through

125 µm sieve and preserved in 70% ethyl alcohol. Samples were collected in three replicates

and pooled for further analysis. The organisms obtained were then counted after identifying

them up to family level. Standard keys were used for the identification of macro invertebrate

samples (Pennek 1953; Edmondson 1959; Macan 1979; Edington and Hildrew 1995).

Crude density (Indiv/m2) = total numbers of individuals in each quadrat/ total quadrats × 11

Density and Diversity of different species was calculated as follows:

a) Density of phytoplankton (cells/lit) and zooplankton (indiv./lit)

b) Density of phytobenthos (cells mm-2)

Total count of cells × cover glass size/length of visual field of microscope × counted rows ×

total sample volume (ml)/observed sample / sampled area

c) Species Diversity Index (Shannon & Wiener 1963): The Shannon diversity

indices were determined on the basis of counts (500 - 600 valves).

Shannon-Wiener Diversity Index H = - Σ (ni/n) x ln (ni/n)

where, pi is the proportion of total number of species made up of the ith species

d) Evenness Index (Shannon & Wiener 1963)

Evenness Index (E) = H / ln(S)

where, H is Shannon Index of general diversity and S is Number of species




Sampling for Fishes

The data on the occurrence of fish species was collected from Fisheries Department of State

Government and through literature review as well. Experimental fishing was done with the

help of local fishermen at various sites in the study area and river stretches both upstream

and downstream of the project site to ascertain the distribution pattern of fish species. The

fishermen used fish traps locally known as Takom. It is a conical shaped fish trap made of

bamboo with a mouth diameter ranging from 0.1 to 0.3 meter. It is fixed against the water

current. Once the fish entered inside, they remained entangled in the base with the pressure

of water current. They also used a conical shaped basket made of cane to collect fishes from

the river. With this fishing gear small sized fishes, especially bottom dwellers, are easily

collected. Identification and of all the fish catch was done and an inventory of the fish species

was also by consulting Nath & Dey (2000) and Bagra et al. (2009). Interviews were conducted

with locals regarding the probable presence of migratory fishes like Mahseer in the area.

3.2.5.9 Socio-economic Surveys

To assess the baseline condition of socio-economic aspects of the study area, following

primary and secondary data were collected:

The data on socio-economic aspects was collected at two levels- at village and individual

household level.

The first level of data collection was done in the villages which are going to be directly

affected by acquisition of land for project construction. A sampling strategy was adopted

based on the observations made during the first phase (Details given in R&R Report).

In the second level data collection Socio-economic survey of Project Affected Families was

conducted. For this format was designed for conducting socio-economic survey which

included questions on demographic, ethnographic, economic, literacy, development,

agricultural, cultural and aesthetic site, infrastructure facilities: education, health and

hygiene, communication network, etc. A door to door survey was conducted to collect

information (Details given in R&R Report).

Data collection from secondary sources was also made to validate some of the primary

information.

The details of surveys conducted for the preparation of R&R plan as well as Social Impact

Assessment (SIA) are given in separate volume as Social Impact Assessment and

Rehabilitation & Resettlement Plan for Etalin HE Project (3097MW).

In order to assess the existing status of public health, the following data on public health

status has been collected from Public Health Department:

Prevalent vectors in the area

Prevalence of malaria and other water and vector-borne diseases in the area.

The details of source of different Environmental parameters are given at Table 3.9.




Table 3.9: Source of data for various Environmental Parameters

Aspect Mode of Data

collection

Parameters monitored Frequency Sources

Meteorology Secondary Temperature, Humidity, Rainfall - Detailed Project Report (DPR)

Hydrology/ Water

Resources

Secondary Flow, Design, hydrograph, and design flood

hydrograph

- Detailed Project Report (DPR)

Geology and seismology Primary and

Secondary

Regional Geology Tectonic and Earthquakes - Detailed Project Report (DPR)

Land use Primary and

secondary

Land use pattern - Remote Sensing and GIS Studies

Ambient Air Primary SPM, RSPM, SO2, NOx Seasonal On-site monitoring and analysis

Surface Water Primary Physico-chemical and biological parameters Seasonal On-site monitoring and analysis

Drinking Water Primary Physico-chemical and biological parameters Seasonal On-site monitoring and analysis

Ambient Noise Primary Leq (Day only), and Mean noise level in dB (A) Seasonal On-site monitoring and analysis

Soil Primary and

Secondary

Physico-chemical parameters Seasonal On-site monitoring and analysis

Terrestrial Ecology Primary and

secondary

Floral and faunal diversity, density and

species composition

Seasonal On-site data collection, Forest

Department,

State Forest Research Institute,

Itanagar, Zoological Survey of India,

Itanagar, Rajiv Gandhi University,

Itanagar, and Literature review

Aquatic Ecology and

Fisheries

Primary and

secondary

Diversity, density and species composition of

planktons and fishes

Seasonal On-site data collection, Fishery

Department, Itanagar, and Literature

review

Socio-economic aspect Primary and

secondary

Demographic profile, Ethnographic profile,

Economic structure, Literacy profile,

Development profile, Agricultural practices,

Cultural and aesthetic sites, Infrastructure

facilities: education, health and hygiene,

communication network, etc., Impact on socio-

cultural and ethnographic aspects due to dam

building activity

- Field Survey, Directorate of

Economics and Statistics, Govt. of

Arunachal Pradesh, Itanagar, District

Statistical Office, Dibang Valley

District, Arunachal Govt. Website,

Revenue Department and Literature

review




3.3 IMPACT ASSESSMENT & MITIGATION MEASURES

Prediction is essentially a process to forecast the environmental conditions of the project area

that might be expected to occur because of implementation of the project. Impacts of project

activities have been predicted using overlay technique (super-imposition of activity on

environmental parameter). For intangible impacts qualitative assessment has been done. The

environmental impacts predicted are as follows:

Loss of cultivable land and forests

Impacts on land use pattern

Impact on socio-economic aspects

Displacement of population, if any, due to acquisition of private and community

properties

Impacts on hydrologic regime

Impacts on water quality

Increase in incidence of water-related diseases including vector-borne diseases

Effect on riverine fisheries, including migratory fish species

Increase in air pollution and noise level during project construction phase

Impact due to sewage generation from construction works camps

Impact due to acquisition of forest land

Impacts on terrestrial and aquatic ecology due to increased human interferences

during project construction and operation phases

Impact due to blasting

3.4 ENVIRONMENTAL MANAGEMENT PLAN

Based on the environmental baseline conditions and project inputs, the adverse impacts were

identified and a set of measures have been suggested as a part of Environmental Management

Plan (EMP) for their mitigation.

The management measures have been suggested for the following aspects:

Biodiversity Conservation and Management Plan

Catchment Area Treatment Plan

Fishery Conservation & Management Plan

Solid Waste Management Plan

Public Health Delivery System

Forest Protection Plan/Energy Conservation Measures

Muck Disposal Plan

Landscaping and Restoration of Quarries and Working Areas

Reservoir Rim Treatment Plan

Dam Break Modeling and Disaster Management Plan

Mitigation Measures for Air, Noise and Water Environment

Compensatory Afforestation Plan

Environmental Monitoring Plan

The expenditure required for implementation of R & R Plan, CAT Plan and other components of

EMP have been estimated and proposed as part of the study report.




3.5 ENVIRONMENTAL MONITORING PROGRAMME

It is necessary to continue monitoring of certain parameters to verify the adequacy of various

measures outlined in the Environmental Management Plan (EMP) and to assess the

implementation of mitigation measures. A comprehensive environmental monitoring

programme including monitoring frequency for critical parameters has been suggested for

implementation during project construction and operation phases. The staff, necessary

equipments and agencies to be involved for implementation of the Environmental Monitoring

Programme and costs have also been indicated.

Draft Environmental Impact Assessment (EIA) Report of Etalin HE Project



4.1 GENERAL

Arunachal Pradesh, the land first to greet sunrise in the country, is a thinly populated hilly

terrain on the North East extremity of India situated between latitude 26°40'N and 29°25'N

and longitude 91°35'E and 97°25'E. The state has international borders with Bhutan in west,

China in north and north-east and Myanmar (Burma) in east and interstate borders with

Nagaland in south west and Assam in south. It covers an area of about 83,743 sq km

extending along south slope of Eastern Himalaya and the western slopes of the Patkoi hills

around the Brahmaputra Valley. Arunachal Pradesh is the largest state area wise in the North

Eastern Region.

Known as North-East-Frontier Agency (NEFA) since British days, the area was awarded the

status of Union Territory on 21st January, 1972 when it was renamed as Arunachal Pradesh.

Subsequently, on 20th February 1987 it was elevated to the status of a full-fledged state. The

capital of the state is Itanagar which is situated in Papumpare district. The State is

administratively divided into 17 districts. Evergreen forests cover about 82% of total area with

its numerous turbulent streams, roaring rivers, deep gorges, lofty mountains, snow clad

shining peaks and hundreds & thousands of species of flora and fauna.

For details on Hydrological aspects Refer Annexure –IV.

Chapter HYDROLOGY

4

Draft Environmental Impact Assessment (EIA) Report of Etalin HE Project



5.1 GENERAL

The proposed Etalin Hydroelectric Project is located in Dibang Valley district of Arunachal Pradesh.

To its west lies Upper Siang district and its southern boundary is shared by Lower Dibang valley

district. The Etalin Hydroelectric project envisages utilization of the discharges of the rivers Dri and

Talo (Tangon) to generate 3097 MW of power including 27 MW installed capacity contributed by two

small hydro schemes at the toe of the Dams at Dri river and Talo (Tangon) river. The project layout

conceived by CEA during pre-feasibility stage and subsequently reassessed by NHPC is more or less

similar. The project envisaged two separate diversion dams each on river Dri and Talo (Tangon)

and a common underground powerhouse at the confluence of Dri and Talo (Tangon) near Etalin

village. The layout has been studied further and the best suitable options for locating the project

features have been evolved.

For details on Geological aspects Refer Annexure –V.

Chapter GEOLOGY &

SEISMOTECTONICS 5




6.1 INTRODUCTION

The Environmental Baseline chapter provides details of data collected during different seasons

i.e. winter/lean season, Summer/pre-monsoon and monsoon in the project study area as

specified in the approved Terms of Reference by MoEF&CC, Government of India. The details

of collection of both primary and secondary data for pertinent environmental components

have been given in Chapter-3 Methodology of the EIA report.

6.2 DRAINAGE

Dri river originates at an altitude of around 5350 m in the glacial ranges of Great Himalaya. It

meets several streams like Ange from the left and Mathun river from the right. It has a palm

shaped drainage basin and is sufficiently steep and flow through narrow valley.

The Dri River after its confluence with Mathun river near village Mathuli is known as Dri /

Dibang river and has got a moderate to steep gradient. The river, as it flows down, is met by

streams called Ange from the left and Mathun from the right. Further downstream Talo

(Tangon) joins the river from the left and following this confluence the river is named as

Dibang. It is further joined by tributaries viz. Emra, Ahi, and Ithun rivers.

River Talo (Tangon) originates in the high ranges of the Himalaya. It flows from east to west

in a sufficiently deep and narrow river basin. Various tributaries meeting the river from its left

are Edzon river, Lalu Pani, Anon Pani and from right Ipi Pani, Emo Pani, Sonko Pani, Echcha

river. River Talo (Tangon) meets River Dri near Etalin village and the combined flow together

is called Dibang River further meets Emra, Ahi, Ithun etc. The proposed dam site is Talo

(Tangon) River near Apanli village and power house is proposed on left bank of Talo (Tangon)

River near the Etalin village. The catchment area drainage map of Dibang River up to Etalin

Hydroelectric Project site is given in Figure 6.1.

The general drainage pattern is pre-dominantly dendritic to trellis type as it branches at

random, apparently with no definite preference for anyone direction and minor branches flow

into another at every conceivable angle.

The catchment area of Etalin project up to the proposed dam site on Dri/Dibang limb is

3,685 sq km whereas the catchment area of the project up to proposed dam site on Talo

(Tangon) limb is 2,573 sq km. Dibang River has a total length 195 km from its origin to

confluence with Lohit. The length of the rivers up to the proposed diversion structures is

estimated at around 90 km and 74 km, respectively, on Dri/Dibang and Talo (Tangon) limbs.

6.3 PHYSIOGRAPHY

The topography of the area is rugged with deep gorges and high hills. The slopes in the valley

are very steep with thick vegetation. Some of the areas are inaccessible. Many streams cut

Chapter ENVIRONMENTAL BASELINE

STATUS: PHYSICO-CHEMICAL PARAMETERS

6




across the valley slopes. The area is marked by characteristic peri-glacial topography with

sharp crested ridges and sculptured „whale back‟ hill slopes and marginal glacial features. The

area is marked by typical U-shaped valleys and presence of terminal and lateral moraines,

which suggest early quaternary glaciations in the area. Digital Terrain Model (DTM) of the

study area of Etalin Hydroelectric project generated from the ASTER G-DEM data is shown

below in Figure 6.2.

Majority of the study area as well as catchment area of Dri limb lies between 2000 m and

4000 m elevations i.e. more than 72% of area lies in this band while about 15% lies above

4000m. Only about 12% lies in 500-2000 m elevation band. However in Talo (Tangon) limb

catchment and study about 57% area lies between 2000 m and 4000 m elevation band and

more than 36% lies above 4000m while only about 6% lies in 500-2000 m elevation band.

Most of the project activities are restricted to the 600-1500 m elevation zone only.

Derived contours from topographical maps were used for preparation of Digital Elevation

Model (DEM) for the Free Draining Catchment area and to prepare a slope map. First of all, a

Digital Terrain Model (DTM) of the area was prepared, which was then used to derive a slope

map. The slope classes and ranges are recommended by Soil & Land Use Survey of India

(SLUSI) has been used for the study.

The slope map of the study area is given at Figure 6.3 and area falling under various slope

categories has been tabulated below in Table 6.1. As seen from the map and table nearly

90% of the study area is under steep to extremely steep slopes. The area under extremely

steep category i.e. with slopes higher than 70% is more than 45% of the total area.

Table 6.1: Areas falling under different slope categories in the study area

Slope in

Percent Category Area (sq km)

Area

(%)

0 - 2 Gently Sloping 10.50 1.16

2 - 8 Moderately Sloping 9.78 1.08

8 - 15 Strongly Sloping 17.50 1.93

15 - 30 Moderately Steep 65.26 7.20

30 - 50 Steep 163.10 17.99

50 - 70 Very Steep 229.00 25.26

>70 Extremely Steep 411.48 45.39

TOTAL 906.62 100.00

6.4 SOIL

6.4.1 Soil Taxonomic Classification

The soil taxonomic (family) classification map of Etalin H.E. Project area was prepared as per the

Soil Atlas of Arunachal Pradesh published by National Bureau of Soil Survey & Land Use Planning

(NBSS & LUP). Soil resource map of the project study area and their description is given in Figure

6.4. Majority of project study area i.e. more than 80% falls under Lithic Udorthents of Entisols

and Entic Haplumbrepts of Inceptisols. Lithic Udorthents are characterized by shallow depth,

and are loamy-skeletal soils found on very steeply sloping hill summit with very severe

erosion hazard while Entic Haplumbrepts are deep, loamy-skeletal soils found on moderately

steep slopes with severe erosion hazard (Table 6.2 & Figure 6.4).




Figure 6.1: Drainage Catchments areas of two limbs of Etalin HE project

Talo (Tangon) Catchment

Talo(Tangon)Catchment




Figure 6.2: Digital Terrain Model (DTM) of the study area generated from ASTER G-DEM data

Talo( )




Figure 6.3: Slope map of the study area generated from DEM




6.4.2 Soil Fertility Status

It is very essential to assess the soil quality of the region for proper planning of a project

whether hydroelectric, road, construction and agricultural or afforestation. The soil quality can be

defined as “capacity of a specific kind of soil to function”. It is generally assessed by measuring a

minimum data set of soil properties to evaluate the soil‟s ability to perform basic functions (i.e.

maintaining productivity, regulating and partitioning of water solute flow, filtering and buffering

against pollutants and storing and cycling nutrients). Evaluation of physical and chemical

characteristic is essential for measuring the soil quality of a particular region or area and it has

also been done for the project area of Etalin H.E. Project.

In order to ascertain the fertility status of the soils in the area the soil samples were collected

from different locations in the area in different seasons. The sampling locations, methodology

and the analysis details have already been given in Chapter 3-Methodology. Among the physical

parameters soil texture, bulk density, water holding capacity and conductivity were analyzed

while chemical characteristics included pH, organic matter, phosphate, nitrate, magnesium and

potassium were analysed (Table 6.3). Physico-chemical analysis of soil samples was carried out

at the Hi-Tech Labs Limited (CPCB accredited Lab.), Okhla, New Delhi. The results of soil analysis

are given in Table 6.3 as an average value of three season‟s values of each parameter.

The bulk density of soil varied from 1.27 to 1.45 (gm/cc). Water holding capacity was recorded

highest near the powerhouse area. The soil of the area is typically sandy loam type. Soil of study

area is slightly acidic in nature at most of the sites with pH values ranging from 4.6 to 5.1 (Table

6.3). Organic matter content also is good. The lower pH values and good organic matter is

mainly due to presence of decomposed leaf litter. This kind of soil is generally good for all kinds

of crops especially citrus fruit crops and banana, pineapple, etc. The texture of soil in general is

medium and is predominantly sandy-loamy. Electrical conductivity ranged between 120

mhos/cm and 150 mhos/cm. The concentration main nutrients like Nitrogen and phosphorus in

the soil is indicative of medium soil fertility rating whereas the concentration of potassium is on

the lower side. Exchangeable Sodium Percentage (ESP) is the amount of sodium held in

exchangeable form on the soil‟s cation exchange complex expressed as a percentage of the total

Cation Exchange Capacity (CEC) whereas the Sodium Adsorption Ratio (SAR) is a measure of the

suitability of water for use in agricultural irrigation, as determined by the concentrations of solids

dissolved in the water. It is also a measure of the sodicity of soil, as determined from analysis of

water extracted from the soil. The ESP and SAR values indicate that soils are stable (Table 6.3).

Salinity also is low at all locations.

6.5 AIR ENVIRONMENT

The air pollutants present in atmosphere, in concentrations that disturbs its dynamic equilibrium

and, thereby, affect man and his environment. There are three potential air pollutants; sulphur

oxides (SO2), nitrogen oxides (NOx) and soot/dust technically known as particulate matter

divided into PM10 and PM2.5. In order to evaluate and quantify the ambient air quality monitoring

is carried out during winter, pre-monsoon and monsoon seasons at different locations in the

study area.




Figure 6.4: Soil Series and their description in the Study Area (For soil unit no. see Table 6.2)




Table 6.2: Description and Area under different Soil Classes

Soil Unit

Order Sub-order

Great Groups Sub-Groups Area

(sq km) Area (%)

1 Entisols Orthents Udorthents Loamy-skeletal, Lithic Udorthents Shallow, excessively drained, loamy-skeletal soils on very steeply sloping hill summit having loamy surface with very severe erosion hazard and moderate stoniness Loamy-skeletal, Typic Udorthents Moderately deep, somewhat excessively drained, loamy-skeletal soils on

moderately steeply sloping side slopes with severe erosion hazard and moderate stoniness

309.64 34.15

2 Inceptisols Umbrepts Haplumbrepts Loamy-skeletal, Entic Haplumbrepts

Deep, somewhat excessively drained, loamy-skeletal soils on moderately steeply sloping summits having loamy surface with severe erosion hazard and moderate stoniness: associated with: Sandy-skeletal, Typic Udorthents Moderately shallow, excessively drained, sandy-skeletal soils on steeply sloping summits with very severe erosion hazard and slight stoniness.

421.84 46.53

3 Entisols Orthents Udorthents Loamy-skeletal, Lithic Udorthents Shallow, excessively drained, loamy-skeletal soils on steeply sloping summits having loamy surface with severe erosion hazard and slight stoniness: associated with: Loamy-skeletal, Dystric Eutrochrepts Moderately deep. Somewhat excessively drained, loamy-skeletal soils on moderately steeply sloping side slopes and slight stoniness

21.97 2.42

4 Entisols Orthents Udorthents Loamy-skeletal, Lithic Udorthents Shallow, excessively drained, loamy-skeletal soils on very steeply sloping summits having loamy surface with severe erosion hazard and strong stoniness: associated

with: Sandy-skeletal Typic Udorthents Moderately deep, somewhat excessively drained, sandy-skeletal soils with very

severe erosion hazard and moderate stoniness

55.18 6.09

46 Rocky mountains covered with perpetual snow and glaciers 98.00 10.81

Total 906.61 100.00




Figure 6.5: Map showing sampling sites for soil sampling, air and noise monitoring stations in the study area




Table 6.3: Physico-chemical Composition of Soil in the Study Area

S.

No.

Soil

Characteristics

Site S1

Near Dri

dam site

Site S2

Punli village

on Dri limb

Site S3

Near Talo

(Tangon)

dam site

Site S4

Chanli

village on

Talo

(Tangon)

limb

Site S5

Powerhouse

near Etalin

village

A. Physical Characteristics

1 Bulk density

(gm/cc) 1.32 1.35 1.27 1.28 1.21

2 Water holding

capacity (%w/w) 39.30 40.65 42.10 36.70 42.10

3 Porosity, (%w/w) 55.63 41.68 53.62 54.22 44.28

4 Soil texture

Sand (%w/w) 74.22 68.16 65.26 72.1 68.12

Silt (%w/w) 24.64 19.33 22.24 26.1 21.40

Clay (%w/w) 1.14 12.51 12.5 1.8 10.48

5

Electrical

conductivity

(mhos/cm)

140 150 120 130 120

B. Chemical Characteristics

6 pH 4.6 5.0 4.7 5.1 4.8

7 Organic matter

(%w/w) 1.8 1.3 1.2 1.6 1.7

8 Nitrogen as N

(kg/ha) 446.69 651.8 479.30 437.38 357.18

9 Phosphorus as P

(kg/ha) 16.9 12.7 13.1 13.3 12.3

10 Potassium as K

(kg/ha) 97.3 63.8 80.4 93.9 78.3

11 Magnesium as Mg

(mg/kg) 85.47 63.50 44.23 58.90 75.33

12 Chloride as Cl

(mg/kg) 875.91 690.33 655.62 953.72 941.11

13 Sodium as Na

(mg/kg) 32.19 31.61 41.43 54.35 33.22

14 Calcium as Ca

(mg/kg) 931.32 623.27 512.29 642.33 948.75

15 Total alkalinity

(mg/kg) 212.10 41.60 81.22 42.87 211.32

16 Salinity, ppt 1.64 1.32 1.12 1.54 1.38

17

Exchangeable

Sodium

Percentage (ESP)

2.98 4.39 10.39 5.49 3.33

18

Sodium

Adsorption Ratio

(SAR)

1.43 1.71 2.48 2.90 1.47

The sources of air pollution in the study area are vehicular traffic, dust arising from unpaved

village roads and domestic fuel burning. The air environment around project site is free from any

significant pollution source. Air quality monitoring was carried out as per the new air quality

parameters conforming to the National Ambient Air Quality Standards for Industrial Residential,

Rural & Other Areas.

The National Ambient Air Quality Standard notified by MOEF&CC are given in Table 6.4.




Table 6.4: National Ambient Air Quality Standard by (MOEF&CC)

Pollutant Time Weighted

Average

Concentration in Ambient Air

Industrial Residential, Rural &

Other Areas

Ecologically

Sensitive Area (Notified by

Central Govt.)

Sulphur Dioxide (SO2) µg/m3 Annual 50 20

24 hour 80 80

Nitrogen Oxides (NO)x µg/m3 Annual 40 30

24hour 80 80

Particulate Matter (size less

than 10µm or PM10) µg/m3

Annual 60 60

24 hour 100 100

Particulate Matter (size less

than 2.5µm or PM2.5) µg/m3

Annual 40 40

24hour 60 60

6.5.1 Ambient Air Quality

Map showing sampling locations for air and noise monitoring locations in the study area is given at

Figure 6.5. The SO2 values ranged from 5.6 to 8.9 g/m3 at various stations covered as a part of

the ambient air quality monitoring study. The SO2 levels observed during the study was much

lower than the permissible limit of 50 g/m3 for industrial, residential and rural areas (Table 6.5).

The NOx values ranged from 12.2 to 16.8 g/m3 at various stations covered as a part of the

study. The NOx level observed at various sampling stations was much lower than the permissible

limit of 40 g/m3 for industrial, residential and rural areas.

The maximum PM10 level observed during ambient air quality monitoring conducted was 27.1

g/m3. The PM10 level at various stations covered during ambient air monitoring was below the

permissible limit (60 µg/m3) specified for industrial, residential, rural and other areas (Table 6.5).

The maximum PM2.5 level observed during ambient air quality monitoring conducted was 12.9

g/m3. The PM2.5 level at various stations covered during ambient air quality monitoring was

below the permissible limit (40 µg/m3) specified for industrial, residential, rural and other areas

(Table 6.5).

Table 6.5: Air Quality Monitoring of the Study Area (unit: µg/m3)

S. No. Monitoring

location SO2 NOx PM10 PM2.5

1 Dam Site Dri River

W 6.2 13.8 22.1 9.8

PM 7.4 15.6 24.7 11.8

M 5.8 12.5 19.9 9.3

2 Punli Village on

Dri Limb

W 6.8 14.2 23.2 10.5

PM 7.8 16.3 25.6 11.2

M 6.1 12.7 21.2 9.8




S. No. Monitoring

location SO2 NOx PM10 PM2.5

3 Dam Site Talo

(Tangon) River

W 6.3 12.4 23.6 11.6

PM 6.9 13.2 26.7 12.9

M 5.6 12.2 21.7 10.6

4 Avonli village

W 6.8 14.7 24.2 12.6

PM 8.1 16.8 26.2 12.9

M 6.5 13.4 21.9 10.2

5

Punli Village on

Talo (Tangon)

Limb

W 7.1 14.3 22.6 10.7

PM 8.6 15.9 24.7 12.6

M 6.5 13.2 23.2 9.8

6 Etalin Village

W 7.9 14.9 24.3 11.2

PM 8.9 16.2 26.2 11.7

M 6.4 14.1 22.1 10.4

7 Power house Area

W 6.3 12.8 24.6 11.2

PM 7.4 13.2 26.0 12.5

M 6.0 12.5 23.1 9.2

8 Near Etalin School

W 7.2 13.2 25.8 10.6

PM 8.5 13.9 27.1 12.5

M 6.7 12.9 23.7 10

* W = Winter, S = Summer, PM = Pre-Monsoon

6.6 NOISE & TRAFFIC

6.6.1 Noise Level

Unwanted sound that is loud and unpleasant or unexpected termed as noise pollution. It has

adverse impact on the daily activities of the human being and animals. The adverse impact of the

noise on human and animals also depends upon time, season and the quality of sound. Noise

levels were monitored during the studies at various locations in the Direct Impact Area of the

project. The Ambient noise standards and results of noise level monitoring in terms of equivalent

sound levels are given in Tables 6.6 and 6.7, respectively. The sound levels on an average

ranged from 55.9 to 61.8 dB(A) (day time observations (see Table 6.7).

Table 6.6: Ambient Noise Standards

Area Code Category of Area Limits in dB(A)Leq

Day time Night time

A. Industrial Area 75 70

B. Commercial Area 65 55

C. Residential Area 55 45

D. Silence Zone 50 40

Note :

1 Day time 6 AM and 9 PM

2 Night time is 9 P. and 6 AM

3 Silence zone is defined as areas up to 100 meters around such premises as hospitals, educational

institutions and courts. The silence zones are to be declared by competent authority. Use of

vehicular horns, loudspeakers and bursting of crackers shall be banned in these zones.

4 Environment (Protection) Third Amendment Rules, 2000 Gazette notification, Government of India,

dt. 14.2.2000




Table 6.7: Equivalent Noise levels in study area during day time [dB(A)]

S.

No. Monitoring location Winter Pre-Monsoon Monsoon

Leq dB(A) Leq dB(A) Leq dB(A)

1 Dam Site on Dri River 59.6 60.2 61.8

2 Punli Village on Dri Limb 58.9 56.4 57.2

3 Dam Site on Talo (Tangon) River

58.5 58.6 59.5

4 Avonli village 57.0 56.4 55.9

5 Punli Village on Talo (Tangon)

Limb 58.6 58.2 57.3

6 Etalin Village 59.7 59.6 60.2

7 Power house Area 59.9 59.6 60.0

8 Near Etalin School 60.9 60.5 60.8

6.6.2 Traffic Density

Traffic density data was recorded by physically counting the number of different types of vehicles

passing through a particular point in a fixed time interval. Some major villages along the road were

considered as nodes for monitoring movement of traffic. Traffic density was recorded maximum at

Etalin village. The traffic density recorded at different sites is presented in Table 6.8.

Table 6.8: Traffic density (per hr) in the study area

Sl.

No. Monitoring location

Winter Summer Monsoon

HV LV TW HV LV TW HV LV TW

1 Dam Site Dri River 1 4 8 2 5 3 1 4 5

2 Punli Village on Dri Limb 2 6 10 2 4 8 2 5 2

3 Dam Site Talo (Tangon) River 1 6 14 1 3 7 2 5 8

4 Avonli village 3 8 11 1 3 7 2 6 6

5 Punli Village on Talo (Tangon)

Limb 4 5 17 2 4 5

3 6 5

6 Etalin Village 8 10 22 6 12 18 9 9 14

7 Power house Area 1 8 15 3 10 12 3 9 10

8 Near Etalin School 2 9 18 5 8 11 4 10 14

HV= Heavy Vehicle; LV= Light Vehicle; TW= Two Wheelers




7.1 INTRODUCTION

The project area is comprised of Mishmi Hills. Bio-geographically Mishmi Hills are situated in the

Eastern Himalayan province (Eastern Himalaya - Province 2D; Rodgers and Panwar‟s (1988)),

and is the richest bio-geographical province of the Himalayan zone and one of the Mega bio-

diversity hotspots of the world. It is a complex hill system of varying elevations and receives

heavy rainfall, which can be as much as 4,500-5,000mm annually in the foothill areas. The pre-

monsoon showers start from March and the monsoon remains active till October. The humidity in

the rainy season is often over 90%. This diversity of topographical and climatic conditions has

favoured the growth of luxuriant forests which are home to myriad plant and animal species.

Vast diversity of species can be attributed to the location which is at the junction of the

Paleoarctic, Indo-Chinese, and Indo-Malayan bio-geographic regions, Biotic elements from all

these regions occur in this area making it very rich in floral and faunal resources.

The Environmental Baseline chapter provides details of data compiled from primary as well as

secondary sources on terrestrial biodiversity. The primary data was collected during different

season‟s i.e. winter/lean season, Summer/pre-monsoon and monsoon in the project study area

as specified in the approved Terms of Reference by MoEF&CC, Government of India. The primary

data was supplemented by data collected from secondary sources like published reports,

research articles, etc. The details of collection of both primary and secondary data for pertinent

environmental components have been given in Chapter-3 of the EIA report.

7.2 LAND USE/ LAND COVER

The land use/ land cover pattern within 10 km radius of proposed dam sites and powerhouse site

was interpreted from LANDSAT satellite data of Path/Row 135/40 of October 2008. The False

Color Composite (FCC) of the study area is given in Figure 7.1 and the classified land use/ land

cover map interpreted from the same is given at Figure 7.2. Almost 90% of the area is covered

with dense vegetation with barren land/ jhum cultivation as second predominant land use in the

area (Table 7.1).

Table 7.1: Area under different land use/ land cover categories in the study area

S.No. Land Use/ Land Cover Area (sq km) Area (%)

1 Dense Forest 772.21 85.15

2 Open Forest 34.98 3.86

3 Barren Land/Jhum Cultivation 95.62 10.54

4 Settlement 0.55 0.06

5 Snow 0.02 0.00

6 Water Body 3.49 0.39

Total 906.88 100.00

Chapter ENVIRONMENTAL BASELINE STATUS: BIOLOGICAL

RESOURCES 7




Figure 7.1: FCC generated from satellite data showing study area




Figure 7.2: Land Use/ Land Cover Map of the project Study Area




7.3 FOREST TYPES

Dibang Valley District is almost entirely hilly and covered mostly by forests which are almost

52% of the total geographical area of the valley. Champion and Seth (1968); Rao and Panigrahi

(1961); Sahni (1981); Rao & Hajra (1986), Kaul & Haridasan (1987) are the prominent workers

who studied forest and vegetation of the region. The Dri and Talo (Tangon) valleys are

characterized by the Tropical evergreen, Tropical semi-evergreen, Sub-tropical forests at lower

elevations and Pine, Temperate Broadleaved, Temperate Conifer and Alpine forests at higher

elevations. The forest types of the study area have been described as per the Revised Survey of

Forest Types of India by Champion & Seth (1968).

7.3.1 Tropical Vegetation

This type of vegetation is spread over the foothill areas and outer valleys in all over the study

area and represents maximum species diversity. It is further divided into two types:

Tropical evergreen forests, and,

Tropical semi-evergreen forests

7.3.1.1 Upper Assam Valley Tropical Evergreen Forest (Tropical Evergreen

Forest) (1B/C2)

The species composition is classified into top storey representing tall trees like Altingia excelsa,

Castanopsis indica, Duabanga grandiflora, Terminalia myriocarpa, etc. Trees are heavily

plastered with lichens and festooned with climbers and epiphytes of the numerous lianas like

Pericamphylus glaucus, Stephania elegans, Parabaena sagitata, and species of Bauhinia, Derris,

Entada, Gnetum, Hodgsonia, Piper, Raphidophora, etc. The second storey mainly consists of

medium to small trees and shrubs, viz., Actiphila excelsa, Ardisia crispa, Bauhinia pupurea,

Grewia disperma, Gynocardia odorata, Leea robusta, Michelia doltsopa, and Mussaenda

roxburghii. Salacca secunda and Wallichia densiflora are found on the drier hill slopes, whereas

Angiopteris evecta, Cyathea spinulosa, and Pandanus nepalensis are found along the shaded

gorges. Calamus erectus, Calamus leptospadix and various other species of similar plants occur

along the swampy areas and form extensive thickets. Arenga pinnata, Caryota obtusa, Livistona

jenkinsiana, and Phoenix rupicola are the palms that occur in these forests. The epiphytic flora is

very rich, some of the common epiphytes are the species of Aerides, Cymbidium, Eria, and

Pholidota.

Along the hills slopes wild species of Musa comprising Musa acuminata, M. balbisiana and M.

rosacea is prominent feature of the vegetation.

7.3.1.2 Eastern sub-montane Semi-evergreen Forest (Tropical Semi-

evergreen forest) – (2B/C1b)

These types of forests occur on slopes in the vicinity of dam as well as powerhouse area and also

on foothills and river bank. The upper storey consists of deciduous trees as well as evergreen

trees. The shrubs, climbers and lianas constitute the rest. Depending on its species contents

Tropical Semi-evergreen forests are further divided into two subtypes.

i) Low hills and plains semievergreen forest

In this forest the upper storey is dominated by tall trees like Altingia excelsa, Bombax ceiba,

Canarium strictum, Elaeocarpus rugosus, Phoebe lanceolata, and Terminalia myriocarpa followed

by small trees and shrubs. The ground flora is dominated by species of Colocacia, Costus, and




Phrynium. Among the climbers and lianas Disocorea alata, Thunbergia coccinia, and T.

grandiflora are common. There are number of epiphytic species of orchids like Dendrobium,

Pholidota, Eria, and Hoya balaensis and several species of ferns in these forests.

ii) Riverine semi-evergreen forest

The top storey is dominated by Bombax ceiba, Bischofia javanica, Canarium strictum, Dalbergia

sissoo, Duabanga grandiflora, and Lagerstroemia parviflora. The next storey is represented by

the species of Calamus, Ficus, Meliosma, Murraya, and Randia. These species are closely

associated with dense clump of species of Phragmitis, Saccharum, Hedychium.

7.3.2 East Himalayan moist mixed deciduous forests (Sub tropical

Broadleaved Forests) – (3/C3b)

The subtropical broadleaved forests occur between 900 and 1200 m and are basically are of

evergreen and dense in nature. The canopy layer consists of Castanopsis indica, Quercus spicata,

Q. lemellosa, Alnus nepalensis, Ulmus lancifolia, Engelhardtia spicata, and Schima khasiana. The

middle storey is comprised mainly of Schefflera, Turpinia, Rhus, Hydrangea sp., Vernonia

arborea, Eurya acuminata, Symplocos racemosa, and Viburnum foetidum. Shrub and herb layers

include number of species of Ardisia humilis, Oxyspora paniculata, Chasalia curviflora, Rubus

ellipticus, Lobelia rhynchopetalum, Begonia palmata and Potentilla nepalensis. Lianas are not

very frequent but climbers are represented by Clematis gauriana, Senecio densiflorus, Crawfordia

speciosa, Jasminum officinale and Holboelia latifolia. Epiphytes are found growing luxuriantly and

comprised mainly of orchids and ferns.

7.3.3 Assam Sub-tropical Pine Forests – (9/C2)

These forests occur between 1200 and 1800 m, the Pine forest is common in catchment area of

Dri and Talo (Tangon) Rivers. The dominant species is Pinus merkusii. There is no middle storey.

However, the shrub and herb layer is gregarious. The main species in this layer is Imperata

cylindrica, Rubus ellipticus, Artemisia nilagirica, Pteridium aquilinum, Polygonum amplexicaule,

Osbeckia stellata, and Desmodium laxiflorum. A few broad-leaved species found associated are

Lyonia ovalifoila, Rhododendron arboreum, Quercus lemellosa, Rhus javanica, and Albizia mollis.

7.3.4 East Himalayan Wet Temperate Forests (Temperate Broadleaved

Forests) – (11B/C1)

They are found in elevation of 1800 – 2800 m and are generally dense in nature. These forests

are dominated by members of Fagaceae and Lauraceae families. Canopy trees are represented

by Qurecus lamellosa, Michelia doltstopa, Acer laevigatum, Populus ciliata, Exbucklandia

populnea, Carpinus viminea, Rhododendron spp., Tetracentron sinensis, Magnolia campbellii, and

Amentotaxus assamica. Middle canopy is composed of Lyonia ovalifolia, Vaccinium donianum,

Corylopsis himalayana, Rhododendron arboreum, Myrsine semiserrata, Spiraea callosa, Berberis

wallichii, and Mahonia nepalensis. Herbaceous layer is usually gregarious and abundant. The

shrub layer is represented by Potentilla polyphylla, Fragaria nubicola, Sedum spp., Desmodium

caudatum, and Rubus ellipticus. Herbs are comprised of Anaphalis busua, Daphne papyracea,

and Ranunculus sceleratus. Epiphytes are represented by Vaccinium chaetothrix, Aeschynanthus

bracteatus, Hoya parasitica. Lichens and ferns are few. These types of forests occur over

Mithumna-Mailang ridge, Chaglagam area and Malinja-Simbi area.




7.3.5 East Himalayan Mixed Coniferous Forest (Temperate Conifer

Forests) – (12/C3a)

These forests are seen above the elevation of temperate broadleaved forests. Among the conifers

Abies densa, A. spectabilis are more extensive than other species. The shrubs are represented by

different species of Berberis, Viburnum, Lonicera, Gaultheria, Rosa, Rubus, and Hydrangea. The

herb layer consists of species of Anaphalis, Hypericum, Podophyllum, Primula, Polygonum,

Rumex, Rheum, Pilea, Potentilla, Plectranthus, and Ranunculus. Climbers are scanty and

epiphytic flora is comprised of lichens.

7.3.6 Alpine Pastures (Alpine Forests) – 15/C3)

These forests occupy the highest altitude, 3500 - 5500m and lack tree cover. The main feature

here is that the area is under snow cover for a longer period resulting in a very brief growing

season. Even the occasional trees seen here are stunted in growth and are bushy or crooked in

appearance. They include Rhododendron spp., Juniperus spp., Betula alnoides, and Acer

oblongum. The shrubs include Berberis wallichiana, Rubus niveus, and Lonicera angustifolia. The

herbs include various species of Pedicularis, Rheum, Rumex, Polygonum, Anaphalis,

Cypripedium, Hypericum, Ranunculus, Sedum, Saxifraga, Delphinium, and Selinum.

7.3.7 Secondary Forests (1B/2S)

The primary forest due to impact of various adverse biotic and abiotic factors like shifting

cultivation or “Jhumming”, development activities and urbanization, landslides, fires, etc., are

destroyed and develop into secondary forests. The secondary forests divided into the three

following types.

7.3.7.1 Degraded Forests

As compared to the original primary forest these degraded ones have very low species diversity

and generally dominated by shrubs and small trees. Among the predominant trees are the

species of Bauhinia, Callicarpa, Glochidium and Mallotus whereas species of Capparis,

Clerodendrum, Eurya and Randia are the commonly occurring shrubs along with species of weeds

like Ageratum, Eupatorium, and Mikania.

7.3.7.2 Bamboo and Musa Forests

This type of secondary forests mostly occurs in the areas which are abandoned after “jhum”

cultivation. The common bamboo species are Arundina graminifolia, Bambusa pallida, B. tulda,

Chimonobambusa callosa, Dendrocalamus hamiltonia, D. hookeri and D. strictus. Musa

comprising Musa acuminata, M. balbisiana and M. rosacea are commonly found.

7.3.7.3 Grasslands

Generally formed due to practice of “jhum” cultivation or sometimes due to fires or over-grazing

and also on sun facing slopes on the hill tops. The more common species of grasses are

Arundinella bengalensis, Chrysopogon aciculatus, Imperata cylindrica, Saccharum spontaneum,

Themeda villosa, Thysanolaena maxima with sedges like Cyperus brevifolius, and Fimbristylis

bisumbellata.




7.4 FLORISTICS

7.4.1 Objectives

The main objectives of the floristic studies are as follows:

To prepare inventory of plants belonging to different groups like Angiosperms,

Gymnosperms, Pteridophytes, Bryophytes, Lichens and macro-fungi occurring in the

study area

To assess the vegetation community structure in the study area

To identify the dominant plant species occurring in the study are by calculating

Importance Value Index

To assess the Diversity of different tree, shrubs and herbaceous species by calculating

the Shannon Wiener Diversity

The study area comprised of power house, dam site, submergence area and area within 10 km

radius of dam site and power house site as per the TOR approved by MoEF&CC, GOI. As already

described in the Methodology Chapter quadrat sampling was undertaken at 8 different locations for

carrying out phytosociological surveys of the vegetation and in addition an inventory of various

floristic elements was also prepared by walking different transects around these sampling sites.

In order to understand the composition of the vegetation, most of the plant species could be

identified in the field itself whereas in case of the species that could not be identified a herbarium

specimen of some flowers were collected without uprooting the plant itself and in addition their

photographs were also taken for identification later with the help of available published literature

and floras of the region.

7.4.2 Taxonomic Diversity

During the field surveys and also based upon secondary data and available information an

inventory of 447 plant species in the study area has been prepared and list of the same is given

at Annexure-VI. The number of plant species recorded in various taxonomic groups is:

Angiosperms - 370, Gymnosperms - 7, Pteridophytes - 29, Bryophytes - 11, Lichens - 14, Algae

– 10 and Macro-Fungi- 6.

A brief description of each group is given in the following paragraphs.

a) Angiosperms

In all total 370 species of angiosperms were recorded. These include 95 trees, 77 shrubs and 198

herbaceous species.

These angiosperm species belong to 102 families of which Asteraceae and Orchidaceae with 26

species each are largest families followed by Poaceae with 21 species and Araceae with 14

species. The dominance of Asteraceae and Poaceae families is the indicator of open and grass

covered slopes in the study area mainly due to jhum cultivation which is prevalent in the area.

However, in the project study area there are patches of primary undisturbed forests which are

mainly seen higher on the slopes and away from the settlements. The vegetation of these areas

is comprised of species such as Altingia excelsa, Canarium strictum, Duabanga grandiflora, Ficus

spp., Terminalia myriocarpa, Lagerstroemia minuticarpa, and Pterospermum acerifolium. The

shrub layer is comprised of species like Acacia pennata, Acacia pruinescens, Boehmeria longifolia,




Boehmeria macrophylla, Calamus erectus, Calamus leptospadix, Clerodendrumcoolebrookianum,

Debregeasia longifolia and Desmodium laxiflorum.

b) Gymnospersms

This group is represented by 7 species of which Pinus merkusii is the most commonly occurring

species in the study area.

c) Pteridophytes

The study area was found to be rich in distribution of Pteridophytes. This group is represented by

29 species belonging to 15 families with Polypodiaceae being the largest family, represented by 9

species. List of all the pteridophytes is given at Annexure-VI.

d) Lichens

14 lichen species were found in the study area belonging to 13 families. Usnea baileyi and

Parmelia wallichiana were the most frequently occurring species found hanging from the trees.

List of lichen species recorded from the study is given at Annexure-VI.

e) Bryophytes

In the study area eleven species of bryophytes were recorded. These belong to 8 families and of

them Marchantia palmata, M. polymorpha, Polytrichum commune and Funaria hygrometrica were

commonly found. Detailed list is given at Annexure-VI.

f) Macro-fungi

From the study area 6 species of macro-fungi could be recorded during the surveys. Their list is

given at Annexure-VI.

7.4.3 Community Structure

Community structure of the vegetation was assessed by quadrat sampling method described in

Chapter on Methodolgy to evaluate various quantitive parameters at different sampling sites

during three seasons and location of the sites is given at Figure 7.3.

The description of vegetation structure at different sampling locations is given in the following

paragraphs

7.4.3.1 Catchment of Dri River (V1)

The site V1 is comprised upstream catchment area of Dri River on Dri dam limb and is located

near Makuni village before the confluence of Mathun river with Dri. The area is predominantly

covered with Sub-tropical and Pine forest at lower slopes while slopes at higher elevations are

covered with Temperate broadleaved and Temperate conifer forests.

The tree layer at this site is represented by 13 species. Among them Pinus merkusii is dominant

tree at higher elevations with highest density of 57 trees/ha (Table 7.2) and highest basal

cover. Albizia procera, Ficus semicordata, and Castanopsis indica are prominant along the river

banks and shaded places with high density and basal cover.

The shrub layer is comprised of 13 species and is dominated by the species of bamboo and

grasses such as Bambusa pallida, Dendrocalamus giganteus, Dendrocalamus hamiltonii,

Arundinaria falcata, Phragmites karka and Saccharum spontaneum with other species like

Oxyspora paniculata and Rhus wallichi (Table 7.2).

The herb layer was represented by 15 species during winter, 29 species in summer and 25 in

monsoon season (Table 7.3). Poa annua, Begonia palmata, Nephrolephis cordifolia,




Thysanolaena maxima, Arisaema concinnum, and Hedychium spicatum were recorded during

winter season. During summer season Thysanolaena maxima, Fragaria indica, Urtica dioica,

Fagopyrum dibotrys, Arundina graminifolia, Pouzolzia fulgens, Pilea scripta, Equisetum

ramosissimum, and Themeda anthera are the common herbs in the catchment area of Dri River.

In addition, fern species like Pteridium, Pteris, Angiopteris, Adiantum are also found at this site.

Table 7.2: Community structure –Site: V1 (Trees & Shrubs)

S. No.

Name of Species Density (no./ ha)

Frequency (%)

Basal Cover (sq m /ha)

TREES

1 Albizia procera 36 28.57 304.78

2 Alnus nepalensis 43 14.29 18.87

3 Aralia armata 36 21.43 153.70

4 Brassiopsis glomerulata 29 28.57 10.52

5 Castanopsis indica 57 28.57 65.97

6 Cyathea spinulosa 21 21.43 13.10

7 Engelhardtia spicata 14 14.29 64.75

8 Ficus semicordata 50 28.57 347.24

9 Macaranga denticulata 21 14.29 43.44

10 Macropanax dispermus 7 7.14 4.72

11 Pinus merkusii 57 28.57 366.90

12 Terminalia chebula 14 14.29 45.05

13 Toona hexandra 7 7.14 6.97

Total 393

1446

SHRUBS

1 Acacia pennata 80 10 0.32

2 Arundinaria falcata 240 15 0.43

3 Bambusa pallida 560 20 37.92

4 Dendrocalamus giganteus 280 20 66.66

5 Dendrocalamus hamiltonii 200 15 17.13

6 Oxyspora paniculata 360 10 0.28

7 Phragmites karka 420 25 0.40

8 Rhus wallichi 160 20 0.16

9 Rubus ellipticus 120 15 0.09

10 Rubus foliolosus 80 15 0.11

11 Saccharum spontaneum 240 25 0.35

12 Schizostachyum polymorphum 100 20 0.09

13 Solanum ciliatum 100 10 0.05

Total 2940




Figure 7.3: Location of terrestrial biodiversity sampling sites in the study area




Table 7.3: Community structure –Site: V1 (Herbs)

S. No. Name of Species Density

(no./ ha)

Frequency

(%)

Winter

1 Anaphalis contorta 8000 20

2 Adiantum philippense 6667 13

3 Alpinia allughas 5333 20

4 Arisaema concinnum 10667 27

5 Aster himalaicus 3333 13

6 Begonia palmata 12000 27

7 Dryoathyrium boryanum 7333 20

8 Fagopyrum dibotrys 3333 13

9 Fragaria indica 4000 13

10 Hedychium spicatum 10000 20

11 Nephrolephis cordifolia 10667 20

12 Poa annua 14667 27

13 Pteridium aquilinum 5333 13

14 Pteris vittata 8000 20

15 Thysanolaena maxima 10667 27

Summer

1 Ageratum conyzoides 3077 7.69

2 Alpinia allughas 1923 7.69

3 Amaranthus hybridus 3846 11.54

4 Anaphalis busua 4615 11.54

5 Anaphalis contorta 3077 7.69

6 Artemisia maritima 1538 11.54

7 Arundina graminifolia 6923 11.54

8 Aster himalaicus 1923 7.69

9 Bidens pilosa 4231 15.38

10 Cyperus rotundus 5769 19.23

11 Dicranopteris linearis 3846 15.38

12 Elsholtzia ciliata 4231 15.38

13 Equisetum ramosissimum 5385 19.23

14 Fagopyrum dibotrys 8077 15.38

15 Fragaria indica 10385 19.23

16 Gnaphalium affine 1923 7.69

17 Lycopodium clavatum 3077 11.54

18 Oxalis corniculata 5385 7.69

19 Pilea scripta 6538 15.38

20 Poa annua 3846 11.54

21 Pouzolzia fulgens 6154 19.23

22 Ranunculus sikkimensis 3077 11.54

23 Rhynchostylis retusa 769 7.69

24 Selaginella bryopteris 4615 15.38

25 Spilanthes oleracea 3077 11.54

26 Tagetes minuta 3846 19.23

27 Themeda anathera 5000 15.38

28 Thysanolaena maxima 10769 15.38





(no./ ha) Frequency

(%)

29 Urtica dioica 8462 19.23

Monsoon





5 Chirita bifolia 8571 23.81

6 Commelina benghlensis 4286 14.29

7 Cynodon dactylon 7143 9.52



10 Dryoathyrium boryanum 3333 14.29


12 Impatiens acuminata 8095 19.05

13 Leucas ciliata 4762 9.52

14 Microsorum punctatum 5238 19.05

15 Persicaria chinensis 6667 19.05


17 Plantago erosa 3810 4.76

18 Poa annua 7619 9.52

19 Pratia nummularia 10000 19.05

20 Pteridium aquilinum 2381 9.52


22 Solanum indicum 2857 14.29

23 Spilanthes paniculata 5714 14.29

24 Strobilanthes rhombifolius 4762 19.05


7.4.3.2 Dam Site Dri River (V2)

This sampling site is located in the vicinity of Dri Dam site and is comprised of Sub-tropical

forest.

At this site 17 species of trees were recorded (Table 7.4). Most dominant and frequent trees

are Castanopsis indica, Albizia lucida, Ficus semicordata, Macropanax dispermus, Saurauia

roxburghii, and Albizia procera.

Bambusa tulda, Bambusa pallida and Dendrocalamus giganteus have highest density at this

site found mostly in the clumps as seen from their basal cover (Table 7.4). Other dominant

shrub species are Oxyspora paniculata, Phragmites karka, Piper clarkei, and Saccharum

spontaneum. In winter ground layer is most prominent in this area and represented by 27

species, summer season comprised with 34 and in monsoon 29 species of herbs were

reported from the area.

Among the herbs Ageratum conyzoides, Alpinia allughas and Lepisorus sordidus were the

most adundant species during winters (Table 7.5). Elatostema sessile, Begonia palmata,

Thysanolaena maxima, Pilea scripta, and Polygonum capitatum were dominant during pre-




monsoon surveys while Cyperus rotundus, Cynodon dactylon and Arundina graminifolia were

the dominant herbs during monsoon.


