TRISHULI JAL VIDHYUT COMPANY LIMITED€¦ · · 2018-01-10TRISHULI JAL VIDHYUT COMPANY LIMITED UPPER TRISHULI 3B HYDROELECTRIC PROJECT ... Topographic Survey and Cadastral Mapping

TRISHULI JAL VIDHYUT COMPANY LIMITED

UPPER TRISHULI 3B HYDROELECTRIC PROJECT (42 MW)

Powerhouse Site

Volume II

Detail Project Report

Prepared by:

Trishuli Jal Vidhyut Company Limited

Sohrakhutte, Kathmandu

Ph : 4363681, Fax No. 4363681, P.O Box 6464

Date: October 2013

Detail Project Report of UT3B HEP


Content of Reports, Drawings and Appendix

Volume 1: Executive Summary

Volume 2: Detail Project Report

Volume 3: Drawings ( Detail Project Report)

Volume 4: Drawing of Structural Design

Appendix A: Topographic Survey and Cadastral Mapping

Appendix B: Hydrology

Appendix C: Geological Study

Appendix D: Hydraulic Design

Appendix E: Rate Analysis

Appendix F: Cost Estimate

Appendix G: Structure Design Report

Engineering Study and Design Team:

S.N Name and Designation Signature

1 Er. Damodar Bhakta Shrestha

(CEO)

2 Er. Bishow Kumar Shrestha

(Structural Engineer)

3 Er. Sunil Basnet

(Hydropower Engineer)

4 Er. Deepak Pandey

(Contract Engineer)

5 Er. Rajesh Sharma

(Civil Engineer)

6 Er. Kalyan Khanal

(Civil Engineer)


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Table of Content

Chapter 1

Introduction

1.1 Study Background ........................................................................................................................... 1-1

1.2 Previous Studies ............................................................................................................................... 1-2

1.3 Objectives and Scope of Work ...................................................................................................... 1-2

1.4 Field Investigation Works ............................................................................................................... 1-3

1.4.1 Topographical Survey and Mapping ...................................................................................... 1-3

1.4.2 Geological and Geotechnical Investigation ........................................................................... 1-3

1.4.3 Project supports facilities ......................................................................................................... 1-4

1.5 Design Work ..................................................................................................................................... 1-4

Chapter 2

Description of Project Area

2.1 Location ............................................................................................................................................ 2-1

2.2 Physical Features ............................................................................................................................. 2-2

2.3 Accessibility ...................................................................................................................................... 2-3

Chapter 3

Field Investigation and Data Collection

3.1 Topographic Survey and Mapping ............................................................................................... 3-1

3.1.1 Previous Study ........................................................................................................................... 3-1

3.1.2 Additional Topographic Mapping and Survey, Fiscal Year-2013 ....................................... 3-1

3.1.3 Scope of works ....................................................................................................................... 3-1

3.1.4 Monumentation of Ground Control Points and Benchmarks ........................................ 3-3

3.1.5 Detail Topographical Survey ................................................................................................ 3-4

3.1.6 Cross- Section Survey ............................................................................................................ 3-4

3.1.8 Location of Bore Holes, Test Pits and Resistivity Line ..................................................... 3-6

3.2 Hydrological Investigations ........................................................................................................... 3-7

3.2.1 Collection of Available Meteorological and Hydrological Data ...................................... 3-7

3.2.2 Establishment of Gauging Station ........................................................................................ 3-7

3.2.3 Water Level Recording and Flow Measurement ................................................................. 3-7

3.3 Geological and Geotechnical Investigations............................................................................... 3-7

3.3.1 Previous Study ........................................................................................................................... 3-8


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3.3.5 Field Investigation .................................................................................................................... 3-9

3.3.5.1 Core Drilling .................................................................................................................. 3-9

3.3.5.2 Geological Mapping .................................................................................................. 3-10

3.3.5.3 Seismic Refraction Survey ........................................................................................ 3-10

3.3.5.4 Construction Material Survey .................................................................................. 3-12

3.3.2 Additional geological geotechnical investigation, Fiscal Year-2013 ............................... 3-13

Chapter 4

Hydrology and Sediment Study

4.1 Introduction ........................................................................................................................................ 4-1

4.2 Basin Characteristic ........................................................................................................................... 4-2

4.3 Review of Catchment Area ............................................................................................................... 4-3

4.4 Climate Study ...................................................................................................................................... 4-3

4.5 Available Hydrological Data ............................................................................................................. 4-4

4.5.1 Installation of Hydrometric Station ............................................................................................ 4-4

4.5.2 Hydrometric Stations .................................................................................................................... 4-5

4.5.3 Discharge Measurement by DHM and NEA ............................................................................ 4-5

4.6 Rating Curves ..................................................................................................................................... 4-7

4.7 Reference Hydrology ......................................................................................................................... 4-7

4.7.1 Mean Monthly Flow .................................................................................................................. 4-7

4.7.2 Long Term Trends in Flows .................................................................................................... 4-9

4.7.3 Correlation between Flows on Trishuli River at Upper Trisuli 3A dam site and Betrawati Gauge station 447 ...................................................................................................................... 4-9

4.7.4 Flow Duration Curve .............................................................................................................. 4-10

4.7.5 Downstream Release Flow ..................................................................................................... 4-10

4.8 Flood Estimates ............................................................................................................................... 4-10

4.8.1 Introduction ............................................................................................................................. 4-10

4.8.2 Flood Estimation by Regional Analysis ............................................................................... 4-11

4.8.3 Flood Frequency Analysis ...................................................................................................... 4-13

4.8.4 Flood levels ............................................................................................................................... 4-15

4.8.5 Construction Flood ................................................................................................................. 4-15

4.9 Glacier Lake Outburst Floods (GLOF) ....................................................................................... 4-15

4.9.1 General ...................................................................................................................................... 4-15

4.9.2 Historical Record of GLOF ................................................................................................... 4-16

4.9.3 GLOF Hazard .......................................................................................................................... 4-24


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4.9.4 Peak Flows from GLOFs ....................................................................................................... 4-24

4.9.5 Peak Flow Attenuation with Distance .................................................................................. 4-25

4.9.6 Longda Glacier Lakes (threat to dam site and powerhouse site) ...................................... 4-26

4.10 Sediment Study ................................................................................................................................. 4-26

4.10.1 Sediment Data ...................................................................................................................... 4-26

4.10.2 Methods of Estimating the Sediment Flow from the River .......................................... 4-26

4.10.3 Regional Analysis ................................................................................................................. 4-26

4.10.4 Estimate based on the Measured Data ............................................................................. 4-28

4.11 Conclusion ........................................................................................................................................ 4-33

4.12 Recommendation ............................................................................................................................. 4-33

Chapter 5

Geological and Geotechnical Studies

5.1 General .............................................................................................................................................. 5-1

5.2 Geology of Project Area ............................................................................................................... 5-1

5.2.1 Intake portal .............................................................................................................................. 5-1

5.2.2 Headrace Tunnel ........................................................................................................................ 5-2

5.2.3 Adit Portal Area ......................................................................................................................... 5-4

5.2.4 Surge Tank (Option I) .............................................................................................................. 5-4

5.2.5 Powerhouse Site (Option I) ..................................................................................................... 5-5

5.2.6 Drop shaft/ Pressure tunnel Alignment ................................................................................ 5-6

5.2.7 Tailrace box Duct ...................................................................................................................... 5-6

5.2.8 Conclusion and Recommendation .......................................................................................... 5-7

5.3 Seismicity .......................................................................................................................................... 5-8

5.3.1 General ....................................................................................................................................... 5-8

5.3.2 Main Central Thrust (MCT) .................................................................................................... 5-8

5.3.3 Main Boundary Thrust (MBT) ............................................................................................... 5-8

5.3.4 Himalayan Frontal Fault (HFF) ............................................................................................. 5-9

5.3.5 Seismicity Evaluation ............................................................................................................... 5-9

5.4 Core Drilling .................................................................................................................................5-15

5.4.1 Core Drilling during feasibility study, July 2007 .................................................................5-15

5.4.2 Drilling Works Result and Analysis ......................................................................................5-15

5.4.3 Core Drilling during Detail Design, June 2013 ...................................................................5-17

5.4.4 Drilling Works Result and Analyses .....................................................................................5-17

5.5 Construction Material Survey .....................................................................................................5-20


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5.5.1 Introduction .............................................................................................................................5-20

5.5.2 Field Exploration .....................................................................................................................5-20

5.5.3 Laboratory Test and Analysis ................................................................................................5-21

5.5.4 Granular Borrow area .............................................................................................................5-21

5.5.5 Quarry Site ..................................................................................................................................5-22

5.5.6 Laboratory Test on Core Samples .........................................................................................5-23

5.5.7 Reserve Estimation of the Borrow Areas and Quarry areas .............................................5-23

5.5.8 Test summary ...........................................................................................................................5-23

5.6 Geotechnical Design: rock support design of underground structure ................................5-28

5.6.1 Methods ....................................................................................................................................5-28

5.6.1.1 Empirical Method ...........................................................................................................5-28

5.6.1.2 Analytical Method ...........................................................................................................5-28

5.6.2 Analysis for support design ....................................................................................................5-29

5.6.3 Design Criteria .........................................................................................................................5-30

5.6.3.1 Analysis using Rock Cover ............................................................................................5-30

5.6.3.2 Analysis using In Situ Stresses .......................................................................................5-30

5.6.3.3 Analysis using Elastic and Plastic Behavior .................................................................5-31

5.6.4 Failure Criteria ..........................................................................................................................5-33

5.6.5 Estimation of In-Situ Deformation Modulus ......................................................................5-35

5.6.6 Rock Mass Classification ........................................................................................................5-36

5.6.8 Empirical Design According to NGI Method ....................................................................5-37

5.6.9 Empirical Design Recommendation According to U.S Corps of Engineers .................5-41

5.6.10 Underground Wedge Stability Analysis ............................................................................5-43

5.6.10.1 Methodology ........................................................................................................................5-43

5.6.10.2 Results of Analysis ...........................................................................................................5-43

5.6.11 Finite Element Method ......................................................................................................5-46

5.6.11.1 Available Data ..................................................................................................................5-46

5.6.11.2 Result of Analysis .............................................................................................................5-47

5.6.12 Slope Stability .......................................................................................................................5-49

5.6.13 Conclusions and Recommendations ................................................................................5-50

5.6.14 Conclusions and Recommendations ...............................................................................5-54

Chapter 6

Layout Optimization

6.1 Introduction .................................................................................................................................... 6-1


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6.2 Study of Possible Alternative Layouts for the Project ............................................................... 6-2

6.2.1 Alternative-I ........................................................................................................................... 6-3

6.2.2 Alternative-II .......................................................................................................................... 6-4

6.2.3 Alternative-III ........................................................................................................................ 6-5

6.3 P r e s e n t a t i o n of Recommended Layout .............................................................................. 6-6

Chapter 7

Project Design and Description

7.1 General ............................................................................................................................................ 7-1

7.2 Design Basis ..................................................................................................................................... 7-1

7.3 Description of Project Components .............................................................................................. 7-2

7.3.1 Project Access ...................................................................................................................... 7-2

7.3.2 River Diversion .................................................................................................................... 7-3

7.3.3 Headpond/Intake Portal .................................................................................................... 7-3

7.3.4 Headrace Pipe .................................................................................................................... 7-5

7.3.5 Headrace Tunnel .................................................................................................................. 7-6

7.3.6 Surge Shaft/Tank ................................................................................................................. 7-8

7.3.7 Pressure Tunnel after Surge Tank ..................................................................................... 7-9

7.3.8 Drop Shaft and Horizontal Pressure Tunnel .................................................................7-10

7.3.9 Manifolds ..........................................................................................................................7-11

7.3.10 Powerhouse ......................................................................................................................7-11

7.3.11 Draft Tube ........................................................................................................................7-15

7.3.12 Tailrace Conduit ..............................................................................................................7-15

7.3.13 Tailrace Outlet Pond .......................................................................................................7-16

7.3.14 Adit Tunnels.....................................................................................................................7-17

7.4 Generating Equipment .................................................................................................................7-17

7.4.1 Mechanical Equipment .....................................................................................................7-17

7.4.1.1 Initial Data ..........................................................................................................7-17

7.4.1.2 Turbine Selection ...............................................................................................7-18

7.4.1.3 Unit Capacity ......................................................................................................7-18

7.4.1.4 Turbine Speed ....................................................................................................7-18

7.4.1.5 Powerhouse Dimensions and Unit Parameters .............................................7-18

7.4.1.6 Turbine ................................................................................................................7-19

7.4.1.7 Governor .............................................................................................................7-19

7.4.1.8 Inlet Valve ...........................................................................................................7-20


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7.4.1.9 High Pressure Oil System .................................................................................7-20

7.4.1.10 Lubricating Oil System ......................................................................................7-21

7.4.1.11 Cooling Water System .......................................................................................7-21

7.4.1.12 Drainage and Dewatering System ....................................................................7-21

7.4.1.13 Compressed Air System ....................................................................................7-22

7.4.1.14 Unit Breaking System ........................................................................................7-22

7.4.1.15 Automatic Grease Lubrication System ...........................................................7-23

7.4.1.16 Oil Handling System ..........................................................................................7-23

7.4.1.17 Air Conditioning and Ventilation System ......................................................7-23

7.4.1.18 Fire Detection and Fire Fighting System........................................................7-24

7.4.1.19 Overhead Traveling Crane ................................................................................7-24

7.4.1.20 Diesel Engine Generating Set ..........................................................................7-24

7.4.1.21 Mechanical Workshop .......................................................................................7-25

7.4.2 Powerhouse Electrical Equipment ..................................................................................7-25

7.4.2.1 Generator ............................................................................................................7-25

7.4.2.2 Excitation System ..............................................................................................7-26

7.4.2.3 Main Power Transformer .................................................................................7-26

7.4.2.4 Station Service Transformer .............................................................................7-26

7.4.2.5 Medium Voltage Switchgear .............................................................................7-26

7.4.2.6 High Voltage Switchgear ..................................................................................7-26

7.4.2.7 Disconnecting Switch ........................................................................................7-27

7.4.2.8 Control System ...................................................................................................7-27

7.4.2.9 Protection System ..............................................................................................7-28

7.4.2.10 Switchyard ...........................................................................................................7-28

7.4.2.11 Communication System ....................................................................................7-29

7.4.2.12 Battery and Battery Charger .............................................................................7-29

7.4.2.13 Grounding System .............................................................................................7-29

7.5 Transmission Line .........................................................................................................................7-30

Chapter 8

Power and Energy Generation

8.1 Background ......................................................................................................................................... 8-1

8.2 Dependable Flow ............................................................................................................................... 8-1

8.3 Gross Head & Net Head .................................................................................................................. 8-2

8.4 Overall Efficiency .......................................................................................................................... 8-3


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8.5 E n e r g y Computation ................................................................................................................. 8-3

Chapter 9

Construction Planning and Schedule

9.1 General ............................................................................................................................................ 9-1

9.2 Objective & Scope of work .......................................................................................................... 9-1

9.3 Site Condition ................................................................................................................................. 9-2

9.3.1 Topography and Land Use .................................................................................................. 9-2

9.3.2 Climatic Conditions ............................................................................................................... 9-2

9.3.3 Telecommunication Facilities .............................................................................................. 9-2

9.4 Access to the Site ........................................................................................................................... 9-2

9.5 Basic Assumptions ......................................................................................................................... 9-3

9.6 Concreting Facilities ...................................................................................................................... 9-4

9.7 Project Construction Work and Construction Planning .......................................................... 9-4

9.7.1 Construction Power, Camp and project road ................................................................... 9-5

9.7.2 Headrace pipe ........................................................................................................................ 9-6

9.7.3 Surface head pond (intake of UT3B HEP) ....................................................................... 9-6

9.7.4 Headrace Tunnel ................................................................................................................... 9-7

9.7.5 Adit Tunnels ........................................................................................................................... 9-8

9.7.6 Underground Surge tank/Shaft ........................................................................................... 9-8

9.7.7 Valve Chamber and Access to Valve Chamber ................................................................ 9-9

9.7.8 Pressure tunnel after Surge tank .......................................................................................... 9-9

9.7.9 Drop Shaft .............................................................................................................................. 9-9

9.7.10 Pressure Tunnel after Drop Shaft ....................................................................................... 9-9

9.7.11 Powerhouse ..........................................................................................................................9-10

9.7.12 Tailrace conduit and Outlet Structure ..............................................................................9-11

9.7.13 Electro-Mechanical Equipment .........................................................................................9-11

9.7.14 Switchyard, ancillary Buildings and transmission line ....................................................9-11

9.7.15 Testing and Commissioning ..............................................................................................9-11

9.10 Construction Planning and Scheduling ................................................................................9-13

9.11 Key Dates .................................................................................................................................9-14

Chapter 10

Environmental Impact Assessment

10.1 Introduction ..................................................................................................................................10-1

10.2 Project Description ......................................................................................................................10-1


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10.3 Study Methodology ......................................................................................................................10-2

10.4 Existing Environment Conditions ............................................................................................10-2

10.4.1 Physical Environment .........................................................................................................10-2

10.4.2 Biological Environment ......................................................................................................10-3

10.4.3 Socio-economic and Culture Environment .....................................................................10-4

10.5 Impact Assessment ......................................................................................................................10-6

10.5.1 Physical Environment ........................................................................................................10-6


10.5.3 Socio-economic and Cultural Environment ....................................................................10-7

10.6 Alternatives Study ........................................................................................................................10-8

10.7 Mitigation Measures ....................................................................................................................10-9

10.7.1 Physical Environment .........................................................................................................10-9


10.7.3 Socio-economic and Cultural Environment ................................................................. 10-10

10.8 Environmental Management Plan .......................................................................................... 10-11

10.10 Review of Plans/policies, acts, rules/regulation, guidelines, conventions strategies and standards ................................................................................................................................................. 10-12

10.11 Conclusion ............................................................................................................................. 10-12

Chapter 11

Cost Estimate

11.1 General .......................................................................................................................................... 11-1

11.2 Criteria, Assumptions and Cost Components ......................................................................... 11-1

11.3 Estimating methodology ............................................................................................................. 11-1

11.4 Civil Works ................................................................................................................................... 11-2

11.5 Electro-Mechanical Equipment ................................................................................................. 11-3

11.6 Hydro-mechanical equipment .................................................................................................... 11-3

11.7 Resettlement, Land acquisition, and Environmental provisions .......................................... 11-3

11.8 Contingencies ............................................................................................................................... 11-3

11.9 Pre operating and management cost ......................................................................................... 11-4

11.10 Project Cost .............................................................................................................................. 11-4

Chapter 12

Project Evaluation

12.1 General ...................................................................................................................................... 12-1

12.2 Methodology ............................................................................................................................ 12-2


ix


12.2.1 Estimation of Project Costs ............................................................................................... 12-2

12.2.2 Estimation of Project Benefits .......................................................................................... 12-2

12.2.3 Construction Period ............................................................................................................ 12-3

12.2.4 Calculation of Net Benefits ................................................................................................ 12-4

12.3 Assumptions ............................................................................................................................. 12-5

12.3.1 Discount Rate ...................................................................................................................... 12-5

12.3.2 Cost Datum .......................................................................................................................... 12-5

12.3.3 Planning Horizon ................................................................................................................ 12-6

12.3.4 Operation and Maintenance Cost ..................................................................................... 12-6

12.3.5 Price Escalation ................................................................................................................... 12-6

12.3.6 Taxes, Duties and VAT ...................................................................................................... 12-6

12.3.7 Royalties ................................................................................................................................ 12-6

12.3.8 Debt Equity .......................................................................................................................... 12-7

12.3.9 Interest Rate ......................................................................................................................... 12-7

12.3.10 Loan Repayment Period ................................................................................................. 12-7

12.3.11 Other Charges .................................................................................................................. 12-7

12.4 Economic Evaluation Result ................................................................................................. 12-8

12.5 Financial Evaluation ............................................................................................................. 12-11

Chapter 13

Conclusions and Recommendations ..........................................................................................................13-1

List of the Table Table 3.1: Co-ordinates and Elevation of Existing Control Points ......................................................... 3-3

Table 3.2: List of Co-ordinates and Elevations of Permanent Benchmarks .......................................... 3-3

Table 3.3: List of borehole locations (core drilling works-August 2013) .............................................. 3-6

Table 3.4 : General Description of Drill Holes (Coordinates based on old survey reports).......... 3-10

Table 3.5: Brief Description of Seismic Refraction Survey .................................................................. 3-11

Table 3.6: A Brief Description of Test Pits ............................................................................................. 3-13

Table 4.1: Average precipitation of the stations located near the project area ...................................... 4-4

Table 4.2: Rainfall records available from China ....................................................................................... 4-4

Table 4.3: Discharge Measurements at Pairobesi Bridge .......................................................................... 4-5

Table 4.4: Hydrometric stations located in the Trishuli River Basin ...................................................... 4-5

Table 4.5: Discharge measurement in Trishuli river at Gauge Station 447, Betrawati ......................... 4-6


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Table 4.6: Discharge measurement in the tributaries of Trishuli River near project area ................... 4-6

Table 4.7: Monthly mean flows (m3/s) for 1967-2005 on Upper Trishuli 3A Dam site .................... 4-8

Table 4.8: Flow duration curve at dam site............................................................................................... 4-10

Table 4.9: Floods and Regression Coefficient (Regional Analysis) ....................................................... 4-13

Table 4.10: Instantaneous peak for the Flood Frequency Analysis ...................................................... 4-13

Table 4.11: Frequency Analysis by Theoretical Distribution ................................................................. 4-14

Table 4.12: Flood water level at different project components ............................................................. 4-15

Table 4.13: Historical GLOF events in Nepal and China (Tibet) ........................................................ 4-18

Table 4.14: Summary of Sediment Concentration Data, Station 447 ................................................... 4-29

Table 4.15: Comparison of Sediment Concentration 1977-1979 .......................................................... 4-30

Table 4.16: Recommended Monthly Sediment Concentration ............................................................. 4-31

Table 4.17: Particle Size Distribution of Bucket Sampling .................................................................... 4-32

Table 5.1: General Description of Boreholes ...........................................................................................5-15

Table No. 5.2: Summary of borehole location, depth, direction and bedrock depth.........................5-17

Table 5.4: Summary of Pits and Sample Description ..............................................................................5-21

Table 5.5: Reserve Estimation of Borrow Area .......................................................................................5-23

Table 5.6: Summary of Laboratory Test Results on Granular Material ...............................................5-24

Table 5.7: Summary of Laboratory Test Results on Quarry Material ...................................................5-25

Table 5.8: Summary of Laboratory Test Results on Core Samples ......................................................5-25

Table 5.9: Summary of Laboratory Test Results on Core Samples ......................................................5-26

Table 5.10: Summary of Laboratory Test Results on Core Samples ....................................................5-26

Table 5.11: Point Load Test Results ..........................................................................................................5-27

Table 5.12: Damage Index ..........................................................................................................................5-32

Table 5.13: Values of constant mi for Intact Rock by rock group ........................................................5-34

Table 5.14: Estimation of In-Situ Modulus of Deformability ...............................................................5-35

Table 5.15: Rock Mass Strength Parameters ............................................................................................5-36

Table 5.16: Rock Mass Classification using Rock Mass Rating (RMR) system (Bieniawski, 1989)..5-36

Table 5.17: Rock Mass Classification from Rock Tunneling Quality Index, Q (Stillborg, 1994) .....5-37

Table 5.18: Typical Design Recommendations after U.S. Corps of Engineers (1980) and Douglas and Arthur (1983) .........................................................................................................................................5-41

Table 5.19: Summary of Analysis for Headrace Tunnel (N256°) ..........................................................5-44





xi


Table 5.24: Summary of Analysis for Horizontal Pressure Tunnel (N140°) .......................................5-45

Table 5.25: Basic Design Parameters for Elasto - Plastic Analysis .......................................................5-48

Table 5.26: Summary of the result of analysis ..........................................................................................5-49

Table 5.26: Rock Support Pattern for Upper Trishuli-3B Hydroelectric Project ..............................5-51

Table 5.27: Chainage wise Support Class Headrace Tunnel ..................................................................5-52

Table 5.28: Geological & Geotechnical Evaluation of Option I & Option II Powerhouse Site .....5-53

Table 6-1: Flow Data Used for the Alternative Studies ........................................................................... 6-3

Table 6.2: summary of Cost Comparison of Different Layouts .............................................................. 6-6

Table 3: Details of Cost Comparison of different layouts ....................................................................... 6-7

Table 7.1: Bend Characteristics of Headrace Pressure Pipe ..................................................................... 7-6

Table 7.2: Lengths of different rock class in headrace tunnel ................................................................. 7-7

Table 7.3: Description of Headrace Tunnel before surge tank ............................................................... 7-7

Table 7.4: Details of Horizontal bends for both alternatives .................................................................. 7-8

Table 7.5: Description of designed surge tank ........................................................................................... 7-8

Table 7.6: Description of water conveyance after surge tank .................................................................. -10

Table 7.7: Details of Pressure Shaft Bends (Vertical Shaft Option) .....................................................7-10

Table 7.8: Design parameters for sizing of Powerhouse ........................................................................7-12

Table 7.9: Design parameters for Draft tube ...........................................................................................7-15

Table 7.10: Design parameters for tailrace Outlet Pond ........................................................................7-16

Table 8.1: Average Head Loss for Design Discharge .............................................................................. 8-2

Table 8.2: Monthly Energy Generation from Upper Trishuli 3B HEP .................................................. 8-4

Table 9.1: Estimate of construction power ................................................................................................ 9-5

Table11.1: summary of cost estimate ........................................................................................................ 11-6

Table 12.1: Result of Economic Analysis ................................................................................................. 12-8

Table 12.2: Result of Sensitivity analysis ................................................................................................... 12-8

Table 12.3: Economic Analysis Detail Table ........................................................................................... 12-9

Table12.4: Financial Analysis Data and Result ...................................................................................... 12-12

List of the Figure Figure 2.1: Physiographic location of the project ...................................................................................... 2-1

Figure 2.2: Location of the Project .............................................................................................................. 2-2

Figure 5.1: Seismic Risk Map of Nepal .....................................................................................................5-11

Figure 5.2: Seismic Hazard Map of Nepal ................................................................................................5-12


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Figure 5.3: Seismic Risk Map of India .......................................................................................................5-14

Figure 5.4: Estimated Support Categories based on the tunneling quality Index Q (After Grimstad & Barton, 1993) .................................................................................................................................................5-38

Figure 12-2: Interest Rate vs FIRR .......................................................................................................... 12-12


1-1 Trisuli Jalvidyut Company Limited

Chapter 1:

Introduction

1.1 Study Background

Nepal is entering a phase of rapid economic development and a major part of this

development is based on the tapping of its immense water resources potential. The total

hydroelectric potential of the country has been estimated at 83,000 MW of which approximately

42000 MW is considered to be economically feasible potential. A number of Hydroelectric schemes

like Modi (14 MW) HEP, Puwa(6.2 MW) HEP, Khimti (60 MW) HEP, Bhote Koshi (36 MW) HEP,

Kaligandaki – A (144 MW) HEP, Chilime (22 MW) HEP, Middel Marsyangdi (70 MW) HEP have

already been completed recently while other projects like Chameliya (30 MW HEP, Kulekhani III

(14 MW) HEP, Tama Koshi (456 MW) HEP, Mai Khola(22 MW) HEP, Lower Modi (20 MW)

HEP are under various stages of construction. The private sector has implemented projects

Khimti, Bhote Koshi, Mai Khola, Lower Modi and other small projects. The independent power

producer (IPP) have generated around 230.5 MW (F/Y 2012/13 NEA Report).

Harnessing of Nepal’s huge hydro-electric potential could not only fulfill much of the energy needs

but could also become the source of prosperity. Hydroelectricity can be the prime mover of

economic development of Nepal and hence deserve special importance. The main attraction of

Hydroelectric is that this clean source of energy does not require fuel cost and the electricity

generating costs decline over the life span of the venture.

The first hydro electric plant was installed in Pharping (500 KW) in 1911. At present, Nepal has an

installed capacity of 762 MW, out of this total capacity, 53.41 MW is generated through thermal

power plants and 7 0 8 .5 MW through hydro power projects under power purchase agreements

with the private sector. Only about 45 % of the country’s population is served by electricity which

shows a per capita consumption to be very low. Nepal has been experiencing load shedding since

the past few years (and the supply deficit is nearly 800 MW in the dry season). The demand

projection made by NEA indicates that the peak load demand for the years 2015 and 2020 will be

1510 MW and 2206 MW respectively. NEA, an undertaking of Government of Nepal has launched



a wide range of study programs aimed at identifying and studying a series of Hydroelectric

projects. The objective of the study program is to identify technically and economically feasible

projects for subsequent implementation.

1.2 Previous Studies

Upper Trisuli 3B HEP (37 MW) is a cascade project of Upper Trisuli 3A HEP and was identified by

NEA Engineering Services in 2004/05 as part of Project Identification Study. NEA has completed

the feasibility study in 2007/08. Four cascade schemes namely Upper Trishuli 1, 2, 3A and 3 B were

identified in the Upper Trishuli basin located between Syabrubesi and Betrawati which has a total

head of 750m. NEA has completed detailed project report study of the Upper Trishuli 3A which has

an installed capacity of 60 MW and is under construction. Upper Trishuli 3B HEP is a downstream

project which utilizes the discharge from the tailrace of Upper Trishuli 3A HEP.

1.3 Objectives and Scope of Work

Trisuli Jalvidyut Company Limited (TJCL) has carried out the review of the Trisuli 3B HEP and

carried out the site verification. The outcome of the review study is as follows:

a) It is urgent need to update the cost of the project according to the prevailing market rate.

b) During the site visit it is found the land slide occurred at the powerhouse location year

in the year 2011, therefore, it is necessary to locate the powerhouse at the alternative

place.

c) Carry out the cost comparison between different alternative layouts.

d) Since the access road is available at the intake area to powerhouse area, the cost of these

item has to reduce from the estimate.

The main objective of this study is to carry out a Detailed Project Report of the Upper

Trishuli 3 B Hydroelectric Project. This is being done by taking into consideration all the relevant

data and information collected from the previous studies, field surveys and investigations conducted

during the present study. The EIA study required to complete the Detailed Project Report is also a

part of the objectives of this study. The scope of work can broadly be divided into the field



investigation work and the design of the project.

1.4 Field Investigation Works

The following additional works were carried out in the design phase apart from the feasibility phase

of study.

1.4.1 Topographical Survey and Mapping

For detail engineering design, following topographical survey and mapping works has been carried

out by the TJCL:

i) Mapping in the dam site area at a scale of 1:500 and with a contour interval of 1 m.

ii) Mapping of the Powerhouse (alternative option and original option) area at a scale of

1:500 and a contour interval of 1m.

iii) Connection with the national grid.

iv) Cross section survey of the river.

v) Mapping of tunnel alignment area at scale of 1:5000.

vi) Cadastral mapping of the project for land acquisition of project

1.4.2 Geological and Geotechnical Investigation

The following geological investigation works were carried out for this phase of the study.

i) A total of 250 m of core drilling was completed at various locations during the

feasibility study. Additional 195 m drilling works were completed at the alternative

powerhouse option I the Fiscal Year 2069/70.

ii) A total of 11 test pits were completed at various locations in and around the project

area.

iii) Laboratory tests were conducted for the test pit samples.

iv) Surface geological mapping of the project were carried out during feasibility study.



Apart from that, new surface geological mapping of the intake area, powerhouse area

and alternative powerhouse area were carried out at appropriate scales.

1.4.3 Project supports facilities

For the construction of the project, the planning will set according to the location of support

facilities such as quarry site, dumping site, muck disposal area, access road and adit at different

location. Therefore, during the detail design, the site visit has been done to locate all these support

facilities.

a) Location of muck disposal area has been identified based on the adit tunnel. For

this purpose most of those places are near the river bank and government land.

b) Location of Quarry site are done based on the availability of construction material

such as sand and gravel.

c) Contractor’s construction camp are located based on the availability of land at the

site. They have been identified near the powerhouse area.

d) Most of the access road has been constructed, the project road is required for the

surge tank access and powerhouse area only. A portion of road from New Bridge

(the Belly Bridge constructed by Trisuli 3A HEP) to Tupche (near the pressure

tunnel alignment) has to be relocated and cost estimate has been done for these

item separately.

e) The construction camps for the company office are designed by the team of TJCL

engineer.

1.5 Design Work

The main part of the design consisted of the alternative layout of the powerhouse and carry out

the hydraulic design and structural design of the different structures. The main works consisted of

the following:

i) Review of available information (feasibility Study);

ii) Collection of basic information/data through field surveys, investigations and



laboratory tests;

iii) Preparation of design drawings;

iv) Alternative studies of powerhouse location;

v) Detail design of the following structures:

• Project road

• Headponds at the outlet of Trisuli 3A HEP tailrace

• Adit tunnel at different location

• Conveyance system including headrace pipe, headrace tunnel, surge tank, drop

shaft

• Surface powerhouse

• Tailrace duct

• Electromechanical Facilities

vii) Computation of Project Energy Outputs and Related Benefits;

viii) Construction Planning in Detail;

ix) Detail Quantity Cost Estimate;

x) Disbursement Schedule;

xi) Project Evaluation for finance.



Chapter 2:

Description of Project Area

2.1 Location

Nepal lies in the foothills of the highest areas of the Great Himalayan Range. It extends from the

Republic of India in the south to the high Tibetan Plateau of the People’s Republic of China in the

north. It is roughly rectangular in shape. Nepal embraces within itself a unique variety of

geographical settings ranging from the southern lowlands at approximately 60 masl to the highest

peaks in the world in its northern parts. Between these marginal zones there are three richly varied

regions, namely, the Terai Region in the south, the Middle Hilly Region in between and the Trans

Himalayan Region in the north. Physiographically, the project is located at Middle Mountains as

shown in Figure 2.1.

Figure 2.1: Physiographic location of the project

TeraiSiwaliks

Middle Mountains High Mountains High Himalaya

Shale

Alluvium

Conglomertate

Sandstone

Granite

Schist

Limestone

Metamorphosed

Argillaceous

Rocks

Gneiss

SchistGranite

Tibetan

Sediments

Physiographic Region of Nepal

Project Location



The Upper Trishuli 3B Hydroelectric Project is located in Nuwakot and Rasuwa District of the

Central Development Region between longitudes of 85O10’11” and 85O12’01”and between latitudes

of 27O59'12” and 28O01'54”. The project lies in the Trishuli River of the Middle Hilly Region which

constitutes a broad complex of hills and valleys. It is a major river of the Gandaki Basin. Rugged

landscapes with a generally north to south flowing rivers like Sapta Gandaki characterizes the

Gandaki Basin. The area of the intake site is located about 5 km upstream from the confluence of

the Salankhu Khola and Trishuli while the powerhouse site is located approximately 0.5 kilometers

upstream from the confluence of Salankhu Khola and Trishuli River. The project location map is

given in Figure 2.2 and DWG No UT-3B HEP 01.

Figure 2.2: Location of the Project

2.2 Physical Features

Owing to the three richly varied regions, Nepal lies in an area with a great difference in elevation

from the north to the south. As a result, Nepal experiences an exceptional variation in climate. From

south to north, five defined climatic zones exist in the country, these are:

Project Location



• Tropical

• Subtropical

• Temperate

• Alpine

• Sub Arctic

The dominant climatic influence is that of the south east monsoon. The climate of the

Gandaki Basin is influenced by the physiography of the region. The difference between the warm

humid summer and the severe cold winter becomes more marked with the increase in altitude.

The south east monsoon is responsible for almost all of the rainfall in the basin. The monsoon

starts in mid June and continues until late September. This is followed by a dry period and the

winter, which starts in November and lasts until February. A short winter rainfall characterizes the

winter. The climate becomes progressively warmer from March until the beginning of the next

monsoon.

2.3 Accessibility

The project site is located about 12 km from Trishuli Bajaar and the existing Trishuli

Hydroelectric project (24 MW), which is the nearest town. The nearest airport is located in

Kathmandu which is approximately 84 km from the project site.

Access conditions to the site are excellent. There is a blacktopped road from Kathmandu to Trishuli

Bajaar which is approximately 72 km long. The black topped road from Trisuli Bazar to Dhunche

highway passes through the Betrawati Bazar at about 10 km from Trisuli Bazar. A graveled road

exists from Betrawati Bajaar to the powerhouse site of the p r o j e c t and it is approximately 2

km long. This gravel road passes through the headworks area of Upper Trisuli 3B Hydroelectric

Project. The distance between powerhouse to headworks area is about 4 km.

It is therefore obvious that the project is accessible by the gravel road. During the construction, the

project has to build the road to powerhouse and road to surge tank adit, this shall be about 0.8 km

long.



Chapter 3:

Field Investigation and Data Collection

3.1 Topographic Survey and Mapping

3.1.1 Previous Study

The overall survey works for the proposed project were conducted in two phases. The first phase

lasted from November end to December end of the year 2006 while the second phase survey was

carried out from first February to last February 2006. The first phase survey works were carried

out to map the project area as a whole including headworks, intake area, surge shaft and

powerhouse area. The second phase of survey works included additional mapping for the

alternate powerhouse location. The details are given in the Detail Project Report, Volume-1 of

Upper Trisuli 3B Hydroelectric Project.

3.1.2 Additional Topographic Mapping and Survey, Fiscal Year-2013

Proper survey and leveling works are necessary to design the components, to prepare drawings and

to calculate the quantities of the project components. The survey data greatly influences the

accuracy of design and quantity take offs. All the survey works were carried out precisely and

correctly again. Therefore, the company TJCL has carried out the detail topographic survey and

mapping for the detail design and construction purpose.

The new topographic mapping covers the survey of alternative location of powerhouse site. Since

the project is cascade development of Upper Trisuli 3A HEP, the ground control points are taken

from the same projects. The detail reports of survey are given in “ Detail Topographic Survey of

Upper Trisuli 3B Hydroelectric Project-February 2013.

3.1.3 Scope of works

a. Review of the topographical map of feasibility study of the project, based on the



available maps of the project area.

b. Finalization of the methodology of survey and plan

c. Interconnection of the Ground Control Points (GCPs) of project area with respect to

the National Grid Co-ordinate System of Nepal.

d. Co-ordinates for Planimetric Control Points can be transferred from Upper Trishuli

“3A”, however verification is required before topographic survey and mapping.

e. Establishment of Benchmarks at various locations in the project area for the marks

required but not limited to are as shown below:

i. Headwork area 6 nos.

ii. Tunnel Adit area 2 nos.

iii. Surge Tank area 3 nos.

iv. Powerhouse area 6 nos.

v. Camp Site area 2 nos.

f. Detail topographical survey of Headwork, Tunnel alignment, Intake, Adit, Surge Tank,

Penstock Pipe/Dropshaft and Powerhouse area (including alternative powerhouse site)

at Scale 1:500. This shall be working drawing at contour interval 1m.

g. Overlay of Topographic Survey Map in GIS database of NGIIP of Nepal.

h. Access Road to the surge tank, the mapping of the access road is to be carried out if

necessary.

i. Strip Mapping of Tunnel alignment covering alternative-I and alternative-II in 1:5,000

Scale.

j. Cross Section survey at Trishuli River along Head pond and Powerhouse area (

Alternative powerhouse site shall be included )

k. The Topographic Map shall include but not limited to :

- Demarcation of road, forest land, agriculture land, barren land, rock cliff, bush and,

land slide area, rivulets and big boulder if any in the topographic mapping. The

verification shall be carried out at the site after draft survey report submission.

- Exact location of manmade structures such as houses, temples, bridges, canals, walls

and etc are to be shown in the topographic mapping and drawings. Such structures

shall be documented by the photographs.



3.1.4 Monumentation of Ground Control Points and Benchmarks

List of Co-ordinates and Elevations of Existing Permanent Points provided by Upper Trishuli-3A

Hydroelectric Project.

Table 3.1: Co-ordinates and Elevation of Existing Control Points

Point No. Easting (m.) Northing (m.) Elevations (m.)

DX 18 617090.576 3101331.156 734.409

DX 19 616865.863 3101139.600 725.862

Monuments made of concrete pillars have been fixed on the strategic locations from where the detail

survey longitudinal sectioning and cross sectioning and setting out of the project components can be

carried out. Some benchmarks have been established on the stable boulders or on manmade

permanent structures which were available in the vicinity of survey area. The List of Co-ordinates of

established control points are given in Table 3:2

Table 3.2: List of Co-ordinates and Elevations of Permanent Benchmarks

S.

No.

Point

Name

Easting

(m.)

Northing

(m.)

Elevations

(m.)

Remarks

1

DX 18 617090.576 3101331.156 734.409 Existing point Fixed on

Concrete Pillar

2 DX 19 616865.863 3101139.600 725.862 “ “

3 BM-1 616058.861 3096433.271 632.334 Fixed on Concrete Pillar

4 BM-2 615909.991 3096472.042 640.407 Fixed on Boulder


6 BM-4 616015.244 3096722.002 749.960 “ “



9 BM-7 616556.547 3100813.820 786.142 “ “

10 BM-8 616850.989 3100640.112 724.497 “ “

11 BM-9 616675.455 3100636.592 724.497 “ “








17 BM-15 616460.537 3097274.502 647.795 “ “

18 BM-16 616289.996 3097599.897 777.605 “ “

19 BM-17 616273.929 3097611.528 782.370 “ “

3.1.5 Detail Topographical Survey

The detail topographical survey has been carried out by using TOPCON Total Stations Survey

instrument with the least count as 5 seconds. The survey has been carried to depict all natural and

manmade features in the study area in order to prepare the topographical map in 1:5,00 scale with 1.0

m contour interval. The topographical survey has been carried out by covering approximately 60 ha.

of land including headwork area, along tunnel alignment, Adit areas, surge tank and powerhouse

areas.

3.1.6 Cross- Section Survey

The Cross-Sections at Trishuli River have been taken at 50m intervals at alternative powerhouse

sites. The spot levels along the cross-section have been taken as per change of ground level to

prepare correct profile along the cross-section line which represents the existing shape. The details of

existing structures those falling along the line of cross-section have been taken properly.

3.1.7 Preparation of maps profiles and reports

Based on the data from the field survey, the topographical maps cross-sections have been prepared

by using the AutoCAD Land Development Software. The complete report and drawings have been

prepared.

(i) A Reference Plan of the Project area in scale as shown in the Bar Scale.

(ii) Detail Topographical Maps of Headwork, Adits and Powerhouse areas in scale 1:500



with contour interval 1 metre.

(iii) Detail Topographical Maps along the strip of Tunnel alignment in scale 1:5,000 with

contour interval 5 metres.

(iv) Cross-Sections drawings

(v) A complete report consisting of survey methodology, outputs of the work, D-Cards

etc.

In general, the maps, other drawings and reports have been prepared as below:

(i) A General Reference Map of the Project Area

In order to prepare the General Reference Map, GIS database of Topographical Map Sheet

No. 2885-13 and 2785-01B were collected from NGIIP, Survey Department of Nepal. By

using ArcGIS 9.2 Software, the data of the project area and its vicinity was selected from the

above mentioned GIS data. Then a Digital Terrain Model (DTM) was created, which consists

of relief model and site model having X, Y, Z Co-ordinates of each point. All the features

were then transferred to the plan and finally the Reference Map has been prepared.

(ii) Detail Topographical Maps

All existing physical and manmade features on the ground; such as structures, utilities features

and the land use information have been shown in the maps. The topographical maps have

been plotted in the scale: 1: 500 with counter interval 1m and 1:5,000 scale with 5 m. interval.

The maps have been prepared to produce DTMs to be enabling direct use to design.

(iii) Cross- Section Drawings

The cross-sections have been drawn and prepared in H = V 1:500 . The drawings have been

prepared in A1 size with a 25 mm border on the left and 10 mm border on three sides.



