Final Theory

Table of Contents1. INTRODUCTION...........................................................................................................................6

1.1 BACKGROUND.........................................................................................................................6

1.1.1 Need for focus upon Hydropower Projects...............................................................................6

1.1.2 History of Hydropower Development......................................................................................6

1.1.3 Hydropower development in Nepal..........................................................................................7

1.1.4 Hydropower Potential of Nepal.............................................................................................10

1.1.5 Justification for Small Hydropower Project.......................................................................12

1.2 OBJECTIVES............................................................................................................................14

1.3 SCOPE AND LIMITATIONS...................................................................................................14

2. LITERATURE REVIEW..............................................................................................................15

2.1 POWER SITUATION IN NEPAL............................................................................................15

2.2 LOAD FORECAST...................................................................................................................16

2.3 ENERGY CONSUMPTION.....................................................................................................17

2.4 DEVELOPMENT OF GRID SYSTEM AND POWER TRANSMISSION PLAN...................17

2.5 POWER DISTRIBUTION PLAN.............................................................................................19

2.6 LEGAL PROVISIONS TO INVEST IN HYDROPOWER SECTORS.....................................20

2.7 CHALLENGES AND ISSUES IN NEPAL’s POWER SECTOR.............................................23

2.8 COMPONENTS OF HYDROPOWER.....................................................................................24

2.8.1 Weir and Undersluice............................................................................................................24

2.8.1.1 General..................................................................................................................................24

2.8.1.2 Design consideration of Diversion weir.................................................................................25

2.8.1.2.1 Elevation of Weir crest......................................................................................................25

2.8.1.2.2 Length of Weir and Undersluice........................................................................................26

2.8.1.2.3 Shape of Spillway..............................................................................................................27

2.8.1.2.4 Forces acting on Weir........................................................................................................27

2.8.1.2.4.1 Water Pressure...............................................................................................................27

2.8.1.2.4.2 Uplift Pressure...............................................................................................................28

Feasibility study of Middle Tadi Khola HEP Page 1

2.8.1.2.4.3 Weight of Weir..............................................................................................................28

2.8.1.2.5 Modes of failure and Criteria for structural stability..........................................................28

2.8.1.2.5.1 Overturning about toe....................................................................................................28

2.8.1.2.5.2 Compression or Crushing...............................................................................................29

2.8.1.2.5.3 Sliding............................................................................................................................29

2.8.2 Intake Structure......................................................................................................................30

2.8.2.1 General..................................................................................................................................30

2.8.2.2 Design considerations of intake.............................................................................................31

2.8.3 Gravel Trap............................................................................................................................32

2.8.3.1 General......................................................................................................................................32

2.8.3.2 Design Consideration.................................................................................................................32

2.8.4 Approach Canal.....................................................................................................................33

2.8.4.1 General..................................................................................................................................33

2.8.4.2 Design Consideration.............................................................................................................33

2.8.5 Settling Basin.........................................................................................................................34

2.8.5.1 Design Consideration.............................................................................................................34

2.8.5.2 Sediment Flushing System.....................................................................................................35

2.8.6 Penstock pipe.........................................................................................................................35

2.8.6.1 General......................................................................................................................................35

2.8.6.2 Design Considerations...............................................................................................................37

2.8.6.2.1 Owner’s Requirement.........................................................................................................37

2.8.6.2.2 Choice of materials.............................................................................................................37

2.8.6.2.3 Site-Specific Requirements.................................................................................................38

2.8.6.2.4 Preliminary Study...............................................................................................................38

2.8.6.2.5 Type of installation.............................................................................................................39

2.8.6.2.6 Conditions for selection of Pipeline....................................................................................39

2.8.6.2.7 Alignment...........................................................................................................................40

2.8.6.3 Economic Diameter...................................................................................................................40

2.8.6.4 Determination of Economic Diameter or Optimizing Penstock Diameter.............................41

2.8.6.6 Economic Diameter Equations...............................................................................................42

2.8.6.7 Water Hammer.......................................................................................................................44

2.8.6.8 Calculation of Head Losses....................................................................................................44


2.8.6.9 Bifurcation.................................................................................................................................44

2.8.7 Anchor Block and Support Piers............................................................................................45

2.8.7.1 General......................................................................................................................................45

2.8.7.1.1 Location of Anchor Block...................................................................................................45

2.8.7.2 Design Considerations...........................................................................................................45

2.8.7.3 Mode of failure and safety against.........................................................................................46

2.8.7.4 Support Piers or Side Blocks.....................................................................................................46

2.7.7.5 Provision of Expansion joints....................................................................................................47

2.8.8 Turbine..................................................................................................................................47

2.8.8.1 General......................................................................................................................................47

2.8.8.2 Selection of turbine....................................................................................................................48