S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)

Basal Cover

(sq m /ha)

Trees

1 Ailanthus integrifolia 29 21.43 140.18

2 Albizia lucida 43 21.43 380.31


4 Aralia armata 36 21.43 93.61


6 Caryota urens 14 14.29 26.45





11 Lagerstroemia parviflora 21 21.43 42.55



14 Pandanus odoratissma 36 21.43 7.62

15 Saurauia roxburghii 43 28.57 77.72

16 Terminalia chebula 21 21.43 151.47

17 Terminalia myriocarpa 29 21.43 155.77

Total 550

1680

Shrubs


2 Agapetes forrestii 60 10 1.53

3 Angiopteris evecta 100 15 0.32


5 Bambusa tulda 580 20 74.06

6 Costus speciosus 80 10 0.28


8 Ficus heterophylla 100 15 7.50

9 Jasminum amplexicaule 140 15 1.86

10 Luculia pinceana 40 5 0.50

11 Musa acuminata 160 15 9.79

12 Musa balbisiana 120 10 7.78



15 Piper clarkei 340 25 0.46

16 Rhaphidophora decursiva 80 10 0.37

17 Hydrangea serrata 100 10 0.48



20 Trevesia palmata 100 20 3.58

21 Myrsine semiserrata 80 10 0.54

Total 3940

238.15






(no./ ha)

Frequency

(%)

Winter

1 Achyranthes bidentata 3333 13


3 Ageratum conyzoides 8333 17

4 Alocasia fallax 2083 8



7 Arundina graminifolia 1667 4

8 Begonia nepalensis 6250 17

9 Bidens pilosa 4583 13

10 Carex longipes 2500 8

11 Commelina appeniculata 1250 4

12 Cynodon dactylon 2083 8

13 Cyperus rotundus 2917 8

14 Elatostema sessile 5833 13



17 Impatiens racemosa 1667 4

18 Lepisorus exavata 5000 4

19 Lepisorus sordidus 7083 8

20 Pilea scripta 2500 8

21 Polygonum flaccidum 4167 17

22 Polystichum aculeatum 2083 8


24 Pteris quadriaurita 2500 13


26 Urena lobata 1667 8

27 Urtica dioica 2917 13

Summer

1 Adiantum caudatum 4800 12.00


3 Angiopteris evecta 3200 8.00



6 Begonia nepalensis 6000 16.00

7 Begonia palmata 11200 32.00


9 Cardamine hirsuta 4800 12.00

10 Colocasia forniculata 2400 16.00

11 Commelina appeniculata 1600 8.00


13 Elatostema sessile 12800 28.00





18 Hedychium spicatum 4800 16.00

19 Impatiens bicornuta 2000 12.00

20 Justicia parviflora 2800 12.00





25 Polygonum capitatum 11200 16.00

26 Pouzolzia glaberrima 4000 12.00






(no./ ha)

Frequency

(%)

28 Solanum nigrum 1600 8.00




32 Viola diffusa 9600 12.00

33 Viola hediniana 3200 12.00

34 Canna indica 8800 16.00

Monsoon



3 Arisaema jacquemontii 1765 11.76

4 Arisaema speciosum 2941 17.65





9 Commelina benghalensis 4706 17.65







16 Hedychium densiflorum 4706 17.65





21 Microsorum punctatum 2941 17.65

22 Persicaria chinensis 3529 17.65


24 Poa annua 7059 17.65






7.4.3.3 Downstream of Dri Dam near Ru Pani (V3)

The sampling location is downstream of the proposed dam on Dri River on the left bank near

the village Punli. The area comes under shadow zone and dominated by Tropical evergreen,

Tropical semi-evergreen and Subtropical forest types.

Tree canopy at Site V3 is represented by 17 species and the most dominant species are

Albizia lucida, Saurauia roxburghii, Engelhardtia spicata, Ficus semicordata, and Aralia armata

(Table 7.6).

The shrub layer is represented by 16 species and most ones are the species of bamboo, and

Musa (Table 7.6). Other dominat species are Oxyspora paniculata, Piper clarkei and

Phragmitis karka.

Herbaceous flora was comprised of 26 species recorded during winter, 29 in summer season

and 25 during monsoon season (Table 7.7). Dominant herb species in the area are Begonia




palmata, Bidens pilosa, Hedychium spicatum, Ageratum conyzoides, Alpinia allughas, Cynodon

dactylon, Themeda anathera, and Thysanolaena maxima. Viola diffusa, Fagopyrum dibotrys,

Equisetum ramossimum, Elatostema sessile, Begonia palmata, and Polygonum capitatum

were most abundant in pre-monsoon and during monsoon Pratia nummularia, Fragaria indica,

Fagopyrum dibotrys, and Polygonum capitatum were most common and abundant.


S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)

Basal Cover

(sq m /ha)

TREES




4 Aralia armata 36 28.57 192.75



7 Cinnamomum obtusifolia 21 14.29 40.13

8 Cyathea giganteus 14 14.29 5.86










457

1211

SHRUBS






6 Jasminum amplexicaule 60 10 0.55

7 Canna indica 240 20 1.82

8 Musa acuminata 280 20 24.10









3700.00

113.36


S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)

Winter





5 Arthromeris wallichiana 800 8

6 Begonia griffithiana 4800 12








S. No.

Name of Species Density

(no./ ha) Frequency

(%)







17 Lepisorus sordidus 4800 8


19 Pogonatherum crinitum 3600 8



22 Sida rhombifolia 1200 8

23 Siegesbeckia orientalis 1600 12

24 Themeda anathera 4400 16



Summer



















19 Lecanthes peduncularis 5455 13.64





24 Pouzolzia glaberrima 5000 18.18





29 Canna indica 6818 13.64

Monsoon











11 Hedychium densiflorum 8571 35.71

12 Hedychium longipedunculatum 3571 21.43




16 Lactuca virosa 3571 14.29




S. No.

Name of Species Density

(no./ ha) Frequency

(%)

17 Lepisorus excavata 6429 7.14


19 Nephrolephis cordifolia 5714 28.57

20 Physalis minima 2143 14.29



23 Pteris quadriaurita 7143 21.43


25 Stellaria monosperma 2857 7.14

7.4.3.4 Catchment Area Talo (Tangon) River (V4)

The catchment area is mainly dominated by Subtropical broad leaved and Subtropical Pine

forest.

The site is comprised of 13 tree species (Table 7.8). The right bank slopes at this site are sun

facing and mainly comprised of Pinus merkusii forest at upper reaches. Left bank slopes are

covered with dense broad leaved vegetation. Pinus merkusii, Ficus semicordata and Albizia

procera are the most dominant plants at higher elevation and Engelhardtia spicata,

Macropanax dispermus and Pterospermum acerifolium are common near river bank and at

lower elevations.

Shrub layer is represented by 16 species comprised of the clumps of bamboo species. On

open places grasses like Saccharum spontaneu and Phragmites karka are common. Oxyspora

paniculata, Rubus foliolosus, Saxifraga sp., Piper clarkei, etc are the other common shrubs

recorded from the catchment area of Talo (Tangon) River.

Herb layer was represented by 20 species in winter, 23 in summer and 25 in monsoon (Table

7.9). The herbaceous layer mainly consists of Poa annua, Anaphalis contorta, Dryoathyrium

boryanum, Eupatorium odoratum, Themeda nathera, Thysanolaena maxima, Artemisia

maritima, Bidens pilosa, Ageratum conyzoides along with fern species like Nephrolephis

cordifolia, and Lecanthes peduncularis.


S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)

Basal Cover

(sq m /ha)

TREES








8 Kydia calycina 14 14.29 13.54


10 Ostodes paniculata 14 14.29 10.37


12 Pinus merkusii 57 28.57 237.83

13 Pterospermum acerifolium 29 21.43 72.36

336

783

SHRUBS

1 Artemisia indica 140 10 0.50




S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)

Basal Cover

(sq m /ha)

2 Arundinaria falcata 240 15 0.41




6 Buddleja asiatica 120 15 2.61






12 Rhus wallichi 100 10 0.92




16 Saxifraga sarmentosa 160 10 1.12

3660

163.90


S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)

Winter







7 Eupatorium odoratum 10000 33



10 Kyllinga brevifolia 6667 20

11 Lecanthes peduncularis 5333 13

12 Leucas ciliata 2667 13

13 Majus pumilus 10000 27


15 Physalis minima 4667 20

16 Poa annua 12000 13

17 Pothos scandens 3333 13

18 Pouzolzia fulgens 6000 20



Summer








8 Centella asiatica 2667 13.33

9 Eupatorium odoratum 8000 26.67



12 Kyllinga brevifolia 8000 20.00



15 Majus pumilus 8000 20.00





S.

No. Name of Species

Density (no./ ha)

Frequency (%)


18 Poa annua 14667 26.67

19 Pothos scandens 2667 20.00

20 Pouzolzia fulgens 2667 13.33




Monsoon

1 Abutilon indicum 1538 15.38








9 Cynoglossum glochidiatum 6154 23.08



12 Dioscorea belophylla 3846 23.08








20 Rhaphidophora decursiva 2308 23.08


22 Sida rhombifolia 4615 23.08


24 Spilanthes paniculata 769 7.69


7.4.3.5 Talo (Tangon) Dam Site Talo (Tangon) River (V5)

Tree layer at Talo (Tangon) dam site sampling location is comprised of 16 species.

Castanopsis indica Alnus nepalensis, Albizia lucida, Engelhardtia spicata and Ficus semicordata

are the most dominant species (Table 7.10). Castanopsis indica and Alnus nepalensis are

dominant only near the river bank and in shaded zone. Ficus semicordata and Albizia lucida

were found with highest basal cover.

As compared to trees, shrubs were represented by 22 species (Table 7.10). Bamboo brakes

are common in this area which comprised mostly of Bambusa tulda, Bambusa pallida,

Dendrocalamus giganteus and Dendrocalamus hamiltonii. Other dominant shrubs were

Oxyspora paniculata, Piper clarkei and Calamus leptospadix found occuring in shaded areas.

Saccharum spontaneum and Phragmites karka are common along river flood plain and

degraded area on the hills.

The herb layer was represented by 20 species in winter 24 species in summer and 23 in

monsoon (Table 7.11). Alpinia allughas, Begonia nepalensis, Bidens pilosa, Poa annua,

Hedychium spicatum, Thysanolaena maxima, Centella asiatica, Plantago erosa, Pteridium

aquilinum and Cyperus rotundus are the common herbs in the area.





S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)

Basal Cover

(sq m /ha)

TREES



3 Alnus nepalensis 57 35.71 55.51






9 Dalbergia pinnata 21 14.29 42.75



12 Itea macrophylla 21 14.29 17.08





571

1002

Shrubs




4 Calamus leptospadix 160 20 1.02

5 Cassia occidentalis 120 15 0.38



8 Eupatorium odoratum 140 10 1.07


10 Girardinia diversifolia 160 15 0.52


12 Murraya paniculata 140 15 1.15









21 Rubus burkillii 120 10 0.83


4680

344.18



(no./ ha)

Frequency

(%)

Winter




4 Arundina graminifolia 3333 13









(no./ ha)

Frequency

(%)






14 Poa annua 2667 13







Summer












12 Impatiens racemosa 4444 16.67


14 Poa annua 6667 16.67

15 Polygonum flaccidum 5556 22.22

16 Polystichum aculeatum 2222 11.11




20 Urena lobata 5000 11.11





Monsoon



3 Arundina grarminifolia 5333 13.33















18 Pteris vittata 6667 20.00





(no./ ha)

Frequency

(%)


20 Smilax aspera 4000 13.33



23 Tinospora crispa 3333 20.00

7.4.3.6 Downstream of Talo (Tangon) Dam near Anon Pani (V6)

In the downstream of the dam site near the Anon Pani area the dense tropical evergreen

forest are present on both the banks of the river.

Tree canopy is represented by 15 species with Albizia procera, Castanopsis indica, Saurauia

roxburghii, Engelhardtia spicata, Ficus semicordata and Lagerstroemia parviflora as the

dominant species (Table 7.12). The frequency of occurence of Albizia procera, Castanopsis

indica, Saurauia roxburghii too was highest amongst all species. However the basal of Albizia

procera was the highest.

Bambusa pallida, B. tulda, Musa balbasiana, Oxyspora paniculata, Piper clarkei, and

Saccharum spontaneum were the dominant shrubs (Table 7.12). The density of Oxyspora

paniculata was the highest amongst 17 species recorded from this location.

The herb layer was represented by 28 species in winter 30 species in summer and 23 in

monsoon (Table 7.13). The herbaceous species dominant in the area are Fagopyrum

dibotrys, Poa annua, Elatostema sessile followed by Begonia nepalensis, Alpinia allughas,

Bidens pilosa and Polystichum aculeatum.


S.

No. Name of Species Density

(no./ ha)

Frequency

(%)

Basal

Cover

(sq m /ha)

TREES










10 Mallotus philippinensis 36 35.71 33.54


12 Sarcosperma griffithii 29 28.57 17.08




536

1066

Shrubs




4 Calamus leptospadix 100 10 0.78




S.


(no./ ha)

Frequency

(%)

Basal

Cover

(sq m /ha)



7 Dendrocalamus strictus 280 10 24.47











4240

153.74


S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)

Winter


2 Amaranthus viridis 4545 14

3 Arisaema speciosum 4091 14





8 Cymbidium aloifolium 4545 18

9 Cyperus exaltatus 3636 9





14 Lepisorus exavata 4545 14


16 Onychium siliculosum 4091 14

17 Ophiopogon intermedeus 2273 9

18 Oxalis corniculata 3636 9

19 Physalis minima 1818 9



22 Pogonatherum paniceum 2273 14

23 Polygonum capitatum 6364 18


25 Pronephrium affine 3636 9




Summer


2 Amaranthus viridis 3182 9.09










S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)

9 Cymbidium aloifolium 3182 13.64

10 Cyperus exaltatus 3636 13.64






16 Lepisorus exavata 2727 9.09






22 Poa annua 11818 18.18

23 Pogonatherum paniceum 3182 13.64



26 Pronephrium affine 1818 9.09





Monsoon


2 Arundina grarminifolia 1765 5.88







9 Cymbidium aloifolium 8824 23.53


11 Erigeron bonariensis 7059 17.65





16 Hypericum densiflorum 2353 17.65


18 Phyrnium pubinerve 4706 17.65




22 Stellaria monosperma 2941 11.76


7.4.3.7 Power House Site (V7)

The power house site is located near the confluence of the Dri and Talo (Tangon) rivers near

Etalin village. This area is covered with dense forest.

The tree canopy at this location is dominated by Engelhardtia spicata, Saurauia roxburghii,

Pterospermum acerifolium, Castanopsis indica and Albizia procera with 20 species recorded

from this site (Table 7.14).




The shrub layer is represented by clumps of bamboos like Dendrocalamus giganteus and

Bambusa pallida. Other common species are Myrsine semiserrata, Oxyspora paniculata, Piper

clarkei, Saccharum spontaneum and Cassia occidentalis which are frequent all over the area

(Table 7.14).

The number of herbaceous species found during winter and monsoon surveys were 23 while

more number (32) of herb species were recorded during pre-monsoon season (Table 7.15).

Commonly occurring herbs in this area are Elatostema sessile, Viola diffusa, Thysanolaena

maxima, Pteridium aquilinum and Urena lobata. Ageratum conyzoides and Bidens pilosa are

common weeds recorded near the village.



(no./ ha)

Frequency

(%)

Basal Cover

(sq m /ha)

TREES




4 Artocarpus chaplasa 21 14.29 51.87

5 Canarium strictum 29 21.43 42.16





10 Duabanga grandiflora 29 21.43 65.48





15 Magnolia cambellii 14 14.29 6.12


17 Pterospermum acerifolium 36 28.57 42.06



20 Vitex altissima 29 21.43 14.68

593

963

Shrubs




4 Callicarpa arborea 100 10 0.34


6 Clerodendrum colebrookianum 160 10 0.57










16 Rhamnus nepalensis 120 15 0.83








(no./ ha)

Frequency

(%)

Basal Cover

(sq m /ha)

20 Saxifraga sarmentosa 160 10 3.30




24 Solanum viarum 80 5 0.28

4200

128.17


S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)

Winter


2 Bidens biternata 5000 10


4 Colocasia forniculata 2667 7






10 Hedychium densiflorum 3333 10


12 Impatiens bicornuta 4000 10






18 Polypodium amoenum 3333 13

19 Pothos scandens 4667 17


21 Solanum indicum 2667 7



Summer

1 Adiantum philippense 1905 4.76

2 Acorus calamus 2857 9.52



5 Ajuga macrosperma 2381 9.52

6 Alocasia fallax 1429 9.52



9 Arisaema wallichianum 952 4.76


11 Begonia roxburghii 5714 19.05

12 Bidens biternata 2381 9.52






18 Eupatorium odoratum 1429 4.76




22 Lepisorus sordidus 2381 4.76




S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)









31 Urena lobata 8095 19.05


Monsoon

1 Abutilon indicum 1667 11.11



4 Blumea procera 2778 11.11



7 Cyanotis vaga 2778 22.22






13 Iris domestica 4444 16.67

14 Justicia khasiana 2778 16.67


16 Pogostemon bengalensis 5556 16.67








7.4.3.8 Downstream of Power House Site (V8)

This sampling site is located about 5 km downstream of the confluence of Dri and Talo

(Tangon) Rivers on the Dibang River. The area is covered with dense tropical evergreen

forest.

The tree canopy is represented by Engelhardtia spicata, Terminalia myriocarpa, Albizia lucida,

Bauhinia purpurea, Cyathea spinulosa, Ficus semicordata and Saurauia roxburghii (Table

7.16).

Shrub layer is represented by 20 species in the area (Table 7.16) with Oxyspora paniculata,

Bambusa tulda, Cassia occidentalis, Bambusa pallida and Piper clarkei as the dominant

shrubs.

The herbaceous layer was represented by 22, 26 and 20 species during winter, pre-monsoon

and monsoon surveys, respectively (Table 7.17). The herbaceous layer was dominated by

species like Fagopyrum dibotrys, Elatostema sessile, Polygonum capitatum, Thysanolaena

maxima, Viola diffusa, Begonia nepalensis, Urena lobata, and Cynodon dactylon.





S.


(no./ ha)

Frequency

(%)

Basal

Cover

(sq m /ha)

TREES





5 Artocarpus chaplasa 7 7.14 3.70

6 Bauhinia purpurea 36 28.57 26.92




10 Ficus roxburghii 14 14.29 14.62


12 Gmelina arborea 14 7.14 22.43

13 Kydia calycina 14 7.14 7.33

14 Livistonia jenkinsiana 21 14.29 11.77




457

606

Shrubs


2 Agapetes forrestii 40 10 1.12




6 Callicarpa arborea 80 10 0.23


8 Clerodendrum colebrookianum 160 10 0.90




12 Luculia pinceana 80 10 3.73









Total 340

214.89


S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)

Winter

1 Abutilon indicum 3000 10


3 Anisomeles indica 7500 20

4 Bidens biternata 9000 25


6 Colocasia forniculata 3500 20

7 Cyathula prostrata 6000 20






S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)


11 Ephedra aspera 5000 10







18 Persicaria chinensis 6000 20

19 Poa annua 12000 15




Summer


2 Arisaema speciosum 1500 10

3 Begonia griffithiana 2000 15


5 Begonia roxburghii 5000 15




9 Equisetum ramosissimum 4000 10

10 Eupatorium odoratum 2500 5




14 Impatiens brachycentra 4000 20


16 Majus pumilus 5000 20


18 Plantago erosa 6500 20




22 Selaginella bryopteris 2000 5

23 Solanum nigrum 2500 20



26 Viola diffusa 11000 25

Monsoon


2 Asplenium nidus 5000 15



5 Chirita bifolia 9000 30

6 Commelina benghlensis 7000 15





11 Imperata cylindrica 6000 20

12 Justicia khasiana 4000 15

13 Lycopodium clavatum 7500 20


15 Pogostemon bengalensis 5500 15





S.

No. Name of Species

Density

(no./ ha)

Frequency

(%)

17 Pratia nummularia 12500 20




7.4.4 Density & Dominance

Density is one of the indicators to assess the dominance of a particular plant species occurring

in a particular area.

The density of trees varied from site to site depending upon elevation and the extent of area

subjected to shifting cultivation in the area current as well as abandoned jhummed area. The

overall tree density throughout the study area ranged from minimum of 336 number of

trees/ha to maximum of 593 trees/ha (Table 7.18 & Figure 7.4). Highest tree density was

recorded near power house site, followed by dam sites of the Dri and Talo (Tangon) River and

lowest was at catchment area of both the rivers.

The shrub layer was quite prominent at all sampling sites and the density of shrub layer

varied from 2940 plants/ha to 4860 plants/ha, lowest density was found at sites located in

catchment area upstream of Dri limb dam site and highest at Dam site on Talo (Tangon) River

(Table 7.18 & Figure 7.5).

The density of herbaceous plant species varied from season to season amongst all sampling

sites (Table 7.18 & Figure 7.6). In winter season herb density is highest at downstream of

power house site (158000 plants/ha) and lowest at downstream of Dri Dam site along the Dri

River (93200 plants/ha). In summer season density of herbs ranged from 135385 to 188800

per ha along the Dri River limb, 135000 to 163182 per ha along Talo (Tangon) River limb;

near Powerhouse area it was 141429; and in downstream of power house after the confluence

of Dri and Talo (Tangon) River it was 168000 per ha. In monsoon season maximum herb

density was observed along the Dri River, ranged from 154286 plants /ha to 172353 plants

/ha. In Talo (Tangon) river limb herb density during monsoon varied in between 129237

plants/ha and 140667 plants/ha. Lowest herb density was recorded from power house

(113889 plants/ha) and downstream area (129500 plants/ha).

Table 7.18: Density (per ha) of Trees, Shrubs and Herbs

Sampling Site

Location

V1 V2 V3 V4 V5 V6 V7 V8

Trees 393 550 457 336 571 536 593 457

Shrubs 2940 3940 3700 3660 4860 4240 4200 4340

Herbs

Winter 120000 104167 93200 121333 110667 134545 98333 158000

Summer 154286 172353 165000 129231 140667 137059 113889 129500

Monsoon 135385 188800 168182 136000 135000 163182 141429 168000

In order to understand the dominance of various species among trees and shrubs, Importance

Value Index (IVI) of most dominant species has been given at Figures 7.7 & 7.8. The tree




species which recorded IVI value of more than 40 are Albizia lucida (at site V3), A. procera (at

site V1 & V6), Engelhardtia spicata (at site V8), Ficus semicordata (at site V1) and Pinus

merkusii ((at site V1 & V4) (Figure 7.7). Pinus merkusii recorded highest IVI values of 58.53

and 51.03 at sites V4 and V1, respectively. At sites V2, V5 and V7 no single tree species

dominanted the composition. At these sites there were mixture of species that dominated. At

V1 the co-dominant species are Albizia lucida, Engelhardtia spicata, Ficus semicordata,

Macropanax dispermus and Terminalia myriocarpa, at site V5 Albizia lucida, Engelhardtia

spicata, and Ficus semicordata were co-dominant while at site V7 Ficus semicordata,

Castanopsis indica, Saurauia roxburghii and Albizia procera are co-dominant.

Figure 7.4: Variation in Tree Density at different Sampling Locations

Figure 7.5: Variation in Shrub Density at different Sampling Locations

0

100

200

300

400

500

600

V 1 V 2 V 3 V 4 V 5 V 6 V 7 V 8

Dri River Talo (Tangon) River Power HouseArea

No

. of

tre

es/

ha

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

V 1 V 2 V 3 V 4 V 5 V 6 V 7 V 8

Dri River Talo (Tangon) River Power HouseArea

De

nsi

ty (

no

. pe

r h

a)




Figure 7.6: Seasonal variation in density of herbs

Figure 7.7: Importance Value Index of dominant tree species at different sampling locations

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

V 1 V 2 V 3 V 4 V 5 V 6 V 7 V 8

Dri River Talo (Tangon River) Power HouseArea

De

nsi

ty (

No

. pe

r h

a)


0

10

20

30

40

50

60

70

V 1 V 2 V 3 V 4 V 5 V 6 V 7 V 8

Im

po

rta

nce V

alu

e I

nd

ex

Albizia lucida Albizia procera Aralia armata Brassiopsis glomerulata

Castanopsis indica Cyathea spinulosa Engelhardtia spicata Ficus semicordata

Lagerstroemia parviflora Macaranga denticulata Macropanax dispermus Pandanus odoratissma

Pinus merkusii Saurauia roxburghii Terminalia myriocarpa




Figure 7.8: Importance Value Index of dominant shrub species at different sampling locations

Amongst the shrubs, Dendrocalamus giganteus was the single most doninant species with

high IVI values i.e. more than 50 at 6 out of 8 sampling sites : V1-V2, V4-V7 (Figure 7.8). It

is indicative of jhum cultivation was being practiced at these sites and has recently been

abandoned as the slopes are covered with this bamboo species. At sites V1 & V2 other

bamboo species Bambusa pallida and B. tulda were the most dominant species with high IVI

values. At rest of the three sites too i.e. at sites V3 and V8) these three species of bamboos

(Bambusa pallida, B. tulda and Dendrocalamus giganteus) together constituted majority of

shrub vegetation.

7.4.5 Diversity

To understand the species richness Shannon Weiner Diversity was calculated for trees, shrubs

and herbs, seperately. The species diversity in tree and shrub was moderately high at all the

sampling locations as the Diversity Index ranged from lowest of 2.38 (Shrubs at Site V1) to

highest of 3.06 (at Site V7) (Table 7.19, Figure 7.9). However the species diversity in

general was very high at majority of the sampling locations, during all seasonal surveys. It

varied from lowest of 2.62 at Site V1 during winter to highest of 3.34 at Site V2 during pre-

monsoon sampling (Table 7.19 & Figure 7.10). In general the Shannon Weiner Index was

recorded around 3 at most of the sites during all seasons.

Table 7.19: Shannon Weiner Diversity Index (H)

Diversity Dri River

Talo (Tangon)

River

Power House

Area

V1 V2 V3 V4 V5 V6 V7 V8

Trees 2.40 2.79 2.71 2.46 2.69 2.61 2.93 2.72

Shrubs 2.38 2.78 2.56 2.65 2.88 2.60 3.06 2.83

Herbs

Winter 2.62 3.17 3.14 2.88 2.92 3.22 3.01 3.02

Summer 3.23 3.34 3.19 3.02 3.12 3.28 3.27 3.09

Monsoon 3.14 3.22 3.04 2.96 3.04 2.96 2.97 2.91

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

V 1 V 2 V 3 V 4 V 5 V 6 V 7 V 8

Im

po

rta

nce V

alu

e I

nd

ex

Angiopteris evecta Bambusa pallida Bambusa tuldaCassia occidentalis Dendrocalamus gigantea Dendrocalamus hamiltoniiFicus heterophylla Hydrangea serrata Musa acuminataMusa balbasiana Myrsine semiserrata Oxyspora paniculataPhragmites karka Piper clarkei Rubus ellipticusRubus foliolosus Saccharum spontaneum Trevesia palmata




Figure 7.9: Species Diversity Index (H) of Trees and Shrubs

Figure 7.10: Species Diversity Index (H) of Herbs

Evenness Index (E) was calculated by using Evenness Index Formula and is indicative of

distribution pattern of vegetation in any area. Amongst the tree species the evenness index

ranged between 0.93 and 0.98 indicating highly regular distribution pattern at all locations

(Table 7.20). The shrubs too were evenly distributed at all the sites (Table 7.20). The

herbaceous species were also found to be evenly distributed at all the sites during seasons

(Table 7.20).

Table 7.20: Evenness Index (E)

V1 V2 V3 V4 V5 V6 V7 V8

Trees 0.93 0.98 0.96 0.96 0.97 0.96 0.98 0.96

Shrubs 0.93 0.91 0.92 0.95 0.93 0.92 0.96 0.94

Herbs

Winter 0.97 0.96 0.96 0.96 0.97 0.97 0.97 0.98

Summer 0.96 0.95 0.95 0.96 0.98 0.96 0.95 0.95

Monsoon 0.97 0.96 0.94 0.92 0.97 0.95 0.96 0.97

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

V 1 V 2 V 3 V 4 V 5 V 6 V 7 V 8

Dri River Tangon River Power HouseArea

Shru

b D

ive

rsit

y

Tre

e D

ive

rist

y

Sampling Location

Tree

Shrub

Talo ( )

Talo ( )




7.4.6 Economically Important Plant Species

During the field survey, numbers of economically important plant species were recorded from

the study area. The local people utilise various plants species in their day to day life. Mainly

plants are used as timber, fuel wood, and fodder, vegetable, medicinal, thatching and wild

edible. Knowledgeable and elder persons of study area villages were interviewed and

information on plants parts (seed, bark, leaf & root) used and indigenous knowledge was

gathered. Secondary information was also collected to know the ethnobotanical importance of

the region. Some of the plant species used by local people for various purposes like timber,

fuel wood, wild edible plants, medicine found in the study area have been given in Tables

7.21-7.23.

Nearly 13 species are most commonly used by local inhabitants for timber, fodder and fuel

wood (Table 7.21).

Table 21: Plant Species used as timber, fodder and fuel wood

S. No. Plant name Uses

1 Altingia excelsa Timber

2 Bambusa pallida Timber

3 Calamus erectus Thatch

4 Dendrocalamus hamiltonii Timber

5 Duabanga grandiflora Timber

6 Ficus roxburghii Fodder, fruits edible

7 Kydia calycina Timber

8 Macaranga denticulata Fuel

9 Pandanus odoratissima Fibre

10 Pinus merkusii Timber

11 Saurauia nepalensis Fodder

12 Terminalia myriocarpa Timber

13 Thysanolaena maxima Broom, fodder

Dibang valley area is mainly inhabited by Idu-mishmi tribe communities. They used various

plant species for curing various diseases and ailments. Some of the most frequently used

medicinal plants species along with their medicinal uses found in the study area are given in

Table 7.22.

Table 22: Commonly used plants species for medicinal purposes in the area

S. No. Plant name Uses Part/s used

1 Abroma angusta Cut and wounds, dysentery

and vomiting, leucorrhoea Leaf, root and stem

2 Achyranthes bidentata Diuretic and astringent Whole plant

3 Acorus calamus Brain tonic, coolant and colic Rhizome, tubers

4 Allium sativum

Infusion of Zanthoxylum

armatum seeds with its bulb

for stomach bloating

Bulb

5 Angiopteris evecta Antidysenteric and

antidiarrhoeic Rhizome

6 Alpinia allughas Rheumatism and fish poison Fruit and seeds

7 Andrographis paniculata Diarrhoea, malaria and

stomach trouble Leaf and whole plant




S. No. Plant name Uses Part/s used

8 Artemisia nilagirica Wound healing, nose bleeding

and muscular pain Leaves

9 Berberis aristata Diabetes, jaundice and

leucoderma Root

10 Calamus erectus Indigestion and stomach

problem Seeds, leaf

11 Cannabis sativa Digestion and dysentery Leaves

12 Centela asiatica Stomachache, diabetes, blood

disorders and brain tonic Whole plant

13 Cinnamom camphora Diarrhoea and skin diseases Leaf

14 Citrus limon

Digestive, dysentery,

dehydration and stomachic

trouble

Fruit

15 Coptis teeta

Improvement of appetite,

jaundice, malarial fever, worm

infestation, cold, cough,

hypertension and diabetes

Root/rhizome

16 Curcuma longa Body pain Rhizome

17 Dioscorea bulbifera Aphrodisiac and tonic Root

18 Engelthardtia spicata Skin diseases, fish poison Bark

19 Ficus relegiosa Ulcer Bark

20 Girardinia diversifolia Diabetes Leaves

21 Hedychium spicatum Joint pain, injury and wound

healing Rhizome

22 Oroxylum indicum For fever and other ailments Bark

23 Piper betle Various ailments Fruits

24 Plantago major Wound healing Whole plant

25 Psidium guajava Dysentery Stem

26 Ricinus communis Constipation, rheumatism Seed

27 Solanum nigrum Liver diseases, dyspepsia,

fever and diarrhoea Fruit

28 Zanthoxylum armatum Digestive, tootache Seed and bark

29 Zingiber officinale Cold and cough, ulcer Rhizome

In addition to medicinal and other uses there are number of wild edible plants that are used

as food by locals and list of the same is given at Table 7.23.

Table 23: Commonly used wild plants species as food

S. No. Name of species Local name

1 Bambusa pallida Dibang

2 Begonia palmata -

3 Centella asiatica Kipum

4 Choerospondias axillaris -

5 Clerodendrum colebrookianum Papa tsitsu

6 Coix lacryma-jobi -

7 Deeringia amaranthoides -

8 Dendrocalamus hamiltonii Epo

9 Dillenia indica Sampa

10 Elaeocarpus floribundus -

11 Hovenia dulcis -

12 Mangifera sylvatica Aru

13 Paedaria foetida Bhidailota

14 Sarcochlamys pulcherrima -

15 Solanum nigrum Koitang

16 Spilanthus paniculata Marsang

17 Spondias pinnata Hitum

18 Sterculia hamiltonii -

19 Syzygium cumini -




7.4.7 Rare & Endangered Flora

An assessment of plant species found in the study area was made using IUCN Redlist Ver3.01.

According to this only one species i.e. Lagerstroemia minuticarpa of Lythraceae has been

categorized as Endangered (EN). Though it has been listed as Endangered, it has been stated

that its status needs updating. This species has been considered as Rare by some authors but

it is has been regularly found in most of the valleys of Arunachal Pradesh. However none of its

plants were recorded in the quadrat studies. During the surveys another related species

Lagerstroemia parviflora was regularly recorded in the quadrats at sites V2, V3 and V6.

Another species Pinus merkusii has been put in Vulnerable category needing updating and it

was regularly found in most of the quadrats studied at most of the sampling sites and was

found as dominant species at these locations. Amongst rest of the species found in the area

none of them fall under any RET category as either they are listed under Least Concern (LC)

category or have been listed as Not Evaluated (NE) category. According to Red Data Book of

published by Botanical Survey of India (BSI), Livistona jenkinsiana is under Endangered

category, Coptis teeta and Cymbidium eberneum are under Vulnerable category. Angiopteris

evecta, a fern also has been listed under Endangered category by some authors.

Calamus leptospadix, Coptis teeta, Cymbidium eberneum and Livistona jenkinsiana are

endemic to Arunachal Pradesh. Dendrobium hookerianum of Orchidaceae and Lagerstroemia

minuticarpa belonging to Lythraceae are endemic to north-east India.

Appropriate measures have been suggested in Biodiversity Conservation Plan prepared under

overall Environmental Management Plan (EMP) for their conservation and adopting mitigation

measures for their protection during construction of the project.

7.5 TERRESTRIAL FAUNA

A three season study was carried out to describe the faunal elements in the region. The

fauna of catchment area is discussed briefly with the help of primary survey and secondary

sources.

7.5.1 Mammals

To study the wild mammalian fauna of the study area, 2 - 5 km long transects and trails were

walked at early morning and evening hours. Direct sighting of animals as well as indirect signs

like scat, pellets, pugmarks, scraps, vocalizations, horns etc. were also recorded during the

survey walk. On each transect, the group size, age and sex and distance of animal/ group

from transect was noted and the locations were marked with the help of a hand held GPS.

Four to five separate walks were done along Dri and Talo (Tangon) Rivers to collect

information on riverine tract. Secondary data as well as information elicited from the locals

were also noted for the presence or absence of wild animals in the area. These indirect

evidences and information were analyzed and checked with the help of literature available.

During the surveys only 5 mammalian species belonging to 5 orders in the study could be

sighted (Table 7.24). The Jungle cat was observed near Punli village, a troop of Assam

Macaque were sighted near dam site at Dri river, Himalayan Striped Squirrel was sighted on a

tree (Pterospermum acerifolium) near powerhouse site, Mithun was found in the wild or semi




domesticated forms near villages and road side while the House Bat was recorded near Etalin

village during evening hours.

However, according to the list prepared based upon secondary data 26 species of mammals

are reported from the area and list of the same is given at Table 7.25.

Table7.24: Mammalian species sighted in the study area

S. No./ Order Common name Scientific name WPA

1972

IUCN Ver 3.1

Carnivora

1 Jungle Cat Felis chaus II LC

Primates

2 Assam macaque Macaca assamensis II NT

Rodentia

3 Himalayan Striped Squirrel Tamiops macClellandi - LC

Artiodactyla

4 Mithun Bos frontalis - -

Chiroptera

5 House Bat Eptesicus hottentotus - LC

VU – Vulnerable; NT- Near Threatened; LC - Least concern

Table 7.25: Mammalian species reported from the study area*

S.

No. Family Scientific name Common name

Conservation Status

IUCN Ver. 3.1

WPA Schedule

ORDER: ARTIODACTYLA

Bovidae

1 Naemorhedus goral Goral NT III

2 Bos frontalis Mithun - -

3 Budorcas taxicolor Mishmi takin VU I

Cervidae

4 Cervus unicolor Sambar VU III

5 Muntiacus muntjak Barking deer LC III

Suidae

6 Sus scrofa Wild boar LC III

ORDER: CARNIVORA

Ailuridae

7 Ailurus fulgens Red Panda VU I

Canidae

8 Cuon alpinus Wild Dog EN II

9 Canis aureus Jackal LC II

10 Vulpes bengalensis Indian fox LC IV

Felidae

11 Panthera pardus Leopard VU I

12 Felis chaus Jungle Cat LC II

13 Prionailurus viverrinus Fishing Cat EN I

Herpestidae

14 Herpestes javanicus Indian Mongoose LC IV

Ursidae

15 Ursus thibetanus Asiatic black bear VU II

Viverridae

16 Viverra zibetha Large Indian Civet NT II

17 Viverricula indica Small Indian Civet LC II

ORDER: CHIROPTERA

Vespertilionidae

18 Scotophilus heathi Common yellow bat LC IV

19 Eptesicus hottentotus House Bat LC -

ORDER: LAGOMORPHA

Leporidae




20 Lepus nigricollis Indian Hare LC IV

ORDER: PHOLIDOTA

Manidae

21 Manis crassicaudata Indian Pangolin NT I

ORDER: PRIMATES

Cercopithecidae

22 Macaca mulatta Rhesus monkey LC II

ORDER: RODENTIA

Hystricidae

23 Hystrix indica Indian Crested Porcupine - IV

Muridae

24 Rattus nitidus Himalayan rat LC IV

Sciuridae

25 Callosciurus pygerythrus Hoary-bellied Squirrel LC II

26 Tamiops macClellandi Himalayan Striped Squirrel LC -

*Source: Secondary data; VU – Vulnerable; EN – Endangered; NT- Near Threatened; LC - Least

Concern

Mithun (Bos frontalis): The mithun is a domesticated form of Gaur. This unique livestock

species is found in the steep slopes of the hills North-east India, Bhutan, Myanmar and China

and is considered to be a descendent of wild gaur. This animal has religious significance and is

intimately related to the socio-cultural life of the Mishmi people. The mithun is considered to

be a source of personal prestige with an economic value far in excess of the material

contribution. Mithuns are considered a unit of wealth and are allowed to move freely in jungle

till used for food on festive occasions or for barter.

7.5.2 Avifauna

As discussed in Methodology Chapter 3 of this report, the survey for birds was carried out on

a fixed width trails of 2 km wherever the terrain permits and point counts were carried out at

a fixed distances at more or less regular intervals. Birds were identified as per the field guide

of Ali & Ripley (1983), Grimmeth and Flaming et al. (1984), Krys Kazmierczak (2006) and

Grimmeth (2007).

The surveys showed the presence of barbets, hornbills, trogon, swiftlet, treepie, drongo,

thrushes, redstart, flycatcher, tits, bulbul, wagtails, forktails, munia, etc. 33 species of bird

species belonging to 22 families inhabit these areas. The sighting of Plumbeous Water

Redstart, White Capped Water Redstart and Brown Dipper recorded mostly near the water

body like river and nalas while other birds were observed in forest area. A single sighting of

the Great Hornbill, Buceros bicornis was also recorded near Etalin village at morning hours

during the visit. List of bird species composition and their conservation status has been

described in Table 7.26.

Table7.26: List of birds sighted from the study area and their conservation status

S.

No. Family / Scientific

Name Common Name

Conservation status

IUCN

(ver 3.1) WPA 1972

Megalaimidae

1 Megalaima asiatica Blue-throated Barbet LC Schedule IV

Bucerotidae

2 Buceros bicornis Great Hornbill NT Schedule I

Trogonidae

3 Harpactes

erythrocephalus

Red Headed Trogon LC Schedule IV




S.

No. Family / Scientific

Name Common Name

Conservation status

IUCN

(ver 3.1) WPA 1972

Cuculidae

4 Centropus sinensis Greater coucal LC Schedule IV

Apodidae

5 Collocalia brevirostris Himalayan Swiftlet LC -

Accipitridae

6 Spilornis cheela Crested Serpent Eagle LC Schedule I

Corvidae

7 Dendrocitta formosae Grey Treepie LC Schedule IV

Dicruridae

8 Dicrurus macrocercus Black Drongo LC Schedule IV

9 Dicrurus aeneus Bronzed Drongo LC Schedule IV

Cinclidae

10 Cinclus pallasii Brown Dipper LC -

Campephagidae

11 Pericrocotus ethologus Long tailed Minivet LC Schedule IV

Muscicapidae

12 Monticola solitarius Blue Rock Thrush LC Schedule IV

13 Phoenicurus hodgsoni Hodgson's Redstart LC Schedule IV

14 Enicurus scouleri Little Forktail LC Schedule IV

15 Ficedula westermanni Little pied Flycatcher LC Schedule IV

16 Rhyacornis fuliginosa Plumbeous Water

Redstart

LC Schedule IV

17 Enicurus maculatus Spotted Forktail LC Schedule IV

18 Chaimarrornis

leucocephalus

White capped Water

Redstart

LC Schedule IV

Sturnidae

19 Acridotheres tristis Common Myna LC Schedule IV

Paridae

20 Parus monticolus Green backed Tit LC Schedule IV

Pycnonotidae

21 Hypsepetes

leucocephalus

Black Bulbul LC Schedule IV

22 Pycnonotus jocosus Red whiskered Bulbul LC Schedule IV

23 Pycnonotus cafer Red-vented Bulbul LC Schedule IV

Cisticolidae

24 Orthotomus sutorius Common Tailor Bird LC Schedule IV

Timaliidae

25 Garrulax leucolophus White crested

Laughingthrush

LC Schedule IV

Chloropseidae

26 Chloropsis hardwickii Orange bellied Leafbird LC Schedule IV

Passeridae

27 Passer montanus Eurasian tree sparrow LC Schedule IV

Motacillidae

28 Motacilla cinerea Grey Wagtail LC Schedule IV

29 Anthus hodgsoni Olive backed Pipit LC Schedule IV

30 Motacilla alba White Wagtail LC Schedule IV

Estrildidae

31 Lonchura punctulata Scaly-breasted Munia LC Schedule IV

Turdidae

32 Myophonus caeruleus Blue Whistling Thrush LC Schedule IV

Rhipiduridae

33 Rhipidura hypoxantha Yellow bellied Faintail LC Schedule IV

VU – Vulnerable; NT- Near Threatened; LC - Least Concern




7.5.3 Herpetofauna

The herpetofauna were sampled on the same transect marked for mammals. During the

survey there were no direct sightings of any herpetofauna in the study area. Following species

of reptiles and lizards are reported from the study area as per discussion with locals and

secondary data source of the area (Table 7.27). In all 11 species of reptiles and lizards are

reported from the study area and these belong to 9 families.

Table 7.27: Herpetofaunal composition of the Study area

S. No. Family Common Name Scientific Name

1 Colubridae Green Trinket Snake Elaphe prasina

2 Colubridae Rat Snake Ptyas mucosa

3 Pythonidae Burmese Python Python molurus bivittatus

4 Hydrophiidae King Cobra Ophiophagus hannah

5 Elapidae Monocled cobra Naja naja kaouthia

6 Viperidae Mountain Pit Viper Ovophis monticola

7 Agamidae Common calotes Calotes versicolor

8 Agamidae Blue throated Forest lizard Ptyctolaemus gularis

9 Gekkonidae Spiny tailed House Gecko Hemidactylus frenatus

10 Scincidae Speckled little Sun skink Mabuya macularia macularia

11 Varanidae Common Asian Monitor Varanus bengalensis

In addition, 5 species of amphibian are also reported from the area and a list of the same is

given at Table 7.28.

Table 7.28: List of commonly found amphibians in the area

S. No. Common Name Scientific Name

1. Amolops formosus Assam Sucker Frog

2. Duttaphrynus himalayanus Himalayan Broad-skulled Toad

3. Duttaphrynus melanostictus Common Indian Toad

4. Euphlyctis cyanophlyctis Indian Skipper Frog / Skittering Frog

5. Fejervarya limnocharis Cricket Frog

7.5.4 Insects

The insects including butterflies are common in the area and are sighted throughout the study

period. The presence of the insects was abundant in monsoon and summer season however

their availability was less in winter months. This might be by the influence of cold weather

which forces them to migrate and hibernate. Insects have a variety of methods for surviving

the coldness of winter. Hibernation is a well-known natural phenomenon among insects. In

general, insects are able to survive cold temperatures easiest when the temperatures are

stable, not fluctuating through alternate thaws and freezes. Many insects can gain shelter and

nourishment through the winter in a variety of microhabitats. Among these niches are under

the soil, inside the wood of logs and trees, and even in plant galls.




Overwintering into different stages larvae, nymphs, eggs, pupae, or as adults of insect life is

very common. Many large wasps seek shelter in the eaves and attics of houses or barns. Tree

holes, leaf litter, and under logs and rocks are common shelters for overwintering adult

insects. A list of insects compiled from primary surveys as well as secondary sources is given

at Table 7.29. Total 18 insect species are reported from the study area.

Moths were recorded from the residential areas of Etalin and Yuron villages the species of

which could not be identified. Some other insects like Pyrrhocorid and Coreid Bugs, and Blue

Bottle Fly, were also recorded from the forests of the study area.

Table 7.29: Insects found in the Study Area

S. No. Family Common Name Scientific Name

1 Acrididae Grasshoper Heteracris sp.

2 Acrididae Grasshoper Stenopola sp.

3 Apidae Honey Bee Apis sp.

4 Calliphoridae Blue Bottle Fly Phormia sp.

5 Cerambycidae Red Ants Oecophyla smaragelina

6 Cicadidae Cicada Cicada sp.

7 Coccinellidae Longicorn beetle Rhytidodera sp.

8 Coccinellidae Red Beetle Chrysolina sp.

9 Coreidae Coreid Bug Coreus sp.

10 Gerridae Gerris Aquarius remigis

11 Libellulidae Black Stream Glider Trithemis festiva

12 Libellulidae Crimson-tailed Marsh Hawk Orthetrum pruinosum

13 Libellulidae Ruddy Marsh Skimmer Crocothemis servilia

14 Phasmidae Stick Insect Ctenomorpha chronus

15 Pyrrhocoridae Pyrrhocorid Bug Pyrrhocoridae sp.

16 Syrphidae Fly Asarkina sp.

17 Theridiidae House Spider Parasteatoda tepidariorum

18 Vespidae Wasp Vespula vulgaris

A large number of butterfly species forage specific host plant for nectar, shelter and to spawn,

while large numbers of species congregate on damp and moist places near streams for water

and salt. Some species are attracted in large numbers of rotting or over ripe fruits, animal

dung and birds‟ droppings. They inhabit open ground, sheltered and shaded areas, among

bushes and over the tree. The area is rich in the diversity and density of butterflies. A total of

45 species of butterflies belonging to 6 families were recorded (Table 7.30) from the

surroundings of proposed project area. Nymphalidae was the most represented family with 16

species followed by Lycaenidae with 13 species. Among the butterflies, Indian Cabbage White

(Pieris canidia indica) was most dominant at all sites while, others were observed only at two

or three sites of the study area.

Table 7.30: List of butterflies/insects recorded from the study area

S. No. Family Common name Scientific name

1 Hesperiidae Blank Swift Caltoris kumara

2

Common Grass Dart Taractrocera maevius

3 Lycaenidae Albocerulean Celastrina albocoeruleus

4

Angled Pierrot Caleta caleta decidia

5

Centaur Oakblue Arhopala centaurus

6

Common Cerulean Jamides celeno




S. No. Family Common name Scientific name

7

Common Hedge Blue Celastrina cardia

8

Dark Caerulean Jamides bochus

9

Dark Pierrot Tarucus ananda

10

Glistening cerulean Lampides kankena

11

Pale Hedge Blue Celastrina cardia

12

Peablue Lampides boeticus

13

Pointed Lineblue Nacaduba helicon

14

Purple Sapphire Heliophorus epicles indicus

15

Small Copper Lycaena phlaeas

16 Nymphalidae Black Prince Rohana parisatis

17

Chocolate Soldier Precis iphita iphita

18

Circe Hestina nama

19

Club Beak Libythea myrrha

20

Common Map Cyrestis thyodamas

21

Common Sailer Neptis hylas

22

Common Threering Ypthima asterope

23

Dark- glassy Tiger Parantica agleoides

24

Dwarf Crow Euploea tulliolus

25

Indian Fritillary Argynnis hyperbius

26

Large Three-Ring Ypthima newara

27

Large Yeoman Cirrochroa aoris

28

Lemon Pansy Precis lemonias

29

Orange Oakleaf Kallima inachus

30

Siren Hestina persimilis

31

Yellow Pansy Precis hierta

32 Papilionidae Common Bluebottle Graphium sarpedon

33

Fourbar swordtail Graphium agetes

34

Great Mormon Princeps memnon agenor

35

Paris Peacock Princeps paris

36

Redbreast Princeps alcmenor

37 Pieridae Indian Cabbage White Pieris canidia indica

38

Mottled Emigrant Catopsilia pyranthe

39

Painted Jazebel Delias hyparete

40

Plain Sulphur Dercas lycoris lycoris

41

Red-breast Jezebel Delias thysbe

42

Redspot Jazebel Delias descombesi

43

Spotted Sawtooth Prioneris thestylis

44

Yellow Orangetip Ixias pyrene

45 Riodinidae Punchinello Zemeros flegyas

Some of the species like Common threering (Ypthima asterope), Dark caerulean (Jamides

elips palissa), Dwarf crow (Euploea tulliolus), Indian fritillary (Argynnis hyperbius) and

Punchinello (Zemeros flegyas) were very common and found during all three seasons in the

study area. Sighting was very good during the pre-monsoon season survey however migration

and hibernation cause sharp decrease in population and diversity during winter season.




7.5.5 Threatened and Endangered Fauna

Only one of the mammals which were sighted in the study area fall under the category RET

fauna. Assam macaque (Macaca assamensis) is a Near Threatened species as per IUCN and

falls under Schedule II as per Wildlife (Protection) Act 1972 (see Table 7.24). One of the

main reasons that has cited for its decreasing populations is human-macaque interaction by

way of crop raiding. It is known to prefer crops like potato, wheat, maize, millets, etc. This

human interaction invariably leads to their killing as they cause loss of crops to the farmers.

The animals resort to crop raiding as their habitat has been shrinking by cutting of trees for

firewood, and forest clearing due to jhum cultivation.

According to list prepared from secondary data two species Prionalurus viverrinus (Fishing

cat) and Cuon alpinus (Wild dog) are listed under Endangered catergory in IUCN Redlist Ver

3.1 (see Table 7.25) while 5 species are under Vulnerable category namely, Panthera pardus

(Leopard), Cervus unicolor (Sambar), Ailurus fulgens (Red panda), Budorcas taxicolor (Mishmi

takin) and Ursus thibetanus (Asiatic black bear). Three species i.e. Goral (Naemorhedus

goral), Indian pangolin (Manis crassicaudata) and Large Indian civet (Viverra zibetha) are

under Near Threatened category.

According to WPA (1972) five species fall under Schedule-I viz. Panthera pardus (Leopard),

Prionalurus viverrinus (Fishing cat), Aliurus fulgens (Red panda), Budorcas taxicolor (Mishmi

takin) and Manis crassicaudata (Indian pangolin). Eight species fall under Schedule-II. Among

rest of the species 5 are under Schedule-III while 2 are under Schedule-IV.

Regarding the Fishing cat though according to secondary data it has been included in the list

however its habitat is wetland and lowlands in Himalayan foothills. Therefore its presence in

the study is highly unlikely. Nothwithstanding one of the reasons for its dwindling populations

is pollution of wetlands, forest clearance, excessive hunting and fishing. Similarly regarding

other RET species reported from the area like Mishmi takin, Wild dog, Leopard, Red panda and

Indian pangolin habitat degradation and fragmentation, prey loss, snaring, and conflict with

livestock are cited as some of the major causes for their decreasing populations.