(iv) Reports

In general, the main report is prepared by incorporating the general approach and

methodology, and other general matters relating to the objective of the work. The secondary

data which would be useful later are annexed with the report. But the whole report is

managed in volume one. The annexure (Detail Topographic Survey-February 2013) which

are attached with the report are as follows:

● Location Map

● General Reference Map of the Project area

● Traverse Chart

● D-Cards of Permanent Benchmarks/Survey Stations

● List of Co-ordinates and Elevations of Existing Permanent Points provided

by Upper Trishuli-3A Hydroelectric Project.

3.1.8 Location of Bore Holes, Test Pits and Resistivity Line

During the feasibility study of Upper Trisuli 3B HEP, Number of bore holes, test pits and Resistivity

line survey were carried out. They are given in the report of “ Upper Trisuli 3B Hydroelectric

Project, Detail Project Report, Volume 1-year 2008”.

During detail design phase, A total of 4 boreholes were located on the ground at the powerhouse

site and surge tank area with given coordinates and elevation. The coordinates and elevation of

all the boreholes are given in Table 3.3.

Table 3.3: List of borehole locations (core drilling works-August 2013)

S. No. Bore Hole Northing Easting Elevation Location

1 DST-1 616196.445 3097625.756 813.15 Surge shaft

2 DPA-1 616353.178 3097447.957 683.07 Penstock alignment

3 DPH-1 616434.629 3097359.831 639.90 Powerhouse Site

4 DPH-2 616397.42 3097410.45 665.545 Powerhouse Site



3.2 Hydrological Investigations

3.2.1 Collection of Available Meteorological and Hydrological Data

The meteorological and hydrological data for the project was obtained from Government of

Nepal, Department of Meteorology and Hydrology. The main data obtained were the

precipitation records, temperature and discharge measurements at available stations. The

details for the available data are given in the following sections and also in chapter 4.

3.2.2 Establishment of Gauging Station

A hydrological team visited the site in the month of January 2006. A total of 5 staff gauges

were installed during the field visit near the Headworks site and Powerhouse site on Trishuli 3B

Khola, and a staff gauge was installed in Salakhu Khola a tributary of Trishuli River at

Pairobesi, Champani and Sole village of Rasuwa and Nuwakot District.

During the site visit the river was traversed along its bank to locate the best possible site for the

staff gauge. The selected site was considered as the best location for the staff gauge as it had a

straight reach and a pool of water near the gauge site.

3.2.3 Water Level Recording and Flow Measurement

During the time of staff gauge installation, discharge measurements were carried out. Average

discharges on 3rd January 2007 were 28.715 m3/s in Trishuli River at Pairobesi and 0.611

m3/s in Salankhu Khola at Solye. Detailed discharge measurement sheets are attached herewith.

3.3 Geological and Geotechnical Investigations

NEA has carried out a lot of geotechnical investigation during the feasibility study of the project for

the given site conditions. They are given in the “Upper Trisuli-3B Hydroelectric Project, feasibility

study, Geology and Geotechnical Study (Appendix B, Year 2007) in detail. Since the proposed

powerhouse site has felt huge land slide in the year 2011, it is forced to see the alternative



powerhouse location. Therefore, the company has carried out new surface and subsurface geological

investigation in the year 2013. The results obtained from the investigation work will be used to

assess the technical viability of the project for the Detailed Design of the project.

3.3.1 Previous Study

Medium Hydro Power Study Project, NEA (1998) had carried out the reconnaissance study of

Upper Trishuli - 3 (UT-3) which is named as Gogane to Betrawati Hydroelectric Project and Upper

Trishuli -3B (UT-3B) is mutually included in UT-3 Project.

Department of Mines and Geology has also prepared and compiled regional geological map

including the project area in the scale of 1:1,000,000 (1994).

During the feasibility study of the project, the field investigation work is carried out to find out the

surface and subsurface geological condition of the project area, to design the support

pattern for the underground structures and to confirm the availability of the construction materials

in terms of quality and quantity.

3.3.2 Scope of Work

The main scope of work in this phase of study is to assess the rock mass condition of the

project area by means of detailed geological mapping, core drilling and geophysical survey and to

produce engineering geological maps, cross-sections and profiles at various scales as deemed

necessary to provide information required for the engineering designs and underground

excavation.

The scope of work in geological mapping is to produce engineering geological maps of the

powerhouse site and the headworks site in the scale of 1:1,000 and 1:1,000 respectively and

engineering geological map of tunnel alignment area in the scale of 1:10,000.

The scope of work for the core drilling includes the assessment of sub-surface geological

condition including rock quality, rock type, joint characteristics and permeability condition of the



rock mass.

Another main scope of work is geophysical investigation for the assessment of sub-surface

geological condition of the major structures during the present investigation.

The scope of work also includes the preliminary geotechnical design including stability

analysis and rock support classification of underground structures.

The scope of work for the construction material investigation includes the assessment for the

quality and quantity of construction material available within the easy haulage distance from the

project area.

3.3.5 Field Investigation

The following geological field investigation works have been carried out to assess the

geological and geotechnical condition of the project area. Geological mapping, core drilling, seismic

refraction survey and construction material investigations are the main activities which have been

carried out during the present study.

3.3.5.1 Core Drilling

A total of 250.00 m of linear core drilling has been carried out during the present investigation.

One bore hole DHP-1 has been drilled in the intake portal, three namely DP-1, DP-2, DP-4

have been drilled in the Powerhouse area and one DP-3 has been drilled in Surge Tank area.

Similarly, a Drill hole DHA-1 has been drilled at Andheri Khola to know the rock cover at headrace

tunnel alignment. The location of drill holes are shown in Drawing No.-6.1,6.2 and 6.3. The

general description of the bore holes are shown in Table No. 3.4.



Table 3.4 : General Description of Drill Holes (Coordinates based on old survey reports)

Drill Hole

No.

Drilling

Machine

Inclination

& Direction

Location Length

(m)

Co-ordinates

X Y Z

DP-1

DP-2

DP-4

DHP-1

DHA-1

DP-3

Acker ‘Ace’

Acker ‘Ace’

Acker ‘Ace’

Tone UD-5

Tone UD-5

Acker 'Ace'

Vertical

Vertical

60°/285°

60°/275°

Vertical

Vertical

Powerhouse

Power house

Powerhouse

Intake Tunnel

Alignment Surge

tank

50.00

30.00

35.00

35.00

50.00

50.00

3097872.018

3097898.200

3097891.240

3100866.415

3100745.980

3097967.715

616658.991

616565.300

616590.128

616665.250

616228.730

616467.863

649.188

655.300

652.430

736.000

814.200

763.865

Total 250. m

3.3.5.2 Geological Mapping

Detailed engineering geological maps of the powerhouse site and headworks site have been

prepared in the scale of 1:1,000. While the engineering geological map of tunnel alignment has

been prepared in the scale of 1:10,000. Detailed joint survey was carried out at each hydraulic

structure site for engineering classification of rock mass. Both RMR and NGI ‘Q’ systems were

used for rock mass classification.

3.3.5.3 Seismic Refraction Survey

A total of 2180.00m of seismic refraction survey has been carried out at major hydraulic

structure sites. Altogether 26 seismic lines were executed for this purpose. The objective of the

survey was to determine the overburden thickness, bedrock quality, thickness of weathered zone

and degree of fracturing in the bedrock. The hammering method was used for the seismic refraction

survey. The result showed mainly three velocity layers which ranges from 400 - 600 m/s, 800 - 1000

m/s and 1400 - 2400 m/s. The bedrock and the compact overburden deposit consisting of large

boulders have shown the velocity in the range of 2200 - 2400 m/s. The details of seismic

refraction survey including investigation results are presented in Annex-B3. The brief description

of seismic refraction survey is shown in Table No. 3.5.



Table 3.5: Brief Description of Seismic Refraction Survey

SN Location Seismic Line Length (m)

1 Headworks Site SLD – 1 115

2 Headworks Site SLD – 2 55 3 Headworks Site SLD – 3 55

4 Headworks Site SLD – 4 55 5 Headworks Site SLD – 5 55

6 Headworks Site SLD – 6 55 Total 390 7 Tunnel Alignment SLT – 1 340

8 Tunnel Alignment SLT – 2 55

9 Tunnel Alignment SLT – 3 115 10 Tunnel Alignment SLT – 4 55 11 Tunnel Alignment SLT – 5 55

12 Tunnel Alignment SLT – 6 55

Total 675 13 Powerhouse site SLP – 1 235

14 Powerhouse site SLP – 2 55 15 Powerhouse site SLP – 3 55

16 Powerhouse site SLP – 4 55 17 Powerhouse site SLP – 5 55 18 Powerhouse site SLP – 6 55

19 Powerhouse site SLP – 7 55




26 Powerhouse site SLP – 14 55 Total 1115 Grand Total 2180



3.3.5.4 Construction Material Survey

• General

The construction material investigation includes mainly the identification of borrow areas, test

pitting, sample collection and laboratory testing. The investigation has been carried out to

assess the availability of required volume of different construction materials such as

impervious core material, coarse and fine aggregates, rip-rap in different borrow areas and

quarry sites within the haulage distance of about 5 km from the project site. The laboratory

tests and analysis of collected samples were also carried out according to ASTM and AASTHO

standards.

Different locations for the construction materials such as cohesive material, fine and coarse

aggregates, fine sand and granular materials are identified within the permissible haulage

distance from the project area. The borrow areas are investigated by digging the test pits.

Two borrow areas for the granular material has been identified in the vicinity of the project

area. Similarly, two quarry sites for granular materials have been also identified during the

present investigation. The borrow areas are located at Trishuli River bed and Salankhu Khola

river bed and quarry sites are located at left bank of Trishuli River which is close to proposed

powerhouse site and another quarry site has been identified at Trishuli River bed deposit in the

vicinity of the project area.

The riverbed material can be used to produce concrete aggregates such as fine and coarse (sand and

gravel) after washing out the fines (No. 2000 sieve). Fine aggregate for concrete can also be

obtained by crushing the oversize material from riverbed (+56 mm)

The field exploration was conducted by pitting method in which test pits of depth up to 3m

were excavated manually with the help of hand shovel. The size of test pits were generally

2.0m x 2.0m. Different samples were collected for different types of soil encountered in a test pit.

The fraction passing 80 mm sieve was collected to carry out the laboratory tests such as Grain

Size Analysis, Index Properties, Specific Gravity, Los Angles Abrasion, Sulfate Soundness.



A total of 11 test pits were excavated during the present field investigation. Out of which 5 test

pits were excavated at Salankhu Khola River Bed and remaining 6 test pits were excavated at

river bed deposit of Trishuli River.

Table 3.6: A Brief Description of Test Pits

Name of the

borrow/quarry area

Location Number of

test pit

No. of

sample

Remarks

GA Saletar 6 12 Weir site

GB Simle bagar 6 13 PH site

GC Andheri Khola bagar 4 9 Andheri Khola

CA Ratamate danda 5 10 Archale VDC

QA Headworks site 1 L/B Trishuli River

QB headworks site 1 R/B Trishuli River

QC Andheri Khola 3 Andheri Khola

3.3.2 Additional geological geotechnical investigation, Fiscal Year-2013

Details of new investigation are presented in the report “ Upper Trisuli-3B Hydroelectric Project, a)

Surface Geological Mapping, Year 2013 May, and b) Core Drilling, Year 2013 August”.



Chapter 4:

Hydrology and Sediment Study

Preamble

The project under study is in the Trisuli River. The headworks is located at 500 m upstream of

the Andheri Khola. The powerhouse is located at 500 m upstream of the Salankhu Khola and

Trisuli River confluence. This is the run of the river cascade scheme with Upper Trisuli 3A

Hydroelectric Project (installed capacity 60 MW). The reference hydrology, basically a monthly

flow, are same in Upper Trisuli 3A and 3B. The Trishuli River is originated from China (Tibet)

and the major portion (80 %) of the catchment area lies in China. This study covers the field

investigation, hydrological data collection and hydrological analysis required for the project

design.

4.1 Introduction

Hydrological study of this project comprises of extensive data collection at the site for discharge

& sediment measurement and their analysis. Field investigation was carried out by establishing

several new Staff Gauge stations in the Trishuli River near the project site. Moreover, an

endeavour has been made to measure the precise catchment area of Trishuli River and its

tributaries located near the project site with the help of Satellite Image and Maps available.

Furthermore, a long term flow at the intake site has been produced by correlating with the long

term observation from the down stream gauge station 447 of the same river situated at Betrawati.

Hydrology, sediment and hydraulic study of the project were carried out to estimate the pertinent

design parameters. These parameters are (a) design flood (b) diversion flood (c) monthly flow (d)

rating curves (e) downstream release (f) sediment inflow (g) GLOF. While, establishing these

parameters, standard software and simple spread sheet have been used. The primary data for the

analysis have taken from “Department of Hydrology and Meteorology (DHM)”, and the related

reports from the other hydropower projects. Besides that the extensive field study were carried

out by the developer.

The major portion of the catchment lies in the China, the physiographic data as well as

precipitation data are not available, therefore, the average basin precipitation study is out of

scope. The hydrological study has been based on the Gauge Station 447 at Betrawati, Trisuli



River. Besides that the NEA has also established the Hydrological gauge station on the Trisuli

River at Pairobesi village to monitor the river flow.

4.2 Basin Characteristic

The head works of Upper Trisuli-3B Hydroelectric Project is on the Trisuli River located 6.5 km

downstream from the confluence of Mailun Khola and Trisuli River, whereas the powerhouse is

located at 500 m upstream from the Salanku Khola and Trisuli river confluence. (right bank of

Trisuli River).

Trishuli is one of the major tributaries of Sapta Gandaki river system. The river flows almost

North-South from Tibet to Nepal. The main source of Trishuli River discharge is the snow and

glacier melt from the higher Himalayas. Langtang Himal is one of the major mountain range in

the basin. The total area of Trishuli River basin up to intake site is 4577 km2 (intake site of Upper

Trisuli 3A HEP) and that of the power house site is 4605 km2. The catchment area in Nepal

covers only 20 % of the total catchment area 4577 km2. 'Inventory of Glacier lakes 2002'

published by ICIMOD have identified about 117 numbers of glacier lakes with total area of 2.03

(km2) and 74 numbers of glacier rivers with total area of 246.65 (km2) inside the Trishuli river

catchment in Nepal. This study have further identified that the ice reserve is 27.47 km3. The

major tributaries of Trishuli River upstream of proposed Dam site are Chilime, Langtang and

Dhunche Trishuli. The Trisuli River basin within the Nepal is shown in Figure 4.1. The Trisuli

River basin including China and Nepal combined is shown in Figure 4.2.

Physiographically, Trisuli River basin upstream of dam site lies in the High Mountain and High

Himalayas. The High Himalayan region is constituted by the extremely high peaks. Some of

those major peaks are highlighted below.

Ganesh Himal (Nepal side) Altitude 7406 m

Lapsang Karubo (Nepal Side) Altitude 7150 m

Lantang Ri (Nepal Side) Altitude 7232 m

Langtang Lirung (Nepal Side) Altitude 7246 m

Gang Benchnen (China Side) Altitude 7211 m



4.3 Review of Catchment Area

The catchment area of the Trisuli river basin upstream of the gauging station 447 has been

revised by different agencies. The previous records of Catchment area of Trishuli River at

Betrawati 447 station from Department of Hydrology and Meteorology (DHM) published in

1998 shows that the area is only 4110 square km. Whereas, the Catchment area indicated by

WECS in 1990 shows as 4640 square km. During the feasibility study of Upper Tama Koshi

HEP, “NEA and Norconsult” has estimated the catchment area of the Trishuli basin upstream

of the Betrawati station 447 as 4850 km2. In this study, this final figure 4850 km2 has been

recommended as the catchment area upstream of the Betrawati Gauge station.

4.4 Climate Study

Since the catchment of this river lies in the High Himalayas and the High Mountain region, the

physiographic characteristic influences the climate in this region. The Climatic condition varies

with respect to the altitude. The catchment area experiences severe cold, subtropical to

temperate climate. The southwest monsoon is dominant from June to the end of September in

the catchment as other parts of Nepal. The region receives approximately 80 % of the annual

rainfall during the Monsoon period. Rainfall intensities vary throughout the basin with maximum

intensity occurring on the south facing slopes. During the monsoon period, relative humidity

reaches at their maximum and the temperatures are lower compared to the pre-monsoon period.

The precipitation on the basin determines the average basin precipitation and flood generation.

The meteorological stations near the project area are tabulated in Table 4.1. It is noticed the

meteorological station Index Nos. 1005 and 1057 are the closest to the project area. The location

of the precipitation stations are shown in Figure 4.3.The precipitation record in the China (Tibet)

catchment area is not known. A short precipitation records of Tingri and Nyalum (Precipitation

station in Tibet) is available and shown in the Table 4.2. The annual precipitations in these

stations are below 800 mm. The mean annual precipitation map of the country shows that the

annual precipitation at the Nepal side lies below the range of 2000mm.



Table 4.1: Average precipitation of the stations located near the project area

Index

No.

Station

Name

Elevation

(m amsl)

Lat. /Long. Year of

Records

Annual Mean

Precipitation (mm)

1001 Timure 1900 27°14'/85°25' 1957-94 950

1004 Nuwakot 1003 27°55'/85°10' 1956-94 1870

1005 Dhading 1427 27°52'/84°56' 1956-94 2195

1015 Thankot 1631 27°41'/85°12' 1967-94 2000

1054 Thamchi 1847 28°10'/85°19' 1972-94 1039

1055 Dhunche 1982 28°06'/85°18' 1972-94 1863

1057 Pansaya Khola 1240 28°01'/85°07' 1973-94 3040

1058 Tarke Ghyang 2480 28°00'/85°33' 1974-94 2859

Table 4.2: Rainfall records available from China

Station Longitude Latitude Altitude

(m)

River

Basin

Time

Interval

Period Mean Annual

Rainfall (mm)

Nyalam N/A N/A N/A Bhote

Koshi

monthly 1966-75 627

Monthly 1976-86 717

Tingri 28O 36’ N 87O 06’ E 4302 Arun

River

Monthly 1960-86, excl

1969-70

285

3.5 Available Hydrological Data

3.5.1 Installation of Hydrometric Station

NEA has installed the Hydrometric Station on Trisuli at Pairobesi Bridge at Manakaman VDC

from 19th Paush 2063. The gauge station is 1500 m downstream of the headworks site of the

Upper Trisuli-3B Hydroelectric Project. Staff gauge reading from this gauging station is

continuously being measured. Gauge readers have been recruited to read the water level thrice a

day at 8:00 hour, 12 hour and 16:00 hour. The location of the staff gauge installation is shown in

Figure 4.4. The summary of discharge measurements at different period is given below.



Table 4.3: Discharge Measurements at Pairobesi Bridge

S. No Date Time Discharge (m3/sec) Gauge Height(m)

1 2063-9-19 11:00 AM 48.384 0.32

2 2064-02-11 10:3 AM 221.488 0.89

3 2064-02-12 10:30 AM 196.64 0.87

4 2064-07-18 7:55 PM 117.702 0.50

4.5.2 Hydrometric Stations

Besides the gauging station installed by the project, there exist the hydrometric stations operated

by Department of Hydrology and meteorology (DHM) located in the Trishuli River basin. Most

of these gauging stations have daily water level recording facilities. They are shown in the Table

4.4.

Table 4.4: Hydrometric stations located in the Trishuli River Basin

S. No

Gauge Station

Type of Station

Name of River Location Comments

1 447 Cable way, Water level

Trishuli Betrawati. Located at 12 km d/s of Intake.

Established in 1967.

2 446.7 Water level Phalakhu (Tributary of Trishuli River)

d/s of TOL and u/s of Betrawati and about 200m u/s of Phalakhu 446.8

Data used in present study

3 446.8 Water level Phalakhu (Tributary of Trishuli River at Betrawati.)

d/s of TOL and u/s of Betrawati at confluence with Trishuli

Data used in present study

4 446.3 Water level Dhunche Trishuli u/s of Intake Data not used in present study

5 446.2 Water level Langtang Khola u/s of Intake Data not used in present study

6 446.25 Water level Bhote Koshi u/s of Intake Data not used in present study

Out of these measuring stations, the station No 447 has been used in the present detail design

study for generating long term daily flow. The gauge station No 447 on the Trishuli River is

located at Betrawati which is about 16 km downstream of Intake site of this project. It is noticed

the station 447 has been operated by DHM since 1967.



3.5.3 Discharge Measurement by DHM and NEA

The discharge of Trishuli River has been measured at the nearest station 447 Betrawati

established by Department of Hydrology. This station is located about 16 km downstream of

intake site. There exist three tributaries in between tailrace outlet and Betrawati station no. 447.

These tributaries are Andheri Khola, Salakhu and Phalakhu Khola. Among these three the

Andheri Khola has drainage area of only 4.5 sq. km and the surface flow is not visible during dry

season. Therefore, latter two tributaries are the major tributaries in between tailrace outlet and

Station no. 447-Betrawati. There exist two staff gauge stations in Phalakhu Khola (446.7 and

446.8). However, the daily flow records in these tributaries are available only for the five years

from 1985 to 1986 and from 1988 to 1990 respectively. There exist no daily flow records in

Salakhu Khola. The measured discharge records are illustrated in the following Table 4.5 and

Table 4.6.

Table 4.5: Discharge measurement in Trishuli river at Gauge Station 447, Betrawati

S. No. Date Time Discharge

(m3/sec)

Gauge

Height(m)

Method Agency

1 8-Oct-05 496 2.6 CM DHM

2 24-Feb-06 13:00 44.33 0.76 CM DHM/NEA

3 24-Feb-06 14:44 43 0.75 CM DHM/NEA

4 12-May-06 8:00 96.03 1.52 CM DHM/NEA

5 12-May-06 16:00 87.72 1.42 CM DHM/NEA

Note: CM= Current Meter

Table 4.6: Discharge measurement in the tributaries of Trishuli River near project area

S.

No

Date Time Tributary

Name

Discharge

(m3/sec)

Gauge

Height

(m)

Method Agency

1 25-Dec-05 16:25 Mailung 2.695 CM NEA

1 25-Dec-05 10:15 Salakhu 1.134 CM NEA

2 24-Feb-06 16:00 Salakhu 0.553 CM DHM/NEA

3 11-May-06 16:00 Salakhu 0.709 CM DHM/NEA

4 12-May-06 10:30 Salakhu 1.057 CM DHM/NEA



S.

No

Date Time Tributary

Name

Discharge

(m3/sec)

Gauge

Height

(m)

Method Agency

1 24-Feb-06 8:25 Phalakhu 446.7 1.247 3.4 CM DHM/NEA



4 11-May-06 15:00 Phalakhu 446.8 3.24 0.52 CM DHM/NEA

5 12-May-06 8:20 Phalakhu 446.8 3.12 0.49 CM DHM/NEA

4.6 Rating Curves

The rating curves at the different site of interest of the project were developed using Manning’s

equation. The rating curve for the tailrace outlet of Upper Trisuli-3A HEP and intake area of

Trsisuli 3B HEP and tailrace outlet of Upper Trisuli 3B HEP was developed. The Manning’s “n”

for the development of rating curve assumed is 0.035.

The rating curve at the proposed intake site (that is, outlet portal of Upper Trisuli 3A HEP) is

shown in the Figure 4.5. Similarly, the rating curve at the inlet portal of tunnel (near the section

PX-15) was developed and shown in the Figure 4.6. Similarly, the rating curve at tailrace outlet of

Upper Trisuli 3B HEP is shown in Figure 4.7.

4.7 Reference Hydrology

3.7.1 Mean Monthly Flow

Since the daily mean discharge at the dam axis of Upper Trsiuli-3A Hydroelectric Project is not

available, the reference hydrology has been derived from the gauging station 447 at Betrawati.

The number of years of data availability in this station is 1967 to 2005. The flow data at the

gauging station 447 were closely examined and found consistent. Therefore, the catchment area

ratio is used to generate the flow at the dam site of the Project. The equation that has been used

in data generation is



QIntake = (A Intake / Aknown)* Q known

Where,

Q Intake = Flow at Intake site (Intake site of Upper Trisuli 3A HEP, 60 MW)

Q known = Flow at known site

A Intake = Area upstream of Intake site

Aknown = Area upstream of known site

The summaries of the mean monthly flow generated are shown in the Table 4.7. The variations

of the monthly flow are depicted in Figure 4.8. The annual mean at intake of Upper Trisuli 3A

HEP is found to be 192.0 m3/s. The minimum monthly flow occurs in the February. The flow

gradually increases from April as the snow in the high mountain start melting. The maximum

monthly flow occurs mostly in August which lies in the monsoon period.

Table 4.7: Monthly mean flows (m3/s) for 1967-2005 on Upper Trishuli 3A Dam site

Year Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec 1967 44.5 35.9 33.6 38.8 60.1 129.9 405.9 489.2 308.0 112.3 63.1 45.5 1968 35.7 30.2 29.2 36.5 61.2 207.8 458.2 452.4 265.2 160.0 71.5 48.1 1969 38.2 33.5 31.2 35.9 58.8 125.8 375.7 425.7 316.2 118.7 63.5 44.8 1970 34.6 30.1 28.2 38.3 61.6 153.1 441.8 482.7 274.1 143.0 78.9 54.7 1971 42.5 36.5 34.8 43.8 61.4 328.4 422.7 518.0 302.0 145.0 76.9 51.7 1972 40.6 35.2 36.7 40.5 95.4 153.5 406.4 448.4 266.7 99.6 59.0 40.6 1973 35.2 34.7 37.9 57.0 91.3 345.6 481.1 625.2 495.6 271.8 94.3 62.0 1974 47.9 37.5 34.2 50.8 77.6 188.7 515.5 603.8 374.1 175.8 81.5 57.2 1975 48.3 43.6 41.8 56.8 86.4 248.8 517.5 529.3 486.8 209.8 104.2 65.8 1976 46.5 39.5 38.0 44.0 80.3 195.6 346.2 459.8 351.4 155.5 93.8 61.8 1977 45.4 43.9 47.0 51.8 73.4 181.5 557.9 574.3 339.7 154.5 88.7 58.2 1978 43.9 41.6 42.8 54.1 142.2 316.0 490.8 589.8 313.0 202.8 101.9 66.1 1979 48.4 41.1 41.4 49.4 86.7 175.0 441.3 475.8 264.2 129.0 78.3 52.5 1980 41.1 38.0 38.5 56.1 76.0 260.4 625.8 640.0 368.0 153.2 86.0 55.6 1981 40.4 34.4 35.1 47.1 80.2 274.3 673.7 584.7 348.7 132.6 82.2 52.8 1982 40.8 37.6 52.9 70.4 76.8 200.2 384.4 562.1 371.0 113.6 73.1 51.0 1983 37.8 32.8 34.3 36.4 66.0 152.1 355.7 477.9 413.8 190.6 89.5 57.0 1984 44.0 31.5 32.3 32.6 100.8 281.6 584.5 487.7 394.1 110.7 65.6 46.2 1985 33.6 31.9 39.5 43.7 51.5 147.7 458.9 407.7 348.4 189.2 86.5 65.2 1986 52.0 51.4 50.9 61.0 72.8 300.9 655.1 561.6 428.5 159.7 91.0 64.1 1987 51.2 48.3 N.A. 48.9 55.1 N.A. N.A. N.A. 178.2 110.0 74.3 58.3 1988 49.3 45.8 46.5 56.4 81.4 167.9 460.1 534.3 245.2 102.8 67.8 55.5 1989 50.8 44.8 45.7 54.0 99.0 177.3 335.6 416.6 266.0 112.8 61.4 45.9 1990 39.2 35.0 33.8 45.2 86.1 297.2 769.3 592.8 427.0 157.5 72.8 46.3 1991 36.4 30.7 30.7 35.9 81.5 198.3 460.2 756.4 618.0 N.A. 55.3 42.5 1992 32.5 27.4 27.0 32.6 40.7 114.8 306.6 668.9 386.8 132.0 62.8 39.4



Year Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec 1993 31.3 28.8 25.7 36.1 79.7 181.6 421.0 687.0 397.9 157.0 63.9 39.7 1994 47.4 40.4 42.3 41.3 77.3 250.6 429.4 513.3 337.6 128.6 64.7 45.5 1995 44.3 40.5 42.5 54.5 183.9 398.4 587.1 713.7 389.9 167.7 102.1 57.1 1996 50.0 44.2 50.1 57.7 114.5 277.4 590.8 778.3 470.3 178.6 85.1 58.2 1997 46.8 42.6 41.3 46.2 64.5 201.1 540.5 533.6 353.3 106.2 62.5 53.3 1998 42.2 37.9 39.4 54.2 141.3 330.8 712.4 822.5 397.7 166.0 68.8 50.4 1999 41.5 35.8 34.6 48.8 81.1 228.5 745.6 735.5 560.1 253.6 87.7 58.2 2000 46.2 39.6 36.6 46.0 100.3 377.0 667.0 820.1 599.0 159.8 74.6 51.6 2001 40.7 36.8 32.7 34.8 68.7 345.7 631.0 713.6 418.4 140.0 66.3 47.7 2002 61.5 53.1 40.9 83.6 182.6 313.9 612.4 798.5 467.7 199.2 83.1 58.1 2003 44.9 39.0 39.0 54.5 79.6 296.6 681.3 819.9 681.0 220.3 97.3 60.7 2004 46.5 36.8 40.6 48.5 106.7 313.1 658.3 825.5 534.2 273.4 91.7 59.9 2005 49.4 51.1 50.6 60.0 98.7 236.9 683.9 818.5 444.1 233.7 81.5 46.4

Mean 43.4 38.4 38.4 48.3 86.8 238.8 523.5 603.8 389.8 161.2 78.3 53.2

4.7.2 Long Term Trends in Flows

The earliest 6 years of the record are noticeable because all the years appear to possess lower

than average flows. Neighbouring Trans-Himalayan catchments, G.S. 445 Budhi Gandaki at Aru

Ghat and G.S. 610 Bhote Koshi at Barabise to the west and east respectively, were examined.

Both of these catchment exhibited particularly low flows for the years 1967-70 and 1972, so it is

considered that this was a regional phenomenon, and the succession of low flows observed on

Trishuli River during 1967-72 are genuine.

Another interesting trend concerns the lowest flows during the dry season. After a fairly low

minimum flow in Feb 1985, the next 5 years produced the 5 highest minimum flows in Feb/Mar

during the 28 years long record, before setting back to normal by 1992. Normal low flows during

this season of year are about 35 m3/s, but these rose to about 50 m3/s during this 5 year period.

There must be some physical explanation for this phenomenon, which needs further

investigation.

3.7.3 Correlation between Flows on Trishuli River at Upper Trisuli 3A dam site and

Betrawati Gauge station 447

To determine the mean annual flow at the intake of Upper Trisuli 3A dam site, the daily flows at

station No 447 Trishuli River at Betrawati is multiplied by the catchment area ratio. The

correlation factor is determined as following.



Correlation factor = (Catchment area of Trishuli at intake dam site) / (Catchment area of

Trishuli at Betrawati 447)

The mean monthly flows at the intake site for the 39 year period Jan 1967 – 2005 are shown in

Table 4.7.

4.7.4 Flow Duration Curve

The prorated 39 year daily flow record at the intake dam site was used to determine the one day

flow duration curve. The flow duration data has been generated and tabulated in the following

Table 4.8. The exceedance flow at 90%, 65% and 45% are 36.0 m3/s, 52.5 m3/s and 89.5 m3/s

respectively. The flow duration curve is depicted in Figure 4.9.

Table 4.8: Flow duration curve at dam site

S. No. Exceedance (%) Flow (m3/s) S. No. Exceedance (%) Flow (m3/s)

1 0 1745.9 11 50 75.7

2 5 669.1 12 55 65.4

3 10 539.8 13 60 57.9

4 15 454.9 14 65 52.5

5 20 374.7 15 70 48.6

6 25 284.1 16 75 45.1

7 30 205.7 17 80 41.9

8 35 148.2 18 85 39.2

9 40 111.4 19 90 36.0

10 45 89.5 20 95 33.1

21 100 23.1

4.7.5 Downstream Release Flow

It is required to release 10% of minimum monthly flow for the downstream benefit. The

minimum monthly flow lies in February with 36.4 cumecs. Therefore, it is required to release

3.84 cumecs of flow through out the years.



3.8 Flood Estimates

3.8.1 Introduction

The important design parameters in hydropower projects are the flood at different return

periods. They are used in design of diversion dam, cofferdam, and stilling basin of the diversion

structures. Therefore, different methods are used to estimate the flood. The best method is the

flood frequency analysis at the gauge site data and the regional flood frequency analysis. The

catchment area for this purpose is taken as the area upstream of Upper Trisuli 3B intake site.

3.8.2 Flood Estimation by Regional Analysis

Most of the time when the data are not available at the site of interest, the regional flood

frequency analysis is the good techniques to determine the floods. For this purpose, the regional

analysis used by the MHSP/NEA have been used to determine the flood.

For the ungauged sites, a regional analysis relating flood peaks (from the gauging stations) at the

selected return periods to basin area, was carried out using regression analysis. To increase the

accuracy of flood estimates from regional analysis, the set of gauging stations was divided into

sub-sets defined according to the large river systems of which they formed an integral part.

Since a reasonably large number of observations is required for regressions to be meaningful, the

sub-regions were limited to three as described below:

(1) The Western Region comprising the following basins:

- the Karnali River basin (the dominant basin);

- the Nepalese part of the Mahakali River basin;

- the smaller basins located between the Mahakali and Karnali with rivers flowing

independently south;

- the Rapti River basin;

- the Banganga River basin.

(2) The Central Region (Figure 4.3) which includes the following basins:



- the Narayani River basin (the dominant basin);

- the Bagmati River basin;

- the numerous smaller basins with rivers flowing independently towards the

border with India.

(3) The Eastern Region which contains the following basins:

- the Sapta Kosi basin (the dominant basin);

- the Kamala River basin;

- the Kankai River basin;

- smaller basins with rivers flowing independently towards the Indian border.

The gauging stations that are in the central region is 404.7, 410, 415, 417, 420, 428, 430, 438,

438.3, 439.7, 439.8, 440, 445, 446.8, 447, 448, 450, 460, 465, 470, 505, 536.2, 540, 550, 570, and

590. The flood flows at six specific return periods at 5, 20, 50, 100, 1000 and 10 000-year

occurrences were estimated. An examination of the records and plots of the frequency

distributions showed that the Log-Pearson type III distribution provided the best estimates.

Linear regression analysis was applied to the logarithmic transforms of both the dependent and

independent variables, i.e., the equation relating flood magnitude for a given return period to

drainage area:

lnQ = a + b(lnA)

where

Q = flow in m3/s

A = drainage area in km2

a and b are regression coefficients.

By inverse log transformation, the above equation was made equivalent to the following

relationship between flood peak and drainage area:

Q = kAb



Where k = exp(a)

The regressions were carried out for the three area parameters, i.e, total drainage area, area below

5000m and area below 3000m respectively. The results showed that drainage area below 3000m

gave the highest correlation for rain generated floods. The area below 3000m was therefore

selected for application of the regional coefficients. The Table 4.9 below shows the coefficients

that were obtained for the regression lines corresponding to each of the six selected return

periods.

Table 4.9: Floods and Regression Coefficient (Regional Analysis)

Return Flow Regional Coefficients

Period (m3/s) k b

5 916 1.68 0.97

20 1378 3.23 0.93

50 1714 4.61 0.91

100 1976 5.99 0.89

1000 3098 12.66 0.84

10000 4614 24.64 0.80

4.8.3 Flood Frequency Analysis

The instantaneous flood data at the G. S. 447, Betrawati are used for the frequency analysis. The

G.S. 447 at Betrawati of the Trisuli River has total catchment area is 4850 km2. The flood data

available at this station is from the year 1976 to 1994. The total number of flood data is 27 years.

These data are transferred to the dam axis by multiplying the effective catchment area ratio. The

effective catchment area means the area below 5000 m amsl. The areas below 5000 m elevation

upstream of dam site and upstream of the gauge site are 2641 km2 and 2154 km2 respectively.

The generated flood data at intake site (Simle) are shown below in the Table 4.10.

Table 4.10: Instantaneous peak for the Flood Frequency Analysis

YEAR DATA ORDERED RANK PROB. RET. PERIOD

1967 717 2152 1 0.019 53.857

1968 661 1906 2 0.052 19.333

1969 670 1906 3 0.085 11.781



YEAR DATA ORDERED RANK PROB. RET. PERIOD

1970 837 1887 4 0.118 8.472

1971 930 1434 5 0.151 6.614

1972 1906 1434 6 0.184 5.424

1973 2152 1359 7 0.218 4.598

1974 1359 1085 8 0.251 3.989

1975 953 1076 9 0.284 3.523

1976 774 1038 10 0.317 3.155

1977 1000 1000 11 0.35 2.856

1978 981 1000 12 0.383 2.609

1979 1000 1000 13 0.416 2.401

1980 1038 991 14 0.45 2.224

1981 991 981 15 0.483 2.071

1982 938 972 16 0.516 1.938

1983 819 953 17 0.549 1.821

1984 1076 938 18 0.582 1.718

1985 1887 930 19 0.615 1.625

1986 972 837 20 0.649 1.542

1987 1000 819 21 0.682 1.467

1988 808 808 22 0.715 1.399

1989 566 774 23 0.748 1.337

1990 1434 717 24 0.781 1.28

1992 1434 670 25 0.814 1.228

1993 1906 661 26 0.847 1.18

1994 1085 566 27 0.881 1.136

The frequency analyses were carried out with the different frequency distribution. The frequency

distributions used are the Gumbel I, Lognormal, Three Parameter Lognormal, and Log Pearson

Type III. The best-fit distribution is “Log Pearson III (moments)” whose Root Mean Square

Error is the smallest among all other distribution.

Therefore, it is recommended to use the frequency value from Three Parameter Log Normal

Distribution. The results of frequency analysis are shown in the Table 4.11. The 100-year and

1000 year floods are 2718 m3/s and 4030 m3/s respectively.



Table 4.11: Frequency Analysis by Theoretical Distribution

Log-Pearson IIIPeriod Gumbel I Log Normal 3P-LGNRML Moments Max. Lklhd

2 1029 1038 1000 1010 10005 1350 1397 1378 1378 135920 1774 1840 1963 1935 1944100 2237 2331 2718 2699 2746200 2435 2539 3086 3076 31611000 2888 3029 4030 4096 4303

10000 3548 3765 5634 5993 6521RMS ERROR: 131.92 120.15 111.25 112.15 114.34

The magnitude of the flood from the (a) frequency analysis and the (b) regional methods are

similar for the return period 1 in 1000 Years. The recommended flood is 1:1000 year return

period. The floods at intake site and at the powerhouse site are 4030 m3/s and 4054 m3/s

respectively.

3.8.4 Flood levels

The flood levels at different important structure of the projects are summarized in the Table

4.12. The levels are at Intake site, tunnel intake, and tailrace outlet. The flood water levels are

before the construction of the project.

Table 4.12: Flood water level at different project components

Return

period

(years)

Water level at tailrace

outlet area (Upper

Trisuli 3A HEP) (m)

Water level at surface

intake pond area (Upper

Trisuli 3B HEP) (m)

Water level at

Tailrace Outlet of

UT3B HEP (m)

20 725.5 718.9 628.8

100 725.9 719.2 629.4

1000 726.3 719.6 630.1

4.8.5 Construction Flood

Since the water is directly tap from Upper Trisuli 3A HEP tailrace to the intake of Upper Trisuli

3B HEP, it is not necessary to do diversion of Trisuli river in this project. However, the

construction of tailrace pond of Upper Trisuli 3B HEP is on the right bank of Trisuli River, the



estimation of diversion flood discharge is required. For the purpose of designing the river

diversion structure, 1:20 year return period flood has been recommended that is 1963 m3/s.

4.9 Glacier Lake Outburst Floods (GLOF)

4.9.1 General

'Inventory of Glacier lakes 2002' published by ICIMOD have identified about 117 numbers of

glacier lakes with total area of 2.03 (km2) and 74 numbers of glacier rivers with total area of

246.65 (km2) inside the Trishuli river catchment in Nepal. This study have further identified that

the ice reserve is 27.47 km3. The three major Glacier lakes are identified. Two of those are

identified as Longda and Khymjung. The name of the third is unknown. These Glacier lakes are

at a distance of about 40 km from the dam site. At present, the risk is not very high. However

monitoring of the Glacial lakes is recommended.

4.9.2 Historical Record of GLOF

The downstream reach of Nepal experienced the number of Glacier Lake Outburst Flood

(GLOF) from Tibet as well as from Nepal side during the recent decades and there are

significant damages have been reported. These are listed hereunder in the Table13. There are

three records of historical GLOF in the Trisuli River valley.

One in September 1996 due to the “Kimjun Tsho Glacier Lake” inside the Langtang Valley. It is

reported that there is no damages.

Second is in 25 August 1964 due to “Longda Glacier Lake” from the Gyrionzangbo river valley,

Trisuli river system. This outburst flood created a debris blockage 800 m long along the river,

200 m wide & 5 m deep in average on the Gyrongzangbo River, source of the Trisuli River.

Third record is in 1947, GLOF from the langtang valley. It is reported that there is loss of

Cattlehouses, but there were no casualties.

Det

ail P

roje

ct R

epor

t of

UT

3B H

EP

4-18

T

risu

li Ja

lvid

yut

Com

pan

y L

imit

ed

Tab

le 4

.13:

His

tori

cal G

LO

F e

vent

s in

Nep

al a

nd

Ch

ina

(Tib

et)

N o D

AT

E

LA

KE

/G

LA

CIE

R

VA

LL

EY

C

OU

NT

RY

CA

USE

FL

OO

D C

HA

RA

CT

ER

IST

ICS

DA

MA

GE

SU

MM

AR

Y

1 M

ay-

2002

N

yana

ng P

hu

Gla

cier

T

shon

gde

Phu

C

hhu

river

va

lley

Tib

et, C

hina

(r

iver

fee

ds in

to

Nep

al)

? ?

Flo

od s

wep

t dow

n to

the

villa

ge o

f N

ylam

, whe

re it

de

stro

yed

the

road

brid

ge.

2 21

-O

ct-

2000

Un-

nam

ed la

ke

abov

e T

agna

g –

info

rmal

ly k

now

n as

‘Tag

nag

Tsh

o’

Hin

ku

Nep

al

Ice

aval

anch

e

Ava

lanc

he a

cros

s de

glac

iate

d ro

ck s

lab

and

onto

sur

face

of

froz

en la

ke.

Lak

e le

vel d

ropp

ed b

y 0.

75 m

, inv

olvi

ng ~

6-7,

000

m3 o

f w

ater

(int

erpr

eted

fro

m

field

insp

ectio

n 2

days

aft

er th

e ev

ent

by R

GSL

sta

ff).

Min

imal

. M

inor

ers

osio

n in

ch

anne

l and

slig

ht d

amag

e to

fo

otpa

th a

t Tag

nag

- pa

ssed

w

ithin

met

res

of th

e vi

llage

of

Tag

nag.

3 3- Se

p-19

98

Saba

i Tsh

o H

inku

N

epal

Ic

e av

alan

che

Bre

achi

ng o

ccur

red

over

sev

eral

hou

rs.

Flo

od/d

ebris

flo

w tr

avel

led

the

35 k

m

from

the

lake

to th

e co

nflu

ence

with

th

e D

udh

Kos

hi in

2 h

rs 1

0 m

ins,

w

here

it f

orm

ed a

tem

pora

ry d

am

30 m

hig

h. R

each

ed th

e K

oshi

B

arra

ge, 1

80 k

m f

rom

the

lake

.

2 pe

ople

rep

orte

d ki

lled;

bri

dges

an

d tr

ails

des

troy

ed, p

rope

rty

with

a

min

imum

com

bine

d va

lue

of £

1.3

mill

ion

also

des

troy

ed (D

wiv

edi e

t al.

, 199

9).

Seve

re e

rosi

on a

long

le

ngth

of

Hin

ku v

alle

y.

4 19

97

Rip

imo

Shar

G

laci

er?