2.8.8.2.2 Specific speed:....................................................................................................................48

2.8.9 Powerhouse............................................................................................................................49

2.8.10 Tailrace..................................................................................................................................50

2.8.10.2 Design Consideration...........................................................................................................50

2.8.11 Transmission Line.................................................................................................................51

2.8.11.1 General..............................................................................................................................51

2.8.11.2 Design Consideration.........................................................................................................51

3. DESCRIPTION OF PROJECT......................................................................................................53

3.1 LOCATION OF PROJECT.......................................................................................................53

3.2 ACCESSIBILITY......................................................................................................................53

3.3 TOPOGRAPHY AND PHYSIOGRAPHY................................................................................53

3.4 CLIMATE.................................................................................................................................53

3.5 AVAILABILITY OF CONSTRUCTION MATERIALS..........................................................54

4. HYDROLOGY AND GEOLOGY................................................................................................55

4.1 HYDROLOGY..........................................................................................................................55

4.1.1 Introduction...........................................................................................................................55

4.1.2 Collection of hydrological data..............................................................................................56

4.1.3 Precipitation...........................................................................................................................57

4.1.4 Discharge and Water Level....................................................................................................57

4.1.5 Estimation of High Flood Levels...........................................................................................58

4.1.6 Recommended flood flow......................................................................................................61


4.1.7 Establishment of design discharge foe power calculation......................................................62

4.1.8 Rating curve...........................................................................................................................63

4.1.9 Suspended matter and bed load..............................................................................................63

4.1.10 Estimation of Downstream Water Rights...............................................................................64

4.2 GEOLOGY................................................................................................................................65

4.2.1 General..................................................................................................................................65

4.2.2 Geology of Nepal...................................................................................................................66

4.2.3 Objective of Geological Study...............................................................................................68

4.2.4 Scope of geological study......................................................................................................68

4.2.5 Regional Geology..................................................................................................................68

4.2.6 General geology and Geomorphology of the project area......................................................71

4.2.7 Soil Types..............................................................................................................................71

4.2.8 Joints......................................................................................................................................72

4.2.9 Project area geology...............................................................................................................72

4.2.10 Engineering geology of the project area.................................................................................73

5. POWER OUTPUT AND ENERGY GENERATION....................................................................77

5.1 GENERAL................................................................................................................................77

5.2 POWER TYPE..........................................................................................................................77

5.2.1 Firm Power............................................................................................................................77

5.2.2 Secondary Power...................................................................................................................77

5.3 TYPES OF HEAD.....................................................................................................................78

5.3.1 Gross head.............................................................................................................................78

5.3.2 Net head.................................................................................................................................78

5.4 OVERALL EFFICIENCY.........................................................................................................78

5.5 INSTALLED CAPACITY.........................................................................................................79

6. ECONOMIC ANALYSIS AND COST ESTIMATION................................................................80

6.1 COST ESTIMATION................................................................................................................80

6.2 POWER-ENERGY STUDY AND REVENUE CALCULATION............................................80

6.3 ECONOMIC ANALYSIS.........................................................................................................81

6.3.1 Pay-Back Period....................................................................................................................82

6.3.2 Benefit-Cost Ratio.................................................................................................................82

6.3.3 Internal rate of return.............................................................................................................82


6.3.4 Conclusion.............................................................................................................................83

7. PROJECT PLANNING AND SCHEDULING.............................................................................84

7.1 GENERAL................................................................................................................................84

7.2 PLANNING...............................................................................................................................84

7.3 PHASES OF CONSTRUCTION...............................................................................................85

7.4 TIME MANAGEMENT IN PROJECT.....................................................................................85

7.5 PROJECT SCHEDULING........................................................................................................85

7.6 PLANNING AND SCHEDULING OF MIDDLE TADI KHOLA HEP...................................86

8. CONCLUSION AND RECOMMENDATION.............................................................................87

9. BIBLIOGRAPHY.........................................................................................................................88


1. INTRODUCTION

1.1 BACKGROUND

1.1.1 Need for focus upon Hydropower Projects

The requirement of energy is increasing day by day while the resources from which they are

generated are overall constant and takes longer time for regeneration. So this is limiting the

supply. The demand of more and more energy has pronounced negative impact on the

environment, natural resources, etc. The depletion of non-renewable resources and

exhaustive source of energy may invite the energy crisis in the future. It is very essential that

the energy production must meet the concept of sustainable development.

Hydropower is the most common and reliable renewable source of energy which is

abundantly available in the nature. It is the energy that comes from the force of moving water

without reducing its quantity or quality. Hydropower means clean and cheap energy for

today and for tomorrow. It is beneficial for multipurpose uses such as irrigation, water supply

etc. Hydroelectricity offers a significant contribution to development and is environmental

friendly. Because of abundant water resources in Nepal, there is huge possibility of

hydropower power production. Since the large hydropower projects require larger amount of

fund and time period small hydropower project are more sustainable from all respects in the

present scenario.