Amongst birds except for Great Hornbill (Buceros bicornis) which is listed Near Threatened

category as per IUCN Redlist Ver 3.1, all the birds recorded from the study area belong to

Least Concern category (Table 7.26). As per the Wildlife (Protection) Act 1972 only two bird

species fall under Schedule I i.e. Great Hornbill and Crested Serpent Eagle (see Table 7.26).

Dibang Wildlife Sanctuary is situated at a distance of about 20 km from the project site.

7.6 WATER QUALITY

Three season study were carried out along the Dri & Talo (Tangon) Rivers and perennial nalas

for the evaluation of water and limnological parameters. Sampling locations for water

sampling have been shown in in Figure 7.11.

The details of methodology have already been discussed in Chapter 3 on Methodology.




7.6.1 Physico–chemical Characteristics

The physico-chemical nature of river water depends upon number of factors like the

hydrological and geological nature of the watershed, the soil and the type of vegetation it

supports and a variety of biological processes both within and outside river.

Water temperature is one of the important ecological factors which play an important role in

the distribution of organisms. The temperature of the river water fluctuated from 9C to 12C

in the winter, 10C to 15C in summer and 15C to 25C in monsoon season. Electrical

conductivity (EC) which is a measure of the ability of water to conduct an electric current and

it mainly depends on concentration of the ions dissolved in water ranged from 20 to 145

µS/cm. Turbidity of surface water tends to increase during runoff events as a result of

increased overland flow, stream flow and erosion. The turbidity levels were almost nil in

winter and summer seasons while in monsoon it was found in the range of 8 to 10 NTU,

however, it has been reported nil at few sites in monsoon (refer Table 7.26).

The pH of river water was observed to be neutral to slightly alkaline in nature and recorded

6.9 to 7.8. Dissolved oxygen in water depends on the temperature and concentration of

various ions. The dissolved oxygen of the river water is quite higher and measured from 9.1

to 11.8 mg/l. The water was soft in nature and total hardness was found between 8 to 48

mg/l in water samples collected from various sites. Nitrate and phosphate concentrations was

quite lower at all the sites and shown in the range of 0.021 – 1.41 and <0.004 – 0.05 mg/l

respectively. The details of physico-chemical characteristics of water are given in Tables 7.31

– 7.33.

7.6.2 Biological Characteristics

Rock surfaces, plant surfaces, leaf debris, logs, silt and sandy sediments and all other spaces

in the stream provide habitats for different organisms. According to these habitats, organisms

are divided into plankton, benthos, nektons and neuston. River water was rich in all biotic

components. The photomicrographs of some of the diatoms and other algae are given at

Plates 7.1 & 7.2. The descrition of various biological components is given in the following

paragraphs.

7.6.2.1 Periphyton

In all total, 58 species of periphyton were identified in the samples collected from proposed

hydroelectric project study area. The periphyton community comprised of 7 species of

Chlorophyceae, 15 species of Cyanophyceae and 36 species of Bacillariophyceae (Table

7.34). The total number of taxa recorded during different seasons varied from 31 in

monsoon and 49 in pre-monsoon 41 in winter season. Among Bacillariophyceae 23, 34 and 20

species were recorded during winter, pre-monsoon and mosoon surveys, respectively. Most

common species are Achnanthidium biasolettianum var. biasolettianum, Achnanthidium

minutissimum var. minutissimum, Cocconeis placentula var. euglypta, Cocconeis placentula

var. lineata, Cocconeis placentula var. placentula, Diatoma mesodon and Planothidium

lanceolata var. elliptica.




Figure 7.11 : Location of sites for water sampling




Table 7.31: Physico-Chemical Characteristics of Water at Different Sampling Sites in the Study Area : Winter (Lean)

Parameters Sampling Sites

Sampling Site W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11

Physical Parameters

Water Temperature (0C) 9.0 9.0 9.0 11.5 10.0 10.5 12.0 10.5 11.5 9.5 9.0

Electrical Conductivity

(µS/cm) 68.0 66.0 43.0 145.0 69.0 91.0 75.0 33.0 45.0 61.0 31.0

Turbidity (ntu) Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil

Chemical Parameters

pH 7.5 7.5 7.2 7.7 7.5 7.6 7.7 7.5 7.6 7.3 7.3

DO (mg/l) 11.3 11.2 11.1 10.9 11.3 11.5 10.9 11.8 11.0 12.2 11.1

TDS (ppm) 45.56 44.22 28.81 97.15 46.23 60.97 50.25 22.11 30.15 40.87 20.77

Ca hardness, mg/l 23.2 23.6 31.2 35.7 29.3 33.4 32.7 21.2 34.9 37.6 27.7

Mg hardness, mg/l 8.8 8.4 8.8 18.3 8.7 8.6 13.3 16.8 8.7 10.4 16.3

Total Hardness (mg/l) 32.00 32.00 40.00 54.00 38.00 42.00 46.00 38.00 43.60 48.00 44.00

Total Alkalinity (mg/l) 18.00 16.00 12.00 22.00 22.00 20.00 26.00 14.60 18.00 18.80 16.80

Chloride (mg/l) 15.33 14.02 13.63 16.47 11.36 15.90 14.77 16.47 15.33 17.04 16.45

Nitrate (mg/l) 0.156 0.157 0.055 0.147 0.025 0.025 0.063 0.042 0.054 0.023 0.024

Phosphate (mg/l) 0.050 0.050 0.010 0.010 0.010 0.050 0.010 0.010 0.020 0.020 0.020

Silica (as SiO2), mg/l 0.152 0.130 0.090 0.160 0.120 0.118 0.090 0.153 0.138 0.100 0.105

Salinity, mg/l <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

Total coliform (P/A) A A A A A A A A A A A

W1-W11 : Sampling sites




Table 7.32: Physico-Chemical Characteristics of Water at Different Sampling Sites in the Study Area (Pre-Monsoon : Summer)



Physical Parameters

Water Temperature (0C) 11.0 10.0 12.0 13.0 11.5 12.0 15.0 13.0 15.0 12.0 12.0

Electrical Conductivity

(µS/cm) 23.0 20.0 32.0 195.0 42.0 36.0 61.0 22.0 42.0 50.0 27.0

Turbidity (ntu) Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil

Chemical Parameters

pH 7.5 7.0 7.2 7.5 7.4 7.5 7.8 7.5 7.6 7.2 7.6

DO (mg/l) 11.2 10.9 11.0 9.8 10.2 10.1 9.8 10.1 9.9 11.1 9.9

TDS (ppm) 15.41 13.4 21.44 130.65 28.14 24.12 40.87 14.74 28.14 33.5 18.09

Ca hardness, mg/l 23.2 13.6 31.2 35.7 29.3 33.4 32.7 21.2 34.9 37.6 27.7

Mg hardness, mg/l 7.8 9.4 3.8 8.3 4.7 3.6 12.3 15.8 8.2 4.4 17.3

Total Hardness (mg/l) 31.00 23.00 35.00 44.00 34.00 37.00 45.00 37.00 43.10 42.00 45.00

Total Alkalinity (mg/l) 13.50 12.00 11.50 19.00 19.00 18.00 27.00 14.20 17.00 16.98 17.98

Chloride (mg/l) 12.12 11.12 12.55 14.44 10.32 13.20 14.89 16.32 15.10 16.93 16.88

Nitrate (mg/l) 0.145 0.134 0.048 0.144 0.019 0.022 0.062 0.041 0.045 0.021 0.025

Phosphate (mg/l) 0.008 0.007 0.009 0.008 0.007 0.045 0.009 0.011 0.021 0.019 0.022

Silica (as SiO2), mg/l 0.135 0.123 0.079 0.156 0.112 0.111 0.088 0.144 0.133 0.091 0.112

Salinity, mg/l <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001






Table 7.33: Physico-Chemical Characteristics of Water at Different Sampling Sites in the Study Area (Monsoon)



Physical Parameters

Water Temperature

(0C) 18.0 25.0 17.0 15.0 22.0 17.0 18.0 17.0 15.0 25.0 24.0

Electrical

Conductivity (µS/cm) 40.0 30.0 45.0 50.0 30.0 30.0 55.0 70.0 70.0 30.0 40.0

Turbidity (ntu) 10.0 10.0 0.0 0.0 8.0 8.0 0.0 0.0 0.0 8.0 10.0

Chemical Parameters

pH 7.1 7.0 7.2 7.2 7.0 7.0 6.9 7.1 7.0 7.0 7.1

DO (mg/l) 10.8 10.4 9.7 10.3 9.7 10.2 10.4 10.6 9.7 9.1 10.1

TDS (ppm) 26.8 20.1 30.15 33.5 20.1 20.1 36.85 46.9 46.9 20.1 26.8

Ca hardness, mg/l 17.2 13.6 21.2 27.7 15.3 23.4 29.7 21.2 34.9 7.6 2.7

Mg hardness, mg/l 6.8 8.4 6.8 8.3 4.7 6.6 6.3 17.8 6.1 4.4 5.3

Total Hardness

(mg/l) 24.00 22.00 28.00 36.00 20.00 30.00 36.00 39.00 41.00 12.00 8.00

Total Alkalinity

(mg/l) 23.60 20.62 26.62 34.06 19.04 14.28 34.18 38.78 39.98 14.28 9.52

Chloride (mg/l) 1.99 1.99 2.13 2.01 3.99 3.99 3.79 3.99 3.91 3.99 3.99

Nitrate (mg/l) 1.410 0.970 0.680 0.690 0.550 1.320 0.460 0.680 0.520 0.970 1.320

Phosphate (mg/l) <0.004 <0.004 <0.004 <0.004 <0.004 <0.004 <0.004 <0.004 <0.004 <0.004 <0.004

Silica (as SiO2), mg/l 3.630 3.560 5.120 5.670 1.970 2.180 4.610 4.320 5.040 2.600 2.490

Salinity, mg/l <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001






The Cyanophyceae family was represned by 15 species wih 14, 9 and 8 species recorded during

winter, pre-monsoon and mosoon surveys, respectively (Table 7.34).

The Chlorophyceae was represented by species like Cladophora sp., Oedogonium sp. and

Spirogyra sp. and 4, 6 and 3 species recorded during winter, pre-monsoon and mosoon

surveys, respectively (Table 7.34).

The density of periphyton ranged from 297 to 2833 in winter season, 458 to 755 in summer

season and 143 to 544 during monsoon (Table 7.35 & Figure 7.12). Species Diversity Index

ranged from 1.50-3.10 in winter season, 2.10-3.10 in summer season and 1.70-2.40 in

monsoon (Table 7.35 & Figure 7.13) while Eveness Index (E) for periphyton ranged from

0.30-0.50 in winter season, 0.40-0.52 in summer season and 0.40-0.50 in monsoon (Table

7.35 & Figure 7.14).

Table 7.34: List of periphyton found in Study Area

S. No. Name of species Winter Pre-monsoon Monsoon

Bacillariophyceae

1 Achnanthes crenulata + + +

2 Achnanthes exigua var. exigua + + +

3 Achnanthidium biasolettiana var. biasolettiana + + +

4 Achnanthidium minutissima var. minutissima + + +

5 Achnanthidium subhudsonis + - +

6 Ceratoneis arcus + + +

7 Ceratoneis arcus var. amphioxus + + +

8 Ceratoneis arcus var. recta + + -

9 Cocconeis placentula var. euglypta + + +

10 Cocconeis placentula var. lineata + + +

11 Cocconeis placentula var. placentula + + +

12 Cymbella excisa - + +

13 Cymbella leavis - + +

14 Cymbella parva - + -

15 Cymbella turgidula - + +

16 Cymbopleura sp. + + -

17 Diatoma mesodon + + +

18 Encyonema minutum + + -

19 Encyonema silisiacum - + -

20 Epithemia sorex - + -

21 Fragilaria capucina + + +

22 Fragilaria rumpens + + -

23 Gomphonema clevei + + +

24 Gomphonema olivaceum - + -

25 Navicula caterva + + +

26 Navicula cryptotenella - + -

27 Navicula radiosa + - +

28 Navicula radiosaffalax + + -

29 Navicula sp. + + -

30 Nitzschia linearis - + -

31 Planothidium lanceolata var. elliptica - + -

32 Reimeria sinuata + + +




S. No. Name of species Winter Pre-monsoon Monsoon

33 Rhoicosphenia abbreviata - + -

34 Surirella angusta + + +

35 Surirella linearis - + -

36 Tabellaria flocculosa - + -

Total (Bacillariophyceae) 23 34 20

Cyanophyceae

37 Amphorocapsa sp. + - +

38 Anabaena anomala + + +

39 Anabaena sp. + + +

40 Aphanocapsa sp. - + -

41 Gloeocapsa sp. + + -

42 Gloeocapsa punctata + - -

43 Gloeocapsa rupestis + - -

44 Lyngbya ambiguum + - +

45 Lyngbya sp. + + -

46 Oscillatoria curviceps + + +

47 Oscillatoria sp. + + +

48 Rivularia sp. + - +

49 Scytonema sp. + + +

50 Stigonema sp. + + -

51 Tolypothrix sp. + - -

Total (Cyanophyceae) 14 9 8

Chlorophyceae

52 Chaetophora sp. - + -

53 Characiosiphora vivularis + - +

54 Cladophora sp. + + -

55 Coleochaete sp. - + -

56 Oedogonium sp. + + +

57 Spirogyra sp. + + +

58 Zygnema sp. - + -

Total (Chlorophyceae) 4 6 3

Total species 41 49 31

-Present; - Absent

Table 7.35: Density, Species Diversity (H) and Evenness Index (E) of periphyton

Sampling Locations W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11

Density (cells/ mm2)

Winter (Lean)

466 297 2833 900 654 822 755 793 1022 700 1122

Summer (Pre-monsoon)

690 529 673 567 579 523 640 458 478 642 755

Monsoon 343 414 443 288 355 466 143 277 317 352 544

Species Diversity

Index

(H)

Winter (Lean)

1.50 1.50 1.90 1.80 3.10 1.80 2.40 2.00 1.80 2.40 2.50

Summer (Pre-

monsoon)

2.10 2.10 2.40 2.50 3.10 2.30 2.20 2.60 2.40 2.30 2.70

Monsoon 1.80 1.90 1.80 2.40 2.10 1.90 1.80 1.70 1.90 1.80 2.00

Evenness Index (E)

Winter (Lean)

0.30 0.30 0.30 0.30 0.50 0.30 0.40 0.40 0.30 0.40 0.50


0.40 0.40 0.50 0.49 0.50 0.40 0.40 0.52 0.47 0.40 0.50

Monsoon 0.40 0.40 0.50 0.40 0.50 0.40 0.40 0.40 0.40 0.50 0.40




Figure 7.12: Seasonal Variation in density of periphyton

Figure 7.13: Seasonal variation in Species Diversity Index (H) of periphyton

Figure 7.14: Seasonal Fluctuation in Evenness Index (E) of periphyton

7.6.2.2 Phytoplankton

In all total, 51 species of phytoplankton were identified in the samples collected from proposed

hydroelectric project study area. The phytoplankton community comprised of 5 species of

Chlorophyceae, 16 species of Cyanophyceae and 30 species of Bacillariophyceae (Table 7.36).

0

500

1000

1500

2000

2500

3000

W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11

Winter (Lean)

Summer(Pre-monsoon)Monsoon

De

nsi

ty (

cells

per

sq

mm

)

Sampling Locations

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11

Winter(Lean)

Summer(Pre-monsoon)Monsoon

Spe

cie

s D

ive

rsit

y In

de

x (H

)

Sampling Locations

0.00

0.10

0.20

0.30

0.40

0.50

0.60

W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11

Winter(Lean)

Summer(Pre-monsoon)

MonsoonEven

nes

s In

dex

(E)

Sampling Locations




The total number of taxa recorded during different seasons varied from 27 in monsoon and pre-

monsoon and 34 in winter season. Among Bacillariophyceae 18 in winter, and 16 species were

recorded during pre-monsoon and mosoon surveys. Most common species are Achnanthidium

biasolettianum var. biasolettianum, Achnanthidium minutissimum var. minutissimum,

Cocconeis placentula var. euglypta, Cocconeis placentula var. lineata, Cocconeis placentula var.

placentula, Diatoma mesodon and Planothidium lanceolata var. elliptica.

The Cyanophyceae family was represned by 12 species wih 12, 9 and 8 species recorded during

winter, pre-monsoon and mosoon surveys, respectively (Table 7.36).

The Chlorophyceae was represented by species like Cladophora sp., Oedogonium sp. and

Spirogyra sp. and 4, 4 and 3 species recorded during winter, pre-monsoon and mosoon

surveys, respectively (Table 7.36).

The density of phytoplankton ranged from 248 to 2179 in winter season, 327 to 627 in summer

season and 98 to 388 during monsoon (Table 7.37). Species Diversity Index ranged from 1.40

-2.50 in winter season, 1.80-2.50 in summer season and 1.60 -2.10 in monsoon (Table 7.37)

while Eveness Index (E) for phytoplankton ranged from 0.30-0.50 in winter season, 0.40-0.51

in summer season and 0.40-0.48 in monsoon (Table 7.37).

Table 7.36: List of phytoplankton species found in Study Area

S. No. Name of species Winter Pre-

monsoon Monsoon

Bacillariophyceae

1 Achnanthes crenulata + + +

2 Achnanthidium minutissima var. minutissima + + +

3 Achnanthidium subhudsonis + - +

4 Ceratoneis arcus + + +

5 Ceratoneis arcus var. amphioxus + + +

6 Cocconeis placentula var. placentula + + +

7 Cymbella excisa - + +

8 Cymbella leavis - + +

9 Cymbella parva - + -

10 Cymbella turgidula - + +

11 Cymbopleura sp. + + -

12 Diatoma mesodon + + +

13 Encyonema minutum + + -

14 Encyonema silisiacum - + -

15 Epithemia sorex - + -

16 Fragilaria capucina + + +

17 Fragilaria rumpens + + -

18 Gomphonema clevei + + +

19 Navicula caterva + + +

20 Navicula cryptotenella - + -

21 Navicula radiosa + - +

22 Navicula radiosaffalax + + -

23 Navicula sp. + + -

24 Nitzschia linearis - + -

25 Planothidium lanceolata v. elliptica - + -

26 Reimeria sinuata + + +

27 Rhoicosphenia abbreviata - + -

28 Surirella angusta + + +

29 Surirella linearis - + -




30 Tabellaria flocculosa - + -

Total Bacillariophyceae 18 16 16

Cyanophyceae

31 Amphorocapsa sp. + - +

32 Anabaena anomala + + +

33 Anabaena sp. + + +

36 Gloeocapsa punctata + - -

38 Gloeocapsa rupestis + - -

39 Lyngbya ambiguum + - +

40 Lyngbya sp. + + -

41 Oscillatoria curviceps + + +

41 Oscillatoria sp. + + +

42 Rivularia sp. + - +

43 Scytonema sp. + + +

46 Stigonema sp. + + -

Total Cyanophyceae 12 7 8

Chlorophyceae

47 Characiosiphora vivularis + - +

48 Cladophora sp. + + -

49 Oedogonium sp. + + +

50 Spirogyra sp. + + +

51 Zygnema sp. - + -

Total Chlorophyceae 4 4 3

Total Phytoplankton species 34 27 27

Table 7.37: Density, Species Diversity (H) and Evenness Index (E) of phytoplankton


Density

(cells/

mm2)

Winter

(Lean) 388 248 2179 692 503 514 472 417 568 411 590

Summer

(Pre-

monsoon)

627 481 561 471 362 327 457 412 318 428 539

Monsoon 264 318 385 206 237 321 98 213 226 271 388

Species

Diversity

Index

(H)

Winter

(Lean) 1.40 1.50 1.40 1.70 2.50 1.90 1.90 1.80 1.70 1.90 2.10

Summer

(Pre-

monsoon)

2.00 1.80 2.10 2.20 2.50 2.20 2.20 2.50 2.30 2.10 2.00

Monsoon 1.70 1.80 1.70 2.00 2.10 1.80 1.70 1.60 1.90 1.90 1.80

Evenness

Index (E)

Winter

(Lean) 0.30 0.30 0.30 0.30 0.50 0.30 0.40 0.40 0.30 0.40 0.50

Summer

(Pre-

monsoon)

0.40 0.42 0.53 0.48 0.51 0.40 0.40 0.51 0.45 0.40 0.50

Monsoon 0.40 0.40 0.48 0.40 0.47 0.40 0.40 0.40 0.40 0.48 0.41

7.6.2.3 Zooplankton

The zooplankton population is quite low in Dri and Talo (Tangon) rivers owing fast flows of

these rivers. Zooplankton were represented by 1 genus of Cladocera, 3 genera of Rotifera and

1 genus of Copepoda (see Table 7.38). The important species of zooplankton were Daphnia

(Cladocera), Trichocera, Keratella and Asplanchana (Rotifera) and Cyclops (Copepoda). Density

of zooplankton was in the range of 3 – 6 individuals per litre. The Shannon-Weiner diversity

index ranged between 1.960 and 2.271 at all the sites (Table 7.38).




Table 7.38: Zooplankton density and Shannon-Weiner Diversity index in study area

Zooplankton


Density

(indiv./l )

Diversity

index

Density

(indiv./l )

Diversity

index

Density

(indiv./l )

Diversity

index

Cladocera

Daphnia sp. 6 0.511 5 0.488 5 0.319

Rotifera

Trichocera sp. 6 0.488 5 0.415 5 0.410

Keratella sp. 8 0.441 6 0.415 3 0.40

Asplanchana sp. 6 0.391 4 0.390 3 0.391

Copepoda

Cyclops sp. 5 0.440 5 0.421 5 0.440

Total 31 2.271 25 2.129 21 1.960

7.6.2.4 Macro-Invertebrates

The macro-invertebrate community contributes immensely to the functioning of the stream or

river ecosystem. It serves not only as a major source of food for fishes but also helps in

processing relatively large amounts of organic matter. The abundance of invertebrate fauna

mainly depends on physical and chemical properties of the substratum. Because of their

extended residency period in specific habitats and presence or absence of particular benthic

species in a particular environment, these can be used as bio-indicators of specific environment

and habitat conditions. The monitoring of macro-invertebrates populations provides an

important tool to assess the short and long term effects of a wide range of environmental

disturbances.

The macro-invertebrate fauna of the study area comprised of six Orders viz. Ephemeroptera,

Trichoptera, Diptera, Coleoptera, Plecoptera, and Odonata during the survey. The density of

macro-invertebrate were observed to be less during monsoon season as compared to summer

and winter which may be due to turbulent flow and deposition of silt on substratum habitat of

these fauna (Figure 7.15 and Tables 7.39).

The percentage composition of macro-invertebrate fauna during different seasins is given in

Tables 7.37 – 7.39.

Figure 7.15: Macro-invertebrates density (individuals/m2)

0 100 200 300 400 500 600

W1

W2

W3

W4

W5

W6

W7

W8

W9

W10

W11

Winter (Lean)


Monsoon

Sam

pli

ng

Site

s

Density (individuals/ sq m)




Table 7.39: Macro-invertebrates density (individuals/m2) in study area

Density (individuals/m2 )

Sites Winter Summer Monsoon

W1 99 33 29

W2 66 88 44

W3 110 88 143

W4 220 583 154

W5 165 253 55

W6 154 396 66

W7 77 264 143

W8 110 132 77

W9 187 440 77

W10 451 77 55

W11 444 99 44

7.6.2.5 Water Quality Assessment

The Macro-invertebrates are one of the indicators of water quality of freshwater streams. The

water quality assessment of Dri and Talo (Tangon) rivers was assessed by calculating BMWP,

ASPT and LQI values which are an indicative of river water qualiy. The methodology to calculate

these indicies has been given in Chaper 3-Methodology of the report.

The evaluation of the performance of the BMWP score in relation to a range of water quality

variables has described by Armitage et al. (1983). BMWP score calculated varied from as low as

4 & 6 a sites to highest at site W11 (Downstream of Dri and angon confluence) 88 during

winter sampling (see Tables 7.40-7.42 & Figure 7.16). However in general the average

BMWP scores during winters were very good (44) and good during pre-monsoon (27) and as

expected were lowest (20) during monsoon when the river flow is very high.

The average sensitivity of the families of the organisms present is known as the Average

Score per Taxon (ASPT). The ASP) index gives an indication of the evenness of community

diversity. ASPT is calculated by dividing the BMWP score for each site by the total number of

scoring families found there, so it is independent of sample size. Likewise BMWP scores, a

higher ASPT indicate better water quality. The ASPT score varied from 3 to 8.8 (Figure 7.17).

The average ASPT scores during differen seasons followed the patern of BMWP scores.

The Lincoln Quality Index (LQI) is biotic indices established to determine pollution effects in

river particularly from organic pollutants based on aquatic macro-invertebrate populations and

is expressed as A for excellent water quality, B for Good, C for Moderate, D as Poor and E as

very poor water quality.

The Lincoln Quality Index (LQI) is biotic indices established to determine pollution effects in

river particularly from organic pollutants based on aquatic macro-invertebrate populations and

is expressed as A for excellent water quality, B for Good, C for Moderate, D as Poor and E as

very poor water quality. As per the LQI the water quality of Dibang & Talo (Tangon) river is of

good quality as it is under Class A & B. No serious stress was observed in this river. Among the

biological characteristics, majority of the taxa were pollution intolerant. During the construction

phase of the hydro project, sedimentation load increase in the river which may affect the total




density, taxonomic richness and total biomass of the benthic diatoms and macro-invertebrates

which are important components of the food chain of aquatic ecosystem.

Figure 7.16: BMWP scores a different sites in different seasons

Figure 7.17: ASPT scores a different sites in different seasons

0

10

20

30

40

50

60

70

80

90

100

W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11Sampling Sites

Winter Pre-monsoon Monsoon

5

7

9

11

13

15

17

19

21

23

25

W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11Sampling Sites

Monsoon Pre-monsoon Winter




Table 7.40 : Percent composition of macro-invertebrates at different sampling locations (Winter Season)

Sampling

Locations W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11 W9 W10 W11

Ephemeroptera

Heptageniidae 44.44 33.33

5.00 20.00 14.29 14.29 10.00 35.29 7.32 10.00 14.29

50

Baetidae 22.22

30.00 5.00 20.00 42.86 14.29 10.00

48.78 35.00

40 50

Caenidae

50.00 10.00 5.00

9.76 6.67

Ephemerellidae

Trichoptera

Brachycentridae 11.11

5.00

14.29 30.00 35.29

8.33

Sericostomatidae

30.00 10.00

7.32 5.00

Rhyacophilidae

6.67

3.33

Hydropsychidae 11.11

5.00

7.14

23.53

Psychomyiidae

28.57

Hydroptilidae

13.33

Leptoceridae

20.00 35.00

10.00

1.67 28.57

Diptera

Chironomidae

33.33 21.43

21.95 15.00

60

Simuliidae

Coleoptera

Elmidae

10.00 15.00 6.67

5.88

Plecoptera

Chloroperlidae

16.67

15.00

28.57 40.00

10.00

Perlidae 11.11

28.57

4.88 3.33 28.57

Nemouridae

Perlodidae

Leuctridae

Odonata

Aeshnidae

7.14

1.67

Libellulidae

7.14

Total 100 100 100 100 100 100 100 100 100 100 100 100 100 100

BMWP 29 27 36 71 34 37 44 44 30 43 88 30 6 14

ASPT 5.8 9 7.2 7.9 5.7 6.2 9 8.8 7.5 7.2 8 7.5 3 7

LQI A B B B A B B B B B B B A B




Table 7.41 : Percent composition of macro-invertebrates at different sampling locations (Pre-Monsoon)


Ephemeroptera

Heptageniidae

3.77 8.70

16.67 27.50

22.22

Baetidae 66.67 75 50 41.51 82.61 94.44 20.83 8.33 67.50 71.43 66.67

Caenidae

Ephemerellidae

4.17

Trichoptera

Brachycentridae 33.33 12.5

4.35

4.17 8.33

Sericostomatidae

Rhyacophilidae

Hydropsychidae

12.5 1.89

8.33

Psychomyiidae

5.66

25.00 8.33

Hydroptilidae

Leptoceridae

37.5 39.62

33.33

2.5

Diptera

Chironomidae

12.5

Simuliidae

5.66

8.33

Coleoptera

Elmidae

Plecoptera

Chloroperlidae

5.56

41.67 2.5

Perlidae

4.35

28.57

Nemouridae

1.89

Perlodidae

12.5

Leuctridae

11.11

Odonata

Aeshnidae

Libellulidae

Total 100 100 100 100 100 100 100 100 100 100 100

BMWP 14 16 19 41 34 14 44 44 34 14 24

ASPT 7 5.3 6.3 5.9 8.5 7 7.3 6.3 8.5 7 8

LQI B A B A B B B B B B B




Table 7.42 : Percent composition of macro-invertebrates at different sampling locations (Monsoon)

Sampling

Locations W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11

Ephemeroptera

Heptageniidae

7.14

28.57 14.29

50

Baetidae 66.67 75 23.08 35.71 100 66.67 30.77

40 50

Caenidae

Ephemerellidae

Trichoptera

Brachycentridae

25 7.69

15.38 28.57

Sericostomatidae

Rhyacophilidae

Hydropsychidae 33.33

23.08 21.43

7.69 42.86

Psychomyiidae

14.29

28.57

Hydroptilidae

Leptoceridae

28.57

Diptera

Chironomidae

23.08

16.67 30.77

60

Simuliidae

15.38 14.29

Coleoptera

Elmidae

Plecoptera

Chloroperlidae

16.67 15.38

Perlidae

7.69 7.14

28.57

Nemouridae

Perlodidae

Leuctridae

Odonata

Aeshnidae

Libellulidae

Total 100 100 100 100 100 100 100 100 100 100 100

BMWP 9 14 36 34 4 16 31 25 30 6 14

ASPT 4.5 7 6 5.7 4 5.3 6.2 8.3 7.5 3 7

LQI A B B B A A B B B A B




7.7 FISH AND FISHERIES

The State of Arunachal Pradesh is rich in fresh water resources in the form of rivulets and lentic

water bodies that is reflected by the presence of rich fish diversity. Around 143 species

belonging to 61 genera, 21 families and 8 orders have been reported by various authors

(Jayram, 1963, Jayram, and Mazumdar, 1964; Srivastava, 1966; Sen, 2006, Nath and Dey

2000) in Arunachal Pradesh during their study.

There is no fish farming community in terms of caste or creed exists in the study area of Etalin

HE Project. For farmers forming the bulk of the population the fish farming is a secondary

employment. Almost the entire population of the state including the area of the project is fish

eater. Incidentally, the local people are dependent on the natural resources for fish protein and

resort to various illegal and spurious fishing methods (different types of traps, gears, fish

poison, blasting, etc.). There is no proper record of fish landings at all from the area. There is

no fish farming community in in the area. The agricultural farming is the main occupation in the

area and only few have taken to fish farming as a secondary employment.

However, some people from the area use cast net or fishing lines, fishing trap, blasting and

electric shock methods for fish capture in the Talo (Tangon) River. As per the discussion with

people, some fishes do migrate upstream during the rainy season of the year. These fishes

were easily captured by the people during the migration and used for self consumption.

To assess fish diversity of the Dri and Talo (Tangon) rivers, experimental fishing was conducted

during the field surveys. The fishing gears like cast and gill net were used at different locations

in Dri and Talo (Tangon) rivers. The fish fauna was caught and identified with the help of keys

given in Day (1878), Jayaram (1981), Menon (1987) and Talwar and Jhingran (1997). During

the experimental fishing, the average daily catch in the study area was maximum during winter

period which around about 1.5 kg/day/fishermen and was lowest during monsoon 0.4-0.8 kg at

different locations while during pre-monsoon sampling it was 0.6 to 1.2 kg/day/fishermen.

Fishes diversity of Dri and Talo (Tangon) Rivers comprises of 12 species belonging to 4 families

with Cyprinidae forming the largest family represented by 8 species (Table 7.43). Though

none of the mahseer species (Tor tor and T. putitora) could be found during experimental

fishing but their occurrence cannot be ruled out as according to local people they have caught

these species in the past. Schizothorax richardsonii and Labeo pangusia of Cyprinidae family fall

under the Near Threatened and Vulnerable category, respectively while all other fish species

falls under the category of Least Concern.

Table 7.43: Fish composition and their status in the Dri and Talo (Tangon) Rivers

S.No. Family/ Scientific Name Local Name River Conservation

Status as per

IUCN Ver 3.1

Cyprinidae

1 Barilius bendelisis Rabiotapia Dri/Talo (Tangon) LC

2 Crossocheilus latius latius Nagoyou Dri/Talo (Tangon) LC

3 Danio dangila Lauputi Dri/Talo (Tangon) LC

4 Garra annandalei Nagop Dri/Talo (Tangon) LC

5 Garra gotyla gotyla Nagoyoutotum Dri/Talo (Tangon) LC




6 Labeo pangusia Ghoria Dri/Talo (Tangon) NT

7 Schizothorax richardsonii Kadang Dri/Talo (Tangon) VU

8 Schizothorax progastus Dri/Talo (Tangon) LC

Balitoridae

9 Acanthocobitis botia Reibo Dri/Talo (Tangon) LC

Olyridae

10 Olyra longicaudata Himalayan loyra Dri/Talo (Tangon) LC

11 Xenentodon cancila Chowki Talo (Tangon) LC

Sisoridae

12 Glyptothorax pectinopterus Dri/Talo (Tangon) LC

Note: VU – Vulnerable; NT- Near Threatened; LC - Least Concern

Fish however plays a major role in the cultural practices of the Idu Mishmis. As per discussion

with the tribal people, a fish folk festival „Aayuha‟ celebrated in the rainy season when fishes

migrate from rivers to perennial nalas and other small tributaries for spawning and breeding

purposes. The people catch the fish from the river and celebrate with their relative and friends.

Plate 7.1: Blue green algae recorded from Dri and Talo(Tangon) rivers




Plate 7.2: Diatoms recorded from Dri and Talo (Tangon) rivers

1-2 : Achnanthes cranulata

3 Cocconeis placentula var. euglypta

4-5 Ceratoneis arcus var. amphioxus

6 Navicula radiosaffalax

7 Gomphonema clevei

8-9 Reimeria sinuata

10 Encyonema minutum

11 Cocconeis placentula var. placentula

12-13 Diatoma mesodon

14-15 Achnanthidium minutissima var. minutissima

16-17 Achnanthidium biasolettiana var. biasolettiana




8.1 GENERAL

Assessment of environmental impacts of any development activity is the key component of EIA

process. Environmental impacts are assessed based on understanding of the project

features/activities, environmental setting in the area and interaction of project activities with

environmental components leading to prediction of likely impacts due to development of project

in a particular area/region. Hydropower projects are location specific, leading to large-scale

construction activities in generally pristine areas. Therefore, impact assessment is carried out by

establishing site-specific environmental settings through baseline data collection and defining

project components from detailed project information. Baseline environmental status in the

project area is established through field studies in different seasons and also obtained from

various secondary sources as discussed in previous chapters. Project related information is

sourced from Detailed Project Report (DPR) of the project to carry out the impact assessment for

project construction and operation phase.

The proposed Etalin HEP would lead to generation of a number of environmental impacts owing

to the activities that would be undertaken during the construction of various project

appurtenances, e.g. drilling and blasting, quarrying for construction material, dumping of muck

generated from various project activities, transportation of material, material handling and

storage, waste generation from labour colonies, operation of construction machinery/equipment,

etc. Additionally, large-scale labour migration to the area, during the construction period,

impacts the local inhabitants. Operation phase of the hydroelectric project is much cleaner as far

as pollution generation is concerned; however a significant impact during operation phase is

permanent change in flow regime of the river impacting aquatic life, fish fauna and downstream

users.

All the likely impacts have been considered for various aspects of environment, including

physico-chemical, ecological and socio-economic aspects. Invariably there are two types of

impacts that occur due to construction and operation of hydroelectric projects viz. permanent

which generally lead to loss of plant species, change of land-use, change in flow regime, etc. and

temporary which can be minimized and mitigated by adopting environmental management plan.

Environmental protection measures can be best enforced through inclusion of relevant clauses in

the contract not only for the main contractors but also for sub-contractors as most of activities

are undertaken through various contractors.

Based on the project details and the baseline environmental status, potential impacts as a result

of the construction and operation of the proposed Etalin HE Project have been identified.

Wherever possible, the impacts have been quantified and otherwise, qualitative assessment has

been undertaken. This Chapter deals with the anticipated positive as well as negative impacts

during the construction as well as operation phase of the proposed Etalin HE project.

Chapter ASSESSMENT OF IMPACTS

8




8.2 IMPACTS DURING CONSTRUCTION

Majority of the environmental impacts attributed to construction works are temporary in nature,

lasting mainly during the construction phase and often do not extend much beyond the

construction period. However, as the construction phase of Hydroelectric Projects is fairly large

and extend into several years, if these issues are not properly addressed, the impacts can

continue even after the construction phase for longer duration. Even though the impacts due to

construction are temporary in nature, they need to be reviewed closely as they could be

significant due to the nature and intensity of the impacts.

Impacts can be discussed in terms of projects activities with their magnitude and potential

impacts on environmental resources or alternatively resource wise in terms of impact on each

environmental resource e.g. Ambient Air Quality and potential impact on this resource from

various project activities. However, as some of the project activities are quite critical and it is

important to understand them along with their impacts on environmental resources, therefore,

they are briefly discussed below to be followed by impacts on resources.

8.2.1 Impacts due to immigration of Construction Workers

At the time of peak construction work in the project, it is estimated to engage 3000 persons as

labour force and 800 as technical staff. Efforts will be made to engage local labour force, as far

as possible and rest will be brought from outside. Even the local population is expected to stay

near the construction sites in the construction camps/colonies. It is estimated that in the first

and second year 60% of the peak force will be required and in the third year 80% of the peak

force will be required, however, to assess the impact of migratory work force it is assumed that

entire labour force and technical staff will stay in the construction colony during the entire

duration of the project.

To calculate the human pressure during the construction phase of the project, the following

assumptions have been considered.

i. Family size is assumed as 5 membered; and 80% of labour and technical staff are

married

ii. Out of total workforce, 80% will be such that both husband and wife will work

iii. 50% of technical staff will come with their families and only husband will work

iv. 2% of total migrating population are assumed as service providers, and

v. 50% of service providers will have families.

Based on these assumptions the peak migrant population has been calculated as 10600 persons

(Table 8.1). This population is expected to reside in the project area at any given time.

Table 8.1: Calculation of Total Migratory Population

A. Migrant Population of Laborers

Total labour force 3000

Married laborers (80% of 3000) 2400

Single laborers (20% of 3000) 600

Husband and wife both working Labour (80% of 2400) 1920

Number of families where both husband and wife work (1920/2) 960




Number of families where only husband work (20% of 2400) 480

Total number of laborers families (960 + 480) 1440

Total Migrant Population of Laborers (1440 x 5 + 600) 7800

B. Migrant Population of Technical Staff

Total technical staff 800

Married technical staff 640

Single technical staff 160

Total migrant population of technical staff (320 x 5 + 320 + 160)

2080

Migrant Workforce (Labor plus Technical) 9880

C. Service Providers

Total service providers (2% of total migrant workforce) 198

Married service providers (50 % as assumed) 99

Single service providers 99

Total migrant population of service providers (99 x 5 + 99) 594

Total Migrant Population 10474

say 10600

Separate accommodation and related facilities for workers, service providers and technical staff

are to be arranged. Migration of 10600 persons during the peak construction period, in otherwise

scarcely populated and pristine area, is likely to create problems of sewage disposal, solid waste

management, tree cutting to meet fuel requirement, etc.

Impact of such activities on land environment arises due to indiscriminate disposal of waste,

littering, dumping of medical waste from dispensary/medical facilities, etc. In addition on

completion of construction work, these colonies needs to be dismantled and land reclaimed as

discussed in Environmental Management Plan.

8.2.2 Construction of Main Project Components

Etalin HEP (6 X 307 MW at Dri Limb + 4 X 307 MW at Talo (Tangon) Limb + 19.6 MW + 7.4 MW)

is a run-of-the-river project that will be using the waters of Dri and Talo (Tangon) rivers in

Dibang Valley district of Arunachal Pradesh. Dri and Talo (Tangon) rivers meet near Etalin

village; downstream of the confluence the river is named Dibang. The project is proposed to be

developed as a run-of-the-river scheme by constructing concrete gravity dams on Talo (Tangon)

and Dri rivers and diverting the water through two (2) separate waterway systems to utilize the

available head in a common underground powerhouse located just upstream of the confluence of

Dri and Tangon rivers.

A 101.5m high concrete gravity dam is proposed at this location to divert water of Dri river into

the water conductor system. The top level of the dam is at El 1047m. The total length of the dam

at top is 213.7m, with fourteen (14) concrete gravity blocks. The riverbed level at the dam site is

around El 968m.

The Full Reservoir Level (FRL) and Minimum Draw Down Level (MDDL) of the reservoir are El.

1045m and El 1039m, respectively. The total area of submergence is 83.32 ha.




The proposed Talo (Tangon) dam is a 80m high concrete gravity structure with top level at El

1052m. The total length of the dam at top is 184.1m, with twelve (12) concrete gravity blocks.

The riverbed level at the dam site is around El 1003m.

The Full Reservoir Level (FRL) and Minimum Draw Down Level (MDDL) of the reservoir are El

1050m and El 1040m, respectively. The total area of submergence is 36.12 ha.

8.2.3 Quarrying Operations

The total requirement of coarse and fine aggregates has been estimated as 32.82 Lakh m3 and

18.92 Lakh m3 respectively, to fulfill the requirement of construction material. Most of the

requirement of coarse aggregate will be met from the rock excavated from tunnels and

underground works and the remaining will be quarried from identified quarries. About 10.75 Lakh

m3 has been anticipated from 2 Nos. of identified Rock Quarries (RQ) (Table 8.2). Similarly the

requirements of fine aggregates will be met from the 4Nos. of identified Shoal & Sand quarries

(PQ). About 9.43 Lakh m3 is anticipated from the various identified quarries for fine aggregates

and the rest will obtained by crushing the potential muck generated from underground

excavation.

Table 8.2: Details of the quarry sites proposed in the Etalin H.E. Project

Quarry Sites Location of Quarry Sites Area needing

restoration (ha)

I. Rock Quarries

RQ1 Right & left bank of Akobe nala 3.12

RQ2 Left & right bank of Ayo Pani nala 10.12

Total rock quarries 13.24

II. Shoal & Sand

Quarries

PQ1 Right bank of Talo (Tangon) river

near Etalin village

6.07

PQ2 Right bank of Talo (Tangon) river

near

15.19

PQ3 Left bank of Talo (Tangon) river near 20.85

PQ4 Upstream of Dri dam 6.77

Total 48.88

Total Quarry Area

I+II

62.12

Opening of the quarries will cause visual impacts because they remove a significant part of the

hills. Other impacts will be the noise generated during aggregate acquisition through explosive and

crushing, which could affect wildlife in the area, air pollution is caused during the crushing

operation to get the aggregates to the appropriate size and transport of the aggregates to the site.

The quarrying operations will be semi-mechanized in nature. Normally, in a hilly terrain,

quarrying is done by cutting the hill face and this leaves a permanent scar, once the quarrying

activities are over with the passage of time, rock from the exposed face of the quarry under the

action of wind and other erosion forces, slowly gets weathered and they become a potential

source of landslide. Thus, it is necessary to implement appropriate slope stabilization measures

to prevent the possibility of soil erosion and landslides at the quarry sites.




8.2.4 Operation of Construction Plant and Equipment

During the construction phase, various types of equipment will be brought to the site and

construction plants and repair workshops will be set up. These include crushers, batching plant,

drillers, earth movers, rock bolters, etc. List of construction equipment to be deployed major

project component wise is given at Table 8.3. The siting of these construction equipments would

require significant amount of space. In addition, land will also be temporarily acquired, i.e. for

the duration of project construction; for storage of the quarried material before crushing, crushed

material, cement, steel, etc.

These construction plant and repair workshops will have impact on ambient air quality due to

fugitive emissions associated with operation of DG sets to meet the power requirements and

other equipment; impact on water quality due to wastewater generation and impact on soil due

to solid waste generation. Management of such impacts with operation control and appropriate

pollution control equipment is essential to minimize their effect on surrounding environment

including local population and wildlife and same is discussed in EMP. Additionally, proper siting of

these facilities can also reduce the impact due to their location. Their locations have been

identified during the preparation of Detailed Project Report, keeping in view the technical and

economic criteria; however, same can be further refined during set up, keeping in view:

Proximity to the site of use

Sensitivity of forests in the nearby areas

Wildlife, if any, in the nearby area

Proximity from habitations

Predominant wind direction

Natural slope and drainage

Table 8.3: List of Construction Equipment

Equipment required for open excavation

Description of Equipment Dri Limb Talo (Tangon)

Limb

Quantity Nos.

3.0 cum Excavator 6 4

25 T Dumpers 24 20

Dozers 90 HP 6 4

Jack Hammers 120 cfm 26 20

Compressors 500 cfm 17 13

Wagon drill 400 cfm 12 9

Equipment required for Construction of Diversion Tunnel per face

Description of Equipment Dri Limb Talo

(Tangon) Limb

Quantity Units

3.0 cum Excavator 1 1 Nos.

2-Boom Drill Jumbo 1 1 Nos.

Front End Loader 2.3 cum 1 1 Nos.

Wagon Drill 400 cfm 4 4 Nos.

Compressor 500 cfm / 1000 cfm 6 / -- 2 / 2 Nos.

25T capacity dumpers 5 5 Nos.

Jack Hammer (120 cfm capacity) 8 10 Nos.

Dozers 90 HP 1 2 Nos.

Gantry shutters 1 1 Set




Concrete pump 40cum/ hr 1 1 Nos.

Hydraulic Platform/Truck Jumbo 1 1 Nos.

Concrete Placer 1cum 1 1 Nos.

Transit Mixers (6 cum capacity) 4 5 Nos.

Needle Vibrators (65 mm dia. Needle) lot lot

Grout Pump 1 1 Nos.

Shotcrete Machine 1 1 Nos.

Welding sets 2 1 Set

Rib Bending Machine 1 1 Set

Blasting Accessories lot lot

Dewatering pumps of different capacity 1 1 Sets

JBC backhoe loader (for excavating the trench for laying gantry track)

1 1 Nos.

Ventilation Blower (110 kW) (One set in front of

each face) 1 1 Sets

Equipment required for cofferdam construction

Description of Equipment Dri Dam

Talo (Tangon)

Dam

1. Excavator 1.57 cum cap. 1 no 1 no.

2. Dumpers 25 MT cap. 4 nos 4 nos.

3. Concrete pump 40 cum /hr capacity 4 no, 4 nos.

4. Concrete mixers 6 cum 6 nos. 8 nos.

5. Drilling machines for curtain grouting 4 nos 4 nos.

6. Grout pumps 4 nos. 4 nos.

7. Hydra crane 8MT to handle concrete blocks 1 no. 1 no.

8. Tractor Trollies 2 nos. 2 nos.

9. Steel shutters, vibrators, welding sets, etc. Lot. Lot.

10. Diesel compressors 300 cfm 2 nos. 2 nos.

11. D.G. Set 500 KVA 1 no. 1 no.

12. Jet Grouting Set 2 no. 2 no.

Equipment Required for Intake works

Description of Equipment Dri Dam

Talo (Tangon)

Dam

1. Hyd. Excavators (1.57 cum) 1 nos. 2 nos.

2. Dumpers (25T) 5 nos. 8 nos.

3. Dozers (90 HP) 1 nos. 1 nos.

4. Wagon drills 2 no. 2 no.

5. Rough Terrain Crane (40T) 1 no. 1 no.

6. Concrete pumps (25 cum /hr) 1 nos. 3 nos.

7. Transit Mixers (6 cum) 10 nos. 15 nos.

8. Steel Formwork and Vibrators Lot Lot

9. Dewatering Pumps (40 kW) 3 nos. 3 nos.

Equipment required for Construction of Headrace Tunnel (Dri limb)

Description of Equipment Dri Limb Talo (Tangon)

Limb

Quantity Quantity

Two-boom drill jumbo 1 No. 1 No.

Front end loader 2.3 cum 1 No. 1 No.

Wagon drill 4 No. 4 Nos.

Compressor 500 cfm 2 No. 2 Nos.

Compressor 1000 cfm 1 No. 2 No.

25T capacity dumpers 8 No. 8 Nos.

Jackhammer (120 cfm capacity) 10 Nos. 10 Nos.

90 HP dozer (One dozer against two loaders has been

provided at muck disposal site for spreading the muck) 1 No. 1 No.




Gantry shutters 1 Set 1 Set

Concrete pump 40cum/ hr 1 No. 1 No.

Hydraulic platform/Truck jumbo 1 No. 1 No.

Concrete placer 1 Nos. 1 No.

Transit mixers (6 cum capacity) 4 Nos. 4 Nos.

Needle vibrators (65 mm dia. Needle) Lot Lot

Grout pump 1 No. 1 No.

Shotcrete machine 1 No. 1 No.

Welding sets 1 set 1 Set

Blasting accessories Lot Lot

Ventilation blower (One set in front of each adit) 1 set 1 Set

Rib bending machine 1 set 1 Set

Dewatering pumps of different capacities 1 1 1 Set

Wheel loader 5 Nos. -- --

Equipment required for Open Excavation in Surge Shaft (Dri & Talo (Tangon) limbs)

Description of Equipment Quantity Unit

Excavator 1.57 cum 1 Nos.

Jackhammers 120 cfm 5 Nos.

Dumpers 15 T 6 Nos.

Compressors 500 cfm 2 Nos.

Dozers 1 Nos.

Equipment required for Construction of Surge Shaft (Dri limb)

Description of Equipment Dri Limb Talo (Tangon) Limb

Quantity Units Quantity Units

Alimak Raise Climber 1 no 1 No.

Hydraulic excavator (2 cum) 1 no 1 No.

25T capacity dumpers 7 nos 7 Nos.

Jackhammer (120 cfm capacity) 15 nos 15 Nos.

Wagon drill 4 nos 2 Nos.

Compressor 500 cfm 7 nos 6 Nos.

Dozers 90 HP 1 no 1 No.

Concrete pump 40cum/ hr 2 no 1 No.

Transit mixers (6 cum capacity) 4 nos 4 Nos.

Needle vibrators (65 mm diameter needle)

4 nos 4 Nos.

Grout pump 1 no 1 No.

Shotcrete machine 1 no 1 No.

Blasting accessories 1 set 1 set

Winch (10T Capacity) 1 no 1 No.

Mobile crane (8/10T capacity) 1 no 1 No.

Gantry crane (30T capacity) 1 no 1 No.

Dewatering pumps of different

capacities 1 Set 1 Set

Loader 2.3 cum 1 no 1 no

Equipment required for Open Excavation in Surge Shaft (Talo (Tangon) limb)

Description of Equipments Quantity Unit

Excavator 1.57 cum 1 Nos.

Dumpers 25 T 6 Nos.

Dozers 1 Nos.

Total equipment required for Pressure Shaft (Dri limb)

Description of Equipment Quantity Unit

Two-boom hydraulic drill jumbo (as available) for horizontal excavation pressure shaft

6 Nos.

Alimak raise climber with stopper drills for excavation of vertical pressure shafts

4 Nos.




Wheel loader of 2.3cum capacity 6 Nos.

Jackhammers (120 cfm) 16 Nos.

Compressors 500 cfm 4 Nos

25T dumpers 12 Nos.

Crawler dozer (90HP) 6 No.

Shotcrete machine 6 Nos.

6 cum transit mixers 8 Nos.

40cum/hour capacity concrete pump 4 Nos.

Concrete placer 4 Nos.

Dewatering pumps of sort 6 Sets

Mobile crane (40T capacity) 4 Nos.

Welding sets 4 Sets.

Flexi shaft needle vibrators 10 Nos.

Winch (10T capacity) 4 Nos.

Winch (30T capacity) 4 Nos.

Rib bending machine 2 Set

Penstock fabrication yard 2

Testing equipment (Ultrasound, radiography, X ray) 4 Sets

Blasting accessories 6 Sets

Hydraulic platform/Truck jumbo 4 Nos.

Grout pump 6 Nos.

Sand blasting equipment 2 Sets.

Powerhouse

The equipment required for excavation of Stage I would be:

1. Two boom drilling Jumbo 2 No.

2. Rock Bolter 2 No.

3. Hyd. Excavator (1.84 cum) for benching 2 No.

4. Dumpers 25 T capacity 10 Nos.

5. Robojet Shotcrete Machine 2 No.

6. Transit mixers 6 cum 6 Nos.

7. Wagon Drills 6 Nos.

8. Compressors 1000 + 450 cfm 2 each

9. DG sets (1000 kVA) 2 No.

10. Scissor Platform 1 No .

The equipment required for excavation of Stage II would be:

1. Wagon drills (for benching) 2 nos.

2. Two boom drill jumbo 2 nos.

3. Hyd. excavator 1.84 cum 2 no.

4. Dumper 25 MT 10 nos.

5. Robojet Shotcrete machine 1 no.

6. Shotcrete machine manual 1 no.

7. Transit Mixers 5 nos.

9. Compressors and DG sets same as above

Equipment Required for Excavation of Transformer Hall from Each Side

Two boom drill jumbo for pilot tunnel 1 no.