Rol

wal

ing

Val

ley,

tr

ibut

ary

of

Tam

a K

oshi

Nep

al

Unk

now

n F

lood

wat

ers

obse

rved

in th

e R

olw

alin

g va

lley

betw

een

Bed

ing

and

Rip

imo

Shar

Gla

cier

. In

flux

of f

lood

w

ater

s in

crea

sed

susp

ende

d se

dim

ent

load

res

ultin

g in

a v

isib

le c

olou

ring

of

the

Rol

wal

ing

Kho

la f

or 4

8 ho

urs.

No

dam

age

or lo

ss o

f lif

e re

port

ed.

5 Se

p-19

96

Kim

jun

Tsh

o L

angt

ang

Val

ley,

tr

ibu

tary

of

Tri

suli

Riv

er

Nep

al

Roc

k av

alan

che

Smal

l lak

e of

ca.

6,0

00 m

2 . GL

OF

was

no

ticed

by

a flo

od o

f di

rty

wat

er.T

ook

2 m

onth

s fr

om th

e av

alan

che

(Aug

) fo

r re

gres

sive

ero

sion

to b

reac

h th

e m

orai

ne.

No

dam

age

dow

nstr

eam

6 m

id-

Jul-

Chu

bung

Lak

e, a

t en

d of

Rip

imo

Shar

R

olw

alin

g V

alle

y,

Nep

al

Ice

Ava

lanc

hV

ery

stee

p si

ded

brea

ch in

mat

rix

supp

orte

d, s

trat

ified

mor

aine

. 2

Dam

age

to h

ouse

s an

d cu

ltiva

ted

field

s, r

iver

terr

aces

was

hed

away

at

Det

ail P

roje

ct R

epor

t of

UT

3B H

EP

4-19

T

risu

li Ja

lvid

yut

Com

pan

y L

imit

ed

1991

G

laci

er

trib

utar

y of

T

ama

Kos

hi

e st

ages

:1 -

Ove

rtop

ping

ero

ded

4-5

m

of m

orai

ne a

nd e

rode

d to

e sl

ope.

2 -

E

xplo

sive

eru

ptio

n th

roug

h m

orai

ne

wal

l. L

ocal

s re

port

ed a

t lea

st f

our

flood

sur

ges.

Bed

ing

villa

ge.

7 4- A

ug-

1985

Dig

Tsh

o G

laci

er

Lak

e H

inku

D

rang

ka

valle

y,

Dud

h K

oshi

ri

ver

syst

em

Nep

al

Roc

k av

alan

che

Initi

al d

isch

arge

2,0

00 m

3 /s. 6

-10

mill

ion

m3 o

f w

ater

rel

ease

d. G

LO

F

last

ed 4

hrs

.Sev

eral

sep

arat

e su

rges

. F

oul m

ud s

mel

l ass

ocia

ted

with

flo

od.

Shoc

k w

aves

5 –

10

m in

hei

ght.

4-5

deat

hs.

Nea

rly c

ompl

eted

N

amch

e hy

drop

ower

pla

nt

dest

roye

d ($

3 m

illio

n). 1

4 br

idge

s,

trai

ls, m

any

hect

ares

of

culti

vate

d la

nd, 3

0 ho

uses

dam

aged

alo

ng th

e L

angm

oche

Kho

la, T

ama

(Bho

te)

Kos

hi, D

udh

Kos

hi r

iver

s do

wn

to

conf

luen

ce w

ith S

un K

oshi

(90

km

from

flo

od s

ourc

e).

8 Ju

l-19

85

? B

arun

Kho

la

rive

r va

lley,

A

run

rive

r sy

stem

Nep

al

Unk

now

n

Tra

ce o

f pa

st G

LO

F o

n riv

er

chan

nel r

ecog

nize

d fr

om a

eria

l su

rvey

9 27

-A

ug-

1982

Jinco

gla

cier

lake

Y

airu

zang

bo

valle

y,

Aru

n ri

ver

syst

em

Tib

et, C

hina

(r

iver

fee

ds in

to

Nep

al)

Ice

Ava

lanc

he

Deb

ris f

low

rec

orde

d.

1,60

0 he

ad o

f liv

esto

ck, 1

86,7

60 m

2 of

cul

tivat

ed f

ield

s de

stro

yed.

D

amag

e to

hou

ses

in 8

vill

ages

, ro

ads,

bri

dges

, etc.

10

11

-Ju

l-19

81

Zha

ngza

ngbo

G

laci

er L

ake

Z

hang

zang

bo

Gul

ly,

Sun

Kos

hi

rive

r

Tib

et, C

hina

(r

iver

fee

ds in

to

Nep

al)

Ice

Ava

lanc

he

Pea

k di

scha

rge

16,0

00 m

3 /s. M

orai

ne

brea

ch 5

0 m

dee

p, 4

0-60

m w

ide.

L

oss

of li

fe, d

amag

e to

Arn

iko

Hig

hway

, Fri

ends

hip

Bri

dge,

cu

ltiva

ted

field

s, li

vest

ock.

Bho

te

(Sun

) Kos

hi H

ydro

pow

er p

lant

di

vers

ion

stru

ctur

e ga

tes

dam

aged

. 11

24

-Ju

n-19

81

Zar

i Lak

e A

run

(Pum

qu)

Riv

er v

alle

y T

ibet

, Chi

na

(riv

er f

eeds

in

to N

epal

)

Ice

Ava

lanc

he

Flo

od a

nd d

ebris

flo

w p

rodu

ced

12

1980

P

huch

an G

laci

er

Lak

e T

amur

Kho

la

Riv

er V

alle

yN

epal

U

nkno

wn

D

amag

e to

for

est,

river

bed

etc.

In

clud

ed h

eavy

deb

ris, l

arge

roc

ks,

Det

ail P

roje

ct R

epor

t of

UT

3B H

EP

4-20

T

risu

li Ja

lvid

yut

Com

pan

y L

imit

ed

etc.

13

be

for

e 1979

Bre

ache

d m

orai

ne,

Sout

hern

sid

e of

R

olw

alin

g V

alle

y

Rol

wal

ing

Val

ley,

tr

ibut

ary

of

Tam

a K

oshi

Nep

alU

nkno

wn

Rel

ativ

ely

smal

l eve

nt, s

ome

lives

tock

lost

.

14

3- Sep-

1977

Gla

cier

lake

on

Nar

e G

laci

er (S

. of

Mt.

Am

a D

abla

m)

Imja

Dra

ngka

va

lley,

D

udh

Kos

hi

rive

r sy

stem

Nep

al

Ice-

core

d m

orai

ne

colla

pse

Rec

orde

d 90

km

dow

nstr

eam

of

sour

ce. M

axim

um r

unof

f 80

0 m

3 /s.

Tot

al v

olum

e of

wat

er 5

mill

ion

m3 .

2 -

3 pe

ople

kill

ed.

Dam

age

to

min

i-hyd

ro p

lant

, roa

d, c

ultiv

ated

fie

lds,

etc.

All

brid

ges

dest

roye

d ov

er a

dis

tanc

e of

35

km

dow

nstr

eam

, man

y ho

uses

was

hed

away

. 15

18

-A

ug-

1970

Ayi

co N

o. 7

(A

yaco

) Lak

e Z

ongb

oxan

va

lley,

A

run

(Pum

qu)

rive

r sy

stem

Nep

al

Ice

Ava

lanc

he

4.59

mill

ion

m3 o

f se

dim

ent d

epos

ited

in d

ebris

fan

at t

he c

onflu

ence

of

lake

dr

aina

ge a

nd m

ain

river

cou

rse

duri

ng

thre

e ev

ents

fro

m th

is la

ke (s

ee a

lso

reco

rds

16 a

nd 1

7).

Low

er r

each

hig

hway

and

con

cret

e br

idge

of

Des

ha N

o. 1

des

troy

ed

duri

ng th

e th

ree

flood

s fr

om th

is

lake

in 1

968,

196

9, 1

970

(see

als

o re

cord

s 16

and

17)

. 16

17

-A

ug-

1969

Ayi

co N

o. 7

(A

yaco

) Lak

e Z

ongb

oxan

va

lley,

A

run

(Pum

qu)

rive

r sy

stem

Tib

et, C

hina

(r

iver

fee

ds in

to

Nep

al)

Ice

Ava

lanc

he

4.59

mill

ion

m3 o

f se

dim

ent d

epos

ited

in d

ebris

fan

at t

he c

onflu

ence

of

lake

dr

aina

ge a

nd m

ain

river

cou

rse

duri

ng

thre

e ev

ents

fro

m th

is la

ke (s

ee a

lso

reco

rds

15 a

nd 1

7).

Low

er r

each

hig

hway

and

con

cret

e br

idge

of

Des

ha N

o. 1

dest

roye

d du

ring

the

thre

e flo

ods

from

this

la

ke in

196

8, 1

969,

197

0 (s

ee a

lso

reco

rds

15 a

nd 1

7).

17

1968

A

yico

No.

7 L

ake

Zon

gbox

an

valle

y,

Aru

n (P

umqu

) ri

ver

syst

em

Nep

al

Ice

Ava

lanc

he

4.59

mill

ion

m3 o

f se

dim

ent d

epos

ited

in d

ebris

fan

at t

he c

onflu

ence

of

lake

dr

aina

ge a

nd m

ain

river

cou

rse

duri

ng

thre

e ev

ents

fro

m th

is la

ke (s

ee a

lso

reco

rds

15 a

nd 1

6).

Low

er r

each

hig

hway

and

con

cret

e br

idge

of

Des

ha N

o. 1

dest

roye

d du

ring

the

thre

e flo

ods

from

this

la

ke in

196

8, 1

969,

197

0 (s

ee a

lso

reco

rds

15 a

nd 1

6).

18

21-

Sep-

1964

Gel

haip

co L

ake

Gel

haip

co

Gul

ley

(Gan

ma

Zan

gbo

Riv

er

Val

ley)

, A

run

rive

r

Tib

et, C

hina

(r

iver

fee

ds in

to

Nep

al)

Ice

Ava

lanc

he

Bre

ach

cut d

own

into

mor

aine

by

as

muc

h as

30

m. W

ater

leve

l in

lake

was

lo

wer

ed b

y ~

40 m

. Tot

al b

urst

wat

er

vol.

~ 2

3.36

mill

ion

m3 .

Dam

age

to C

heta

ng-R

iwo

Hig

hway

, 12

truc

ks w

ashe

d aw

ay,

”hea

vy e

cono

mic

loss

es”

dow

nstr

eam

.

Det

ail P

roje

ct R

epor

t of

UT

3B H

EP

4-21

T

risu

li Ja

lvid

yut

Com

pan

y L

imit

ed

syst

em

19

25-

Aug

-19

64

Lon

gda

Gla

cier

la

ke

Gyr

ion

zan

gbo

rive

r va

lley,

T

risu

li ri

ver

syst

em

Tib

et, C

hina

(r

iver

fee

ds in

to

Nep

al)

Ice

Ava

lanc

he

Flo

od a

nd d

ebris

flo

w p

rodu

ced.

Out

burs

t flo

od c

reat

ed a

deb

ris

bloc

kage

800

m lo

ng a

long

the

rive

r, 20

0 m

wid

e &

5 m

dee

p in

av

erag

e on

the

Gyr

ongz

angb

o R

iver

, sou

rce

of th

e T

risul

i Riv

er.

20

Jul-

1964

Z

hang

zang

bo

Gla

cier

Lak

e Z

hang

zang

bo

Gul

ly,

Sun

Kos

hi

(Poi

qu) r

iver

sy

stem

Tib

et, C

hina

(r

iver

fee

ds in

to

Nep

al)

Mor

aine

co

llaps

e du

e to

se

epag

e

Wat

er le

vel r

ose

8 m

and

and

the

outb

urst

pro

duce

d a

debr

is f

low

. D

epos

ition

of

debr

is f

low

mat

eria

l.

21

~19

64

? A

run

(Pum

qu)

Val

ley

Nep

al

Unk

now

n

GL

OF

not

iced

by

loca

l peo

ple

alon

g th

e A

run

(Pum

qu) R

iver

. T

imbe

r, co

ncre

te b

lock

s &

par

ts o

f tr

ucks

flo

win

g do

wn.

22

16

-Ju

l-19

54

Sang

wan

g la

ke

Nya

ngqu

riv

er

valle

y,

Hea

dwat

ers

of

the

Aru

n (P

umqu

) riv

er

syst

em

Tib

et, C

hina

(r

iver

fee

ds in

to

Nep

al)

Ice

Ava

lanc

he

Flo

od s

urge

was

40

m h

igh.

Tow

ns a

nd c

ultiv

ated

fie

lds

serio

usly

dam

aged

. 3-5

m o

f gr

avel

de

posi

ted

on v

alle

y pl

ain.

23

1947

Lan

gtan

g V

alle

y.

Tri

bu

tary

of

Tri

suli

Riv

er

Nep

al

Ice

Ava

lanc

he

? C

attle

hous

es lo

st, b

ut th

ere

wer

e no

cas

ualti

es

24

sinc

e 19

40

(in

livin

g m

emo

ry)

Smal

l for

mer

lake

N

W o

f C

hubu

ng

(Om

ai T

sho

?)

Rol

wal

ing

Val

ley,

tr

ibut

ary

of

Tam

a K

oshi

Nep

alU

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.



4.9.3 GLOF Hazard

Glacier lake outburst flood (GLOF) events can constitute a serious risk to hydroelectric projects

for the following reasons:

- at a given site, the peak flow from a GLOF can exceed monsoon rain-generated

floods of very low probability such as the 10 000-year flood;

- GLOFs usually carry more sediment and debris than rain-caused floods;

- advanced warning of GLOF events is hardly possible as the glacier lakes are too

remotely located for continuous monitoring.

- The risk of a GLOF actually occurring will depend on the inherent stability or

instability of the lake damming material combined with the likelihood of external

triggering events such as earthquakes, storms, landslides or avalanches.

The above characteristics of the GLOF have been compiled, where available, to assess the

likelihood of a GLOF occurring in the near future (during the coming decades) and thus

affecting the projects concerned. It should be noted that if a lake has already burst, even fairly

recently, the GLOF threat from that lake is not automatically eliminated as illustrated by

Zhangzangbo lake which burst twice (in 1964 and 1981) indicating that a lake’s outlet can

become naturally plugged shortly after a burst. Thus Ayco glacier lake in the Arun River

catchment produced a GLOF in three consecutive years (1968, 1969 and 1970).

In hydro-scheme catchment where the existence of glacier lakes point to the possibility of

GLOFs occurring, it is therefore necessary to assess the impact of both the peak flow and the

possible sediment load on the hydropower infrastructure installation.

4.9.4 Peak Flows from GLOFs

Although several occurrences of GLOF have been noted in the Nepal Himalayas over the last 30

years, quantitative data from these events is scarce. Peak discharges at the lake of origin can only

be estimated from post-event modeling. Discharges further downstream have been recorded

only in basins which were equipped with gauging stations that were not washed away or

destroyed by the GLOFs. Nevertheless, the scarce data available is sufficient to demonstrate the

importance of GLOF in hydroelectric development studies and planning.



Two recent GLOFs that occurred in Nepal can illustrate the potential threat posed by GLOFs:

The first occurred on July 10, 1981 in the Sun Koshi (Bhote Koshi) originating from the

Zhangzangbo glacier lake in Tibet. Considerable damages have done to the Sun Koshi power

plant where heavy sluice gates were carried away and the powerhouse control room was flooded

to the control deck level. The maximum instantaneous flow recorded at station 610 during the

GLOF was 3300 m3/s. Compared with flood peak estimates obtained from frequency analysis

of recorded monsoon floods, this GLOF peak would correspond to a monsoon flood having a

return period of 500 to 1000 years.

The other GLOF occurred on August 4, 1985 in the Dudh Koshi, originating from the Dig Tsho

glacier lake in Nepal. The event was recorded at gauging station 670 near Rabuwa Bazar. The

maximum instantaneous flow recorded at station 670 during the 1985 GLOF was 11,600 m3/s.

Frequency analysis of monsoon peaks recorded at station 670 show that the GLOF would

correspond to a monsoon flood peak with a return period between 1000 and 2000 years.

4.9.5 Peak Flow Attenuation with Distance

Flow recording from the two GLOFs mentioned above were made at sites located rather far

downstream of the bursting glacier lake. Estimates of maximum discharge at the lake outlet

were made by modelling. These estimates indicate that although the peak flow decreases

considerably with distance down the river channel, the GLOF remains a potent destructive force

even at long distances from the bursting glacier lake. The table below shows the peak flow

attenuation between originating lake and observation site for the two GLOFs

.

Peak Flow Distance Peak Flow GLOF of River at Lake to Gauge at Gauge

Bhote Koshi 16 000 m3/s 71 km 3 300 m3/s

Dudh Koshi 20 000 m3/s 90 km 11 600 m3/s

It is interesting to note that the degree of attenuation was much greater in the Bhote Koshi than

in the Dudh Koshi despite the Dudh Koshi gauging station being further away from the bursting

lake. The explanation could lie in the comparative amount of water stored in each lake before



the breach occurred and the river bed characteristics or the values could be in error as already

suggested by the reservations expressed concerning the validity of the peak flow recorded at

station 670. In any event, the impact of a GLOF on a project site will depend on the distance

along the river between the site and the Glacier Lake identified as a potential GLOF source.

4.9.6 Longda Glacier Lakes (threat to dam site and powerhouse site)

This is the lake from the China (Tibet) side and should thoroughly examine. Therefore, the

GLOF hazard from these lake is regarded negligible, there remains a ”residual risk” of possibly

with (a) climate change resulting faster melting of the damming ice body (b) high increase of

seepage from the dam (c) potential triggering by earthquakes and etc.

4.10 Sediment Study

4.10.1 Sediment Data

The daily sediment concentration on the gauging station 447 at Betrawati is available for the year

1977 and 1979. This is the published data from DHM. Besides that there is sediment

concentration measurement at Trisuli Power Centre (24 MW) in the Year 2005 August. Recently,

NEA has carried out the Bucket Sampling near the Betrawati in the year 2007. These data are

used in the sediment analysis in this study.

4.10.2 Methods of Estimating the Sediment Flow from the River

Different methods are used to estimate the sediment flow. The methods adopted in this study

are:

- Regional analysis

- Estimate by measurement on the river

4.10.3 Regional Analysis

As in the other subject, the regional analysis is not applicable in the field of sediment study.

However, the yield will be estimated in the region based on the past studies and measurement



carried out by different agencies and the department on the rivers of Nepal. The yield ranges

from 1500 t/km2/year to 6000 t/km2/year in the normal conditions. For the reference, the

sediment yield estimate in the different rivers of Nepal are summarised below.

A. Kulekhani-I Storage Project

The total siltation rate (trapped sediment) in the reservoir is 9573 m3/km2/year from the

year1982 to 2000 (NEA report 2001, February). The siltation rate was 3175 m3/km2/year on year

1996, 1746 m3/km2/year on year 1997, 4444 m3/km2/year on year 1998, 5238 m3/km2/year on

year 1999 and 2063 m3/km2/year on year 2000.

B. Andhi Khola Storage Project, Feasibility Study

The feasibility study revealed that, sediment concentration was measured in the year 1995, 1997,

1998 and 1999. The results of sediment analysis of these data are as follows:

Total yield 2600 m3/km2/year on year 1995

Total yield 600 m3/km2/year on year 1997 very low, due to dry year



C. Sarada Storage Project Study

The analysis with the measured data on the Sarada River at Daredhunga Gauging station (286)

were carried out. Scattered data on suspended sediment for the Sharada River at the Daredhunga

gauging station (286) are available for the years 1973, 1974, 1976-78 and 1985-87. Based on the

adjusted sediment-rating curve, the sediment yield is 3022 t/km2/year (2014 m3/km2/year).

D. Jhimruk Hydroelectric Project

From the analysis of sediment and flow data during monsoon 1995 to 1997, the sediment yield

in the Jhimruk river was estimated to be in the range of 5000 to 6500 t/km2/year (3333 to 4333

m3/km2/year).



E. Pancheswor High Dam

The project has carried out the extensive field measurement program on the year 1990 and 1991.

The suspended yield estimate is as follows:

Year Sediment Yield

1990 3904 m3/km2/year (5857 t/km2/year)

1991 1852 m3/km2/year (2779 t/km2/year)

F. Feasibility Study of different Projects

Feasibility study of hydropower projects through out the country has lot of variation in the

siltation rate. These data are reproduced here under:

River/Project Total Sediment Yield (m3/km2/year)

1. Kaligandaki-A 4000

2.Budhi Gandaki River(West) 2260

3.Rahu Ghat 1330

4. Likhu River 1327

5. Kabeli River 2700

6. Tamur River 1693

7. Karnali 1213

8. Dudh Koshi (Storage) 1483

9. Karnali Chisapani Study 3968

10. Arun III 880

4.10.4 Estimate based on the Measured Data

a) Data from DHM

The daily concentrations at the gauging station 447 are used to estimate the daily concentration

as well as yield of the sediment concentration. These data are shown in the appendix. The

monthly mean concentration and maximum concentration during the year 1977 and 1979 is

shown in the Table 4.14. The methods of sampling are not known in these stations.



Table 4.14: Summary of Sediment Concentration Data, Station 447

Year 1977

Mean 24 29 38 72 113 343 1018 715 291 84 39 39

Min 9 10 12 22 28 40 480 228 97 37 18 20

Max 92 49 219 280 484 993 2560 2170 1180 247 61 140

N.S 15 15 24 30 31 30 31 31 29 29 29 31

Year 1979

Mean 30 40 193 155 202 611 1377 578 235 140 64 52

Min 14 23 12 14 22 30 56 90 55 33 10 26

Max 86 62 3870 556 471 3050 6810 1890 1020 2200 1020 105

N.S 20 20 30 29 28 30 31 31 29 31 30 31

From the table the maximum concentration of sediment is 6810 ppm and maximum monthly

concentration is 1377 ppm for these two years of records. The sediment concentration time

series of the two years 1977 and 1979 at the gauge station 447 are shown in the Figure 4.10 and

4.11 respectively.

These data are analysed to estimate the sediment yield from the Trisuli River at Betrwati

(G.S.447). The direct sediment yield has been estimated based on the measured values. The

average sediment yield from the year 1977 and 1979 is 840 tonne /km2/year. The sediment

rating curves of the year 1977 and 1979 are shown in Figure 4.12 and Figure 4.13 respectively.

b) Sediment Study from the Upgrading Study of Trisuli Power Station 24 MW (Year

1990)

There are three sets of suspended sediment data available on the Trisuli River in the vicinity of

the project, collected by three different agencies, as below: The Details of the data are not given

in the report

a) by National Hydropower Corporation (NHPC) for 1977-1979.

b) By the department of Hydrology and Meteorology (DHM) for 1977 to 1980.

c) By Nepal Electricity Authority (NEA) for 1977 to 1979 and 1985 to 1989.

These data are collected by differing techniques and at different locations. NHPC data was



collected from various locations along the Trisuli conveyance system, downstream of the head

regulator, downstream of the gravel rejecter and from the outlet of the desander. The data was

collected by both surface and mid-depth samples. The coverage spans the period 1977 – 1979

but sampling was only carried out during the monsoon period.

NEA also collected samples. All NEA samples were taken from Trisuli bridge and all were

surface samples. NEA data covers the period 1977 to 1999 and 1985 to 1989, but only during

the monsoon season. Finally DHM collected sediment data at their gauging station near

Betrawati some 2 km upstream of the project. Their data was collected using a depth integrated

sampler. Coverage of their data was from 1977 to 1980 on a twelve month per year basis.

Data about the gradation of the sediment samples is limited. Both NHPC and NEA record

proportions of coarse and medium sand and fines, but not analyses were provided by DHM. The

proportion of clay sizes appears to the negligible from, an examination of the texture of

sediment deposits. This observation is supported by tests carried out by Himalayan Power

Consultant (HPC, 1989) on suspended sediment samples from the Karnali Project- which

indicated a very small percentage of clay in suspension.

All three sets of data overlap for the period 1977 to 1999. These data were reduced to equivalent

units and are compared in the following Table.

Table 4.15: Comparison of Sediment Concentration 1977-1979

Months Flow Data sources

NEA (mg/l) NHPC (mg/l) DHM (mg/l)

June 1977 192 944 474 367

July 1977 591 2823 1180 1020

August 1977 609 2050 954 715

Sept. 1977 360 1189 757 291

May 1978 151 N.A. 351 442

June 1978 335 2392 1081 624

July 1978 520 2997 2474 437

August 1978 625 3036 371

July 1979 468 3664 1744 1380

August 1979 504 3146 578



From an inspection of above table, it can be seen that NEA values are much larger than those

measured by NHPC or DHM. However there is much closer agreement between NHPC and

DHM measurement. For purpose of this study, it was concluded that the NHPC data set was

most relevant as it was collected within the Trisuli conveyance system. Table 4.16 recommends

monthly mean sediment inflow rates which can be used for sizing of sediment handling facilities

in the feasibility report.

Table 4.16: Recommended Monthly Sediment Concentration

Months River Flow (m3/s) Mean Monthly Sediment Concentration (mg/l)

January 44.0 35

February 38.4 51

March 39.6 80

April 49.3 96

May 83.0 351

June 226.6 778

July 498.7 1798

August 548.4 1231

September 368.0 757

October 165.4 272

November 85.8 79

December 57.8 65

Note: NHPC data for May-September, DHM data for rest of month

The proportion of coarse and medium sediments to total suspended sediment, based on NHPC

data was about 25%. No such breakdown was available for DHM data.

c) Data from Trisuli Power Station (24 MW)

The sediment concentration measurements were carried out in the year 2005 in the existing

project “Trisuli Power Station 24 MW”. During the fieldwork, the bucket samplings were carried

out in the moving water at the following three locations.

(a) Before the inlet of desander

(b) After the outlet of desander



(c) Before the penstock (forebay)

The sampling were done during the monsoon season (2005 August-September) to see the

effectiveness of existing desander. The sampling data is shown in the appendix. The daily

sediment concentration at three different locations is shown in the Figure 4.14. The maximum

sediment concentration is 1445 ppm (16th August 2005, at the desander inlet). This is the

sediment sample collected after the headworks and inside the water conveyance system.

d) Bucket Sampling at Pairobesi at Upper Trisuli-3B Hydroelectric Project

In the year 2007, the sediment concentrations are measured using the bucket sampling at the

powerhouse site at Pairobesi of Upper Trisuli-3B Hydroelectric Project. The bucket sampling

was carried out from the bridge of Pairobesi suspension bridge. This is the surface sampling at

left bank, right bank and middle of the river. The date of measurement is from 24th May 2007 to

1st August 2007. All the data are given in the Appendix. The maximum concentration recorded in

this project is 3453 ppm.

The gradation analysis of the collected sediment sample was carried out using the sieve analysis.

It is seen from the following table, the sand particle finer than 0.2 mm is more than 80 %. The

particle size distribution of the bucket sampling is shown in the Table 4.17. This is the sample

collected from the water surface.

Table 4.17: Particle Size Distribution of Bucket Sampling

Sieve No. Sample, No-1 Sample, No-2 Sample, No-3

5 100 100 100

2 100 99.24 99.77

1 100 97.87 99.45

0.5 99.98 93.63 98.38

0.25 99.88 81.73 95.41

0.125 77.75 65.21 88.34

0.063 52.4 49.3 75.59

0.052 36.2 36.2 49.2

0.038 31.7 31.7 44.2

0.027 28.2 29.2 38.7



Sieve No. Sample, No-1 Sample, No-2 Sample, No-3

0.019 25.2 23.7 33.2

0.014 21.2 21.7 27.2

0.01 18.7 20.2 23.2

0.007 16.2 15.7 21.2

0.005 14.2 14.7 17.2

0.003 13.7 13.7 15.7

0.002 13.2 13.2 14.2

0.001 12.7 12.7 12.7

e) Recommended Sediment Concentration

For the purpose of desander design, the recommended value of concentration is 3500 ppm and

the particle finer than 0.2 mm is 60 %.

4.11 Conclusion

Following are the conclusions of hydrological study:

1. Trishuli is a perennial river having a significant share of dry season flow.

2. The hydrological data of 1967-2005 for the Betrawati gauging station located 15 km

south of powerhouse have been acquired from Department of Hydrology and

Meteorology (DHM).

3. Long term daily flow has been estimated at the dam site based on catchment area ratio.

The flow duration has been computed from the 39 years daily flow records at Betrawati.

4. The 100 years and 1000 years recurrence period of flood are estimated at 2718 cumecs

and 4030 cumecs at the dam site. Similarly, the 1000 year flood at powerhouse site is

about 4054 cumecs

4.12 Recommendation

1. The sediment parameters needs to be determined carefully for manufacturing the

turbine.

2. GLOF study needs to be carried out in more detail.

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5-1

Trishuli Jalvidhyut Company Limited

Chapter 5:

Geological and Geotechnical Studies 5.1 General

During the feasibility study of project, the extensive geology and geotechnical study has been carried

out by Nepal Electricity Authority (NEA) in 2007 July. This report is the abstract of the findings in

feasibility study and new study carried out by the Trishuli Jalvidhyut Company Limited (TJVCL) in

2013. Followings are the documents of geological and geotechnical study of the project.

a) Geology and Geotechnical study, Appendix B, 2007 July studied by NEA

b) Surface Geological Mapping, 2013 May studied by TJVCL

c) Core Drilling of the alternative powerhouse site done by TJVCL, Year 2013 June

d) Rock support design of underground structures done by TJVCL, Year 2013 July

5.2 Geology of Project Area

The Upper Trishli 3B Hydroelectric Project belongs to Kunchha Group of Lesser Himalayan

Metasediments in Central Nepal. In the project area the Lesser Himalayan Metasedimentary Units

are represented by schist, quartzite and gneiss. The Surface geological map of project area is given in

DWG NO UT3B-GEO-01(A) and 01(B) (Scale 1:10,000). The details of Surface geological mapping

are given in the report “Surface Geological Mapping, 2013 May done by TJVCL”

5.2.1 Intake portal

Previously the study was carried out for two different options for intake portal surface option and

underground option. Later on the surface intake option was decided to adopt. The intake portal is

located at about 500m upstream from the confluence of Andheri Khola and Trishuli River. The

intake portal of Trishuli 3B HEP is the outlet portal of Upper Trishuli 3A HEP as shown in DWG

NO UT3B-02. This project has been proposed to utilize the tailrace water of Upper Trishuli 3A

hydroelectric project. The dominant rock type around intake area is gneiss. The slope around surface

intake portal is gentle and lies at an elevation of 736 m. The slope is represented by colluvium and

alluvium deposits with an estimated thickness 20-25m whereas the slope is comparatively steeper at

underground intake option and lies at an elevation of 785m which represents colluvium deposits


5-2


with estimated thickness 10-15m. Bedrock outcrops along the intake area were mapped extensively

and detailed joint measurements were taken. Rock exposures near intake portal is gneiss with light

and dark colored minerals which is slightly to moderately weathered and hard. Based on surface

mapping, the rock mass in the intake is classified as good to fair rock type according to rock mass

classification. The attitudes of the discontinuities are as follows.

Dip/Dip Dir Joint Set

1. 25°/228° (Foliation Joint)

2. 60°/132° J1

3. 52°/060° J2

4. 45°/090° Hill Slope

Stereographic projection of major discontinuities with foliation and friction circle shows less

possibility of plane failure and wedge failure.

5.2.2 Headrace Tunnel

Initially the study was carried out for three different options of headrace tunnel and ultimately one is

selected which is shown in DWG NO UT3B-GEO-02(A) and 02(B) (geological section from intake

to powerhouse). Tunnel alignment with surface intake option I is about 3744.69 m long whereas it is

3250.9 m option II and III. There are four tunnel bending points viz. between intake and Andherai

Khola, at Andheri khola, at Sukhaura khola and at Sisno kholsi. The tunnel will pass through the

Right Bank of Trishuli River. The majority of tunnel crosses mainly two types of rock namely

intercalation of schist and quartzite and small portion will pass through gneiss. It is expected that

about 15% of tunnel alignment passes through gneiss, about 20% through quartzite and remaining

65% through schist. However, the quartzite rock is found in the form of interbeded with schist. The

maximum thickness of quartzite in the schist is found to be 2 to 3 m.

In general, the rock along the tunnel is considered to be medium strong to strong in strength. The

rock is slightly to moderately weathered. The rock is exposed in most of the parts of the tunnel

alignment except between intake and Andheri Khola and between Santi Bazar and Sukaura Khola in

the map boundary. Rocks are exposed in the small creeks and at higher elevation in the form of cliff

along the tunnel alignment. No major faults crossing the tunnel are noticed during the present

mapping however several thin bands of fractured zones are noticed in the tunnel route mainly along


5-3


the tributaries. The mapping in the river sections and along the existing roads and trails was

projected to the tunnel horizon in order to produce the required geological information along the

tunnel route. The geological traverse was also carried out along the small tributaries and ridge to get

more information for the preparation of geological map. The geological condition along the tunnel

alignment is largely based on surface mapping. The maximum cover above the tunnel alignment is

about 380m at chainage 2+507.9 and minumum cover is about 83.5m at Sukaura khola at chainage

1+732.6.

A detailed discontinuity survey was carried out in several directions on the different rock exposures

along the headrace tunnel alignment, on the slopes and along the small creeks and streams. More

than 200 joint measurements were collected from the rock exposures and have been statistically

analyzed. The detailed joint mapping revealed mainly three sets of joint along the tunnel with some

random sets. The joints are tight to moderately open, close to moderately spaced, continuity less

than 3 m, rough, irregular and occasionally smooth and altered surfaces with iron stained and filling

materials as clay, silt and few are free of filling materials. Based on surface mapping, the rock mass

along the tunnel alignment varies from good rock to very poor rock according to Rock Mass

Classification. RMR value along the tunnel alignment ranges from <20 to 70 and Q value <1 to 23.

The statistical analysis of joints in the headrace tunnel area revealed the following main joint sets.



2. 64°/160° J1

3. 55°/090° J2

4 45/035 J3

There are three major bending points along the tunnel alignment. The first major bending point is

located at Andheri Khola, second major bending point lies at Sukaura khola and third one is near the

Siano Kholsi. There is also one minor bending point between Andheri khola and Sukaura khola. The

tunnel construction seems favorable to fair condition from the stability point of view, as the strike of

the beds is nearly perpendicular to the first stretch of the tunnel (portion between intake and

Andheri khola where the rock is gneiss. Similarly second stretch (between Andheri khola and

Sukaura Khola where the rock is intercalation of schist and quartzite) is also nearly perpendicular to

the strike of the tunnel axis whereas third stretch (between Sukaura khola and surge tank where the


5-4


rock is intercalation of schist and quartzites) runs more or less parallel to the strike of the foliation.

However, wedge failure is expected due to presence of intersecting joints.

5.2.3 Adit Portal Area

An adit tunnel (adit - II) has been proposed for construction purpose at the right bank slope of

Sukaura khola for the surface intake option whereas two adit tunnels have been proposed for the

construction purpose, one at underground S/T area (Adit II) and the other near the powerhouse

area (adit - III) for the headrace tunnel. The adit - II tunnel will be excavated through intercalation

of quartizt and schist. The proportion of schist is more than quartzite. Gneiss is composed of light

and dark colored minerals, slightly to moderately weathered and hard. Based on surface geological

mapping, the rock mass in the intake is classified as good to fair rock type according to rock mass

classification. Schist is moderately strong, grey to dark grey, slightly to moderately weathered. Based

on surface mapping, the rock mass is classified as fair rock type according to rock mass

classification. The statistical analysis of the joints in the adit portal area revealed the following main

joint sets.



2. 44°/120° J1

3. 52°/060° J2

4 50°/025° Hill Slope

Stereographic projection of major discontinuities with hill slope and friction circle shows less

possibility of plane failure as well as wedge failure. The detailed geological map of adit portal area is

shown in DWG NO UT3B-GEO-01(A) and 1(B).

5.2.4 Surge Tank (Option I)

The surge tank is located on the right bank of the Trishuli River near Siureni Village in the

community forest area which is about 185 m above the river level. The rock exposed around the

surge tank area is schist with thin layers of quartzite. The schist exposed around the surge tank area

is dark grey to dark brown, medium grained, medium to thinly foliated, slightly to moderately

weathered. Based on surface mapping, the rock mass in the surge tank is classified as fair to poor


5-5


rock type according to Rock Mass Classification. The joints are tight to moderately open,

discontinuous and moderately spaced with rough to smooth and planar to irregular surfaces. The

major three sets of joints were identified around the surge tank site are as follows



2. 85°/160° J1

3. 45°/095° J2


The detailed geological map of the surge tank area and geological section from surge tank to

powerhouse are presented in DWG NO UT3B-GEO-01(A) and 01 (B). One borehole has been

carried out to investigate the sub-surface geological condition at the surge tank location.

5.2.5 Powerhouse Site (Option I)

The powerhouse is proposed as an alternative powerhouse on the terrace deposit at the right bank

of Trishuli River about 700m downstream of the previously proposed powerhouse. The rock mass

condition at the upslope of this powerhouse location has been extrapolated from the mapping along

the road sections and was projected to the powerhouse in order to produce the required geological

information. The predominant rock type upslope of the powerhouse area is schist and quartzite but

comparatively proportion of schist is higher than quartzite.

The surfacial deposit in the powerhouse area is mainly alluvial terrace and minor colluvial deposits.

The deposit consists mainly of sub-angular to sub rounded few angular boulder to gravel sized rock

fragments of schist, gneiss and quartzite in sandy - silty matrix with little fines. Maximum size of

boulders upto 3m are lying on the terrace of powerhouse site. The thickness of the alluvial deposit is

estimated to be more than 50 m.

The geological mapping has not identified any significant faults and major instabilities in the

powerhouse area. Detailed joint mapping at the upper slope of powerhouse site has been carried out

in the exposed rock outcrops. These measurements have been carried out on the rock exposed in

slope, in small tributaries in vicinity of the powerhouse area. The rocks exposed around the

powerhouse area are schist and quartzite. Schist and quartzite are intercalated but quartzite


5-6


dominates over schist. Quartzite is blocky to seamy whereas schist is thinly banded. Based on

surface mapping, the rock mass at the upslope of powerhouse site is classified as fair to poor rock

type according to Rock Mass Classification. The statistical analysis of major joints was carried out

which showed the following main joints.



2. 74°/165° J1

3. 55°/085° J2


Stereographic projection of major discontinuities with slope and friction circle shows less possibility

of plane failure however there is a possibility of wedge failure formed by the intersection of foliation

and J2. The detailed geological map of the alternative powerhouse (option I) and geological section

from surge tank to powerhouse are presented in DWG NO UT3B-GEO-01(A) and 01 (B).

5.2.6 Drop shaft/ Pressure tunnel Alignment

Pressure tunnel alignment is divided into two stretches. First stretch is between surge tank and drop

shaft and another is between drop shaft and powerhouse. Surge tank is followed by first stretch of

pressure tunnel followed by the vertical drop shaft and further followed by pressure tunnel that

carries the water to powerhouse. The surface geological mapping from surge tank to the

powerhouse indicates that the area above the alignment is mostly covered by colluvium.

Extrapolation of bedrock from the exposed area indicates that the drop shaft and pressure tunnel

alignment area passes through schist and quartzite intercalation. The rocks exposed are moderately

weathered, foliated, medium thick to thinly bedded and medium strong. The rock mass of the drop

shaft and pressure tunnel alignment area is categorized as poor to fair quality rock. The trend of rock

and joint system are similar to that of surge tank area. The slope in and around the proposed

alignment is stable at present. During construction period, attention should be paid to stabilize the

areas disturbed by construction activities.

5.2.7 Tailrace box Duct

The tailrace box duct passes through the alluvial deposit. The alluvial deposit in tailrace box duct


5-7


consists mainly of rounded to sub surround boulders and gravel of schist, quartzite and gneiss mixed

in sandy - silty matrix. Hence, the tailrace tunnel will have to be excavated in alluvial deposit for

which soft ground tunneling method is recommended and cut and cover structure is also

recommended for the tailrace channel.

Bhangale kholsi is present downstream of tailrace box duct area that does not cross the tailrace.

Along the route of kholsi, many big boulders are lying. At the time of study the amount of water

flowing through the kholsi is not sufficient to move the debris to have negative impact to tailrace

structure however it is safe to construct the tailrace safety structures to avoid possible damages due

to debris flow from this kholsi.

5.2.8 Conclusion and Recommendation

The Upper Trishuli 3B HEP is a run of type project scheme cascaded with Upper Trishuli 3A HEP

that belongs to Kuncha Group of Lesser Himalayan Metasediments in Central Nepal. In the project

area the Lesser Metasedimentary Units are represented by schist, gneiss and quartzite. The main

lithology of the project area is gneiss, schist and quartzite. The main rock type of intake area is gneiss

whereas along the tunnel alignment, surge tank and powerhouse it is schist with thin bands of

quartzite.

Similarly headrace tunnel alignment is about 3744.69 m long in option I whereas it is 3250.9 m for

option II and III. The tunnel construction seems favorable to fair condition. There are three major

tunnel bending points with one minor bending point between intake portal and Andherai khola.

One major bending point is at Andherai khola, one major at Sukaura khola and one near the Sisne

kholsi. The rock cover is adequate along the tunnel alignment. For the surface intake option the

maximum cover above the tunnel alignment is about 380m at chainage 2+507.9 and minimum cover

is 83.5m at Sukaura khola at chainage 1+732.6.

There are two options for surge tank and powerhouse one is previously proposed location (option-

II and III) and the other is new alternative location (option-I). Surge tank to powerhouse area at

both options is covered by colluvium and alluvium deposit. The estimated thickness of the

overburden materials at surge tank is 10-15m whereas it is expected more than 50m at powerhouse

location.


5-8


There were no major geological hazards observed in and around the project area except few small

scaled slide observed along the existing road from intake to powerhouse. A landslide has recently

been activated at the upslope of previously proposed powerhouse site (option-II and III). Hence, it

is recommended to adopt the alternative powerhouse (option I) from geological point of view. In

general, the geology of project area is considered to be fair.

5.3 Seismicity

5.3.1 General

The evolution of the Great Himalayan Arc is the result of collision between the Indian and Eurasian

Tectonic Plates over a distance of 2400 km from Pakistan in the west and Burma in the east. The

Himalayas are located near plate boundary. Therefore, the Himalayan region is considered to be

seismically active zone. Thus, being a part of Himalayas, Nepal Himalaya is considered to be active

seismic zone. However, the existence of tectonic features such as Main Central Thrust (MCT), Main

Boundary Thrust (MBT) and Himalayan Frontal Fault (HFF) further accelerates the rate of seismic

risk. Therefore, proximity to such structural features are important while assessing the seismicity of

the hydroelectric project.

5.3.2 Main Central Thrust (MCT)

This is the tectonic contact between the Higher Himalayas and Lesser Himalayas. It is a north

dipping thrust fault which at one time was a convergent plate boundary. The MCT was active during

the early phases of Himalayan orogeny but is now considered to be less active as compared

to Main Boundary Thrust (MBT). Based on historical records (1800’s to 1986) the largest earthquake

recorded in the MCT zone in the Himalaya was a 7.5 magnitude event in August 28, 1916. The

project area is located at about 30 km south of MCT. Therefore, seismic risk associated with MCT is

considered to be less.

5.3.3 Main Boundary Thrust (MBT)

This is the active tectonic contact between the Lesser Himalayas and the Siwaliks. The MBT has

been the source of very large earthquakes in the past. It is reported that the maximum potential

earthquakes in this feature has a magnitude of 8.0. The project site is located at about 75 km


5-9


north of MBT which is considerably at greater distance. Therefore, less seismic risk associated with

this feature is expected for the project.

5.3.4 Himalayan Frontal Fault (HFF)

This is a tectonic feature located at the boundary of the Siwalik and the Terai. This fault is also

considered to be active. The maximum earthquake potential of this fault is 6.5 in magnitude. The

project site is located very far (more than 100 km) from this feature hence less seismic risk

caused due to this feature is expected.

5.3.5 Seismicity Evaluation

The specific project related seismic studies have not been carried out so far. The records of seismic

activities are limited in the Nepal Himalayas and hence correlation of seismic events with

adjacent Himalayan region would be a useful source of information for designing the hydraulic

structures.