1.1.2 History of Hydropower Development

The use of energy generated from water has been started since the very beginning of the

human civilization. Nearly 2000 years ago Greeks used water to grind wheat into flour. There

are other evidences of it in Roman civilization as well. In the 1700’s, hydropower was

broadly used for milling of lumber and grain and for irrigation purposes while the actual

development and use of electrical energy started after 1880. In 1878 the world's first

hydroelectric power scheme was developed

at Cragside in Northumberland, England by William George Armstrong. Within the next 20

years roughly about 300 hydropower plants were operational around the world. The

invention of the hydraulic reaction turbine also created sudden expansion of hydropower. By

1900, 40% of the United States’ electricity was provided by hydropower. However, in early


http://en.wikipedia.org/wiki/William_Armstrong,_1st_Baron_Armstrong

http://en.wikipedia.org/wiki/England

http://en.wikipedia.org/wiki/Northumberland

http://en.wikipedia.org/wiki/Cragside

19th century, progress in the hydropower development was slow because of the less efficiency

in power transmission over the long distance. The pace of hydropower development

increased dramatically after 1930. In the former Soviet Union, hydropower was considered

synonymous with industrialization and economic prosperity after 1920. United States also

made different policies regarding the water based project to create jobs and to stimulate

economic recovery.

After 2nd World War, African and Asian nations also used hydropower power to meet energy

and water needs of their countries and many large hydropower projects were built in India,

Pakistan, and Egypt between 1950 and 1980.

1.1.3 Hydropower development in Nepal

The development of hydropower started some hundred years ago but has not been very

encouraging. The history of hydropower development in Nepal can be traced to 1911. The

first hydropower of Nepal was 500kW Pharping Hydropower Project which was followed by

Morang hydro in 1918. After the first approach in hydropower development in Nepal in

1911, the progressive development was gradual only after the Sundarijal with capacity of

600kW and Panauti with capacity of 2400kW hydropower stations came into operation in

1934 and 1940 respectively.

Nepal has a huge potential of hydropower development, however, the development has

always been disturbed because of the economical condition. There were many large projects

that couldn’t come into action because of the larger fund required for it. So because of this,

many small and micro hydropower has come into action. The establishment of Small hydel

development board in 1975 and Nepal Micro Hydropower Development Association in 1992

was another milestone in development of hydropower. Some of such hydropower are Jhupre

with capacity of 345kW, Jumla with capacity of 200kW, Doti with capacity 200kW

established during 1975 to 1985. Nepal Electricity Authority (NEA) was established in 1985

which was responsible for generation, transmission, and distribution of electric power

brought the revolution in hydropower development.

According to 1960, all hydropower stations were constructed through grant aid from friendly

countries like the USSR (Panauti) India (Trisuli, Devighat, Gandak, and Surajpura Koshi).

The major donor countries in those periods were Japan, Germany, Norway, South Korea,


Canada, Finland, Denmark, Sweden and USA. The financial lending agencies were World

Bank, Asian Development Bank, Japanese Bank for International Cooperation, Saudi Fund

for Development etc. In 1992 Hydropower Development Policy was formulated by the

government of Nepal that allowed participation of private sector in hydropower development.

This policy was later replaced by Hydropower Development Policy 2001 that allowed further

movement to active participation of private sectors.

In the 8th Plan (1992/1997) 3.2 MW of power was generated. According to the 9 th Plan

(1997/2002) the targeted power to be generated was 293MW but only 261MW of power was

generated with success percentage of 89.07% which was quite a good performance. While in

10th Plan (2002/2007) the targeted capacity was 314MW out of which only 13.26% was

generated i.e. 41.63MW. And according to the Interim Plan (2007/2010) the targeted power

to be generated was 105MW but only 82MW of power was generated with success

percentage of 78.09%.

Development of hydropower in Nepal is a complex task as it faces numerous challenges and

obstacles. The hydropower development has been seriously affected by the inefficiency,

politicization and mismanagement in state owned electricity utility-(NEA) as well as in its

line ministry. Neither NEA, nor its line ministry has ever created an investment friendly

environment to foster a private as well as community development of hydropower in Nepal.

Moreover, Government of Nepal lacks serious vision for the short-term as well as long term

hydropower development in Nepal. Other than this, lack of capital, high cost of technology,

and lower load factors due to lower level of productive end-use of electricity and high

technical and non technical losses have also attributed for the low level of development in

this field. However, hydropower business can be a great way for Nepal to progress - It has

the potential to uplift poverty, provide electricity to every household and even allow Nepal to

sell electricity to other countries. Popularity of Hydropower comes closer to becoming

Nepal's third most important business for earning foreign-revenue and every year, lots of

foreign companies visit Nepal for project studies.