Shotcreting Robojet 1 no.

Transit Mixers 6 cum 3 nos.

Hand-held rock drills 6 nos.

Hyd. Excavator 1.84 cum 1 no.

Dumpers 25 T 9 nos.

Bulldozer 90 HP 1 no.

Compressors 600 cfm 2 nos.

DG sets 1000 kVA 1 no.




8.2.5 Muck Disposal

The project would generate substantial quantity of muck from excavation of various structures.

The total quantity of muck generated from open excavation including construction and widening

of the roads is 165.65 lakh cum after considering swell factor of 45%. After the utilization of

muck for different project components as aggregates total estimated quantity to be disposed of

is about 117.35 lakh cum. Most of the excavated material is proposed to be dumped at 12

suitable locations identified specifically for this purpose with 7 sites along Dri limb, 1 site near

powerhouse location and 4 sites along Talo (Tangon) limb. The details of total muck generated

and to be disposed of are given in Table 8.4.

Table 8.4: Details of Excavation work in Etalin Hydroelectric Project

S. No. COMPONENT

Total muck to be

generated

including swell

factor

Muck to be

used as

aggregate

Muck to be

disposed after

aggregate use

Cum Cum Cum

A DRI LIMB

1 DAM- DRI 560725 112145 448580

2 Dam toe SHP- DRI 44675 8935 35740

3 Intake- DRI 36912 7382 29530

4 Coffer Dam- DRI 8754 0 8754

5 Diversion Tunnel Excavation from

U/S- DRI 456930 84188 372742


D/S- DRI 345655 45242 300413

7 HRT Excavation from Intake 331197 115919 215278

8 HRT Excavation from Adit D-1 749380 256686 492694




12 Surge Shaft- DRI 180967 49341 131627

13 Valve Chamber- DRI 48363 16927 31436

14 Pressure Shaft-vertical- DRI 119411 41794 77617

15 Pressure Shaft-horizontal- DRI 74625 26119 48507

16 Power House Adits- DRI 136990 37268 99722

17 MAT- DRI 73752 24871 48881

18 Power House- DRI 434581 152103 282478

19 Transformer Hall- DRI 125429 43900 81529

20 D/s surge chamber- DRI 188705 66047 122658

21 Tailrace Tunnel- DRI 219963 57914 162049

B TALO (TANGON) LIMB

22 Power House Adits - TALO (TANGON) 329950 45134 284816

23 MAT – TALO (TANGON) 154382 46351 108031

24 Power House - TALO (TANGON) 388060 135821 252239

25 Transformer Hall - TALO (TANGON) 122200 42770 79430

26 D/s surge chamber- TALO (TANGON) 125803 44031 81772

27 Tailrace Tunnel- TALO (TANGON) 136907 39877 97030

28 Switchyard 192491 0 192491

29 HRT Excavation from Adit T-4 598502 202355 396147


31 Surge Shaft- TALO (TANGON) 130769 33568 97202

32 Valve Chamber- TALO (TANGON) 28979 10143 18837

33 Pressure Shaft-vertical- TALO

(TANGON) 62589 21906 40683

34 Pressure Shaft-horizontal- TALO

(TANGON) 65932 23076 42856




S. No. COMPONENT

Total muck to be

generated

including swell

factor

Muck to be

used as

aggregate

Muck to be

disposed after

aggregate use




38 Coffer Dam- TALO (TANGON) 5947 0 5947

39 Diversion Tunnel- open Excavation-

TALO (TANGON) 291697 0 291697


U/S- TALO (TANGON) 178826 62589 116237


D/S- TALO (TANGON) 178826 62589 116237

42 Desanding chamber- TALO

(TANGON) 831962 291187 540775

43 Inlet Tunnels- TALO (TANGON) 189617 66366 123251

44 Silt flushing tunnel- TALO (TANGON) 56285 19170 37115

45 Link Tunnels- TALO (TANGON) 34057 11920 22137

46 Desanding basin-Adits- TALO

(TANGON) 147213 49887 97327

47 DAM- TALO (TANGON) 789077 157815 631261

48 Dam toe SHP- TALO (TANGON) 28442 5688 22754

49 Intake- TALO (TANGON) 174567 34913 139654

C PROJECT ROADS

Roads leading to various project

components for both Dri & Talo

(Tangon) Limb

3671850 1101555 2570295

TOTAL 16564523 4829797 11734726

Muck, if not securely transported and dumped at pre-designated sites, can have serious

environmental impacts, such as:

Can be washed away into the main river which can cause negative impacts on the

aquatic ecosystem of the river.

Can lead to impacts on various aspects of environment. Normally, the land is cleared

before muck disposal. During clearing operations, trees are cut, and undergrowth

perishes as a result of muck disposal.

In many of the sites, muck is stacked without adequate stabilisation measures. In such a

scenario, the muck moves along with runoff and creates landslide like situations. Many a

times, boulders/large stone pieces enter the river/water body, affecting the benthic fauna

and other components of aquatic biota.

Normally muck disposal is done at low lying areas, which get filled up due to stacking of

muck. This can sometimes affect the natural drainage pattern of the area leading to

accumulation of water or partial flooding of some area which can provide ideal breeding

habitat for mosquitoes.

A detailed Muck Disposal Plan has been prepared to minimize the impact and is given in

Environmental Management Plan.

8.2.6 Road Construction

A network of roads is required to approach various locations of project site such as Dam sites,

Adits, surge shaft, powerhouse, pothead yard, Main Access Tunnel (MAT) and Tailrace Tunnel

(TRT) portal, Dumping yards, quarry locations etc. It has been assessed that about 50km length




of new road is required to be constructed to facilitate construction of various components. An

average gradient of 1(V) to 15(H) has been considered for proposed roads from the construction

point of view. Apart from the Project roads 35km stretch of existing roads with in project area

needs to be widened and strengthened for the movement of heavy equipment and machinery in

all weathers and round the year. All the major roads have been proposed of 40R loading class as

per IRC standards and allowing clearances on the sides, drains and parapets, the required

formation width of the road works out to be 7.5m for the free flow of traffic mostly comprising of

rear end dumpers, tippers, transit mixers and loading equipment like loaders, excavators,

backhoes. The details of the roads proposed to be constructed are given at Table 8.5.

Table 8.5: Details of Road Construction

S. No. Nomination Description of work

Road Length

based on

pegging (m)

Road alignment - Dri Limb

Upstream of dam

1 DRD1a Existing road to Ayo Pani Bridge DTB3 550

2 DRD1b DTB3 to Dri U/s Bridge DTB1 594

3 DRD1c DTB1 to DTR Inlet 585

4 DRD5 Realignment of Existing Road 672

DRD9a DTB1 to Dam top 690

DRD9b Dam top to DTB2 1240

Sub Total 4331

Downstream of Dam

5 DRD2a Existing Road to Dri D/s Bridge (DTB2) 4028

6 DRD2b DTB2 to DTL-1 Outlet 956

7 DRD2c DTL-1 Outlet to DTL-1 Inlet 638

8 DRD3 Dri Bridge DTB2 to Dam Top & Intake 1168

9 DRD4a Dri Bridge DTB2 to DTR Outlet 717

10 DRD4b Dri Bridge DTB2 to DMD3 1839

Sub Total 9346

Dri HRT

11 DRD6 Junction to Adit D1 (Kabo Pani) 1474

12 DRD7 Existing road to Adit D2 (Ru Pani) 1121

13 DRD8a Existing Road to junction (PHRD4a to

Adit D3) 2240

DRD8b Existing Road to New Dumping Yard 405

Sub Total 5240

Total (Dri Limb) 18917

Road alignment - Power House area

14 PHRD1a Existing Road to Power House Bridge

PTB1 239

15 PHRD1b Bridge PTB1 to Dri MAT MD1 861

16 PHRD2 Bridge PTB1 to Talo (Tangon) MAT MT1

than to Existing Road 995

17 PHRD3a Existing Road to Pot Head Yard 495

18 PHRD3b Pot Head Yard to Adit T9 (Talo (Tangon)

Pressure Shaft) 719

19 PHRD3c Adit T9 to Junction 1329

20 PHRD3d Junction to Dumping Yard TMD7 926




S. No. Nomination Description of work

Road Length

based on

pegging (m)

21 PHRD4a Adit D3 to Junction 2154

22 PHRD4b Junction to Adit D4 (Dri Surge Shaft

Bottom) 979

23 PHRD4c Adit D4 to Adit T5 (Talo (Tangon) Surge

Shaft Bottom) 1390

24 PHRD4d Adit T5 to Adit T4 (Masa Pani) 4074

25 PHRD5 Junction to Surge Shaft Top 1793

26 PHRD6 Existing Road to Adit D8 (Dri Pressure

Shaft) 750

Total (Power house area) 16704

Road alignment - Talo (Tangon) Limb

Talo (Tangon) Desilting basin

27 TRD1a Existing Road to TTB1 (Talo (Tangon)

River) 400

28 TRD1b TTB1 to TTB2 (Kun Nalla) 269

29 TRD1c TTB2 to Adit Ta (Desilting Basin) 61

30 TRD1d Adit Ta to SFT 420

Sub Total 1150

Talo (Tangon) Dam

32 TRD2 TTB1 to DT Outlet 405

33 TRD3 TTB1 to Dam Top & Intake 774

34 TRD4 Existing Road to DT Inlet 1064

Sub Total 2243

Talo (Tangon) HRT

35 TRD5a Existing Road to Talo (Tangon) Bridge

TTB3 640

36 TRD5b Talo (Tangon) Bridge TTB3 to Junction 928

37 TRD5c Junction to Dumping yard TMD6 3275

38 TRD5d TMD 6 to Adit T2 (Ron pani) 755

39 TRD6 Junction to Adit T3 (Maru Pani) 2652

TRD7 TMD 6 to Adit T1 3125

Sub Total 11375

Total (Talo (Tangon) Limb) 14768

Total Road Length for the Project 50389

The major impacts likely to accrue as a result of construction of the roads are:

Loss of forest and vegetation by cutting of trees

Geological disturbance due to blasting, excavation, etc.

Soil erosion as the slope cutting operation disturbs the natural slope and leads to land

slips and landslides.

Interruption of drainage and change in drainage pattern

Disturbance of water resources with blasting and discriminate disposal of fuel and

lubricants from road construction machinery

Siltation of water channels/ reservoirs from excavated debris

Effect on flora and fauna

Air pollution due to dust from debris, road construction machinery, etc.




The indirect impact of the construction of new roads is the increase in accessibility to otherwise

undisturbed areas, resulting in greater human interference and subsequent adverse impacts on

the ecosystem. Appropriate management measures required to mitigate adverse environmental

impacts during road construction have been recommended. The details of the same have been

covered in Environmental Management Plan.

8.2.7 Flora and Fauna

The most important direct impact will be the loss of forest area and other natural vegetation

coming directly under submergence; clearances for road construction, for construction of labour

camps, working areas, muck disposal sites and rock quarry sites. As there are patches of

degraded forest in the vicinity of project components due to shifting cultivation more areas will

come under degraded category due to clearing and project construction activities. The land

acquisition for project construction would require felling of large number of trees and along with

the ground vegetation too would be lost. This loss would adversely impact not only the

vegetation composition in the area but would also impact the birds and other faunal species

dependent on these forests. As from the study area 17 species of orchids were recorded and

except for 2 species all are epiphytes therefore felling of trees would lead to loss of their

populations and this aspect needs careful attention while clearing of vegetation.

Vegetation might also be lost due to erosion and land slips induced by the construction activities on

roads, camps and working sites. Excessive earth cutting along steep slopes could trigger landslides.

As already mentioned in section 8.2.1 among the indirect impacts would result from the influx

of large numbers of workers into the area during the construction period as this might will put an

additional burden on the natural resource base in the area, in particular the forest resources.

Unless otherwise provided for, the people will harvest fuel wood, timber for construction and

various plants and wildlife for food. The contractor is supposed to provide kerosene for light and

cooking in the camps. More difficult will be to control use of forest and land resources caused by

the influx of casual labourers and employment seekers.

Regarding the wildlife in the study area no significant impact however is foreseen as the habitats

of some of the large mammals reported from the area listed as vulnerable in IUCN Red list

(Asiatic Black Bear and Wild dog) will not be significantly influenced by the project development,

as they are found in the dense forests which are located on higher reaches part of the upper

catchment far away from the settlements and are restricted primarily in Dibang Wildlife

Sanctuary which is more than 28 km away (aerial distance) from the project area.

8.2.8 Impacts Summary during Construction Phase

Impact of above activities on various components of the environment during construction phase

of the project are tabulated and given at Table 8.6.




Table 8.6: Summary of Impacts During Construction Phase

Component of

Environment

Source/Reason of Impact Quantification, where possible

Air Environment

Fugitive Emissions from

storage of construction

material in open area

Fine and coarse aggregate requirement for construction has been estimated as 18.92 lakh m3 and

32.82 lakh m3; open storage in different construction areas will lead to generation of fugitive dust

in the area

Increase in movement of

vehicles

In addition to coarse and fine aggregate; structural steel, cement and other raw material will be

transported to the area requiring movement of heavy transport vehicles (trucks, dumpers, etc.) in

the area; additionally transport vehicles (jeeps) will be required for movement of manpower in the

area. This will substantially increase the traffic in other wise low traffic density area and hence lead

to air and noise pollution.

Operation of construction

Plants, Machineries, Workshops

For construction of project components plants and workshops will be set up and construction

machinery and equipment will be deployed. A list of such equipment is prepared project component

wise and is enclosed as Table 8.3. Their operation will generate pollution in all manifestations viz.

air, water, noise including solid and hazardous waste.

Operation of DG sets for power

Requirement

27MW of power supply through DG sets has to be arranged. 7 DG-Houses has been envisaged with

different capacities of DG sets to meet the project demand. It would lead to emissions due to fuel

burning in the area where ambient air is free from such pollutants.

Quarrying Operations 62.12 ha of land is identified as rock quarry area divided between two quarry sites viz. near Akobe

Nala and near Ayo Pani Nala. Quarrying operation and transportation of quarried material generate

air and noise pollution.

Muck handling and transport The project would generate substantial quantity of muck from excavation of various structures. The

total quantity of muck generated from open excavation including construction and widening of the

roads is 165.65 lakh cum and the utilization of muck for different project components and

considering the swell factor total estimated quantity to be disposed of is about 117.34 lakh cum.

Most of the excavated material is proposed to be dumped at 12 suitable locations identified

specifically for this purpose with 7 sites along Dri limb, 1 sites near powerhouse location and 4 sites

along Talo (Tangon) limb. Transportation and handling such large quantity of muck will lead to air

pollution in the area.

Noise and

Vibration

Increase in movement of

vehicles

As discussed above

Operation of construction

Plants, Machineries, Workshops

As discussed above

Operation of DG sets for power

Requirement

As discussed above

Blasting operations for

tunneling and quarrying

Potential environmental impacts of blasting include ground vibration (seismic waves), air

overpressure, noise, dust and fly rock. Vibrations transmitted through the ground and pressure

waves through the air are the most common impacts of blasting operations. Depending upon the




Component of

Environment


location of the habitation, it can even damage the houses during the operation.

Water

Environment

Effluent from construction plant

and workshops

A list of construction equipment is prepared project component wise and is given at Table 8.3.

Their operation will generate pollution in all manifestations viz. air, water, noise and solid and

hazardous waste. As some of the equipment will use water and discharge effluent, uncontrolled

discharge will led to ground and surface water pollution.

Muck Disposal The project would generate substantial quantity of muck from excavation of various structures. The

total quantity of muck generated from open excavation including construction and widening of the

roads is 165.65 lakh cum and the utilization of muck for different project components and

considering the swell factor total estimated quantity to be disposed of is about 117.35 lakh cum.

Most of the excavated material is proposed to be dumped at 12 suitable locations identified

specifically for this purpose with 7 sites along Dri limb, 1 sites near powerhouse location and 4 sites

along Talo (Tangon) limb. As most of the operation is along the riverbank, spillage of muck will lead

to water pollution unless the operation is efficiently controlled.

Sewage from construction

camp and colonies

It is estimated that during the peak construction period, about 10600 persons will migrate to the

area to stay in construction camps and work on project. Sewage from workers colony/construction

camp can lead to serious water pollution if adequate treatment measures are not put in place.

Land

Environment

Change of Land use 1155.11 ha of land will be acquired for the project construction and land use of this land will

change permanently. This is a permanent impact and no mitigation/management measures can be

implemented for the entire land. However, land acquired for temporary construction camps, muck

dumping and quarrying, etc. will be restored to bring back it to its original land use.

Loss of top cover in

quarry/burrow area

62.12 ha of land is identified as burrow area. Quarrying operation lead to removal of top cover and

unless the area is restored it impacts the land environment and spoils the aesthetics of the region.

Restoration of quarrying area is included in the Environment Management Plan (EMP).

Land deterioration due to muck

disposal

12 dumping sites have been identified with 7 sites along Dri limb, 1 sites near powerhouse location

and 4 sites along Talo (Tangon) limb with total area of 113.70 ha. This land will be impacted due to

muck dumping; however, Muck Disposal Plan will ensure that area is restored on completion of the

muck dumping process so that impact remains temporary.

Land deterioration due at

construction sites, labour

camps/colonies

16 ha of land have been identified as construction facilities area. This land will get impacted due to

movement of vehicles, installation and use of construction equipment leading to discharge of

pollutants in atmosphere. However, these impacts will be temporary as the land can be restored

after completion of construction phase. Restoration of construction facility area is included in the

EMP.

Indiscriminate solid waste

disposal

About 10600 persons are expected to migrate in the area during peak construction period.

Construction and colony for workers and officers will generate solid waste - biodegradable as well as

non-biodegradable. Littering of solid waste on hill slopes creates an unaesthetic scene also.

Therefore, there is a need to implement a solid waste management plan to ensure that this waste

will not create serious land and ground water pollution.




Component of

Environment


Disposal of hazardous and

biomedical waste on land

Hazardous waste will be generated during construction phase from machinery and equipment using

fuel, lubricating oil, batteries, etc. Empty oil drums, used oil, maintenance/cleaning clothes, used

batteries, etc. will constitute hazardous waste. Quantity of the hazardous waste expected to be

generated cannot be estimated at this stage however, it is not expected to be large and can be

managed by developing a temporary secured storage location and then transporting the waste to

the nearest available TSDF.

Biomedical Waste will be generated from the dispensaries set up to take care of workers medical

needs; however, quantity is not expected to be very large. Therefore, biomedical waste will be

securely kept in dispensary and will be transported to the nearest government/private hospital

where an incinerator is installed for disposal of biomedical waste. As the quantity is not expected to

be large, capacity of the host incinerator should not pose a constraint.

Flora

Loss of forest area due to

project construction

The project construction would require acquisition of 1165.66 ha of forest land (1074.329 ha

surface area including river bed + 91.331 ha underground area). All the vegetation on this land will

be cleared for construction of project component. This is a permanent impact and can only be

compensated by Compensatory Afforestation for which detailed plan shall be prepared by the State

Forest Department as per Forest (Conservation) Act, 1980.

Tree cutting by workers for fuel

wood/heating/furniture etc.

In addition to loss of forestland due to project construction, there is a potential impact of tree

cutting by migratory labour force that would have fuel wood requirement and timber requirement

for heating, furniture, etc. This impact can be mitigated by ensuring that labor’s fuel and timber

requirement is taken care of. A plan prepared in this regard is included as part of EMP.

Fauna

Impact on Fish migration The obstruction created by the dams would hinder the migration of certain commercial species

especially Schizothorax spp. These fishes undertake annual migration for feeding and breeding.

Therefore, fish migration path may be obstructed due to 101.5m and 80m high Dri and Talo

(Tangon) dams and fishes are expected to congregate below the dam walls. Under this situation

poaching activities may increase in the area.

Most of the species will shift to the section of the river where they find favorable environment for

breeding since the dams are 101.5m and 80m high, the construction of fish ladder is not feasible in

the proposed dams. However, it is proposed that the artificial seed production in hatchery may be

adopted which can be stocked in the river stretches downstream and upstream of the proposed

dams.

The Schizothorax species are steno-thermal. During winter months, they migrate from headwaters

near flood plains in search of suitable feeding and breeding grounds. The sampling in Dri and Talo

(Tangon) rivers both on upstream and downstream of the proposed dam sites for macro-benthic life

gave 2 units/sq m of fry of Schizothorax sp. This observation further strengthens the fact that

Schizothorax spp. migrate during winter months. With the onset of summer season, these species

migrates upstream. These species during project construction phase are likely to congregate in the

reservoir. It is expected that in due course of time these species will adapt themselves to the




Component of

Environment


changed habitat.

Noise and vibration from

construction activities including

blasting, increased traffic, etc.

As discussed above, there will be higher sound levels in the area due to construction activities,

operation of DG sets and other equipment's, blasting, etc. Blasting will also lead to ground

vibration. Noise and vibration in the area will impact the fauna in the area especially avifauna, who

may move away from the area permanently.

Hunting and poaching Hunting and poaching activities can be undertaken by migratory workforce and this will impact

fauna of the region. As part of EMP, anti-poaching measures are suggested which needs to be

implemented strictly that impact is eliminated.

Loss of forest area 1165.66 ha of forest land (1074.329 ha surface area + 91.331 ha underground area) will be

cleared for the project construction and will directly impact habitats of wildlife in the area.

Socio-economic

Social and cultural conflicts

with migratory labour force

Influx of people in otherwise isolated area may lead to various social and cultural conflicts during

the construction stage. Developers need to take help of local leaders, Panchayat and NGOs to

ensure minimum impact on this count.

Increased incidence of Water

Related Diseases

The construction of a reservoir replaces the riverine ecosystem by a lacustrine ecosystem. The

vectors of various diseases breed in shallow water areas not very far from the reservoir margins.

The magnitude of breeding sites for mosquitoes and other vectors in the impounded water is in

direct proportion to the length of the shoreline. The construction of the reservoir would increase the

shoreline by many times as compared to the pre-project shoreline of Dri and Talo (Tangon) rivers

under submergence. Thus, the construction of the proposed reservoir would lead to increase in

potential breeding sites for various diseases vectors. There are chances that incidence of malaria

may increase as a result of the construction and operation of the proposed project.

Increase incidents of diseases

due to migratory labour force

Large scale activity in the area due to the proposed project may become a cause of spread of

various communicable diseases including HIV/AIDS in the project area as project requires long-term

input of labour from outside the area and many of them may remain separated from their families

for a long period of time.

Direct job opportunities for

locals

Locals will get direct employment opportunity in the project based on their qualifications and skill

set. In addition, There will be various opportunities for local contractors to be involved in

construction, fabrication, transportation, etc.

Secondary jobs/service due to

increased activity in the area

Due to construction of project there will be increased activity in the area. Migratory workforce will

settle in the area and also there will be increased movement in the area due to material transport,

consultants, engineers, etc. This will give job/service opportunity to the locals to meet their daily

requirements of food, stay, etc.




8.3 IMPACTS DURING OPERATION PHASE

On completion of the construction of the project, the land used for construction activities, muck

dumping, quarrying, etc. will be restored. Construction workers who have resided in that area

will move to other areas. By ensuring all the mitigation and management measures, as planned

for this project, are implemented to minimize the impact of construction phase, large part of the

area will go back to its original form. However, there will be some permanent changes such as

dam across the river, reservoir formation, powerhouse and project colony. Hydropower projects

are considered as clean source of renewable energy as there are no significant pollution

generation sources during project operation. There is no air and water pollution from the project

operation. Similarly generation of solid and hazardous waste is also insignificant.

One critical impact of operation of hydropower projects has received substantial attention from

environmentalists in last two to three decades based on the observations made on operational

projects in developed countries is the decrease in flow in the downstream stretch. Diversion of

water from dams to powerhouse will make the intermediate stretch of the river almost dry

especially during lean season. Impact becomes significant if several projects are planned in

cascade and/or large headrace tunnels making the intermediate stretch (es) very large. Low flow

in the section of the river adversely impacts the aquatic ecology including fish fauna, riparian

vegetation and fauna dependent on it; and downstream users. These impacts cannot be totally

mitigated, however, they can be minimized by scientifically assessing the environmental flow

requirement of the intermediate stretch not only in lean season but also in other months.

8.3.1 Downstream Impacts

During construction phase the water of the river will be not stored and the natural flow of the

river will be available throughout the stretch. However during the operation phase, flow in the

stretch downstream of dam due to diversion of water through head race tunnel would lead to

reduction of water in the downstream river stretch. It will leave areas dry and the river water will

remain mainly in the centre portion especially in the 16.5 km downstream stretch of Dri river and

about 18 km stretch of Talo (Tangon) river (see Figure 8.1). Thereafter one small stream Ari

Pani joins Dri about 800m downstream but good contribution is made by Emi Pani on the right

bank about 1.8km downstream of Dri dam. Then another stream named Ayu Pani contributes

good amount of discharge on the right bank further 1.3 km d/s.

Similarly, in case of Talo (Tangon) limb also immediately about 800m downstream of dam axis

Kun Nala joins Talo (Tangon) on its right bank and adds significant flow into main channel.

Thereafter Anon Pani meets Talo (Tangon) river on its left bank at a distance of about 1.80 km

from the dam and significantly contributes to the discharge of Talo (Tangon) river. In addition 2

more tributaries contribute to the discharge of Talo (Tangon) within 3 km downstream of Talo

(Tangon) dam axis. These streams are Shu and Non nalas. Further about 4.7 km downstream 3

to 4 streams contribute significantly to the flow of Talo (Tangon) river.

Therefore, the reduced flow in river in the initial 1.8 km stretch on Dri Limb and about 3 km on

Talo (Tangon) limb will affect the habitat of many aquatic species which are located along the

shallow banks. At certain places in the river some water might remain in shallow pools subjecting

the fish to prey by birds and human beings. Such situations will result in indiscriminate fishing.

The condition will be more critical during the lean season when volume of water is significantly




reduced in the river. Certain stretches of the river may even create semi-desiccation condition

due to reduction of flow rate which ultimately affect the river ecology and some aquatic species

might perish due to arid conditions of the river. The inhabitants of downstream area villages will

also be affected which are involved in fishing activity for themselves and sometimes to sell in

local market as an alternative means for procurement of food and other requirement of daily

needs.

It is well established that running waters have a self-purifying capacity, which is directly related

to its flow regime. After the reduction in water discharge it loses its capacity of self-purify due to

the changes in chemical composition. Creation of a reservoir would lead to siltation; therefore,

downstream section would receive water with low turbidity and lower water current velocity. The

downstream stretch would receive lower nutrients in the water and free of any turbidity as silt

carries essential nutrients. The regulated flow of water in the downstream would lead to

instability in the biotic communities. The shallowness in water of downstream in lean season

would increase the water temperature, which would affect the dissolved oxygen contents

adversely. Aquatic life comprised of algae, macro-invertebrates, macrophytes, fish, etc. will be

affected adversely. The species like desmids, chironomids and loach fish can thrive

predominantly in downstream stretch that would carry low nutrient, high TDS, low DO and high

BOD in water.

8.3.2 Impact on Migratory Fishes

About 16.5 km and 18 km downstream of Dri and Talo (Tangon) river stretches, respectively will

experience comparative scarcity of water due to the diversion which would lead to changes in the

water quality. The proposed dams would act as permanent barrier in the way of fish movement.

Ichthyofauna of Dri and Talo (Tangon) rivers comprised of number of fish species out of which

Schizothorax richardsonii is only species which is harvested for fishery purpose. It undertakes

annual upward and downstream migration for feeding and breeding purposes. Therefore, fish

migration path may be obstructed due to 101.5 m and 80 m high Dri and Talo (Tangon) dams

and fishes are expected to congregate below the dam walls. Under this situation poaching

activities may increase in the area.

Most of the species will shift to the section of the river where they find favourable environment

for breeding and spawning. The Schizothorax species are steno-thermal fish and they migrate

during winter months from headwaters zone to near flood plains in search of suitable feeding and

breeding grounds. The present study indicated that the Schizothorax spp. found in the Dri and

Talo (Tangon) rivers only during the winter months of the year. This observation further

strengthens the fact that Schizothorax spp. undertakes migration during winter months when the

temperature of water reaches near freezing point. This induces them to migrate downstream and

frequent the warmer spring-fed streams in search of suitable spawning grounds and travels back

with the onset of summer season. During project construction phase this species is likely to

congregate in the reservoir. It is expected that in due course of time this species will adapt to the

changed habitat.

8.3.3 Impact on Downstream Users

Due to diversion of water for power generation the flow in the downstream stretch would be

considerably reduced and impact would most visible during lean. There are 5 villages viz. Emilin,




Akobe, Cheyo, Granli, and Ahunli which fall between Dri limb dam site and power house and who

could be directly or indirectly dependent upon river. In case of Talo (Tangon) limb axis 6 villages

cum hamlets are located in the downstream stretch viz. Punli, Echanli, Arumli, Amoli, Aninka,

and Emilin. A small population resides in this stretch. During the surveys it was observed that

people are not dependent on the main channel i.e. Dri and Talo (Tangon) rivers for their drinking

water needs or any other purpose except for occasional fishing. They instead are dependent upon

the streams that join the main river.

8.3.4 Impact on Reservoir Water Quality

The flooding of previously forest and agricultural land in the submergence area will increase the

availability of nutrients resulting from decomposition of the vegetative matter. Phytoplankton

productivity can supersaturate the euphotic zone with oxygen before contributing to the

accommodation of organic matter in the sediments. Enrichment of impounded water with organic

and inorganic nutrients will be the main water quality problem immediately on commencement of

the operation. However, this phenomenon is likely to last for a short duration of few years from

the filling up of the reservoir.

Other impacts of the operation phase include formation of reservoir impacting the water quality

and aquatic ecology, pollution generation from colony and plant and positive as well negative

impacts on socio-economic environment mainly due to improved infrastructure in the area. These

impacts are summarized at Table 8.7.

8.3.5 Minimum Environmental Flow Requirement

In order to conform to the guidelines of MoEF&CC regarding the minimum environmental flows to

be released especially during the lean season a provision of additional units of 19.6 MW on Dri

Limb and 7.4 MW on Talo (Tangon) Limb power stations have been planned in the design of

Etalin HE project to ensure that adequate flow is released for aquatic life in downstream stretch

at all the time. The proposed additional units totaling 27 MW would operate continuously

throughout the year (24 x 7). The rated discharge worked out as 30.64 m and 19.52 m3/s,

respectively. The rated discharge value has been taken as 20% of the average mean value of the

lean season (December – March: 4 months). In addition as already discussed in previous

sections there are number of tributaries that join Dri and Talo (Tangon) rivers immediately

downstream of respective dams. However the requirement of minimum environmental flow has

been assessed by Central Inland Fisheries Research Institute, (CIFRI), Barrackpore as per TOR

requirement. The Environmental Flow report of CIFRI, Barrackpore has been appended as a

separate report.




Table 8.7: Summary of Impacts During Operation Phase

Component of

Environment


Air Environment No significant air pollution during operation phase

Noise and

Vibration

Noise and vibration from

turbines

A common underground power house of size 352m(L) x 23.5m(W) x 59.73m (H) with six

units of 307 MW at Dri Limb and four units of 307 MW at Talo (Tangon) Limb and two tail

race channel discharging into the river is envisaged. Noise and vibration inside the

powerhouse will be high especially during operation time when turbines are running at under

capacity. Noise levels are expected to be in the range of 95-100 dB(A) at 1m from the

source. These turbines will be housed within the underground powerhouse building, which

will provide sufficient attenuation, therefore, impact of noise outside the powerhouse on the

surface is not significant. Work instructions will be developed for workers working in the high

noise area so as to limit their exposure to high noise and encourage the use of PPEs.

Water

Environment

Reduced flow round the year

in the river stretch between

dams and powerhouse

This is one of the most serious impacts of hydropower projects during their operation phase.

Operation of the plant will involve diversion of water by 101.5m and 80m high Dri and Talo

(Tangon) dams, through HRTs of 10.722 km and 13.045 km lengths, respectively to a

underground powerhouse. The intermediate Dri river length of 16.5 km and 18 km of Talo

(Tangon) river will become dry throughout the year but for the mandatory environmental

flow releases. Reduced flow in the intermediate stretch will alter the aquatic ecology and

change the fish habitat altogether. To minimize this impact, a detailed environment flow

assessment exercise will be carried and recommended flow will be released.

Formation of reservoir The flooding of previously forest and agricultural land in the submergence area will increase

the availability of nutrients resulting from decomposition of the vegetative matter.

Phytoplankton productivity can supersaturate the euphotic zone with oxygen before

contributing to the accommodation of organic matter in the sediments. Enrichment of

impounded water with organic and inorganic nutrients will be the main water quality problem

immediately on commencement of the operation. However, this phenomenon is likely to last

for a short duration from the filling up of the reservoir.




Component of

Environment


The damming of river Dri and Talo (Tangon) rivers will result in creation of 83.32 ha of Dri

reservoir 36.12 ha of Talo (Tangon) reservoir. The dams will change the fast flowing river to

a quiescent lacustrine environment. The creation of a pond will bring about a number of

alterations in physical, abiotic and biotic parameters both in upstream and downstream

directions of the proposed dam sites. The micro and macro benthic biota is likely to be most

severely affected as a result of the proposed project.

The positive impact of the project will be the formation of a water body which can be used

for fish stocks on commercial basis to meet the protein requirement of region. The

commercial fishing in the proposed reservoir would be successful, provided all tree stumps

and other undesirable objects are removed before submergence. The existence of tree

stumps and other objects will hinder the operation of deep water nets. The nets will get

entangled in the tree stumps and may be damaged.

The reduction in flow rate of Dri and Talo (Tangon) rivers especially during lean period is

likely to increase turbidity levels downstream of the dams. Further reduction in rate of flow

may even create condition of semi-desiccation in certain stretches of the river. This would

result in loss of fish life by poaching. Hence, it is essential to maintain minimum flow

required for sustenance of riverine fisheries till the disposal point of the tail race discharge

Sewage from project colony During the operation phase, due to absence of any large-scale construction activity, the

cause and source of water pollution will be much different. Since, only a small number of

O&M staff will reside in the area in a well-designed colony with sewage treatment plant and

other infrastructural facilities, the problems of water pollution due to disposal of sewage are

not anticipated. The treated sewage will be reused for gardening and green belt around the

colony.




Component of

Environment


Land

Environment

There will not be any negative impact on land during operation phase. Change of land-use is

a permanent impact and has been covered under construction phase. There will be positive

impact on land as part of the land used for temporary activities will be restored to natural

conditions. This would include quarry areas (62.12 ha), muck disposal area (91.79 ha) and

land used for construction work.

Flora and fauna

There will be no negative impact on flora of region during the operation phase. Impact on

riparian vegetation and aquatic flora due to reduced flow in the intermediate stretch has been

covered under water environment. Implementation of biodiversity conservation and

management plan, catchment area treatment plan and compensatory afforestation plan will

have positive impacts on flora in the area. Development of green belt in the project activity

area and along the periphery of the reservoir will also have positive impact. Additionally,

restoration of land used for muck dumping, construction activity, etc. will also have positive

impact on the flora.

During project operation phase, the accessibility to the area will improve due to construction

of roads, which in turn may increase human interferences leading to marginal adverse

impacts on the terrestrial ecosystem. Since significant wildlife population is not found in the

region, no major adverse impacts are anticipated on this account.

Socio-economic

Project construction will lead to large-scale infrastructure development in the area. Due to

development of road network, accessibility to the area will significantly improve. Local area

development activities planned as part of the project will not only benefit the project-affected

families but also other people residing in the area including that of nearby villages. Setting up

of school, health care facilities, skill development activity center, vocational training center,

etc. will ensure higher education and skill levels of the local population. Provision of

scholarships will help deserving students to go for higher studies. Overall it is expected that

quality of life of the local population will improve due to setting up of the project in the area.




Figure 8.1: Drainage downstream of Dri and Talo (Tangon) dam sites

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Annexure-I

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OF MOEF LETTER

Annexure - III

ToR Compliance-Etalin HEP

S. No

Clause in ToR Compliance Remarks

ToR letter No.12011/60/2006-IA.I,

dated 30-11-2009

I General Introduction giving details of the salient features of the proposed project

Covered in Table 2.1 of EIA, Project Description, Chapter-2.

Layout map of the project to be given

along with contours with project

components clearly marked with a proper scale and printed at least on A3 scale for clarity, Study area to be demarcated properly on the appropriate scale map,

Sampling sites to be depicted on map for each parameter with proper legends

Covered in Figure 2.2 of EIA, Project

Description, Chapter-2.

Covered in Figure 3.1 of EIA,

Methodology, Chapter-3.

II Environmental Impact Assessment (EIA) Report

The baseline studies should consist of 3 seasons field data (i.e. Pre–monsoon, Post monsoon and winter season) covering one calendar year.

Covered in Environmental baseline status i.e. Chapter 6, Physico-Chemical Environment and Chapter- 7: Biological Environment.

Study Area:

1 The study area should comprise of the following: Catchment Area up to the dam site Submergence Area Project Area or the direct impact area should comprise of area within 10 km

radius of the main project components like dam, power house, etc. and also area within 10 km upstream of reservoir tail & 10 km distance from the reservoir rim along both the river banks.

Covered in 3.2 of Methodology i.e. Chapter 3.

2 Detailed methodology followed for the

analysis of various parameters required for EIA.

Covered in Chapter 3.

3 Various details regarding the project layout etc. should be depicted in proper scale maps at least at 1:15,000 like:

Location map of proposed HE project

Location map of the project area with contours indicating main project features,

Drainage map of the river catchment up to the proposed project site,

Soil map of the project area Geological and Seismo-

Location map is given in Figure 1.1 of Introduction i.e. Chapter 1

Drainage map covered in Fig no. 2.1 of CAT plan, Chapter- 2

tectonic map of the area surrounding the proposed project site showing location

of barrage site, power house site and tunnel alignment, and

False Color Composite (FCC) generated from satellite data of project area and land-

use/land-cover prepared from these images.

Soil map covered in Fig no. 2.6 of CAT plan, Chapter- 2

Land use/ land cover map covered in Fig no. 2.4 of CAT plan, Chapter- 2

4. The details of the baseline data/information that should be collected are as follows:

(A) Physical-Chemical Environment

i Physical geography, Topography, Stratigraphy, Regional Geology of the catchment area. Landslides zone or areas prone to landslide existing in

the study area especially along the periphery of the reservoir should be examined.

Covered in 6.3 of Baseline status-Physico–Chemical Parameters, Chapter-6

Geology covered in Chapter-5 as Annexure-V of EIA Volume

ii Tectonics and seismicity of the study area.

Covered in 5.1 of Chapter-5 as Annexure-V of EIA Volume

iii Presence of important economic mineral deposit if any.

Covered in 5.1 of Chapter-5 as Annexure-V of EIA Volume

iv Ambient air quality with parameters, viz suspended particulate

matter(SPM), Respirable Particulate

Matter(RPM), Sulphur Dioxide(SO2) and Oxides of Nitrogen) in the study area.

Covered in Air Environment, 6.5, Baseline status-Physico –Chemical

Parameters, Chapter-6.

v Existing noise levels and traffic density in the area.

Covered in Noise & Traffic, 6.6, Baseline status-Physico –Chemical Parameters, Chapter-6.

vi Soil classification, physical parameters, viz. texture, moisture content, porosity, bulk density and water holding capacity and chemical characteristics viz. pH, electrical conductivity, sodium, potassium,

calcium, magnesium, nitrogen, total

nitrogen, exchangeable sodium percentage (ESP), organic matter, phosphorus, etc should be analyzed for the samples collected from different locations in the study area.

Covered in 6.4 -Baseline status-Physico –Chemical chapter, Chapter-6

vii Identification of free draining/directly draining catchment.

Covered in 2.4 of CAT plan, Chapter-2 of EMP

viii Remote Sensing & Studies- Generation of thematic maps viz. slope map, drainage map, soil map,

land use land cover map, etc. Based on these, thematic maps, an erosion intensity map should be prepared.

Covered in Figures 2.1 to 2.6 of CAT plan, Chapter-2

x Delineation of sub and micro

watershed, their location and extent

based on soil and Land use Survey of

Covered in Figure 2.4.1 of CAT plan,

Chapter-2

India (SLUSoI), Deptt. Of Agriculture, Govt. of India. Erosion levels in each micro-watershed and prioritization of

micro-watersheds through Silt Yield Index(SYI) method of SLUSoI.

Covered in Fig 2.6 of CAT plan, Chapter-2

B Water Environment

i Hydro-Meteorology of the project (viz.

precipitation (snowfall, rainfall), temperature, relative humidity etc.)

Covered in 4.1 of Hydrology, Chapter

4 as Annexure – IV of EIA Volume

ii Run-off, discharge, water availability for the project, sedimentation rate, etc.

Covered in 4.1 of Hydrology, Chapter 4 as Annexure – IV of EIA Volume

iii Establishment of Raingauge and G&D sites in the project catchment to

make a proper assessment of the yield at the intake sites for making energy calculations

These have been established by the proponent

iv In order to maintain the ecology of river in the downstream stretch, a separate study should be conducted by an independent reputed agency which should analyze on the downstream impact on fisheries, aquatic ecology due to sudden water

release from the reservoir in the monsoon and increased flood vulnerability due to boulder extraction from the river bed to be used in the

construction materials etc. , and should come out with a minimum environmental flows that should be

required to be released during the lean season to sustain the aquatic life and recommendation of the same should be binding on the project developer. Downstream release of water should be decided on the basis

of scientific study based on depth and velocity of water. The study area, however, be limited up to Dibang Multipurpose project located more than 50 km downstream of the

proposed powerhouse of the project.

Covered in Chapter 8 Impacts under section 8.3 during Operation phase, Assessment of Impacts

v Basin Characteristics

vi Hydrology, sedimentation rate etc. Backwater level study along the tributaries at FRL should be conducted (pre- sedimentation

condition)

Covered in 4.1 of Hydrology, Chapter 4 as Annexure – IV of EIA Volume

vii Physical and chemical parameters of surface water quality. Physical parameters include temperature, pH, electrical conductivity, total dissolved solids (TDS), DO, turbidity. Chemical

parameters are salinity, alkalinity, Ca, Mg, and total hardness, chlorides,

nitrate nitrogen, phosphate, silicates, and total coliforms. Sampling should

Covered in water Quality,7.6, Environmental Baseline status-Biological Resources, Chapter-7

be covering entire area of influence, including main river system and important tributaries of the river.

C. Biological Environment

i Characterization of forest types in the study area. It should be based upon Forest Working Plan.

Covered in 7.3 Forest Types, of Environmental Baseline Status-Biological Resources, Chapter-7

ii Land details to be furnished both for Forest land as well as Community Land as most of the land to be acquired is Forest land and even community land also to be treated as Forest land and Compensatory

afforestation plan to be prepared

accordingly.

Given in Chapter 2 of EIA report and also in Chapter 13 of EMP report

iii General vegetation pattern and floral diversity viz. trees, shrubs, grasses, herbs, significant microflora, etc.

Vegetation should cover all groups of plants including lichens and orchids.

Covered in 7.4 of Environmental Baseline Status-Biological Resources, Chapter-7 of EIA Volume

iv Species frequency, density, abundance to be detailed. Biodiversity index (Shannon- Wiener Diversity index) and Importance Value Index

(IVI) of the species to be provided. Methodology used for calculating the various diversity indices along with details of locations of quadrates, size

of quadrates, etc. to be reported.

Covered in 3.2 of Methodology i.e. Chapter 3 of EIA Volume

v Economically important species viz. medicinal, timber, fuel wood etc.

Covered in 7.4.6 of Environmental Baseline Status-Biological Resources, Chapter-7 of EIA Volume

vi Flora under Rare, Endangered and Threatened (RET) categories should be documented using International

Union for the Conservation of Nature and Natural Resources (IUCN) criteria and Botanical Survey of India ‘s Red Data list along with economic significance.

Covered in Chapter-1, Biodiversity conservation & Management plan of EMP Volume.

vii Cropping and Horticulture pattern and

practices in the study area.

Covered under 6.8 of R&R plan of

EMP report

viii Faunal Elements a) Inventorisation of terrestrial wildlife including reptiles and Herpetofauna, their present status in

the project area b) Zoo-geographic distribution /affinities, Endemic, threatened and endangered species. c) Avifauna 1. Status 2.Resident/Migratory/Passage

migrants 3.Impact of project on threatened/endangered taxa, if any

d) Butterflies, if any found in the area


ix For RET species, voucher specimens GPS reading of RET species not

should be collected along with GPS readings to facilitate rehabilitation. RET faunal species are to be classified

in two ways viz. as per IUCN Red Data list and as per different schedule of Indian Wildlife Protection Act, 1972.

Provided rather areas of occurrence have been given

x To document the existence of barriers

and corridors (if any) for wild animals, the habitat fragmentation and destruction of wild animals due to project.

Covered in Chap 7 of EIA report

xi Effect on fish migration and habitat degradation due to project.

Covered in Chapter 8 Impacts under section 8.3 during Operation phase,

Assessment of Impacts of EIA Volume

xii Existence of National Park, sanctuary, Biosphere, Reserve forest etc. in the study area if any, should be detailed.

Covered in 7.5.5, of Environmental Baseline Status-Biological Resources, Chapter-7 of EIA Volume

D Aquatic Biology

i) Aqua-fauna like macro-invertebrates, zooplankton, phytoplanktons, benthos, etc. ii) Conservation Status iii) Fish & Fisheries

iv) Fish migrations, if any v) Breeding grounds vi) Impact of dam building on fish migration and habitat degradation

Covered in 7.6.2, of Environmental Baseline Status-Biological Resources, Chapter-7 of EIA Volume Conservation covered in Biodiversity Management Plan,Chapter-1 of EMP

volume

Covered in Chapter 8, Assessment of Impacts of EIA Volume

E. Socio-economic Environment

i) Land details ii) Demographic profile iii) Ethnographic profile iv) Economic structure

v) Development profile vi) Agricultural practices vii) Cultural and aesthetic sites viii) Infrastructure facilities: education, health and hygiene, communication network, etc. * Report should include list of all the

project Affected families with their names, education, land holdings, other properties, occupation, source of income, land and other properties to be acquired, etc. In addition to socio-economic aspects

of the study area, a separate chapter on socio-cultural aspects based upon study on Ethnography of the area.

Covered in R&R plan, in a separate volume

5. Impact Prediction

Impact prediction is a way of

‘mapping’ the environmental consequences of the significant aspects of the project and its

alternative. Environmental Impact can never be predicted with absolute

Details are given in subsequent

paragraph. Alternatives have been discussed in

Chapter 1 of EIA report

certainity and this is all the more reason to consider all possible factors and take all possible precautions for

reducing the degree of uncertainity. The following impact of the project should be assessed.

Air

A. Changes in ambient levels and ground level concentrations due to total emissions from the point, line and the area sources B. Effects on soils, material, vegetation, and humen health

C. Impact of emissions DG sets used for construction power if any, on air environment

Covered in Chapter 8 Impacts under section 8.3 during Operation phase, Assessment of Impacts of EIA Volume

Noise -

a. Changes in ambient levels due to noise generated from equipments, blasting operations and movement of vehicles b. Effect on fauna and human health

Covered in Assessment of Impacts chapter -8 of EIA Volume

Water

a)Changes in quality b) Sedimentation of reservoir c) Impact on fish fauna d) Impact of sewage disposal


Land

a)Changes in land use and drainage pattern b) Changes in land quality including effects of waste disposal c) Riverbank and their stability

d) Impact due to submergence


Biological

a)Deforestation and shrinkage of animal habitat

b) Impact on fauna and flora (including aquatic species if any) due to decreased flow of water c) Impact on rare and endangered

species, endemic species, and migratory path/route of animals, if any

d) Impact on breeding and nesting grounds, if any e) Impact on animal distribution, migration routes (if any), habitat fragmentation and destruction due to dam building activity


Socio – Economic Aspects

a)Impact on the local community including demographic changes b) Impact on economic status c) Impact on human health

d)Impact on increased traffic e) Impact on Holy Places and Tourism


Downstream impact on water, land & human environment due to drying up of the river at least 10 km

downstream of the dam

Covered in 8.3.1 of Assessment of Impacts chapter -8 of EIA Volume

Positive as well as negative impacts likely to be accrued due to the project are to be listed


Positive impacts like benefits from carbon trading.


6 Environmental Management Plan (EMP)

i Resettlement and Rehabilitation(R&R) plan should be prepared with due

consultation with Project affected

Families (PAFs). It should include community development strategies and a list containing name of PAF’s age, educational qualification, family size, sex, religion, caste, source of income, house with type and amount

of land holding, house/land to be acquired, any other property, possession of cattle, etc. The R&R plan should be according to the National Resettlement & Rehabilitation Policy (NRRP-2007) as

well as State Resettlement and Rehabilitation Policy(SRRP 2008).

Detailed budgetary estimates are to be provided. The compensation to be paid for forest as well as community land.

Covered in R&R plan as a separate volume

ii Muck Disposal Plan

Cross-sections of muck disposal sites should be given in Auto CAD format.

Covered in Fig. 7.1, Dumping Sites, Muck Dumping plan,Chapter-7 of EMP Volume

iii CAT plan .

Cover both direct/indirectly draining catchment areas and CAT plan should be prepared micro-watershed wise. Areas/watersheds falling under ‘very

severe’ and ‘severe’ erosion categories are required to be treated. Both biological and engineering measures should be proposed in consultation with State Forest Department. Year wise schedule of work and monetary allocation should

be provided. CAT plan to be completed prior to reservoir impoundment.

Covered in CAT plan Chapter-2 of EMP report

iv Layout map showing land slide/ land slip zones if any, around the reservoir

periphery should be prepared. Suitable engineering and biological

measures for the identified land slip zones treatment must be provided

Covered in Chapter-9, Reservoir RIM Treatment Plan of EMP volume.

with physical and financial schedule.

v Public Health Management Plan-

including the provision for drinking water facility for the local community.

Covered in Public Health Delivery

system, Chapter-5 of EMP volume

vi Compensatory Afforestation

In lieu of the forest land required for

the project needs to be proposed. Choice of plants should be made in consultation with State Forest Department.

Covered in Compensatory

Afforestation Chapter 12 of EMP report

vii Green Belt

Suitable species of plants for the proposed green belt along periphery of reservoir (Reservoir Rim Treatment

Plan), colonies, approach road, canals etc. must be suggested. Complete plan with physical and financial

details with layout of the proposed sites of green belt development to be included.

Covered in Chapter-8, landscaping, restoration and Green belt development of EMP Volume.

viii Biodiversity Conservation Plan

Consultation with State Forest Department to be included.


ix Wildlife Conservation Plan Covered in Chapter-1, Biodiversity conservation & Management plan of

EMP Volume.

x Fishery Management Plan

Baseline data on catch composition, fish density, fish standing crop, fish population dynamics in and around

project area, presence of migratory/endangered fish if any to be checked and mitigation measures should include monitoring the impact of the proposed construction on the fish resources

Covered in Fishery Conservation & Management plan, Chapter-3.

Xi Dam Break Analysis & Disaster Management Plan

The output of the Dam Break Model should be illustrated with appropriate

graphs and maps clearly bringing out

the impact of the dam break scenario.

Covered in Dam Break modeling, Chapter-11.

Xii Design Earthquake Parameters

A site specific study of earth quake parameter should be done. The

results of the site specific earth quake design parameters should be sent for approval of the NCSDP (National Committee of Seismic Design Parameters, Central Water Commission, New Delhi for large dams.

Covered in Geology & Seismicity Chapter appended as Annexure – V in

EIA report

xiii Construction Methodology and Equipment Planning including the

tunnel driving operations, machinery and charge density etc.

Covered in Chapter 2 of EIA report

xiv Management during the Road Construction

Covered in Chapter 10 of EMP report

xv Sanitation & Solid Waste Management Plan for domestic waste from colonies and labour camps, etc.

Covered in Solid waste Management plan, Chapter-4.

xvi Water & Air Quality & Noise Environment Management during

construction and post construction periods.

Covered in Air, Water Environment Management plan, Chapter-10.

xvii Fisheries Conservation Plan for conservation/management of fishes. Probability of having fish ladder or fish pass is to be examined in case

there is any migratory fish species in

the area.

Covered in Fishery Conservation & Management plan, Chapter-3.

xviii Local Area Development Plan to be formulated in consultation with the Revenue Officials and Village

Panchayats.


xix Tribal area development plan as the area is predominantly tribal inhabited.


xx Mitigations measures to check shifting cultivation in the catchment area with

provision for alternative and better agricultural practices. CAT Plan should cover impact of shifting cultivation.