Several seismicity studies have been carried out for the various projects in the country during the

engineering design phases and seismic design coefficients are derived for those projects. There is no

well established theory about the relationship between the maximum acceleration of the earthquake

motion and the value of the design seismic coefficient. However, there are several methods to

convert the maximum acceleration of the earthquake motion into the design seismic coefficient.

Generally three methods i.e. simplest method, Empirical method and Dynamic analysis using

dynamic model are common to establish the seismic coefficient. The simplest method is represented

by α = Amax/980, where α = Design Seismic Coefficient and Amax = Maximum acceleration of

the motion (gal). However, this method will evaluate rather large value of seismic coefficient

compared with the real value. The empirical method is denoted by αeff = R α = R Amax/980.

Where the αeff is effective design coefficient and R is Reduction Factor (Empirical value of R is

approximately (0.5 – 0.65). The results obtained from this method are found to be similar in

the recent studies carried out by using the dynamic analysis and the static analysis. Therefore, this

method is considered to be most common method to establish the design seismic coefficient at

present. The third method is Dynamic Analysis Method using Dynamic model. This method is

considered to be most reasonable method at present. However, to apply this method the


5-10


parameters like design input motion, the soil structure model, the properties of rock materials

etc. are to be known. Therefore a detailed study is required to use this method. Therefore,

empirical method is considered to be reliable method to establish the design seismic coefficient for

this level of the study.

A project specific seismicity study has been carried out for the Budhi Gandaki Hydroelectric Project

and the recommended design seismic coefficient is 0.2 for the probable earthquake of VIII

intensity MM. The Budhi Gandaki Hydroelectric Project lies in Gandaki Basin and the Upper

Trishuli 3B HEP is located in the same river basin. The Budhi Gandaki Hydroelectric Project

lies about 70 km West of Upper Trishuli – 3B Hydroelectric Project.

The design seismic coefficient for the Upper Trishuli – 3B Hydroelectric Project is derived based on

above empirical method and seismic coefficient recommended for the Budhi Gandaki Hydroelectric

Project.

The evaluation of seismic coefficient for the Upper Trishuli 3B HEP is made during the present

study based on Nepalese standard and Indian standard.

Nepalese Standard

In order to determine the seismic coefficient a seismic design code for Nepal has been prepared.

The country is divided into three seismic risk zones based on allowable bearing capacity of three

types of soil foundation. The Upper Trishuli 3B HEP is located in the third seismic risk zone of

Nepal, Figure No. 5.1 and the soil foundation at the powerhouse site belongs to average soil type.

Therefore, the basic horizontal seismic coefficient is considered to be 0.08. By using above empirical

method, the effective design coefficient according to seismic design code of Nepal is given by the

equation,

α

eff = R * α = R * Amax/980

Where, α

eff = effective design seismic coefficient

R = Reduction Factor (Empirical value of R = 0.5 – 0.65)

For the maximum acceleration of 250 - 300 gal according to Seismic Hazard Map of Nepal (Figure


5-11


5.2), Published by DMG, National seismological Center, September 2002) and reduction factor of

0.5 the calculated effective design seismic coefficient for the Upper Trishuli 3B Hydroelectric

Project is approximately 0.13 to 0.15.

Figure 5.1: Seismic Risk Map of Nepal


5-12


Figure 5.2: Seismic Hazard Map of Nepal

Indian Standard

In order to determine the design horizontal coefficient a seismic risk map for India has been

prepared. The map is published in the Indian Criteria for Earthquake Resistant Design of structures.

The country is divided into five seismic risk zones in the Indian Standard, Figure No. 5.3.

According to seismic risk map of India, Nepal lies in the fifth seismic risk zone of India (zone

V). Therefore, it can be considered that the Upper Trishuli-3B HEP is located in the fifth seismic

risk zone of India (zone V), and the basic horizontal seismic coefficient (αo) can be taken as 0.08.

The design horizontal seismic coefficient in the Indian Standard is defined by the equation,


5-13


α h = β * I * αo

Where, αh = Design horizontal seismic coefficient

Β = Soil foundation factor (1 for dam)

I = Importance factor (2 for dam)

αo = Basic horizontal seismic coefficient

Therefore, the design horizontal seismic coefficient for Upper Trishuli 3B HEP dam is 0.16

according to the Indian standard.

By comparing all above evaluations and recommended seismic coefficient for Budhi Gandaki

HEP, the design horizontal seismic coefficient for the Upper Trishuli 3B HEP can be taken as

0.15 for the present level of study.


5-14


Figure 5.3: Seismic Risk Map of India


5-15


5.4 Core Drilling

5.4.1 Core Drilling during feasibility study, July 2007

A total of 250.00 m of linear core drilling has been carried out during the feasibility study. One

borehole DHP-1 has been drilled in the intake portal, three namely DP-1, DP-2, DP-4 have been

drilled in the Powerhouse area and one DP-3 has been drilled in Surge Tank area. Similarly, a

Borehole DHA-1 has been drilled at Andheri khola to know the rock cover at headrace tunnel

alignment. The locations of boreholes are shown in DWG NO UT3B-GEO-03, 04, 05. The general

descriptions of the boreholes are shown in Table 5.1.

Table 5.1: General Description of Boreholes

Borehol

e

No.

Drilling

Machine

Inclination

& Direction Location

Length

(m) Co-ordinates

X Y Z

DP-1

DP-2

DP-4

DHP-1

DHA-1

DP-3

Acker ‘Ace’

Acker ‘Ace’

Acker ‘Ace’

Tone UD-5

Tone UD-5

Acker 'Ace'

Vertical

Vertical

60°/285°

60°/275°

Vertical

Vertical

Powerhouse

Power house

Powerhouse

Intake

Tunnel Alignment

Andheri Khola

Surge tank

50.00

30.00

35.00

35.00

50.00

50.00

3097872.018

3097898.200

3097891.240

3100866.415

3100745.980

3097967.715

616658.991

616565.300

616590.128

616665.250

616228.730

616467.863

649.188

655.300

652.430

736.000

814.200

763.865

Total 250. 00m

5.4.2 Drilling Works Result and Analysis

(a) Intake portal

The intake portal is located at about 500m upstream from the confluence of Andheri Khola and

Trishuli river. This project has been proposed to utilize the tailrace water of Upper Trishuli 3A

HEP. The slope around intake portal is gentle while slope protection is necessary towards tailrace

options of Upper Trishuli 3A HEP. The slope is represented by colluvium and alluvium deposits

with a thickness of 5-20 m. An inclined borehole DHP-1 was drilled at intake portal area and


5-16


bedrock was encountered at a depth of 19.00m (vertical depth is 16.m). The intake site has been also

investigated seismic SLD-1 to SLD-6. The bed rock encounter is gneiss at 19 m depth.

(b) Andheri Khola

A horseshoe shaped headrace tunnel is about 3962 m long and will have an excavated diameter of

6.6 m . The rock is exposed in most of the parts of the tunnel alignment except between intake and

Andheri Khola and between Santi Bazar and Sukaura Khola in the map boundary. Drilling was

carried out at Andheri Khola to confirm the minimum rock cover along the tunnel alignment. The

bed rock is found at depth 28.3 m and the rock type is schist with quartz veins.

(c ) Surge Tank (alternative option II & III)

The surge tank is located on the right bank of the Trishuli River at Sirupani Village which is about

125 m up from the river level and it will have finished diameter of 20 m. The rock exposed around

the surge tank area is quartzite and schist. Quartzite and schist are intercalated however quartzite is

dominant over schist. The surge tank area is investigated by borehole DP-3 which was drilled up to

50.00 m depth. The surficial rock outcrop exposed around the surge tank area is fractured and

moderately weathered but it improved with as shown by drilling result. The bedrock is encountered

at 3.00 m. The bed rock encounter is phyllitic schist.

(d) Powerhouse Site (alternative option II & III)

The surface powerhouse is proposed on the terrace deposit at the right bank of Trishuli River in the

alternative option I. The powerhouse has been investigated by boreholes DP-1, DP-2, DP-4 which

have been drilled up to 50 m, 30 m and 35 m respectively. DP-1 and DP-2 are vertically drilled holes

whereas DP-4 is an inclined at 286° / 60° (direction / inclination). The bedrock was not

encountered in borehole DP-1. But in DP – 2 and DP – 4 the bedrock was encountered at 15.40 m

and 18.00 m (vertically 15.6 m) respectively. The bed rock encounter is phyllitic schist with quartze

vains. The surfacial deposit in the powerhouse area is mainly alluvial terrace and minor colluvial

deposits. The deposit consists mainly of angular to sub-angular boulder, to gravel sized fragments in

sandy - silty matrix with little fines.


5-17


(e) Tailrace Tunnel (alternative option II)

The tailrace tunnel alignment has been investigated by borehole DP-1 which was drilled up to 50.00

m. The bedrock has not been encountered in the borehole and the bedrock level is expected to be at

more than 50.00 m depth. The tailrace tunnel passes through the alluvial deposit.

5.4.3 Core Drilling during Detail Design, June 2013

Boreholes were drilled at Surge shaft, Penstock Alignment and Powerhouse site as per site

investigation priority provided by Trishuli Jal vidhyut Company Limited (TJVCL). The total drilling

length was 195.00 m. The locationS of boreholes are shown in DWG NO UT3B-GEO-06

(Location of borehole at new alternative surge tank and powerhouse site). The summary of

boreholes is shown in Table 5.2.

Table No. 5.2: Summary of borehole location, depth, direction and bedrock depth.

S. N. Location Borehole

No.

Depth

m Orientation

Drilling

Rig

Bedrock

depth, m

1 Surge Shaft DST-1 75.00 Vertical XY200 11.4

2 Drop Shaft /

Pressure Tunnel Alignment

DPA-1 25.00 Vertical XY200 14.00

3 Powerhouse Site I DPH-1 50.00 Vertical XY200 -

4 Powerhouse Site II DPH-2 45.00 800 XY200 37.5

5.4.4 Drilling Works Result and Analyses

The detail reports of boreholes prepared by geologist making observation of core boxes and driller's

daily report sheets are given in Annex-1. The summary of each borehole drilling result and analysis

are as follows:

(a) Surge Shaft Area

Hole no. DST-1

The borehole, DST-1 was vertically drilled at Manakamana VDC ward no 4, Champani, having

given drill location coordinate X = 616196.445, Y = 3097625.756 and Z = 813.15 m. Total depth of


5-18


borehole is 75.00 m; out of 75.00 m depth borehole , 11.40 m depth drill on overburden and 63.60

m at bedrock. The bedrock is characterized by fresh to moderately weathered, light to dark grey

Schist and gneiss. The core recovery ranges from 0 to 100%. The RQD varies between 0 to 4 –

41.00 %. The average recovery in this borehole is 60.92% whereas average RQD is 19.3%. Based on

the overall RQD of this borehole, the rock can be classified as very poor to fair rock quality. The

water table is dry in condition and more than 65% grey to white, milky white color water was return

from the hole during drilling.

(b) Drop Shaft/Pressure Tunnel Alignment

Hole no. DPA-1

The borehole, DPA-1 was drilled at Manakamana VDC ward no 3 Pokhare village having coordinate

X = 616353.178, Y = 3097447.957 and Z = 683.07 m. Total 25.00 m depth of borehole was drilled

at vertical direction. Out of 25.00 m depth 14.00 m drill at overburden and 11.00 m at bedrock. The

bedrock is characterized by fresh to moderately, fractured light gray dolomite. The core recovery

ranges from 0 to 100%.The RQD varies between 13 to 36 %. The average recovery is 47.50 %

whereas the average RQD is 29.63 %. Based on the overall RQD of this borehole, the rock can be

classified as very poor to fair rock quality. The water table was recorded at a depth of 15.00 m and

more than 50% milky white color water was return from the hole during drilling.

(c) Powerhouse Area

Hole no.: DPH-1

The borehole, DPH-1 was drilled at Manakamana VDC ward no 3 Pokhare village having

coordinate X = 616434.629, Y = 3097359.831 and Z = 639.90 m. Total 50.00 m depth of borehole

was drilled at vertical direction. The borehole data and core shows that bed rock was not

encountered at 50.00 m depth. The overburden is generally slightly weathered to moderately

weathered gravel and boulder of schist and gneiss. The core recovery ranges from 0 to 100%. The

average recovery is 49.97 %. The water table was recorded at a depth of 15.50 m and 25% brownish

grey and 75% milky white color water was return from the hole during drilling.

Hole no.: DPH-2

The borehole, DPH-2 was drilled at Manakamana VDC ward no 3 Pokhare village having

coordinate X = 616392.773, Y = 3097403.054 and Z = 667.5 m. Total 45.00 m depth of incline


5-19


borehole (800) was drilled. The borehole was drill both on overburden and bed rock. The

overburden thickness is 37.50 m; the overburden materials are gravels, cobbles and boulders of light

to dark grey schist and gneiss. The bedrock is characterized by fresh to moderately weathered, light

gray to dark grey fractured schist. The core recovery ranges from 0 to 100%. The RQD varies

between 13 to 36.00%. The average recovery is 55.9% and the average RQD is 27.4%. Based on the

overall RQD of this borehole, the rock can be classified as poor to fair. The water table was

recorded at a depth of 22.00 m and 6.00 % – 10.00 % yellowish grey to light grey color water was

return from the hole during drilling. Water loss was observed at most part of borehole section

i.e.3.00 – 22.50 m and 24.00 – 45.00 m.

(d) Insitu test

Permeability test by Lugeon method was performed in all 2 boreholes (DST-1 and DPA-1). Five

numbers of Lugeon test, five numbers of DCPT and five numbers of constant head test data were

taken during the drilling. The summary of analysis of insitu test is given at Table 5.3 and the details

of the test are given in "Core Drilling Works - August 2013".

Table No. 5.3: Summary of Insitu Test.

SN

Drill hole no.

Insitu testing Depth (m) Test Value Remarks

DCPT Lugeon Permeability N - value

Permeability

Lugeon

1 DST-1

- Lugeon 37.50 - 40.50 m - - Pressure not raised

- Lugeon 47.50 - 50.50 m - 9.00

Lugeon - 57.00 - 60.00 m - 13.50

Lugeon - 72.00 - 75.00 m 20.00

2 DPA-1 - Lugeon - 22.00 - 25.00 m -

- Pressure

not raised DCPT - 6.00 m - -

3 DPH-1

DCPT - - 8.50 m -

DCPT - - 14.50 m 75 -

Permeability 8.50 m 1.48E-02



4 DPH-2

Permeability 12.00 m 1.23E-02 - - Permeability 15.00 m - 1.10E-02 -

DCPT 6.00 m DCPT 12.00 m


5-20


5.5 Construction Material Survey

5.5.1 Introduction

The construction material investigation of the Upper Trishuli -3B Hydroelectric Project was

conducted by Soil, Rock and Concrete Laboratory, NEA from April to May, 2007 for the feasibility

study of the project. The investigation comprised of identification of potential borrow areas in the

close vicinity of the project site, exploring borrow areas by test pits excavation and collection of

representative samples for laboratory tests and analysis. The investigation included a wide range of

relevant laboratory tests and their interpretation.

The investigations show that there is adequate quantity of construction material within the close

vicinity of project site. The reserve estimation of granular material from the proposed borrow area is

about 0.5 million m3 and need to be processed for fine and coarse filters and for concrete ingredient.

For this proposes, crushing of this material through a jaw crushes, may be required. The quarry site

can also be served as an alternate source for back fill materials,

Additional investigation of laboratory test for granular material will be required to verify quantity

and quality of material during the construction phase of the project. More laboratory test and

analysis on riverbed material will be required for the assessment of strength character and evaluation

of deleterious effect of aggregate for concreting work. Potential alkali reactivity by mortar bar test

should be carried out before making final decision on suitability of this material for production of

concrete aggregates.

5.5.2 Field Exploration

The field exploration was carried out to identify the potential borrow areas and quarry sites for the

construction materials. A total of 2 nos. of possible borrow areas were identified within 5 km range

of project area during feasibility study. Borrow areas GA is located in Trishuli River bed. Borrow

area GB is located at Salankhu Khola bed. Two-quarry sites (QA and QB) were identified. Quarry

site QA is located at Right bank of Tirshuli River near proposed powerhouse site. Borrow areas and

Quarry area are presented in DWG NO UT3B-GEO-07 (Location map of borrow area and quarry

site).


5-21


A total of 11 test pits were excavated for granular material at two borrow areas (GA and GB). The

description of number of test pits excavated in each borrows area and quantity of samples taken for

laboratory test is presented separately. Summary of Test Pits and sample description are presented

in Table 5.4 Test pit log records are presented in Geology and geotechnical study, Appendix-B,

2007 July.

Table 5.4: Summary of Pits and Sample Description

Name of the borrow/quarry area

Location Number of test pit

No. of sample

Remarks

GA Trishuli bagar 6 17

GB Slakhu Khola 5 10

QA Trishuli bagar 3 Boulder Sample

QB Trishuli River L/B 1

5.5.3 Laboratory Test and Analysis

All laboratory tests and analysis had been carried out at Soil, Rock and Concrete Laboratory (SRCL).

5.5.4 Granular Borrow area

Borrow Area GA

Borrow area GA is located at Trishuli River. Laboratory test results show that fines passing from 80

micron vary from 2.2 to 20.6 percent. Wear value in Los Angeles abrasion of the material ranges in

between 32.0 to 42.6 percent. Total loss in sulphate soundness test varies 0.8 to 1.9 percent in five

cycles. Specific gravity value ranges in between 2.69 to 2.721. Absorption of the aggregate recorded

max 1.1 percent. Aggregates considered deleterious in alkali reactivity test. As per United Soil

Classification System (USCS), a group symbol “GP, SP,GP - GM SW - SM , SP – SM and SM “are

assigned for the samples.

Borrow Area GB

Borrow area GB (Falake Bagar) is located at 1.5 km downstream of proposed powerhouse site.

Laboratory test results show that fines passing from 80 micron vary from 4.0 to 8.5 percent. Wear


5-22


value in Los Angeles abrasion of the material ranges in between 32.4 to 35.9 percent. Total loss in

sulphate soundness test varies 0.5 to 1.2 percent in five cycles. Specific gravity ranges in between

2.67 to 2.69. Absorption of the aggregate is recorded as less than 0.8 percent. Aggregates considered

deleterious in alkali reactivity test. According to United Soil Classification System (USCS) a group

symbol, “GW, GP – GM, SW-SM, and SP - SM"are assigned for the samples.

5.5.5 Quarry Site

Two quarry areas (QA and QB) were identified during investigation. Quarry site, QA is located at

Tirshuli bagar boulder deposit near proposed powerhouse and quarry site QB is located at left bank

of Tirshuli River .Bulk samples were collected from these sites and transported to SRCL, KTM to

execute different types of laboratory tests. Summary of laboratory test results are presented at Table

5.5.

Quarry Area, QA ( left bank of Trishuli River)

Quarry area QA is located at left bank of Trishuli River near proposed powerhouse site. Schist rock

is the host rock of this site.

During study, one sample was collected from quarry site and tested at SRCL. Wear value in Los

Angeles Abrasion of the material is recorded as 31.2 percent. Total loss in sulphate soundness test is

recorded as 1.3 percent in five cycles. Specific gravity has recorded 2.69 Absorption of samples has

recorded as 0.4 percent. Aggregates are considered as deleterious in alkali reactivity test.

Quarry Area, QB

Quarry area QB is located at Trishuli bagar near vicinity of project site.

During study, three samples was collected from quarry site and tested at SRCL. Wear value in Los

Angeles abrasion of the material has recorded varies from 19.2 to 50.4 percent. Total loss in sulphate

soundness test is recorded which varies from 0.4 to 1.3 percent in five cycles. Specific gravity has

varies from 2.61 to 2.67 Absorption of samples has recorded 0.1 percent. Aggregates are considered

as deleterious in alkali reactivity test. Summary of laboratory test results are presented at Table 5.5.


5-23


5.5.6 Laboratory Test on Core Samples

Uniaxial compression test, absorption, specific gravity, unit weight tests and point load tests were

performed on core samples. Summary of laboratory test results on core samples are given in

“geology and geotechnical study, Appendix-B, 2007 July” and “Core Drilling of the alternative

powerhouse site done by TJVCL, Year 2013 June”

5.5.7 Reserve Estimation of the Borrow Areas and Quarry areas

Volume of Granular material was estimated on the basis of field measurement of test pits depth,

material quality, laboratory test result of pit samples and area of different proposed borrow areas.

Estimated volume of material in different borrow areas is 0.32 million cubic meter for GA and that

of 14 million cubic meter for GB borrow area. Individual borrow areas volume calculation for total

granular material are presented at Table 5.5.

Table 5.5: Reserve Estimation of Borrow Area

Name Location Measurement Area m2 Average depth (m) Volume (m3)

GA Trishuli bagar 1005*100 100500.00 3.17 318585.00

GB Falake bagar 776 * 65 50440.00 2.75 138710.00

Total 457295.00

5.5.8 Test summary Various laboratory tests carried out on soil samples obtained by test pitting and on rock by core

drilling are summarized on the following table from table no. 5.6 to 5.11.

Det

ail P

roje

ct R

epor

t of

UT

3B H

EP

5-24

Tri

shu

li Ja

lvid

yut

Com

pan

y L

imit

ed

Tab

le N

o 5.

6: S

um

mar

y of

Lab

orat

ory

Tes

t R

esu

lts

on G

ran

ula

r M

ater

ial

Tes

t

Pit

No.

D

epth

m

Sam

ple

No.

Bor

row

A

rea/

L

ocat

ion

Gra

in s

ize

dist

ribu

tion

%

S

peci

fic

Gra

vity

U

SC

S

Cla

ssif

icat

ion

Abs

orpt

ion

%

Los

Ang

eles

Abr

asio

n S

ulph

ate

Sou

ndne

ss

Tot

al L

oss

%

Alk

ali

Rea

ctiv

ity

Gra

vel

San

d

Fin

es

Wea

r

%

U

nifo

rmit

y fa

ctor

S

C

m

mol

/l

Rc

m

mol

/l

GA

TP

- 0

1

0.00

- 0

.60

DS

- 1

Pah

irob

esi

baga

r

46.5

49

.5

4.0

S

P

0.60

- 1

.00

DS

- 2

47

.4

50.3

2.

3 2.

72

SP

1.

1 32

.0

0.3

1.9

1.00

- 3

.00

DS

- 3

48

.8

48.4

2.

8

GP

GA

TP

- 0

2 0.

00 -

0.8

0 D

S -

1

3.4

75.9

20

.6

S

M

0.80

- 3

.00

DS

- 2

52

.4

42.4

5.

2

GP

-GM

GA

TP

- 0

3

0.00

- 0

.60

DS

- 1

Thu

loba

gar,

S

irup

ani

0.3

86.2

13

.5

S

M

0.60

- 1

.20

DS

- 2

2.

4 88

.7

8.9

S

W-S

M

1.20

- 1

.80

DS

- 3

19

..7

69.1

11

.2

S

P-

SM

1.80

- 3

.25

DS

- 4

52

.6

39.7

7.

7 2.

69

GP

- G

M

1.0

42.6

0.

3 0.

8 12

93

117

GA

TP

- 0

4

0.00

- 0

.70

DS

- 1

S

anob

agar

, S

irup

ani

37.4

60

.5

2.0

S

P

0.70

- 1

.30

DS

- 2

41

.8

51.3

16

.9

S

M

1.30

- 3

.00

DS

- 3

43

.5

54.0

2.

5

SP

GA

TP

- 0

5

0.00

- 0

.85

DS

- 1

Kha

lte

33.2

64

.5

2.2

2.70

S

P

1.0

32.0

0.

3 0.

8 12

78

133

0.85

- 1

.50

DS

- 2

2.

9 90

.1

7.0

S

P -

SM

1.50

- 3

.75

DS

- 3

2.

5 94

.3

3.2

S

P

GA

TP

- 0

6 0.

00 -

1.5

0 D

S -

1

Nau

bise

21

.0

71.9

7.

1

SW

- S

M

1.50

- 3

.00

DS

- 2

18

.7

73.6

7.

7

SW

- S

M

GB

TP

- 0

1 0.

00 -

1.0

0 D

S -

1

Ban

sbot

e,

Sal

akhu

khol

a

42.6

48

.9

8.5

S

W -

SM

1.00

- 2

.50

DS

- 2

47

.1

45.8

7.

2 2.

68

GP

- G

M

0.7

GB

TP

- 0

2 0.

00 -

1.5

0 D

S -

1

43.1

51

.7

5.1

S

P -

SM

32.4

0.

3 1.

0

1.50

- 2

.75

DS

- 2

47

.1

47.6

5.

3

SP

- S

M

GB

TP

- 0

3 0.

00 -

1.0

0 D

S -

1

Pah

are,

S

alak

hukh

ola

40.8

51

.5

7.9

S

P -

SM

1.00

- 2

.95

DS

- 2

46

.9

47.1

5.

9 2.

69

SP

- S

M

0.8

34.8

0.

3 1.

2 13

26

106

GB

TP

- 0

4 0.

00 -

0.9

0 D

S -

1 42

.9

50.4

6.

7

SP

- S

M

0.90

- 3

.00

DS

-2

45.5

47

.6

6.9

S

P -

SM

GB

TP

- 0

5 0.

00 -

0.6

0 D

S -

1 42

..4

52.3

5.

3

SP

- S

M

0.60

- 2

.50

DS

-2

64.4

31

.6

4.0

2.67

G

W

0.7

35.9

0.

2 0.

5 11

14

120


5-25

Trishuli Jalvidyut Company Limited

Table No. 5.8: Summary of Laboratory Test Results on Core Samples

Drill Hole No.

Depth m

Location Specific Gravity

Absorption %

Unit Weight gm/cm3

Uniaxial Compressive

Strength kg/cm2

DP - 3

31.60 - 32.00

Powerhouse

2.64 0.5 2.6 380.1

46.33 - 46.90 2.66 0.3 2.6 930.8

59.00 - 59.55 2.65 0.3 2.6 504.5

69.55 - 70.00 2.70 0.4 2.6 1006.2

DP - 4

26.0 - 26.50

Surgetank

2.66 0.3 2.6 880.4

35.23 - 35.70 2.67 0.3 2.6 955.9

46.00 - 46.70 2.68 0.3 2.6 883.4

58.00 - 58.65 2.64 0.4 2.6 1257.1

Table No. 5.7: Summary of Laboratory Test Results on Quarry Material

Quarry

Area

Sample

No.

Specific

Gravity

Absorption

%

Los Angeles

Abrasion

Sulphate

Soundness

Total Loss

%

Alkali Reactivity

Wear

%

Uniformity

factor

SC

mmol/l

Rc

mmol/l

QA S # 1 2.69 0.4 31.2 0.3 1.3 1362 104

QB

S # 1 2.61 0.8 28.3 0.2 1.0 1238 132

S # 2 2.67 0.7 50.4 0.1 1.3 1171 102

S # 3 2.65 0.6 19.2 0.3 0.4


5-26



Drill Hole No.

Depth m

Location Specific Gravity

Absorption % Unit Weight gm/cm3

Uniaxial Compressive

Strength kg/cm2

DP - 3 31.60 - 32.00 Powerhouse 2.64 0.5 2.6 380.1

46.33 - 46.90 2.66 0.3 2.6 930.8

59.00 - 59.55 2.65 0.3 2.6 504.5

69.55 - 70.00 2.70 0.4 2.6 1006.2

DP - 4 26.0 - 26.50 Surgetank 2.66 0.3 2.6 880.4

35.23 - 35.70 2.67 0.3 2.6 955.9

46.00 - 46.70 2.68 0.3 2.6 883.4

58.00 - 58.65 2.64 0.4 2.6 1257.1


Drill Hole No. Depth, m Eav N/mm2

DHP - 1 27.45 - 27.70 3812

DHA -1 45.58 - 45.92 4146

DP - 2 15.80 - 16.25 6572

27.00 - 27.30 3278

DP - 3 36.70 - 36.84 4063

43.00 - 43.25 4011


5-27


Table No. 5.11: Point Load Test Results

Drill Hole No.

Rock Type

Depth m

Test Width

mm Height

mm P

kPa De^2 De

Is MPa

F Is (50) MPa

DHP -1 27.45 - 27.70

Diametrical 59.50 45.00 4750 2,025.00 45.00 2.66 0.954 2.54

Diametrical 45.90 45.00 4375 2,025.00 45.00 2.45 0.954 2.34

Diametrical 48.10 45.00 4500 2,025.00 45.00 2.52 0.954 2.41

Axial 45.00 46.00 12000 2,635.60 51.34 5.17 1.012 5.23

Axial 45.00 44.00 5750 2,521.01 50.21 2.59 1.002 2.59

Axial 45.00 26.50 3500 1,518.33 38.97 2.62 0.894 2.34

DHA -1 45.58 - 45.92

Diametrical 213.00 45.00 4500 2,025.00 45.00 2.52 0.954 2.41

Diametrical 124.80 45.00 6875 2,025.00 45.00 3.85 0.954 3.67

Diametrical 87.90 45.00 7000 2,025.00 45.00 3.92 0.954 3.74

Axial 45.00 39.60 6875 2,268.91 47.63 3.44 0.978 3.36

Axial 45.00 66.00 4000 3,781.51 61.49 1.20 1.098 1.32

Axial 45.00 61.50 9000 3,523.68 59.36 2.90 1.080 3.13

DP - 2 15.80 - 16.25

Diametrical 114.10 45.00 3875 2,025.00 45.00 2.17 0.954 2.07

Diametrical 95.50 45.00 9000 2,025.00 45.00 5.04 0.954 4.81

Diametrical 48.50 45.00 11750 2,025.00 45.00 6.59 0.954 6.28

Axial 45.00 48.70 5500 2,790.30 52.82 2.24 1.025 2.29

Axial 45.00 45.90 6625 2,629.87 51.28 2.86 1.011 2.89

Axial 45.00 51.90 10000 2,973.64 54.53 3.82 1.040 3.97

DP - 2 27.00 - 27.30

Diametrical 159.40 44.80 6750 2,007.04 44.80 3.82 0.952 3.63

Diametrical 91.60 44.80 5500 2,007.04 44.80 3.11 0.952 2.96

Diametrical 65.60 44.80 6000 2,007.04 44.80 3.39 0.952 3.23

Axial 44.80 35.80 7500 2,042.07 45.19 4.17 0.955 3.98

Axial 44.80 44.50 8250 2,538.32 50.38 3.69 1.003 3.70

Axial 44.80 55.40 10000 3,160.07 56.21 3.59 1.054 3.79

DP - 3 36.70 - 36.84 Diametrical 64.60 45.00 6250 2,025.00 45.00 3.50 0.954 3.34

Axial 45.00 23.30 3750 1,334.99 36.54 3.19 0.868 2.77

DP - 3 43.00 - 43.25

Diametrical 82.30 44.80 8125 2,007.04 44.80 4.59 0.952 4.37

Diametrical 53.10 44.80 4000 2,007.04 44.80 2.26 0.952 2.15

Diametrical 40.50 44.80 6750 2,007.04 44.80 3.82 0.952 3.63

Axial 44.80 34.60 9000 1,973.62 44.43 5.18 0.948 4.91

Axial 44.80 23.60 5500 1,346.17 36.69 4.64 0.870 4.03

Axial 44.80 24.60 5750 1,403.21 37.46 4.65 0.878 4.08


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5.6 Geotechnical Design: rock support design of underground structure

The tunnel is an underground structure and thus its stability is mainly concerned with underground

wedge formed by the intersection of multiple joints and in- situ stress condition at tunnel. The

stability analysis mainly involves the analysis of underground wedges and stress analysis of the

tunnel. The report describes the design criteria used for the design of underground openings

including mainly headrace tunnel. The report also describes the stability analysis and stress analysis

of the openings including safety factor, displacements and nature of stress distribution using the

Finite Element Method for the proposed underground openings. The geotechnical design also

includes the rock support requirements for the underground excavation using both NGI 'Q' system

and RMR system, and the U.S. Corps of Engineers recommendations. An underground wedge

stability analysis for the underground opening was carried out to confirm the adequacy of the

support. At present, due to lack of unavailabity of parameters such as in-stresses values, modulus of

deformability, poisson's ratio, friction angle etc. These parameters are to be derived from the rock

mechanics test carried in adit tunnel or main tunnel. Therefore, during this stage of study,

underground wedge stability analysis and stress analysis based on assumption of above parameters

have been performed to assess the support design of the tunnel.

5.6.1 Methods

Generally, there are two methods for support design of underground opening to estimate the

support requirements.

5.6.1.1 Empirical Method

In this method, the analysis is based on the past experience and practice. This method is used when

there is limited geological information and empirically derived relations are used to predict the

support type.

5.6.1.2 Analytical Method

This method uses the numerical modeling and is considered to be best method for the support

analysis. This method is used to analyze the rock stress, deformation, rock support analysis etc.

Among the different numerical modeling, Finite Element Method using PHASE2 software has been


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used for the present analysis. The analytical method also includes wedge stability analysis.

Underground wedge stability analysis has been performed using UNWEDGE software to assess the

stability of the wedge condition during the present study.

5.6.2 Analysis for support design

A horseshoe shaped headrace tunnel is about 3745 m long and will have an excavated diameter of

6.10 m and 6.80 for shotcrete and concrete lining respectively. The tunnel will pass through the right

bank of Trishuli River at an average elevation of 715 m (amsl). The tunnel runs approximately in

NE-SW direction however there are four major bending points. The approximate direction of

tunnel at each bending points are as follows, N090° and N256° at chainage 0+532m, N076° and

N194° at chainage 0+939m, N014° and N176° at chainage 1+771 m and N346° and N140° at

chainage 3+980m. About 10% of the tunnel passes through gneiss and remaining 90% through

intercalation of schist and quartzite. The maximum rock cover is about 380m at chainage 2+160 and

mimimum cover is about 88m at Sukaura khola at chainage 1+700.

The stability of underground excavations are primarily governed by two principal modes of failures

e.g. structurally - controlled failure and stress - induced failure. In structurally controlled failure,

excavation stability may be dominated by gravity falls and sliding along inclined discontinuities. In

structurally controlled failure, Rock Mass Classification such as NGI's Q-system or CSIR's RMR-

system is the important factors to assess the stability of the rock mass and design of support

systems. In stress induced failure, high induced stresses and weathering are the important factors.

In-situ stress measurement, various laboratory and rock mechanics testing on rock mass are required

to carry out to define its engineering properties. However, such tests were not performed at this

stage of study. At this stage in-situ stresses are assumed based on in-situ stress measured for other

hydroelectric projects and major principal stresses are assumed to be equal to vertical stress due to

overburden. Therefore, the support designs of the tunnel are carried out based on structurally

controlled failure, stress analysis and other empirical criteria.

It is presumed that the excavation of the tunnel shall be carried out by the conventional drill and

blast method consisting of blasting, mucking and support installation. The New Austrian Tunneling

Method (NATM) shall be employed during the construction period.


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5.6.3 Design Criteria Generally the problems associated with pressurized tunnels are well known and are generally related

to a rapid interaction during the first filling, or progressive interaction after a certain period of

operation, between the pressurized flow in the tunnel and the surrounding rock

5.6.3.1 Analysis using Rock Cover

At initial stage, the minimum depth of rock cover above the headrace tunnel is taken from a thumb

rule where the rock cover is selected to the hydrostatic head. A minimum safety factor of 1.3 is

adopted in the following relationship:

Hr / Hw = (w / r) x FS

Where, Hr = rock cover thickness Hw = water head

w = unit weight of water ( w = 0.01 MN/m3 )

r = unit weight of rock FS = safety factor (FS = 1.3)

The headrace tunnel of Upper Trishuli 3B hydroelectric project is almost horizontal with about 0.34

% slope over its 3.745 km length. The water head measured from the full supply level to the spring

line of tunnel, Hw = 23.5 m, gives a maximum internal hydrostatic pressure of Hw.w = 0.235 MPa.

This pressure is too low compared to the rock cover hence the governing parameter for the stability

of the rock mass is the rock cover. The rock cover criteria assuming the tunnel is empty must be

respected over the whole length of the tunnel.

5.6.3.2 Analysis using In Situ Stresses

The analysis using rock cover is a very simplified approximation whereas analysis using in-situ

stresses, both gravitational and tectonic is a more elaborate method. In order to avoid hydraulic

fracturing of the rock with the consequent opening of existing joints, the minor principal

component of the in-situ stresses should be higher than the internal hydrostatic pressure in the

tunnel.

In-situ stresses are not measured during the present study. Therefore, a parametric study is carried

out to evaluate the in-situ stresses for this present study. At this level of study, the stress analysis was


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carried out for the maximum depth of overburden which is about 380 m for Upper Trishuli 3B

hydroelectric project. The ratio of horizontal to vertical stress 'k' is compared with in-situ stresses

measured at Arun - III (k=0.3) and Middle Marsyangdi Hydroelectric Projects (k=0.5).

Another theoretical method to estimate the 'k' value is from Sheorey's (1994) equation. Sheorey has

developed an elasto-static thermal stress model of the earth and provided a following simplified

equation for estimating the value of the horizontal to vertical stress ratio, k. This model considers

curvature of the crust and variation of elastic constants, density and thermal expansion coefficients

through the crust and mantle.

k = 0.25 + 7Eh (0.001+1/Z)

Where,

Z (m) is the depth below the surface

Eh (GPa) is the average deformation modules of the upper part of the earth's crust measured in a horizontal direction

The above equation forms a large scale model, and hence does not take into account local

topographic and geological features.

Using the maximum rock cover in the tunnel, z = 380 m and average value of Eh (from Table 5.14),

in-situ stress ratio of k for very poor rock (schist) is 0.31, 0.46 for poor rock (schist), 0.6 for fair rock

(schist) and 1 for good rock (schist and gneiss). The 'k' ratio obtained from the overburden depth

varies from 0.31 to 1. Middle Marsyangdi lies about 80km NW of Upper Trishuli 3B and both

projects lies in the same Gandaki Basin. Therefore,' k' value of 0.5 is considered for the present

study.

5.6.3.3 Analysis using Elastic and Plastic Behavior

The ratio of the maximum tangential boundary stress to the unconfined compressive stress of the

rock mass is referred as the Damage Index (Di),

Di = max / c

Where,

Di = Damage Index


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max = max. tangential boundary stress , = Pvert (3k-1) Kirsch equation (Hoek and Brown),

c = lab tested unconfined compressive strength,

k = horizontal to vertical stress ratio (hor /vert), Pvert = vertical stress.

The Damage Index indicates that for Di 0.4, the rock mass behaves as an elastic condition and no

visible damage is recorded. The practical experience is that stress-induced damage occurs when the

damage Index (Di) exceeds 0.4 and the rock mass displays a plastic behavior. The damage index

estimated for the rock mass of the project area is shown in Error! Reference source not found..

Table 5.12: Damage Index

Rock Class k Maximum Rock

Cover (m)

Pvert

(Mpa)

UCS, c

(MPa)

max Di

Good Rock (Gneiss) 1.08 380 10 100 22.9 0.23 Good Rock (Schist with quartzite)

0.96 380 10 80 19.2 0.24

Fair Rock (Schist with quartzite)

0.60 380 10 70 8.1 0.11

Poor Rock (Schist with quartzite)

0.46

380

10

50

3.8

0.07

Very Poor Rock (Schist with quartzite)

0.31 380 10 35 -0.6 -0.02

As the dominant rock type in intercalation of schist and quartzite is schist, the unconfined

compressive strength for schist is considered for calculating the necessary parameter. So 80, 70, 50

and 35 Mpa values are used for good, fair, poor and very poor as obtained from laboratory test

results in the previous study. Similarly, 100 Mpa value is used for good quality gneiss.

The damage index Di shown in Error! Reference source not found. is calculated for gneiss and

schist. The result showed that 'D'i for the schist rock varies from -0.02 to 0.23 which are less than

0.4 hence the rock mass behaves as elastic-brittle. Thus for present analysis the overall rock mass of

the tunnel area is considered to be elastic brittle nature. When the strength of the rock mass is

exceeded, a sudden strength inclined occurs which is associated with significant dilation of the

broken rock pieces.


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5.6.4 Failure Criteria

The rock mass properties are assumed to be adequately characterized by the biaxial failure criteria

developed by Hoek and Brown. The most general form of Hoek-Brown criterion which

incorporates both original and modified form is given by following equations for both intact and

fractured rock.

1 = 3 + (mb. c . 3 + s. c2)1/2

where,

1 = major principal stress at failure

3 = minor principal stress applied to the specimen

c = uniaxial compressive strength of the intact rock material in the specimen (measured in laboratory)

mb & s = constants which depend upon the properties of the rock and upon the extent to which

it has been broken before being subjected to the stresses 1 and 3.

The uniaxial compressive strength of the specimen is given by substituting 3 = 0 in above equation,

giving following equation:

cs = (s. c2 ) 1/2

For intact rock, cs = c and s = 1. For previously broken rock, s<1 and the strength at zero

confining pressure is given by above equation, c is the uniaxial compressive strength of the pieces

of intact material.

The strength parameters, m and s, for intact and fractured rock are as follows:

Intact rock : s = 1 Very fractured rock : s = 0 Good quality rock : mi = 25

Weak rock : mi = 0 Values of mb and s used in the analysis are determined from the following equations and the RMR

(Rock Mass Rating) coefficient is determined according to Bieniawski's classification (1989).

For GSI > 25 (Undisturbed rock masses) mb / mi = exp (GSI-100)/28

Where mi = 25 for intact rock mass


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s = exp (GSI-100)/9 Where, GSI is called Geological Strength Index and the relation between GSI and

RMR is given by the equation, GSI = RMR89' - 5

The values of constant mi for intact rock are shown in Error! Reference source not found.

Table 5.13: Values of constant mi for Intact Rock by rock group

Rock Type Class Group Texture

Coarse Medium Fine Very fine

SEDIMENTARY

Clastic

Conglomerate Sandstone Siltstone Claystone (22) 19 9 4 Greywacke (18)

Non-Clastic

Organic

Chalk 7 Coal (8-21)

Carbonate Breccia Sparitic Limestone Micritic Limestone (20) (10) 8

Chemical Gypstone Anhydrite 16 13

METAMORPHIC

Non Foliated Marble Hornfels Quartzite 9 (19) (24)

Slightly Foliated

Migmatite Amphibolite Mylonites (30) 31 (6)

Foliated Gneiss Schists Phyllites Slate 33 (10) (10) 9

IGNEOUS

Light Dark

Granite Rhyolite Obsidian 33 (16) (19) Granodiorite Dacit (30) (17) Diorite Andesite

(28) 19 Gabbro Dolerite Basalt 27 (19) (17) Norite 22

Extrusive Pyroclastic Type

Agglomerate Breccia Tuff (20) (18) (15)

* These values are for intact rock specimens tested normal to foliation. The value of mi will be

significantly different if failure occurs along a foliation plane (Hoek, 1983). Note that values in

parenthesis are only estimated values.


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5.6.5 Estimation of In-Situ Deformation Modulus

The in-situ deformation modulus of a rock is an important parameter in any form of numerical

analysis. Since this parameter is difficult and expensive it is not determined in the field at this level of

study. However, it can be empirically determined by using following equations for the present study

level.

E = 2RMR – 100, GPa (Bieniawski, 1978) for RMR > 50

E = 10(RMR-10)/40, GPa (Serafim and Pereira, 1983) for RMR <50

E = 25 log10 Q, GPa (Grimstad and Barton, 1993) for Q>1

E= √ (σc/100) x 10(GSI-10)/40 (Hoek and Brown, 1998) for UCS<100MPa

E= 10 x [(σc x Q)/100] 1/3, GPa (Barton, 2002)

For the stability analysis a mean value of E (Emean) has been estimated from above equations for each

type of rock (gneiss and intercalation of schist and quartzite).

The estimation of in-situ modulus of deformability E and rock mass strength parameters, mi, mb and s are shown in Error! Reference source not found. and Error! Reference source not found. respectively.