Legends of the Power Development in Nepal

Major Power Plants in Operation

S.N. Power PlantCapacity

(MW)

Annual Energy

(GWh) Owned By Type

1 Trisuli 24 292 NEA ROR

2 Sunkoshi 10 66 NEA ROR

3 Gandak 15 53 NEA ROR

4 Kulekhani 1 60 164 NEA STO

5 Devighat 14.1 13 NEA ROR

6 Kulekhani 2 32 96 NEA STO

7 Marsyangdi 69 519 NEA PROR

8 Puwa 6.2 41 NEA ROR

9 Modi 14.8 87 NEA ROR

10 Kaligandaki 144 791 NEA PROR

11 Andhi Khola 5 38 BPC ROR

12 Jhimruk 12 81 BPC ROR

13 Khimti 60 353 HPL ROR

14 Bhotekoshi 36 246 BKPC ROR

15 Indrawati 7.5 1.2 SHC ROR

16 Chilime 20 102 CVC PROR


17 Piluwa 2.6 18 AVHCO ROR

19 Chaku Khola 1.5 14.5

Alliance

Power

20 Small Hydro 14.2 NEA ROR

21

Small Hydro

Isolated 4.53 26 NEA ROR

22 Microhydro 14.5

Total 762

Table (1-i): Major Power Plants in Operation

Major Power plants under construction

S.N Power Plant Capacity(MW) Owned By

1 Chamelia 30 NEA

2 Upper Tamakoshi 456 NEA

3 Middle Bhotekoshi 102 MVJCL

4 Bhairabkunda 3 BHPL

5 Upper Modi Khola 25 GITEC

6 Rahughat 30 NEA

7 Khudi 4 KHL

8 Upper Seti 127 NEA

9 Mai 22 SMHPL


10 Kulekhani III 14 NEA

11 Kabeli A 30 ROR

Table (1-ii): Major Power Plants under construction

1.1.4 Hydropower Potential of Nepal

Nepal land is blessed with enormous amount of Water, sources of which comes from the

mighty Himalayan Range. The rivers in Nepal are mostly originated from Himalayas of

Tibetan plateaus. Due to steep topography, abundant precipitation and perennial nature of

most of the rivers; there exists tremendous hydropower potential in Nepal. The theoretical

potential is estimated to be about 83GW out of which 42GW has been considered as

financially viable and 44GW as technically viable. There are approximately 6000 large and

small rivers identified in the territory of Nepal carrying about 174*109 m3 of surface runoff

annually which is 0.5% of the total surface runoff of the world.

Basin wise Hydropower Potential of Nepal

River

Basin

Capacity on small

river courses

Capacity on

Major River

Courses

Gross

Total

(GW)

Economic

potential

(GW)

Sapta

Koshi

3.6 18.75 22.35 10.86

Sapta

Gandaki

2.7 17.95 20.65 5.27


Karnali

and

Mahakali

3.5 32.68 36.18 25.1

Southern

Rivers

1.04 3.07 4.11 0.88

Total 10.84 72.45 83.29 42.14

Table (1-iii): Basin wise hydropower potential of Nepal

Identified Potential Hydropower Project

S.N

. Project Capacity(MW) Type

1 West Seti 750 Storage

2 Budi Gandaki 600 Storage

3 Kali Gandaki II 660 Storage

4 Lower Arun 308 PROR

5 Upper Arun 335 PROR

6 Karnali Chisapani 10800 Storage

7 Arun III 900 ROR

8 Upper Karnali 900 PROR

9 Pancheswor 6480 Storage

10 Thulothunga 25 ROR

11 Tamor/Mewa 100 PROR


12 Dudh Khosi 300 Storage

13 Budi Gandaki 20 ROR

14 Likhu IV 51 PROR

15

Upper Marsyangdi

II 121 PROR

16 Andhi khola 180 Storage

17 Khimti II 27 ROR

18 Upper Modi A 42 ROR

19 Lantang Khola 218 Storage

20 Madi Ishaneshwor 86 Storage

21 Kankai 60 Storage

Table (1-iv): Identified Potential Hydropower Project

1.1.5 Justification for Small Hydropower Project

According to the power output NEA has classified the hydropower into the followings

groups:

I. Micro Hydro Power Plant: Less than 100 KW

II. Mini Hydro Power Plant: 100 KW – 1MW

III. Small Hydro Power Plant: 1MW – 10 MW

IV. Medium Hydro Power Plant: 10 MW – 300 MW

IV. Large Hydro Power Plant : More than 300 MW


For a developing country like Nepal hydro power project is a big one as it requires lots of

manpower and money. Small hydropower is more advantageous than large and micro

hydropower in Nepal as the cost of large hydropower is very high. Also the losses in micro

hydro are very high which makes per unit cost very high. So the Small Hydropower is a best

choice in context of Nepal. Also it produces electricity at competitive price. Small

hydropower ranges from 1MW – 10 MW for which the head and discharge requires for it is

also easily available.