Covered in Chapter-2 of CAT Plan.

xxi Environmental Monitoring Programme (With physical & financial details

covering the aspects form EMP).

Covered in Environmental Monitoring programme of EMP, Chapter-13.

6. As per the provisions of the EIA Notification 2006, you are requested to submit draft EIA/EMP report as per the above terms of reference to the State

Pollution Control Board/ Committee for conducting the Public Hearings/Public Consultation.

The Public Hearing will be conducted as per EIA notification of Sep, 2006

7. All the issues discussed in the

Public Hearing/Public Consultations should be addressed to and incorporated in

the final EIA/EMP report and submitted to the Ministry for considering the proposal for Environmental Clearance.

The Public Hearing proceeding will be

attached with Final EIA report.

Revised ToR letter No.12011/60/2006-IA.I, dated 26-04-2013

A.

EIA/EMP reports should clearly give 90% flow series data along with 4 years observed data in form of a table along with ecological releases

Given in Hydrology Chapter and in Environmental Flow Assessment report by CIFRI

B.

The CIFRI should conduct the study during monsoon period also so as to establish ecological releases during monsoon season also. This is already there in the original TOR.

Environmental Flow Assessment report by CIFRI appended as a separate volume

C. A study on minimum Environmental flow requirement should be conducted

Environmental Flow Assessment report by CIFRI appended as a

by the project proponent. The study should include assessment of minimum environmental flow requirement for

three seasons i.e. lean, non-lean & non-monsoon and monsoon seasons. Ecological release shall take into account all downstream needs including sustenance of aquatic life. The cumulative release to the

downstream of both Dri and Tangon dam's supplemented release of dam toe powerhouse should be of the order of 25% and should attain 30% within 2 Km from the dams.

separate volume

D.

Daily observed flow data at site along

with the observed rainfall data to be submitted in hard copy as well as in soft format.

Covered in Annexure IV EIA,

Hydrology, Chapter-4.

E.

The Consultant engaged for preparation of EIA/EMP report has to be registered with Quality Council of

India (QCI)/NABET under the scheme of Accreditation & Registration of MoEF. This is a pre-requisite.

Attached at the beginning of EIA report

F.

Consultants shall include a "Certificate" in EIA/EMP report regarding portion of

EIA/EMP prepared by them and data provided by other organization(s)/

laboratories including status of approval of such laboratories.

Attached at the beginning of EIA report

G.

Information pertaining to Corporate Environmental Responsibility and

Environmental Policy shall be provided in the EIA/EMP Report as per this Ministry’s circular dated 19.5.2012

Covered in Annexure V & VI EMP, Environmental Monitoring Plan,

Chapter-13.

Details of the Project and Site General introduction about the

proposed project. Details of project and site giving L-

sections of all U/S and D/S projects of Dri/Dibang & Tangon Rivers with all relevant maps and

figures. Connect such information as to establish the total length of

interference of Natural River, the total length of the main of the river and the committed unrestricted release from the site of diversion into the main river.

A map of boundary of the project site giving details of protected

areas in the vicinity of project location.

Location details on a map of the project area with contours indicating main project features.

The project layout shall be

superimposed on a contour

Covered in Table 2.1 of EIA, Project Description, Chapter-2.

Covered in Section 3.1 of EIA, Introductin, Chapter-1.

Covered in Figure 2.2 of EIA, Project Description, Chapter-2.

map of ground elevation showing main project features (viz. Location of dam, Head works,

main canal, branch canals, quarrying etc.) shall be depicted in a scaled map.

Layout details and map of the project along with contours with project component clearly marked

with proper scale maps of at least a 1:50,000 scale and printed at least on A3 scale for clarity.

Existence of National Park, Sanctuary, Biosphere Reserve etc.

in the study area, if any, should be detailed and presented on a

map with distinct distances from the project components.

Drainage pattern and map of the river catchment up to the proposed project site.

Delineation of critically degraded areas in the directly draining

catchment on the basis of silt Yield Index as per the methodology of All India Soil and Land Use Survey of India.

Soil characteristics and map of the

project area.

Geological and seismo-tectonic details and maps of the area surrounding the proposed project site showing location of dam site and powerhouse site.

Remote Sensing studies, interpretation of satellite imagery,

topographic sheets along with ground verification shall be used to develop the land use/land cover pattern of the study using overlaying mapping techniques viz. Geographic Information

System (GIS), False Color

composite (FCC) generated from satellite data of project area.

Land details including forests, private and other land.

Demarcation of snow fed and rain fed areas for a realistic

estimate of the water availability.

Different riverine habitats like rapids, pools, side pools and variations in the river substratum - bedrocks, rocks, boulders, sand/silt or clay etc.

need to be covered under the

study.

Given at Figure 6.1 in Chapter 6- Environmental Baseline- Physico-

chemical Parameters Given in Chapter 2 of EMP Volume – Catchment Area Treatment Plan

Given at Figure 6.4 in Chapter 6- Environmental Baseline- Physico-chemical Parameters Given Geology Annexure –V of EIA Volume

Maps generated through Remote Sensing studies given at Figures 7.1 – 7.3 in Chapter 7- Environmental Baseline- Biological Parameters

Land details given in Chapter 2 of EIA

volume

Sampling for aquatic ecology covered all such habitats and details given in Chapter 3 on Methodology in EIA

Volume

Description of Environment and Baseline Data To know the present status of

environment in the area, baseline data with respect to Environmental components air, water, noise, soil, land and biology & biodiversity (flora & fauna), wildlife, socio-economic status etc. should be collected with I

0 km radius of the main components of the project/site i.e. dam site and power house site. The air quality and noise are to be monitored at such locations which are environmentally &

ecologically more sensitive in the study area. The baseline studies should be

collected for 3 seasons Pre-Monsoon, Monsoon and Post Monsoon seasons). The study area should comprise of the following: Catchment area up-to the dam site. Submergence Area

Project area or the direct impact area should comprise of area falling within 10 km radius from the periphery of reservoir, land coming under submergence and

area downstream of dam up-to the

point where Tail Race Tunnel (TRT) meets the river.

Downstream up to 10 km from tip of Tail Race Tunnel (TRT).

Covered in Figure 3.1 of EIA,

Methodology, Chapter-3

Details of the Methodology The methodology followed for

collection of base line data along with details of number of samples and their locations in the map should be included. Study area should be demarcated properly on the appropriate scale map. Sampling sites should be depicted on map

for each parameter with proper legends. For forest classification, Champion and Seth1968) classification should be followed .

Details given in Chapter 3= Methodology of EIA Volume.

Study area delineated according to norms defined in TOR

Methodology for collection of

Biodiversity Data The number of sampling locations should be adequate to get a reasonable idea of the diversity and other attributes of flora and fauna. The guiding principles should be the size of the study area

(larger area should have larger number of sampling locations) an

inherent diversity at the location, as known from secondary sources (e.g. eastern Himalayan and low

Sampling for Biodiversity was done according to standards terrestrial ecology techniques with detailed methodologies adopted for vegetation, mammals, avi-fauna, butterflies, insects and herpetofauna in Chapter 3 – Methodology in EIA Volume

altitude sites should have a larger number of sampling location owing to higher diversity).

The entire area should be divided in grids of 5km X 5km preferably on a GIS domain. Thereafter 25% of the grids should be randomly selected for sampling of which half should

be in the directly affected area (grids including project components such a reservoir, dam, powerhouse, tunnel, canal etc.) and the remaining in the rest of the area (areas of

influence in 10 km radius form project components). At such chosen

location the size and number of sampling units (e.g. quadrats in case of flora/transects in case o fauna) must be decided by species area curves and the details of the same (graphs an cumulative number of species in a tabulated form) should

be provided in the EIA report. Some of the grids on the edges may not be completely overlapping with the study area boundaries. However these should be counted and considered for

selecting 25% of the grids. The

number of grids to be surveyed may come out as a decimal number (i.e. it has an integral and a fractional part) which should be rounded to the next whole number. The conventional sampling is likely

to miss the presence of rare, endangered an threatened (R.E.T.) species since they often occur in low densities and in case of faunal species are usually secretive in behaviour. Reaching the conclusion about the

absence of such species in the study

area based on such methodology is misleading. It is very important to document the status of such species owing to their high conservation value Hence likely presence of such species should be ascertained from secondary

sources by proper literature survey for the said area including referring to field guides which are no available for many taxonomic groups in India. Even literature from studies/surveys in th larger landscapes which include the study area for the concerned project

must be referred to since most species

from adjoining catchments is likely to be present in the catchment in

This methodology was not possible and was not required for this project as sampling for all the biodiversity parameters had already been

completed and even twice according to the TOR already granted. The present TOR was granted only in April, 2013 when primary surveys were had already finished.

The identification of RET species was

done following this method only and same has been discussed in Chapter 3 under sections 3.2.5.5 and 3.2.5.6 in Methodology of EIA volume

question: In fact such literature form the entire state can be referred to. Once a listin of possible R.E.T. species

form the said area is developed, species specific methodologies should be adopted to ascertain their presence in the study area which would be far more conclusive as compared to the conventional sampling. If the need be,

modern method like camera trapping can be resorted to, particularly for areas in the eastern Himalayas an for secretive/nocturnal species. A detailed listing of the literature

referred to, for developing lists of R.E.T. species should be provided in

the EIA reports. The R.E.T. species referred to in this point should include species listed in Schedule I an II of Wildlife (Protection) Act, 1972 and those listed in the red data books (BSI, ZSI an IUCN).

Components of the EIA Study Various aspects to be studied and provided in the EIAIEMP report are as follow:

Physical and Chemical

Environment

Geological & Geophysical Aspects and Seismo - Tectonics

• Physical geography, Topography, Regional Geological aspects and structure of the Catchment.

• Tectonics, seismicity and history of past earthquakes in the area. A site specific study of the earthquake parameters will be done. The results of the site specific earthquake design shall be sent for approval of the

NCSDP (National committee of Seismic Design Parameters, Central Water Commission, New Delhi

for large dams. • Landslide zone or area prone to landslide existing in the study area should be examined.

• Presence of important economic mineral deposit, if any. • Justification for location & execution of the project in relation to structural components (dam height). • Impact of project on geological

environment.

Covered in Geology & Seismo-tectonics as Annexure –V of EIA Volume

Covered in Geology & Seismo-tectonics as Annexure –V of EIA Volume

Meteorology, Air and Noise:

• Meteorology (viz. Temperature,

Relative humidity, wind

speed/direction etc.) to be collected

Covered in Hydrology as Annexure –

IV of EIA Volume

from nearest IMD station. • Ambient Air Quality with parameters viz. Suspended Particulate Matter

(SPM), Respirable Suspended Particulate Matter (RSPM) i.e. suspended particulate materials <10 microns, Sulphur Dioxide (S02) and Oxides of Nitrogen (NOx) in the study area at 6 locations.

• Existing noise levels and traffic density in the study area at 6 locations

Covered in Air Environment, 6.5, Baseline status-Physico –Chemical

Parameters, Chapter-6.

Covered in Noise & Traffic, 6.6, Baseline status-Physico –Chemical Parameters, Chapter-6.

Soil Characteristics

• Soil classification, physical

parameters (viz., texture, porosity, bulk density and water holding capacity) and chemical parameters (viz. pH, electrical conductivity magnesium, calcium, total alkalinity, chlorides, sodium, potassium, organi carbon, available

potassium, available phosphorus, SAR, nitrogen and salinity etc.) (6 locations).

Covered in 6.4 -Baseline status-

Physico –Chemical chapter, Chapter-6

Remote sensing and GIS Studies

Generation of thematic maps viz., slope map, drainage map, soil map, land use and land cover map, etc.

Based on these, thematic map, an erosion intensity map should be prepared.

Covered in Fig nos. 2.1 to 2.6 of CAT plan, Chapter-2

Water Quality

History of the ground water table fluctuation in the study area. • Water quality for both surface water and ground water for (i)

Physical parameters (pH, temperature, electrical conductivity, TSS); (ii) Chemical parameters (Alkalinity, Hardness, BOD, COD, N02, P04, CI, S04, Na, K, Ca, Mg, Silica, Oil & Grease, phenolic compounds,

residual sodium carbonate); (iii)

Bacteriological parameter (MPN, Total coliform) and (iv) Heavy Metals (Pb, As, Hg, Cd, Cr-6, total Cr, Cu, Zn, Fe) (6 locations). • Delineation of sub and micro-watersheds, their locations and

extent based on the All India Soil and Land Use Survey of India (AISLUS), Depat1ment of Agriculture, Government of India. Erosion levels in each micro-watershed and prioritization of micro-watershed through silt yield

index (SYI) method of AISLUS.

Covered in water Quality,7.6, Environmental Baseline status-

Biological Resources, Chapter-7 Sampling done at 11 locations

Covered in Fig 2.4.1 of CAT plan, Chapter-2

Covered in Fig 2.6 of CAT plan, Chapter-2

Water Environment & Hydrology

• Hydro-Meteorology of the

project viz. precipitation (snowfall, rainfall), temperature, relative humidity, etc. Hydro-meteorological studies in the catclm1ent area should be established along-with real time telemetry and

data acquisition system for inflows monitoring. • Run off, discharge, water availability for the project, sedimentation rate, etc. • Basin characteristics

• Catastrophic events like cloud

bursts and flash floods, if any, should be documented. • For estimation of Sedimentation Rate, direct sampling of river flow is to be done during the EIA study. The study should be conducted for minimum one year.

Actual silt flow rate to be expressed in ha-m km2 year-1. • Set up a G&D monitoring station and a few rain gauge stations in the catchment area for collecting data during the investigation.

• Flow series, 10 daily with 90%, 75% and 50% dependable years discharges. • Information on the 10-daily flow basis for the 90 per cent dependable year the flow intercepted at the dam, the flow diverted to the power house and the spill comprising the

environmental flow and additional flow towards downstream of th dam for the project may be given. • The minimum environmental flow shall be 20% of the flow of four consecutive lean months of 90% dependable year, 30% of the average

monsoon flow. The flow for remaining months shall be in between 20-30%, depending on the site specific requirements. A site specific study shall be carried out by an expert organization.

• Hydrological studies/data as approved by CWC shall be utilized in the preparation of EIA/EMP report. Actual hydrological annual yield may also be given in the report. • Sedimentation data available with CWC may be used to find out the loss

in storage over the years.

• A minimum of 1 km distance from the tip of the reservoir to the tail race tunnel should be maintained between

Covered in 4.1 of Hydrology, Chapter

4 of EIA Volume

Covered in 4.1 of Hydrology, Chapter 4 of EIA Volume Covered in 4.1 of Hydrology, Chapter

4 of EIA Volume

Covered in 4.1 of Hydrology, Chapter 4 of EIA Volume

These have been established by the proponent

Covered in 4.1 of Hydrology, Chapter 4 of EIA Volume

Covered in Chapter 8 Impacts under section 8.3 during Operation phase, Assessment of Impacts. Separate study has been conducted by CIFRI

whose report is appended separately

Covered in 4.1 of Hydrology, Chapter 4 of EIA Volume Covered in 4.1 of Hydrology, Chapter 4 of EIA Volume

This condition has been complied and L-section given at Figures 1.2 and 1.3 in Chapter 1 of EIA Volume

upstream and downstream projects.

Biological Environment

Besides primary studies, review of secondary data/literature published for project area on flora & fauna including RET species shall be reported in EIA/EMP report

All these points covered in

Environmental Baseline Status-Biological Resources, Chapter-7

Flora • Characterization of forest types (as per Champion and Seth method) in the study area and extent of each forest type as per the Forest Working Plan. • Documentation of all plant species

i.e. Angiosperm, Gymnosperm, Pteriodophytes, Bryophytes (all groups). • General vegetation profile and floral diversity covering all groups of flora including lichens and orchids. A species wise list may be provided.

• Assessment of plant species with respect to dominance, density, frequency, abundance, diversity index, similarity index, importance value index (IVI) , Shannon Weiner index etc. of the species to be

provided. Methodology used for

calculating various diversity indices along with details of locations of quadrates, size of quadrates etc. to be reported within the study area in different ecosystems. • Existence of National park,

Sanctuary, Biosphere Reserve etc in the study area, if any, should be detailed. • Economically important species like medicinal plants, timber, fuel wood etc. • Details of endemic species found in

the project area.

• Flora under RET categories should be documented using International Union for the Conservation of Nature and Natural Resources (IUCN) criteria and Botanical Survey of India's

Red Data list along-with economic significance. Species diversity curve for RET species should be given. • Cropping pattern and Horticultural Practices in the study area.

Covered in 7.3 Forest Types, of Environmental Baseline Status-Biological Resources, Chapter-7 of EIA Volume Covered in 7.4 of Environmental

Baseline Status-Biological Resources, Chapter-7 of EIA Volume Covered in 7.4 of Environmental Baseline Status-Biological Resources, Chapter-7 of EIA Volume

Covered in sections 7.4.4 & 7.4.5 of Environmental Baseline Status-Biological Resources, Chapter-7 Methodology Covered in 3.2 of Methodology i.e. Chapter 3 of EIA

Volume

Covered in 7.5.4 of Environmental

Baseline Status-Biological Resources, Chapter-7 of EIA Volume Covered in 7.4.6 of Environmental Baseline Status-Biological Resources, Chapter-7 of EIA Volume Covered in 7.4.7 of Environmental

Baseline Status-Biological Resources,

Chapter-7 of EIA Volume

Covered under 6.8 of R&R plan of EMP report

Fauna:

• Fauna study and inventorisation should be carried out for all groups of animals in the study area. Their

present status alongwith Schedule of the species. • Documentation of fauna plankton


(phyto and zooplankton), periphyton, benthos and fish should be done and analysed.

• Information (authenticated) on Avi-fauna and wildlife in the study area. • Status of avifauna their resident/ migratory/ passage migrants etc. • Documentation of butterflies, if any, found in the area. Details of endemic

species found in the project area RET species-voucher specimens should be collected along-with GPS readings to facilitate rehabilitation.

RET faunal species to be classified as per IUCN Red Data list and as

per different schedule of Indian Wildlife (Protection) Act, 1972. • Existence of barriers and corridors, if any, for wild animals. • Compensatory afforestation to compensate the green belt area that will be removed,

if any, as part of the proposed project development and loss of biodiversity. • Collection of primary data on agricultural activity, crop and their

productivity and irrigation facilities

components. • For categorization of sub-catchment into various erosion classes and for the consequent CAT plan, the entire Catchment (Indian Portion) is to be considered and not only the directly the draining

catchment.

GPS reading of RET species not Provided rather areas of occurrence have been given. Voucher specimen

not collected as it is prohibited RET faunal species identified as per

IUCN & WPA schedules in section 7.5.5 in 7.5 of Environmental Baseline Status-Biological Resources, Chapter-7 of EIA Volume Covered in Compensatory Afforestation Chapter 12 of EMP

volume Covered in R&R plan

Covered in CAT plan Chapter 2 of EMP volume

Aquatic Ecology • Documentation of aquatic fauna like macro-invertebrates, zooplankton, phytoplantktons, benthos etc. • Fish and fisheries, their migration

and breeding grounds. • Fish diversity composition and maximum length & weight of the measured populations to be studies for estimation of environmental flow. • Conservation status of aquatic

fauna. • Sampling for aquatic ecology and fisheries and fisheries must be conducted during three seasons - Pre-monsoon (summer), monsoon and winter. Sizes (length & weight) of important fish species

need to be collected and breeding

and feeding grounds should also be identified along the project site or in vicinity.

Covered in 7.6.2, of Environmental Baseline Status-Biological Resources, Chapter-7 of EIA Volume

Socio-Economic

• Collection of baseline data on human settlements, health status of the community and existing infrastructure facilities for social welfare including sources of livelihood, job opportunities and

safety and security of workers and surroundings population. • Collection of information with respect to social awareness about the developmental activity

in the area and social welfare measures existing and proposed by

project proponent. • Collection of information on sensitive habitat of historical, cultural and religious and ecological importance. • The socio-economic survey/ profile within 10 km of the

study area for demographic profile; Economic Structure; Developmental Profile; Agricultural Practices; Infrastructure, education facilities; health and sanitation facilities;

available communication network etc.

• Documentation of demographic, Ethnographic, Economic Structure and development profile of the area. • Information on Agricultural Practices, Cultural and aesthetic sites, Infrastucture facilities etc. • Information on the dependence of

the local people on minor forest produce and their cattle grazing rights in the forest land. • List of all the Project Affected Families with their name, age, educational qualification, family size,

sex, religion, caste, sources of

income, land & house holdings, other properties, occupation, source of income, house/land to be acquired for the project and house/land left with the family, any other property, possession of cattle, type of house

etc. • Special attention has to be given to vulnerable groups like women, aged persons etc. and to any ethnic/indigenous groups that are getting affected by the project.

Covered in R&R plan and SIA report, in a separate volume

Impact Prediction and Mitigation

Measures The adverse impact due to the proposed project should be

Covered in Chapter 8 Impacts under

section 8.3

assessed and effective mitigation steps to abate these impacts should be described.

Air Environment Changes in ambient and ground level concentrations due to total emissions from point, line and area sources.

• Effect on soil, material, vegetation and human health. • Impact of emissions from DO set used for power during the construction, if any, on air environment.

• Pollution due to fuel combustion in

equipments and vehicles • Fugitive emissions from various sources

Covered in Chapter 8 Impacts under section 8.3 during Operation phase, Assessment of Impacts of EIA Volume

Water Environment • Changes in surface and ground water quality

• Steps to develop pisci-culture and recreational facilities • Changes in hydraulic regime and downstream flow. • Water pollution due to disposal of sewage

• Water pollution fi:om labour

colonies/ camps and washing equipment.


Land Environment

• Adverse impact on land stability, catchment of soil erosion, reservoir sedimentation and spring flow (if any) (a) due to considerable road construction I widening

activity (b) interference of reservoir with the inflowing stream (c) blasting for

commissioning ofHRT, TRT and some other structures. • Changes in land use I land cover and drainage pattern

• Immigration of labour population • Quarrying operation and muck disposal • Changes in land quality including effects of waste disposal • River bank and their stability • Impact due to submergence.

Covered in Assessment of Impacts

chapter -8 of EIA Volume

Biological Environment • Impact on forests, flora, fauna including wildlife, migratory avi-

fauna, rare and endangered species, medicinal plants etc.


• Pressure on existing natural resources • Deforestation and disturbance to

wildlife, habitat fragmentation and wild animal's migratory corridors • Compensatory afforestation-identification of suitable native tree species for compensatory afforestation and green belt.

• Impact on fish migration and habitat degradation due to decreased flow of water • Impact on breeding and nesting grounds of animals and fish.

Socio-economic aspects • Impact on local community including demographic profile. • Impact on socio-economic status • Impact on economic status. • Impact on human health due to water I vector borne disease

• Impact on increase traffic • Impact on Holy Places and Tourism • Impacts of blasting activity during project construction which generally destabiliz the land mass and leads to landslides, damage

to propet1ies and drying up of natural springs and cause noise population will be studies. Proper record shall be maintained of the baseline information in the post project period. • Positive and negative impacts likely

to be accrued due to the project are listed


Environmental Management Plans

Catchment Area Treatment (CAT)

Plan should be prepared micro-watershed wise. Identification of free draining/ directly

draining catclm1ent based upon Remote Sensing and Geographical Information System (GIS) methodology and Sediment Yield Index

(SYI) method of AISLUS, Deptt. of Agriculture, Govt. of India coupled with ground survey. Areas or watersheds falling under 'very severe' and 'severe' erosion categories should be provided and required to be treated. Both biological as well as engineering

measures should be proposed in consultation with State Forest Department for areas requiring

treatment. Year-wise schedule of work and monetary allocation should be provided. Mitigation

Covered in CAT plan Chapter-2 of EMP report

measures to check shifting cultivation in the catchment area with provision for alternative and better

agricultural practices should be included.

Compensatory Afforestation shall be prepared by the State Forest

Department in lie of the forest land proposed to be diverted for construction of the project as per the Forest (Conservation) Act, 1980. Choice of plants for afforestation should include

native and RET species,

if any. This will be a pat1of the forest clearance proposal.

Covered in Compensatory Afforestation Chapter 10 of EMP

report

Biodiversity and Wildlife Conservation and Management Plan for the conservation and preservation of rare, endangered or

endemic floral/faunal species or some National Park/Sanctuary/ Biosphere Reserve or other protected area is going to get affected directly or indirectly by construction of the project, then

suitable conservation measures should

be prepared in consultation with the State Forest Department and with th physical and financial details. Suitable conservation teclmiques (in-situ/ex-situ) will b proposed under the

plan and the areas where such conservation is proposed will be marked on a project layout map.


Fisheries Conservation and Management Plan - a specific fisheries management measures

should be prepared for river and reservoir. If the construction of fish ladder/ fish-way etc. is not feasible then measures for reservoir fisheries

will be proposed. The plan will detail out the number of hatcheries, nurseries, rearing ponds etc. proposed under the plan with proper drawings. If any migratory fish species is getting affected then the migratory routes, time/season of upstream and

downstream migration spawning grounds etc will be discussed in details.

Covered in Fishery Conservation & Management plan, Chapter-3 of EMP

volume

Resettlement and Rehabilitation Plan needed to be prepared on the

Covered in R&R plan as a separate

basis of finding of the socio-economic survey coupled with the outcome of public consultation held. Th

R&R package shall be prepared after consultation with the representatives of the project affected families and the State Government. Detailed budgetary estimates are to be provided. Resettlements site should

be identified. The plan will also incorporate community development strategies.

volume

Green Belt Development Plan along the periphery of the reservoir,

approach roads

around the colonies and other project components, local plant species must be suggested with physical and financial details. A layout map showing the proposed sites for developing the green belt should be prepared.

Covered in Chapter-8, landscaping,

restoration and Green belt

development chapter EMP Volume.

Reservoir Rim Treatment Plan for stabilization of land slide/ land slip zones, if any, around the reservoir periphery is to be prepared based on detailed survey of geology of the

reservoir rim area. Suitable

engineering and biological measures for treatment of identified slip zones to be suggested with physical and financial schedule. Layout map showing the landslide/landslip zones shall be prepared and appended in the

chapter.

Covered in Chapter-9, Reservoir Rim Treatment Plan chapter EMP Volume.

Muck Disposal Plan suitable sites for dumping of excavated materials should be identified in

consultation with State Pollution Control Board and State Forest Department. All muck disposal sites

should be minimum 30 m away from the HFL of river. The quantity of muck to be generated and the quantity of muck proposed to be utilized shall be

calculated in consultation with the project authorities. Details of each dumping site viz. area, capacity, total quantity of muck that can be dumped etc. should be worked out and discussed in the plan. Plan for rehabilitation of muck disposal sites

should also be given. The L-section I cross section of muck disposal sites and approach roads should be given.

The plan shall have physical and financial details of the measures proposed. Layout map showing the

Covered in Muck Dumping plan,Chapter-7 of EMP Volume

Covered in Figures 7.2 – 7.19,

Dumping Sites cross sections, Muck Dumping plan,Chapter-7 of EMP Volume

Covered in Figure 7.1, Layout map

dumping sites vis-a-vis other project components will be prepared and appended in the chapter.

showing Dumping Sites in Chapter Muck Dumping plan,Chapter-7 of EMP Volume

Restoration Plan for Quarry Sites and landscaping of colony areas, working areas, roads etc. Details of the coarse/fine aggregate/clay etc. required for construction of the project

and the rock/clay quarries/river shoal sites identified for the project should be discussed along-with the engineering and Biological measures proposed for their restoration with physical and financial

details. Layout map showing quarry

sites vis-a vis other project components, should be prepared

Covered in Landscaping and Restoration of Quarry areas, construction areas Chapter-8 of EMP Volume

Study of Design Earthquake Parameters: A site specific study of earthquake parameters should be done. Results of the site specific

earthquake design parameters should be approved by National Committee of Seismic Design Parameters, Central Water Commission (NCSDP), New Delhi.

Covered in Geology & Seismicity Chapter appended as Annexure – V in EIA report

Dam Break Analysis and

Disaster Management Plan The outputs of dam break model should be illustrated with appropriate graphs and maps clearly bringing out the impact of Dam Break scenario. To

identify inundation areas, population and structures likely to be affected due to catastrophic floods in the event of dam failure. DMP will be prepared with the help of Dam Break Analysis. Maximum water level that would be

attained at various points on the downstream in case of dam break will be marked on a detailed contour map

of the downstream area, to show the extent of inundation. The action plan will include Emergency Action and Management plan including measures

like preventive action notification, warning procedure and action plan for co-ordination with various authorities.

Covered in Dam Break modeling, Chapter-11.

Water, Air and Noise Management Plans to be implemented during

construction and post-construction periods.

Covered in Air, Water Environment Management plan, Chapter-10.

Public Health Delivery Plan including the provisions of drinking

water supply to local population

shall be in the EIA/EMP Report.

Covered in Public Health Delivery System, Chapter-5 of EMP volume

Status of the existing medical facilities in the project area shall be discussed. Possibilities of strengthening of

existing medical facilities, construction of new medical infrastructure etc. will be explored after assessing the need of the labour force and local populace.

Labour Management Plan for their Health and Safety. Sanitation and Solid waste management plan for domestic waste from colonies an labour camps

etc.

Covered in Solid waste Management plan, Chapter-4.

Local Area Development Plan to be formulated in consultation with the Revenue Officials and Village Pancahayats. Appropriate schemes shall be prepared under EM for the Local Area Development Plan with

sufficient financial provisions.


Environmental safeguards during construction activities including Road Construction.

Covered in Chapter 10 of EMP report

Energy Conservation Measures for the work force during construction with physical and financial details.

Alternatives will be proposed for the labour force so that the exploitation of the natural resource (wood) for the domestic and

commercial use i curbed.

Covered in Energy Conservation Measures Chapter-6 of EMP volume.

Environmental Monitoring Programme to monitor the mitigatory measure implemented at the project site is required will be

prepared. Provision for Environmental Management Cell should be made. The plan will spell out the aspects required to be monitored, monitoring indicators/parameters with respect to

each aspect and the agency responsible for the monitoring

of that particular aspect throughout the project implementation.

Covered in Environmental Monitoring programme of EMP, Chapter-13.

A summary of Cost Estimates for all the plans, cost for implementing all the

Environmental Management Plans.

Given in Cost Estimates of EMP, Chapter-14.

Etalin Hydroelectric Project (3097 MW) Detailed Project Report

Volume-I: Main Report Part-A: Chapters 1 to 9

169126-40ER-0009-00 i

TABLE OF CONTENTS

PAGE NO. 1. PROJECT HYDROLOGY ......................................................................................... 1-1

1.1 Introduction ...................................................................................................... 1-1

1.1.1 Adopted Conventions ........................................................................... 1-1

1.2 Basin Characteristics ....................................................................................... 1-2

1.2.1 River System and Basin Characteristics ............................................... 1-2

1.2.2 River Brahmaputra ............................................................................... 1-2

1.2.3 River Dibang ........................................................................................ 1-2

1.2.4 The Catchment ..................................................................................... 1-3

1.2.5 Hypsometric Details ............................................................................. 1-4

1.2.6 Assessment of Snowfed and Rainfed Catchment Areas ....................... 1-5

1.3 Water Availability Studies ................................................................................ 1-5

1.3.1 Data Availability .................................................................................... 1-5

1.3.2 Consistency Checks of Rainfall and Discharge Data ............................ 1-5

1.3.3 Type of Project ..................................................................................... 1-6

1.3.4 Period of Data Required ....................................................................... 1-6

1.3.5 Computation of Water Availability Series .............................................. 1-7

1.3.6 Flow Duration Curves ......................................................................... 1-13

1.4 Design Flood ................................................................................................. 1-14

1.4.1 General .............................................................................................. 1-14

1.4.2 Criteria for Estimation of Design Flood ............................................... 1-14

1.4.3 Computation of Design Flood - PMF .................................................. 1-14

1.4.4 Physiographic Parameters of the Catchment ..................................... 1-15

1.4.5 Derivation of Unit Hydrograph ............................................................ 1-16

1.4.6 Design Storm ..................................................................................... 1-18

1.4.7 Design Loss Rate ............................................................................... 1-20

1.4.8 Critical Sequence of Rainfall Excess .................................................. 1-20

1.4.9 Base flow and Snow melt ................................................................... 1-21

1.4.10 Surface Flow Hydrograph ................................................................... 1-21

1.4.11 Flood Hydrograph .............................................................................. 1-21

1.4.12 Design Flood for River Diversion Works ............................................. 1-24

1.4.13 Data ................................................................................................... 1-24

1.4.14 Statistical Parameters ........................................................................ 1-25

1.4.15 Flood Frequency Analysis .................................................................. 1-26

1.4.16 Selection of Diversion Flood ............................................................... 1-26

1.5 Sedimentation ................................................................................................ 1-30

1.5.1 Need for Sediment Evaluation ............................................................ 1-30

1.5.2 Reservoir Sediment Rate ................................................................... 1-30

Arun

Typewritten Text

Annexure-IV



169126-40ER-0009-00 ii

1.5.3 Reservoir Elevation-Area-Capacity ..................................................... 1-30

1.5.4 Sedimentation Aspects of Reservoirs ................................................. 1-32

1.5.5 Type and Shape of the Reservoirs ..................................................... 1-32

1.5.6 Sediment Accumulation ...................................................................... 1-32

1.6 Glacial Lake Outburst Flood (GLOF) .............................................................. 1-34

1.7 References .................................................................................................... 1-35



169126-40ER-0009-00 iii

LIST OF TABLES

PAGE NO. Table 1: Details of minimum length of flow data ................................................................. 1-7

Table 2: 10-Daily Average flow series (m3/s) for Dri Limb (1986-87 to 2008-09) ................ 1-9

Table 3: 10-Daily Average flow series (m3/s) for Talo (Tangon) Limb (1986-87 to 2008-09) . 1-11

Table 4: Classification Criteria of Hydraulic Structures ..................................................... 1-14

Table 5: Breakup of Catchment Area ............................................................................... 1-15

Table 6: River Length Parameters .................................................................................... 1-15

Table 7: Sub-Zone 2a Unit Hydrograph Parameters ......................................................... 1-16

Table 8: Standard Project Strom (SPS) and Probable Maximum Precipitation (PMP) Values ......................................................................................................................................... 1-19

Table 9: Temporal Distribution of the SPS and PMP ........................................................ 1-19

Table 10: PMP Distribution for Dri limb ............................................................................. 1-20

Table 11: PMP Distribution for Talo (Tangon) limb ........................................................... 1-20

Table 12: Design Flood (PMF) ......................................................................................... 1-21

Table 13: Design Flood Hydrograph (PMF) Values .......................................................... 1-23

Table 14: Transfer Factor for Elopa and Munli Peak Flows .............................................. 1-25

Table 15: Final Peak Flows at Dri and Talo (Tangon) Limbs ............................................ 1-25

Table 16: Statistical Parameters of Peak Flows at Dri and Talo (Tangon) Limbs .............. 1-26

Table 17: Detail of 25 year Return Period Flood (m3/s)..................................................... 1-26

Table 18: Diversion Flood (m3/s) at Etalin dam sites ........................................................ 1-27

Table 19: Revised Area Capacity of Dri Reservoir after Sediment Accumulation to Crest Level of El. 990 m ............................................................................................................ 1-33

Table 20: Revised Area Capacity of Talo (Tangon) Reservoir after Sediment Accumulation to Crest Level of El. 1018 m ............................................................................................. 1-34



169126-40ER-0009-00 iv

LIST OF FIGURES PAGE NO

Figure 1: Hypsometric Curve of Etalin on Dri/Dibang .......................................................... 1-4

Figure 2: Hypsometric Curve of Etalin on Talo (Tangon) ................................................... 1-4

Figure 3: Details of Data Availability ................................................................................... 1-6

Figure 4: Flow Duration curve for Dri Limb of Etalin.......................................................... 1-13

Figure 5: Flow Duration curve for Talo (Tangon) Limb of Etalin ........................................ 1-13

Figure 6: SUH of Dri limb ................................................................................................. 1-17

Figure 7: SUH of Talo (Tangon) limb ................................................................................ 1-18

Figure 8: PMF Hydrograph for Dri Limb ............................................................................ 1-22

Figure 9: PMF Hydrograph for Talo (Tangon) Limb .......................................................... 1-22

Figure 10: Return Period Flood for Different Working Seasons on Dri Limb ..................... 1-28

Figure 11: Return Period Flood for Different Working Seasons on Talo (Tangon) Limb .... 1-29

Figure 12: Elevation-Area-Capacity Curve of Dri Reservoir .............................................. 1-31

Figure 13: Elevation-Area-Capacity Curve of Talo (Tangon) Reservoir ............................ 1-31



169126-40ER-0009-00 1-1

1. PROJECT HYDROLOGY

1.1 Introduction

Hydrological inputs play a vital role in planning, execution and operation of any water

resources development project. Hydrological studies are carried out at all stages of project

development starting from the pre-feasibility stage and are continued even during the

operation of the project. Hydrological assessment of a river valley project is carried out with

a view to:

Assess quantity of water available in the river for power generation and its variation

with time.

Estimate design flood and diversion flood required for hydraulic design of spillway

and temporary diversion structure as well as for safety of the structure.

Assess impact of sedimentation on the live storage with reference to the life of

reservoir.

Etalin Hydroelectric Project envisages diversion of water of two rivers, namely Dri/Dibang

and Talo (Tangon), having their confluence at village Etalin. The project consists of two

limbs, one on Dri river and another on Talo (Tangon) river, each consisting of a diversion

structure and a water conductor system with the later culminating in a single powerhouse

located underground in hill mass at the confluence of the two rivers. The project is located

upstream of Dibang Multipurpose Project which is being developed by NHPC. The proposed

dam site of Dibang project is located at Munli village.

As per the project planning based on detailed reconnaissance of site and assessment of

topographic and geological features, the project envisages construction of a 101.5 m high

Concrete Gravity Dam on Dri/Dibang and a 80 m high Concrete Gravity Dam on Talo

(Tangon). The dam on Dri/Dibang is located at Latitude 28º42'24"N and Longitude

95º51'52"E, while the dam on Talo (Tangon) is located at Latitude 28º39'18"N and Longitude

96º00'07" E. Dam site of Dibang project is proposed at Munli village, with Latitude

28º20'07"N and Longitude 95º46'38"E.

1.1.1 Adopted Conventions

The following conventions have been adopted for the present study:

The hydrological year runs from June to May of the following calendar year;



169126-40ER-0009-00 1-2

The monsoon season is defined from May to September;

The non-monsoon season is defined from October to April of the following calendar

year.

1.2 Basin Characteristics

1.2.1 River System and Basin Characteristics

The Dri and Talo (Tangon) rivers form part of the Dibang basin, which is situated in the

North Eastern part of India with its catchment entirely within the Indian Territory bordering

Tibet. Barring a small portion in the Tinsukia district of Assam, the basin mostly lies in the

Dibang Valley District / Lower Dibang Valley District of Arunachal Pradesh. The basin is

bounded by Tibet on its North, Lohit basin towards East, Siang basin on its West and

Lohit/Brahmaputra River on its South. Although, the whole of the catchment falls within the

Indian boundary, the Northern most catchment lies within the snowbelt. However, most of

the discharge contribution of the river comes from rainfall.

1.2.2 River Brahmaputra

Brahmaputra River which is known as Yarlung Tsangpo in Tibet originates from

Kailash Mansarovar Lake located in the western part of Tibet. This river traverses through

the Shigatse town and Yarlung Valley and crosses Lhasa, the capital of Tibet. It then takes

an eastern turn and crosses Kongpo area before turning to south and then enters Arunachal

Pradesh where it is known as Siang. After meeting its two important tributaries, Lohit and

Dibang this river enters the Assam plains, where it is called Brahmaputra. The river drains to

Bangladesh before joining the Ganga to form Meghna and also create a large delta called

Sunderbans.

1.2.3 River Dibang

The river Dibang is one of the major tributaries of the Brahmaputra river system, contributing

about 8.5% of its annual discharge. The river originates from the snow covered southern

flank of the Himalayas close to the Tibet border at an Elevation of more than 5000m. It cuts

through deep gorges and difficult terrain in its upper reach through the great Himalayan

range in Dibang Valley district of Arunachal Pradesh and finally meets the river Lohit near

Sadia in Assam. The combined flow meets Brahmaputra near Kobo Chapari.



169126-40ER-0009-00 1-3

The river emerges from hills and enters the sloping plain areas near Nizamghat in Arunachal

Pradesh, from where the river flows for a distance of about 50 km to meet the river Lohit.

Although there is no hill in between this reach, the river gradient is very steep for such a

large river; in this 50 km reach, the river looses a height of about 160 m. In this portion, the

river is highly braided and destructive in nature. It branches out into a number of channels,

somewhere as many as 15 numbers and occupies a width of about 4 to 9 km. The river

changes its course quite often destroying large tracts of jungle and cultivable land and floods

occur in the low lying areas of Sadiya in Tinsukia District of Assam.

The Dri River after its confluence with Mathun near village Mathuli is known as Dri / Dibang

and has got a moderate to steep gradient. The river, as it flows down, is met by streams

called Ange from the left and Mathun from the right. Further downstream Talon/Talo

(Tangon) joins the river from the left and following this confluence the river is named as

Dibang.

Talo (Tangon) river, originate at an altitude of more than EL 5000 m and joins it near village

Etalin. The river after originating near Kayapass flows in Western direction before meeting

Dibang. Pothe Pani, Edzon River, Edza River, Ipi Pani, Davu Pani are some of the tributaries

of the Talo (Tangon) river.

1.2.4 The Catchment

The catchment area of Etalin project up to the proposed dam site on Dri/Dibang limb is

3685 km2 whereas the catchment area of the project up to proposed dam site on Talo

(Tangon) limb is 2573 km2. Dibang River has a total length 195 km from its origin to

confluence with Lohit. The length of the rivers up to the proposed diversion structures is

estimated as around 90 km and 74 km, respectively, on Dri/Dibang and Talo (Tangon) limbs.

The project is in highly mountainous terrain where NE-SW trending Himalayan ranges meet

with the Arakan Yoma range. The project area is marked by highly dissected topography

having precipitous hills and deep comparatively narrow valleys. Emra, Talo (Tangon) and

Mathun are the main tributaries in the upper reach of the river. Small tributaries like Ahi,

Ithun, Airi Pani, Ashu Pani, Ephi Pani, Deo Pani etc., meet the river in its lower reach.

The important feature is that all the tributaries barring Ephi Pani and Deo Pani join Dibang in

its hilly catchment. The catchment of the Dibang River is comparatively wider in its upper

reach.



169126-40ER-0009-00 1-4

1.2.5 Hypsometric Details

The catchment area detail with elevation has been worked out for both the catchments on

Dri/Dibang and Talo (Tangon). The hypsometric curves for the two dam sites of the project

are given below:

HYPSOMETRIC CURVE OF ETALIN ON DRI (DIBANG)

0

1000

2000

3000

4000

5000

6000

0 500 1000 1500 2000 2500 3000 3500 4000Area above Elevation (km2)

Elev

atio

n (m

)

Figure 1: Hypsometric Curve of Etalin on Dri/Dibang

HYPSOMETRIC CURVE OF ETALIN ON TANGON

0

1000

2000

3000

4000

5000

6000

0 500 1000 1500 2000 2500 3000Area above Elevation (km2)

Elev

atio

n (m

)

Figure 2: Hypsometric Curve of Etalin on Talo (Tangon)

TALO (TANGON)



169126-40ER-0009-00 1-5

1.2.6 Assessment of Snowfed and Rainfed Catchment Areas

The permanent snow line has been taken at an elevation of 4500 m as approved by CWC in

the case of Dibang Multipurpose Project, which, as mentioned earlier, is located just

downstream of this project. Using this assumption, the snowfed catchment area at Etalin on

Dri/Dibang has been worked out to be 128 km2 and at Etalin on Talo (Tangon) has been

worked out to be 176 km2. The rainfed catchment areas at Etalin on Dri/Dibang and Etalin on

Talo (Tangon) are 3557 and 2397 km2, respectively. It may therefore be concluded that only

3.5% and 6.8% of the total area at Etalin on Dri/Dibang and Etalin on Talo (Tangon) are

covered with permanent snow.

1.3 Water Availability Studies

1.3.1 Data Availability

Data relevant to hydrological assessment of the project, as available for the present study, is

shown in Figure 7-3. Most of the rainfall and G&D data of Dibang basin has been collected

from Brahmaputra Board. Data for Munli dam has been collected from NHPC, while the

rainfall data at Roing has been sourced locally.

1.3.2 Consistency Checks of Rainfall and Discharge Data

Detailed calculations on water availability and flood magnitude will lead to selecting the

design features of the project (installed capacity, turbine flow, spillway capacity, etc.).

Those features will directly reflect on the project cost and on the quantity and value of

energy produced. It is therefore necessary to confirm the validity of the basic data used in

the calculations. This verification was carried out for the two types of data, namely

precipitation and discharge, which is most likely to be subject to uncertainties. The details of

consistency checks has been provided in the Volume II (Hydrological Studies) of DPR.



169126-40ER-0009-00 1-6

Chapakhowa

Epipani F F

Aharline

Anini

HunliRoing

Jiagaon

Elopa

Munli F

Asupani

Christian Basti F

LegendFull Year (>330 days)270 -330 days95 - 270 days

F < 95 days (Few data)

Daily precipitation data

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1997

1991

1992

1993

1994

1995

1996

2010

2003

2004

2005

2006

2009

1998

2007

2008

1999

2000

2001

2002

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2010

2002

2003

2004

2005

2009

2006

2007

2008

Rain Gauge Station

Daily discharge data

G&D Station

Figure 3: Details of Data Availability

1.3.3 Type of Project

This project is a combination of two "run-of-the-river” Schemes which are being developed

purely for hydroelectric power generation purpose. Both the schemes involve a large dam

and a long water conductor system in the form of a headrace tunnels. The underground

powerhouse complex houses the turbine-generator units.

1.3.4 Period of Data Required

As per the Working Group constituted by the Ministry of Water Resources, Govt. of India for

setting “Guidelines for Preparation of Detailed Project Reports of Irrigation & Multipurpose

Projects”, minimum length of flow series at different project sites should be:



169126-40ER-0009-00 1-7

Table 1: Details of minimum length of flow data

Type of Project Minimum length of data

Diversion Project 10 years

Within year storage project 25 Years

Over the year storage project 40 Years

However, perhaps these guidelines were evolved when Irrigation projects, requiring 75%

reliability in meeting the targets, were far more common. The hydroelectric projects are

generally required to meet the targets with 90% reliability, and thus only one failure here

would be allowable in a 10 year data. Thus, a 10 year series may perhaps be not very

representative of the failure years and it is felt that for run-of-the-river hydroelectric projects,

if possible, a longer series needs to be developed.

1.3.5 Computation of Water Availability Series

The methodologies of flow series assessment for the project at the two dam sites are as

follows:

Concurrent data of rainfall at Roing and discharge at Elopa for the period from

1998-2008/09 and concurrent data of average of rainfall at Roing and Jiagaon is

available for the period of 1998-2005.

Correlation between the standardized values of the concurrent period (1998-2008/09)

discharge data at Elopa with Roing rainfall has been done for the high flow months

i.e., May to October.

Correlation between the standardized values of the concurrent period (1998-2005)

discharge data at Elopa with the average of Roing and Jiagaon rainfall has been

done for the high flow months i.e., May to October.

Based on the correlation of Roing rainfall with Elopa discharge data, discharge at

Elopa has been extended for the month of May to Oct for the period of 1986 to 1991

and based on the correlation result obtained with the average of Roing and Jiagaon

rainfall, discharge at Elopa has been extended for the for the month of May to Oct for

period of 1991 to 1997. The details of correlations and analysis have been given in

the Volume II (Hydrological Studies) of DPR.

Because auto correlation and the earlier period flows forms a causative factor with

the current period rainfall, extension of low flow months i.e., Nov-Apr at Elopa for the



169126-40ER-0009-00 1-8

period 1986 to 1997 has been carried out based on the percentage of ratio of non-

monsoon (low-flow) flow with that of monsoon (high-flow) period. The percentage of

ratio of non-monsoon (low-flow) flow with that of monsoon (high-flow) period for the

available discharge data (1998-2008) has been found to be 0.364 and proposed to

maintain the same ratio for the extended period also (1986-1997). The methodology

of extension of low flows has been arrived amid consultation with CWC.

Correlation between the total inflow of high flow months (May-Oct) and low flow

(Nov-Apr) months for the available discharge data at Elopa for the period from

1998 to 2008 has been worked out. Based on the correlation developed the total

inflow (MCM) for low-flow months has been worked out from the total inflow (MCM) of

high flow months for the extended period of 1986 to 1997.

Assuming that the low-flow months i.e., non-monsoon period flows behave in a

similar pattern for all the years, the total inflow for low-flow months (Nov-Apr) has

been distributed to 10-daily average values based on the percentage of each 10-daily

worked out from the available discharge data for the period from 1998 to 2008.

To this extended period of data, the observed data at Elopa from 1998-2008/09 were

appended. Thus a complete series from the period from 1986 to 2008/09 has been

developed at Elopa.

Finally, the discharge series at Elopa for the period from 1986-2008/09 has been

transposed to Etalin project sites i.e., Dri limb and Talo (Tangon) limb. The

methodology of transposition has been derived in consultation with CWC.

Elopa Series has been reduced by 10% for observational errors. After reducing Elopa

series by 10%, the flow series has been transposed to the respective dam sites of

Etalin by catchment area proportion with a rainfall variability of 0.958 for Dri limb and

0.874 for Talo (Tangon) limb.

Thus the flow series at Etalin has been worked out as per the methodology adopted/arrived

in consultation with CWC are given in Table 7-2 and Table 7-3, respectively.

The details of the methodology and subsequent analysis has been provided in the

Volume II (Hydrological Studies) of DPR.

CEA/CWC has already given the concurrence for the Water Availability and the

Methodology.