Table 5.14: Estimation of In-Situ Modulus of Deformability

Rock Type/ Quality

Q RMR E=2RMR-100 Gpa

E=10(RMR-10)/40

GPa E=25Log10

Q GPa E=√(σci/100)x 10(GSI-10)/40 GPa

E =10 x [(σcix Q)/100] 1/3,

GPa

E, Mean GPa

Good Rock (Gneiss)

22 68 36 N/A as RMR>50

33 21.1 28 32.5

Good Rock (Schist & quartzite

intercalation)

22 67 34 N/A as RMR>50

33 17.8 26 27.8

Fair Rock (Schist & quartzite

intercalation)

7 52 4 N/A as RMR>50

21 7.5 17.8 12.6

Poor Rock (Schist & quartzite

intercalation)

3 35 N/A as RMR<50

4 12 2.8 13.4 8.1

Very Poor Rock

(Schist & quartzite

0.18 16 N/A as RMR<50

1.4 N/A as Q<1

0.9 5.2 2.5


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intercalation)

Note: Q & RMR average values are based on report of geological mapping whereas UCS values for gneiss and schist are taken as 100 and 80 Mpa.

Table 5.15: Rock Mass Strength Parameters

Site Location

Rock Type

GSI mi mb s ci

(Mpa) r

MN/m3

Headrace Tunnel

Gneiss (Good Rock)

63 33 8.8 0.016 100 0.027 0.20

Schist & quartzite (Good Rock)

62 10 2.6 0.015 80 0.027 0.25

Schist & quartzite (Fair rock)

47 10 1.5 0.003 80 0.027 0.25

Schist & quartzite (Poor rock)

30

10 0.8 0.0004 80 0.027 0.30

Schist & quartzite (Very poor rock)

11 10 0.4 0.0 80 0.027 0.35

mi values for gneiss and schist is 33 and 10 respectively (from Error! Reference source not

found.5.15). The uniaxial compressive strength test for the intact gneiss and schist is assumed to

be 100 MPa and 80 Mpa which is used for the analysis.

5.6.6 Rock Mass Classification

The rock mass classification has been carried out for the rock mass along the tunnel based on

detailed joint mapping on surface rock outcrops along the tunnel alignment. Geomechanical

classification using both Rock Mass Rating (RMR) system (Bieniawski, 1989) and Tunneling Quality

(Q) (Barton et al, 1974) for the jointed rock mass has been carried out and the rock mass along the

tunnel has been classified based on these classifications shown in Error! Reference source not

found..16 and Error! Reference source not found..

Table 5.16: Rock Mass Classification using Rock Mass Rating (RMR) system (Bieniawski, 1989)

Rating 100 - 81 80 - 61 60 - 41 40 - 21 <21

Class Number

I II III IV V

Description Very good rock Good rock Fair rock Poor rock Very poor rock


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Table 5.17: Rock Mass Classification from Rock Tunneling Quality Index, Q (Stillborg, 1994)

Q - Value Rock Mass Description Class number

> 40 Very good rock I

10 - 40 Good rock II

4 - 9 Fair rock III

1 - 3 Poor rock IV

< 1 Very poor rock V

5.6.7 Method of Analysis for Assessing Support Requirements

Both empirical method and elasto-plastic analysis are used for determining support requirements

and a numerical method is used for stability analysis of underground openings as discussed in

previous chapter. Empirical assessments of rock reinforcement provide a useful supplement to any

detailed analytical analysis. The empirical assessment of rock support was carried out at present

based on assumed data since the geotechnical data such as rock density, in-situ stresses, and

deformation modules, etc are not available at present.

5.6.8 Empirical Design According to NGI Method

The empirical method is used for determining support requirements in headrace tunnel. The

equivalent dimension, De, is plotted against the value of 'Q', is used to define a number of support

categories in a chart published by Barton et al. (1974) shown in Figure 5.4. The equivalent dimension

De is given by:

)(

)(,

RatioSupportExcavationESR

mheightorDiameterSpanExcavationDe


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Figure 5.4: Estimated Support Categories based on the tunneling quality Index Q (After Grimstad &

Barton, 1993)

The headrace tunnel falls into category of water tunnels for hydropower and is assigned an

Excavation Support Ratio, ESR = 1.6 (Stillborge, 1994). Hence, for an excavation span of 6.8 m of

headrace tunnel, the equivalent dimension, De = 6.9/1.6 = 4.3 = 4

It is estimated that approximately 20% of the total length of the headrace tunnel will be driven in

rock mass of good quality with Q = 20 - 23, 50% in fair rock mass with Q = 3.5 - 15 and 20% in

poor rock mass with Q = 2 - 3.5 and 10% through very poor rock mass (Q<1). This estimation is

based on detailed joint mapping carried out in the surface outcrops exposed along the tunnel

alignment.

From Error! Reference source not found., a value of De of 4 and a 'Q' value of 22, places 20% of the

total length of the headrace tunnel excavation falls in category 1 and according to which no support

is recommended but this is not possible in real practice. However, based on underground wedge

stability analysis and stress analysis, support type at least 2.5 m long grouted bolt at 2.0 m x 2.0 m

spacing with 100 mm thick fibre-reinforced shotcrete is recommended for this portion of the tunnel.

Similarly, a value of De of 4 for 'Q' value of 7 (fair rock) places 50% of the tunnel excavation falls


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still in category 1 showing the unsupported category. The underground wedge stability analysis and

stress analysis recommends at least 2.5 m long grouted bolt at 2 m x 2 m spacing with 100 mm thick

fibre-reinforced shotcrete for this portion of the tunnel. Similarly, for poor rock, a value De of 4 and

a 'Q' value of 3, 20% of the tunnel excavation falls still in category 4 showing systematic bolting with

40-100mm unreinforced shotcrete which is not enough in practice. Hence for this tunnel section

shall be treated with pattern rock bolt 2.5 m long grouted bolt at 2.0 m x 2.0 m spacing with 100 mm

thick fibre-reinforced shotcrete along with 30 cm thick concrete lining. The very poor rock section

10% of the tunnel falls in the category 6 showing fibre reinforced shotcrete 90 – 120 mm and

bolting. In practice this support is not enough hence this section of the tunnel shall be treated with

pattern rock bolt of length 2.5 m at 1.5 m x 1.5 m spacing with 15 cm fibre-reinforced shotcrete

with 30 cm concrete lining along with steel ribs of ISMB 200 x 100 @ of 1.5 m spacing.

The minimum required length (L) of rock bolts can be estimated from the excavation width (B) and

the Excavation Support Ratio, ESR as follows:

L = (2 + 0.15B)/ESR Hence, for headrace tunnel having B = 6.8 m, the minimum length of rock bolt, L = 1.9 2.0 m.

Similarly for drop shaft having B = 5.0 m, the minimum length of rock bolt, L = 1.7 m 2.0 m and

for horizontal pressure tunnel having B = 5.0, the minimum length of rock bolt, L = 1.7 m 2.0 m.

Calculated minimum rock bolt length for horizontal pressure tunnel is 2.0 m but due to high

pressure flow in the structure the recommended rock bolt length for horizontal pressure tunnel is

2.5 m for safety.

The maximum unsupported span can be estimated as follows:

Maximum span (unsupported) = 2 ESR Q0.4 (for good rock)

= 2 x 1.6 x 220.4

= 11 m

Maximum span (unsupported) = 2 ESR Q0.4 (for fair rock)

= 2 x 1.6 x 70.4

= 7 m

Maximum span (unsupported) = 2 ESR Q0.4 (for poor rock)


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= 2 x 1.6 x 30.4

= 4.8 m = 5 m

Biron & Arioglu (1982) developed a relation between rock bolt length & roof span as follows:

For strong roof: Bolt length = 1/3 of the roof span For weak roof: Bolt length = 1/2 of the roof span For very strong roof: Minimum recommended bolt length is 3-4 inches.

So, for good rock (very strong roof), the minimum bolt length is 0.1 m. For fair rock, (the strong

roof), the minimum bolt length should be 2.3 m. Similarly, for poor to very poor rock (weak roof),

the minimum bolt length is 3.4 m.

Similarly, according to general thumb rule, the maximum bolt spacing should at least be following:

One half of the bolt length

6 ft

One and one-half of critical and potentially unstable blocks.

Maximum bolt spacing should not be less than 3 ft. Hence, for present support design, maximum bolt spacing should not be less than 1 m.

The permanent roof support pressure, Proof for good rock is given by:

Proof = 2√Jn Q-1/3

3 Jr

= 2 x √9 x 22-1/3

3 x 1.5

= 0.47 kg/cm2

The permanent roof support pressure, Proof for fair rock is given by:


3 Jr

= 2 √9 x 7-1/3

3 x 1.5

= 0.70 kg/cm2


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The permanent roof support pressure, Proof for poor rock is given by:


3 Jr

= 2 x √9 x 3-1/3

3 x 1.5

= 0.93 kg/cm2

5.6.9 Empirical Design Recommendation According to U.S Corps of Engineers

A system of simple recommendations for rock bolt reinforcement design has been formulated by

the U.S. Corps of Engineers. The empirical rules, given in Table are a summary of many important

rock reinforcement case histories. This recommendation may be used as a guide for minimum

reinforcement required for the tunnel.

Table 5.18: Typical Design Recommendations after U.S. Corps of Engineers (1980) and Douglas and Arthur (1983)

Parameter Empirical Rule Headrace Tunnel

Horizontal Pressure Tunnel

Valve Chamber


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Minimum Length & Maximum Spacing Minimum length Maximum Spacing Minimum Spacing

Greatest of: (a) 2 x bolt spacing (b) 3 x thickness of

critical and potentially unstable block. (Note 1)

(c) For elements above the spring line: Spans < 6m = 0.5 x span Spans (18 m - 30 m) = 0.25 x span Spans (6 m - 18 m) = interpolate between 3 m and 4.5 m.

(d) For elements below the spring line: Height < 18 m = same as (c) above Height > 18 m = 0.2 x height

Least of: (a) 0.5 x bolt length (b) 1.5 x width of

critical and potentially unstable blocks

(a) 2.0 m Note 2 0.8 to 1.25 m

Greatest of: (a) 2 x 2 m = 4.0 m (b) 3 x 1.0 m = 3.0 m (Note 1) ( c) 3 m (d) For elements below spring line: For height 6.6 m = 3 m Least of: (a) 0.5 x 2.5 m = 1.25 m (b) 1.5 x 1.0 m

= 1.5 m (a) 2.0 m Note 2

0.8 to 1.25m

Greatest of: (a) 2 x 1.25 m =

2.50 m (b) 3 x 1.0 m =

3.0 m (Note 1)

(c) 0.5 x 4.8 m = 2.4 m (Note 1) (d) For elements below spring line: For height 4.8 m = 2.4 m Least of: (a) 0.5 x 2.0 m =

1.50 m (b) 1.5 x 1.0 m =

1.5 m (a) 2.0 m Note 2

0.8 to 1.25 m

Greatest of: (a) 2 x 1.5 m = 3.0

m (b) 3 x 1.0 m = 3.0

m (Note 1)

(c) 0.5 x 4.2 m = 2.1 m (Note 1) (d) For elements below spring line: For height 4.2 m = 2.1 m Least of: (a) 0.5 x 5.0 m =

2.50 m (b) 1.5 x 1.0 m =

1.5 m (a) 2.0 m Note 2 0.8 to 1.25 m

Note 1: Thickness of critical and potentially unstable rock blocks at the headrace tunnel is 1.0 m

obtained from joint mapping.

Note 2: Greater spacing than 2.0 m makes attachment of surface support elements (e.g. weldmesh to

chain link mesh) difficult.

From the above table, the minimum bolt length shall be 4 m the minimum spacing shall be 1.12 m

and maximum spacing shall be 1.25 m for headrace tunnel. Similarly minimum bolt length shall be

2.50m, minimum spacing shall be 1.12m and maximum spacing shall be 1.50 m for horizontal


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pressure tunnel. Minimum bolt length shall be 3.m, minimum spacing shall be 1.12m and maximum

spacing shall be 1.50 m for valve chamber.

5.6.10 Underground Wedge Stability Analysis

The analysis for the stability of the underground wedges that are likely to form around the headrace

tunnel is carried out to determine the size of the wedges, their mode of failure and factor of safety.

UNWEDGE software is used for the analysis.

5.6.10.1 Methodology

UNWEDGE program is a quick, interactive and simple tool which is used for the analysis of the

geometry and the stability of underground wedges defined by intersecting structural discontinuities

in the rock mass surrounding an underground excavation. The analysis is based on the assumption

that the wedges, formed by three intersecting discontinuities, are subjected to gravitational loading

only. Therefore, the stress field in the rock mass surrounding the excavation is not taken into

account. The program is mainly used to assess the structurally controlled failure of the rock mass.

The required length of rock bolt and thickness of shotcrete lining along with safety factor for the

wedge developed at the underground cavern will be analyzed by using this software. The analysis

needs in-put parameter such as dip direction; dip amount and spacing of major discontinuities,

cohesion, friction angle, rock unit weight and water pressure.

5.6.10.2Results of Analysis

Joint parameters required for the analysis have been extracted from the geological mapping and

analysis for headrace tunnel has been carried out for different excavation directions. Unwedge

stability analysis provides the shape and size of potential wedges and the support required to

stabilize them. The Unwedge program provides several options for sizing wedges. One of the most

commonly measured lengths in structural geological mapping is the length of a joint trace on an

excavation surface and seizing option is based upon this trace length. The discontinuity of measured

joint or trace length of joint has been obtained from geological report. The surface area of the base

of the wedge, the volume of the wedge and apex height of the wedge is calculated by the program.

Tunnel has been divided into four main portions such as T-1, T-2, T3 and T-4 based on the

direction. T-1 portion of the tunnel will run in N230° direction, T-2 in N194° direction, T-3 in


5-44


N175° direction and T-4 in N138°. The detailed analysis results are discussed below. The entire

headrace tunnel passes through gneiss and intercalation of schist and quartzite rock mass. The

tunnel has three major bending points. The unwedge stability analysis has been carried out for

tunnel excavation in four major direction viz. N230°, 194°, 175° & 138°.Three major joint sets are

obtained from geological mapping for this option. The major joint sets are:

SN Dip/Dip Direction Joint Sets

1 32°/235° J1

2 64°/160° J2

3 55°/090° J3

Similarly the analyses have been carried out for valve chamber and horizontal pressure tunnel. The results of analysis are summarized in following Table 5.19 to 5.24.

Table 5.19: Summary of Analysis for Headrace Tunnel (N256°)

S

N

Critical

Wedges

Size of Wedge FS before

Support

Required Supports FS

after

Support Vol.

(m3)

Face

Area

(m2)

Apex

Height

(m)

Pattern Rock

Bolts

Shotcrete

(cm)

1 Wedge No.1

Wt.= 168

Tons

62.07

44.37

5.83

0.28 Length

(m)

Spacing

(m)

10

2.75 4 1.5


S

N

Critical

Wedges


Support


after

SupportVol.

(m3)

Face

Area

(m2)

Apex

Height

(m)

Pattern Rock

Bolts

Shotcrete

(cm)

1 Wedge No.1

Wt.=2.0

Tons

0.75

3.21

0.83

0.28

Length

(m)

Spacing

(m)

10

13.40 1.5 2.0

2 Wedge No.6

Wt.= 23

Tons

8.49

12.79

2.12

0.49

Length

(m)

Spacing

(m)

10

4.25 2.5 2.0


S

Critical

Wedges


Support


after Vol. Face Apex Pattern Rock Bolts Shotcrete


5-45


N (m3) Area

(m2)

Height

(m)

(cm) Support

1

Wedge No.1

Wt.= 14

Tons

5.21

12.97

1.50

0.28

Length

(m)

Spacing

(m)

10

2.63 2.50 2.0

2 Wedge No.6

Wt.=41

Tons

15.29

28.61

2.26

0.49

Length

(m)

Spacing

(m)

10

4.66 2.5 2.0


S

N

Critical

Wedges


Support


after

Support

Vol.

(m3)

Face

Area

(m2)

Apex

Height

(m)

Pattern Rock Bolts Shotcrete

(cm)

1

Wedge No.1

Wt.= 7.7

Tons

2.85

6.64

1.65

0.28

Length

(m)

Spacing

(m)

10

4.43 2.0 2.0

2 Wedge No.5

Wt.= 12

Tons

4.40

9.59

1.57

0.40

Length

(m)

Spacing

(m)

10

5.47 2.0 2.0

Table 5.23: Summary of Analysis for Valve Chamber (N140°)

S

N

Critical

Wedges


Support


after

Support

Vol.

(m3)

Face

Area

(m2)

Apex

Height

(m)


(cm)

1 Wedge No.1

Wt.= 7.7

Tons

1.33

5.25

1.05

0.05

Length

(m)

Spacing

(m)

10

15.11 1.0 1.5

2 Wedge No.5

Wt.= 12

Tons

86.54

53.05

5.37

0.82

Length

(m)

Spacing

(m)

10

4.67 5.0 1.5

Table 5.24: Summary of Analysis for Horizontal Pressure Tunnel (N140°)

S

N

Critical

Wedges


Support


after

Support

Vol.

(m3)

Face

Area

(m2)

Apex

Height

(m)


(cm)


5-46


1

Wedge No.1

Wt.= 7.7

Tons

0.05

0.66

0.35

0.05

Length

(m)

Spacing

(m)

10

31.09 1.0 1.5

2 Wedge No.5

Wt.= 12

Tons

5.57

8.49

2.22

0.82 Length

(m)

Spacing

(m)

10

7.11 2.0 1.5

5.6.11 Finite Element Method

The failure of a rock mass around an underground opening depends upon the in-situ stress level and

upon the characteristics of the rock mass. PHASE2 program is used to estimate the safety factor in

the surrounding rock mass and mode of post failure nature. This program uses a two-dimensional

hybrid finite element /boundary element model.

5.6.11.1 Available Data

Available data for the design of underground structures are reasonable for the current stage of study.

The required data were extracted from present detailed surface geological mapping, parametric

studies and empirical techniques. Detailed surface geological mapping was carried out. The major

joints, ‘Q’ and RMR values are derived from the surface geological mapping and the engineering

properties of the rock mass were obtained from the empirical relations and from the similar rock

types in other projects of Nepal.

The following assumptions were considered for the support design of underground structures of the project.

The in- situ stresses and elastic properties of the rock mass were not available at this

stage of the study. However, with reference to in-situ stresses measured at Arun III

and Middle Marsyangdi Hydropower Projects, stress analysis for the underground

opening of Upper Trishuli 3B Hydropower Project was carried out at this level of

study. Since no in-situ measurements were carried out at this study, the major principal

stress (1) was assumed to be equal to the vertical stress due to overburden, the minor

principal stress (3) was assumed to be 0.5 times the vertical stress with addition of

tectonic stress component of 1 Mpa and the intermediate principal or out-of plane


5-47


stress (2) was assumed to be the sum of the minor principal stress and a tectonic

stress component of 1 MPa. A tectonic stress was added to the horizontal stresses.

This tectonic stress was added based on stress measurement carried out at Middle

Marsyangdi Hydropower Project.

It is assumed that the orientation of major principal stress (1) in vertical direction and

the minor principal stress (3) in the horizontal direction perpendicular to tunnel axis

and intermediate or out-of-plane stress (2) in the horizontal direction parallel to the

tunnel alignment.

Elastic and plastic parameters for the gneiss, schist and quartzite rock masses were not

available at this stage. These parameters were obtained from empirical relations, past

precedence and experiences from other projects of Nepal. The rock mass was

considered ideally to be elastic- plastic material with no strength drop once yield is

reached.

5.6.11.2Result of Analysis

The elastic–plastic stress analysis by finite element method using PHASE2 program was carried out

for tunnel in good, fair and poor to very poor rock. The results of analysis are summarized in Table

5.26 and parameters used for the analysis is shown in Table 5.25.

Det

ail P

roje

ct R

epor

t of

UT

3B H

EP

5-48

Tri

shu

li Ja

lvid

yut

Com

pan

y L

imit

ed

Tab

le 5

.25:

Bas

ic D

esig

n P

aram

eter

s fo

r E

last

o -

Pla

stic

An

alys

is

S.N

IN

- S

ITU

ST

RE

SS

ES

R

OC

K C

LA

SS

E

LA

ST

IC

PR

OP

ER

TIE

S

RO

CK

MA

SS

ST

RE

NG

TH

P

RO

PE

RT

IES

B

OL

T P

RO

PE

RT

IES

(25

mm

di

amet

er)

1

2

3

H

OE

K –

BR

OW

N

E

PE

AK

C

AP

AC

ITY

R

ES

IDU

AL

C

AP

AC

ITY

M

Pa

MP

a M

Pa

Deg

E

(M

pa)

(

) m

b

(pea

k)

s (p

eak

) m

r (r

es)

s (

res)

In

tact

UC

S (M

Pa)

(M

Pa)

(M

N)

(MN

)

1 H

ead

race

Tu

nn

el

1.1

10

7 6

90

Roc

k T

ype-

clas

s II

(G

ood

Roc

k), G

neis

s 32

500

0.20

8.

8 0.

016

8.8

0.01

6 10

0 20

0000

0.

2 0.

02

1.2

10

7 6

90

Roc

k T

ype-

clas

s II

(G

ood

Roc

k), (

Schi

st

with

qua

rtzi

te)

2780

0 0.

25

2.6

0.01

5 2.

6 0.

015

80

2000

00

0.2

0.02

1.3

10

7 6

90

Roc

k T

ype-

clas

s II

I (F

air

Roc

k) (S

chis

t w

ith q

uart

zite

)

1260

0 0.

25

1.5

0.00

3 1.

5 0.

003

80

2000

00

0.2

0.02

1.4

10

7 6

90

Roc

k T

ype-

clas

s IV

(P

oor

rock

), (S

chis

t w

ith q

uart

zite

)

8100

0.

30

0.8

0.00

04

0.8

0.00

04

80

2000

00

0.2

0.02

1.5

10

7 6

90

Roc

k T

ype-

clas

s V

(V

ery

Poor

roc

k),

(Sch

ist w

ith q

uart

zite

)

2500

0.

35

0.4

0.0

0.4

0.0

80

2000

00

0.2

0.02


5-49


Table 5.26: Summary of the result of analysis

S

N

Loc

atio

n

Rock

Type

Total Displacement

(mm) FS

Before Support

FS

After Support Before

Support

After Rock bolt &

Shotcrete

1

Tu

nn

el

Good

Rock

Crown Side

Wall

Floor Crown Side

Wall

Floor Crown Side

Wall

Floor Crown Side

Wall

Floor

1.24 0.52 1.43 1.25 0.52 1.35 1.28 0.85 1.28 2 1.2 1.2

2 Fair

Rock

Crown Side

Wall

Floor Crown Side

Wall

Floor Crown Side

Wall

Floor Crown Side

Wall

Floor

3.52 1.60 3.84 3.2 1.28 3.5 1.28 0.85 1.28

1.28 0.85 1.28

3 Poor

Rock

Crown Side

Wall

Floor Crown Side

Wall

Floor Crown Side

Wall

Floor Crown Side

Wall

Floor

5.2 2.4 6.0 4.8 2.0 5.2 0.86 0.86 0.86 7.6 17.2 6.4

4

Very

Poor

Rock

Crown Side

Wall

Floor Crown Side

Wall

Floor Crown Side

Wall

Floor Crown Side

Wall

Floor

16.6 8.9 17.9 12 5.0 14.0 0.86 0.86 0.86 1.7 0.86 1.28

2.6 1.9 2.8 2.6 2.6 2.88 1.28 0.85 1.28 1.28 0.85 1.28

The analysis showed a maximum displacement of 17.9 mm for very poor rock, 6.0 mm for poor

rock, 3.84 mm in fair rock and 1.43 mm for good rock. These displacements have been decreased to

some extent after installing the support as shown in above Table 5.25.

5.6.12 Slope Stability

The surface slope stability condition is mainly focused on backslope of powerhouse site. The slope

is stable during the present study. The backslope of powerhouse site mainly consists of colluvium

and alluvium deposits. The colluvial deposit is estimated about 20 – 25 m thick. It comprises of

angular to subangular boulder to gravel sized fragments of schist and quartzite in sandy silty matrix.

Therefore it is recommended to maintain the slope angle less than 45° after the excavation of

backslope of the powerhouse site from safety point of view. The backslope after excavation shall be

treated with 30cm of shotcrete with soil nailing about 8 - 10m long at an interval of 5 m grid.


5-50


5.6.13 Conclusions and Recommendations

The rock support recommended for the different underground structures during this stage of study

is mainly based on above empirical/numerical analysis and rock mass classification. Gneiss and

intercalation of schist and quartzite are the rock types exposed in the project area. Rock mass

classification has been carried out using RMR and Q systems. Thus, the analysis is mainly carried out

for good, fair, poor and very poor rock. The rock mass classification showed the good to very poor

quality rock types and accordingly support types S-2, S-3, S-4 and S-5 are recommended. These

support patterns will have to be re-evaluated through detailed analysis supported by rock mechanics

tests, in-situ stress measurement in tunnel and the rock mass classification carried out in the tunnel

after excavation during the construction phase.


5-51


Table 5.26: Rock Support Pattern for Upper Trishuli-3B Hydroelectric Project

S. N

SUPPORT TYPE

LOCATION FIBRE REINFORCED SHOTCRETE

CONCRETE LINING

ROCK BOLTS, = 25 mm LENGTH SPACING

IN-PLANE

OUT-OFPLANE

1 Headrace Tunnel ( L ≈ 3.745 Km, Excavated Dia. = 6.8 m, 6.1m)

1.1

Support Type – S2

(Rock Class – Q2)

(Good Rock)

Crown 100 mm

-

2.50 m 2.50 m 2.50 m

Sidewalls 100 mm 2.50 m 2.50 m 2.50 m

1.2

Support Type – S3

(Rock Class – Q3)

(Fair Rock)

Crown 100 mm 300 mm (50% concrete lining

& 50% shotcrete

lining)

2.50 m 2.00 m 2.00 m

Sidewalls 100 mm

2.50 m

2.00 m

2.00 m

1.3

Support Type – S4

(Rock Class – Q4)

(Poor Rock)

Sidewalls 100 mm

300 mm

2.50 m 2.00 m 2.00 m

Sidewalls 100 mm 2.50 m 2.00 m 2.00 m

1.4

Support Type - S5

(Rock Class - Q5)

(V.Poor Rock)

Crown 150 mm 300 mm with steel ribs of ISMB 200 X 100 at 1.25 m

spacing

2.50 m 1.50 m 1.50 m

Sidewalls

150 mm

2.50 m

1.50 m

1.50 m

2 Surge Tank (Excavated, Dia.= 15.0 m, height = 37.5 m)

2.1

Rock Class – Q3

(Fair Rock) -

200 mm

500 mm

6 .00 m

2.50 m

2.50 m

3 Adit Tunnel (Exca Dia.= 4.2m)

3.1

Support Type - S3

Rock Class - Q3

(Fair Rock)

Crown 100 mm

-

2.0 m 1.50 m 1.50 m

Sidewalls 100 mm 2.0 m 1.50 m 1.50 m

4 Drop Shaft (Exca Dia.= 5.0m)

4.1 Rock Class -

Q3 (Fair Rock)

- 100 mm 300 mm

2.0 m 1.50 m 1.50 m

5 Horizontal Pressure Tunnel (Exca Dia.= 5.0m)

5.1

Rock Class - Q3

(Fair Rock)

Crown 100 mm 300 mm concrete lining

with steel lining

2.5 m 1.25 m 1.25 m

Sidewall 100 mm 2.5 m 1.25 m 1.25 m

6 Valve Chamber (L: 15.9m, Exca W: 8.5m, Exca H: 11.9m)

6.1 Rock Class -

Q3 (Fair Rock)

Crown 100 mm 300 mm

concrete lining

5.0 m 1.5 m 1.5 m Sidewall 100 mm 5.0 m 1.5 m 1.5 m


5-52


Table 5.27: Chainage wise Support Class Headrace Tunnel

Chainage (m) Rock Class Support Type

From To

0+383 0+633 II S-2

0+633 0+742.5 III S-3

0+742.5 0+828 IV S-4

0+828 0+946.5 III S-3

0+946.5 1+032.5 V S-5

1+032.5 1+110 III S-3

1+110 1+258 II S-2

1+258 1+483 III S-3

1+483 1+715 III S-3

1+715 1+898 III S-3

1+898 2+230 III S-3

2+230 2+435 II S-2

2+435 2+538 IV S-4

2+538 2+800 II S-2

2+800 2+897 IV S-4

2+897 3+079.5 III S-3

3+079.5 3+216.5 II S-2

3+216.5 3+382.5 III S-3

3+382.5 3+565 V S-5

3+565 3+741 IV S-4

3+741 3+978 III S-3

3+978 4+080 IV S-4

4+080 4+240 III S-3


5-53


Table 5.28: Geological & Geotechnical Evaluation of Option I & Option II Powerhouse Site

SN

Parameters

Option - I Option - II Remarks Powerhouse

Surge Tank Penstock Align.

Powerhouse Surge Tank

Penstock Align.

1 Rock Type

Quartzite & Schist intercalation



Schist Schist Schist Quartzite portion dominates over schist in option -I

2 Bedrock Depth

15 m - 18 m (from core drilling)

3.10 m (from core drilling)

3-10 m (estimated)




3

Overburden Material

Alluvial - Colluvial deposit (highly permeable)

Colluvium (highly permeable

Colluvium (highly permeable), estimated

Alluvium (highly permeable)

Colluvium (highly permeable)

Colluvium (highly permeable), probably old slide deposit

4 Lugeon value

50 - 140 (highly permeable)

36 - 51 (highly permeable)

Core Drilling & testing has not been carried out

No rise of pressure hence considered to highly permeable

9 - 20 (moderately high permeable

No rise of pressure hence considered to highly permeable

5 Slope Stability

Landslide Landslide Landslide Stable at present

Stable at present

Stable at present

Landslide is not deep seated and has only occurred in overburden material

6 Faults/ Thrust

No No No No No No

7

Rock Mass Classification

Fair Poor to Fair Fair Poor to Fair Poor to Fair

Poor to Fair

8

Geological Evaluation

Geologically, option -I powerhouse site is considered to be fair condition; however the present slide must be stabilized to prevent the powerhouse by trimming the slide materials and applying the bio-engineering works. Underground penstock (drop shaft) is recommended for this option.

Geologically, option -II powerhouse site is considered to be poor to fair condition, Surface penstock is recommended for this option.


5-54


5.6.2 Conclusions and Recommendations The rock support recommended for the different underground structures during this stage of study

is mainly based on above empirical/numerical analysis and rock mass classification. Gneiss and

intercalation of schist and quartzite are the rock types exposed in the project area. Rock mass

classification has been carried out using RMR and Q systems. Thus, the analysis is mainly carried out

for good, fair, poor and very poor rock. The rock mass classification showed the good to very poor

quality rock types and accordingly support types S-2, S-3, S-4 and S-5 are recommended. These

support patterns will have to be re-evaluated through detailed analysis supported by rock mechanics

tests, in-situ stress measurement in tunnel and the rock mass classification carried out in the tunnel

after excavation during the construction phase.

The following investigations are recommended before the construction of the project.

Drilling Extra work needed

- One vertical borehole (60 m) in the new alternative powerhouse location

- One vertical borehole (90 m) in the new alternative surge tank area

Test Adit

- At least one test adits about 440 m long to carry out in-situ rock mechanics tests

- In-situ stress measurement

- Modulus of deformation

- Shear Test

Construction Materials The following recommendations are made for the construction phase. More detailed field and laboratory investigation on river bed material including petrographic analysis,

slake durability etc. should be carried out before making final decision on suitability of this material

for production of concrete aggregates. Other alternative borrow area has to be investigated to

confirm the quality and quantity of construction materials in the construction phase and detailed

investigation on quarry site materials has to be also carried out in the construction phase.

615

400E

615

600E

615

800E

616

000E

616

200E

3098400N

3098600N

3098800N

3099000N

3099200N

3099400N

3099600N

3099800N

3100000N

3100200N

3100400N

3100600N

3100800N

3101000N

3101200N

3101400N

Land Slide

FOREST

FOREST

SwitchyardArea

Archale Gaun

To S

hant

i Baz

arTo

Dan

da G

aun

To Mailung Khola

To S

hant

i Baz

ar

T o D

anda

Gau

n

To Ma ilun

g Khola

To Shanti Bazar

To Colony

To S

irupa

ni

Ghalegaun

Pairegaun

Simle

SwitchyardArea

To Ma ilun

g Khola

616

400E

616

600E

616

800E

617

000E

617

200E

Leg

end

s

30

02

001

00

04

005

00m

TR

ISH

UL

I JA

LA

VID

YU

T C

OM

PA

NY

LIM

ITE

DS

orh

aKh

utte

, K

athm

andu

Ph:

01-

4360

011,

01-4

373

781,

01-

4384

443

SC

ALE

UP

PE

R T

RIS

HU

LI 3

BH

YD

RO

EL

EC

TR

IC P

RO

JEC

TN

uwa

kot,N

epal

Pro

ject

:T

itle:

DW

G N

o

UT

3B-G

EO

- 01

(A)

GE

OL

OG

ICA

L M

AP

& L

AY

OU

T O

FP

RO

JEC

T A

RE

A1

:10,

000

615

400

E

615

600

E

615

800

E

616

000

E

616

200

E

616

400

E

616

600

E

616

800

E

617

000

E

617

200

E

3096600N

3096800N

3097000N

3097200N

3097400N

3097600N

3097800N

3098000N

3098200N

3098400N

3098600N

3098800N

3099000N

3099200N

3099400N

LAND SLIDE ANDVERTICAL CLIFF

Land Slide

HFL

LINE

Kul

o

FOREST

FOREST

To Kaule and Bhalche

To S

ole

Ba z

ar

To Shanti Bazar

To Betrawati

PokharI

Champani

Ghalegaun

Sirupani

Siureni

EL 6 36

msl

6. 64

Le

ge

nd

s

30

02

00

10

00

400

50

0mT

RIS

HU

LI

JAL

AV

IDY

UT

CO

MP

AN

Y L

IMIT

ED

So

rha

Kh

utt

e,

Ka

thm

an

du

Ph

:01

-43

60

01

1,0

1-4

37

37

81

,01

-43

84

44

3

SC

AL

EU

PP

ER

TR

ISH

UL

I 3

BH

YD

RO

EL

EC

TR

IC P

RO

JEC

TN

uw

ako

t,N

ep

al

Pro

ject

:T

itle

:D

WG

No

UT

3B

-GE

O-

01

(B)

1:1

0,0

00

GE

OL

OG

ICA

L M

AP

& L

AY

OU

T O

FP

RO

JEC

T A

RE

A

0+00

00+

160

0+32

00+

480

0+64

00+

800

0+96

01+

120

1+28

01+

440

1+60

01+

760

1+92

02+

080

2+24

02+

400

2+56

02+

720

2+88

03+

040

3+20

03+

360

3+52

03+

680

3+84

04+

000

722.43

721.86

721.01

723.20

718.50

747.71

815.75

836.39

837.80

822.57

835.00

828.24

896.82

938.44

941.85

932.97

931.64

926.54

912.04

900.60

879.07

844.81

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Chapter 6:

Layout Optimization

6.1 Introduction

During the feasibility study, NEA has described two alternative option of Upper Trisuli 3B

Hydroelectric Project. The headworks of these two alternative are same in both cases, the

difference is the location of the powerhouse site. The lower alternative option has powerhouse

site at the confluence of Salankhu Khola and Trisuli River having the installed capacity 46 MW.

This option has cancelled based on the boundary available for the survey license of Upper Trisuli

3B Hydroelectric Project, Therefore, during the feasibility study, the alternative option of

powerhouse located at Champani village near the New bridge has selected. The installed capacity

of this alternative option is 37 MW.

The review study and field verification were conducted by the team of engineers from Trisuli

Jalvidyut Company Limited. Four important remarks were made.

a) Upper Trisuli 3A HEP has a provision of Upper Trisuli 3B intake at the tailrace

pond of the Upper Trisuli 3A HEP, the same intake has been considered in the

design of Upper Trisuli 3B HEP.

b) The proposed powerhouse has undergone land slide activity at the powerhouse area

in the year 2011, these needs to be taken care in the detail engineering phase.

Alternatively, it seems suitable to shift the powerhouse area by 500 m downstream

from the proposed powerhouse area.

c) The rock cover of the headrace tunnel at Andheri Khola crossing is not sufficient;

therefore, the tunnel alignment has to shift inward by around 200 m inside.

d) In order to exploit the available resources, it is due consideration given to maximize

the energy from the layout.

The alternative studies with three different project layout/configurations were appraised based

on two different location of powerhouse site for the detail design of the project. In alternative

option I, the location of the powerhouse is nearly 0.5 km further south and 0.6 km upstream of

Salankhu Khola. The following sections describe the different aspects of the alternate study in

detail.



6.2 Study of Possible Alternative Layouts for the Project

The company TJCL has studied three different alternative layout options in the detail design

phase. The cost estimate corresponding to quantity estimate of each alternative have been carried

out separately. The energy estimate and installed capacity of each alternative have been estimated

as per the water conveyance layouts. The details of head loss estimate are given in Design

Calculation. The separate economic and financial analyses were carried out to select the best

project layout optimization.

However, following layout option are not considered in the layout optimization of the project.

a) Underground intake

Since, the Upper Trisuli 3B HEP is constructing the head pond for Upper Trisuli 3B

HEP, in the layout optimization, the underground intake option is not considered.

b) Surface surge tank

It is noticed from the topographic mapping and survey, the space is not available to

locate the surface surge tank. From the drilling results at the proposed surge tank area,

the bed rock is found at 19 m below the ground level.

c) Underground powerhouse

Since the rock available at the powerhouse area is soft schist, the possibility of

underground power house is over ruled in the layout optimization. The unconfined

compressive strength of the bed rock available at the powerhouse area varies from 179

kg/cm2 to 899 kg/cm2.

d) The powerhouse at the alluvial/colluvial bed is not considered. The foundation of the

powerhouse considered is on the bed rock.

e) Since the penstock alignment needs heavy excavation for the bed rock anchoring, surface

penstock is not considered in the layout optimization. The drop shaft option is

considered in the layout optimization.

The layouts of all the alternatives were done in the topographic map and survey in 1:500 scale.

Quantity estimate of all the structure are based on the structural optimization. The diameter of

the concrete lined tunnel is 5.5 m (circular) and that of the shotcrete lined tunnel is 6.6 m (horse

shoe shape). The diameter of pressure tunnel and drop shaft is 4.2 m. The dimensions of the



surge tank are based on the surge analysis. The height of the surge tank is 37.4 m and diameter is

15 m.

The energy estimate is based on the hydrology of the project after deduction of environmental

release 3.84 m3/s. Following table shows the monthly power flow to estimate the total energy.

Table 6-1: Flow Data Used for the Alternative Studies

Month River Flow Flow for Energy

Jan 43.40 39.56

Feb 38.40 34.56

Mar 38.40 34.56

Apr 48.30 44.46

May 86.80 82.96

Jun 238.80 234.96

Jul 523.50 519.66

Aug 603.80 599.96

Sep 389.80 385.96

Oct 161.20 157.36

Nov 78.30 74.46

Dec 53.20 49.36

Following paragraph deals the separate alternative options in brief.

6.2.1 Alternative-I

This project taps water from the tailrace pond proposed by Trisuli 3A HEP and passes to the

headrace pipe, Headrace tunnel, dropshaft and then to pressure tunnel. This is a longer tunnel

length option. The full supply level was fixed at EL726.00 m. The tailrace water level is varies

from 626.49 m to 627.91 m. the total number of adit required is three. This alternative layout

consists of the following physical parameters:

a) Intake Water directly taps from the outlet of the Trisuli 3A

Tailrace outlet (Surface intake).

b) Surface Conveyance 364.27 m headrace pipe (concrete cover) from Tailrace of



UT3A HEP to tunnel intake.

c) Underground Conveyance 3744.69 m tunnel from Intake to surge Tank

d) Underground Conveyance 98.17 m horizontal tunnel after S/T, 69.07 m drop shaft,

181.65 m horizontal pressure tunnel after drop shaft

Followed by powerhouse and tailrace

e) Total length of Adit 1017 m

f) Length of Tailrace tunnel 123.93 m

g) Design Discharge 51 m3/s

h) Total net head 95.13 m

i) Installed Capacity 42 MW

j) Plant Efficiency 88.25 %

k) Dry season Energy 94.54 GWh

l) Total Energy 337.88 GWh

m) Energy Price 4.5 NPr/unit (3% escalation in Energy Price for 9 years)

n) Cost of the project 7040.98 Million NPr

o) B/C Ratio 1.67

p) FIRR of the project 18.53

q) NPV 4,396,546

6.2.2 Alternative-II

This option is similar to feasibility study carried out by Nepal Electricity Authority. Water from

the tailrace pond proposed by Trisuli 3A HEP and passes to the headrace pipe and then to

Headrace tunnel. This is a shorter tunnel length option. The full supply level was fixed at

EL726.00 m. The tailrace water level is varies from 638.95 m to 640.13 m. The total number of

adit required is three. This alternative layout consists of the following physical parameters:


Tailrace outlet (Surface intake)


UT3A HEP to tunnel intake and tunnel intake.


r) Underground Conveyance 92 m horizontal tunnel after S/T, 47.81 m inclined

drop shaft, 311.3 m horizontal pressure tunnel after



inclined drop shaft followed by powerhouse and tailrace

d) Total length of Adit 1165.5m

e) Length of Tailrace tunnel 53 m

f) Design Discharge 51 m3/s

g) Total net head 83.32 m

h) Installed Capacity 36.0 MW

i) Plant Efficiency 86.83 %

j) Dry season Energy 81.17 GWh

k) Total Energy 289.81 GWh

l) Energy Price 4.5 NPr/unit (3% escalation in Energy Price for 9 years)

m) Cost of the project 6,457 Million NPr n) B/C Ratio 1.56

o) FIRR of the project 16.56

p) NPV 3,380,264

6.2.3 Alternative-III

This option is similar to feasibility study carried out by Nepal Electricity Authority, it has longer

tailrace channel to gain the head. Water from the tailrace pond proposed by Trisuli 3A HEP and

passes to the headrace pipe and then to Headrace tunnel. This is a shorter tunnel length option. .

The full supply level was fixed at EL726.00 m. The tailrace water level is varies from 634.58 m

to 635.43 m. the total number of adit required is three. This alternative layout consists of the

following physical parameters:


Tailrace outlet (Surface intake)


UT3A HEP to tunnel intake and tunnel intake.


d) Underground Conveyance 92.0 m horizontal tunnel after S/T, 52.51 m inclined

drop shaft, 311.3 m horizontal pressure tunnel after

inclined drop shaft followed by powerhouse and tailrace

e) Total length of Adit 1165.5 m

f) Length of Tailrace tunnel 179.84 m

g) Design Discharge 51 m3/s



h) Total net head 87.43 m

i) Installed Capacity 37.5 MW

j) Plant Efficiency 86.67 %

k) Dry season Energy 85.25 GWh

l) Total Energy 304.56 GWh

m) Energy Price 4.5 NPr/unit (3% escalation in Energy Price for 9 years)

n) Cost of the project 6742 Million NPr

o) B/C Ratio 1.57

p) FIRR of the project 16.75

q) NPV 3,595,820

6.3 P r e s e n t a t i o n of Recommended Layout

For the appraisal of the best alternative layout, a financial evaluations were carried out for all the

alternatives. The separate energy estimate is done for all the alternatives.

Table 6.2: summary of Cost Comparison of Different Layouts

Option Installed

Capacity

Base cost civil

(NPr)

Base cost

E/M (NPr)

Total Cost

including tax and

price

contingencies

(NPr)

B/C FIRR

I 42 MW 3,706,834,348

1,757,868,074 7,040,982,060 1.55 17.23%

II 36 MW 3,395,929,907

1,615,086,635 6,457,027,468 1.45 15.27%

III 37.5 MW 3,566,985,714

1,663,036,400 6,742,057,025 1.46 15.46%

The economic indicators were calculated on the basis of 4.5 NPr per kWh for energy values.