Unlike large hydropower, Small-hydro power mainly targets the rural areas which usually are

not connected to the grid and thus promotes rural industrial growth and improvement in the

general welfare of the people. The Impact of small hydropower on environment is minimal if

sufficient precautions are taken. For example, the dams built for some run-of-the-river small

hydropower projects are very small and impound little water - many projects do not require a

dam at all. Negative side effects associated with dams such as oxygen depletion, increased

temperature, decreased flow, and interference with upstream migration like fish are not

problems for many run-of-the-river projects.

The investments required for the Small hydropower are within Nepalese entrepreneurs’, so

this encourages involvement of local people in this field. The involvement of the local people

minimizes the social problems for the construction. By the Year 2001, number of major

hydropower projects completed was 18 and number of projects proposed was 28. And by the

same period, over 45 Small hydropower projects were located throughout the country,

providing electricity to otherwise rural areas such Dhading, Dolpa, Helambu. Hence small

hydropower is best suited to produce electricity in Nepal.


1.2 OBJECTIVES

The objective of this project is to analyze and design the suitable hydropower effectively and

efficiently and also to tackle the practical problems that arise according to the field condition

and to enhance the skill of engineering.

The main objectives of the project are as follows:

To fulfill the partial requirement of the final year project for the completion of

Bachelors Degree in Civil Engineering.

To analyze the geo-hydrological situation of the site.

To prepare the layout of the project at feasibility level.

To design the hydraulic components of the hydropower plant at the site.

To familiarize the practical problems likely to face while designing and under taking

such projects.

1.3 SCOPE AND LIMITATIONS

The main scopes of the project undertaken are as follows:

To work throughout the project under the supervision of supervisors from Kathmandu

University and Sanima Hydro & Engineering Pvt. Ltd.

To collect and analyze the hydrological and geological data of the site.

To assess the site condition.

To design the hydraulic components of the hydropower.

To prepare a volume of comprehensive project report.

The following are the limitations of the project:

Detailed survey data were not available so all the design are based on the study of

topographical map and digital map of the site location.

Only one day visit was made at the site so detailed hydrological and geological data

could not be collected and had to rely on the data from our host organization.

The designs were carried out referring to several materials due to lack of unified

guidelines. So the design outputs may not fulfill all the standards.


2. LITERATURE REVIEW

2.1 POWER SITUATION IN NEPAL

At present, the Integrated Nepal Power System (INPS) has a total installed capacity of some

706MW of which 652 (92%) is generated from hydro resources. The installation of total

installed capacity is shown in figure below:

Source MW % of Total

Major Hydro (NEA) - grid connected 472.99 67

Small Hydro (NEA) - isolated 4.54 0.7

Total hydro (NEA) 477.53 67.7

Hydro (IPP) 174.53 24.7

Total hydro (Nepal) 652.06 92.4

Thermal (NEA) 53.41 7.6

Solar (NEA) 0.1 0

Total capacity including private and others 705.57 100

Table (2-i): Installed Capacity of Nepal

The power sector presents the most severe infrastructure constraint for economic growth. In

the fiscal year 2010/2011, peak demand was 946 MW, versus 885MW in the prior year. In

the same fiscal year, annual energy demand increased 10% from the previous year to

4833GWh of which 982GWH (about 20%of the demand) was curtailed as loadshedding.

Domestic generation accounted for 3,157GWh, and 694GWh was met with net imports from

India.17 Thermal power generation represents less than 1% of grid-connected capacity.This

represents some improvement over the 2008/2009 fiscal year when system capacity shortage

was about 50% of the demand at the peak-load (813 MW) period during the winter months.

System losses were over 28% in fiscal year 2010/2011, an increase from 26.2% in fiscal year

2008/2009.

Demand is projected to continue growing at 7.6% annually until 2020. Due to the shortfall in

power delivery capacity, the NEA introduced scheduled service interruptions (load shedding)


of 12 hours per day in 2010. These conditions provide a major opportunity for supply side

and demand side energy efficiency improvements, as well as for use of other renewable

energy (RE) sources to provide immediate relief to the grid.

The peak load in Nepal occurs during the winter when the run-of-river power plants generate

at a lower capacity due to low river flows. The peak demand met by NEA rose steadily from

603 MW in 2006 to 946 MW in 2011, a compound annual growth rate (CAGR) of 9.4%.

Likewise, the total available energy increased from 2,781GWh to 3,858GWh at a CAGR of

6.8% during the same period. The total number of consumers increased at a CAGR of 10.0%

from 1.28 million in 2006 to 2.05 million in 2011, of which 95% comprise domestic

connections.