169126-40ER-0009-00 1-9

Table 2: 10-Daily Average flow series (m3/s) for Dri Limb (1986-87 to 2008-09)

No of days 1986-87 1987-88 1988-89 1989-90 1990-91 1991-92 1992-93 1993-94 1994-95 1995-96 1996-97 1997-98

10 I 448.19 480.96 480.96 490.66 448.55 453.22 452.71 489.05 448.03 478.07 445.13 766.53

10 II 609.67 639.22 639.22 616.66 626.47 587.58 609.88 595.86 599.32 667.67 597.40 954.08

10 III 537.91 624.17 624.17 865.41 487.65 527.08 568.46 558.04 581.55 766.13 717.34 715.79

10 I 561.55 573.44 633.23 565.17 531.89 589.63 625.60 651.10 610.91 666.24 710.41 763.99

10 II 698.71 712.28 683.33 517.04 530.91 548.53 600.05 702.89 501.61 559.64 1,041.17 809.84

11 III 587.39 793.08 610.77 512.87 517.89 563.64 535.30 563.36 507.77 497.08 898.42 518.17

10 I 430.88 595.93 407.95 381.48 672.65 568.40 648.06 502.20 425.46 532.70 474.11 437.02

10 II 512.29 715.03 499.21 445.60 460.80 440.54 400.32 542.04 551.40 905.20 765.85 496.00

11 III 558.20 598.08 421.68 439.49 760.94 614.22 634.61 440.97 453.37 460.08 515.64 361.55

10 I 456.91 523.61 590.22 445.35 525.57 669.81 614.08 387.30 421.32 335.45 474.51 404.67

10 II 434.89 312.34 366.35 579.45 522.39 426.56 433.33 317.94 379.95 373.12 352.64 471.88

10 III 274.64 385.34 347.22 573.23 611.99 286.11 325.77 343.82 259.83 514.30 407.25 461.37

10 I 371.26 321.48 318.60 716.11 434.01 434.65 409.59 357.44 584.69 385.50 415.78 335.05

10 II 242.97 250.22 235.76 305.11 280.22 266.78 268.44 248.58 243.34 297.56 257.37 239.66

11 III 178.99 215.46 218.70 247.87 249.90 178.99 208.87 242.80 203.32 203.32 246.88 223.57

10 I 149.67 162.11 153.56 167.27 160.63 154.31 155.47 150.68 148.32 159.11 168.23 166.49

10 II 145.67 157.78 149.45 162.80 156.33 150.18 151.31 146.65 144.35 154.85 163.73 162.04

10 III 127.13 137.70 130.43 142.08 136.44 131.07 132.05 127.99 125.98 135.14 142.90 141.42

10 I 111.62 120.89 114.51 124.74 119.78 115.07 115.94 112.37 110.61 118.65 125.45 124.16

10 II 107.21 116.12 109.99 119.81 115.06 110.53 111.36 107.93 106.24 113.97 120.50 119.25

11 III 101.37 109.79 104.00 113.28 108.79 104.50 105.29 102.05 100.45 107.75 113.94 112.76

10 I 105.02 99.48 108.36 104.06 99.96 100.71 97.62 96.08 103.07 108.98 107.85 122.25

10 II 103.14 97.70 106.42 102.20 98.18 98.92 95.87 94.37 101.23 107.04 105.93 112.50

11 III 106.57 100.94 109.96 105.59 101.43 102.20 99.05 97.50 104.59 110.59 109.44 112.29

10 I 108.41 102.69 111.86 107.42 103.19 103.97 100.77 99.19 106.40 112.51 111.34 150.05

10 II 122.57 116.10 126.47 121.45 116.67 117.55 113.93 112.14 120.30 127.20 125.88 140.60

8 III 145.69 138.00 150.32 144.36 138.67 139.72 135.42 133.29 142.99 151.19 149.62 150.94

10 I 154.97 146.79 159.90 153.55 147.51 148.62 144.04 141.78 152.09 160.82 159.15 211.19

10 II 185.71 175.91 191.62 184.01 176.77 178.10 172.62 169.91 182.26 192.72 190.72 205.00

11 III 271.18 256.87 279.81 268.70 258.12 260.06 252.06 248.11 266.15 281.42 278.50 273.45

10 I 301.23 285.33 310.81 298.47 286.72 288.88 280.00 275.60 295.64 312.60 309.36 244.39

10 II 428.39 405.78 442.02 424.47 407.76 410.83 398.20 391.95 420.45 444.57 439.96 566.93

10 III 465.76 441.18 480.58 461.51 443.34 446.67 432.93 426.14 457.13 483.35 478.34 527.51

10 I 382.23 382.23 626.70 367.56 370.03 363.00 408.42 365.26 400.34 345.46 329.81 414.34

10 II 434.48 434.48 584.60 375.75 455.81 419.23 436.28 379.98 415.20 444.45 550.14 366.42

11 III 461.95 461.95 558.89 497.38 428.46 389.34 345.44 423.64 370.05 409.34 576.73 493.98

10041 10728 10703 10746 10633 10094 10204 9790 9778 10714 11596 11281

2724.9 2911.2 2904.5 2916.2 2885.4 2739.1 2769.1 2656.8 2653.6 2907.5 3146.9 3061.3 Runoff Depth (mm) =

Apr

May

Month

Nov

Dec

Jan

Feb

Jul

Aug

Inflow (MCM) =

Sep

Oct

Mar

Jun

Contd. on next page……



169126-40ER-0009-00 1-10

Table 2 (Contd…): 10-Daily Average flow series (m3/s) for Dri Limb (1986-87 to 2008-09)

No of days 1998-99 1999-00 2000-01 2001-02 2002-03 2003-04 2004-05 2005-06 2006-07 2007-08 2008-09

10 I 636.45 466.63 796.32 376.86 179.60 428.14 381.81 589.85 751.43 458.02 401.30

10 II 840.42 539.95 894.03 399.67 301.44 652.61 663.69 803.21 883.03 905.53 510.83

10 III 569.25 694.65 1,065.74 348.15 282.87 825.62 968.93 683.03 510.48 596.13 448.19

10 I 777.01 921.03 612.87 375.65 483.45 815.36 962.18 608.13 530.51 402.69 406.03

10 II 1,339.46 387.51 501.85 364.86 607.24 577.34 1,449.22 565.00 471.35 749.32 357.11

11 III 1,053.98 244.32 560.25 551.36 555.72 413.10 714.09 439.59 441.08 1,089.84 561.87

10 I 717.92 348.09 774.65 454.63 354.56 334.47 455.24 689.51 285.88 519.97 314.47

10 II 1,391.50 442.84 607.88 452.17 379.99 429.94 383.03 661.75 248.21 566.30 711.27

11 III 1,153.36 496.65 496.13 531.31 200.56 287.24 364.49 1,168.12 360.62 355.65 772.10

10 I 979.16 267.82 437.84 464.69 138.68 374.84 356.73 735.98 423.23 883.32 678.61

10 II 211.21 270.78 377.00 353.62 252.83 362.23 321.22 651.86 625.53 476.99 300.16

10 III 179.72 158.87 318.78 256.09 559.51 262.87 335.80 1,137.94 260.17 207.23 208.11

10 I 200.94 192.07 303.44 326.98 849.07 368.72 616.77 434.78 291.82 213.52 466.59

10 II 234.29 187.31 233.34 234.41 315.61 259.73 309.02 278.73 139.41 312.63 271.26

11 III 394.48 186.38 216.24 144.69 167.03 209.03 210.85 430.33 103.64 157.18 213.96

10 I 183.76 175.93 158.35 200.81 115.64 146.56 192.45 246.81 86.65 89.49 145.42

10 II 163.26 169.76 154.12 208.07 130.31 116.86 193.01 214.61 90.39 110.85 144.06

10 III 158.85 165.30 134.50 186.31 99.20 101.90 132.78 192.37 113.26 75.28 119.79

10 I 146.67 159.12 118.09 173.35 94.60 93.62 122.76 172.40 88.19 63.24 66.92

10 II 145.12 154.78 113.43 185.81 90.67 80.84 104.62 148.47 90.25 57.56 76.14

11 III 132.07 148.18 107.24 168.45 88.12 75.07 117.61 140.71 77.17 52.39 72.68

10 I 141.57 144.60 131.92 153.61 82.49 66.11 107.07 58.97 71.13 48.70 85.24

10 II 128.82 145.41 130.16 137.38 78.48 67.20 114.42 72.52 67.07 54.31 83.91

11 III 116.44 146.21 131.15 173.24 73.17 71.87 107.44 62.90 63.35 86.99 83.96

10 I 117.61 146.53 124.54 131.31 82.28 62.97 120.19 73.98 63.09 92.34 91.86

10 II 114.37 142.43 121.30 142.81 110.31 62.19 239.44 68.34 77.21 98.04 96.19

8 III 133.02 142.74 124.51 140.09 118.12 59.03 233.11 303.46 75.06 85.33 273.03

10 I 157.90 161.03 146.10 122.60 127.93 123.64 256.63 158.59 102.99 96.51 254.03

10 II 118.22 164.98 137.12 136.01 180.74 130.24 332.91 211.84 111.51 266.85 287.99

11 III 99.61 174.84 196.26 173.85 221.47 504.10 564.75 159.21 183.81 362.46 257.97

10 I 248.04 359.56 233.84 165.10 290.09 277.49 534.86 296.31 323.10 263.92 319.01

10 II 299.90 623.41 263.88 354.75 337.35 251.88 839.10 414.14 240.99 410.74 366.57

10 III 466.75 677.36 271.62 257.65 400.28 214.89 587.50 446.86 602.23 551.98 357.70

10 I 449.37 438.93 287.19 212.67 483.49 201.47 467.98 453.47 309.02 511.88 335.27

10 II 396.37 398.73 215.68 246.23 341.85 833.31 602.19 546.82 487.40 466.29 277.49

11 III 603.23 524.08 220.67 220.27 344.96 293.97 636.45 807.75 591.20 430.04 339.79

13417 9791 10269 8375 8347 9167 13241 13296 8993 10719 9446

3641.0 2657.0 2786.8 2272.8 2265.2 2487.7 3593.2 3608.1 2440.4 2908.7 2563.3

Avg. Inflow (MCM) = 10494.34Avg. Runoff Depth (mm) = 2848

Runoff Depth (mm) =

Apr

May

Month

Nov

Dec

Jan

Feb

Jul

Aug

Inflow (MCM) =

Sep

Oct

Mar

Jun



169126-40ER-0009-00 1-11

Table 3: 10-Daily Average flow series (m3/s) for Talo (Tangon) Limb (1986-87 to 2008-09)

No of days 1986-87 1987-88 1988-89 1989-90 1990-91 1991-92 1992-93 1993-94 1994-95 1995-96 1996-97 1997-98

10 I 285.50 306.38 306.38 312.56 285.73 288.71 288.38 311.53 285.40 304.54 283.55 488.29

10 II 388.37 407.19 407.19 392.82 399.07 374.30 388.50 379.57 381.78 425.31 380.55 607.76

10 III 342.66 397.61 397.61 551.28 310.64 335.75 362.11 355.48 370.45 488.04 456.96 455.97

10 I 357.72 365.29 403.37 360.02 338.82 375.60 398.52 414.76 389.16 424.40 452.54 486.67

10 II 445.09 453.73 435.29 329.36 338.20 349.42 382.24 447.75 319.53 356.50 663.24 515.88

11 III 374.18 505.20 389.07 326.71 329.90 359.04 340.99 358.87 323.46 316.65 572.30 330.08

10 I 274.47 379.61 259.87 243.01 428.49 362.07 412.82 319.91 271.03 339.33 302.02 278.39

10 II 326.34 455.48 318.00 283.86 293.53 280.63 255.01 345.29 351.25 576.62 487.85 315.96

11 III 355.58 380.99 268.62 279.96 484.73 391.27 404.26 280.90 288.80 293.08 328.47 230.31

10 I 291.06 333.55 375.98 283.70 334.79 426.68 391.18 246.72 268.38 213.68 302.27 257.78

10 II 277.03 198.97 233.37 369.12 332.77 271.73 276.03 202.53 242.03 237.68 224.63 300.59

10 III 174.95 245.47 221.18 365.16 389.85 182.26 207.52 219.02 165.52 327.61 259.43 293.90

10 I 236.50 204.79 202.95 456.17 276.47 276.88 260.91 227.69 372.45 245.57 264.86 213.43

10 II 154.78 159.39 150.18 194.36 178.51 169.94 171.00 158.35 155.01 189.55 163.95 152.67

11 III 114.02 137.25 139.31 157.90 159.19 114.02 133.05 154.67 129.52 129.52 157.27 142.42

10 I 95.34 103.27 97.82 106.55 102.32 98.29 99.03 95.99 94.48 101.35 107.17 106.06

10 II 92.79 100.50 95.20 103.70 99.59 95.67 96.39 93.42 91.95 98.64 104.30 103.22

10 III 80.99 87.71 83.09 90.51 86.91 83.49 84.12 81.53 80.25 86.09 91.03 90.08

10 I 71.10 77.01 72.94 79.46 76.30 73.30 73.85 71.58 70.46 75.58 79.92 79.09

10 II 68.29 73.97 70.07 76.32 73.29 70.41 70.94 68.76 67.68 72.60 76.76 75.97

11 III 64.57 69.94 66.25 72.16 69.30 66.57 67.07 65.01 63.99 68.64 72.58 71.83

10 I 66.90 63.37 69.03 66.29 63.68 64.16 62.18 61.21 65.66 69.42 68.70 77.87

10 II 65.70 62.24 67.79 65.10 62.54 63.01 61.07 60.11 64.48 68.18 67.48 71.66

11 III 67.88 64.30 70.04 67.26 64.61 65.10 63.10 62.11 66.63 70.45 69.72 71.53

10 I 69.06 65.42 71.26 68.43 65.73 66.23 64.19 63.18 67.78 71.67 70.93 95.58

10 II 78.08 73.96 80.56 77.37 74.32 74.88 72.58 71.44 76.63 81.03 80.19 89.56

8 III 92.80 87.91 95.76 91.96 88.34 89.00 86.26 84.91 91.08 96.31 95.31 96.15

10 I 98.72 93.51 101.86 97.81 93.96 94.67 91.76 90.32 96.89 102.44 101.38 134.53

10 II 118.30 112.06 122.06 117.22 112.60 113.45 109.96 108.23 116.10 122.76 121.49 130.59

11 III 172.74 163.63 178.24 171.16 164.43 165.66 160.57 158.05 169.54 179.27 177.41 174.19

10 I 191.89 181.76 197.99 190.13 182.65 184.02 178.36 175.56 188.33 199.13 197.07 155.68

10 II 272.89 258.49 281.57 270.40 259.75 261.71 253.66 249.67 267.83 283.19 280.26 361.14

10 III 296.70 281.04 306.14 293.98 282.41 284.54 275.78 271.46 291.20 307.90 304.71 336.03

10 I 243.49 243.49 399.21 234.14 235.71 231.24 260.17 232.68 255.02 220.06 210.09 263.94

10 II 276.77 276.77 372.40 239.35 290.36 267.05 277.92 242.05 264.49 283.12 350.45 233.41

11 III 294.27 294.27 356.02 316.84 272.94 248.01 220.05 269.86 235.73 260.75 367.39 314.67

6396 6834 6818 6845 6773 6430 6500 6236 6229 6825 7387 7186

2486.0 2656.0 2649.9 2660.5 2632.4 2499.0 2526.3 2423.8 2420.9 2652.5 2870.9 2792.9

Jun

Sep

Oct

Mar

Apr

May

Month

Nov

Dec

Jan

Feb

Jul

Aug

Inflow (MCM) =

Runoff Depth (mm) = Contd. on next page……



169126-40ER-0009-00 1-12

Table 3 (Contd….): 10-Daily Average flow series (m3/s) for Talo (Tangon) Limb (1986-87 to 2008-09)

No of days 1998-99 1999-00 2000-01 2001-02 2002-03 2003-04 2004-05 2005-06 2006-07 2007-08 2008-09

10 I 405.43 297.25 507.27 240.07 114.41 272.73 243.22 375.74 478.67 291.77 255.63

10 II 535.36 343.96 569.51 254.59 192.02 415.72 422.78 511.65 562.50 576.83 325.41

10 III 362.62 442.50 678.89 221.78 180.19 525.93 617.22 435.10 325.18 379.74 285.50

10 I 494.96 586.71 390.41 239.29 307.96 519.40 612.92 387.39 337.94 256.52 258.64

10 II 853.26 246.85 319.68 232.42 386.82 367.77 923.17 359.92 300.26 477.32 227.48

11 III 671.40 155.63 356.89 351.22 354.00 263.15 454.88 280.02 280.98 694.25 357.92

10 I 457.33 221.74 493.46 289.60 225.86 213.06 289.99 439.22 182.11 331.23 200.32

10 II 886.40 282.10 387.23 288.04 242.06 273.87 244.00 421.54 158.11 360.74 453.09

11 III 734.70 316.37 316.04 338.45 127.76 182.98 232.19 744.11 229.72 226.56 491.84

10 I 623.73 170.60 278.91 296.01 88.34 238.78 227.24 468.83 269.60 562.69 432.29

10 II 134.55 172.49 240.16 225.26 161.06 230.75 204.62 415.24 398.47 303.85 191.21

10 III 114.49 101.20 203.07 163.13 356.41 167.45 213.91 724.88 165.73 132.01 132.57

10 I 128.00 122.35 193.30 208.29 540.87 234.88 392.89 276.96 185.89 136.01 297.22

10 II 149.25 119.32 148.64 149.32 201.05 165.45 196.85 177.55 88.81 199.15 172.80

11 III 251.29 118.73 137.75 92.17 106.40 133.16 134.32 274.12 66.02 100.13 136.29

10 I 117.06 112.07 100.87 127.92 73.66 93.36 122.60 157.22 55.20 57.00 92.63

10 II 104.00 108.14 98.18 132.54 83.01 74.44 122.95 136.71 57.58 70.61 91.77

10 III 101.19 105.30 85.68 118.68 63.19 64.91 84.59 122.54 72.15 47.95 76.31

10 I 93.43 101.36 75.22 110.42 60.26 59.64 78.20 109.82 56.18 40.29 42.63

10 II 92.45 98.60 72.25 118.36 57.76 51.50 66.65 94.58 57.49 36.67 48.50

11 III 84.13 94.39 68.32 107.31 56.13 47.82 74.92 89.64 49.16 33.37 46.30

10 I 90.18 92.11 84.03 97.85 52.55 42.11 68.20 37.57 45.31 31.03 54.30

10 II 82.06 92.63 82.91 87.51 49.99 42.81 72.89 46.20 42.72 34.60 53.45

11 III 74.17 93.14 83.55 110.36 46.61 45.78 68.44 40.07 40.35 55.41 53.48

10 I 74.92 93.34 79.33 83.65 52.41 40.12 76.56 47.13 40.19 58.82 58.51

10 II 72.86 90.73 77.27 90.97 70.27 39.62 152.52 43.53 49.18 62.45 61.28

8 III 84.73 90.93 79.32 89.24 75.24 37.60 148.50 193.31 47.81 54.36 173.92

10 I 100.59 102.58 93.07 78.10 81.49 78.76 163.48 101.03 65.60 61.48 161.82

10 II 75.31 105.09 87.35 86.64 115.13 82.96 212.07 134.95 71.03 169.98 183.45

11 III 63.45 111.37 125.02 110.74 141.08 321.12 359.75 101.42 117.09 230.89 164.33

10 I 158.01 229.04 148.96 105.17 184.79 176.76 340.71 188.75 205.82 168.12 203.22

10 II 191.04 397.12 168.09 225.98 214.89 160.45 534.52 263.81 153.52 261.65 233.51

10 III 297.33 431.49 173.03 164.12 254.98 136.89 374.24 284.66 383.63 351.62 227.86

10 I 286.25 279.61 182.94 135.47 307.99 128.34 298.11 288.87 196.85 326.07 213.57

10 II 252.50 254.00 137.39 156.85 217.76 530.83 383.60 348.33 310.48 297.03 176.76

11 III 384.27 333.85 140.57 140.31 219.74 187.26 405.43 514.55 376.60 273.94 216.45

8547 6237 6542 5335 5317 5840 8435 8470 5729 6828 6017

3321.7 2424.1 2542.5 2073.6 2066.6 2269.6 3278.2 3291.7 2226.4 2653.7 2338.5

Avg. Inflow (MCM) = 6685.03

Avg. Runoff Depth (mm) = 2598

Jun

Sep

Oct

Mar

Apr

May

Month

Nov

Dec

Jan

Feb

Jul

Aug

Inflow (MCM) =

Runoff Depth (mm) =



169126-40ER-0009-00 1-13

1.3.6 Flow Duration Curves

Having prepared the long term 10-daily average flow series for Dri limb of Etalin and Talo

(Tangon) limb of Etalin, the flow duration curves for both these sites have been prepared

which are shown in the following figures.

10 Daily Flow Duration Curve-Etalin (Dri Limb)

0

200

400

600

800

1000

1200

1400

1600

0 10 20 30 40 50 60 70 80 90 100Percentage of Exceedence

Dis

char

ge (c

umec

)

Figure 4: Flow Duration curve for Dri Limb of Etalin

10 Daily Flow Duration Curve-Etalin (Tangon Limb)

0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40 50 60 70 80 90 100Percentage of Exceedence

Dis

char

ge (c

umec

)

Figure 5: Flow Duration curve for Talo (Tangon) Limb of Etalin

TALO (TANGON)



169126-40ER-0009-00 1-14

1.4 Design Flood

1.4.1 General

Estimation of design flood is a significant component of hydrological studies. Proper

selection of design flood value is important as an over-estimated value results in increase in

the cost of hydraulic structures, while an under-estimated value will place the structure and

population at risk.

1.4.2 Criteria for Estimation of Design Flood

As per the Manual on Estimation of Design Flood (CWC, 2001) as well as BIS: 11223-1985

(Reaffirmed 2004), “Guidelines for Fixing Spillway Capacity”, the inflow design flood for

safety of a dam is decided based on gross storage and static head at FRL (from FRL to the

minimum tail water level) at a given project. The following criteria are recommended.

Table 4: Classification Criteria of Hydraulic Structures

Classification Gross Storage ( x106 m3)

Hydraulic Head (m)

Inflow Design Flood

Small 0.5 - 10 7.5 –12 100 year return period

Intermediate 10 - 60 12 –30 SPF

Large > 60 > 30 PMF

The diversion structures proposed in the present project are dams. The hydraulic head on

Dri limb dam is about 77 m and that on Talo (Tangon) limb dam is about 47m. Therefore, as

per the above criteria, spillway capacity at both locations should be sufficient to pass

Probable Maximum Flood (PMF).

1.4.3 Computation of Design Flood - PMF

In the present case, the design floods at the project are estimated using the

Hydro-meteorological approach. Since site specific short interval rainfall-runoff records are

not available, the procedure for estimating unit hydrograph given in “Flood Estimation

Report for North Brahmaputra, subzone 2(a), Central Water Commission, 1991” has been

adopted.

The methodology comprises of the following steps:

First, the Probable Maximum Precipitation (PMP) is defined



169126-40ER-0009-00 1-15

A typical unit hydrograph is then defined for the basin, and the flood hydrograph is

computed by convolution of this hydrograph.

1.4.4 Physiographic Parameters of the Catchment

a) Catchment Area (A):

The project catchment area is derived by delineating the relevant topo sheets. The snowline

elevation of 4500 m (suggested by IMD) has been taken to delineate the rain-fed area of the

project catchment. As mentioned above, the breakup of project catchment areas on the

Dri and Talo (Tangon) limbs is:

Table 5: Breakup of Catchment Area

Name of Project Catchment

Rain-fed Area (km2)

Snow-fed Area (km2)

Total Area (km2)

Dri limb 3557 128 3685

Talo (Tangon) limb 2397 176 2573

b) Parameters of the Main Stream (L & Lc):

River length (L) implies the longest length of the main river from the farthest watershed

boundary of rain-fed catchment to the downstream boundary point, whereas Lc is defined as

the length of the longest main stream from a point opposite to centroid of the catchment area

to the gauging site (i.e., the outlet point) along the main stream. The stream may or may not

pass through the centre of gravity but the point of the river nearest to the centre of gravity is

considered to find the length of the main river from the centre of gravity to the point of study

(Lc). In the present case, the details of these parameters as extracted from the available

information are given below.

Table 6: River Length Parameters

Name of Project Catchment L (km) Lc (km)

Dri limb 93.98 56.46

Talo (Tangon) limb 72.58 45.42

c) Equivalent Stream Slope (S):

This is one of the physiographic parameters used in the derivation of Synthetic

Unit Hydrograph. The L-section of the river is derived from relevant topo sheets. It is broadly



169126-40ER-0009-00 1-16

divided into segments representing broad ranges of slopes. The following formula is used to

compute equivalent slope (S).

2

)1( )(

L

DDLS

iii

Elevations of riverbed at intersection points of contours reckoned from the bed elevation at

the diversion site are considered as datum. D(i-1) and Di are the heights of successive bed

locations at contour intersections. The equivalent slope thus computed for Dri limb is

21.17 m/km and that for Talo (Tangon) limb is 31.33 m/km.

1.4.5 Derivation of Unit Hydrograph

The Central Water Commission (CWC), in association with the Indian Meteorological

Department (IMD), Ministry of Railways and Ministry of Surface Transport, has prepared

flood estimation reports for small and medium rain-fed catchments for efficient

hydro-meteorological homogenous sub-zones. These reports illustrate the procedure for

derivation of synthetic unit hydrograph based on physiographic parameters. The unit

hydrograph for the rain-fed catchment area of the project has been derived as per

procedures and guidelines given in the regional flood report of sub zone 2a.

SUH parameters for the present project are derived using project specific information and

are included in Table 7-7.

Table 7: Sub-Zone 2a Unit Hydrograph Parameters

Parameter Definition Formula Unit Dri Limb

Talo (Tangon) Limb

L Length of longest main stream along the river course

Measured from Topographical Map km 93.98 72.58

Lc

Length of longest main stream from a point opposite to centroid of the catchment

area to intake site

Measured from Topographical Map km 56.46 45.42

A Rain fed Area Measured from Topographical Map km² 3557 2397

S Equivalent Stream Slope

2

1

L

DDLS

iii

m/km 21.17 31.33

qp Peak Discharge of unit

hydrograph per km²

409.0

272.2

S

LLq c

p m³/s/km² 0.24 0.34

Qp Peak Discharge of unit

hydrograph pp qAQ m³/s 844 811



169126-40ER-0009-00 1-17

Parameter Definition Formula Unit Dri Limb

Talo (Tangon) Limb

tp Time from the centre of

effective rain fall duration to the unit hydrograph Peak

940.0164.2

pp qt hrs 8.37 5.99

tm Time from start of rise to the

peak of unit hydrograph 5.0 pm tt hrs 8.87 6.49

TB Base width of unit hydrograph 852.0428.5 pB tT hrs 33.16 24.96

W50 Width of unit hydrograph

measured at 50% of Peak Discharge Ordinate

065.1

50 084.2

pqW hrs 9.64 6.61

W75 Width of unit hydrograph measured at 75% of peak

discharge ordinate 071.1

75 028.1

pqW hrs 4.80 3.28

WR50

(Width of the rising limb of unit hydrograph measured at

50% of Peak Discharge Ordinate

865.0

50 856.0

pR qW hrs 2.97 2.19

WR75 Width of the rising limb of unit hydrograph measured at 75% of Peak Discharge Ordinate

918.0

75 44.0

pR qW hrs 1.65 1.19

The 1-hour Synthetic Unit Hydrograph (SUH) representing effective rainfall depth of 1 cm

has been obtained for both the catchments on the Dri and Talo (Tangon) limbs using the

above parameters. The SUH for Dri and Talo (Tangon) river catchments up to the proposed

dam sites are shown in figures below:

Unit Hydrograph - Dri Limb

0

100

200

300

400

500

600

700

800

900

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36Time (hr)

Flow

(m³/s

)

Figure 6: SUH of Dri limb



169126-40ER-0009-00 1-18

Unit Hydrograph - Tangon Limb

0

100

200

300

400

500

600

700

800

900

0 2 4 6 8 10 12 14 16 18 20 22 24 26Time (hr)

Flow

(m³/s

)

Figure 7: SUH of Talo (Tangon) limb

The important parameters for deciding critical storm duration are size and shape of the

catchment, travel time/base period of unit hydrograph and the direction of the storm

movement with reference to the direction of river flow. For all practical purposes, the UG

base governs the duration of the storm. As can be seen from the above figures, the base

period of unit hydrograph is 33 hours for Dri limb and 25 hours for Talo (Tangon) limb.

Therefore, design storm of 1 day has been used for the flood estimation of Talo (Tangon)

limb and design storm of 2 days has been used for the design flood estimation of Dri limb.

1.4.6 Design Storm

Design storm studies for the project have been carried out by the Indian Meteorological

Department (IMD), on the basis of the available rainfall data in the area. The Standard

Project Storm (SPS) and Probable Maximum Precipitation (PMP) values along with time

distribution for 1-day and 2-day storm, provided by IMD, are given in Table 7-8 and

Table 7-9, respectively.

TALO (TANGON)



169126-40ER-0009-00 1-19

Table 8: Standard Project Strom (SPS) and Probable Maximum Precipitation (PMP) Values

Project Stages Duration Design SPS (cm) PMP (cm)

Dri limb 1 day 18.0 22.7

2 day 29.80 37.5

Talo (Tangon) limb 1 day 16.00 20.20

2 day 26.4 33.30

Note: As recommended by IMD, the above 1-day precipitation values may be increased by 15% to convert them into any 24 hour values.

Table 9: Temporal Distribution of the SPS and PMP

Duration (hrs) 24-hour (%) 48-hour (%)

3 35 25

6 53 38

9 65 46

12 74 52

15 82 58

18 89 63

21 95 68

24 100 73

27 77

30 81

33 85

36 88

39 91

42 94

45 97

48 100

The autographic records for storms in India are indicative of a pattern of two bells per day of

the storm with high intensity spells lasting for 9 to 12 hours. Therefore, the design storm of

1-day and 2-day values is distributed into 12-hour bells, which are given as under.



169126-40ER-0009-00 1-20

Table 10: PMP Distribution for Dri limb

Design Storm (cm) Ratio of 12/24 hr rainfall

Storm Distribution (cm)

PMP I-Bell II-Bell I-Bell II-Bell

1st Day 22.7 0.74 0.26 16.80 (1A)

5.90 (1B)

2nd Day 14.8 (=37.5-22.7) 0.74 0.26 10.95

(2A) 3.85 (2B)

Table 11: PMP Distribution for Talo (Tangon) limb

Design Storm, cm

Ratio of 12/24 hr rainfall

Storm Distribution (cm)

PMP I-Bell II-Bell I-Bell II-Bell 1st Day 24-hr

23.23 (=1.15*20.2) 0.74 0.26 17.2

(1A) 6.0 (1B)

For obtaining the largest practicable value of the PMF, the bell arrangement (sequencing) for

Dri limb has been considered to follow the sequence like: 2B-2A-1B-1A. It has also been

ensured during bell sequencing that the summation of storm value of any two consecutive

bells doesn’t exceed the 24-hour value of 1-day PMP which has been obtained by adding

the clock hour correction factor of 15% on 1-day PMP storm. In other words the critical

sequencing of bells for Dri limb is done in such a way that no two consecutive bells exceeds

the value of 26.105 cm (=22.7*1.15) which is 1.15 times that of 1-day PMP of 22.7 cm.

For the Talo (Tangon) limb, the bell arrangement would be 1B-1A.

1.4.7 Design Loss Rate

In the present study, design loss rate of 0.1 cm/hr has been adopted for the computation of

design flood for both the dams.

1.4.8 Critical Sequence of Rainfall Excess

To obtain the critical sequence of rainfall excess, the highest rainfall depth has been placed

against the maximum UG ordinate and the next ranking rainfall depth has been placed

against the next ranking ordinate of hydrograph. This critical arrangement is then reversed to

obtain the maximum flood peak.



169126-40ER-0009-00 1-21

1.4.9 Base flow and Snow melt

The total base-flow, including snowmelt, has been estimated as 246 m3/s for Dri and

181 m3/s for Talo (Tangon).

1.4.10 Surface Flow Hydrograph

The Surface Flow Hydrograph has been computed by convoluting 1-hour rainfall excess

increments with the ordinates of the 1-hr Unit Hydrograph. For this purpose, the rainfall

excess increments have been arranged in a critical sequence. Each of the individual

incremental hydrographs has been lagged 1-hour from the previous one in the assumed

critical sequence and added to obtain the surface flow hydrograph.

1.4.11 Flood Hydrograph

The Flood Hydrograph has been obtained by adding a uniform base flow, including

snowmelt, to the ordinates of the surface flow hydrograph. The Probable Maximum Flood

(PMF) for Dri and Talo (Tangon) limbs thus computed are given in the following table and

the PMF hydrograph are given in subsequent figures.

Table 12: Design Flood (PMF)

PMF (m3/s)

Dri Limb 11811

Talo (Tangon) Limb 10218



169126-40ER-0009-00 1-22

PMF Hydrograph- DRI Limb11811

0

2000

4000

6000

8000

10000

12000

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80

Time (hr)

Dis

char

ge (c

umec

)

Figure 8: PMF Hydrograph for Dri Limb

PMF Hydrograph- TANGON Limb

10218

0

2000

4000

6000

8000

10000

0 4 8 12 16 20 24 28 32 36 40 44 48 52

Time (hr)

Dis

char

ge (c

umec

)

Figure 9: PMF Hydrograph for Talo (Tangon) Limb

The tabulation of the PMF hydrograph for both Dri limb and Talo (Tangon) limb is given

below:

The detail calculation and analysis of design flood can be referred in Volume-II (Hydrological Studies) of DPR.

TALO (TANGON)



169126-40ER-0009-00 1-23

Table 13: Design Flood Hydrograph (PMF) Values

Hours PMF of Dri limb (m3/s)

PMF of Talo (Tangon) limb

(m3/s)

Hours PMF of Dri limb (m3/s)

PMF of Talo (Tangon) limb

(m3/s) 0 246 181 41 5819 641 1 249 186 42 5762 494 2 254 200 43 5757 368 3 265 230 44 5955 277 4 283 285 45 6380 227 5 307 386 46 6928 200 6 347 534 47 7572 185 7 406 739 48 8290 181 8 498 1006 49 9085 9 633 1343 50 9981 10 792 1734 51 10935 11 969 2190 52 11704 12 1158 2675 53 11811 13 1384 3077 54 11321 14 1653 3297 55 10460 15 1968 3318 56 9447 16 2272 3270 57 8471 17 2459 3318 58 7563 18 2584 3520 59 6731 19 2728 3910 60 5991 20 2979 4498 61 5308 21 3364 5310 62 4676 22 3813 6298 63 4081 23 4312 7499 64 3538 24 4846 8803 65 3045 25 5434 9820 66 2620 26 6095 10218 67 2235 27 6806 9863 68 1918 28 7402 9018 69 1637 29 7574 7908 70 1394 30 7374 6739 71 1191 31 6968 5585 72 1016 32 6524 4559 73 859 33 6169 3692 74 705 34 5888 2971 75 557 35 5679 2389 76 433 36 5541 1913 77 331 37 5493 1541 78 278 38 5538 1248 79 255 39 5673 1017 80 246 40 5820 813 81



169126-40ER-0009-00 1-24

1.4.12 Design Flood for River Diversion Works

In general, it is not economical to design the diversion works for the greatest flood which is

likely to occur. As per IS 14815:2000, the diversion design flood for concrete dams and

barrages must be the higher of the following two values:

Maximum non-monsoon flow observed at the dam site

25 years non-monsoon flow, calculated on the basis of non-monsoon yearly peaks.

However, the design flood selected is usually a compromise between the cost of diversion

works and the risk involved. In case of earth dam, overtopping of embankment during

construction may result in extensive damage, whereas in concrete dams, overtopping may

be tolerated to some extent if it results in minimal damages. In Etalin Hydroelectric Project,

both dams are concrete gravity type. As per IS 14815 – 2000, titled “Design flood for river

diversion works – Guidelines”, the following factors should be considered interalia.

The period of stoppage of work during flood season and number of flood seasons

which are to be managed during the work.

The cost of delay in completion of the work.

In addition to the above, the time required for all the activities to be completed in the riverbed

(such as excavation, foundation treatment and concreting up to about the original riverbed

level) plays an important role in selecting the diversion flood. If the aforesaid activities cannot

be completed in one lean season, then higher flood must be considered for diversion.

In view of the above, the diversion flood studies for the project have been carried out for both

non-monsoon and monsoon periods.

1.4.13 Data

At present, no observed flood peak data are available at the diversion sites. However, flood

peaks are available at Elopa and Munli dam sites, which are downstream of the proposed

project at Etalin. Therefore, the diversion flood studies have been carried out using these

available data at Elopa (CA = 11666 km2) and Munli (CA = 11276 km2) G&D sites. The flows

at both these sites have been transferred to the project at Etalin, based on Dicken’s formula.

The multiplying factors as used for transferring the Elopa and Munli peak flows to the

Etalin project site are given below:



169126-40ER-0009-00 1-25

Table 14: Transfer Factor for Elopa and Munli Peak Flows

Dri Limb (CA=3685 km2)

Talo (Tangon) Limb (CA=2573 km2)

Elopa Peak Flow (CA = 11666 km2) 0.421 0.322

Munli Peak Flow (CA = 11276 km2) 0.432 0.330

Using the above multiplying factors to the available Elopa and Munli peak flows and

increasing them by 15% on account of instantaneous peak, the final peak flows (both for

monsoon and non-monsoon) on Dri and Talo (Tangon) are obtained as follows:

Table 15: Final Peak Flows at Dri and Talo (Tangon) Limbs

Period Monsoon Peak Flows (m3/s) Non-Monsoon (Oct-Apr) Peak

Flows (m3/s) Dri Limb Talo (Tangon)

Limb Dri Limb Talo (Tangon) Limb

1998-99 4037.23 2681.56 1530.54 1016.60

1999-00 2764.85 1836.43 1320.85 877.32

2000-01 3592.09 2385.89 593.70 394.34

2001-02 1978.65 1314.24 1213.98 806.33

2002-03 3885.75 2580.94 2030.44 1348.64

2003-04 3833.49 2546.23 1667.47 1107.55

2004-05 4743.74 3150.83 2426.22 1611.51

2005-06 4390.46 2916.17 3053.53 2028.18

2006-07 3373.97 2241.02 2202.45 1462.89

2007-08 3241.14 2152.79 2203.74 1463.74

2008-09 2646.48 1757.82 962.14 639.06

2009-10 2812.22 1867.90

1.4.14 Statistical Parameters

Details of important statistical parameters for the flood peaks at the two dam sites for the two

different periods (monsoon and non-monsoon) are given in the following table.



169126-40ER-0009-00 1-26

Table 16: Statistical Parameters of Peak Flows at Dri and Talo (Tangon) Limbs

Parameters Monsoon Period Non-Monsoon Period (Oct-Apr)

Dri Limb Talo (Tangon) Limb Dri Limb Talo (Tangon) Limb

Mean(Xm) 3441.67 2628.88 1745.92 1333.60

SD (Sx) 797.47 609.13 716.22 547.08

Variance 635951 371045 512973 299294

Skewness -0.17 -0.17 0.17 0.17

Kurtosis -0.44 -0.44 -0.34 -0.34

No. of Data 12 12 11 11

1.4.15 Flood Frequency Analysis

For estimating the 25-year return period flood, Extreme Value Type-I i.e., Gumbel,

Log-Normal and Log Pearson Type-III distributions have been used to model the annual

maximum monsoon and non-monsoon flows in the present study. The results of the analysis

are shown in the table below.

Table 17: Detail of 25 year Return Period Flood (m3/s)

Log-Normal

Log-Pearson Gumbel Chow’s

Method Observed Maximum

Dri limb Monsoon 5171 4846 5627 5072 4743.74 Non-Monsoon 3634 3142 3744 3210 3053.53

Talo (Tangon) limb

Monsoon 3950 3701 4298 3874 3623.45 Non-Monsoon 2776 2400 2860 2452 2332.4

1.4.16 Selection of Diversion Flood

The Chi Square test confirms that distributions involving both observed and log-transformed

series fit well to the flood peak data. However, based on the skewed nature and kurtosis of

the data series, the Gumbel distribution has been adopted for selecting the diversion design

flood. The details of the return period flood for Monsoon and Non-Monsoon period has been

tabulated below.



169126-40ER-0009-00 1-27

Table 18: Diversion Flood (m3/s) at Etalin dam sites

Return Period Years)

Flood (m3/s) at Dri Limb Flood (m3/s) at Talo (Tangon) Limb

Monsoon Non-Monsoon (Oct-Apr) Monsoon Non-Monsoon

(Oct-Apr) 2 3331 1647 2544 1258

5 4250 2486 3246 1899

10 4858 3042 3711 2323

20 5442 3575 4157 2730

25 5627 3744 4298 2860

50 6198 4264 4734 3257

100 6764 4781 5167 3652

In addition to the above mentioned two working periods, frequency analysis for different

working seasons have also been carried out and are presented in Figure 7-10 and

Figure 7-11 for both dam sites of Etalin HEP. The diversion floods for the present project at

Etalin can be used for planning of diversion works, depending on the period of construction.



169126-40ER-0009-00 1-28

Return Period Floods for Different Working seasons-Dri Limb

0

1000

2000

3000

4000

5000

6000

7000

8000

Floo

d D

isch

arge

(m3 /s

)

2 Yr 3331 1647 1932 2035 2243 1558 1731 2192 1734 2461

5 Yr 4250 2486 3082 3407 3556 2421 2877 3537 2524 3774

10 Yr 4858 3042 3843 4314 4425 2992 3635 4428 3046 4643

20 Yr 5442 3575 4574 5185 5259 3541 4362 5282 3548 5477

25 Yr 5627 3744 4805 5462 5524 3714 4593 5552 3707 5742

50 Yr 6198 4264 5519 6313 6338 4250 5304 6387 4196 6557

100 Yr 6764 4781 6227 7158 7147 4782 6009 7215 4682 7366

12 months 7 months 7.5 months 8 months 8.5 months 6.5 months 7 months 8 months 6 months 7.5 months

FULL YEAR 1st Oct- 30 Apr 1st Oct- 15 May 1st Oct- 31 May 1st Oct- 15 June 16th Oct- 30 Apr 16th Oct- 15 May 16th Oct- 15 Jun 1st Nov - 30 Apr 1st Nov - 15 Jun

Figure 10: Return Period Flood for Different Working Seasons on Dri Limb



169126-40ER-0009-00 1-29

Return Period Floods for Different Working seasons-Tangon Limb

0

1000

2000

3000

4000

5000

6000

Floo

d D

isch

arge

(m3 /s

)

2 Yr 2544 1258 1476 1555 1713 1190 1322 1675 1325 1880

5 Yr 3246 1899 2354 2602 2716 1849 2197 2702 1928 2883

10 Yr 3711 2323 2936 3296 3380 2286 2776 3382 2327 3547

20 Yr 4157 2730 3493 3961 4017 2704 3332 4034 2710 4184

25 Yr 4298 2860 3670 4172 4219 2837 3508 4241 2831 4386

50 Yr 4734 3257 4215 4822 4841 3246 4051 4879 3205 5008

100 Yr 5167 3652 4756 5467 5459 3653 4590 5511 3577 5626

12 months 7 months 7.5 months 8 months 8.5 months 6.5 months 7 months 8 months 6 months 7.5 months

FULL YEAR 1st Oct- 30 Apr 1st Oct- 15 May 1st Oct- 31 May 1st Oct- 15 June 16th Oct- 30 Apr 16th Oct- 15 May 16th Oct- 15 Jun 1st Nov - 30 Apr 1st Nov - 15 Jun

Figure 11: Return Period Flood for Different Working Seasons on Talo (Tangon) Limb

Talo (Tangon)



169126-40ER-0009-00 1-30

1.5 Sedimentation

1.5.1 Need for Sediment Evaluation

Etalin Hydroelectric Project is located in the Himalayas where river gradients are steep and,

as a result, the rivers may have enormous capacity for sediment transportation.

Both the dams in the project will be high dams; however, the reservoir volumes will be quite

small due to the steepness of the slopes of the valley and river. It is anticipated to use the

reservoirs only for providing enough storage to allow daily peaking during the non-monsoon

season.

1.5.2 Reservoir Sediment Rate

Due to non-availability of site specific long-term data, total sediment rate of

0.075 ham/sq.km/year has been adopted based on the Preliminary Feasibility Report (PFR)

of the project. For Dibang multipurpose project which is downstream of the Etalin project, a

sediment rate of 0.1 ham/sq.km/year, i.e. 1mm/year, has been adopted and hence the same

has been proposed to be used for both the dam sites of Etalin.

1.5.3 Reservoir Elevation-Area-Capacity

The reservoir elevation-area-capacity curves for the project have been prepared from the

contour map of the reservoirs. The reservoir survey has been done in scale of 1:5000 with

5 m contour interval. The area enclosed within the contours has been evaluated using

AutoCAD. The volume between any two elevations is calculated using the cone formula:

2121*3

AAAAHV

Where

V =Volume between two contours

H =Contour interval

A1 =Area at level of first contour

A2 =Area at level of second contour

The resulting area capacity curve for Dri limb and Talo (Tangon) limb has been given in

subsequent figures.



169126-40ER-0009-00 1-31

965

975

985

995

1005

1015

1025

1035

1045

1055

0 10 20 30 40 50 60 70 80 90 100Area (Ha)

Elev

atio

n (m

)036912151821242730

Capacity (MCM)

MDDL

Area Capacity

FRL

Figure 12: Elevation-Area-Capacity Curve of Dri Reservoir

1000

1005

1010

1015

1020

1025

1030

1035

1040

1045

1050

1055

1060

0 10 20 30 40 50 60Area (Ha)

Elev

atio

n (m

)

0369121518Capacity (MCM)

MDDL

FRL

CapacityArea

Figure 13: Elevation-Area-Capacity Curve of Talo (Tangon) Reservoir



169126-40ER-0009-00 1-32

1.5.4 Sedimentation Aspects of Reservoirs

The total sediment inflow rate for the basin of Dri River is 3.685 MCM/year (Catchment

Area=3685 km2) and for Talo (Tangon) river is 2.573 MCM/year (Catchment Area = 2573

km2). The capacity-inflow ratio for the reservoirs on Dri River is 0.002 and on Talo (Tangon)

river is 0.0007. As per the codal provision of IS 12182:1987, the sedimentation problem is

usually said to be serious if the capacity-inflow ratio is more than 0.005. Hence, the

sedimentation problem at both Dri limb and Talo (Tangon) limb reservoirs is not serious.

The corresponding trap efficiency, as per Brune’s curve, is around 5% for Dri reservoir

whereas the trap efficiency for Talo (Tangon) reservoir is nil.

Assuming 20% of bed load which would be entirely trapped in the reservoir represents a

volume of (3.685-3.685/1.2) = 0.614 MCM/yr for Dri limb and a volume of (2.573-2.573/1.2) =

0.428 MCM/yr for Talo (Tangon) limb. Brune’s Curve showed a trap efficiency of 5% for the

suspended sediment which corresponds to a trap volume of (0.05*3.685/1.2) =

0.1535 MCM/yr for Dri limb reservoir whereas the trap volume for Talo (Tangon) limb

reservoir is nil. Thus, the total volume of trapped sediment in the reservoir of Dri limb is

0.614 + 0.1535 = 0.77 MCM/yr and for Talo (Tangon) limb is 0.428 MCM/yr.

1.5.5 Type and Shape of the Reservoirs

The reservoir operation is of type I, because the sediments are always submerged.

The reservoir shape is determined with the depth-capacity curve, based on the area-capacity

curve of the reservoir. Both the reservoir shape is of type II as per IS 5477 (Part 2): 1994.

The detail analysis of shape of reservoir has been given in Volume-II of DPR.

1.5.6 Sediment Accumulation

The average river bed level at Dri limb dam site is at El. 968m and under sluice type

spillways are proposed at El. 990 m which is about - 22 m above the river bed level.

The FRL and MDDL at dam site are at El. 1045 m and El. 1039 m, respectively.

The average river bed level at Talo (Tangon) limb dam site is at El. 1003 m and under sluice

type spillways are proposed at El. 1018 m which is about 15 m above the river bed level.

The FRL and MDDL at dam site are at El. 1050 m and El. 1040 m, respectively.

Since, both the dam is planned for enough storage to allow daily peaking during the

non-monsoon period, it is customary to determine the period at which the sediment



169126-40ER-0009-00 1-33

accumulation would attain/reach the crest level. This is determined using empirical area

reduction method as described in IS: 5477 (part-II):1994 and the revised area capacity of

both the reservoirs are shown in the following tables.

Table 19: Revised Area Capacity of Dri Reservoir after Sediment Accumulation to Crest Level of El. 990 m

Elevation (m)

Original Area (Ha)

Original Capacity (MCM)

Revised Area (Ha)

Revised Capacity (MCM)

1045 83.320 21.97 83.32 15.74

1040 72.247 18.08 65.27 12.03

1039 69.953 17.42 62.49 11.39

1035 60.781 14.76 51.89 9.11

1030 53.805 11.90 43.75 6.72

1025 47.071 9.38 36.29 4.72

1020 39.069 7.23 27.86 3.12

1015 32.360 5.44 20.95 1.90

1010 23.688 4.05 12.29 1.08

1005 19.716 2.97 8.51 0.56

1000 15.914 2.08 5.09 0.22

995 12.543 1.37 2.29 0.04

990 9.487 0.82 0.00 0.00

985 6.229 0.43

980 4.326 0.17

975 1.409 0.03

970 0.041 0.0003

968 0.000 0.00

The time required to reach the crest level of El. 990m is 8.1 years (= [21.97-15.74]/0.77).



169126-40ER-0009-00 1-34

Table 20: Revised Area Capacity of Talo (Tangon) Reservoir after Sediment Accumulation to Crest Level of El. 1018 m

Elevation (m)

Original Area (Ha)

Original Capacity (MCM)

Revised Area (Ha)

Revised Capacity (MCM)

1060 52.871 10.60 52.87 7.87

1055 44.721 8.17 40.08 5.55

1050 36.123 6.15 30.31 3.79

1045 28.857 4.53 22.42 2.48

1040 23.909 3.21 17.16 1.49

1035 18.525 2.15 11.72 0.77

1030 12.845 1.37 6.19 0.33

1025 9.621 0.81 3.31 0.09

1020 6.536 0.41 0.78 0.00

1018 5.466 0.29 0.00 0.00

1015 3.859 0.15

1010 1.353 0.03

1005 0.027 0.0002

1003 0.000 0.00

The time required to reach the crest level of El. 1018m is 5.5 years (= [6.15-3.79]/0.429).

Once, sediment deposition reaches the crest level, regular flushing of the reservoir is

foreseen to flush the sediments from the reservoir.

CEA/ CWC has already given the concurrence for the Design Flood & Sedimentation

Studies.

1.6 Glacial Lake Outburst Flood (GLOF)

The melt water released from glaciers is the main source of water for most Himalayan rivers.

The glaciers are vulnerable to climate changes and as the glaciers retreat due to global

warming, glacial lakes are formed behind at the exposed moraines. Several glacial lakes

have been reported to be formed in the past decades. The sudden break of a moraine

releases large volumes of water causing floods downstream. These floods are called Glacial

Lake Outburst Floods (GLOF).



169126-40ER-0009-00 1-35

The tentative peak discharge estimated at the dam site on Dri limb is reported as

1170 cumec for an assumed condition that Lake Burst and 100 year flood (6764 cumec)

occur simultaneously. The time of travel of flood wave from lake to the dam site is

approximately 3.13 hours.

The tentative peak discharge estimated at the dam site on Talo (Tangon) limb is reported as

2143 cumecs for an assumed condition that lake burst and 100 year flood (5167 cumec)

occur simultaneously. The time of travel of flood wave from lake to the dam site is

approximately 1.75 hours. The details of GLOF study has been given in Volume-II (Hydrological Studies) of DPR. CEA/ CWC has already given the concurrence for GLOF

Studies and same has been used for planning purposes.

1.7 References

1) Bureau of Indian Standards, Indian Standard No. IS 11223-1985, “Guidelines for

Fixing Spillway Capacity”.

2) Bureau of Indian Standards, Indian Standard No. IS 14815-2000, “Design Flood for

River Diversion Works – Guidelines”.

3) Bureau of Indian Standards, Indian Standard No. IS 12182-1987, “Guidelines for

Determination of Effects of Sedimentation in Planning and Performance of

Reservoirs”.

4) Bureau of Indian Standards, Indian Standard No. IS 5477 (Part II)-1994, “Fixing the

Capacities of Reservoirs-Methods”.

5) Guide to Hydrological Practices, “WMO No-168”, 5th Edition, 1994.

6) Flood Estimation Report for North Brahmaputra Basin-Subzone 2(a), Hydrology

Directorate, CWC, New Delhi, 1991.

7) Manual on Estimation of Design Flood, CWC, New Delhi, March-2001.

8) Preliminary Feasibility Report, 4000 MW Etalin H.E. Project, April, 2004.



169126-40ER-0009-00 i

TABLE OF CONTENTS PAGE NO.

6 PROJECT GEOLOGY .............................................................................................. 6-1

6.1 Introduction ...................................................................................................... 6-1

6.2 Geology of Project Area ................................................................................... 6-2

6.3 Field Investigations .......................................................................................... 6-2

6.3.1 Geological mapping.............................................................................. 6-3

6.3.2 Sub-surface Investigations ................................................................... 6-3

6.4 Geotechnical Appraisal of Project Components ............................................. 6-13

6.4.1 Dri Diversion site ................................................................................ 6-13

6.4.2 Headrace Tunnel (HRT) Dri Limb ....................................................... 6-17

6.4.3 Talo (Tangon) Diversion Site .............................................................. 6-18

6.4.4 Headrace Tunnel (HRT) Talo (Tangon) Limb ..................................... 6-25

6.4.5 Underground Powerhouse Complex ................................................... 6-26

6.5 Seismicity and Seismotectonics ..................................................................... 6-35

6.6 Conclusion ..................................................................................................... 6-36

Arun

Typewritten Text

Annexure-V



169126-40ER-0009-00 ii

LIST OF TABLES PAGE NO.

Table 6-1: List of Seismic Profiles at Etalin HEP ................................................................ 6-3

Table 6-2: Details of Exploratory Drill holes at Etalin HEP .................................................. 6-4

Table 6-3: Exploratory Drift details at Etalin HEP ............................................................... 6-9

Table 6-4: Laboratory Test Results .................................................................................. 6-12

Table 6-5: Insitu test results of the drifts ........................................................................... 6-13

Table 6-6: Average Orientation of Discontinuities at Dri Diversion Site ............................. 6-14

Table 6-7: Average orientation of discontinuities at Talo (Tangon) Diversion Site – Alternative-II .................................................................................................... 6-19

Table 6-8: Details of Discontinuity in the Desander Area – Talo (Tangon) Headworks ..... 6-23

Table 6-9: Average Orientation of Discontinuities Traversing the Rock Mass in Powerhouse Complex Area in order of Prominence ........................... 6-28

Table 6-10: Details of exploratory Drifts at powerhouse area ........................................... 6-28



169126-40ER-0009-00 iii

LIST OF PLATES

Plate 6-1 Project Area - Geological Map

Plate 6-2 Dri Limb - Dam Site Geological Plan of

Plate 6-3 Dri Limb - Dri Dam Axis Geological Section

Plate 6-4 Talo (Tangon) Limb - Dam Site Geological Plan

Plate 6-5 Talo (Tangon) Limb - Talo (Tangon) Dam Axis Geological Section

Plate 6-6 Powerhouse Complex - Geological Plan of

Plate 6-7 Powerhouse Complex - Geological Section along Surge shaft, Pressure shaft, Powerhouse and TRT



169126-40ER-0009-00 6-1

6 PROJECT GEOLOGY

6.1 Introduction

The proposed Etalin Hydroelectric Project is located in Dibang Valley district of

Arunachal Pradesh. To its west lies Upper Siang district and its southern boundary is shared

by Lower Dibang valley district. The Etalin Hydroelectric project envisages utilization of the

discharges of the rivers Dri and Talo (Tangon) to generate 3097 MW of power including 27

MW installed capacity contributed by two small hydro schemes at the toe of the Dams at Dri

river and Talo (Tangon) river. The project layout conceived by CEA during pre-feasibility

stage and subsequently reassessed by NHPC is more or less similar. The project envisaged

two separate diversion dams each on river Dri and Talo (Tangon) and a common

underground powerhouse at the confluence of Dri and Talo (Tangon) near Etalin village. The

layout has been studied further and the best suitable options for locating the project features

have been evolved.