Based on the results of the economic analysis as shown in above table, Alternative I (longer

tunnel) option is better than other options.

Detail comparison studies of all the alternatives are given in Table 6.3.



Table 3: Details of Cost Comparison of different layouts

S.N. Description of Item Option I (42MW)

Option II (36MW)

Option III (37.5MW)

A Land & Support 210000000.00 210000000.00 210000000.00

B Pre-Operating Expenses & Management Cost

720000000.00 720000000.00 720000000.00

C Infrastructure Works 93358372.01 93358372.01 93358372.01

D Civil Cost

2,683,475,975.92

2,372,571,534.96

2,543,627,342.29 D1 General Items

272,800,000.00

272,800,000.00

272,800,000.00

D2 Main Civil Works

2,410,675,975.92

2,099,771,534.96

2,270,827,342.29 100

Head Pond at Tailrace of UT3A

141,313,974.08

141,313,974.08

141,313,974.08 200

Adit Tunnel-1

71,682,594.60

71,682,594.60

71,682,594.60 300

Adit Tunnel-2

46,459,700.74

61,736,091.32

61,736,091.32 400

Adit Tunnel-3

34,857,066.02

44,687,027.89

44,687,027.89 500

Headrace Pressure Pipe

133,113,563.53

133,113,563.53

133,113,563.53 900

Headrace Tunnel (Upto Surge Tank)

1,208,813,207.42

1,042,432,538.83

1,042,432,538.83 1000

Underground Surge Tank

113,601,089.16

113,601,089.16

113,601,089.16 1100

Valve Chamber & Access Tunnel

22,491,035.66

22,242,140.52

22,242,140.52 1700

Pressure Tunnel & Vertical Shaft

146,823,748.75

178,513,361.82

179,721,482.01 2600

Powerhouse

330,993,710.58

189,226,268.94

197,180,839.76 2700

Tailrace Conduit

97,389,898.20

38,086,497.09

199,979,613.43 2800

Tailrace Pond

43,460,900.12

43,460,900.12

43,460,900.12 3000

Switchyard (Civil Works)

19,675,487.06

19,675,487.06

19,675,487.06 E

Hydro Mechanical Cost

451,363,073.81

495,225,206.65

496,514,078.31 3200

Gates/Stoplogs/Valve

142,728,782.28

142,728,782.28

142,728,782.28 3300

Steel Lining in Pressure Shaft

164,568,649.58

208,430,782.41

209,719,654.08 3400

Headrace Pressure Pipe

142,982,920.15

142,982,920.15

142,982,920.15 3500

Trash Rack

301,497.89

301,497.89

301,497.89 3600 Air Suction Pipe (Surge Tank to

Valve Chamber)

781,223.91

781,223.91

781,223.91



F Electro-Mechanical Cost

1,306,505,000.00

1,119,861,428.57

1,166,522,321.43

3700 Turbine Equipment

388,858,750.00

333,307,500.00

347,195,312.50

3800 Generator

521,360,000.00

446,880,000.00

465,500,000.00

3900 Auxiliaries - Hydraulic Equipment

27,431,250.00

23,512,500.00

24,492,187.50

4000 Auxiliaries - Electrical Equipment

359,955,000.00

308,532,857.14

321,388,392.86

4100 Gantry Crane

8,900,000.00

7,628,571.43

7,946,428.57

G 132kV Single Circuit Transmission Line and bay extension and metering arrangement in Trishuli 3B Hub

28,500,000.00

28,500,000.00

28,500,000.00

Total (A+B+C+D+E+F+G)

5,493,202,421.74

5,039,516,542.19

5,258,522,114.05

VAT @ 1% (E/M, H/M &Transmission Line) & @13% in others

499,752,145.97

457,906,754.26

480,623,506.86

Base Cost as of 2013

5,992,954,567.71

5,497,423,296.45

5,739,145,620.90

Physical Contingencies

460,001,839.00

420,347,323.00

439,850,392.00

5.0 % of E/M &H/M Works and Transmission Line

89,318,403.69

80,754,331.76

83,151,819.99

10.0 % of Main Civil Works & Others

370,683,434.79

339,592,990.70

356,698,571.43

Total Cost as of 2013

6,452,956,407.00

5,917,770,620.00

6,178,996,013.00

Taxes & Duties (1.5%)

96,794,346.11

88,766,559.30

92,684,940.20

Total Cost with Taxes & Duties

6,549,750,753.11

6,006,537,179.30

6,271,680,953.20

Price Contingencies (7.5%)

491,231,306.48

450,490,288.45

470,376,071.49

Total escalated cost at the end of the construction

7,040,982,060.00

6,457,027,467.75

6,742,057,024.68

Interest during construction (10%)

704,098,206.00

645,702,746.77

674,205,702.47

Total financial cost of the project at the end of Construction NRs.

7,745,080,266.00

7,102,730,215.00

7,416,262,728.00

Exchange Rate 1 US$ is equivalent to NRs. 95.00

95 95 95

Total financial cost of the project at the end of construction in US$.:

81,527,161 74,765,581 78,065,923

Specific Cost of the project (US $ / kW):

1,941 2,077 2,082

B/C Ratio 1.55 1.45 1.46

FIRR 17.23 15.27 15.46


7-1

Trisuli Jalvidyut Company Limited

Chapter 7:

Project Design and Description

7.1 General

This project is a tailrace cascade development of Upper Trisuli 3A Hydroelectric Project (60 MW).

The discharge from the tailrace of Upper Trisuli 3A Hydroelectric Project (UT3A HEP) is conveyed

to the head pond of Upper Trisuli 3B Hydroelectric Project (UT3B HEP) located in the tailrace

outlet of UT3A HEP, downstream side. The Upper Trisuli 3A HEP tailrace pond or the head pond

for Upper Trisuli 3B has been arranged in such a way that the flow from the tailrace outlet of UT3A

HEP is released into the UT3B HEP surface headpond. The intake to the headrace pipe of Upper

Trisuli 3B Hydroelectric Project is located at the southern end of the headpond. The maximum

gross head is 99.31 m with a reference to a head water level of EL 726 masl and tail water level of

EL 626.69 masl.

The length of headrace pipe from intake pond to the tunnel entry is 384.27 m including 20 m

concrete duct. The headrace tunnel is 3744.694 m long and has two Adits. The surge tank is located

at 150 m northwest of the powerhouse. The water conveyance from surge tank to powerhouse

comprises of pressure tunnel, drop shaft and pressure tunnel after drop shaft. The semi surface

powerhouse is located on the right bank of Trisuli, 3 km upstream of Betrawati. The tailrace consists

of a 123.93 m long cut and cover conduit which finally discharges the flow into Trisuli River. The

switch yard is located in front of the powerhouse. The Trisuli 3B hub, 220 kV, is under

construction, located near the Shanti Bazar, is 3 km far from the Trisuli 3B HEP powerhouse site.

This hub is used to evacuate the power from Upper Trisuli 3B HEP.

7.2 Design Basis

The layout optimization has been carried out to confirm the best alternative of Trisuli 3B HEP. The

alternative option I is the final layout option, which has the following arrangement of project

components configuration,


7-2


a) Headrace pipe after Trisuli 3B tailrace pond

The intake of Trsuli 3B HEP is comprising of a Trisuli 3A tailrace pond, this pond is directly

connected to the headrace pipe via square concrete conduit. The length of headrace pipe is

464.27 m.

b) Headrace tunnel

Consisting of 3744.69 m long headrace tunnel before surge tank.

c) Surge tank,

Diameter and height of surge tank is 15 m and 37.4 m respectively.

d) Pressure Tunnel after surge tank,

Consisting of 98.17 m long pressure tunnel after surge tank.

e) Drop shaft

Consisting of 69.07 m long vertical pressure shaft

f) Pressure tunnel before powerhouse

Consisting of 181.65 m long horizontal pressure tunnel

g) Semi surface powerhouse

A semi surface powerhouse with two Francis turbines with a total installed capacity of 42

MW

h) Tailrace box canal. 123.93 m long box canal

The project structures lie entirely on the right bank of Trisuli River. The planning and hydraulic

design for Upper Trisuli 3B Hydroelectric Project is governed by the design discharge of Upper

Trisuli 3A Hydroelectric Project. The general arrangement of the whole project is as shown in DWG

NO UT3B HEP-02.

7.3 Description of Project Components

7.3.1 Project Access

Upper Trisuli 3B Hydroelectric Project has a good road infrastructure. As this project is envisaged to

be constructed during Upper Trisuli 3A HEP construction, the basic infrastructures are already

there. The access road from Tupche bazaar to the powerhouse area is a track road newly

constructed. This road needs upgrading. The powerhouse is also well accessible from Betrawati


7-3


Bazar via new bridge on Trisuli river. The new bridge is constructed across the Trisuli at about 700

m upstream of the tailrace outlet of Upper Trisuli 3B Hydroelectric Project. The road will then use

the right bank of Trisuli to reach the intake pond area. This road is built by UT3A HEP.

The project road of 1.447 km length needs to be built for the project construction purpose, which

comprises of roads in surge tank adit, powerhouse area, road diversion. The project road is shown in

DWG NO UT3B-HEP-14 and details are shown in DWG NO UT3B-HEP-35 to 42.

7.3.2 River Diversion

Since the tailrace pond of Trisuli-3A HEP acts as the intake portal of Trisuli 3B HEP, the river

diversion is not required for the construction of the intake. Similarly, no diversion structures will

be required for the construction of the powerhouse as well. However, for the construction of

tailrace pond of Trisuli 3B HEP, the diversion of Trisuli river is required. The river diversion plan at

the tailrace pond is shown in DWG NO UT3B-HEP-28 and 29.

7.3.3 Headpond/Intake Portal

The intake portal or head pond is downstream of Upper Trisuli 3A HEP tailrace connected to the

headrace pipe of UT3B HEP. The construction of intake portal shall be done by the Trisuli 3A

HEP. The layout plan of intake portal and headrace pipe is shown in DWG NO UT3B-HEP-06 and

08. In this design phase, the surface area and volume of head pond adopted is 1888.6 m2 and 11200

m3 respectively. In the study of Upper Trisuli 3A HEP, the volume of the pond estimated is 8260

m3.

The pondage area located immediately downstream of the tailrace outlet for Upper Trisuli 3A

Hydroelectric Project will act as the tailrace pond for UT3AHEP and will function as the headpond

for Upper Trisuli 3B Hydroelectric Project. The intake pond is controlled by the vertical lift gate

provided at the inlet to the headrace pipe of UT3B HEP. The upstream part of the headrace pipe

consist of concrete duct rectangular in shape while the downstream part of the headrace pipe is

steel penstock pipe with concrete cover. As the upper reaches of Trisuli River along the headpond

is comparatively narrower than the lower reaches this arrangement will prevent any damage to the


7-4


headrace pipe structure and will maintain a safe passage for the 1:1000 year.

The invert level of the intake is kept at EL 714.90 masl whereas the deck level of intake is at EL

729.00 masl. The height of the pond intake varies from 8 m to 16.8 m.

For insuring minimum required head for the submergence, the tailrace pond of UT3A HEP is

modified into the head pond for UT3B HEP. Originally, the invert level of tailrace pond is at El.

721.0. To insure the sufficient submergence at the intake, the invert bed level of pond is lower down

to El. 712.2 msl. The slope length of tailrace pond is 17.6 m having slope of 0.5 H: 1V. The

remaining 13 m of the pond invert level is fixed at El 712.2 msl. The normal water level at UT3A

HEP. The Full supply level of tailrace pond has been set as 726 msl. The submergence depth of 6 m

from the crown level of concrete pressure duct. The length of the concrete duct is 20 m from the

bell mouth entry. The pressure pipe has been proposed after the concrete duct. The length and

diameter of concrete cover steel pipe diameter are 364.27 m and 5.1 m respectively. The longitudinal

section of headpond and box duct are shown in DWG NO UT3B-HEP-09 and 10 respectively.

Since the depth of the pond is lower down to 712.2 msl from 721.0 msl, the volume of the pond has

been increased to 11200 m3 from 8260 m3. This modification of head pond has to be done by Upper

Trisuli 3A HEP.

Hydraulic Steel Structures

The intake will have the following hydraulic steel structures:

• Trashrack

• Fixed wheeled gate

• Stoplogs

One set of fixed wheel gates and stoplog will be provided at the entrance to the headrace tunnel.

The gate will be operated from the operating platform constructed at an elevation of EL 729.00

masl. A sliding slot will be provided along its height to slide the gate and stop logs to its position in

the headrace pipe. A 5.0 m wide permanent access road connects this operating platform with the


7-5


main access road.

Trashrack

The intake gates will be provided with a set of trashracks to prevent the entry of debris. The

submergence depth of 6 m from the crown level of pressure pipe has been proposed for the

pressure pipe diameter of 5.1 m. The trash rack bar spacing of 20 cm clear span is proposed at the

start of bell mouth entry for checking the entry of large sized unwanted debris.

Stoplogs

Stoplog will be provided at the intake of the headrace tunnel just upstream of the intake of the

headrace pipe. These will have a clear width of 5.1 m and a height of 5.1 m. The stoplog will be

operated with the help of hoisting devices installed at the operating platform.

Fixed Wheeled Gates

A fixed wheeled vertical sliding gate will be installed at the start of headrace pipe in order to enable

maintenance work. The gate has a clear width of 5.1 m and a height of 5.1 m. The sill level of the

gate is at an elevation of EL 714.90 masl. It will be operated with the help of a proper

hoisting device installed at the operating platform.

7.3.4 Headrace Pipe

For the purpose of passing design discharge of 51 m3/s from the UT3A HEP tailrace pond to inlet

of UT3B HEP, steel pressure pipe with concrete cover has been adopted in the design. The pressure

pipe is covered by structural concrete box of pentagonal shape. The minimum thickness of 0.75 m

has to be ensured in case of concrete cover box for pressure pipe. The thickness of the pressure pipe

has obtained as 14 mm. The internal dimension of the pressure has been designed to be circular

shaped of 5.1 m.

The water collected at intake is conveyed to the intake box duct which is ultimately connected to

the headrace p ipe . The intake box duct is lined with a 1.0 m thick concrete and the size of the

box duct is 5.1 m x 5.1 m. The square portion of pressure pipe covers the total length of 20.0 m

including transition to circular shaped steel pipe. After the transition headrace pressure pipe of

length 364.27 m follows by to tunnel inlet portal. After this the headrace tunnel starts. The circular


7-6


headrace pipe has a diameter of 5.1 m. The layout plan of headrace pipe is shown in DWG NO

UT3B-HEP-06.

There are two minor bends at the pressure pipe whose arc lengths, deflection angles and bend radius

are shown in Table 7.1:

Table 7.1: Bend Characteristics of Headrace Pressure Pipe Bend No

IP Coordinates Radius of Bend

(R) m Length of bend

(m) Deflection Angle

1 X= 616829.903 m Y= 3101160.749 m

5 0.68 7.833°

2 X= 616732.362m Y= 3101046.187m 10 4.23 24.255°

Crossing

The headrace pipe crosses the Kholsi from Paire Gaun at chainage 0+073.29. The discharge from

this Kholsi at 5 years return period is 2.18 m3/s. This flood is being diverted through the

construction of aqueduct crossing over the headrace pipe. The arrangements are shown in DWG

NO UT3B-HEP-11 and 12.


The water conveyance from the tunnel intake portal (end of headrace pipe) to the surge tank is the

combination of shotcrete lined and concrete lined tunnel. The optimized diameter of 5.5 m (circular)

and 6.6 m (horse shoe) diameter for concrete lined section and shotcrete lined section were adopted

respectively. The slope and the total length of the headrace tunnel are 0.315 % and 3744.694 m

respectively. The layout plan and longitudinal section are shown in DWG No UT3B-HEP-02 and

details of chainage are shown in DWG No UT3B-HEP-02(A) to 02(D).

The headrace tunnel crosses three major Kholsi. The tunnel alignment crosses these Kholsi above at

about 100 m. The characteristics of these Kholsi are given below:


7-7


S. No.

Name of Kholsi

Catchment Area (km2)

Kholsi at Chainage 1:100 Year flood (m3/s)

1 Torme Khola 2.20 0+744.54 24.46 2 Andheri Khola 9.08 0+907.22 81.29 3 Sukaura Khola 3.905 1+720.37 39.91

As per the geotechnical study, concrete lined section is required in rock support class IV and V

while the shotcrete lined section is found to be sufficient in rock support class II and III. The

lengths of different type of rock support in headrace tunnel are shown in Table 7.2 below. The

geotechnical design of headrace tunnel are shown in “Rock Support Design-October 2013”. The

details of headrace tunnel have been illustrated in the Table 7.3 given below:

Table 7.2: Lengths of different rock class in headrace tunnel

Support Class II

Support Class III

Support Class IV

Support Class V

788.25 m 1970.35 m 729.64 m 256.45 m

As per the description of the rock support type, the different type of cross sections are shown in

DWG No UT3B-HEP-13.

Table 7.3: Description of Headrace Tunnel before surge tank

Description of Item Parameters

Total Length of Headrace Tunnel 3744.694 mSlope 0.315%Length of Concrete lined section 1971.271 m (52.6%)Length of Shotcrete lined section 1773.423 m (46.4 %)Invert Level Elevation at the beginning of the sloped portion of headrace tunnel

El. 713.9 msl

Invert Level Elevation at the end of the sloped portion of headrace tunnel El. 702.5 msl

The headrace tunnel has four numbers of horizontal bends whose details are illustrated in table 7.4 given below.


7-8


Table 7.4: Details of Horizontal bends for both alternatives Bend Chainage Invert El. Length Radius Def. Angle Coordinates

1 0+532.0 714.4 2.1m 8.25m 14° 18' 32" X= 616521.82 m, Y= 3100877.7 m

2 0+938.79 713.00 4.7 m 8.25m 32° 18' 45" X= 616127.411 m Y= 3100776.402 m

3 1+771.3 709.9 2.5 m 8.25m 17° 34' 39" X= 615928.964 m Y= 3099967.298 m

4 3+980.47 702.61 6.4 m 8.25 m 44 °35 '38 " X= 616075.252 m Y= 3097762.85 m

Rock trap

Since the headrace tunnel has 46.4 % of shocrete lined tunnel, the wedge failure lead to the shotcrete

or rock fall inside the tunnel. This type of lump material shall be trap into the rock trap. The width

and height of the rock trap is 5.5 m and 7.2 m respectively, whereas the length of the rock trap is 30

m. The distance between rock trap and surge tank is 61.9 m. The details of rock trap is shown in the

DWG No UT3B HEP- 15.

7.3.6 Surge Shaft/Tank

The type of surge tank is restricted orifice type of surge tank for the selected option. The design of

cross section of the surge tank is based on the D Thoma criteria limit cross sectional area method

which considers the pressure parameters of the power tunnels. The location of surge shaft is chosen

as per adequacy of required rock cover over the roof of surge shaft. The adopted diameter of surge

tank and its throttle diameter are of 15 m and 2.0 m respectively. The details of rock support design

of surge tank is given in “ Rock Support Design – October 2013”. The detail dimensions as well as

elevations of various water levels in the design of surge shaft are listed below:

Table 7.5: Description of designed surge tank Diameter of Surge shaft 15 m

Throttling Diameter 2.0 m

Maximum Upsurge 15.57 m

Maximum Down surge 9.1 m

Maximum Upsurge Level 738.9 msl

Minimum Down surge Level 714.22 msl


7-9


Invert Level of tunnel floor at Centre line of Surge shaft 702.5 msl

Hydrostatic Water level at surge shaft 726 msl

Hydrodynamic Water Level at Surge shaft 723.32 msl

The crown level of the surge shaft has been fixed at EL 747.40 msl. The total height of surge shaft

from the crown of the headrace tunnel up to the base of surge shaft is 37.4 m. The surge shaft will

have a 20 cm thick shotcrete and a 50 cm thick reinforced concrete lining. The excavated diameter

of the surge shaft is estimated to be 16.4 m.

For the purpose of emptying the pressure tunnel a butterfly valve with air suction pipe is proposed

at 30 m downstream of surge tank.

Construction of the surge shaft will be carried out through Adit No. 2 located near the rock trap

of tunnel. Details of the surge tank are presented in the in DWG NO UT3B-HEP - 14, 16 and 18.

7.3.7 Pressure Tunnel after Surge Tank

The length of the pressure tunnel after surge tank to drop shaft is 98.17 m including valve chamber

cavern and transition from concrete line tunnel to steel lined tunnel and is basically a continuation

of the headrace tunnel. In the transition length the diameter of tunnel changes from 5.5 m to 4.2 m,

first is concrete lined tunnel and second is steel lined tunnel with concrete reinforced. The thickness

of steel lined tunnel after valve chamber is 66.87 m and the thickness of steel line is 14 mm.

The distance between valve chamber and surge tank is 31.3 m. The cavern size of the valve chamber

is 15.4 m long, 7 m wide and 11.9 m height which is accessible through adit no. 2. The valve

chamber is equipped with the butterfly valve and its diameter is 3.5 m. Provision of this valve will

enable dewatering of water in the vertical shaft without having to empty the water in the surge

tank. The invert level of the valve chamber is at El. 699.15. Layout plan of Valve chamber is

presented in the DWG NO UT3B-HEP - 19.


7-10


7.3.8 Drop Shaft and Horizontal Pressure Tunnel

Total length of vertical shaft is 69.07 m including the bends. The vertical shaft is fully steel lined

and provided with concrete backfill of 30 cm thickness. The diameter of vertical shaft is 4.2 m.

The steel lined thickness varies from 14 mm to 18 mm at end of drop shaft. Steel thickness is based

on the assumption that 50% of the stress is catered by the rock and remaining 50 % only by the steel

lining.

The horizontal pressure tunnel from the end of drop shaft to the penstock bifurcation is 181.65 m.

The thickness of steel lined is 18 mm along the horizontal pressure tunnel. The shape of the

excavation along the horizontal pressure is D-shape and finished diameter is the circular. Both

horizontal pressure tunnel have been proposed to be excavated in downward slope of -7 % so as to

reduce the vertical drop shaft height. Layout plan section of vertical shaft and Pressure tunnel are

shown in DWG NO UT3B-HEP – 14 and 16 respectively.

Table 7.6: Description of water conveyance after surge tank

Description

Pressure Tunnel after

S/T(including Transition length

of 8.2 m)

Vertical Pressure Shaft (including

Curve Part)

Pressure Tunnel after

Vertical Pressure Shaft

Manifolds after

Bifurcation

Length 98.17 m 69.07 m 181.65 m 49.32 m

Diameter 4.2 m 4.2 m 4.2 m 3.0 m

Steel Thickness 14 mm

14mm (L =29.07m) 16mm (L= 20m) 18mm (L=20m)

18 mm 28 mm

There are two almost right angled bends in the vertical shaft whose details are shown in Table 7.7 given below:- Table 7.7: Details of Pressure Shaft Bends (Vertical Shaft Option) 1st Bend and 2nd Bend

Arc Length of bend 9.46 m

Radius of Bend 6.3 m

Deflection angle 85 ° 55' 49"


7-11


7.3.9 Manifolds

Manifolds will be provided at the end of the horizontal pressure tunnel. This will feed the discharge

into each turbine. The diameter of the last portion of the manifold which will directly feed the water

to the turbine is estimated to be 3.0 meter. The thickness of the steel lining in this portion is

estimated to be 28 mm. Total length of manifold is 49.23 m including transition. The symmetrical

type of Y branching has been proposed in our case. The angle between the Wye Branching has been

adopted as 55° to avoid the grater head loss at the bifurcation point. Longitudinal section and layout

plan of bifurcation are presented in DWG NO UT3B-HEP – 21 and 25 respectively.

7.3.10 Powerhouse

The proposed semi surface powerhouse is located about 0.6 km upstream of the Salankhu and

Trisuli confluence on the right bank of Trisuli River. The powerhouse site is situated on

cultivated terrace and is founded on bed rock. The area comprises of terrace deposits on the surface

with bedrock at a depth of about 37.5 m below the ground. The powerhouse accommodates two

Francis turbine generators with a total capacity of 42 MW and ancillary facilities for control and

protection. Considering the topography, utilization of maximum head and structural stability, the

powerhouse will be semi-underground concrete box structure. The powerhouse location is so

chosen that availability of the rock foundation is ensured. Thus the powerhouse will be designed on

rock foundation.

The overall layout of the powerhouse complex including the horizontal pressure tunnel and tailrace

is presented in DWG. No. UT3B HEP-14.

The powerhouse dimensions have been fixed based on the space requirement for electro-mechanical

items. The spacing of the turbines, dimension of the spiral casings, space for service and

maintenance of equipment, the geometry of the bifurcation, inlet penstock pipe and outlet

arrangement, etc have been considered in the dimensioning of the powerhouse. The machine block

rest on south-west portion of powerhouse complex and its dimensions is 25.6m (L) X 14m (W) X

26.9 m (H). Erection bay block lies at north-west corner and its dimension is 12 m (L) X 14 m (W)

X 9.2 m (H). The control building lies at North-East corner of powerhouse complex whose


7-12


dimensions are 12m (L) X 9.6 m (W) X 12.7m (H). Following design parameters are listed below for

the sizing of powerhouse.

The powerhouse contains two vertical 21 MW Francis turbine/generator units, spaced at 12 meters

centers, associated electrical and mechanical equipment, a service bay and a control room. The

erection bay lies one floor (3.0 m) above the machine hall floor and is connected with the access

road. The powerhouse accommodates the control building on the west side. Two draft tubes

discharge into individual draft tubes and ultimately to the single tailrace via a manifold.

Table 7.8: Design parameters for sizing of Powerhouse

Gross head 99.31 m

Net head 95.13 m

Design discharge 51 m3/s

Turbine efficiency 0.92

Rated speed 375 rpm

Specific Speed 213.96 rpm

Normal tail water level 626.86 msl

No of Poles 16

Outer Diameter of Turbine Runner (D3) 1.86 m

Length, breadth, height of Powerhouse 37.6 m, 14 m, 28.4 m

Elevation of Drainage Floor 620.50 msl

Elevation of Valve Floor 621.45 msl

Elevation of Turbine Floor 625.35 msl

Elevation of Generator Floor 630.70 msl

Elevation of Machine Hall Floor 633.70 msl

Elevation of Erection Bay Floor 637.20 msl

Elevation of Basement Floor of Control Building 637.20 msl

First Floor Level of Control Building 640.70 msl

Second Floor Level of Control Building 643.40 msl

Roof Top Level of Control Building 648.40 msl


7-13


The turbine centre line has been fixed based on the annual monsoon flood level in tailrace outlet

and turbine setting requirement to prevent cavitations. The control building arrangement has been

fixed based on the space requirement for installation of different controlling equipment and other

general purpose usage. The generator floor level has been fixed above the High Flood level of

recurrence period of 1000 years. The elevation equivalent to 1:1000 years return period flood of

4030 m3/s came out to be 630.10 msl. The rating curve is also utilized in fixing the maximum tail

water at Tailrace outlet corresponding to the annual mean river flow of 603.8 m3/s.

The layouts of different floor levels are illustrated in DWG. No. UT3B HEP-23, 24, 25 and 26 while

the cross sections are shown in DWG. No. UT3b HEP-21 and 22.

Erection Bay and Workshop

The erection bay and the workshop at EL 637.20 m accommodate the turbine and generator

components during erection of the units and future maintenance periods. Space is provided for

vehicular access, assembly of the draft tube liner, the turbine stay ring, the head cover of the

main shaft, the guide bearing and the rotor. This area also serves as a lay down area for the

runner. It is anticipated that the generator stators will be wound and piled within the generator pits.

The workshop will be located adjacent to the erection bay in the same level. The 11kV switchgear

room, the DC supply room and the battery charger are also accommodated in the service building

on this floor.

Machine Hall floor

The machine hall floor located at an elevation of EL 633.7 masl. The machine hall is 14 m wide, by

35.3 m long and 13.7 m high, covering the combined area of the generator floor and the service bay.

The powerhouse crane spans 12.5 m and is supported on reinforced concrete columns. The Gantry

Crane has a capacity of 75 ton / 5 ton.

The machine floor is provided with removable steel grating near the machines. Two octagonal

enclosures house the generators between the elevation of EL 630.7 masl and the elevation of EL

633.7 masl respectively. Equipment hatches between the 2 units provide crane access to the turbine


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floor and the service area. The unit control panels are located adjacent to the excitation panels.

Generator Floor

This floor at EL 630.7 m provides access to the lower part of the generator. The generator is

supported on bearing pads just beneath this floor.

Turbine Floor

The turbine floor is at EL 625.35 m and is accessible via stairs located in between the units. The

equipment hatch located in between the two units provides crane access to the turbine floor level

for removal of the turbine runners without dismantling the generator. Hatches will also be

provided for the removal of the inlet valves. A concrete barrel with a diameter of 6.2 m supports the

generator bearings. Access to the power shaft and the turbine runner will be provided through

openings in the concrete barrel. Governors of the turbine are provided on this floor along with its

accessories.

Valve Floor

This is located at EL 621.45 m and covers the support of inlet butterfly valves at EL 635.3 m as well.

Drainage Gallery Floor

The drainage gallery floor is located at an elevation of EL 620.5 masl. This gallery is located in

between the two units and contains the drainage sumps and the dewatering pumps. Access to the

draft tube of each unit will be provided through a manhole. Access to the powerhouse crane for

lifting equipment is available adjacent to the units.

Two numbers of draft tube gates each with a dimension of 5 m x 2.8 m will be provided at the

end of the draft tube.


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Control Room and Accessories

A control room with electrical utilities and office facilities will be provided at the service

building adjacent to the entrance to the powerhouse. The control room at an elevation of EL

637.2 masl overlooks the generator hall and contains all the necessary equipment to control the

powerhouse operation and monitor the operation of the headworks structures.

7.3.11 Draft Tube

The elbow type draft tube has been adopted in this project. The elbow type of draft mainly

comprised of the three parts i.e. vertical part in circular cross section, bend part in gradual transition

from the circular section into rectangular section and an almost horizontal part in rectangular

section, gradually expanding to direct the flow into tailrace. The recommended empirical relations

suggested by de Siervo and de Leva (1976) as shown above have been adopted for obtaining

dimensions of an elbow-type draft tube.

Table 7.9: Design parameters for Draft tube Total Length of the both Draft tubes 43.32 m

Type of Draft Tube Elbow type Draft tube

Diameter of the Elbow Varies from 1.86m to 4.5 m

Radius of inner bend 1.3 m

Radius of outer bend 1.85 m

Final Width of Draft Tube 4.5 m

Final Depth of Draft Tube 4.5 m

Invert Level of Draft tube 618.2 msl

Centre line Elevation of Penstock Pipe 623.3 msl

7.3.12 Tailrace Conduit The tailrace comprises of two individual conduits from the draft tube gates that are j o ined

into a single box conduits. The tailrace conduit is designed as pressure flow conduit of square

shaped .The dimension of the square shaped tailrace conduit has adopted as 4.5 m X 4.5 m. The


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length of the tailrace conduit is 123.93 m and has a 1.2 m thick RCC lining. Details of the tailrace

conduit and outlet structure are shown in DWG. NO. UT3B HEP-17.

7.3.13 Tailrace Outlet Pond The tailrace outlet is the final hydraulic structure which helps in conveying discharge from tailrace

conduit back to the river flow. The control gate has been provided at the end of the tailrace conduit

for dewatering tailrace conduit during maintenance of conduit. The dimension of vertical lift gate

will be 5.5 m X 5.5 m. For the purpose of diminishing the exit head loss the exit dimension from

tailrace conduit has been enlarged from 4.5m X 4.5m to 5.5 m X 5.5 m. The dimension of levelled

floor section is 20m (L) X varying H from 12.7 to 7.2 m and varying width of 5.5 m to 20 m. The

elevation of floor at Tailrace Pond is 618.62 msl. The weir is raised at the outlet point at outlet

portion for the purpose of blocking the sediment load entering the tailrace pond. The details of

tailrace outlet are shown in DWG. No. UT3B HEP-28 and 29.

Table 7.10: Design parameters for tailrace Outlet Pond Lowest Level of Tailrace Outlet 620.315 msl Exit Velocity 1.685 m/s Max Water Level at Pond 627.91 msl Mean Water Level at Pond 626.49 msl Crest Elevation at outlet to river 625.815 msl Exit Loss 0.14 m

Tailrace Gate

The outlet structure will have one fixed wheeled gates installed at the end of the tailrace outlet. These gates

will be fully opened to allow the design discharge to pass from the tailrace conduit into the river. The size of

the gates will be 5.5 m x 5.5 m and will be operated with the help of a hoisting device installed at the

operating platform. The details of adit-1 are shown in DWG. No. UT3B HEP-30.


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7.3.14 Adit Tunnels Adit Tunnel-1: adit tunnel to middle of headrace tunnel

The first adit tunnel is for the middle of the headrace tunnel and it is at the chainage 1+771.3 m.

The length of adit-1 is 463.6 m, D-shape, 4 m diameter slope toward the headrace tunnel (S= +1.479 %).

The details of adit-1 are shown in DWG. No. UT3B HEP-30.

Adit Tunnel-2: adit tunnel near the surge tank

The second adit tunnel is at the end of the headrace tunnel and it is at the chainage 4+060.75 m. The

length of adit-2 is 288.9 m, D-shape, 4 m diameter slope is toward of the headrace tunnel (S= + 7.962 %).

The details of adit-2 are shown in DWG. No. UT3B HEP-31 and 32.

Adit Tunnel-3: adit tunnel at the surge tank crown

The third adit tunnel is at the crown of the surge tank. The length of adit-3 tunnel is 191.6 m, D-shape,

4 m diameter, height 4 m, slope is toward of the headrace tunnel (S= + 8.99 %). The details of adit-3 are

shown in DWG. No. UT3B HEP-33 and 34.

7.4 Generating Equipment

7.4.1 Mechanical Equipment

Among the various items of the powerhouse mechanical equipment, the main and the most

important component is the runner. The selection criteria and parameters of the runner are the

function of the rated head of the power plant, under which it is supposed to run and act as the

prime mover. So, the determination of the rated head becomes an important aspect.

7.4.1.1 Initial Data

The Following initial data have been used for the computation of rated head and the turbine type:

Full supply level 726.0 m

Minimum operating level 726.0 m

Tail water level 626.86 m

Installed capacity 42.0 MW


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7.4.1.2 Turbine Selection

The selection of the type of turbine primarily depends upon the rated head for the generating

unit. As confirmed above, a Francis turbine with a vertical axis is the turbine of choice for the net

head of 95.13 meters available for the project.

7.4.1.3 Unit Capacity

The total output capacity of the project is calculated to be 42 MW. Generally, unit capacity is chosen

in such a way that a minimum number of units can be installed with the assumption that it will result

in a more economical condition for the project, the upper limiting factor being the system capacity.

The present system capacity of the national grid of Nepal allows the installation of units up to the

capacity of 75 MW.

On the other hand, a single unit is not preferred due to the fact that total generation loss will

occur in time of the unit breakdown. Besides, various guidelines give the value for minimum output

for continuous operation for Francis turbine as 50 %.

So, two generating units, capable of generating 21 MW each, are selected. A minimum rated turbine

power of 25 MW will be required at the generator shaft as the value of generator and transformer

efficiencies being equal to 96 % and 99 % respectively.

7.4.1.4 Turbine Speed

The calculated specific speed for the given net head of 95.13 is 213.96 and the corresponding

turbine speed is 375 rpm. The calculated runway speed is 562.5 rpm for a frequency of 50 Hz.

7.4.1.5 Powerhouse Dimensions and Unit Parameters

The computed discharge diameter of the runner for each unit is 1.90 m. The runaway speed of the

turbine is 562.5 rpm. The static head at the runner distributor center line is equal to 2.18 m with the

value of Thoma cavitation coefficient being calculated as 0.13. Sixteen poles have been adopted in


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the rotor of the generator.

The unit-to-unit center line distance is a function of the installed capacity and the net head, the

calculated value of which comes to be 12 m. The span of the overhead travelling crane is computed

to be 13.5 m. In order to accommodate various other auxiliary structures a floor area of

approximately 490 m2 has been provided.

7.4.1.6 Turbine

The turbine will have a single runner attached to the end of the turbine shaft. The runner will be

made of integrally cast solid steel of minimum 13% chromium and 4 % nickel. The runner will be

protected against erosion by a coating of carbide-metal material deposited on it by a high

velocity oxygen fuel thermal spray process to a thickness of 0.4 mm.

The guide bearing will be of self-oil-lubricated type. It will be designed to withstand without damage,

the natural retardation of the turbine and generator from maximum runaway speed to rest

without the use of the brakes. The lining material of the bearing shell will be suitable high- grade

anti-friction metal securely anchored to the shell, grooved for lubricant circulation and accurately

bored for a proper fit on the shaft.

Guide vanes will be designed for the appropriate hydraulic pressure and constructed to produce the

most uniform flow possible of water. They will be mechanically linked with a servomotor and

operated under the appropriate command of the governor. The guide vanes will be made of cast

stainless steel of 13% chromium and 4% nickel. They will be protected against erosion by a coating

of carbide-metal material deposited on them by a high velocity oxygen fuel thermal spray

process to a thickness of 0.4 mm.

7.4.1.7 Governor

Each turbine will be supplied with an electro- evice, electro-hydraulic actuator etc. required for

regulating the speed and controlling the openings of the guide vanes of the turbine.


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The maximum momentary speed rise caused by sudden full load rejection of two units under any

net head will not exceed 85% of rated speed. The maximum momentary pressure rise, when the full

load of two units is thrown off under any conditions, will not exceed 25% of maximum gross head.

7.4.1.8 Inlet Valve

One set of butterfly valve operated by a servomotor will be installed for each turbine unit as the

inlet valve. The pressurized oil for the servomotor will be supplied from the high-pressure oil

system. The servomotor shall be of double-acting type. The opening and closing times of the

inlet valve will be adjustable.

Each inlet valve will be supplied with a pressurized-oil operated needle - type valve and a by- pass

valve. A mechanical locking device will be provided on the servomotor so that the inlet valve could

not be opened inadvertently. The diameter of inlet valve is 2.10 m. The layout plan of Inlet valve are

shown in DWG. No. UT3B HEP-23.

7.4.1.9 High Pressure Oil System

Each set of generating unit will have a high pressure oil system, which will consist of two sets of

direct-coupled alternating current motor-driven self-priming pump of sufficient capacity, one acting

as the main and the other as the stand-by. It will supply the pressure oil to the pressure tank

from the sump tank through a strainer. Each pump will be equipped with a check valve and a

safety release valve. The pressure tank supplies the necessary amount of oil under the required

pressure to the governor and the inlet valve servomotors.

The main pump automatically starts pumping, when the pressure in the pressure tank goes below a

preset value. If, it still goes down to another preset value, both the pumps operate simultaneously.

When the pressure rises to a fixed pressure, the pumps automatically stop. These preset values can

be adjusted as per requirements. The control of these operations is carried out through pressure

switches.


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7.4.1.10 Lubricating Oil System

The lubricating oil system will consists of necessary equipment for supplying and cooling the oil for

all guide and thrust bearings of the generating units. The oil will be pressure-fed to the bearings.

Lubricating oil used for guide bearings will be forced-cooled by circulating the oil through heat

exchangers with the help of oil pumps. Cooling of the thrust bearing lubricating oil will be

carried out by using at least two oil coolers of sufficient capacity for each unit.

The lubricating oil cooling system will be designed in such a way that the maximum temperature of

the bearings will not exceed 650C under continuous operation.

7.4.1.11 Cooling Water System

The cooling water system provides necessary amount of cooling water for lubricating oil coolers,

generator air coolers, transformer oil coolers, and oil sump tank coolers.

The water will be tapped from each of the penstock and passed through a pressure-reducing

valve. Two sets of strainers, one on duty and one as stand-by, of appropriate size will be

provided for each unit. Then it will lead through a common header pipe, after which it will

branch out to individual generating units.

7.4.1.12 Drainage and Dewatering System

All leakage and drainage water in the powerhouse will be collected in a sump pit constructed at the

lowermost floor to an appropriate level. Two drainage pumps, one main and the other stand- by, of

submersible type of appropriate capacity will be installed for pumping out the water collected in the

sump pit. The water will be discharged to the tailrace downstream of the draft tube gates.

Two dewatering pumps, one as the main and the other as the stand-by, will be installed for the

purpose of dewatering the draft tube portion of the unit. The capacity of the pumps will be so

determined that the total dewatering of the draft tube portion could be carried out in about 2


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hours.

The penstocks can be emptied of water, whenever necessary, by discharging the water to the sump pit

by gravity through drain valve and drain pipe and then to the tailrace. The arrangement of drainage pump are

shown in DWG. No. UT3B HEP-23.

7.4.1.13 Compressed Air System

The compressed air system comprises of two sub-systems. One supplies high-pressure air, which is

used for high-pressure oil system as well as for unit braking and jacking system. The other pump

supplies low-pressure air, which is used for maintenance purposes.

The system consists of two sets of air-cooled compressors with separate air tanks for

accumulating high pressure and low-pressure air. One set of compressor acts as the main and the

other one as stand-by. Pressure-activated switches starts the main compressor, when the pressure in

the high pressure air tank reduces below a set point and stops when the pressure increases up to

another set point. If the pressure still reduces to another set point, both the compressors starts

pumping air. The high-pressure air tank will have enough capacity to fulfill the requirements of air

for all units even when the air compressors are not operating. The low-pressure air tank is connected

with the high pressure one via a pressure-reducing valve.

7.4.1.14 Unit Breaking System

A unit breaking system will be installed to quickly bring the rotating parts of the turbine and

generator to a stand still position, when the unit is being shut down. It is generally required that the

time taken by the rotating parts to come to a stand still from 30% of the normal operating speed

should be less than 3 minutes.

The brake may be engaged pneumatically as well as hydraulically. If air is being used, it will be

supplied by the compressed system. Hydraulic brake will be fed by the high-pressure oil system.


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7.4.1.15 Automatic Grease Lubrication System

A centralized automatic grease lubrication system will be provided for each generating unit for

automatically injecting preset amount of lubricants for bushings and all working parts of the turbine

including the guide vane and butterfly valve operating mechanisms.

The system will consist of alternating current motor-driven pump for normal service and a

standby hand-operated pump. The system will have a means of controlling the volume of grease to

each grease point and of assuring that each grease point is lubricated in sequence in the greasing

cycle.

7.4.1.16 Oil Handling System

An oil handling system will consist of an oil purifier capable of removing all contamination such as

water solids, sludge etc. from lubricating oil system as well as high-pressure oil system. It will also

have oil pumps with appropriate length of flexible hose pipes. A separate oil handling system

of appropriate type for purification of transformer oil will be provided with necessary accessories.

7.4.1.17 Air Conditioning and Ventilation System

An air conditioning system will be installed for the control room. The fresh air will be provided

from the ventilation system. The system will comprise of two sets of air conditioners, one acting as

the main and the other as the stand-by unit. Each unit will consist of a compressor of appropriate

capacity, a thermostat and a hydrostat. The operative temperature will be kept in the range of 20 to

260C and the relative humidity will be maintained around 60 %.

The ventilation system will mainly consist of necessary numbers of axial ventilation fans

installed in appropriate locations along the air duct. All the floors of the powerhouse will have

proper number of ventilation ports. Also all rooms in the powerhouse will have access to the

ventilation system. Number of air exhaust fans of appropriate capacity will also be installed.


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7.4.1.18 Fire Detection and Fire Fighting System

A complete fire detection system will be installed in the powerhouse. The system will comprise of

smoke detectors and heat sensors installed in appropriate locations. The fire detection system will

automatically activate the appropriate fire fighting equipment as well as produce audible and visible

alarm signals.

The firef ighting equipment will consist of high pressure water deluge and sprinkle system as well

as low pressure water hose system. It will also consist of carbon dioxide deluge system and halon gas

deluge system. The last, but not the least items, are the portable fire fighting system.

The transformers will be protected by a deluge system. A low-pressure water hose system will be

provided at regular intervals in the powerhouse and the switchyard. A carbon dioxide (CO2) battery

system will be provided for the protection of the generator fire.