Electricity sales by NEA increased from 2,033 GWh in 2006 to 2,735 GWh in 2011 at a

CAGR of 6.1%. The domestic sector accounted for 43% of the total consumption in 2011,

followed by the industrial sector at 38%, commercial (7.5%), non-commercial (4.0%), street

lighting (2.4%), water supply & irrigation (2.0%), community sales (1.7%), and bulk supply

to India (1.1%).

2.2 LOAD FORECAST

The energy and demand forecast for years 2010-11 to 2027-28 is provided in Figure below.

Electricity demand is forecast to reach about 3,679 MW in year 2027-28 (medium growth

scenario) which is an increase of some 2,800 MW from the present peak demand. The energy

forecast indicates an energy output of 17,404GWh by 2027-28.

Meeting the projected demand presents several challenges. Investment in generation

transmission and distribution is insufficient, and private investors and development partner

have been reluctant to invest in the power sector because of several factors including,

governance and institutional structures, which need strengthening; lack of institutional

arrangements to mobilize the private sector; limited availability of domestic funds; relatively

low consumer tariffs; technical and commercial losses; a financially stressed public sector

utility; and inadequate human resource capacity.


2.3 ENERGY CONSUMPTION

Total energy consumption in Nepal in the year 2008-09 was about 9.4 million tons of oil

equivalents (401 million GJ). As can be seen from the Figure, only 12% of energy

consumption is from commercial energy sources such as petroleum and electricity. Petroleum

products, which are imported, and account for about 8% of the total energy consumed, and

electricity represented only 2% of the total energy consumption in 2010.

Woody biomass and animal waste

87%

Commercial energy(petroleum and electricity)

12%

Small RE1%

Figure (2-i): Energy Consumption of Nepal

2.4 DEVELOPMENT OF GRID SYSTEM AND POWER TRANSMISSION PLAN

At present, the INPS consists of 1,132 Km of 132 KV single circuit, 412.1 Km of 132KV

double circuit, 231.46 Km of 66 KV single circuit, 161.3 Km of 66 KV double circuit, 22Km

of 66 KV and 132 KV double circuit, 3.37 Km of 66 KV four circuit and 2,362Km of 33 KV

single circuit transmission line. Total substation capacity of the system is 902.45 MVA. In

the field of transmission, NEA is operating at system voltage levels of 132 KV and

66KV.Only about 35 percent people, who are receiving power from the national grid, are

facing uncertain hours of power cuts. However, only seven percent of the population gets the

power from alternative energy sources, including solar, micro-hydro and others. There is no

access to power for the 58 percent of population.


Nepal Electricity Authority is the sole institution responsible for construction, generation,

transmission and distribution of power; it is also given the authority to construct the east-west

transmission lines. However, the present state of NEA is that it is unable to complete its

task. NEA is now busy to construct 592 MW project, including 456 MW Tamakoshi. Due to

the political instability and poor planning or to be said poor implementation, Nepal's power

sector has been passing through a critical stage. Although electricity is one of the necessary

ingredients for the overall development of the country, the state, government and NEA have

rarely shown any interest in the transmission lines. If Nepal's economy, had a capacity to

absorb 11500 MW (peak hour), it would have required 845 KM long 400 KV lines, the total

cost for which would have been Rs. 41 billion and for 612 north south 400KV would require

Rs. 33 billion, according to the Twenty Year’s Power Generation Report.

NEA is now busy to construct 592 MW project, including 456 MW Tamakoshi. Due to the

political instability and India's apathy, Nepal's power sector has been passing through a

critical stage. Although electricity is one of the necessary ingredients for the overall

development of the country, the state, government and NEA have rarely shown any interest

in the transmission lines. Over the period of 100 years, Nepal has built just 981 kilometers

circuit of transmission lines. If Nepal's economy, had a capacity to absorb 11500 MW (peak

hour), it would have required 845 KM long 400 KV lines, the total cost for which would

have been Rs. 41 billion and for 612 north south 400 kV would require Rs. 33 billion,

according to the Twenty Year’s Power Generation Report.

The corridor transmission line projects include Kabeli Damak 132, Kosi corridor

(Bashantapur-Kusha) 220 kV, Katari-Okhaldhunga, Solu, Singati-Lamosanghu,Sunkosi-

Dolkha,Ramecchap –Garjyan-Khimti, Middle Marsyangdi-Manang, Kaligandaki 220 KV,

Katari-Okhaldhunga-Solu, Singati-Lamosanghu, Sunkosi-Dolkha, Ramecchap-Garjyan-

Khimit, Middle Marsyangdi-Manang, Karnali Corridor (Lamki-Upper Karnali)132 kV.