Initially, two alternative sites were proposed for river diversion at Dri site. The Alternative-I

dam site is located near Eron village, about 1.5km downstream of the Ayo Pani nallah

confluence. Another Alternative-II dam site was proposed at about 250m downstream of

Alternative-I. Although the geological environs at both the alternative sites were almost

similar, but keeping in view the curvature in the course of river and grossly inadequate width

of the valley required to route 11811 cumecs of design flood at the diversion site

Alternative-I, it was felt that diversion site Alternative-II, where river flows along a straight

course through about 110m wide valley is adequate to route the design flood.

In case of Talo (Tangon) limb, the diversion site Alternative-I, identified by NHPC during PFR

stage, is located about 600m downstream of the Anon Pani nallah confluence. On the Talo

(Tangon) limb, the left bank at the selected dam axis did not appear very favorable due to

the existence of a large terrace. Upstream and downstream of this axis, the river flows along

the right bank in a width of 20m while shoal formation on the left bank extends up to 50m in

width at places and is covered by large boulders as big as 5 cubic meter in size. With the

riverbed elevation at this location being around El. 945m, the height of dam for an FRL of

El. 1050m would be around 110m above the existing riverbed level. Subsequent to

geological mapping and exploration at riverbed through two drill holes at Alternative-I site,

it was found that the thick terrace deposits extending upto a considerable height on the left

abutment and the thickness of overburden is more than 70m in the riverbed at this site.

Keeping in view the results of initial explorations and other aspects discussed above, It was



169126-40ER-0009-00 6-2

decided not to pursue the site Alternative-I further and concentrate further explorations on

the identified Alternative-II site, located about 2.3 km upstream Based on the results of

subsequent detail investigations the Alternative-II site was found favourable for a concrete

dam which was finally adopted.

Finally, the project envisages construction of 101.5m and 80m high diversion dams across

rivers Dri and Talo (Tangon), respectively, and two separate water conductor systems

conveying the designed discharge to a common underground powerhouse located near the

confluence of both the rivers at Etalin.

6.2 Geology of Project Area

The area of the proposed project is located on the eastern limb of the Eastern Syntaxial

Bend (ESB) in eastern part of Arunachal Pradesh. The major rock units exposed in and

around the proposed project belong to Ithun Formation, Hunli Formation and Diorite –

Granodiorite – Granite Complex or Lohit Plutonic Complex and Mishmi Group. However,

rocks of Hunli Formation which are exposed on the southern side of Talo (Tangon) river are

not likely to be encountered in any of the project components. Ithun Formation comprises a

sequence of biotite gneiss with quartzite, amphibolite, calcareous quartzite, carbonate bands

and garnetiferous mica schist with kyanite and sillimanite. The Mishmi diorite - granodiorite –

granite complex, commonly known as the Lohit diorite - granodiorite – granite complex, is

characterized by a wide variation in rock types from diorite, granodiorite to granite, with

gradational contact between them.The diorite – granodiorite – granite complex in the area

has undergone polyphase deformation.

6.3 Field Investigations

After assessing and optimizing different alternative layouts suggested in PFR, preliminary

alternative layouts were identified for DPR stage and extensive surface and subsurface field

investigations were undertaken, since 2010, at different locations of both the limbs of

proposed project layout.

The investigations include detailed geological mapping of project components and reservoir

area, petrography of samples; exploratory drilling (46 no. of drill holes of cumulative length

2892.15m), exploratory drifting (7nos of cumulative length of 531m), geophysical exploration

(1342 m) and construction material survey .



169126-40ER-0009-00 6-3

6.3.1 Geological mapping

Geological mapping on 1:1000 scale of the project area was carried out at Dri and Talo

(Tangon) dam, diversion tunnel, underground powerhouse sites. The HRT alignments and

reservoir area was covered on 1:10,000 and 1:5000 scale respectively. Efforts were made to

collect geotechnical parameters of each outcrop and interface of outcrops and overburden

delineated on the map as shown in Plate 6-1, 6-2, 6-4 and 6-6, in spite of constraints posed

by limited accessibility to the area and existence of dense forest.

6.3.2 Sub-surface Investigations

Geophysical Investigation

Geophysical investigation comprising seismic refraction profiling at the project area was

carried out by M/S Tojo Vikas International (Pvt.) Ltd during March - April, 2010. The seismic

refraction survey carried out in the area indicated that the P- wave velocity for compact

strata comprising of overburden or highly weathered rock varies from 2650 to 3370 m/s.

The detail report is appended in Volume-IIIC. The details of seismic refraction profile are

summarised in the Table 6-1 given below.

Table 6-1: List of Seismic Profiles at Etalin HEP

S.No. Site Seismic Line No.

Length (m)

1 Dri Diversion site DP-5 115

2 Dri Diversion site DP-6 115

3 Powerhouse Area EP-1 115




7 Talo (Tangon) Diversion Site Alternative-1

TALO (TANGON)-

1 115


TALO (TANGON)-

2 115


TALO (TANGON)-

3 92

TOTAL 1342



169126-40ER-0009-00 6-4

Exploratory Drilling

The summary of subsurface exploration carried out by exploratory drilling is given in the

Table 6-2.

Table 6-2: Details of Exploratory Drill holes at Etalin HEP

S. No. Drill hole No.

Location Collar Elevation

(m)

Total dept

h (m)

Depth of Overburden

& Bedrock

Elevation (m)

Dri Diversion Site

1 DH-D1 Riverbed; Dam Axis El. 972.030 93 17.7 & 956.39

2 DH-D2 Riverbed; Dam Axis El. 968.07 102 19.3 & 948.77

3 DH-D3A Left bank terrace; Dam

Axis

El. 970.17 102 10.5 & 959.67

4 DH-D4 Right bank; about 150m

D/S of Dri Dam Axis

El. 971.25 30 10.5 & 960.75

5 DH-D5 Left bank; about 150m

D/S Dri Dam Axis

El. 965.020 52.5 7 & 958.02

6 DH-D6 Riverbed; plunge pool

area

El. 962.79 46.5 7.22 & 955.57

7 DH-D9 Riverbed –upstream

cofferdam.

El. 976 48.5 15.5 & 961.85

8 DH-D10 Right bank –Diversion

tunnel Inlet area

El. 1000.28 29.3 12 & 988.28



169126-40ER-0009-00 6-5

9 DH-D11 Riverbed – spillway area El. 969.715 36 18.76 &

950.955

10 DH-D12 Right bank - Diversion

tunnel outlet area

El. 1000 40.5 10.06 & 989.4

Talo (Tangon) Diversion Site Alternative-I

11 DH-T2 On left bank, Dam Axis El. 953.23 97.5 81 & 875.23

12 DH-T3 On left bank, Dam Axis Abandoned 21 Abandoned

13 DH-T4 On left bank, Dam Axis El. 957.159 102.5 61 & 896.159

Talo (Tangon) Diversion Site Alternative-II

14 DH-T5 On right abutment, Dam

Axis

El. 1050.35 60 18 & 1032.35

15 DH-T6 On right abutment, Dam

Axis

El.

1028.135

64.5 39.6 &

988.535

16 DH-T7 Riverbed on right side,

Dam Axis

El. 1003.15 80 26 & 977.2

17 DH-T8 Terrace on left side, Dam

Axis

El.

1006.741

19 5.30 &

1001.391

18 DH-T8A Riverbed on left side,

Dam Axis

El. 1006.43 100 13 & 993.423

19 DH-T9 Center of rive bed,

Upstream of Dam Axis

El. 1004.15 47 29 & 975.15



169126-40ER-0009-00 6-6

20 DH-T10 Intake portal area El. 1032.02 60 40 & 992.02

21 DH-T11 Intake portal area El. 1080.23 40 18 & 1062.23

22 DH-T12 Left bank.Upstream of

Intake area

El. 1020.63 48.5 27 & 993.68

23 DH-T13 Riverbed, Upstream of

Intake area.

El. 1007.15 48 12 & 995.15

24 DH-T14 Left bank, Spillway area El.

1005.939

47.5 6 & 999.939

25 DH-T15 Riverbed, Spillway area El. 1000.35 47 33.5 & 966.85

26 DH-T16 Riverbed, Plunge pool

area

El. 1000.30 45 29 & 971.3

27 DH-T17 Left bank – diversion

tunnel outlet area

El. 1050.55 52.5 9.2 & 1041.35


tunnel outlet area

El.

1019.714

26.5 7 & 1012.714


tunnel inlet area

El.

1044.712

24.5 10 &

1034.712


tunnel inlet area

El.

1021.138

35 22.1 &

999.038

31 DH-T21 Feeder tunnel crossing

with Kun nallah. Desilting

area

El.

1050.539

55 5 & 1045.644



169126-40ER-0009-00 6-7


with Kun nallah, Desilting

area

El. 1075.50 70 11.5 &

1064.089


with Kun nallah, Desilting

area

El.

1085.954

60 3.5 &

1082.454

34 DH-T24 Right bank at about 100m

D/S of dam axis

El. 1040.16 43 26 & 1014.16

35 DH-T25 Desanding area El. 1095.20 140 9 & 1087.41

Dri Headrace Tunnel Area

36 DH-DHR1 HRT crossing with Kabo

Pani nallah – Old

alignment

El.

1257.346

65 21 &

1236.346

37 DH-DHR2 HRT crossing with Ru

Pani nallah at lower

elevation

El.

1100.975

93.5 42.5 &

1058.475

38 DH-DHR3 HRT crossing with

Chambo Pani nallah

El.

1100.541

100 0.0 &

1100.241

39 DH-DHR4 HRT crossing with Ru

Pani nallah.

El.

1115.068

142 15 & 1102.8

Talo (Tangon) Headrace Tunnel Area

40 DH-THR1 HRT crossing with Ron

Pani nallah

El. 1120m –

proposed

In progress



169126-40ER-0009-00 6-8

41 DH-THR2 HRT crossing with Maru

Pani nallah

El. 1118.3 102 7.5 & 1110.80

42 DH-THR3 HRT crossing with Masa

Pani nallah

El. 1085m -

proposed

In progress

43 DH-T1 Adit T1 portal area In progress

44 DH-T2 Adit T2 portal area In progress

Surge Shaft and Penstock Area

45 DH-SS1 Surge Shaft area – Talo

(Tangon) limb

El. 1127.80 71 50.152 &

1077.68

46 DH-SS2 Surge Shaft area – Dri

limb

El.

1111.589

150 18 &

1093.589

47 DH-SS3 Surge Shaft area – Talo

(Tangon) limb

El.

1099.084

130.2 13.5 &

1086.34

48 DH-SS4 Surge Shaft area – Dri

side

El.

1126.298

40 4.5 & 1122.15

49 DH-PS1 Pressure Shaft area – Dri

limb

El. 978.407 45 4 & 974.407

50 DH-PS2 Pressure Shaft area –

Talo (Tangon) limb

El.

1109.371

90 59 &

1050.371

51 DH-PS3 Pressure Shaft area – Dri

limb

El.

1022.290

25 0.5 &1021.79

Powerhouse and TRT Area



169126-40ER-0009-00 6-9

52 DH-TR2 TRT area El. 677.96 72.1 6 & 671.96

53 DH-AD1 Adit portal El. 857.256 25 11 & 846.256

54 DH-AD2 Adit portal El. 783.879 46.5 36.5 &

747.379

55 DH-MD1 MAT portal AREA – Dri

side

In progress

56 DH-MT1 MAT portal area – Talo

(Tangon) side

In progress

The drill hole log sheets appended in Volume-IIIC of the DPR.

Exploratory Drift

The following exploratory drifts were undertaken to study the nature of insitu rock mass at

major project component sites.The details are given below in Table 6-3.

Table 6-3: Exploratory Drift details at Etalin HEP

S. No. Drift No.

Location Elevation (m)

Total Length (m)

Dri Dam Site

1 DR -

D1

Left abutment of Dri

Dam axis

1030 40.5m (proposed 10m cross cut

upstream and downstream at RD

40.5m)

2 DR –

D2

Left abutment of Dri

Dam axis

1000 30m (proposed 10m cross cut


30m)



169126-40ER-0009-00 6-10

3 DR –

D3

Right abutment of Dri

Dam axis

1000 In progress (38m as on

02.07.2012) (proposed 10m

cross cut upstream and

downstream at RD 40m)

4 DR –

D4

Right abutment of Dri

Dam axis

1030 In progress(15m as on

02.07.2012) (proposed 10m

cross cut upstream and

downstream at RD 40m)

Talo (Tangon) Dam Site

5 DR -

T1

Right abutment of

Talo (Tangon) Dam

axis



46m)

6 DR –

T2

Left abutment of Talo

(Tangon) Dam axis



40m)

7 DR-T3 Desilting chamber 1023 In progress (130m as on

09.04.2013)

Surge Shaft area

8 DR -

SS1

Surge Shaft – Bottom

Drift

964 286m as on 09.04.2013

Powerhouse Area

9 DR –

EP1

Powerhouse

Chamber

628 In progress (436m as on

09.04.2013)

The 3D Geological logs of drifts are appended in Volume-IIIC of the DPR.



169126-40ER-0009-00 6-11

Rock Mechanics Testing

Insitu and Laboratory rock mechanics tests were conducted in exploratory drifts and on core

samples of drill holes to determine physico mechanical properties of rock mass and intact

rock.The testing was carried by DBM, Mumbai.

The results of these tests are summarised in the Table 6-4 and 6-5 as given below.



169126-40ER-0009-00 6-12

Table 6-4: Laboratory Test Results

Physical / Mechanical tests

DRI TALO (TANGON) POWERHOUSE

Granodioritic Gneiss

Hornblende Granodioritic

Gneiss Granodioritic

Gneiss Calcareous Quartzite

Micaceous Pegmatite

Granodioritic Gneiss Pegmatite Amphibolites Biotite

Gneiss Calcareous Quartzite

Dry Density gm/cm3 2.72 - 2.88 2.89 2.58 - 2.91 2.72 - 2.78 2.65 2.65 - 2.87 2.66 - 2.75 2.97 2.91 - 2.97 2.62

Bulk Density gm/cm3 2.72 - 2.89 2.9 2.59 - 2.91 2.72 - 2.78 2.66 2.66 - 2.86 2.66 - 2.75 2.9 – 2.97 2.91 - 2.98 2.62

Specific Gravity 2.71 - 2.98 - 2.78 - 2.93 2.78 - 2.86 2.77 2.71 - 2.93 2.74 - 2.8 2.93 – 2.97 2.96 - 2.99 2.69

Void Index % 0.03 0.01 0.08 0.02 - 0.03 0.04 0.01 - 0.04 0.02 - 0.03 - 0.01 - 0.02 0.03

Slake Durability Index % 97 - 98 - 95 - 98 98 98 95 - 99 96 – 98 98 98 - 99 98

Porosity % 0.29 - 0.38 0.24 0.3 - 0.65 0.04 - 0.17 0.34 0.25 - 0.78 0.1 - 0.39 0.05 – 0.43 0.06 - 0.77 0.23

Water Absorption % 0.11 - 0.13 0.08 0.05 - 0.22 0.02 - 0.06 0.13 0.09 - 0.28 0.04 - 0.14 0.02 – 0.15 0.02 - 0.26 0.09

UCS (kg / cm2) 232 - 587 240 - 300 188 - 562 177 - 498 262 279 - 1043 747 – 797 742 712 - 1239 -

Point load Index (kg/cm2) 30.21 - 47.78 - 3.67 - 50.97 19.49 -

59.13 37.01 35.15 - 81.07 26.29 - - 77.33

Tensile Strength (kg/cm2) 1.01 - 1.05 1.05 0.6 - 1.11 1.45 - 2.07 0.92 0.94 - 1.85 - - 1.02 -

Modulus of Elasticity (kg/cm2)

2.07x105 - 5.79x105 - 1.96x105 - 4.27 x 105 4.50 x 105 - 2.59x105 - 6.40 x 105 2.59 x 105 5.17 x 105

2.40 x 105 3.12 x 105

Poisson's ratio 0.12 - 0.16 - 0.13 - 0.14 0.13 - 0.11 - 0.15 0.11 0.12 0.13 0.14

Triaxial Compression Test - 'C' kg/cm2

74.99 - 113.41 53.35 - 70.91 - 78.67 - 119.92 152 148.294 - 158 152 -

- ф Degree 24.11 - 45.87 24.22 - 50.96 - 31.33 - 33.32 37 30.2 - 34.6 - -



169126-40ER-0009-00 6-13

The results of laborataoy test is appended in Vollume-IIID.

Table 6-5: Insitu test results of the drifts

Location Test Ed (Gpa) Ea (Gpa) Test C (Mpa) ф (Degree)

Peak Residual Peak Residual

Dri Dam DR-D2

Plate Load Test

2.23 - 3.64 3.05 - 5.79 Shear

Parameters Rock to Rock

0.44 0.16 46º 42o

Plate Jacking

Test 6.7 - 9.75 -

Shear Parameters Concrete to

Rock

0.41 0.15 44º 41o

Talo (Tangon) DR-T2

Plate Load Test

3.00 - 3.25 4.73 - 8.22 Shear

Parameters Rock to Rock

0.41 0.28 40º 38o

Plate Jacking

Test 4.5 - 5.0 -

Shear Parameters Concrete to

Rock

0.43 0.4 39.5º 35o

The detailed report appended in Volme-IIID of the DPR.

Petrography studies of about 26 rock samples were carried out by DBM, Mumbai and AECS

Noida. For this purpose the rock samples were collected from the drill cores, drifts, shoal

deposits and rock exposures in an around project area. The reports are appened in

Volume-IIID and Volume-VIII of the DPR.

Water Pressure Tests (WPT)

The water pressure tests were conducted in all the drill holes using double packer method in

assending order at 3m interval. All the data pertaining to respective drill holes are appended

in geological logs in Vol IIIC of the DPR. In general, the permeability of the bed rock is very

low and recorded up to 2 lugeons. Whereas in the case of closely jointed and fractured rock

mass higher values up to 41 lugeons are observed. The drilling for groutability tests in river

bed of both the dams are in progress the results will be appended in due course.

6.4 Geotechnical Appraisal of Project Components

6.4.1 Dri Diversion site

Two alternative axes at about 250m distance on Dri river have been considered for

identifying suitable location of Dri diversion site. Topography around the area and

preliminary over all assessment at Alternative-I site does not favour for placement of dam



169126-40ER-0009-00 6-14

axis at this site as Dri river flows in meandering course through narrow to wide V-shaped

valley with westerly curvature and convexity towards left bank. Moreover, left bank of river

bank is covered with shoal deposit consisting of large size boulders (up to 3m diameter)

mixed with sand deposits. The Alternative-II site, located 250m down stream, was preferred

based on the topography and preliminary over all assessment.

The bedrock exposed at the site comprises granodiorite/ diorite gneiss, belonging to Mishmi

diorite-granodiorite-granite complex also known as Lohit plutonic Complex. Few exposures

of quartzites have also been mapped in the area along the road sections. Pegmatite veins

ranging in thickness from less than 1m to as much as 5m have been observed at road level

traversing the granodiorite-diorite-gneissic complex. They are mostly emplaced along the

foliation. The general strike of foliation on both the banks is almost N-S, which is across the

flow direction of the river Dri.

The rock discontinuity data, collected during the course of detailed geological mapping

(Plate 6-2) from rock outcrops on both banks of the river and exploratory drifts at the

diversion site has been analyzed with the help of “DIPS” software. The stereographic

projection based on the rock outcrop and exploratory difts data have been used to decipher

different sets of discontinuities as given in Table 6-6.

Table 6-6: Average Orientation of Discontinuities at Dri Diversion Site

Corrected Set No. Aver. Dip Amount Aver. Dip Direction

S2 64º 177º

S3 42º 352º

S4 86º 091º

S5 22º 302º

S1 78º 247º *S1 – Foliation indistinctly scattered developed, and at places gentle dips along it have been observed

It is observed from the analysis of discontinuity data that the granodiorite/diorite gneiss rock

mass is traversed by five prominent joint sets. Among the five joint sets, the joint set S1, S2

and S4 dip into the hill and the other two joint sets S3 and S5 dip valley ward in case of left

bank. In case of right bank the disposition of joint sets with respect to the valley will be just

reverse. While joint set S2 is found most vulnerable for right bank, the joint set S3 is

observed to be most vulnerable for left bank. Inter-section of valley-ward dipping joints may



169126-40ER-0009-00 6-15

lead to formation of unstable planes and wedges during excavation on abutments. All these

aspects have been considered while planning the excavation on both the abutments.

Dam

The river bed is occupied by river borne material (RBM) consisting of boulders, cobbles,

pebbles of granodiorite, amphibolites, quartzite, granodioritic gneiss etc. embedded in sandy

matrix. The depth of overburden in the river section proved by exploratory drilling varies from

10.5m to 19.5m corresponding to EL 959.67m to 948.5m respectively. In order to found dam,

removal of about 19.5m thick RBM followed by about 2.5m weathered rock mass would be

required to achieve acceptable foundation grade at deepest foundation of the Dam. The bed

rock is expected to be reasonably fresh and strong in the riverbed portion and on the

adjoining banks. Provision of dental treatment has been kept where ever shear zone /weak

zones are encountered at foundation grade. In view of Lugeon values, drill core data and

blocky nature of rock mass, consolidation grounting and curtain grouting in dam foundation

will be provided up to a suitable depth for making the foundation monolithic. The geological

section along the dam axis is given in Plate 6-3.

The proposed concrete dam will be founded on strong, jointed, fresh granodioritic gneiss

rock mass. The bedrock exposed on both the banks is strong and generally fresh, however,

degree of weathering increases towards the valley side. Considerable stripping limit (10 to

12m) has been assessed on either bank and accordingly, excavation is required to be

planned to achieve the acceptable foundation grade. Minor rock excavation may be required

for accommodating the spillway for which excavated slopes need to be adequately protected

for proper restoration of stability.

Intake Site

The long axis of the intake structure is aligned suitably as per the requirement of hydraulics

and sediment management. However, in this area, the foundation for intake will have to be

raised from elevation of around El 995m to keep its alignment in line with spillway

arrangement to provide better sediment management and thus structure would have to be

founded on about 26m high concrete pedestal. The bedrock comprising slightly weathered,

jointed and medium strong to strong granodioritic/ dioritic gneiss is exposed at the site.

The rock mass is traversed by five sets of prominent joints including foliation joints. It is

observed that the joint sets S1, S2, and S4 dip into the hill and joint sets S3 and S5 dip

towards valley. Provision of rockbolts has been kept to stabilize the valley dipping joints sets.



169126-40ER-0009-00 6-16

Cofferdams

A 20m high coffer dam from river bed has been proposed at about 57m upstream of dam

axis, to facilitate the river diversion. This structure is concrete-faced with plum concrete core.

Since the river borne deposits in the river bed are expected to be thick and highly

permeable, grouting as cut-off is proposed to minimize the seepage through the foundation

and jet grouting will be resorted in the foundation to bring its permeability to acceptable limit.

The depth of riverinne material at coffer dam is considered as per the exploration data at

dam axis. However a drill hole DH-D9 would be taken up shortly with the objective of

establishing the actual thickness of overburden (RBM) in the river bed.

The down stream coffer dam is proposed to be a random fill dam. Adequate pumping

arrangement may be kept to control the seapage from downstream side.

Diversion Tunnels

In order to divert river water during project construction, four circular shaped diversion tunnel

of 10.9m finished diameter is proposed out of which three are located on right bank and one

is located on left bank. The invert level of inlet structure is at El 975m, where as the outlet

level is EL 964m. Adequate rock cover varing between 40 and 90m is available above the

diversion tunnels along with sufficient lateral cover. The bed rocks anticipated to be

negotiated during tunneling are granodiorite /diorite gneiss with intrusions of pegmatite veins

at the places. Warping and folding on local scale have also been observed in outcrops.

Due to intersection of joint sets, unstable wedge on the roof of tunnels are anticipated and

accodingly suitable design measures are recommended. Based on the surface rock

exposures and exploratory drift data, the anticipated rock mass along the diversion tunnels

are categorized as about 25% of Class II (Good rock), 50% of Class III (Fair rock), 15% of

Class IV (Poor rock) and 10% of Class V (Very Poor rock).

Reservoir and rim study

The construction of 101.5m high concrete gravity dam across river Dri will develop 4.00km

long reservoir with FRL 1045m covering 83.32 hectare area. The geological mapping on

1 : 5000 scale was carried out for assessment of reservoir rim stability and possibility of

leakage of water from this reservoir to near by area. About 1.3km upstream of dam site,

major tributary known as Captain nalah joins the Dri river on left bank. It is very deep nallah

and has deposited a large fan deposit at its mouth near confluence with Dri river. Slopes are

covered with slope wash material and limited rock outcrop of granodiorite /dioritie gneiss and



169126-40ER-0009-00 6-17

quartzite are exposed. In general slopes along the reservoir rim are moderate with

occasional steep rocky outcrops with a thin veneer of overburden cover.

Few landslides, observed along the Etalin-Anini road section at high above the reservoir rim,

have been mapped on 1:5000 scale. Among them, a very prominent landslide is observed

on the left bank of Captain/Ayopani nallah, with its crest at about El 1215m and the bottom at

El 1100m, which is about 55m above the reservoir rim. The width is about 80m on the road

cut and width reduces to 20m at the top. This is an active landslide and the materials

triggered in this slide are angular and sub-angular rock fragments of granodioritic gneiss,

micaceous schist with silty and clayey matrix. Similarly, just opposite to this landslide on the

right bank of Captain/Ayopani nallah, a comparatively small slide is mapped, which is more

or less similar in nature. Few more small slides are observed in the area but their location is

above the road and has almost no impact on the reservoir rim.

The ground above the reservoir rim is continuously rising and the river valley within the

submergence is water-tight and no pervious and cavernous rock formations are observed.

Therefore apprehension of leakage through reservoir to adjacent area is almost negligible.

6.4.2 Headrace Tunnel (HRT) Dri Limb

A 11.3m finished diameter and 10722m long circular shaped headrace tunnel (HRT) has

been proposed on left bank of river Dri, with a view to convey 480.3 cumecs of design

discharge from diversion site to the underground powerhouse.

The headrace tunnel, immediately downstream of the intake tunnels, for a length of about

400m, is aligned in N162º - N342º direction. Thereafter, the HRT is aligned in N062º - N242º

direction up to RD 2550m. Further downstream, between RD 2550m and 5700m, it is

aligned in N149º - N329º directions. The HRT, downstream of RD 5700m, follows

N194º - N014º direction up to RD 8100m where it again turns towards N175º and follows

N355º -N175º direction until it joins surge shaft at RD 10750m.

The proposed HRT at Dri limb is expected to encounter rock mass comprising granodioritic

gneiss and biotite gneiss in most of its lengths. However, a considerable stretch from

RD1400m to RD 2480m is expected to encounter rock mass with thick calcareous

quartzite/marble bands. Thickness of individual calcareous quartzite/marble bands may be

about 230m. The proposed HRT is expected to encounter a thick zone comprising

multiple/closely spaced shear seams within gneisses between RD 7200m and RD 7450m.

In addition to above, few more such shear seams and weak rock mass zones are expected



169126-40ER-0009-00 6-18

to be encountered below nalah crossings. Bed rock is traversed by four sets of rock

discontinuities, in general. Developement of unstable wedges are expected mainly on roof

and left wall of the Headrace tunnel.

Drill hole DH-DHR1, DH-DHR2, DH-DHR3 and DH-DHR4 drilled along HRT alignment at its

intersection with major cross-drainages have indicated presence of bed rock at tunnel grade

along the proposed tunnel alignment and thickness of rock cover has been inferred as 70 to

200m.

Because of heavy precipitation, experienced in the area and presence of jointed rock mass

at the crossings of the major drainage, moist to heavy dripping water condition in genral

along with isolated pocket of water charged zones, may be encountered during tunneling.

About 10% of total length of tunnel has more than 500m superincumbent cover. Stress

related problems may encounter in such high cover reaches of HRT. A tentative estimate of

rock mass rating indicates that RMR values will mainly vary between 38 and 78 along HRT.

However, RMR values between 15 and 25 are expected in rock mass below major nallah

crossing and also in shear seams pegmatite zones and high cover reaches. Tentative rock

mass classes expected along the HRT are Class II, Class III, Class IV and Class V 25%,

47%, 20% and 8% repectively.

To fecilitate the excavation of 10722m long HRT, three intermediate construction adits at

Kabo pani, Rupani and Chabo pani nala of 301m, 740m and 355m length, joining at HRT at

RD 3045m, 5484m and 8322m repectively have been proposed. A fourth adit of length 267m

is at surge shaft. Although the proposed portals, more or less, are located suitably in bed

rock, yet considerable support measures are required to stabilize the portal slopes. All these

adits are having suffient cover and tunnel alignments are fair to favorable with respect to the

prominent discontinuity planes. All the proposed adits expected to encounter mainly good to

fair rock mass with RMR variying from 40 to78.

6.4.3 Talo (Tangon) Diversion Site

The investigations of Dam site on river Talo (Tangon) were taken up at two alternative dam

sites vide Alternative-I, located 600m downstream from the confluence of Annon pani and

Talo (Tangon) river, and Alternative-II, located 2.3km upstream of the Alternative-I. The

Alternative-I Site is charaterized by the presence of river terrace material on left bank and

limited granodiorite/diorite gneiss rock outcrop along the valley. Further the slopes are

moderate and covered with thin veneer of slope wash material. The subsurface investigation



169126-40ER-0009-00 6-19

comprising three seismic profiling, two drill holes DH-T2 and DH-T4 (Vol IIIC) on left bank

terrace were carried out. The bed rock comprising gradioritic/diorite gneiss encountered at

81m (EL 875.23m) and 61m (EL 896.159m) depths repectively. This site was not found

suitable due to existence of thick overburden (RBM) on left bank terrace and very deep

overburden in river bed at Dam site. Consequent upon the above findings, the Alternative-I

site was abandoned and investigations at Alternative-II site were taken up. At this

Alternative-II site, Talo (Tangon) river flows in NNE - SSW directions with gentle gradient

and a more or less straight course for a considerable length through narrow valley and

moderate to steep abutments.

This area is occupied by slightly weathered granodioritic /dioritic gneiss, biotite gneiss and

quartzite which grade into calcareous quartzite and impure marble. All the rock mass

exposed in this area is characterized by profuse emplacement of pegmatite and silica veins.

The rock mass on both the abutments is prominently foliated, jointed with occasional

sheared and fractured zones. The river bed is covered by fluvial deposits (RBM) comprising

boulders cobbles and pebbles with sand matrix. The right bank is occupied by limited rock

outcrops of granodiorite/diorite gneiss and beyond this, the slope is covered by a thin veneer

of slope wash material.

Bed rock is traversed by four prominent sets of rock discontinuities at this site. The rock

discontinuity data collected during the course of surface mapping (Plate 6-4) and exploratory

drift mapping have been analysed using DIPS software. The details of Joints are

summarised as below in Table 6-7.

Table 6-7: Average orientation of discontinuities at Talo (Tangon) Diversion Site – Alternative-II

Set Aver. Strike Aver. Dip Amount

Aver. Dip Direction

Continuity (m)

Spacing (cm)

Aperture (mm) Roughness

S1 082º-262º 84º 352º >20 6-20 Tight to 0.5 RU**

S2 000º-180º 76º 090º >20 20 - 60 0.25 to 0.5 RU**

S3 052º-232º 36º 142º 10 - 20 >200 0.25 to 0.5 RU**

S4 000º-184º 25º 274º 03 - 10 >200 Tight SP*

*Smooth Planar ** Rough Undulatory

It is observed that joints belonging to sets S1 and S4 dipping at high and low angle towards

valley on the left bank. Similarly, other joints S2 and S3 dipping at steep to moderate angle



169126-40ER-0009-00 6-20

towards valley on the right bank. The joint set dipping towards valley would need attention

while stripping the abutments in relation to possible unstable planes and wedges.

Dam

The proposed dam site on Talo (Tangon) River is characterized by presence of bed rock

exposures on both banks. While the left bank is occupied by bed rock exposures all along

the abutment, isolated bed rock outcrops are observed on the right bank at the site. The river

bed is occuipied by riverine material (RBM) consisting of boulders, cobbles and pebbles of

various rock type within sandy matrix which extends up to about 29m depth, as revealed

from drill hole DH-T9. In view of rock outcrops on both the banks, depth of overburden in

river bed and topography of this site, this site appears to be suitable for concrete gravity dam

with deepest foundation level at El. 972m, top of dam at El. 1052m and spillway located

within dam body. Based on the detailed study of rock mass characteristics on both banks

and exploratory drifts data, 10-12m stripping limit is recommended on abutments. Suitable

slope stability measures would be provided during the abutment excavation to avoid slope

instability due to the presence of vulnerable valley dipping joints. Water pressure test

conducted in drill holes indicates lugeon values of low order and in genral varies from 0.5 to

3.1. In few cases, where fracture zones are encountered, lugeon value has gone up to about

40 lugeon. The bed rock underneath the river bed is fresh and strong. The shear

seams/fractured rock mass or weak zones are anticipated at or near the contact between

calcareous quartzite and granodiorite/diorite gneiss mainly. Dental treatment would be

required along weak zones depending upon their extent and orientation. Provisions of

consolidation grouting and curtain grouting have been kept for making foundation monolithic

and impervious. Geological section along the proposed dam axis is given in Plate 6-5.

Diversion Tunnels

In order to divert river water for the construction of concrete dam, three 11.5m finished

diameters, circular shaped diversion tunnels ranging in length from 368m to 631m, are

proposed on the left bank at this site. The diversion tunnels are aligned in such a way that

sufficient lateral and superincumbent rock cover is available. The tunnels, in genral, are

anticipated to negotiate foliated and jointed granodiorite gneiss, calcareous quartzite and

biotite gneiss, with occasional shear seams and pegmatite veins. Inlet portal of the tunnels

are suitably located on bed rock. Outlet portals, although located on overburden, are

expected to encounter bed rock at depth of less than 20m and these tunnels at the outlet

portion will be designed as structural tunnels till adequate rock cover is available.

The alignment of the diversion tunnels are fair to favorable with repect to the strike of



169126-40ER-0009-00 6-21

prominent rock discontinuities. Formation of unstable wedges is expected on the right wall

and roof of the tunnels. The proposed diversion tunnels are expected to encounter rock

mass of class II, III, IV and V for about 25%, 40%, 25% and 10% of their lengths,

respectively.

Cofferdams

The 22.5m high coffer dam having top elevation at El. 1028.5m and of plum concrete with a

upstream concrete face has been proposed at upstream of main dam. The left bank slope is

occupied by granodiorite rock with pegmatites and the right bank is occupied by huge shoal

deposit in the form of river borne material. This site has been explored by three dirll holes

DH T-10, DH T12 and DH T13. The depth of overburden is ranging from 12m to 40m. The

coffer dam is to be founded on riverine material which is highly permeable in nature. In order

to minimize the ingress of water, provision of cut-off extending to bed rock has been

proposed.

A 9m high embankment type down stream coffer dam is proposed about 200m down stream

of the main dam. A 28.9m (EL971.4m) deep riverine material has been encountered in drill

hole DH-T16 at this site. It is advisable to keep adequate pumping arrangement so that

seapage does not affect the working environment.

Intake Structure and Feeder Tunnels

Three intake structures are envisaged, about 20m upstream of the dam axis on the right

bank of river Talo (Tangon), to convey design discharge of 320.2 cumecs to HRT with invert

at El 1028m. Proposed intakes are followed by three feeder tunnels up to the underground

desilting chambers. The feeder tunnels are aligned in N111º - 291º direction in the initial

reaches. Thereafter, the tunnels turn towards N040º - 220º through a broad curve to join

desanding chambers

Thick fluvial deposits (river terraces) extend up to about 45m above the riverbed i.e., upto

El 1050m at the proposed Intake site. Isolated rock exposurs between EL 1070m and 1085m

are found in the area. The remaining portion of the hill slope above is covered with slope

wash material. The bedrock is traversed by four major joint sets including foliation joints.

This area has been investigated by three drill holes, DH-T10, DH-T11 and DH-T12 and the

bedrock levels were encountered at El. 992.02m, El 1062.23m and El 993.68m, respectively.



169126-40ER-0009-00 6-22

The area is covered by fluvial deposits (RMB) comprising rounded to sub-rounded boulders,

cobbles and pebbles embedded in fine riverine sand. In order to locate the portals of intake

tunnels in the bedrock, an excavation for about 25m in the overburden would be required.

Shallow slope wash material along the gentle hill slope exists which may not cause major

slope stability problem. Suitable support arrangement has been kept to place the portals of

intake tunnels in view of the steeply inclined valley dipping joints.

Considering increasing thickness of the overburden towards the river, hydraulic and silt

management, and crest elevation of intake it was decided to keep the intake structure on a

concrete pedestal raised from about El 995m, where bedrock is expected to be available.

All the three feeder tunnels will be driven through granodioritic gneiss, biotite gneiss and

calcareous quartzite that grades to impure marble along their lengths up to the location of

desanding chambers. Granodioritic gneiss and quartzite, which is of calcareous nature, are

the predominent litho-units which are likely to be encountered along these tunnels.

Minor shear seams and pegmatite veins are also expected at few locations along the tunnel

alignments.

These feeder tunnels will cross below a surface drainage, namely Kun nallah. Three drill

holes DH-T21, DH-T22 and DH-T23, have been drilled in the Kun nallah with a view to

delineate the thickness of the overburden in the nallah section and assess the adequacy of

the rock cover. The rock covers above feeder tunnels are ranging from 35m to 65m. Based

on the data obtained from surface mapping and subsurface explorations carried out at site,

rock mass likely to be met along feeder tunnels are 25% of Class-II, 40% of Class-III, 25% of

Calss-IV and 10 % of Calss-V.

Desanding Arrangement

An underground desanding arrangement has been proposed on the right bank of Talo

(Tangon), beyond Kun nallah. Three numbers of desanding chambers each having size of

18.5m (W) x 26.5m (H) x 350m (L) have been propose. The silt flushing arrangement back to

river Talo (Tangon) will be through 5m (W) x 5.7m (H) x 515m (L) flushing tunnel at outlet

level El. 999.55m. The desanding chambers are aligned in N0400-N2200 direction with cover

varying from 80 to 270m above which is considered sufficient.

The area around the site proposed for the desanding arrangement is, in general, covered by

slope wash deposits consisting of fragments of granodiorite, quartzite and biotite gneiss in

sandy and silty matrix. Isolated rock outcrops comprising granodiorite gneiss with



169126-40ER-0009-00 6-23

intercalated biotite gneiss and quartzite of calcareous nature which grades into impure

marble at places, is observed in the vicinity of Kun nallah. Pegmatite veins impregnating

extensively all the litho-units have been observed in the area. Rock mass is traversed by

three prominent joint sets in addition to foliation joints. The discontinuity data collected

during the course of geological mapping has been analysed using DIPS software, results of

which are given in Table 6-8.

Table 6-8: Details of Discontinuity in the Desander Area – Talo (Tangon) Headworks

Set Strike Average Strike

Aver. Dip Amount

Aver. Dip Direction

Continuity (m)

Spacing (cm)

Aperture (mm)

Rough-ness

S1 075º- 098º 089 º 88º 179º >20 6-20 Tight to 0.5 RU**

S2 037º- 065º 052º 70º 142º >20 20 - 60 0.25 to 0.5 RU**

S3 172º- 187º 180º 86º 270º 10 - 20 >200 0.25 to 0.5 RU**

S4 220º- 311º 271º 09º 001º 03 - 10 >200 Tight SP*

*Smooth Planar ** Rough Undulatory

This area has been explored through three drill holes, DH-T21, DH-T22 and DH-T23, and

exploratory drift DR-T3 (16m length) of which logs is appended in Volume-IIIC. Further the

drift excavation is under progress. The bedrock comprising granodiorite gneiss, biotite

gneiss, and quartzite intruded by pegmatites has been encountered at depth varying

between 3.5m and 11.5m, as revealed from drill hole logs.

Relationship of long axis of underground desilting chambers with strike of major rock

discontinuities indicates that it is fairly to favourably aligned with respect to the average

strike of joints belonging to sets S1, S3 and S4 is concerned, and the situation is adverse as

far as average strike of the joints belonging to set S2 is concerned.

Keeping in view the size of the underground desilting chambers and pattern of the rock

discontinuities, wedge analysis has been carried out. The results of the analysis for the most

adverse case indicate that altogether eight wedges are likely to form due to intersection of

joints belonging to sets S2, S3 and S4. Out of these, all the wedges are stable, except for

roof wedge which is found to be unstable. Provision of sufficient rock supports has been kept

accordingly.

The in-situ rock mechanics test such as hydrofrac test etc. would be conducted at

appropriate loation of chamber. The results of rock mechanics test and geological



169126-40ER-0009-00 6-24

assessment of exploratory drifts will be utilized to optimize the alignment of the chamber and

design supports. However, the provision of dywidag rock bolts has been kept at present.

Based on the data obtained from surface mapping and subsurface explorations carried out

at site, percentage of rock mass classes with respect to total length of desilting chambers

are estimated as 30% of Class-II, 40% of Class-III, 20% of Class-IV and 10 % of Class-V.

However, in view of very limited rock outcrops around the proposed structure, the estimation

is based on such limited data. The rock support will be reviewed after the rock mechanics

test and data from the balance drifting is analysed.

Silt flushing arrangement for desanding chambers has been proposed downstream of

confluence of Kun nallah with Talo (Tangon) river. Flushing ducts, in the initial reaches, are

aligned in N177º - N357º direction. It is observed that alignment of the flushing ducts in the

upstream reaches is askew by 88º with respect to strike of joints belonging to set S1, which

is most favorable condition. It is askew with respect to joints belonging to sets S2, S3 and S4

by 55º, 03º and 86º, respectively. It indicates that flushing ducts, in this reach, are aligned

very favorably in case of joints belonging to sets S1, S2 and S4 and very unfavorably in case

of to set S3. Further alignment of the flushing ducts, downstream of the bend, and the single

flushing tunnel thererafter up to outlet portal is askew with respect to the strike of the joints

belonging to sets S1, S2, S3 and S4 by 43º, 80º, 48º and 41º, respectively which indicates

fair to favorable alignment for the feeder tunels. The proposed outlet portal of flushing tunnel

is suitably located on bed rock comprising granodioritic gneiss.

Based on the data obtained from surface mapping and subsurface explorations carried out

at site, percentage of different rock mass classes along flushing tunnel are estimated

tentatively as 35% Class for II, 40% for Class-III, 15% for Class-IV and 10 % for Calss-V.

Talo (Tangon) Reservoir

The construction of 80m high concrete gravity dam with Dam top at 1052m and FRL of

1050m across river Talo (Tangon) shall develop a reservoir inundating approximate 36.12 ha

area with respect to FRL and about 2.5km length.

The geological mapping of the reservoir area was carried out on 1:5,000 scale with a view to

assess the reservoir rim stability and identifying the vulnerable reaches with special

reference to landslides and possibility of any seepage after impounding of reservoir.

The traverses in the reservoir area indicated that along the valley slopes upto FRL

(Full Reservoir Level) and between FRL and MDDL (Minimum Draw Down Level), bedrock is



169126-40ER-0009-00 6-25

exposed at few reaches and most of the area is occupied by river borne material at lower

reaches followed by slope wash material above. No major landslide scar or evidences of

slope instability were observed during surface geological mapping at this site except a few

small slide scars. Five minor slide scars on the left bank and one on the right bank have

been noticed. Slope instability around these slide zones due to heavy precipitation cannot be

ruled out; however, reservoir impoundment may not play any role for its activation.

Thus, protection measures to stabilize the slide may be kept for safety of the reservoir rim.

6.4.4 Headrace Tunnel (HRT) Talo (Tangon) Limb

A 9.7m finished diameter and 13045m long circular shaped headrace tunnel (HRT) has been

proposed on the right bank of Talo (Tangon) river with a view to convey 320.2 cumecs of

design discharge from diversion site to the underground powerhouse at the confluence of

Talo (Tangon) and Dri rivers near Etalin Village.

The headrace tunnel, immediately down stream of desanding chambers, is aligned in

N040º - N220º direction for about 320m length. Then it turns towards N094º - N274º

direction up to RD 3460m near Ron pani nallah crossing in Sector -1. From RD 3460m up to

RD 6500m near Maru pani nallah crossing, the Headrace tunnel is alingned in N088º -

N268º direction in Sector-2. Further down stream, from RD 6500m upto RD 9820m near

Masa pani nallah crossing the headrace tunnel is aligned in N052º - N232º direction in

Secter-3. The HRT down stream of RD 9820m upto the surge shaft is aligned in N061º -

N241º direction in Sector-4. Invert at Intake is at EL1028m and it joins surge shaft at

EL970m, and over all gradient along the HRT is 1in 235.13.

The proposed HRT at Talo (Tangon) limb is expected to encounter bed rock comprising

granodiorite gneiss and biotite gneiss with occasional quartz and pegmatite veins. Few

shear seams, fractured zone and weak rock mass are expected to be encountered below the

major nallah crossings and along litho-contacts. In general, the rock mass is jointed blocky

in nature and about 30% of total length of the tunnel has superincumbent cover of more than

500m. Possibilities of stress related problem in such high cover zones is anticipated. The

bed rock is traversed by more than four joint sets in general. Development of unstable

wedges are mainly expected on the roof and left wall.

The HRT, along its route, will pass under prominent cross drainages, Shu Pani, Ron pani,

Maru Pani and Masa pani. In order to assess the extent of rock cover available above HRT

at those nallah crossings, subsurface exploration by three deep drill holes has been



169126-40ER-0009-00 6-26

proposed at Ron pani, Maru pani and Masa pani nallah crossings. The drilling activity at

Maru pani nallah crossings is under progress.

In general superincumbent cover varies from 90m to 966m. Tentative estimate of rock mass

class indicates that the RMR value varies between 30 and 83. However, RMR values

between 17 and 27 are expected at the tunnel stretches below major nallah crossings and in

shear seams/pegmatite zones and hign cover zones. The tentative rock mass classes

expected to meet along the HRT length are Class-II, III, IV and V as 27%, 44%, 19% and

10% of the tunnel length respectively.

To facilitate the excavation of 13045m long Headrace tunnel, four intermediate construction

adits of length 523,324,514 & 355m are proposed in addition to construction faces from both

ends of HRT. Another adit of length 372m from surge bottom is also foreseen. The bed rock

is exposed at the proposed portals sites for adit T3 but the area around proposed portals for

Adit T1, Adit T2 and Adit T4 is covered with overburden. However, the depth of overburden

is expected to be shallow at the portal site for Adit T1, Adit T2 and T4. The Adits are

expected to encounter good to fair rock mass mainly with RMR variying between 41 and 76.

Provision of suitable slope stabilization measures have been kept for developing portal

structures. The rock classes are almost to be encountered similar to anticipated in HRT.

6.4.5 Underground Powerhouse Complex

The proposed underground powerhouse will be housing 10 units of 307 MW each and is

located within the hill ridge between Talo (Tangon) and Dri rivers, near their confluence.

The underground powerhouse complex has the following componants.

a) Two separate restricted orifice type underground surge shafts - one on Dri limb (26m

diameter and 132m high) and another on Talo (Tangon) limb (21m diameter and 137m

high).

b) Three pressure shafts are proposed on dri limb (each with 5.6m diameter) followed by

six unit pressure shafts (each having 4m dia. and 512m length).

c) Similarly, two pressure shafts are proposed on Talo (Tangon) limb, each with 5.6m

diameter. These preassure shafts further branch into four unit pressure shafts (each

having 4m diameter and 512m length).

d) An underground powerhouse cavern of dimensions 352m(L) X 23.5m(W) X 59.73m(H),

with installed capacity of 3070MW (10X307 MW) is proposed. A 349.6m long, 16.5m



169126-40ER-0009-00 6-27

wide and 24m high underground transformer hall is also proposed about 50m

downstream of powerhouse cavern.

e) Two numbers of Main Access Tunnels were proposed for the project, one accessing the

powerhouse from Dri Side (473m long) and another from Talo (Tangon) side (779m

long). Both the access tunnes are D shapped 8m (H) and 8m (W).

f) Tailwater discharge arrangement from the proposed powerhouse up to the tailrace

outfall on Dri side includes three connecting tunnels followed by one 555m long and

11.3m diameter circular shaped main tailrace tunnel, for discharging the tailwater back

into the river.

g) Similarly, the proposed tailwater discharge arrangement from powerhouse up to the

tailrace outfall on Talo (Tangon) side includes, two connecting tunnels followed by one

544m long and 9.5m diameter circular shaped main tailrace tunnel, for discharging the

tailwater back into the river.

The area around proposed powerhouse complex is confined to a ridge delimited by the

rivers Dri and Talo (Tangon) on either side. Most of the area is covered by thick overburden

that supports very dense vegetation. The rock outcrops are scanty in general and mostly

confined to lower level near confluence of both the rivers and in the slope cut along the

existing road.

Detailed geological map of the powerhouse site (Plate 6-6) indicates that the left bank slope

of Dri river is moderate up to the Etalin – Anini road, above which it is moderate to steep and

becomes very steep as one approaches the crest of the ridge. The hill slope in the area is

covered by slope wash deposits.The slope wash material is mainly composed of angular to

sub-angular fragments of granodioritic gneiss, calcareous quartzites, biotite gneiss and

pegmatites with silty and clayey matrix. Two small ephemeral nallahs descend on the slope

and join river Dri at about 500m and 850m upstream of the confluence. These nallahs have

limited catchment and are of little consequence. Sporadic bedrock exposures are observed

on the valley slope above Etalin-Anini road. However, the bedrock is extensively exposed

along the road cuts and below, mainly upto the riverbed near the confluence.

The right bank slope of river Talo (Tangon) is, in general, gentle and gradually becomes

moderate to steep above El. 775m. The right bank slope of Talo (Tangon) river rises steeply

along the ridge. The hill slope is covered by slope wash deposits comprising angular to sub-

angular fragments of calcareous quartzite, biotite gneiss, granodiorite and pegmatite with

clayey and silty matrix.



169126-40ER-0009-00 6-28

Bedrock comprising granodiorite gneiss, diorite gneiss, calcareous quartzite, biotite gneiss,

and pegmatite has been observed along the river edge and/or along the road cuts near

Etalin village and downstream of Etalin village, near the confluence. Besides this, bedrock

on the valley slope is also occasionally observed in patches at higher elevations.

The foliation is not very well developed within the rock mass in this area. However, the

general strike of the foliation is E-W with sub-vertical dips swinging its dip direction from

north to south due to warping. The rock mass in the area is traversed by four major sets of

joints (Table 6-9). The geological map of powerhouse area is given in Plate 6-6.

Table 6-9: Average Orientation of Discontinuities Traversing the Rock Mass in Powerhouse Complex Area in order of Prominence

Joint set

Strike Dip Dip direction

Average Range Average Range Average Range

S1 263º 276º - 245º 88º 63º - 89º 353º 335º -006º

S2 166º 140º - 187º 52º 35º - 65º 256º 230º - 277º

S3 346º 315º - 010º 20º 12º - 28º 076º 045º - 100º

S4 006º 358º - 014º 82º 75º – 86º 096º 088º - 104º

In addition to eight drill holes as mentioned in Table 6-2, this area has been further

invesitigated by two exploratory drifts to understand rock mass condition and assessment of

support requirement. Subsurface exploration plan of the powerhouse includes two

exploratory drifts with a view to explore the actual rock mass condition and assess the

support requirement. The details of the drifts are given below in Table 6-10.

Table 6-10: Details of exploratory Drifts at powerhouse area

Drift No. Location Total Length (m) Remarks

DR – SS1 Up to surge shaft bottom – Dri Limb - Completed 286m

DR – EP1 Upto powerhouse 800 (proposed) Completed 436m

The details 3D geological logs of these drifts are appended in Vol-IIIC of the DPR. These

drifts are still in progress. The hydrofrac test in powerhouse drift is to be undertaken by

NIRM, Bangalore shortly to measure stresses and substantiate the orientation of the loger

axis of the powerhouse cavern.