7.4.1.19 Overhead Traveling Crane

An overhead traveling crane of sufficient capacity will be installed in the powerhouse. The crane will

be capable of lifting the heaviest piece of equipment installed. The crane will have one main hoist

and one auxiliary hoist. The span of the crane will be such that it will cover all the major equipment

to be serviced.

The weight of the heaviest single piece of equipment required to be lifted by the crane being that of

the assembled rotor and being computed as 75 ton, the approximate capacity of the crane will be as

follows:

Capacity of main hoist 75 tons

Capacity of auxiliary hoist 5 tons

7.4.1.20 Diesel Engine Generating Set

A diesel engine generating set will be installed in the vicinity of the powerhouse for acting as the


7-25


stand by source for Plant auxiliaries in case of power failure. The approximate capacity required for

the diesel generating set would be 300 kVA. The exact capacity required may vary according to the

equipment to be actually installed and will be finalized in detail design. The appropriate location for

the generating set will be in the vicinity of the outdoor switch-yard.

7.4.1.21 Mechanical Workshop

A fully-equipped mechanical workshop will be provided in the vicinity of the powerhouse for the

general maintenance of the powerhouse equipment. Among the equipment provided will be a

general-purpose lathe, a vertical drilling machine, a grinding machine, an electric welding machine of

appropriate capacity and a set of gas welding apparatus. A set of different types and sizes of

wrenches will also be available. The mechanical services and mechanical workshops are are shown in

DWG. No. UT3B HEP-24 and 25.

7.4.2 Powerhouse Electrical Equipment

The major electrical equipment, which shall be installed inside the powerhouse, are synchronous

generators, main transformers, station service transformers, control panels and battery with charger.

Step-up transformers and high voltage switching equipments shall be located in the switchyard,

outside of the powerhouse. The control panel, switchgear, PLCC, AC/DC panel are in housed in

the control building and shown in DWG. No. UT3B HEP-25 and 26.

7.4.2.1 Generator

Two sets of 3-phase, 50 Hz synchronous AC generators of 25 MVA rated capacity at 0.85

power factor will be installed. Each generator shall be directly coupled with a vertical shaft Francis

turbine. The generators shall be of salient pole, self-ventilating type equipped with brushless

excitation system. The rated voltage will be 11 kV with rated power factor 0f 0.85 lagging. F class of

insulation will be used for stator and rotor. The generator will be totally enclosed, air cooled with air

to water heat exchangers located in the generator pit. Generator fire protection will be provided by a

CO2 deluge system.


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7.4.2.2 Excitation System

The excitation system shall be brushless from the standpoint of ease of maintenance. It shall be

composed of excitation transformer, an alternating current exciter, rotating rectifier, voltage

regulating equipment, excitation circuit breaker, field circuit breaker, field flashing unit,

excitation limiters, control modules and other accessories.

7.4.2.3 Main Power Transformer

Two main power transformers of 25 MVA each for stepping up the generation voltage from 11 kV

to 132 kV, will be installed in the switchyard. The transformers will be oil immersed, ONAN

cooling, outdoor type. The power transformers will have their own oil catchment basin connected

to the drainage system.

7.4.2.4 Station Service Transformer

Two three-phase station service transformers of 250 kVA for stepping down the voltage from 11

kV to 400/230 V, dry epoxy-resin molded type, self-cooled indoor type will be installed in

powerhouse.

7.4.2.5 Medium Voltage Switchgear

These switchgear shall include all 12 kV switchgear equipment and apparatus for the operation and

control of the generators, station and local supply transformers and local feeders. These

equipments are grouped into one lot of 12 kV metal clad, cubicle type indoor switchgears. The

connections between 11 kV switchgear, located in the switchgear room and the main step-up

transformer, located outdoor, will be done with insulated cables.

7.4.2.6 High Voltage Switchgear

The equipment to be furnished for high voltage switchgear will be appropriate set of SF6 132 kV

circuit breakers in the switchyard, all accessories and auxiliary equipment required for the


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successful operation and also special tools required for operation and maintenance.

7.4.2.7 Disconnecting Switch

Appropriate sets of disconnecting switches with grounding switch, three pole, single throw,

motor / hand operated outdoor type shall be provided in the switchyard. All accessories required for

successful operation will also be supplied.

7.4.2.8 Control System

The control system shall be divided into unit control board in the turbine generator floor and

control room. Each turbine-generator shall have unit control board, where all signals, process

inputs, outgoing commands pertaining to the unit shall be gathered and the turbine-generator be

operated.

The complete control and supervision of the power plant shall be concentrated and operated mainly

from the control room. The control room shall have two basic sections.

• The control panels shall have all alarm lamps pertaining to the unit in an alarm tableau e.g.

mechanical and electrical failure, trips, etc. It shall also consist of recorders for generator MW,

Mvar and temperature etc. The panel shall be unit wise.

• The control desk shall consist of indicating alarms tableau for a sequence control indication, group

alarms and mimic bus displaying single line diagram units, indicators of speed set point, guide

vane opening, load limiter position, AVR voltage balance, etc. push buttons for governor and AVR

control for increase and decrease commands, all necessary keys, switches for release blocking and

start and stop as well as covered push buttons/handle for "emergency stop" and any other

switches and indicators that may be necessary for obtaining the specified function. The desk shall

also contain sequential event recorder for alarm and trip event print out and a visualization

computer (PC) with VDU (monitor) and Keyboard.


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7.4.2.9 Protection System

The following protections shall be provided for the electrical equipment installed in the power

station:

• Protection for turbine-generator unit

• Protection for main transformer

• Protection for station service transformer

• Protection for local supply transformer

• Protection for local feeders

Numerical or solid state type protective relays of the flush-mounted, back-connected, dustproof,

switchboard type, with rectangular case equipped with an operation indicator and with an

external front operated resetting device, will be installed.

7.4.2.10 Switchyard

The main power transformer, local supply transformer, 132 kV busbar, disconnecting switches,

circuit breakers current transformer, capacitor voltage transformer, lightning arrestor and wave trap

etc. shall be installed in the switchyard located outside of the powerhouse. The space required for

the installation of outdoor switchyard equipment will be 80 m x 40 m approximately. The

space allocation of switchyard is shown in DWG. No. UT3B HEP-20.

There shall be one 132 kV, SF6 circuit breaker for each of the main transformer and transmission

line whereas space for a future line bay shall be provided. Two disconnecting switches shall be

installed, one on both sides of circuit breakers in the line bay. One disconnecting switch shall be

installed on the incomer from main transformer circuit breaker. Instrument transformers and

lightning arrestors shall be installed in each bay. Line Trap and other coupling equipment shall be

installed in line bay.


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7.4.2.11 Communication System

The communication system will consist of the followings equipment:

• Power line carrier communication

• Communication channel for distance relaying

• Line traps

• Coupling capacitor

• Line protective device

• Co-Axial cable

• PABX

7.4.2.12 Battery and Battery Charger

One set of battery and battery charger for 110 V.DC of 350 Ah capacity will be supplied as auxiliary

power for protection, control, emergency lighting etc. One set of battery and battery charger for 48

V DC will be supplied for communication system. All batteries will be of alkaline Ni.-Cd type. The

batteries shall be assembled in heavy-duty-steel designed for easy stackability.

Battery charging equipment will be of automatic constant voltage output type designed for float

charge operation. They shall be suitable for operation from the 400/230V+ 10% A. C. supply

50Hz.

Suitable control and operation cabinet with the DC distribution system will be provided in each

voltage levels.

7.4.2.13 Grounding System

The complete station grounding work shall be in accordance with the recommendation in the

"Guide for Safety in Substation Grounding" IEEE No.80. The ground grid inside power house

and switch yard, test link chamber, grounding of all equipment located in the power house,

access tunnel, control rooms, 11KV switchgear rooms, 132 KV switchyard and other necessary


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locations will be as required. Ground conductor shall be calculated by measuring soil resistivity. The

grounding resistance shall be less than 1 ohm.

7.5 Transmission Line

For the power evacuation of the project, the transmission line is connected to NIPS at the Trisuli 3B

hub. The transmission line length to Trisuli 3B hub substation 3 km and north of the powerhouse

site. The transmission voltage is 132 km and conductor is ACSR "WOLF" conductor, optical

ground wire and along with insulators and line hardware for about 3 km Upper Trishuli 3B HEP to

Trishuli 3B Hub Transmission Line.

Detailed survey along the route alignment has to be carried out. Tower spotting, optimization of

tower locations and check survey has to be carried out during the construction of transmission line.

TRANSMISSION LINE SYSTEM DATA

Item Description Unit Data

1.1 System nominal voltage kV 132

1.2 System maximum voltage kV 145

1.3 System nominal frequency Hz 50



Chapter 8:

Power and Energy Generation

8.1 Background

This chapter describes the methodology for the estimation of power and energy generation

considering the efficiencies of equipment and outages. Upper Trishuli 3B HEP is a cascade

development designed with and installed capacity of 42 MW. Discharge, head and the efficiency are

the prime factors responsible for the power generation from a plant. Discharge through the turbine

depends on the availability of water in the river. Hence, it varies considerably at different time of a

year. Available head depends on the level of water in the river, which depends on the river flow.

Because of this fact, the available gross head for the generation varies in accordance with the

available flow in the river. But in case of Upper Trishuli 3B HEP, the governing water level is at

headpond which is just downstream of the tailrace of Upper Trishuli 3A HEP (UT3A). The water

level in the headpond considered remains constant throughout the year. Next parameter is

efficiency, which is directly related to the equipment quality and the generation capacity. Efficiency

of a equipment changes if the flow and head is other than the designed parameters. For the

energy estimate, overall efficiency of the plant is assumed to be constant. Generation parameters

of the plant are estimated based on the following:

• Average monthly flow at headwork site.

• Normal operating level is assumed at the headpond where as normal tail water level is

used to estimate gross head. The headpond level remain constant through out the year.

• Overall efficiency of power plant remains constant throughout the year.

8.2 Dependable Flow

Discharge is a prime component for the power generation. Discharge rate is responsible for the

power where as the discharge volume is related to the energy. As the project under consideration is

the cascade development of Upper Trisuli 3A HEP (UT3A), the energy generation is in accordance

with the generation from the Upper Trisuli 3A HEP. The energy generation pattern is similar to



the generation pattern of UT3A. Average plant discharge from UT3A is used to estimate the

monthly energy of the project. The dry season month is Paush, Magh, Falgun and Chaitra and

wet season month is considered as Baishkh to Mangsir. The 90 % firm flow of the river is

estimated to be 36.00 m3/s. Design flow of the plant is same as the design flow of UT3A which is

51.00 m3/s (about 70 % dependable flow).

8.3 Gross Head & Net Head

Gross head is based on the normal water level at head pond and the tail water level. The gross

head of the project is estimated to be 99.31 meter. Average head loss correspond to the design

discharge is estimated to be 4.17 meter. The details of the head loss calculation are presented in

Design Appendix-D of this report. The average head loss varies from 1.82 meter to 4 . 1 7 meter.

This would give the net head of 97.59 meter to 9 5 . 1 3 meter. Summary of the estimated head

loss from intake to tailrace corresponding to the design discharge is presented in the Table No. 8.1.

Table No. 8.1: Average Head Loss for Design Discharge

Item Description Head loss (m)

1. Entrance loss 0.03

2. Friction head loss at approach conduit 0.21

3. Friction loss in the tunnel 2.10

4. Minor losses in bends 0.10

5. Losses in Contraction and expansion 0.09+0.05 = 0.14

6. Friction loss in pressure tunnel, drop shaft and pressure

tunnel after S/T

0.55

7. Friction head loss in surface penstock 0.32

8. Transition from tunnel to 4.2 m diameter steel lined tunnel 0.06

9. Bifurcation losses 0.06

10. Butterfly valve loss 0.10

11. Minor loss in bends (dropshaft bends) 0.33

12. Head loss in draft tube 0.22

13. Friction loss in tailrace conduit 0.14



Item Description Head loss (m)

14. Exit loss at tailrace 0.14

Total Losses from Headpond to tailrace water level at Trisuli 4.17 m

8.4 Overall Efficiency

Overall efficiency of power plant depends on the efficiency of transformer, generator and

turbine. Among these three, efficiency of turbine varies with the head and discharges other than

the designed parameter. For this stage of study, the variation of the turbine efficiency is not

considered. Hence, the overall efficiency of the power plant at design discharge is is equal to 88.25

%. This value corresponds to the transformer efficiency of 99.0%, generator efficiency of 96.0% and

turbine efficiency of 92.80%.

8.5 E n e r g y Computation

A spreadsheet model was used in order to provide the necessary input into the economic and

financial analysis. Assumptions made during the estimation are as follows:

• The normal water level at the headpond remains constant and is maintained at the normal

operating level of 726.00 masl.

• Normal tail water level at powerhouse varies from 926.49 m to 927.91 m. (In reality, the

tail water level varies with the flow in the river.)

• The gross head of the plant is 99.310 meter trough out the year.

• Maximum head loss corresponds to the design discharge of the project.

• Total head loss for the power discharge order than the design discharge is estimated

proportionately.

• Minimum downstream release of 3.84 m3/s corresponding to the 10 % of the minimum

monthly flow is considered from the head work of Upper Trisuli 3A HEP.

• Scheduled and unscheduled outage are not considered while estimating the energy.

Total annual energy of 337.88 GWh has been estimated for this study. This value is based on the



average monthly flow. The annual firm power is estimated to be 29.19 MW. This value corresponds

to the 90% annual dependable flow. Total annual firm energy is estimated to be 258.93 GWh

where as total secondary energy is 77.94 GWh. As mentioned above, the total dry season energy is

estimated to be 94.54 GWh where as total wet season energy is 243.34 GWh.

The summary of the monthly generation from the project is presented in the Table No. 8.2.

Average monthly power in this table is estimated on the basis of the average monthly flow

from the tailrace of Upper Trisutli 3A HEP (UT3A). The energy estimate is depicted in the Figure

8.1.

Table No. 8.2: Monthly Energy Generation from Upper Trishuli 3B HEP

Downstream release 3.84 m3/s

Net Head 95.13 m

Efficiency 88%

Design discharge 51.00 m3/s

Installed Capacity 42.00 MW

Month River Flow for Monthly Monthly

Flow Energy Power(kW) Energy(GWh)

Jan 43.40 39.56 33,195.29 24.697

Feb 38.40 34.56 29,197.19 19.621

Mar 38.40 34.56 29,197.19 21.723

Apr 48.30 44.46 37,029.83 26.661

May 86.80 82.96 42,000.04 31.248

Jun 238.80 234.96 42,000.04 30.240

Jul 523.50 519.66 41,580.61 30.936

Aug 603.80 599.96 41,456.99 30.844

Sep 389.80 385.96 41,792.53 30.091

Oct 161.20 157.36 42,000.04 31.248

Nov 78.30 74.46 42,000.04 30.240

Dec 53.20 49.36 40,769.09 30.332

Total Energy 337.88



0

5

10

15

20

25

30

35

En

erg

y (G

Wh

)

Months

Figure 8.1: Monthly Energy Generation

Dry Season - Sec Dry season - Firm

Wet Season - Sec Wet Season - Firm



Chapter 9:

Construction Planning and Schedule

9.1 General

Construction planning is a major component of project studies that transpires into successful

development of the project within time and estimated budget. Upper Trishuli 3B is tailrace cascade

scheme of Upper Trisuli 3A Hydroelectric Project (UT 3A) and is located in Nuwakot and Rasuwa

district. The intake channel is located at Simle which lies 9 km north of existing Trishuli

hydropower project(24 MW) headworks. The powerhouse is located at Siruwapani (Champani

Village) which lies about 4 km to the south of Simle. All the project structure from headworks to

powerhouse site lies within 5 km. The project comprises of a surface head pond, headrace pipe,

tunnel intake, 3744.69 m long headrace tunnel, 37.4 m high surge shaft, 98.17 m long pressure

tunnel after surge tank, 69.07 m high drop shaft, 181.65 m long pressure tunnel after drop shaft

surface powerhouse and 123.93 m long tailrace with an installed capacity of 42 MW.

9.2 Objective & Scope of work

The objective of construction planning is to accomplish the project development within time and

within budget. Construction method for the major work items has been recommended in-order to

complete the tasks in the optimum manner. This report also comprises of assessment of

transportation facilities for project implementation, construction power & camp facilities, availability

of construction materials etc. The study of various pre-construction and construction activities,

construction methodologies, preparatory works and optimum construction duration have been

carried out. A master construction schedule has been prepared for the project development which

shows all the major items of construction work including their duration.



9.3 Site Condition

9.3.1 Topography and Land Use

The project site is located in the mid hill region of Central Region of Nepal. The elevation of the

intake site is approximately 726 masl. The intake is surface type where as the powerhouse are located

in terrace deposits (cultivated land) on the right bank of Trishuli River. Most of the tunnel passes

through community forest. The construction road is available from powerhouse site to surface

intake. All the adit tunnels are accessible by the available construction road. It is noted that the

excavation of powerhouse disturb the road from New Bridge to Tupche Village and this road has to

be relocated during the construction of the powerhouse site.

9.3.2 Climatic Conditions

The project area has a hot summer season with a maximum temperature ranging from 36OC to

41OC. The minimum temperature during winter ranges from 1.5OC to 7OC. The average annual

rainfall at the project site is approximately 2000 mm which occurs during the month July-September.

9.3.3 Telecommunication Facilities

Currently, mobile telephone net work exists at Pairobesi near the powerhouse area and at the

intake site. For the project construction, telephone link with the project site will be made using

appropriate network. Mobile communication equipment will be used to communicate with the

various project sites. Once the project is commissioned, power line cable communication (PLCC)

will be used for information exchange between the powerhouse and load dispatch center.

9.4 Access to the Site

Calcutta is the most appropriate sea port for the transportation of construction materials and

equipment from the third world countries. Similarly, Raxual would be considered as the appropriate

rail way station for this project. The total distance from Calcutta to Raxaul is 860 km.



With regard to onward transportation by road, the route from Raxual to the intake site via

Galchhi on Prithivi highway is about 235 km. The road from Galchi to Betrawati Bazar is about 32

km along the Trisuli Dhunche Highway. Since the UT3A has already constructed a bridge over the

Trisuli River at Pairobesi, the road distance from Betrawati Bazar to the project site of UT3B is

about 3 km and accessible by the gravel road. Upper Trisuli 3 A HEP (UT3A) is under construction,

since Upper Trisuli 3B Hydroelectric Project (UT3B) lies along the access road to UT3A, the same

road along right bank of Trishuli river is used during the construction of the project. It is envisaged

that the 5 km road from powerhouse are to the proposed UT 3A powerhouse area will be upgraded

for the implementation of UT3B. The upgrading shall include widening, improvement in geometry,

drainage, slope stability, selected gravel filling and compaction.

The following modes of transportation are recommended:

• Transport all light offshore general cargo by road.

• Transport the heavier offshore cargo by Indian railway directly to Raxaul

• Transport from Raxaul to the project site by road.

9.5 Basic Assumptions

Following are the basic assumptions used for the construction planning:

• The entire construction work will be undertaken through EPC contract which will

require 6 months for awarding.

• Eight hours per shift is assumed.

• Underground works are generally carried out in two shifts.

• Five months of a year starting from the month of June is considered as wet

season.

• Financial arrangement and official clearances will be made by the end of contract

award.

• Award of the main contract will be on July 31, 2014.

• Mobilization period of 30 days is assumed immediately after the award of the

contract.



Progress rates assumed for different major work items of construction works are as follows:

Overburden Excavation : 2000 cubic meter per day

Headrace Tunnel Excavation : 3 meter per day per face

Tunnel Lining : 8 meter per day per face

Concreting : 100 cubic meter per day

9.6 Concreting Facilities

One concrete batching plant shall be needed for the construction. The unit rate has been

developed based on the maximum distance to be cover by concrete batching plant. This means the

batching plant shall be located at the middle of headworks and powerhouse area. It shall also have

aggregate production unit, silo for cement storage etc. Concrete will be transported to the site in

mixer trucks. Concrete placement will be made through buckets attached to crane, sloping ramp,

concrete pump etc.

9.7 Project Construction Work and Construction Planning

All construction activities will be mainly concentrated in the dam site and the powerhouse site.

Following are the main activities during construction.

• Project road, camp and construction power

• Adit tunnels

• Surface headpond and surface intake

• Headrace pressure pipe

• Headrace tunnel

• Surge shaft

• Valve Chamber and access to valve chamber

• Pressure tunnel after surge tank

• Drop shaft

• Powerhouse and switchyard.

• Tailrace structures.



• Transmission line and interconnections

The layout of the project is shown in DWG NO UT3B HEP-01 and the construction schedule is

summarized in Figure 9.1. The work involved at each of these areas is outlined below:

9.7.1 Construction Power, Camp and project road

Construction power requirement is estimated at about 1 MW which is shown below in Table 9.1.

Table 9.1: Estimate of construction power

Description of Item Power(kW)

Batching Plant 100Construction camp 200Crane at powerhouse 50Air compressors (50x4) 200Workshop 50

Welding 50Power Winch 50

De-watering Pumps(25x4) 100Office 50Vent fan (50x4) 200Powerhouse 100

Construction. site Lighting 100Sub Total 1250Diversity Factor 0.8Peak Power Requirement 1000

The project area is connected with 11 kV transmission line from existing Trishuli project 6.6/11 kV,

5 MVA transformer. This transformer at Trisuli Substation is going to upgrade into 10 MVA within

6 months. This transmission line passes through the powerhouse area and headpond area of the

project. Apart from the existing transmission line, backup power will be needed for critical works

like tunnel lighting, ventilation and batching plant etc. The backup power will be provided through

diesel generators placed at suitable places.



Construction camps will be required to house both the employer's staff and the contractor's staff.

The permanent campsite will be located about 1 km south of the intake site. It is envisaged

that permanent structures of the camp will be used for accommodation of the operation and

maintenance staff once the construction is completed. The construction of the permanent camp will

take 6 months.

Temporary camp will be 500 m upstream of the powerhouse site and will be located at cultivated

land. Much of the temporary camp will be built from pre-fabricated units which will be dismantled

once the project is completed. About 3 months time will be required to complete the

temporary construction camp and power supply.

A total of 1.546 km of project road needs to be built as a pre-requisite for the mobilization of heavy

civil construction equipment. This comprises of about 263 m in powerhouse area, about 447 m in

the surge shaft adit and 836 m road realignment from New bridge to Tupche. Three months will be

required to build access road.

9.7.2 Headrace pipe

The length of the headrace pipe from tailrace of UT3A HEP (Intake portal) to the headrace tunnel

is 384.27 m. The headrace pipe is steel lined and covered concrete box on it. The diameter of

headrace pipe is 5.1 m and the steel lining thickness is 14 mm. The minimum concrete cover is 0.75

m. The volume of earth work in excavation is 11536 m3. The total estimated time to complete the

work is 4 months including laying of steel at the site and concrete cover.

9.7.3 Surface head pond (intake of UT3B HEP)

The underground headpond is located on the left bank of Trisuli River just downstream of the UT

3A draft tube. The separate adit-1 shall be constructed to reach the headpond via headrace tunnel.

The size of the adit tunnel is 4m, D-shape. The headrace tunnel acts as the access tunnel to the

underground headpond. The headpond comprises of UT3A draft tube outlet, intake of Trisuli 3B

HEP, outlet to tailrace channel. The size of the headpond is 30 m length by 10 m width and design

for the submergence depth of the headrace tunnel. The volume of rock excavation is about 16560



m3, that includes, headpond, underground spillway, tunnel intake, intake gate chamber, access to

headpond. The underground excavation, rock bolting and shotcreting shall take 5 months and

concrete finish shall take another 4 months. The total estimated period is 9 months to complete the

construction of underground headpond. It will be required for the task which will involve both semi

mechanized and manual construction methods.


The total length of headrace tunnel up to the surge shaft is 3744.69 m, 47.21 % shotcrete lined and

52.79 % concrete lined tunnel. The weaker rock portion, length about 306.45 m required steel ribs

apart from the concrete lining. In-order to expedite the construction, two construction adits would

be provided at chainage 1+771.3 m and 3+563.5 m. The tunnel will be excavated from six work

faces. The maximum length of excavation from the face is about 1073 m. 50 % of the tummel

passes through S5 type (weak) rock is excavated by heading and benching method and the

remaining length of the tunnel is excavated by drill and blast method. The tunnel excavation will be

carried out using 2 boom drilling jumbo while dump trucks and wheel loaders will be used for

mucking. The tunnel will have pipelines for ventilation, dewatering, compressed air supply in

addition to the low voltage power supply for lighting, vent fan, pumping. As tunneling is one of the

critical components of the project construction, it will be carried out in two shifts per day.

The anticipated progress rate of tunneling is 3 m per day per face. 52.79 % of the tunnel is

envisaged to be fully lined with concrete of 30 cm thickness. Concrete lining will be placed using

mobile steel formwork & concrete pump once full excavation has been made. Moreover, some

stretch of the tunnel (306.45 m) will have to be provided with steel rib support. The tunnel

excavation envisaged to be completed over a period of 15 months which includes provision of rock

bolting, shotcreting as well. The concrete lining, grouting will require a period of 9 months. The total

time of construction of headrace tunnel from intake to surge tank is 24 months.

The total quantity of muck from the headrace tunnel is 135036 m3. The volume of concrete work

inside the tunnel is 14405m3.



9.7.5 Adit Tunnels

Two adit tunnels are envisaged in the headrace tunnel and one adit tunnel at surge tank crown.

Excavation for these tunnels will require a period of five months and this activity has to be started

on a priority basis in order to complete the waterways in time. The longer adit is at the chainage

1+771.3 m and the length is 479.88 m.

Adit Tunnel-1: adit tunnel to middle of headrace tunnel

The first adit tunnel is for the middle of the headrace tunnel and it is at the chainage

1+771.3 m. The length of adit-1 is 463.60 m, D-shape, 4 m diameter slope toward the headrace

tunnel (S= +1.479 %). Muck from this adit-1 tunnel is disposed into the “Muck Disposal Area # 1

and 2”. The construction of adit-1 will take 6 months. Therefore, these matters are taken into

account of the construction schedule. The estimated muck disposal from this adit tunnel is about

8135 m3.

Adit Tunnel-2: adit tunnel near the surge tank

The second adit tunnel is at the end of the headrace tunnel and it is at the chainage

4+060.75 m. The length of adit-2 is 288.9 m, D-shape, 4 m diameter slope is toward of the

headrace tunnel (S= + 7.96 %). Muck from this adit-2 tunnel is disposed into the “Muck Disposal

Area # 2 and 3”. The estimated muck disposal from this adit tunnel is about 5042 m3. The

construction of adit-2 will take 6 months.

Adit Tunnel-3: adit tunnel at the surge tank crown

The third adit tunnel is at the crown of the surge tank. The length of adit-4 tunnel is 191.6 m,

D-shape, 4 m diameter, height 4 m, slope is toward of the headrace tunnel (S= + 8.99 %). Muck

from this adit-3 tunnel is disposed into the “Muck Disposal Area # 3”. The estimated muck disposal

from this adit tunnel is about 5052 m3. This adit tunnel-3 is used to transport the surge tank gate as

well access to the surge tank. The construction of adit-3 will take 6 months.

9.7.6 Underground Surge tank/Shaft

The surge tank has a finished diameter of 15 m and a height of the tank from base to the



crown is 37.4 m. The pilot shaft will be excavated from the bottom, using raised boring. Once the

pilot shaft is completed, full diameter excavation will be carried out from the top to bottom using

benching. Finally, shotcrete and concrete lining will be provided in the tank from the bottom to the

top portion. Excavation, shotcreting and rock bolting will be completed over a period of three

months while concrete lining will require two months. Volume of excavation is 8415 m3 including

the surge tank gate groove. The total volume of concrete is 2120 m3. The construction of surge tank

will take 6 months.

9.7.7 Valve Chamber and Access to Valve Chamber

In order to carry out the maintenance of turbine, draft tube, draft tube gates, butterfly valves, the

valve chamber is used to control and stop the water flow from tunnel to powerhouse. The size of

the valve chamber is 15.9 m x 7 m x 9.5 m. For the access purpose to valve chamber, access tunnel

of length 56.35 m, diameter 4 m has been proposed. The muck obtain from the valve chamber and

access tunnel is disposed into the “ muck disposal area #3”. The estimated muck disposal from this

chamber and the tunnel is 2327 m3.

9.7.8 Pressure tunnel after Surge tank

The length of the pressure tunnel after surge tank is 106.4 m and this is completely a concrete lined

tunnel. The muck from this tunnel directly disposed into the “Muck Disposal Area # 3” at the

powerhouse site. The total muck from this tunnel is estimated as 2623 m3.

9.7.9 Drop Shaft

The length of the drop shaft is 69.2 m (including bandings) which is to be excavated in circular

shape (4.2 m diameter) with concrete lined finishing. The estimated quqntity of muck from drop

shaft is 1434 m3 and shall be disposed into the “ Muck disposal Area #2”

9.7.10 Pressure Tunnel after Drop Shaft

The length of the pressure tunnel after drop shaft is 181.6 m and is completely concrete lined. The



excavated diameter of tunnel is 5.0 m , D-shape and finished diameter is 4.2 m circular shape. The

muck obtained from the tunnel is directly disposed into the “Muck Disposal Area # 2”. The total

muck from the tunnel is 4400m3. The construction of drop shaft, pressure tunnel and valve

chamber will take 9 months.

9.7.11 Powerhouse

Retaining Structure upslope of Powerhouse

The concrete retaining structure of length about 169 m is proposed to construct upslope of the

powerhouse site. The main objective of this structure is to reduce the excavation of upslope by

stabilizing the existing sloping land escape. In the design, the retaining structure has been proposed

at an elevation 681 m. The maximum height of the retaining wall is 14.75 m. The retaining structure

shall be built before the excavation of the powerhouse earth work. The total volume earth work for

the construction of retaining structure is estimated as 47095 m3 and the total volume of concrete

work is estimated is 2900 m3. The foundation of the retaining structure shall be anchor to the

bedrock. The excavation work of the retaining wall take place 3 months and concreting of the

retaining wall will take 5 months.

The proposed powerhouse is semi surface and the machine foundation is on the bedrock (schist).

Therefore, the maximum depth of excavation is about 45 m from the surface. The total volume of

earth excavation is about 191744 m3. The plan dimension of powerhouse is 37 m x 14.0 m. The

elevation of erection bay is 637.2 m while the turbine floor is at elevation 625.35 m. The

powerhouse accommodates 2 vertical Francis turbine generators with ancillary equipment for

control & protection. The total volume of concrete work is about 6198 m3.

Firstly road to the powerhouse site diversion shall be built which will be followed up by excavation

for the powerhouse subsurface structure. The excavation of powerhouse will be then carried out

through benching. The powerhouse excavation will be followed by concreting of the foundation.

Sub-surface concreting and superstructure concreting will then be carried out. Powerhouse

excavation is estimated to be completed over a period of 5 months while the structure and finishing

works will require another 11 months. Erection of the equipment will be made once the gantry



crane has been installed and is expected to require a period of 6 months.

9.7.12 Tailrace conduit and Outlet Structure

The tailrace conduits have length of 123.93 m. The box culvert type section of tailrace conduit

has a section of 4.5 m x 4.5 m size. The tailrace will be made by cut and cover method. The

outlet structure works comprises of excavation and slope stabilization, concrete works and erection

of gates. The volume of excavation material is 90761 m3. The volume of concrete work is 2766 m3.

It is anticipated that the tailrace conduit and outlet works will be completed in 6 month.

9.7.13 Electro-Mechanical Equipment

The electromechanical equipment and its accessories are imported from the third countries. The

design, manufacturing and forwarding will require 14 months while erection at site will require

another six months.

9.7.14 Switchyard, ancillary Buildings and transmission line

The proposed switchyard is in front of the powerhouse. The size of the switch yard is 60 m x 100 m.

the construction of switch yard shall proceeds after the construction of powerhouse and tailrace box

canal. The switchyard civil works and installation of switch yard towers and transformer will require

6 months while the Switchyard Control Building will require 6 months. The size of the control

building is 9 m x 12 m in plan.

The length of the transmission line is about 4 km. The erection of transmission line and

interconnection with the Trisuli 3B hub shall take 6 month.

9.7.15 Testing and Commissioning

This activity will require a period of two months. It shall comprise of wet testing and generation

testing before the commercial operation date (COD).



9.8 Quarries and Borrow Areas

The field exploration was carried out to identify the potential borrow areas and quarry sites for the

construction materials. A total of 2 nos. of possible borrow areas were identified within 5 km range of

project area during feasibility study. Borrow areas GA is located in Trishuli River bed. Borrow area

GB is located at Salankhu Khola bed. Two-quarry sites (QA and QB) were identified . Quarry site QA

is located at Right bank of Tirshuli river near perposed powerhouse site .

Volume of Granular material was estimated on the basis of field measurement of test pits depth,

material quality, laboratory test result of pit samples and area of different proposed borrow areas.

Estimated volume of material in different borrow areas is 0.32 million cubic meter for GA and that of

14 million cubic meter for GB borrow area.

Two quarry areas (QA and QB) were identified during investigation. Quarry site, QA is located at

Tirshuli bagar boulder deposit near proposed powerhouse and quarry site QB is located at left bank of

Tirshuli River.

9.9 Spoil Area

Spoil deposit area has to be provided in the project area to accommodate excavated rock from the

underground project components like headrace tunnel, surge tank, powerhouse, tailrace and adits.

The spoil areas should be located close to the tunnel and adits as much as possible. The total fill

volume of underground excavations is 46300 m3, assuming a bulk factor of 1.5 from solid rock to

spoil fill.

The build-up of the spoil deposits will be a continuous process during the construction period. Most

of the areas would be finalized within 2 to 3 years. The longest duration is associated with headrace

tunnel excavation. The finished spoil areas at the powerhouse and tailrace outlet are suitable for use

by Electro-Mechanical Contractors for lay down areas, storages, offices and camp facilities.

During the operation period of the project, some areas would be required as redundancy space for

major overhaul etc. The local community might use most of the spoil areas for other activities. All

spoil deposits should be made stable and should preferably be shaped with a flat area on the top,



though a slope of 1:20 would facilitate later usage. Typically a side sloping of 1:1.5 is stable for most

purposes. The deposit should, therefore, be built up in layers rather than dumped from high

elevation. Top soil should be shaved off and piled up separately on dedicated storage prior to any

deposit of tunnel spoil. Spoil deposits should be shaped into forms merging to the landscape and

covered by the stored top soil as far as possible.

9.10 Construction Planning and Scheduling

It is envisaged that the project will be implemented under EPC contract. The preparatory

activities like EIA arrangement and construction of site road, upgrading of existing roads,

construction power and camp facilities should be taken up on a priority basis. Some activities in

these tasks could be done in parallel. The total time duration required for the actual construction

after contract award is estimated to be 36 months. EPC tendering awarding will require 6 months

while mobilization will require 1.5 month. Construction of the site road, upgrading of existing roads

and temporary camp facilities will require three months.

Four separate groups are required to construct the three adit tunnel. Since the length of adit tunnel

no 1 is longer, adit tunnel number 1 has to construct faster than other adit tunnel. The construction

of headrace tunnel is in the critical component of project schedule. Therefore, the construction of

tunnel has to be started from four face.

Similarly, the construction of powerhouse is in the critical path also. Excavation and subsurface

concreting, superstructure concreting of the powerhouse shall takes about 20 months. After

completing the powerhouse civil works, the construction of tailrace canal starts followed by the

switchyard civil works. The erection and installation of switch yard start after 31 months only.

The project could be completed by the middle of early 2018, if actual construction is started in

September 1, of the year 2015. The project implementation schedule is shown in Figure 9.1. The

construction schedule is shown in Figure 9.2.



9.11 Key Dates

The Department of Electricity Development, DoED has recently issued conditional Generation

License for Upper Trishuli 3'B' HEP to NEA. The process for transferring the license in the name

of Trishuli Hydropower Company needs to be initiated at the earliest. The Environmental Impact

Analysis, EIA needs to be completed within the next 6 months as public hearing as a part of EIA

was made in September, 2013. The implementation schedule starts with the preconstruction

activities such as power purchase agreement with NEA, arrangement of equity and arrangement of

loan for financial closure. These preconstruction activities are planned to be completed within July

2014. At the same time, bidding documents for EPC Contract will be prepared in parallel. An

international consultant will be appointed as Owner’s Engineer for review and finalization EPC

design, drawings and EPC documents and to assist the Employer in construction supervision and

management of the project. Procurement process for construction of the main works (main civil

works, hydro mechanical and electro mechanical works) under EPC basis will be started at the

beginning of FY 071/72. It is anticipated that the EPC contract for construction of the project will

be awarded in the mid of FY 071/72.

This project will use the same access road constructed for Upper Trishuli 3A Hydroelectric Project.

Preparatory works of the project for main construction works consist of land acquisition followed

by construction of access road, camp facilities and transmission line for construction power. As land

acquisition can be initiated immediately after receipt of the Generation License, the corresponding

works have to be planned accordingly to ensure timely start of the construction of main works. The

actual duration of project completion period will be three and half years from the date of award of

contract. All preparatory works including land acquisition, construction camp and infrastructure

development will be started this Fiscal Year and will be completed by the mid of next FY 071/72.

The main construction works of the project will start from June 2015 and will be completed by

October 2018. The commercial generation will start from November 2018. The key dates for project

implementation proposed are summarized below.

• Generation License : Oct, 2013

• EIA

– EIA Document review & Public hearing : Oct, 2013



– EIA Approval : May, 2014

• PPA with NEA : July, 2014

• Financial Closure : August, 2014

• Consultant selection & Award : July, 2014

• EOI & RFP Document Preparation : December, 2013

• EOI Notice & Short listing : Jan-March, 2014

• RFP Issue, selection and Contract ward : April-June, 2014

• EPC Design Drawings and Bidding Documents

– Finalizations of Design & Drawings : January, 2014

– EPC Document Preparation : April, 2014

– Review & Finalization by the Consultant : July - September, 2014

• Tendering & award of EPC Contract : October, 2014 – March, 2015

• Mobilization Period : April to May, 2015

• Construction and Completion : June 2015 to October, 2018



Chapter 10:

Environmental Impact Assessment

10.1 Introduction

The proposed Upper Trishuli-3B (UT-3B) Hydroelectric Project with an installed capacity of 42

MW has been recommended by the study team as one of the attractive schemes for the

development in the near future. This scheme utilizes the tailrace flow of the Upper Trishuli -3 "A"

Hydroelectric Project. This project which is a Run-of-River cascade schemes is located in

Manakamana and Laherepauwa VDCs of Nuwakot and Rasuwa Districts respectively. The intake is

located at Simle village of Manakamana VDC while the powerhouse at Champani village of

Manakamana VDC.

This report is the Environmental Impact Assessment (EIA) of the Upper Trishuli-3B HEP prepared

by the Environment and Social Studies Department (ESSD) of Nepal Electricity Authority (NEA).

This EIA Report is an integral part of project feasibility study and the purpose of the EIA is to

ensure that the project is designed and developed in a manner that minimizes negative social and

environmental effects while maximizing project benefits. This EIA report is valid only for

generation and does not include transmission line.

10.2 Project Description

The proposed Upper Trishulli -3B HEP Run-of -River project with the installed capacity of 42 MW

is located in Rasuwa and Nuwakot Districts in the Central Development Region of Nepal. The

proposed intake is located at Simle village of Manakamana VDC whereas the powerhouse at

Champani village of Manakamana VDC. The left bank of the proposed headpond lies in the buffer

zone of the Langtang National Park.



10.3 Study Methodology

The EIA study has been completed in compliance with the requirements of Environment

Protection Act, 2053, Environmental Protection Rules, 2054 and its amendment, based on field

investigation and studies, consultation with local people & officials and the approved ToR.

10.4 Existing Environment Conditions

10.4.1 Physical Environment

The Upper Trishuli 3B HEP is located in the Gandaki River Basin. The core project area lies in

relatively flatter topography and watershed of the proposed project is fairly good. The land use in

the project area mainly consists of patches of agricultural land and forest. The powerhouse lies in

flat agricultural land.

The project area lies in the Lesser Himalayan Metasediments in Central Nepal. The dominant rock

type around intake is Gneiss. Rock exposures near intake portal is Gneiss with light and dark

coloured minerals which is slightly to moderately weathered and hard. A horseshoe shaped headrace

tunnel which is about 4228 m long crosses mainly two types of rock namely schist and quartzite. A

very small section will pass through gneiss. The rock exposed around the surge shaft area is quartzite

and schist. The predominant rock type in the powerhouse area is schist and quartzite with the

proportion of quartzite is higher than schist.

Trishuli River is one of the major perennial river of Saptagandaki river systems with the catchment

area of 4542 km2 at the proposed headworks site. The major tributaries of the Trishuli River

upstream of proposed intake sites area Mailung, Bhote Koshi, Chilime, Langtang and Dunche

Trishuli. The annual mean at intake is found to be 192.0 m3/s. The maximum mean monthly

discharge is 825.5 m3/s (August, 2004) and minimum mean monthly discharge is 25.7 m3/s (March

1993).

The core project area lies in the sub-tropical climate zone with the annual average maximum and

minimum temperature of 19.75O C and 10.02 O C respectively. (Nuwakot District Profile, Nuwakot,



2005). The project area lies in the interior part of the country, therefore the air and noise pollution is

very less in the project area except for the dust pollution from the vehicles plying through Upper

Trisuli 3A HEP road and Betrawati-Pairebesi gravel road which appears to be within the range of

national standard.

10.4.2 Biological Environment

Almost all of the core project area lies within the subtropical zone . The left bank of the dewatered

stretch lies in the buffer zone of the Langtang National Park (LNP). However, no forest part of the

LNP will be affected by the implementation of the proposed project. Major forest types are hill Sal

forest, Pine forest, Schima-Castanopsis forest, Rhododendron forest, Alder forest, lower temperate

mixed broad leaf forest, Upper temperate mixed forest of the Langtang National Park and its buffer

zone.

The vegetation found in the headworks area is sparse and consists of Githi/Dar (Deberegesia

salicifolia), and domestic fruit trees such as Albizia sp, and Magnifera indicia. and some fodder tree

and shrub species. The vegetation in the surge tank and access road to surge tank area mainly consist

of Sal (Shorea robusta), Chilaune (Schima wallichii), Mauwa (Engelhardia spicata), Khanayo (Ficus

semicordata), Simal (Bombax ceiba), Kutmero (Litsea monopelata), Bot Dhaero (Lagerstromea

parviflora), Datiwon (Alstomiasp). Amala (Phyllanthus emblica), Gogan (Sauravia nepalnsis), and

this forest area belong to Sirupani Community Forest.

There is poor vegetation composition and distribution around power house area. Few scattered trees

and common shrubs like chutro (Berberies asiatica) and trees like Simal (Bombax ceiba) and Gogan

(Saurauia nepalensis), are found in the power house and camp area. The camp area consist of

mainly cultivated land.

Subtropical evergreen forest consisting of sal, simal, and pine mixed can be observed along the

access road and surge tank area. The canopy cover was estimated around 60% during the field

survey. Other main associated tree species in the forest observed were Mauwa, (Engelhardia spicata),

Erythrina suberosa etc. The undergrowth forest surface was dominated by Titepati (Artimesia spp),

Banmara (Eupatorium Spp), Fern spp, kauchho (Mucuna nigricans) etc.



Cultivated terraces, shrub lands, mixed forest of Rani Sallo (pinus roxburghii), Chilaune (Schima

wallichii), Mauwa (Engelhardia spicata), Sal, mixed with undergrowth of a few shrubs and climbers,

kadam (Anthocephalus chinensis) were observed along the headrace tunnel of about 4.228 km

length. Dense vegetation patches along the north west slope of the proposed tunnel. Similar type of

vegetation has been found at the proposed adits. No registered private land and leasehold forest lies

in the project construction sites. Altogether 4 Community Forests namely Jambaipakha CF,

Thulobagara CF, Goddung CF and Sirupani CF will be indirectly affected by the construction of

the project . Similarly, three Buffer zone User committee will be affected.