Under the absorption project are Thanko-Chapagaun-Bhaktapur, 132 kV, Syangja132

substation, Kamane Substation, Kushum-Hapure 132 kV transmission line, Butwal-

Kohalpur, Chapali 132, Matatirtha 132 kV station. Similarly, the primary phase of project

include Bajhang-Dipayal-Attariya Transmission line, Hapure-Tulsipur Transmission line

Surkhet-Dailekh-Jumla Transmission like, Kaligandai-Gulmi (Jhimruk)132 kV Transmission

line, Hetauda Butwal 400 KV Transmission line, Butwal-Lamki 400 kV Transmission line


and Lamki-Mahendranagar 400 kV Transmission line. Without construction of transmission

lines, one cannot expect any private investment and even NEA cannot build any project. For

instance, a total project cost includes the road construction and transmission line. The

government has no plan to construct the transmission line in the attractive power generation

sites like roads. If there are sites with cheap power generation, the government should

construct the transmission line. The government has already issued the license to public and

private sector with promises for over 17,000 MW. However, there is no transmission line in

most of the areas.

2.5 POWER DISTRIBUTION PLAN

The fact that about 85% of the population is not getting electricity as a source of energy

shows the need to extend distribution over Nepal. So, the distribution of electricity should be

done strategically. NEA has taken systematic studies of carrying out rural electrification and

distribution system reinforcement (DSR) feasibility on district wise basis.The organizational

restructuring of NEA in FY 2010/11 split the Distribution and Consumer Services (DCS)

Business Group into two Business Groups: DCS, East and DCS, West to manage the overall

distribution and consumer services in more effective and better way.

The Distribution and Consumer Services, West (DCSW) Business Group is entrusted with

the key responsibility of overall management of electricity distribution network of NEA in

Lumbini, Ganadaki, Bheri, Rapti , Dhaulagiri, Seti , Karnali and Mahakali zones of Nepal.

The responsibilities of DCS, West include construction, operation, maintenance,

rehabilitation and expansion of the network up to the 33 kV voltage levels and consumer

services such as new consumer connections, meter reading, billing, and revenue collection. It

is also entrusted with the work of operation and maintenance of off grid small hydro power

plants. DCS West is the second largest business group of NEA in terms of number of

employees and business activities. Approximately 18% of the total staffs of NEA is

employed in DCS, West. Also, DCS, West is on the forefront to earn revenue for sustaining

operation and maintenance and development activities of NEA.

The Distribution and Consumer Services, East (DCSE) Business Group is entrusted with the

key responsibility of overall management of electricity distribution network of NEA in


Mechi, Kosi, Sagarmatha, Janakpur, Narayani and Bagmati zones of Nepal. The

responsibilities of DCS East include construction, operation, maintenance, rehabilitation and

expansion of the network up to the 33 kV voltage levels and consumer services such as new

consumer connections, meter reading, billing, and revenue collection with the jurisdiction of

its territory. It is also entrusted with the work of operation and maintenance of off grid small

hydro power plants. DCS East is the largest business group of NEA in terms of number of

employees and business activities.

2.6 LEGAL PROVISIONS TO INVEST IN HYDROPOWER SECTORS

Hydropower industry is one of the major industries with wider scope in Nepal. For an

industry to prosper there should be support of government policies and legal provisions. Only

the potential cannot do the development of a nation if the policies cannot be harnessed.

Clearly defined conditions and attractive policy are always essential to harness the

innumerous resources. Realizing this fact, Nepal Government has developed certain policies.

a. Why to invest in Nepal?

Attractive Investment Features

One-Window Policy

Repatriation of Foreign Exchange

Income Tax Incentives

Fixed Royalty Payments

Import Concessions

Export Opportunities

No Nationalization of Projects

b. Policies, Act and Regulations:

Hydropower Development Policy-1992

Industrial Policy- 1992

Foreign Investment and One Window Policy- 1992

Electricity Act- 1992

Industrial Enterprises Act-1992


Foreign Investment and Technology Transfer Act -1992

Environment Conservation Act – 1996

National Environment Impact Assessment Guidelines – 1993

c. Legal Framework:

Survey License issued within 30 days

Survey License Period up to 5 years

Project License issued within 120 days

Project License period up to 50 years

Exclusive Water Rights

Public Consultation before issuance of Project License

Government land available on lease

d. Institutional Framework for Electricity Development as "One Window"

Issuance of Survey & Survey licenses

Provision of tax concessions & incentives

Assistance in importing goods, land permits, approvals etc.