169126-40ER-0009-00 6-29

Surge Shaft

As conceived, the project has two headrace tunnels (HRTs) – the Talo (Tangon) limb HRT

located within the right bank of Talo (Tangon) river and the Dri limb HRT is located within the

left bank of Dri river. Each HRT has been planned to terminate into their respective surge

shafts located with sufficient lateral distance from each other on the ridge between Talo

(Tangon) and Dri rivers near confluence.

The HRT on Dri limb would terminate at El 970m into an open to sky surge shaft with top

elevation at El 1107m. Similarly, other open to sky surge shaft is proposed with the bottom of

surge shaft at El 970m and top at El 1107m.

Since slope wash deposits mostly cover the entire area, four drill holes (DH SS-1, DH SS-2,

DH SS-3 and SS-4) were drilled to determine the depth to bedrock and assess the rock

mass condition likely to be encountered during the excavation of surge shafts. The drill holes

indicated the presence of granodioritic/dioritic gneiss predominently intruded by pegmatite

veins. From the summary of drill hole data at powerhouse complex, it is evident that rock

mass likely to be encountered during the excavation of surge shafts would, in general, be fair

to good. In the drill hole DH SS-2 overburden thickness of about 50.15m is recorded and,

thereafter, bedrock of granodioritic/dioritic gneiss with numerous pegmatite are observed.

The depth of overburden comprising slope wash deposits varies between 4.5m and 20m at

the proposed surge shaft top area.

Apart from this, an exploratory drift DR SS-1 of 230m length have been proposed from invert

level El 964.39m and it is already driven up to 286m length. The over all rock mass in this

drift is granodiorite with pegmatite and quartz vein intrusions. These geological sections

(Plate 6-7) also indicate that the surge shafts would be excavated mostly through fresh, hard

and jointed blocky rock mass. A pegmatite zone may be encountered at the bottom level of

the surge shaft at El 970m; otherwise surge shaft will be mainly excavated through

granodioritic/dioritic gneiss rock mass. As the rock mass is traversed by four sets of joints,

formation of unstable wedges along the surge shaft walls is anticipated, wherein S2 joint set

will play important role for north-east wall and S4 joint will play as failure surface for

north-west wall. Thus, necessary protection measures will be taken to contain the wedges

formed during excavation.



169126-40ER-0009-00 6-30

The entire surge shaft of Dri limb will be excavated in granodioritic/dioritic gneiss rock mass

traversed by pegmatite bands and small amphibolites bodies. Formation of wedges would be

similar to that of the surge shaft of Talo (Tangon) limb

Both the surge shafts are proposed as open to sky structures. A platform connecting both

the surge shaft is to be developed by removing the overburden and thereby stabilizing the

back slope towards the northern side. As such, no major problem is anticipated, as rock

mass likely to be encountered during excavation has been assessed as fair to good class.

Two adits have been proposed one from Dri side and other from Talo (Tangon) side up to

the bottom of two surge shafts to facilitate construction. Geological Section along surge

shaft, pressure shaft, power house and Tailrace tunnel is given as Plate 6-7.

Pressure shafts

Two pressure shafts are proposed to originate from Talo (Tangon) limb surge shaft, which

will be bifurcated into total four unit pressure shafts. The pressure shafts are proposed to be

steel lined throughout entire length. A valve chamber has been envisaged downstream of

surge shaft. Keeping this in view, an intermediate construction adit has been provided at El

775m. Drill holes DH-SS1 and DH-SS3 indicate availability of bedrock at El 1077.68m and

El 086.34m, respectively whereas DH PS-2 indicates presence of bedrock at El 1050.37m.

Result of all the three drill holes are taken in to consideration, while deciding the alignment of

the pressure shafts. It is apparent that the pressure shafts will be excavated in a rock mass

of granodiorite/diorite gneiss intruded by pegmatite veins and amphibolites. The initial reach

of about 15m, the pressure shaft may encounter pegmatite. The rock mass is traversed by

four prominant joint sets including those oriented along the foliation. The horizontal limbs of

pressure shafts are aligned in N39º-N219º direction and are askew with respect to the strike

of the joints belonging to sets S1, S2, S3 and S4 by 44º, 54º, 53º and 33º, respectively.

This indicates that the horizontal limbs of the pressure shaft will be aligned fair to favourable

with respect to the strike of major joint sets. The vertical limbs of the pressure shafts will also

be excavated through fair to good granodioritic/dioritic gneiss. However if any thin shear or

weak zone is encountered in the vertical limb, it may have to be negotiated for a

considerable length as the foliation is steeply dipping.

The geological section reveals that the pressure shafts will be excavated through

granodioritc/dioritic gneiss intruded by pegmatite and amphibolite. Similarly, three steel lined

pressure shafts are envisaged to originate from the Dri limb surge shaft, each of which will

bifurcate in to total six unit pressure shafts. As the arrangement of Dri limb pressure shafts is



169126-40ER-0009-00 6-31

similar to those of Talo (Tangon) limb and the rock attitude in this area is also same, it is

evident that similar geological condition will be prevailed during construction of these

stretches. One valve chamber each has been envisaged downstream of the two surge shafts

in upper horizontal limb. Beyond the valve chamber, the pressure shafts are designed to

have vertical drop in two stages. Drill hole indicates availability of bedrock at El 1053.589m

(DH SS-2) and El 974.047m (DH PS-1) at proposed penstock area. An intermediate

construction adit has been provided at El 775m. Geological Section along surge shaft,

pressure shaft, powerhouse and Tailrace tunnel is given as Plate-6.7.

Powerhouse Cavern

A 3070MW (installed capacity) underground powerhouse is proposed within the hill ridge

between Talo (Tangon) river and Dri river near the confluence of the said two rivers.

It is observed that bedrock in powerhouse area is traversed by four sets of rock

discontinuities. Joints belonging to set S1 are parallel to foliations with strike nearly E-W and

dipping on an average by 88º towards 353º. Joints belonging to next prominent joint set S2

dip on an average by 52º towards N256º. The joint set S3 dips towards N076º by 20º and set

S4, on an average, dips by 82º towards N096º.

Based on the analysis of discontinuity data, the long axis of the powerhouse cavern

orientation has been aligned at N130º – N310º. In this case, rock discontinuities with respect

to powerhouse alignment indicates that the orientation of long axis of powerhouse is askew

by 47º, 36º, 36º and 56º, with the strike of joints sets S1, S2, S3 and S4. At this juncture, the

orientation of powerhouse with respect to the rock attitude has been optimized. However,

the final orientation of the powerhouse cavity will be further optimized when the discontinuity

data from rest of the exploratory drift is obtained and analyzed in conjunction with results of

in-situ rock mechanics tests including in situ stress measurement proposed to be carried out

at RD 225m and RD 540m, repectively.

The geological map of the area and geological sections along the long axis of powerhouse

cavern (Plates 6-6 & 6-7) indicate that the rock cover above crown of the powerhouse

cavern is around 315m to 440m. Bedrock in the area is characterized by granodioritic gneiss

with occasional amphibolites intrusives and emplaced pegmatite veins. Bedrock likely to be

encountered in powerhouse cavern is foliated, jointed along with pegmatite and silica veins

emplaced within it can be observed at several places. In addition to joints, some shear/



169126-40ER-0009-00 6-32

fracture zone, mostly oriented along the foliation, have been observed traversing the rock

mass.

The proposed powerhouse cavern will encounter bedrock comprising granodioritic gneiss

with pegmatite and amphibolites bodies along its full length and width. However, based on

surface outcrop studies and nearby drill hole results, a pegmatitic zone of about 20m

thickness comprising thin pegmatite veins intruded in close intervals within the parent

granodioritic rock mass is interpreted towards the Talo (Tangon) side of the powerhouse

cavern. This zone is expected to be encounterd at the lower reaches of the powerhouse

cavern below El 585m. Based on surface manifestation of isolated bedrock outcrops around

the area and results of geological logging, it is estimated that the proposed powerhouse

cavern will encounter rock mass belonging to Class II and Class III with RMR varying

between 51 and 78. Tentatively, the powerhouse cavern is likely to encounter rock mass

belonging to Class II for 35% and Class III for about 65% of total length.

Keeping in view the size of the openings and pattern of the discontinuities, wedge analysis

has been carried out in case of powerhouse cavern, considering different combinations of

joint sets. Analysis has been done by assuming unit weight of rock as 2.7 tons/m3, friction

angle as 42º, cohesion as 0.16 tons/m3 and water as 0.981tons/m3.

Wedge analysis has been carried out considering two different combinations of joint sets out

of all four joint sets observed in the area. Result of the wedge analysis considering

combination of joint sets S1, S2 and S3 was found to be unstable. The results of analysis

carried out by considering the sets S1, S2 and S3 indicate formation of seven wedges

altogether. Out of those, four wedges including two roof wedges (unstable) with factor of

safety 1.854 and 0.0, one Upper Left side wedge (unstable) with factor of safety 2.223, and

one far End wedge (marginally stable) with factor of safety 3.942, are considered vulnerable.

This aspect has considered in the designing the supports so that these unstable wedges will

be taken care of during excavation.

Transformer hall cavern of dimensions 349.6m (L) x 16.5m (W) x 24m (H) is proposed to be

located about 50m downstream of powerhouse cavern and is oriented in the same direction.

Therefore, geotechnical aspects of both the caverns are more or less similar.



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Main Access Tunnels

Keeping in view the length of the proposed powerhouse cavern (352m) it has been decided

to access it through two Main Access Tunnels (MATs) located one each on Dri and Talo

(Tangon) sides.

Main Access Tunnel – Dri side

The proposed portal area of this access tunnel is characterized by bedrock outcrop

comprising granodioritic gneiss from El. 625m to El. 650m. Thereafter, the hill slope along

access tunnel alignment is mostly covered with overburden, except for a small portion at

about El 745m above the road section, where a small rock outcrop of granodioritic gneiss is

present. Bed rock below the overburden at this area is comprised of granodioritic gneiss with

pegmatite veins at places.

The hill slope along the access tunnel follows a slope of about 50º up to the elevation of

about 675m. Thereafter, the hill slope maintains a gentle slope of about 5º along a high level

terrace. The hill slope above this terrace again maintains a slope of about 45º upto the

elevation of El 975m. The cover above the tunnel varies between 10m and 360m. It is

observed that the portal is suitably located on bedrock.

The proposed access tunnel is likely to encounter granodioritic gneiss traversed by

pegmatite veins as tunneling media. One such thin pegmatite vein is expected at the portal

area. One more pegmatitic zone of considerable thickness comprising numerous pegmatite

veins within gneisses is also expected at about 450m from portal area. Thickness of this

pegmatitic zone is expected to be 20m.

Unstable wedges on the right wall and roof of the tunnel resulting from the combination of

prevailing joint sets is anticipated.

The proposed access tunnel will encounter Class II and Class III rock mass of fair to good

quality mainly with RMR varying between 55 and 70. Few stretches along this tunnel may

encounter rock mass having Class IV with RMR value between 30 and 38. The anticipated

rock Classes to be encountered in the entire tunnel length are estimateted tentatively as

Class II for15%, Class III for 65%, Class IV for 15% and Class V for 5%.



169126-40ER-0009-00 6-34

Main Access Tunnel – Talo (Tangon) side

The proposed portal area for this access tunnel is characterized by overburden. The bedrock

comprising biotite gneiss is exposed in this area at a lower elevation than the proposed

portal invert elevation. Main Access Tunnel is likely to encounter bedrock including biotite

gneiss, calcareous quartzite with chlorite bands and granodioritic gneiss with pegmatite

veins at places. Occasional shear seams varying in thickness from a few millimeters and

0.5m may also be encountered. The ground cover above the tunnel varies between 10m and

448m. The bedrock has been encountered at 36m depth from the ground surface based on

drill hole DH-AD2. Seismic profile EP- 4 meeting the hill slope above this access tunnel at

about 625m from the portal has also inferred depth of overburden is of the order of about

32m along the proposed tunnel alignment. It is indicated that initially open excavation will be

required for a length of about 70m in overburden for locating the portal in the bedrock.

Thereafter it will be followed by structural tunnel till adequate rock cover is available above

the tunnel overt. The slope cuts resulting from this excavation would be suitably designed for

restoring the stability.

The proposed access tunnel is expected to negotiate biotite gneiss, calcareous quartzite and

granodioritic gneiss as the tunneling media. Initially from portal up to about 200m, the tunnel

will pass through biotite gneiss. Thereafter, the tunneling media is expected to be quartzite

for a stretch of about 130m. Rest of the tunnel is expected to encounter granodioritic gneiss

as tunneling media. Few thin pegmatite veins and small amphibolites intrusive bodies are

also expected to be encountered along the proposed alignment.

The bedrock is traversed by four sets of rock discontinuites. The most prominent

discontinuity S1 shows favorable orientation with the proposed tunnel alignment. The set S2

shows fair orientation with the tunnel alignment. The third discontinuity set S3 shows fair

orientation due to very low dip angle and set S4 show very unfavourable orientation with

tunnel alignment. Unstable wedges on the right wall and roof of the tunnel resulting from the

combination of above joint sets may occur.

Based on surface manifestation of isolated bedrock outcrops around the area, it is estimated

that the proposed access tunnel will encounter Class II and Class III rock mass of fair to

good quality mainly with RMR varying between 51 and 70. However, few stretches along this

tunnel may encounter rock mass having Class IV with RMR value between 32 and 38.

Tentatively, this access tunnel is likely to encounter rock mass of Class II -15%, Class III

55%, Class - IV 20% and Class V-10% of total length respectively.



169126-40ER-0009-00 6-35

Tailrace Tunnels

Two numbers of Tailrace tunnels; one of 11.3m diameter for Dri side and another of 9.5m

diameter for Talo (Tangon) side have been proposed to take the discharge water from

powerhouse back into Talo (Tangon) river near confluence with Dri and Talo (Tangon) river.

The bedrock exposed in this area comprises granodioritic gneiss with intrusion of

amphibolite, calcareous quartzite, quartzite with chlorite schist bands and biotite gneiss with

pegmatite veins at places. Biotite gneiss is well exposed at both the portal locations and

beyond EL 625m the hill slopes are covered by overburden comprises slope wash material.

Few shears along the road cuts at about El. 720m are observed along chloritic schistose

band, the same formation shall be encountered during the exacavation of Tailrace tunnel as

depicted in Plate 6-7. Bedrock is traversed by four sets of discontinuities in this area.

The ground cover above the tunnel varies between 25m in the initial reaches up to maximum

of about 290m. Formation of unstable wedges due to intersection of prevailing joints in the

crown portion are observed and due care has been taken in the design. The proposed TRT

is likely to negotiate good to fair quality rock mass along major portion of the tunnel length

excluding the initial reaches of about 15-20m from the out fall portal where the rock mass

appeared to be disturbed. The alignment of both (Dri and Tanogn limb) TRT are almost

parallel to each other and hence the rock mass properties of both TRT remain same.

Geological Section along surge shaft, pressure shaft, powerhouse and Tailrace tunnel is

given as Plate 6-7.

A tentative rock mass classification indicates that both the Tailrace tunnels are likely to

encounter rock mass Class II for 15%, Class III for 55%, Class IV for 20% and Class V for

10% of total length.

6.5 Seismicity and Seismotectonics

The project area lies in the seismic Zone V of the seimic zoning map of India [IS1893:

part-1(2002)]. The seismic Zone V is broadly associated with seismic intensity IX and above

on MMI scale. It may be mentioned that the intensity IX corresponds to horizontal ground

acceleration of greater than 250cm/sec2 in any direction. The ground acceleration and,

hence, seismic intensity of an earthquake at a place depends on the magnitude of

earthquake, distance from the focus, duration of earthquake, type of underlying soil and its

damping characteristics. The damage to the buildings founded on soft or filled up earth will

be higher than that in similar types of buildings founded on hard bedrock. Also, the damage



169126-40ER-0009-00 6-36

will be higher for higher magnitude and long duration earthquakes, less epicentral distance,

soft soil conditions and areas with high liquefaction potential.

Keeping in view the high seismicity of the area, the site specific seismic studies for the

project have been carried out by Department of Earthquake engineering, IIT Roorkee.

Based on parameters like regional geology, seismotectonic setup, characteristics of various

seismogenic sources present in the region and seismic history of the area (IMD data), the

following recommendatios have been made.

The maximum credible earthquake (MCE) that can occur in the area with peak ground

acceleration has been estimated to be of magnitude 8.5, occurring along Lohit Thrust.

By obtaining spectra and time history for MCE conditions, the design basis spectra is

evaluated by using appropriate reduction factors.

The PGA values for MCE and DBE has been estimated as 0.56g and 0.32g,for horizondal

and 0.37g and 0.21g fro vertical components respectively.

Conclusion

The proposed Etalin HE Project area is located on the eastern limb of the Eastern

Syntaxial Bend (ESB) in the eastern part of Arunachal Pradesh that exposes rocks

ranging in age from Proterozoic to Tertiary and Recent deposits. The major rock units

exposed in and around the project area belong to Ithun Formation, Hunli Formation

and Diorite – Granodiorite – Granite Complex or Lohit Plutonic Complex.

Notwithstanding, rocks of Hunli Formation, exposed on the southern side of Talo

(Tangon) river, are not likely to be encountered in any of the project components.

Extensive sub-surface investigations were undertaken which includes 46 Nos. of drill

holes with cumulative depth/length of 2892.15m, exploratory drifting (7 Nos.) with

cumulative length of 531m and geophysical exploration comprising of seismic

refraction profiling aggregating to 1539m length. Apart from this, laboratory tests on

core samples including petrography, insitu permeability test/water percolation test in

drill holes and insitu rock mechanic tests in drifts were also conducted.

Ithun Formation comprises a sequence of biotite gneiss with quartzite, amphibolite,

calcareous quartzite, carbonate bands and garnetiferous mica schist with kyanite and

sillimanite. The diorite - granodiorite – granite complex is characterized by a wide



169126-40ER-0009-00 6-37

variation in gneissic rocks from diorite, granodiorite to granite with gradational contact

between them. These rocks have undergone polyphase deformation.

The project envisages diversion of water from Dri river and Talo (Tangon) river

through two separate water conductor systems up to powerhouse. Initially two

separate powerhouse caverns were proposed for Dri limb and Talo (Tangon) limb

water conductor system. However, considering the construction and operational point

of view and limitation of space, it was decided to have one single powerhouse cavern

for both the limbs of the water conducting systems.

Two alternative sites (Alternative-I and Alternative-II) were proposed for river

diversion at Dri site near Eron village. However, keeping in view the curvature in the

course of river, inadequate width of the valley required to route design flood the

diversion site Alternative-II was preferred.

The proposed Dam site on Dri River has been found suitable where rocks comprising

granodioritic gneiss are exposed on either abutment and overburden in the riverbed

vary in thickness between 10.5m and 19.5m which is confirmed by drilling.

The permeability of rock mass is also of low order and varies between 0.1 and

0.97 lugeon. Exploration by drifting on the abutments has established an admissible

stripping limit up to 10m and 12m. Based on the geological explorations carried out,

the site is found suitable for concrete gravity dam as diversion structure with the

deepest foundation at El 945.5m and top of the dam at El 1047m. The height of the

dam above deepest foundation would be 101.5m.

Investigations indicate that bedrock is present at the foundation level of spillway and

plunge pool and no major excavation would be required on the abutments in order to

accommodate the width of spillway except on the right bank to accommodate the

plunge pool which is at lower level and occupied by riverine deposit. The cut slopes

are to be properly designed and adequately protected wherever required.

The proposed intake structure is located in the rock mass comprising foliated and

jointed blocky granodioritic / dioritic gneiss. The rock mass is traversed by four sets

of prominent joints including those oriented along the foliation. It is also observed

from geological section along the intake structure that all the joints, except those of

set S3 are dipping towards valley. This indicates that slope cuts above the structure

would have to be stabilized. The proposed intake is found to be favorably aligned

with respect to the strike of the most prominent rock discontinuities, except the valley

dipping joints of set S3 which needs to be stabilized by rock bolts.



169126-40ER-0009-00 6-38

At the site of upstream coffer dam a concrete faced structure with plum concrete core

is proposed. It is proposed to explore the river bed at the site through a drill hole

DH- D9 to decipher overburden thickness in the riverbed so that grouting is planned

to minimize the seepage through foundation. The downstream coffer dam is

proposed to be a random fill dam.

Three numbers of diversion tunnels are proposed at Dri diversion site on the right

bank and one diversion tunnel is proposed on the left bank at this site. Portals of all

tunnels are sited on bed rock. In case of the diversion tunnel on left bank, sufficient

gap is maintained between the HRT and the diversion tunnel at crossing over portion.

Based on the surface and subsurface explorations carried out so far, it is expected

that about 25% of Class II (Good quality), 50% of Class III (Fair quality), 15% of

Class IV (Poor quality) and 10% of Class V (Very Poor quality) rock mass may be

encountered in the diversion tunnels.

The proposed HRT at Dri limb is likely to encounter rock mass comprising

granodiorite gneiss and biotite gneiss in most of its’ length. However, a considerable

stretch from about RD 1400m to RD 2480m is expected to encounter rock mass with

thick (about 230 m) calcareous quartzite/marble bands and a zone comprising

closely spaced shear seams within gneisses between RD 7200m and RD 7450m.

Shear seams and weak zones are also expected to be encountered below the nala

crossings. Bed rock is traversed by four sets of structural discontinuities.

Development of unstable wedges are expected on the roof and left wall mainly.

About 10% of the total length of the tunnel is having cover more than 500m above

HRT alignment. Stress related condition may be encountered here. Tentative rock

mass class expected along the HRT indicates that Rock mass of Class II (RMR >60),

Class III (RMR >40), Class IV (RMR >20) and Class V (RMR <20) are expected by

25%, 47%, 20% and 8% respectively along the total length of HRT.

In case of Talo (Tangon) limb also, two alternative sites (Alternative-I and Alternative-

II) were identified. However, during geological mapping and exploration by drilling in

river bed at Alternative-I site the thickness of overburden was found to be more than

70m and thus it was decided not to pursue the site Alternative-I further.

The Alternative-II site (about 2.3 kms. upstream) has been finally adopted after

achieving satisfactory results of detailed investigations.

The proposed Dam site on Talo (Tangon) river is characterized by presence of bed

rock exposures on both the banks. Maximum depth of overburden in the riverbed



169126-40ER-0009-00 6-39

proved by drilling is 29.0m. The site has been found to be suitable for concrete

gravity dam with top of dam at El 1052m, deepest foundation level at El 972m and

spillway located in the dam body. The valley ward dipping joints on either abutment

on the cut slopes beyond the stripping limits will be stabilized by rock bolting

wherever needed. Based on detailed study of rock mass on both the banks, through

exploratory drifts, abutment stripping limit of 10m to 12m is recommended. The

results of the water percolation tests indicate that permeability of the foundation is of

low order. It is recommended that, since the rock mass is foliated and jointed;

consolidation grouting may be carried out in the foundation to make it monolith.

Proposed diversion tunnels on left bank (3 Nos.) are expected to encounter foliated

and jointed granodiorite gneiss, calcareous quartzite and boitite gneiss with

occasional shear seams and pegmatite veins as tunneling media. Inlet portal of the

tunnels are suitably located on bed rock. Outlet portal, when located on overburden,

are expected to encounter depth of overburden less than 20m and for the initial

lengths of the tunnels structural tunnel is required until adequate rock cover is

obtained. Formation of unstable wedges is expected on the right wall and roof of the

tunnels. The proposed diversion tunnels are expected to encounter rock mass of

Class II, III, IV, and V for about 25%, 40%, 25% and 10% respectively.

The proposed underground desilting chambers on right bank are expected to

encounter tunneling media as granodioritic/diorite gneiss, biotite gneiss and

calcareous quartzite with minor pegmatite veins and thin shear seams occasionally.

It is observed that long axis of the proposed desanding chambers is aligned favorably

with respect to most of rock discontinuity sets except the joint set 2 in which case the

alignment is fair. However, the final orientation of the desilting chamber cavity will be

reviewed after results of in-situ rock mechanics test in the drift at structure grade are

obtained along with the discontinuity data available. The ground cover over the

proposed chambers varies between 80m and 270m. It is also observed that

formation of unstable wedges in the roof and on the left walls is expected and

therefore same have to be designed and support has to be provided accordingly.

The proposed desilting chambers are expected to encounter rock mass of Class II,

III, IV, and V for about 30%, 40%, 20% and 10% respectively.

The proposed HRT at Talo (Tangon) limb is expected to encounter rock mass

comprising granodiorite gneiss and biotite gneiss with occasional silica and

pegmatite veins. Few shear seams and weak zones are expected to be encountered



169126-40ER-0009-00 6-40

below the nala crossings and along lithological contacts. In general, the rock mass is

jointed, blocky; however, at few locations it may become very blocky. About 33% of

the total length of the Headrace tunnel is having more than 500m cover above overt.

Hence, stress related problem cannot be ruled out. Bed rock is traversed by more

than four sets of rock discontinuities.

A tentative estimate of rock mass class along the HRT alignment indicates that the

RMR values will vary between 30 and 83. However, RMR value between 17 and 27

is expected at the tunnel stretches below major nala crossings and shear

seam/pegmatite zones. Tentative rock mass class expected along the HRT indicates

that Rock mass of Class II (RMR >60), Class III (RMR >40), Class IV (RMR >20) and

Class V (RMR <20) are expected by 27%, 44%, 19% and 10% respectively along the

total length of HRT.

Both surge shafts will be excavated through granodioritic gneiss mainly with

pegmatite bands intruded within the rock mass. Formation of unstable wedges along

the surge shaft walls is anticipated. Bedrock likely to be fair to good in general during

the excavation of surge shafts. Two self draining construction adits from either side of

surge shafts have been planned to access the surge shaft at bottom elevation to

facilitate its construction. The tunneling media for the adits are expected to be of fair

to good quality comprising granodioritic/dioritc gneiss associated with pegmatite

bands. The portals of both the adits will be suitably founded on bed rock.

The proposed underground powerhouse complex is located within a ridge delimited

by the rivers Dri and Talo (Tangon) on either side. Most of the area is covered by

thick overburden that supports very dense vegetation. Depth of loose overburden

encountered in this area widely varies between 4m and 60m along the hill slopes.

The underlying rocks mainly comprise granodiorite, diorite, calcareous quartzite,

biotite gneiss with pegmatite veins and minor shear seams present occasionally.

Bed rock is traversed by four prominent sets of discontinuities. Localized warping of

foliation is present at many places.

The proposed underground powerhouse is located under the ridge between Dri river

and Talo (Tangon) river near confluence. The proposed powerhouse cavern will

encounter rocks comprising granodioritic gneiss with pegmatite veins and

amphibolites bodies along its’ full length and width. The long axis of the powerhouse

cavern is orientated at N130º – N310º direction which is most suitable as per the

strike of prominent discontinuity sets as observed in the surface outcrops and also in



169126-40ER-0009-00 6-41

the exploratory drift driven at the Powerhouse location. However, the final orientation

of the powerhouse cavity will be reviewed after results of in-situ rock mechanics test

in the drift at structure grade are obtained along with the discontinuity data available.

Unstable wedged are expected on the roof and left wall in the powerhouse cavern.

The extent of rock cover over the crown of the powerhouse cavern is around 315m to

440m which is adequate. A zone with thin pegmatite veins intruded in close intervals

within the parent gneissic rock mass is interpreted at the lower reaches towards the

Talo (Tangon) side end of the powerhouse cavern. The powerhouse cavern is likely

to encounter rock mass belonging to Class II 35%, III 65% of total length.

Transformer Hall cavern of 350m (L) X 16.5m (W) and 24M (H) size is located about

50m downstream of Powerhouse cavern and is oriented in the same direction.

Two numbers of Main access tunnels (MAT) are proposed for the powerhouse, one

from Talo (Tangon) side and one from Dri side. Both the access tunnels are having

sufficient cover above the overt and are oriented favorably with respect to prominent

rock discontinuities. The tunnels are expected to encounter biotite gneiss, calcareous

quartzite and granodioritic gneiss as the tunneling media mainly with minor inclusions

of pegmatite veins.

Two numbers of Tailrace Tunnels are proposed for the project to discharge tail water

from powerhouse into the Talo (Tangon) river. Both the alignments of tailrace tunnels

are more or less parallel to each other. Portals of the Tailrace tunnels are suitably

located within bed rock and the tunnels are having sufficient cover above overt level.

The likely tunneling media is biotite gneiss, calcareous quartzite and granodioritic

gneiss intruded by pegmatite veins/ bands and small amphibolites bodies that have

intruded into parent rock. Both the tunnels are found to be oriented favorably in most

of its portion. Expected rock mass class along the Tailrace tunnels are Class II to

Class III mainly and as Class IV and Class V also due to presence of shear seams.

As per the seismic zoning map of India (IS 1893: Part- I (2002)), the area around the

proposed Etalin Hydroelectric Project is located in Zone V. The maximum credible

earthquake (MCE) that can occur in the area with peak ground acceleration has been

estimated to be of magnitude 8.5. The PGA values for MCE and DBE has been

estimated as 0.56g and 0.32g, for horizondal and 0.37g and 0.21g for vertical

components respectively. The valley slopes between FRL and MDDL in most of the

reaches of Dri reservoir area, comprise river borne deposits and bedrock with

occasional presence of slope wash materials. No major landslide is observed along



169126-40ER-0009-00 6-42

the reservoir rim. Hence, no major problem due to reservoir rim stability is

anticipated. Possibility of any reservoir leakage is not anticipated due to a low order

of permeability observed in drill holes as well as absence of any saddles or any other

avenue through which water can escape out.

ANNEXURE-VI

I. ANGIOSPERMS

Trees

S. No. Family

Name of Species

1 Adoxaceae Viburnum nervosum

2 Anacardiaceae Lannea coromandelica

3 Anacardiaceae Spondias pinnata

4 Anacardiaceae Mangifera sylvatica

5 Araliaceae Aralia armata

6 Araliaceae

Brassaiopsis

glomerulata

7 Araliaceae Macropanax dispermus

8 Araliaceae Macropanax undulatus

9 Araliaceae

Parapentapanax subcordatum

10 Araliaceae Schefflera hypoleuca

11 Arecaceae Caryota urens

12 Arecaceae Livistona jenkinsiana

13 Averrhoaceae Averrhoa carambola

14 Betulaceae Alnus nepalensis

15 Bignoniaceae Oroxylum indicum

16 Bombacaceae Bombax ceiba

17 Burseraceae Canarium strictum

18 Burseraceae Garuga floribunda

19 Caesalpinaceae Acrocarpus fraxinifolius

20 Caesalpinaceae Cynometra polyandra

21 Caesalpiniaceae Bauhinia purpurea

22 Clusiaceae Kayea assamica

23 Clusiaceae Garcinia cowa

24 Combretaceae Terminalia bellirica

25 Combretaceae Terminalia chebula

26 Combretaceae Terminalia myriocarpa

27 Datiscaceae Tetrameles nudiflora

28 Dilleniaceae Dillenia indica

29 Dilleniaceae Dillenia scabrella

30 Dipterocarpaceae Dipterocarpus gracilis

31 Elaeocarpaceae

Elaeocarpus floribundus

32 Euphorbiaceae Bischofia javanica

33 Euphorbiaceae Macaranga denticulata

34 Euphorbiaceae Mallotus philippinensis

35 Euphorbiaceae Ostodes paniculata

S. No. Family

Name of Species

36 Fabaceae Dalbergia pinnata

37 Fabaceae Erythrina variegata

38 Fagaceae Castanopsis indica

39 Fagaceae Castanopsis tribuloides

40 Fagaceae Castanopsis hystrix

41 Fagaceae Castonopsis lanceifolia

42 Fagaceae Lithocarpus dealbatus

43 Fagaceae

Lithocarpus pachyphyllus

44 Fagaceae Lithocarpus fenestratus

45 Fagaceae Lithocarpus falconeri

46 Flacourtiaceae Gynocardia odorata

47 Hammamelidaceae Altingia excelsa

48 Iteaceae Itea macrophylla

49 Juglandaceae Engelhardtia spicata

50 Lamiaceae Premna bengalensis

51 Lythraceae

Lagerstroemia

minuticarpa

52 Lythraceae

Lagerstroemia parviflora

53 Lauraceae Actinodaphne obovata

54 Lauraceae

Cinnamomum glanduliferum

55 Lauraceae

Cinnamomum obtusifolium

56 Lauraceae Phoebe cooperiana

57 Magnoliaceae Magnolia campbellii

58 Magnoliaceae Magnoila griffithii

59 Magnoliaceae Michelia champaca

60 Magnoliaceae Michelia excelsa

61 Magnoliaceae Talauma hodgsonii

62 Malvaceae Kydia calycina

63 Meliaceae Amoora wallichii

64 Meliaceae Chukrasia tabularis

65 Meliaceae Dysoxylum hamiltonii

66 Meliaceae Toona hexandra

67 Mimosaceae Cassia nodosa

68 Mimosaceae Albizia chinensis

69 Mimosaceae Albizia lucida

S. No. Family

Name of Species

70 Mimosaceae Albizia procera

71 Moraceae Artocarpus chaplasha

72 Moraceae Ficus cunia

73 Moraceae Ficus roxburghii

74 Moraceae Ficus semicordata

75 Moraceae Morus laevigata

76 Myrtaceae Psidium guajava

77 Myrtaceae Syzygium formosum

78 Pandanaceae Pandanus odoratissima

79 Primulaceae Maesa chisia

80 Primulaceae Maesa indica

81 Rhamnaceae Hovenia acerba

82 Rutaceae Citrus aurantium

S. No. Family

Name of Species

83 Rutaceae Citrus lemon

84 Salicaceae Populus gamblei

85 Sapotaceae Sarcosperma griffithii

86 Saurauriaceae Saurauia roxburghii

87 Simaroubaceae Ailanthus integrifolia

88 Simaroubaceae Alangium begoniifolium

89 Sonneratiaceae Duabanga grandiflora

90 Sterculiaceae

Pterospermum acerifolium

91 Sterculiaceae Sterculia villosa

92 Ulmaceae Trema orientalis

93 Verbenaceae Callicarpa arborea

94 Verbenaceae Gmelina arborea

95 Verbenaceae Vitex altissima

Shrubs

S. No.

Family Name of Species

1 Acanthaceae Adhatoda vasica

2 Acanthaceae Anisomeles ovata

3 Acanthaceae Phlogacanthus tubiflorus

4 Acanthaceae Strobilanthes coloratus

5 Anacardiaceae Rhus wallichii

6 Apocynaceae Thevetia peruviana

7 Araliaceae Trevesia palmata

8 Arecaceae Calamus erectus

9 Arecaceae Calamus flagellum

10 Arecaceae Calamus floribundus

11 Arecaceae Calamus inermis

12 Arecaceae Calamus leptospadix

13 Asclepiadaceae Calotropis gigantea

14 Asclepiadaceae Marsdenia roylei

15 Asteraceae Artemisia nilagirica

16 Asteraceae Artemisia indica

17 Asteraceae Eupatorium odoratum

18 Asteraceae

Veronica anagallis-

aquatica

19 Bischofiaceae Bischofia javanica

20 Buddlejaceae Buddleja asiatica

21 Cactaceae Opuntia dillenii

22 Caesalpinaceae Cassia occidentalis

23 Canabinacae Cannabis sativa

S. No.


24 Cannaceae Canna indica

25 Costaceae Costus speciosus

26 Ericaceae Agapetes forrestii

27 Ericaceae Agapetes griffithii

28 Euphorbiaceae Euphorbia pulcherrima

29 Euphorbiaceae Ricinus communis

30 Fabaceae Desmodium laxiflorum

31 Hydrangeaceae Hydrangea serrata

32 Hypericaceae Hypericum hookerianum

33 Lamiaceae Plectranthus striatus

34 Melastomataceae

Melastoma malabathricum

35 Melastomataceae Oxyspora paniculata

36 Mimosaceae Acacia pennata

37 Moraceae Ficus heterophylla

38 Musaceae Musa acuminata

39 Musaceae Musa balbisiana

40 Musaceae Musa paradisiaca

41 Myrsinaceae Myrsine semiserrata

42 Oleaceae Jasminum amplexicaule

43 Piperaceae Piper clarkei

44 Piperaceae Piper griffithii

45 Poaceae Arundinaria falcata

46 Poaceae Bambusa pallida

47 Poaceae Bambusa tulda

48 Poaceae Cephalostachyum

S. No.


latifolium

49 Poaceae Chimnobambusa callosa

50 Poaceae

Dendrocalamus giganteus

51 Poaceae

Dendrocalamus

hamiltonii

52 Poaceae Dendrocalamus strictus

53 Poaceae Phragmites karka

54 Poaceae Saccharum spontaneum

55 Poaceae

Schizostachyum

capitatum

56 Poaceae

Schizostachyum

polymorphum

57 Rhamnaceae Rhamnus nepalensis

58 Rosaceae Rubus ellipticus

59 Rosaceae Rubus foliolosus

60 Rosaceae Rubus burkillii

61 Rubiaceae Luculia pinceana

62 Rutaceae Murraya paniculata

S. No.


63 Rutaceae Zanthoxylum armatum

64 Saxifragaceae Saxifraga sarmentosa

65 Solanaceae Datura suaveolens

66 Solanaceae Lycianthes rantonei

67 Solanaceae Solanum ciliatum

68 Solanaceae Solanum viarum

69 Sterculiaceae Abroma augusta

70 Thymelaeaceae Edgeworthia gardneri

71 Tiliaceae Grewia disperma

72 Tiliaceae Triumfetta bartramia

73 Urticaceae Boehmeria longifolia

74 Urticaceae Boehmeria macrophylla

75 Urticaceae Girardinia diversifolia

76 Verbenaceae Callicarpa arborea

77 Verbenaceae

Clerodendrum colebrookianum

Herbs

S.

No. Family Name of Species

1 Acanthaceae Andrographis paniculata

2 Acanthaceae Asystasia neesiana

3 Acanthaceae Justicia khasiana

4 Acanthaceae Justicia parviflora

5 Acanthaceae

Strobilanthes rhombifolius

6 Acanthaceae Thunbergia coccinea

7 Amaranthaceae Achyranthes bidentata

8 Amaranthaceae Amaranthus viridis

9 Amaranthaceae Cyathula prostrata

10 Amaranthaceae Amaranthus hybridus

11 Apiaceae Centella asiatica

12 Apiaceae Oenanthe javanica

13 Araceae Aglaonema hookerianum

14 Araceae Alocasia fallax

15 Araceae Ariopsis peltata

16 Araceae Arisaema concinnum

17 Araceae Arisaema decipiens

18 Araceae Arisaema jacquemontii

19 Araceae Arisaema nepenthoides

20 Araceae Arisaema speciosum

S. No.


21 Araceae Arisaema wallichianum

22 Araceae Colocasia forniculata

23 Araceae Lasia spinosa

24 Araceae Pothos scandens

25 Araceae Rhaphidophora decursiva

26 Asclepiadaceae Periploca calophylla

27 Asteraceae Ageratum conyzoides

28 Asteraceae Anaphalis contorta

29 Asteraceae Anaphalis busua

30 Asteraceae Artemisia indica

31 Asteraceae Artemisia maritima

32 Asteraceae Aster himalaicus

33 Asteraceae Bidens biternata

34 Asteraceae Bidens pilosa

35 Asteraceae Blumea procera

36 Asteraceae

Crassocephalum crepidioides

37 Asteraceae Erigeron bonariensis

38 Asteraceae Eupatorium odoratum

39 Asteraceae Gnaphalium affine

40 Asteraceae Gynura nepalensis

41 Asteraceae Lactuca virosa

S. No.


42 Asteraceae Senecio cappa

43 Asteraceae Siegesbeckia orientalis

44 Asteraceae Sonchus oleraceus

45 Asteraceae Spilanthes oleracea

46 Asteraceae Tagetes minuta

47 Asteraceae Mikania micrantha

48 Asteraceae Spilanthes paniculata

49 Balsaminaceae Euodia trichotoma

50 Balsaminaceae Impatiens brachycentra

51 Balsaminaceae Impatiens acuminata

52 Balsaminaceae Impatiens bicornuta

53 Balsaminaceae Impatiens racemosa

54 Basellaceae Basella alba

55 Begoniaceae Begonia griffithiana

56 Begoniaceae Begonia nepalensis

57 Begoniaceae Begonia palmata

58 Begoniaceae Begonia roxburghii

59 Boraginaceae

Cynoglossum

glochidiatum

60 Brassicaceae Cardamine hirsuta

61 Caesalpinaceae Bauhinia ovalifolia

62 Caesalpinaceae Caesalpinia spinosa

63 Campanulaceae Campanumaea parviflora

64 Campanulaceae Lobelia succulenta

65 Caryophyllaceae Cerastium cerastoides

66 Caryophyllaceae Drymaria cordata

67 Caryophyllaceae Stellaria monosperma

68 Commelinaceae Commelina appeniculata

69 Commelinaceae Commelina benghalensis

70 Commelinaceae Cyanotis cristata

71 Commelinaceae Cyanotis vaga

72 Commelinaceae Murdannia nudiflora

73 Convolvulaceae

Ipomoea fistulsa ssp. fistulosa

74 Convolvulaceae Ipomoea nil

75 Convolvulaceae Porana paniculata

76 Convolvulaceae Argyreia nervosa

77 Convolvulaceae Ipomoea batatas

78 Cucurbitaceae Solena heterophylla

79 Cucurbitaceae

Momordica

cochinchinensis

80 Cucurbitaceae Hodgsonia macrocarpa

81 Cucurbitaceae Solena amplexicaulis

S. No.


82 Cucurbitaceae Thladiatha calcarata

83 Cyperaceae Carex longipes

84 Cyperaceae Cyperus brevifolius

85 Cyperaceae Cyperus exaltatus

86 Cyperaceae Cyperus alulatus

87 Cyperaceae Cyperus rotundus

88 Cyperaceae Kyllinga brevifolia

89 Dioscoreaceae Dioscorea glabra

90 Dioscoreaceae Dioscorea pentaphylla

91 Dioscoreaceae Dioscorea belophylla

92 Dioscoreaceae Dioscorea alata

93 Ephedraceae Ephedra aspera

94 Fabaceae Mucuna bracteata

95 Fabaceae Pueraria wallichii

96 Fumariaceae Corydalis geraniifolia

97 Gentianaceae Exacum tetragonum

98 Gesneriaceae Platystoma violoides

99 Lamiaceae Clinopodium capitellatum

100 Lamiaceae Ajuga macrosperma

101 Lamiaceae Anisomeles indica

102 Lamiaceae Elsholtzia ciliata

103 Lamiaceae Leucas ciliata

104 Lamiaceae Leucas aspera

105 Lamiaceae

Pogostemon

benghalensis

106 Liliaceae

Chlorophytum tuberosum

107 Liliaceae Ophiopogon intermedius

108 Malvaceae Abutilon indicum

109 Malvaceae Sida rhombifolia

110 Malvaceae Urena lobata

111 Melastomataceae Osbeckia nutans

112 Melastomataceae Osbeckia stellata

113 Menispermaceae Cissampeos pariera

114 Menispermaceae Diploclisia glaucescens

115 Menispermaceae Stephania elegans

116 Menispermaceae Tinospora crispa

117 Mimosaceae Acacia pruinescens

118 Mimosaceae Acacia pennata

119 Mimosaceae Entada phaseoloides

120 Myrsinaceae Embelia ribes

121 Oleaceae Jasminum dispermum

122 Orchidaceae Aerides multiflora

S. No.


123 Orchidaceae Arundina graminifolia

124 Orchidaceae Bulbophyllum affine

125 Orchidaceae

Bulbophyllum careyanum

126 Orchidaceae

Bulbophyllum

cauliflorum

127 Orchidaceae Bulbophyllum guttulatum

128 Orchidaceae Calanthe griffithii

129 Orchidaceae Coelogyne barbata

130 Orchidaceae Coelogyne corymbosa

131 Orchidaceae Cymbidium aloifolium

132 Orchidaceae Cymbidium eberneum

133 Orchidaceae Cymbidium elegans

134 Orchidaceae Cymbidium cyperifolium

135 Orchidaceae Cymbidium iridioides

136 Orchidaceae Dendrobium densiflorum

137 Orchidaceae

Dendrobium hookerianum

138 Orchidaceae Dendrobium moschatum

139 Orchidaceae Dendrobium lituiflorum

140 Orchidaceae Goodyera procera

141 Orchidaceae Eria flava

142 Orchidaceae Lepanthes pedunculata

143 Orchidaceae Liparis delicatula

144 Orchidaceae Phaius flavus

145 Orchidaceae Pholidota imbricata

146 Orchidaceae Rhynchostylis retusa

147 Orchidaceae Spiranthes sinensis

148 Oxalidaceae Oxalis corniculata

149 Piperaceae Piper betle

150 Plantaginaceae Plantago erosa

151 Poaceae Cynodon dactylon

152 Poaceae Imperata cylindrica

153 Poaceae Miscanthus sinensis

154 Poaceae Molinera cuboides

155 Poaceae Poa annua

156 Poaceae Pogonatherum paniceum

157 Poaceae Themeda anathera

158 Poaceae Thysanolaena maxima

159 Polygonaceae Fagopyrum dibotrys

160 Polygonaceae Persicaria chinensis

S. No.


161 Polygonaceae Polygonum capitatum

162 Polygonaceae Polygonum flaccidum

163 Primulaceae Diploclisia glaucescens

164 Ranunculaceae Ranunculus sikkimensis

165 Ranunculaceae Coptis teeta

166 Ranunculaceae Clematis gauriana

167 Rosaceae Agrimonia pilosa

168 Rosaceae Fragaria indica

169 Rosaceae Potentilla microphylla

170 Rubiaceae Paederia foetida

171 Rubiaceae Paederia foetida

172 Scrophulariaceae Lindenbergia indica

173 Scrophulariaceae Mazus pumilus

174 Smilacaceae Smilax aspera

175 Solanaceae Nicandra physaloides

176 Solanaceae Physalis minima

177 Solanaceae Physalis peruviana

178 Solanaceae Solanum indicum

179 Solanaceae Solanum nigrum

180 Urticaceae Elatostema sessile

181 Urticaceae Pilea scripta

182 Urticaceae Pouzolzia fulgens

183 Urticaceae Pouzolzia glaberrima

184 Urticaceae Urtica dioica

185 Verbenaceae

Clerodendrum colebrookianum

186 Violaceae Viola betonicifolia

187 Violaceae Viola diffusa

188 Violaceae Viola hediniana

189 Vitaceae Vitis flexuosa

190 Zingiberaceae Acorus calamus

191 Zingiberaceae Alpinia allughas

192 Zingiberaceae Alpinia zerumbet

193 Zingiberaceae Curcuma montana

194 Zingiberaceae Globba clarkei

195 Zingiberaceae Hedychium densiflorum

196 Zingiberaceae

Hedychium longipedunculatum

197 Zingiberaceae Hedychium spicatum

198 Zingiberaceae Phrynium pubinerve

II. GYMNOSPERMS

S. No. Family Name of species

1 Cupressaceae Cupressus torulosa

2 Gnetaceae Gnetum montanum

3 Pinaceae Abies densa

4 Pinaceae Pinus wallichiana

5 Pinaceae Tsuga dumosa

6 Pinaceae Pinus merkusii

7 Taxaceae Cephalotaxus griffithii

III. PTERIDOPHYTES

S. No.

Family Botanical Name

1 Adiantaceae Adiantum caudatum

2 Adiantaceae Adiantum philippense

3 Angiopteridaceae Angiopteris evecta

4 Polypodiaceae Arthromeris wallichiana

5 Aspleniaceae Asplenium nidus

6 Cyatheaceae Cyathea gigantea

7 Cyatheaceae Cyathea spinulosa

8 Gleichiaceae Dicranopteris linearis

9 Athyriaceae Diplazium bentamense

10 Polypodiaceae Drymoglossum heterophyllum

11 Athyriaceae Dryoathyrium

boryanum

12 Equisetaceae

Equisetum ramossimum

13 Gleicheniaceae Gleichenia longissima

14 Polypodiaceae Lepisorus excavata

S. No.

Family Botanical Name

15 Polypodiaceae Lepisorus sordidus

16 Polypodiaceae Lepisorus nudus

17 Lycopodiaceae Lycopodium clavatum

18 Polypodiaceae

Microsorum membranaceum

19 Polypodiaceae Microsorum punctctum

20 Polypodiaceae Microsorum pteropus

21 Nephrolepdaceae Nephrolepis cordifolia

22 Cryptogrammaceae Onychium siliculosum

23 Polypodiaceae Polypodium amoenum

24 Aspidiaceae Polystichum aculeatum

25 Thelypteridaceae

Pronephrium affine

26 Hypoleppidaceae Pteridium aquilinum

27 Pteridaceae Pteris quadriaurita

28 Pteridaceae Pteris vittata

29 Selaginellaceae Selaginella indica

IV. BRYOPHYTES S. No. Family Botanical name

1 Anthocerotaceae Anthoceros sp.

2 Funariaceae Funaria hygromerica

3 Leucodontaceae Leucodon sp.

4 Marchantiaceae Marchantia palmata

5 Marchantiaceae Marchantia

polymorpha

S. No. Family Botanical name

6 Pelliaceae Pellia scripta

7 Polytrichaceae Polytrichum commune

8 Polytrichaceae Atrichum undulatum

9 Polytrichaceae Pogonatum inflexum

10 Ricciaceae Riccia fluitans

11 Sphagnaceae Sphagnum strictum

V. LICHENS

S.

No.

Family

Species

1 Coccocarpaceae Coccocapia sp.

2 Collemataceae Leptogium sp.

3 Cryptotheciaceae Cyptothecia sp.

4 Graphidaceae Phaeographina sp.

5 Letrouitiaceae Letrouitia sp.

6 Parmeliaceae Parmelina wallichaina.

7 Physciaceae Physcia sp.

S.

No.

Family

Species

8 Pilocarpaceae Byssolma sp.

9 Pyrenulaceae Anthracothecium sp.

10 Rhizocarpaceae Rhizocarpon sp.

11 Teloschistaceae Brigantiaea sp.

12 Thelotremataceae Diplochistes sp.

13 Usneaceae Bryonia sp.

14 Usneaceae Usnea baileyi

VI. MACRO-FUNGI

S. No. Family Botanical name

1 Agariceae Agaricus campestris

2 Dacrymycetaceae Calocera viscosa

3 Hymenochaetaceae Hymenochaete rubiginosa

4 Polyporaceae Polyporussquamosus

5 Tricholomataceae Armillaria tabescens

6 Xylariaceae Daldinia concentrica

VII. ALGAE

S. No. Family Botanical Names

1 Characeae Chara sp.

2 Chlamydomonadaceae Chlamydomonas sp.

3 Hydrodictyaceae Hydrodictyon sp.

4 Nostocaceae Anabaena sp.

5 Nostocaceae Nostoc sp.

6 Oedogoniaceae Oedogonium sp.

7 Sargassaceae Sargassum sp.

8 Vaucheriaceae Vaucheria sp.

9 Zygnemataceae Spirogyra sp.

10 Zygnemataceae Zygnema sp.


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) i


PHOTOGRAPHS


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) ii


Dri Limb Dam Site on Dri River

Tangon Limb Dam Site on Tangon River


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) iii


Catchment Area of Dri River along Dri Limb

Catchment Area of Tangon River along Tangon Limb


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) iv


Two views of Etalin HEP Power House Site

Sampling for Terrestrial Ecology near Dri Limb & Power House

Conifer and Broadleaved forests in Study area


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) v


Jhummed slopes and Ground vegetation in forests in Study area

Viola sp. Gaultheria sp.

Clematis sp. Rubus ellipticus


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) vi


Pteridophyte Marchantia polymorpha

Lichens

Fungi


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) vii


Trophy of Tahr

Mithun

Scanning for birds during surveys


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) viii


Red Whiskered Bulbul near Etalin village Red Headed Trogon

BUTTERFLIES

Indian Cabbage White Orange Oakleaf

Common Cerulean Common Hedge Blue


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) ix


INSECTS

Bug Beetle

AQUATIC ECOLOGY

Water Sampling in Dri river at Dam Site of Dri Limb


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) x


Water Sampling in Tangon river at Dam Site of Tangon Limb

Phytobenthos (Periphyton) sampling near Dri Limb Dam Site on Dri River


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) xi


Water sampling in of downstream of Power House Site

Experimental fishing in Dri River


Proponent: M/s Etalin Hydro Electric Power Company Limited (EHEPCL) xii


Fish Sampling in Dri River near Power House Site

River Cat (Glyptothorax pectinopterus)

Snow trout (Schizothorax richardsonii)

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