Fish sampling along the Trishuli River and local information collected in the field reveal the

presence of 31 species of fish. Out of which 15 species are collected during the present survey and

remaining 16 are reported by local fishermen.

Altogether 18 species of mammals and 13 species of birds were reported in the project area. Nine

types of fish species were identified during the sampling in the Trishuli River. Asala (Shizothorax

richardsonii (Gray) represented more than 80% of the local catch in all sampling stations.

10.4.3 Socio-economic and Culture Environment

The Upper Trishuli- 3B Hydroelectric project is located in two districts namely Resuwa and

Nuwakot of Bagmati Zone, Central Development Region of Nepal. The total area of the project

affected district is 2,665 sq. km (Rasuwa~1,544 sq.km and Nuwakot~1,121sq.km) with average

population density of 160.5 person/sq km. Administratively, there are 80 VDCs and one

municipality of 2 districts (62 VDCs and 1 Municipality in Nuwakot districts & 18 VDCs in Rasuwa

district). The total population of surveyed households is 332 with male 180 and female 152. The

percentage of male and female population of surveyed households is 54.22 and 45.78 respectively.

The male population of surveyed households is comparatively higher than the female population.

Similarly, the average sex ratio of the surveyed population is 1.18 and the households size is 5.72.

The project area is dominated by native born population. The major settlements of the project

affected VDCs are Simle, Arachale,Shanti Bazar, Chhampani Baru Gaun, Pairebenshi, and Betrawati.

Brahmin, Chhetri, Tamang, Gurung and Magar are the major dominant castes/ethnic groups among



the surveyed households. According to household survey, Buddhism is the dominant religion among

the surveyed households while Hinduism practiced by the people in the project area. The household

survey indicates that the average literacy rate of the surveyed population is 73.84%, which is

comparatively higher than the average literacy rate (50.46%) of the project affected VDCs and the

average literacy (42.85%) rate of the project affected districts.

Agriculture, wage/labor and services are predominant occupation of the surveyed population

followed by labors inside and outside country, business and small industries. According to

household survey data, 67.71% of the surveyed population is economically active (population of 14-

59 years of age).

Due to the lack of sufficient irrigation facilities and low cultivated land, the average production in

the project affected area is very low. Overall average land holding size is calculation to be

0.57ha/Hh, which is comparatively lower than the average land holding size of the project affected

VDCs (0.65ha/Hh). Paddy, wheat, maize, millet are the major food crops and oilseeds and potato

are the major cash crops grown by the surveyed households. Among the crops produced, maize and

paddy are the major crops for earning and feeding. The household survey reveal that about 48.48%

of farming land is occupied by paddy field. Food insufficiency problem is common in the project

area. The household survey indicated that about 63.79% surveyed households are fall under

insufficiency of food grain for their own production. Only 36.21% of surveyed household have

sufficient food for their own production throughout the year.

Remittance, wage/labor, agriculture, animal husbandry, pretty trade/business, service, pension

transportation and trekking are the major income source of the surveyed households in the project

area. The households of the project area also raise livestock both for cash income and farming

purpose. The average income of the project affected household is 136,483 per annum and the

average annual expenditure of the surveyed households is calculation to be Rs 1,17.746.

piped water, spring/well, river/stream and public tap are the major sources of drinking water in the

project affected area.

Fuel wood is the major source is the major of energy for cooking purpose of the surveyed

households. Electricity is the major source of lighting fuel of most of the project affected



households. Similarly, fuel wood, electricity, bio-gas are the major source of energy for Cooking

purpose of the surveyed households. On this provision, about 68.97% have been using bio-gas and

3.45% surveyed households have been using electricity for cooking purpose.

There are no historical, archeological and religious sites of significance in the core project area.

10.5 Impact Assessment


A total of approximately 22.15 ha of land under different land use will be permanently converted to

project facilities, whereas 5 ha of land will be used for temporary and permanent camps during the

construction period. The permanent land use change may result in permanent loss of production

resource base particularly of the cultivated land, private forest and barren land. Approximately 8.13

ha of the total land take is agricultural land, 2.53 ha forest, and the rest barren land. The impact is

expected to be high, local in extent and for a long duration.

The construction activities like clearing of land, blasting, excavation work and muck disposal will

have impact on the land stabilities and surface soil erosion in the project area. Furthermore, there

might be an alteration in localized drainage and storm runoff patterns.

The settlements close to the construction sites like Champani, Simle and Archale like will be

affected by the air pollution. The impact will be moderate in magnitude, localized and will be for

short duration. Construction activities and operation of diesel plants, vehicles, and ventilators,

cement batching and aggregate crushing plant at various project sites will generate noise and

vibrations. The increase in ambient noise levels will have pronounced impacts on settlements in

close proximity to noise source at the headworks, powerhouse site and some sections of the access

road.

The diversion of water though the tunnel will have an impact on the river flow and morphology.

The river will divert up to 51 m3/s of flow and approximately 5 km of the river stretch between the

proposed intake and powerhouse site will be dewatered. The flow during the dry and wet season will



fluctuate between 3.84-597.9 m3/s in the river which will change the river morphology and

hydrology. Change in the water quality of surface water bodies are likely to occur due to

construction activities.

During the construction of headpond, powerhouse, tunnel, adits and penstock pipe, considerable

amounts of excavation material will be generated. Reuse of spoils for aggregates and backfill, and

the careful disposal of the balance are necessary to avoid any adverse impacts on the environment.


The implementation of the project will affect the existing ecosystems in the project impact area. The

major impact on the biological environmental will include the loss of individual plants and

vegetation cover of access road construction and construction of head pond, surge tank, access road

to the surge tank, power house site, etc. Approximately 2.53 ha of forest land will be acquired for

the aforementioned components, out of which 1.03 ha consists of is disturbed forest and 1.5 ha is

mostly belong to herbaceous vegetation with sparse presence of bushes scattered where clearance is

not required. The left bank of the dewatered stretch lies in the buffer zone area of the LNP, but no

forest have to be cleared from LNP.

Within 1.03 ha the disturbed forest for hydropower components, it has been estimated that

Altogether 404 tress including 377 pole size and 27 above pole size trees needs to be felled and 408

are sapling belonging to partly Community Forest and mostly from Sirupani Community Forest. The

volume of matured trees is 4344.265 cubic feet.

As the proposed project. will use tail water of Trishuli 3A HEP the impacts on fish migration is

negligible. Furthermore the lack of long distance migrant and important mid rang migratory species

except Snow trout also limits the impacts. As mentioned in baseline the upstream migration of

major migration species is already due to construction of dam at existing Trishuli HEP and further

diversion of water for Devighat Powerhouse the likely impact due to construction of intake on fish

migration is insignificant.



10.5.3 Socio-economic and Cultural Environment

The proposed Project will affect 22.15 ha of land out of which 8.13 ha is cultivated land. The total

permanent cultivated land to be acquired for the different project components is estimated to be

5.13 ha. Similarly, 3.0 ha of cultivated land will be used temporarily by the project. A total of 47

household will be affected directly due to land and property acquisition for the project. Out of total

affected household, 9 households have to be displaced from their place of residence. The magnitude

of impact is considered to be high, local and long termed in duration.

The total production loss annually of different crops due to project implementation is estimated to

be 13.3 MT. Considering the availability of agricultural land. This impact is expected to be high in

magnitude, local in extent and long term in duration.

Due to the influx of large number workforce (1000) during construction phase there will be

significant stress on the existing infrastructures.

Altogether, 15 structures (9 house and 6 cowsheds) belonging to 8 households are required to be

relocated due to the implementation of the project. Most of the structures are located on

powerhouse/camp site and access road.

The employment opportunity and economic activities are the areas of income during construction

period. This short term economic boon will contribute to the development of local economy. The

project area and region will benefit from the royalty paid by the licensee of the hydropower project

to the DOED. Besides from the aforementioned benefits from the project implementation the local

people will be able to invest in the proposed project and get economic benefit which will ultimately

play a major role in poverty alleviation and bring position change in their economic status.

10.6 Alternatives Study

During the feasibility and EIA study process a comparison of alternative project strategies, sites for

facilities, technologies and designs were carried out. These alternatives were based on site condition

and practical option developed by the technical and environmental team.



10.7 Mitigation Measures


The main impacts associated with this type of project will firstly be those related with land take.

However, minimization of land takes wherever feasible and minimization of ground disturbances

caused by construction activities and access to sites will be made. Slop protection structures such as

revetment wall at the right bank of Trishuli river at the intake along the steep access road surge tank.

The minimum average monthly flow for the driest month, February, at the intake site is 38.4 m3/sec.

As per the Hydropower Development policy 3.84 m3/sec will be released from the headwork

(connecting chamber) corresponding to 10% of this flow (or the minimum required quantum as

identified in the EIA which ever higher). This flow will augment the minimum release from Upper

Trishuli 3"A"HEP.


Selected felling will be the best approach to minimize the loss of vegetation at the project

construction site. Trees that are likely to be felled or construction works will be counted, marked

and harvested with proper forestry techniques and involving technical staff from the District Forest

Office. However, the compensation for the felled trees will be provided to the respective owner.

The products from Community Forests and private forest recovered during site clearance will be

handed over to the concerned CFUG and the owners. AS a compensatory measure for the loss of

trees plantation in a ratio of 1:25 will be done in the project area. The land for the compensatory

plantation and the type of species will be decided with coordination with the District Forest Office

and CFUG.

Illegal cutting trees and encroachment on forest will be restricted. Use of kerosene and LPG in the

construction and the labor camps as well as in tea stalls and restaurant by establishing will be



encouraged. The project will also grant subsidy on kerosene and LPG to the project affected

communities.

A wildlife conservation programmed in co-ordination with Department of National Parks and

Wildlife Conservation (DNPWC) and LNP will be implemented. The locals and the CFUG around

for the head works sites, Buffer Zone User Groups and Buffer Zone Council will be consulted for

wildlife conservation Awareness Programs and trainings.

Finish will be prohibited in 4 km reduced flow zone for about 5 dry months. The project

management will develop some enforcement mechanism in association with local administration,

local leaders, District Agriculture Development Office and Nepal Fisheries Society (NEFIS) to ban

the illegal fishing in the project area. Project works will be strictly prohibited for fisheries. Hoarding

board containing information and warning sing regarding river pollution, use of fishing gears,

dynamite, importance of fish conservation and habitat management will be placed at 1 km intervals

along the reduced flow stretch and at public places close to Trishuli River to award and pre inform

the people about restriction of fishing.

The open water stocking will be done to minimize the impact of the project on native fauna. The

open water stocking including the indigenous current loving fish. Release of 5,00,000 fingerlings at

the rate of 1,00,000 fingerlings per year is proposed for 5 years in upstream of the Trishuli River to

minimize the impact on fish fauna. Since Trishuli Fish of Nepal Agriculture Research Council is

within the project area, the required fingerlings can be easily purchased from the farm.

10.7.3 Socio-economic and Cultural Environment

The land required for construction activities will be acquired according to the Land Acquisition Act,

2034 & Land Acquisition Regulation,2045BS. As per this act Compensation Fixation Committee

(CFC) will be formed under the chairmanship of Chief District of the concerned district including

chairperson of affected VDCs, representative of affected people, representative of Land Revenue

Office and the project. Compensation will be distributed as per rate fixed by CFC. Based on the

discussion with the local people, observation at site and from the conclusion made by the

environmental team, compensation will be provided by the following two methods.



Cash Compensation

Land-for-Land and House-for-House Compensation

Project will provide technical and financial for the local development of the project area. Field

investigation and perception of the local people show that there is need of some support on the

following sectors like Education, health, water supply and sanitation.

10.8 Environmental Management Plan

During the planning and pre-construction phase the prime responsibility for the environment

management will be of Nepal Electricity Authority (NEA) as The proponent of the project. A

project company has been already formed under the name Upper Trishuli 3B Jalbidyut Company

Ltd. which will operate in BOOT model. In that case a project Company1 will take over all rights

and responsibilities associated with the implementation of this EMP.

A unit will be established to implement the day-to-day Environment Management Plan. Upper

Trishuli 3B Environment Unit will be formed which will consist of expert from ESSD, Ministries,

local administrators and other qualified personnel from the local market. This unit will function

under the direct supervision of the Project Director. This unit will carry out the community related

activities on behalf of the project and implement the mitigation measures as prescribed in the EMP.

This unit also be responsible for formulating the annual Environmental Protection Plan (EPP). This

plan will outline the implementation mechanisms of the environmental mitigation measures foreseen

in the EMP.

Environmental monitoring will be carried out at all the project impact areas in a regular or

intermittent schedule. The environmental monitoring will be carried out by the Ministry of Energy

as per the EPR. An environmental audit will be required two years after the commencement of the

project. The Ministry of Environment will be responsible for the auditing as mentioned in the EPR,

1997.



The total cost for implementing the Environmental Management Plan is estimated to be NRS

15,41,43,730. This cost including mitigation and enhancement cost, monitoring cost and auditing

cost. The total Environmental Management Cost amounts to approximately 2.5% of the total

project cost.

10.10 Review of Plans/policies, acts, rules/regulation, guidelines, conventions strategies

and standards

The prevailing Acts, Policies, Regulation and Guidelines which are required for the development of

hydropower projects in Nepal have been reviewed while preparing the present EIA report of the

Upper Trishuli 3B Hydroelectric Project. Some of the important Guidelines and Acts and their

relevance in hydropower development have also been reviewed and discussed. The regulation and

acts related to power and water sector like Hydropower Development policy (1992), Water

Resources Act (1992), Electricity Act(1992), Electricity Act (1992), water Resources Regulations

(1993) have also been referred while preparing the report. Important Acts like Land Acquisition

Acts, Forest Acts and Aquatic Animal Protection Acts have also been extensively reviewed while

preparing the report. As the left bank of the proposed weir lies in the buffer zone of the Langtang

National Park, the National Park and wildlife protection Act,2029, Buffer zone Management

Regulation,1994 and policy for construction and operation of physical infrastructure within

Conservation Area, 2065 has also been reviewed while preparing the EIA report.

10.11 Conclusion

The environmental impacts of Upper Trishuli 3B Hydroelectric Project identified during the

Environmental impact Assessment Study are fairly unproblematic. Land take, changes in land use

pattern land degradation and soil erosion, dewatering of river, waste disposal and forest loss are

some of the impacts identified in construction of river, The key environmental issues during the

operation phase of the project include downstream flow variations, waste disposal, safety hazards

for the plant staff. The impacts are moderate, within acceptable limits and can generally be mitigated

.

There are environmental risk reduction opportunities to be reaped on behalf of the local

communities, which will experience positive rural development activities. Other direct benefits of



the project will be form opportunity for local people for share investment in the project,

establishment of industries and general improvement of infrastructures and services in the project

impact area due to reliable electricity and some employment to the local people.



Chapter 11:

Cost Estimate

11.1 General

This Cost Estimation Report describes the methodology used and presents the project cost

estimate. The project cost estimate is carried out in parallel with the quantities of various

items taken off from the detail design drawings and quantities derived from quantity estimate.

Most of the area and lengths are measured in the AUTOCAD drawings and given in the quantity

estimate sheets.

11.2 Criteria, Assumptions and Cost Components

The following criteria and assumptions are the basis of the cost estimate:

i) All costs are in July 2013 price level.

ii) For currency conversion, the following rate, valid in July 2013 was used:

iii) US $1 = NRs 95

iv) Identifiable Nepalese taxes and custom duties are included.

A key assumption is that the project management and procurement policy will stress t o open

competitive bidding and those government policies will not hinder cost-effective construction.

11.3 Estimating methodology

The major component breakdowns for the estimating process are:

i) support facilities such as project roads, camps, construction power and etc

ii) main civil construction works

iii) electromechanical equipment

iv) hydro metal works



v) transmission and iterconnection facilities

v) engineering, management, and administration

vi) resettlement, land acquisition, and environmental provisions

vii) contingencies

11.4 Civil Works

The cost estimate was prepared on the basis of the sequential execution of the following

steps:

i) Subdivision of the total project into a number of distinct structures (camp

construction, project road, adit tunnels, underground intake, headrace tunnel, surge

tank, penstock, powerhouse, tailrace, metal works, transmission line works,

electromechanical works etc.).

ii) Breaking down of structures into a number of distinct construction tasks. These are

overburden excavations, rock excavation, underground rock excavation, backfill work,

concrete works, shotcrete works, rock bolting, grouting, haulage, form works, steel

works etc.).

iii) Calculation of the quantities of each items according to the above mentioned tasks for

the two units of 21 MW installed capacity are considered. Detail quantity estimate of

each items have been carried out in 1:500 scale map and detail design drawings.

Quantities of each item are measured in AUTOCAD and given in the appendix.

iv) Unit rates of all the required items have developed by the Trisuli Jalvidyut Company

Limited (TJCL) with the prevailing market rates. The hourly rates of the machines are

taken from different companies that have been already working in Nepal.

v) The unit rates comprises of 5 % contingencies of unforeseen works, 15 % overhead

and 13 % VAT. The labor rates are used as per the district rate given in the Rasuwa

Nuwakot District. 7.5 % contingencies cover the market price of labor rate as well as

unforeseen works in the item.

v) The summation with allowances for, contingency and allowances for engineering and

management and provision for price contingencies gives the total project cost.



The total estimated cost for civil work is 2683 million N P r without p h y s i c a l

contingencies, Price contingencies and project management cost. The headrace tunnel is the

major cost in civil structure followed by powerhouse civil works. Cost of the headrace tunnel,

pressure tunnel and dropshaft is 1491 million NPr and the powerhouse cost is 331 million NPr.

11.5 Electro-Mechanical Equipment

The two numbers of 21 MW unit capacities are installed to generate 42MW of power. The cost of

supply, transportation and installation of turbines, generators are 1306.5 Million NPr. This cost are

taken from the similar project that have been under construction. The cost per kW is 1541 US $

with 95 NPr per unit of US $

11.6 Hydro-mechanical equipment

The hydromechanical works are required in the headrace pipe, gates, steel lining in the drop shaft,

pressure tunnel, tailrace gates. The cost of these materials are 451.3 Million NPr, includes

installation and manufacturing.

11.7 Resettlement, Land acquisition, and Environmental provisions

Cost for resettlement and Environmental mitigation and monitoring of the project during pre-

construction and construction is estimated of 154.143 million NPr.

11.8 Contingencies

Contingencies were applied to various areas of work to cover changes in physical scope, which

cannot be presently identified and estimated. For the present level of studies the following

allowances were applied:

• 10 % on civil works, (underground and surface)

• 5% on Electro-mechanical equipment, metal works and Transmission works

• 1.5 % Tax and duties



• 7.5 % Price contingencies

• VAT @ 1% (E/M, H/M &Transmission Line) & @13% in others

Civil contingencies for the project is 370.68 million NPr and Electro mechanical works of the

project is 89.31 million NPr.

11.9 Pre operating and management cost

A sum of 10% of the cost is provided for engineering, management and administration during

construction. The total cost for this is 720 million Npr.

11.10 Project Cost

The Sub Committee during discussion with the Project team suggested that the team follow the

unit rate norms used by the subsidiary companies of Chilime Hydropower Company Limited for

estimating the cost of their projects. Accordingly, it was noted that the rate analysis/ unit rates

followed in Middle Bhotekosi Hydroelectric Project have been taken by the Project as the

reference while estimating the cost of UT3'B'HEP. The cost estimates prepared by the Project

team at the price level of 2013 have been reviewed and finalized under the following cost

component categories

(i) Land and Support Cost,

(ii) Pre-operating Expenses,

(iii) Infrastructure Works,

(iv) Main Civil Works,

(v) Hydro-mechanical Works,

(vi) Electro-mechanical Works,

(vii) Taxes and Duties,

(viii) Physical Contingency, and

(ix) Price Contingency.



Land and Support Cost

The land support cost includes the cost of land acquisition, RoW acquisition and

compensation, environmental mitigation, local development and the provision for

corporate social responsibility, CSR. The total cost estimate under this category is

estimated at NRs 210,000,000.

Pre-operating Expenses

The pre-operating expenses include the cost of project preparation for implementation

including feasibility and detail design, environmental study, cost of project engineering

and management and developers’ fee. The total cost estimate under this category stand

at NRs 720,000,000.

Infrastructure Works

The infrastructure cost comprises of access road, camp facilities, construction power etc.

The total cost estimated for this category stand at NRs 93,358,372.

Main Civil Works

The main civil works cost includes the cost of main civil structures of the hydropower

project. The major components included under this cost category includes the head

pond, headrace tunnel, power house, adit tunnels, surge tank, tailrace conduit and

tailrace pond etc. The total cost under this category is estimated at NRs 2,683,475,976.

Hydro-mechanical Works

The category includes the cost of gates, stoplog, trash rack, steel pipe for penstock etc.

The total cost estimate under this category is NRs 451,363,073.

Electro-mechanical Works

The electro mechanical costs include the cost of transmission line, turbines, generators

and the auxiliaries. The total cost estimate under this category stands at NRs

1,306,505,000.

Taxes and Duties

This cost category mainly includes the custom levied on import of equipment local taxes

etc. and VAT levied on civil works and installation portion of hydro mechanical and



electro mechanical equipment. The total cost under this category is estimated at NRs

596,546,492

.Physical Contingencies

An amount equal to 5% of the electromechanical cost, 10% of the main civil costs and

other costs is provisioned for the purpose of physical contingency to cover unforeseen

works during the execution of the project. The total cost under this category is calculated

to be NRs 460,001,839.

Price Contingency

An amount equal to 7.5 of the total cost with taxes is provisioned for the purpose of

price contingency to cover the escalation allowed by the provision of the contract. The

price contingency stands at NRs 491,231,306.

The total cost of the project estimated as of November 2013 stands at Rs. 6,613,219,874 as

summarized in Table 11.1 below. Total project cost for installed capacities of 2 X 21 MW is

7040.98 million Npr with price contingencies, VAT, Tax and duteis. Details cost estimates of

the project is given in the appendix. The total financial cost including 10 % Interest during

construction is 7745.08 million Npr. Therefore, the cost of project per MW is 18.44 Crore.

Table11.1: SUMMARY OF COST ESTIMATE

S.N. Description of Item Amount (NPr) A Land & Support 210000000 B Pre-Operating Expenses & Management Cost 720000000 C Infrastructure Works 93358372 D Civil Cost 2683475976 D1 General Items 272800000 D2 Main Civil Works 2410675976 100 Head Pond at Tailrace of UT3A 141313974 200 Adit Tunnel-1 71682595 300 Adit Tunnel-2 46459701 400 Adit Tunnel-3 34857066 500 Headrace Pressure Pipe 133113564 900 Headrace Tunnel (Upto Surge Tank) 1208813207 1000 Underground Surge Tank 113601089



1100 Valve Chamber & Access Tunnel 22491036 1700 Pressure Tunnel & Vertical Shaft 146823749 2600 Powerhouse 330993711 2700 Tailrace Conduit 97389898 2800 Tailrace Pond 43460900 3000 Switchyard (Civil Works) 19675487

E Hydro Mechanical Cost 451363073.8 3200 Gates/Stoplogs/Valve 142728782 3300 Steel Lining in Pressure Shaft 164568650 3400 Headrace Pressure Pipe 142982920 3500 Trash Rack 301498 3600 Air Suction Pipe (Surge Tank to Valve Chamber) 781224

F Electro-Mechanical Cost 1306505000 3700 Turbine Equipment 388858750 3800 Generator 521360000 3900 Auxiliaries - Hydraulic Equipment 27431250 4000 Auxiliaries - Electrical Equipment 359955000 4100 Gantry Crane 8900000

G

132kV Single Circuit Transmission Line and bay extension and metering arrangement in Trishuli 3B Hub 28500000

Total (A+B+C+D+E+F+G) 5493202422

VAT @ 1% (E/M, H/M &Transmission Line) & @13% in others 499752146

Base Cost as of 2013 5992954568 Physical Contingencies 460001839

5.0 % of E/M &H/M Works and Transmission Line 89318404

10.0 % of Main Civil Works & Others 370683435 Total Cost as of 2013 6452956407 Taxes & Duties (1.5%) 96794346 Total Cost with Taxes & Duties 6549750753 Price Contingencies (7.5%) 491231306.5 Total escalated cost at the end of the construction 7040982060 Interest during construction (10%) 704098206

Total financial cost of the project at the end of Construction NRs. 7745080266

Exchange Rate 1 US$ is equivalent to NRs. 95.00 95



Total financial cost of the project at the end of construction in US$.: 81527161

Specific Cost of the project (US $ / kW): 1941 B/C Ratio 1.69 FIRR 19.02


12-1


Chapter 12:

Project Evaluation

12.1 General

A hydropower project has significant impacts in terms of employment and consumption of scarce

national finances. The number of people and industries affected through the tariff implications of

the project require that the costs and benefits of the project must be evaluated from the broad

social context. The project must be able to demonstrate appropriate return to the nation in

economic analysis. The Upper Trishuli 3B Hydroelectric Project has been evaluated on economic

and financial terms.

Financial planning is concerned with the estimation of the financial implications of a

proposed development. It is based on the use of market prices and, therefore, includes any taxes

or royalties which will be levied on the factors of production and any subsidies, capital or

operating, which may be received as part of the development. All costs are charged and all

revenues credited to the analysis in the actual amounts expended or received and in the case of

foreign costs converted at the anticipated official exchange rate at the time of expenditure. For

this analysis the financial rate of return and cash flow is assessed from the perspective of a utility

owner/operator.

A number of specific items are treated differently in an economic analysis when compared to a

financial analysis specifically:

• Subsidies are not included as benefits to the project. Subsidies are considered to be

government transfer payments and as such are not part of the economic price. Subsidies are,

however, included in financial prices;

• Similarly, Taxes and Duties and Royalties are not included as costs in the economic

analysis but, included in the financial analysis;

• The economic analysis does not include Price Contingencies. Unless, otherwise

specified, inflation (the reason price contingencies are included) is assumed to affect both

project inputs and outputs equally. Physical contingencies are, however, retained in both

financial and economic analyses;

• In economic analysis, interest on capital is not separated in the analysis, as it is part of the


12-2


return to society, which is to be captured. In the financial analysis, interest and capital

repayment are separable costs and are not part of the benefit.

12.2 Methodology

The evaluation methodology follows the traditional practice in project analysis where

benefits and cost streams are first estimated. The project cost is expressed in terms of economic

cost by using "shadow prices" for the economic analysis. For a project to be acceptable, project

benefits should outweigh costs.

In general terms, both economic and financial evaluations involve the following tasks:

12.2.1 Estimation of Project Costs

Cost components include construction of head ponds, intake and powerhouse construction, water

conveyance, and other civil works, transmission and sub-station costs associated with the project,

environmental mitigation, management and monitoring costs, annual operating and maintenance

expenditures and any other costs identified for the specific project. The costs are allocated to the

year of expenditure and expressed at constant prices. The financial analysis extends the costing to

include taxes and duties, insurances, escalation, loan processing fees, interest during construction,

capital repayment and interest on debt.

International goods are typically priced at their actual cost. The major inputs to the project are

cement, steel, construction fuel, thermal generation fuel, labor and equipment.

12.2.2 Estimation of Project Benefits

For the economic analysis, the principal project benefits are revenues which can be derived from

the operation of the project. For the estimation of salable energy generated from the project,

transmission loss, self consumption and outages (scheduled & unscheduled) is assumed to be 3%.

It is assumed that the commercial operation of the project is from November 2018.

Thermal power projects emit gases which contribute to the greenhouse gas effects, whereas

hydropower projects are considered to be a clean source of energy in terms of air pollution and


12-3


emissions. An added benefit is thus attributed to hydropower projects by allocating a benefit equal

to the equivalent amount of greenhouse gases that would be emitted by an equivalent thermal

plant considering the quantity of CO2, SO2 and NOx emissions and proxies for the

environmental cost of those emissions. As yet there is no mechanism to issue emission benefit

credit to the developer, the emission benefit is not considered in the present financial analysis.

The energy generated by the project will be supplied to a distribution utility, Nepal Electricity

Authority by entering into a power purchase agreement (PPA). NEA has published the following

buying rates for the electricity generated from small plants (installed capacity up to 25 MW) in

2009:

For four dry season months (mid-Dec to mid-April) NRs 8.40/kWh

For eight wet season months (mid-April to mid-Dec) NRs 4.80/kWh

The prices will be escalated at 3% per annum (on simple rate basis) for nine years from

commercial operation date and will be flat thereafter.

For the projects bigger than 25 MW, the prevailing average energy price is around 6 USc/kWh.

For the financial analysis, the principle project benefits are revenues, which can be derived from

the operation of the project. Average energy is considered for financial analysis.

For this project the selling price of average energy is targeted to 4.50 NPr/kWh.

12.2.3 Construction Period

The project construction period will be four years. Cost disbursement will be as given in below:

Year

Project Cost ( 7745.08 Million Rs.)Equity (30 %) Debt (70 %)

2015 (15 %) 348.5 813.2

2016 (35 %) 813.2 1897.5

2017 (40 %) 929.4 2168.6

2017 (10 %) 232.4 542.2

Total (100 %) 2323.5 5421.6

The major portions of the project cost are disbursed within the construction period. However,


12-4


annual cost including operation and maintenance cost is spread over the analysis duration.

Similarly, the project benefits are received during the operation period only.

In the economic analysis, project costs and benefits are compared using discounted measured of

project worth. Discounting is the technique used to convert a stream of benefits or costs to its

Present Value to account for the time value of money. In general, three decision making tools are

estimated during this analysis:

12.2.4 Calculation of Net Benefits

In the economic analysis, project costs and benefits are compared using discounted measures of

project worth. This method uses discounting technique to convert a stream of benefits or costs to

its net present value to account for the time value of money. In general, three discounted measures

of project worth will be used in this analysis:

• the Net Present Value (NPV) is the present value of the incremental net benefit stream, that is,

the sum of the discounted flow of project benefits net of project costs. In the analysis, all costs

and benefits have been expressed in constant terms and discounted at 10 percent per annum

in the reference case. A positive NPV indicates that the project generates benefits in excess of

those required by the discount rate. A project with a positive NPV is, therefore, considered

economically feasible.

• The Internal Rate of Return (IRR) is the discount corresponds to the zero NPV. That is the

discounted rate at which the present value of the benefits equals the present value of costs.

The IRR indicates the economic profitability of the investment project. The IRR is used to

assess whether a project meets a minimum threshold or not. If the IRR is less than the

discount rate, which has been used, the project is thought to be uneconomical, as the

discounted benefits do not outweigh the discounted costs. Projects are attractive if the

calculated IRR exceeds the cut-off-rate or opportunity cost of capital.

• The Benefit- Cost Ratio (B/C) is the ratio of the present value of the benefit stream to

the present value of the cost stream. The B/C Ratio indicates the extent to which the

discounted stream of benefits exceeds the discounted stream of costs. A ratio greater than one

indicates that benefits exceed costs while a ratio that is less than one indicates that costs


12-5


exceed benefits.

• Specific Energy Cost is the ratio of discounted cost and the discounted energy within the

economic life of the project. This indicates the long term average cost of the generation.

Lower the value of specific energy cost, better the project is. In case of avoided cost method,

the hydro project is considered to be feasible if the specific energy cost of the hydro

project is lower than that of the alternative source of energy which is candidate thermal

plant.

In the financial analysis, the main tool for the evaluation of the project is the return on equity. The

project with minimum average tariff yielding desired return on equity is termed as financially

viable project. Apart from this, the debt service ratio should be acceptable to the bankers.

12.3 Assumptions

The economic and financial evaluation is based on a number of key assumptions and parameters.

A reference or base case for the economic and financial analysis was prepared and then sensitivity

cases were prepared for the economic analysis. The principal criteria and parameters are discussed

below.

12.3.1 Discount Rate

The discount rate is a key variable in any economic analysis. It is necessary parameter for obtaining

time value of money to compare future costs and benefits in terms of today’s currency values.

However, a discount rate is not an interest rate. It reflects not the borrower’s cost of capital but

rather the social cost of capital; that is the social (economic) returns which are foregone by using

the funds for the project under consideration rather than elsewhere in the economy. The reference

discount rate or opportunity cost of capital selected for the study is 10%.

12.3.2 Cost Datum

All costs and benefits are expressed in constant prices (i.e., excluding general escalation).


12-6


12.3.3 Planning Horizon

The economic life of the project has been taken as 50 years. Replacement of electrical and mechanical components is considered after 25 years of operation. Costs and benefits may occur

after the 50 year planning horizon, however, their inclusion will have little effect on the evaluation

results because of the discounting procedures employed in the analysis.

For financial analysis, 25 years of commercial operation has been considered.

12.3.4 Operation and Maintenance Cost

It has been assumed that 1.5% of the project cost will be required annually to meet operation and maintenance cost including repair and replacement costs. This value has been derived from the

experience of hydropower projects in the country. For financial evaluation, this cost will be escalated annually taking suitable inflation rates.

In addition, for the financial evaluation the following parameters are also considered:

12.3.5 Price Escalation

One of the major parameters to be considered in the financial evaluation is the price escalation. It is required to anticipate fund requirement at any given period. An escalation of 3 % per annum has

been used for 9 years.

12.3.6 Taxes, Duties and VAT

Taxes, duties and VAT payable to the government or its bodies have to be considered in the

financial evaluation. At present, the government charges 1 % custom duties for import of machinery and equipment for use in the project. However, as per prevailing regulations, no

income tax concession has been provided.

12.3.7 Royalties

Royalties are payable to the government for natural resource usage. As per the prevailing Electricity Regulations, the following royalties are levied:

for the first fifteen years

capacity royalty NRs 100 per kW of the installed capacity per year


12-7


energy royalty 2 % of energy sales revenue

from the sixteenth year onwards capacity royalty NRs 1000 per kW of the installed capacity per year energy royalty 10 % of energy sales revenue

12.3.8 Debt Equity

As hydropower projects are highly capital intensive, funds has to be obtained from various

financial institutions like banks, credit organizations. It is also imperative that such a project could

not be built solely on loans as the lender will require that the Developer also put some funds.

Generally, loan portion of the cost varies from 60 to 85 %. For the present study, debt-equity ratio

of 70:30 has been assumed.

12.3.9 Interest Rate

The loan amount will require some interest to be paid on the amount borrowed. The interest will

be capitalized till the project starts producing revenue. Generally, the banks charge 8 to 12 % for

such loans. For the present study, an interest rate of 10 % has been considered.

12.3.10 Loan Repayment Period

The debt portion will have a grace period equal to the construction period and the repayment

starts after the revenue generation starts. It will take 6 to 10 years for total repayment of the loan

for small projects and may extend to 15 - 20 years for larger projects. For this project, a loan

repayment period of 8 years has been considered.

12.3.11 Other Charges

In addition, the banks may charge guarantee money for the loan provided, insurance charges,

registration charges, if any, to be levied from the project. These charges are bank specific and are

unknown at this stage. For this preliminary analysis, 1 % of financial cost has been considered to

account for such expenses.


12-8


12.4 Economic Evaluation Result

With the assumptions stated above, economic analysis has been carried out. Cash flow series has

been developed for the project economic life and the cash streams have been discounted to the

first year of construction. Required economic indicators were then determined. The input

parameters and results of economic analysis cash flow are shown in Table 12.3 and are

summarized below:

Table 12.1: Result of Economic Analysis

Net Present Value of the project 3,551 million NPr.

Internal Rate of Return 15.36

B/C ratio 1.55

Specific Energy Cost 2.81 NPr/kWh

Sensitivity Analysis

In order to check the sensitivity of the economic indicators, analysis was carried considering

different scenarios. The different scenarios considered are as follows:

Sensitivity Test

(a) Discount Rate 8, 10, 12, 14 %

(b) Project Cost - 10 % and + 10 %

The results of the sensitivity analysis are shown below: Table 12.2: Result of Sensitivity analysis

Disc Rate Cost Factor

8% 10% 12% 14% 10% -10%

PV Cost 6,978,878 6,418,430

5,982,289

5,625,708

7,060,273

5,776,587

PV Bene

13,238,669

9,979,006

7,780,492

6,227,184

9,969,567

9,969,567

NPV 6,234,828 3,551,137

1,794,570

600,054

2,909,294

4,192,980

B/C 1.89 1.55

1.30 1.11

1.41

1.73

IRR 15.36% 14.08% 16.87% Sp Cost 2.30 2.81 3.36 3.94 2.81 0.36


12-9

It is evident from the above table that the project is economically viable for all the cases. A graph of B/C ratio versus discount rate is depicted in Figure 12-1.

Figure 12-1: B/C Ratio vs Discount Rates

Table 12.3: Economic Analysis Detail Table

Capacity 42.00 MW IRR 15.36%

Construction Cost 7,040,982

Energy - Firm

91.70

GWh B/C 1.55

E&M Cost 1,757,868

Energy - Sec

236.04

GWh NPV 3,551,137

Year Constn Cost O&M Cost Total Cost

Firm Energy Benefit

Secondary Energy Benefit

Total Benefit N C F

1 1,056,147 - 1,056,147 - - - (1,056,147)

2 2,464,344 - 2,464,344 - - - (2,464,344)3 2,816,393 - 2,816,393 - - - (2,816,393)4 704,098 - 704,098 - - - (704,098)

5 - 105,615 105,615

412,667 1,062,179 1,474,846 1,369,231

6 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

7 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

8 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

9 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

10 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

11 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

12 - 1,369,231

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1.90

2.00

8% 9% 10% 11% 12% 13% 14% 15%

B/C

rat

io

Discount Rate


12-10


105,615 105,615 412,667 1,062,179 1,474,846

13 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

14 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

15 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

16 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

17 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

18 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

19 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

20 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

21 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

22 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

23 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

24 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

25 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

26 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

27 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

28 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

29 1,757,868

105,615

1,863,483

412,667

1,062,179

1,474,846

(388,637)

30 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

31 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

32 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

33 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

34 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

35 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

36 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

37 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

38 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

39 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

40 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

51 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231


12-11

52 - 105,615 105,615 412,667 1,062,179 1,474,846 1,369,231

53 - 105,615

105,615

412,667

1,062,179

1,474,846 1,369,231

12.5 Financial Evaluation

A preliminary financial analysis was carried out as cash flow of revenue and expenditure. It has

been assumed that debt equity ratio will be 70:30 with an interest rate of 10 % on debt. It was also

assumed that the loan will have a grace period during construction and will be paid in twelve years

from the start of commercial operation. Royalties and taxes, if applicable, have been deducted

from the revenue to derive net cash flow. Escalation factors based on price index has also been

considered. The assumptions and results of the financial analysis are shown in Table 12.4.

The analysis showed that the project gives return on equity is 17.23 % for a loan interest rate of

10% and repayment period of 8 years for a debt-equity ratio of 70:30. So the project can be

termed financially viable.

Figure 12.2 shows the relation between interest rate and rate of return for the base case of energy

price.

Figure 12-2: Interest Rate vs FIRR

17.23%

8%

10%

12%

14%

16%

18%

20%

8% 9% 10% 11% 12% 13% 14% 15% 16%

FIR

R

Loan Interest Rate


12-12


Table12.4: Financial Analysis Data and Result

Basic Data

Base Year 2015 Project Economic Cost 704.10 Crores NRs O&M Cost 1.50% Construction Period 4 Years Start Year of Construction 2015

Financial Factors Insurance Charges 1.0% of Total Financial Cost Cost Price Escalation 3% per year

Financial Costs Total Project Cost with Inflation 715.94 Crores NRs Interest During Construction 112.77 Crores NRs Total Project Cost with IDC 828.72 Crores NRs

Loan Debt : Equity 70 : 30 Loan Amount 493.75 Crores NRs Interest During Construction 10.00% Repayment Period 8 years

Energy Production Installed Capacity 42.00 MW Firm or Dry Season 94.54 GWh Secondary or Wet Season 243.34 GWh

Energy Prices Energy Benefit

Firm or Dry Season 4.5000 NRs/kWh Secondary or Wet Season 4.5000 NRs/kWh Base Year for Energy Pricing 2019 Escalation of Energy Prices 3% Number of years for above escalation 9 Energy Price after 9 years Dry Season Energy Price 5.7150 NRs/kWh Wet Season Energy Price 5.7150 NRs/kWh

Results

Financial Rate of Return 17.23%



Chapter 13:

Conclusions and Recommendations

Upper Trishuli 3B Hydroelectric Project is being proposed as a cascade development project of

Upper Trishuli 3A Hydroelectric Project and is located immediately downstream of Upper Trishuli

3A Hydroelectric Project (60 MW). After slide modification of tailrace pond of Upper Trisuli 3A

HEP, the same tailrace pond has been adopted as the head pond of Upper Trishuli 3B

Hydroelectric Project. The powerhouse of Upper Trisuli 3B HEP is located approximately 1 km

upstream of the confluence of Salankhu Khola and Trishuli River and 3 km north of the Betrawati

Bazar.. Most of the relevant basic project parameters of Upper Trishuli 3A Hydroelectric Project has

been adopted in Upper Trishuli 3B Hydroelectric Project. These include the monthly flow data, the

flood data, the design discharge and the rating curve at the interface of the two projects. Other

parameters has been calculated independently for this project.

No plant capacity optimization has been done for Upper Trishuli 3B Hydroelectric Project. The

design discharge 51 m3/s applied for Upper Trishuli 3A Hydroelectric Project has been used for

Upper Trishuli 3B Hydroelectric Project as well. This flow comes under 70 % exceedance flow for

the intake site of Upper Trishuli 3A Hydroelectric Project. All energy calculations for Upper Trishuli

3B Hydroelectric Project has been based on monthly flows and the flow through Upper Trishuli 3A

Hydroelectric Project. Power and energy calculations indicate that the Upper Trishuli 3B

Hydroelectric Project will have an installed capacity of 42 MW and will generate approximately

94.54 GWh during the dry season and 243.34 GWh during the wet season with a net head of 95.13

m.

Immediately after the head pond, the water conveyance is carried out by the headrace pipe to the

tunnel intake. The length of the headrace pipe is 384.27 m up to the tunnel intake. The headrace

tunnel is approximately 3744.69 m long and has four bends and intersect two major Kholsi as

shown in layout plan. The optimized diameter of the tunnel is 5.5 m (circular, 52.5%) concrete lined

and 6.6 m (Horseshoe, 46.4% ) in shotcrete lined. The surge shaft will be located on the hillside

above the powerhouse and will have a finished diameter of 15 m. An underground valve chamber

is located at 31.3 m downstream of the surge tank. The length of the pressure tunnel after surge



tank to drop shaft is 98.17 m including valve chamber cavern. Total length of vertical shaft is 69.07

m including the bends. The horizontal pressure tunnel from the end of drop shaft to the penstock

bifurcation is 181.65 m. The thickness of steel lined is 18 mm along the horizontal pressure tunnel.

The surface powerhouse is located approximately 1.2 km upstream of the confluence of Salankhu

Khola and Trishuli Rivers. The Trisuli 3B hub substation 220/132 kV is under construction, 3km

north of the powerhouse site and will be used for power evacuation. The project construction will

require a period of nearly 4 years and can be completed in middle of the year 2018.

Based on the detailed project study, the total cost of the project is 7040.98 Million Npr. This project

has a B/C ratio of 1.55, an financial internal rate of return of 17.23 % and specific energy cost of the

project is 2.81 cents/kWh at 4.50 Npr per unit selling price of energy.

As Upper Trishuli 3B Hydroelectric Project is a downstream cascade development of Upper Trishuli

3A Hydroelectric Project, it is envisaged that it will be implemented parallel to the upstream project.

Much of the infrastructure and all of the preparatory works proposed for Upper Trishuli 3A

Hydroelectric Project are already in place prior to the implementation of Upper Trishuli 3B

Hydroelectric Project. This creates a very favorable situation for the construction of Upper Trishuli

3B Hydroelectric Project. In addition to this, no headworks structures, desander or river diversion

works and less transmission line will be required for this project.

Based on the above parameters, Upper Trishuli 3B Hydroelectric Project is technically and

financially a very attractive project. It is hence recommended that this project should be expedited in

order to meet the power/energy demand of the country at the earliest.