Regulation and monitoring of projects

e. Incentive Income Tax

Generation :- 15 years tax holiday

Transmission :- 10 years tax holiday

& M Contracts:- 5 year tax holiday

After tax holiday:- 10 percent less than period prevailing

Foreign Lenders:- 50 percent capital cost allowance

Equity Investors:- No tax on interest earned

No tax on dividend

f. Import Facilities:-

Plant and Equipment including Construction Equipment

1% Custom Duty on items not manufactured in Nepal


import License Fee and sales tax exempted

effective from the date of commercial operation

g. Repatriation of Foreign Exchange

Principal and interest on debt

Return on equity

Sale of share equity

Prevailing Market rates

h. Royalty Payments:

For first 15 years

Installed Capacity/annum - NRs. 100/KW

Energy Generated - 2% of energy sales

After first 15 years

Installed Capacity/annum - NRs. 1000/KW

Energy Generated - 10% of energy sales

i. Market:

Domestic: Nepal Electricity Authority (NEA)

Foreign: India

Under Power Exchange Agreement

Under Power Trade Agreement between two countries

Regional: Government

Probably under the Regional Cooperation especially

Quadrangle concept within SAARC

j. Nepal Government/ NEA Policy on Purchases from Small Project

The private sectors should do the Power Purchase Agreement (PPA) with NEA to sell

the energy produced. To promote the private sectors in national level and to provide

the opportunity to invest in the hydropower sectors for the Nepalese people, NEA has

the provision to purchase the energy of small hydropower plants with first priority.


k. Export Opportunities:

Existing Power Trade Agreement between Nepal and India

Existing Interconnection Facilities with India

Power Deficit in India

Oriented Projects in Nepal

2.7 CHALLENGES AND ISSUES IN NEPAL’s POWER SECTOR

Around 40% of the population has access to some form of electricity, the majority being in

the urban areas. In a steep terrain country like Nepal with the dispersed villages in hills and

mountains, electrification is very costly. This situation poses challenges in managing the

financial resources to expand the electrification network. The electricity tariff in Nepal is

high, and is beyond the capacity of many of the customers. The reasons are manifold. The

basic infrastructure is not well developed. The cost of project often includes infrastructure

such as long approach roads, transmission lines and so on. The majority of the equipments

also have to be imported, which requires foreign currency and transportation overland for a

long distance from the port. The major share of the financing of the project is from the

foreign loans and investment, which are to be paid back in terms of foreign currency under

strict conditions. The ever weakening local currency against foreign currency escalates the

tariff further. The total loss in the system is about 24% indicating the scope for the

improvement. The challenges lie in the developing cheap and reliable hydropower projects so

as to keep the tariff within the reach of everyone. Nepalese Government is, therefore,

undertaking power sector reform measures with a view point to bring about improvements to

remedy the situation. It is encouraging to note that the private sector is gradually the power

market. The main challenge to the private sector is the transfer of technical knowhow and

easy access to the international markets for financing mechanisms.

The domestic demand over the forecast period of 25 years is relatively small, limiting many

developments. The challenge lies in the ability to establish a number of energy-intensive

industries and transport system within the country for creating a greater demand foe

hydropower, which will lead to a higher energy growth rate than the load forecast. A break-


through along the line will provide ample opportunities for development of this clean and

renewable energy.

Nepal’s own resources both in public and private sector cannot meet the financial investment

needed for hydropower development. A large investment is required from foreign investment

has been attracted in recent years, much still remains to be invested for meeting both internal

demand and the significant potential for the export of power. Nepal needs to utilize the

commitments on renewable energy made by the international development. Donors and

friends of Nepal are requested to come ahead in helping it in making best use of these

opportunities.

Nepal has given priorities for the use of electricity in transport, tourism, industry and

agriculture sectors. Special attention is provided to increase the load factor of small and

isolated generations through the use of electricity in domestic industries. Considering high

liquidity in the local financial market, efforts should be made to canalized local resources in

electricity fund, power development fund and encouraging other financial investments. The

involvement of private sector in generation is encouraging. The Government is open to

public-private partnership.

2.8 COMPONENTS OF HYDROPOWER

2.8.1 Weir and Undersluice

2.8.1.1 General

Weir is a structure constructed at the head of canal, in order to divert the river water towards

the canal so as to ensure a regulated continuous supply of silt free water with certain

minimum head into the canal. The types of weir and its use depend upon the topography,

geology, discharge, river morphology etc. If the major part or the entire pounding of water is

achieved by a raised crest and smaller part or nil part of it is achieved by the shutters then it

is called weir.

Undersluice is the structure constructed adjacent to the weir for the purpose of flushing the

deposited silt by providing openings on the weir portion. The crest level of the undersluice is


positioned at lower level than the crest of the weir i.e. usually it is kept 1.0 to 1.5m below the

crest level of the weir. They are designed to pass 10 to 20% of the design flood during the

rainy seasons. It creates comparatively less turbulent pocket of water near intake.

Undersluiced length of weir is divided into no. of ways by piers and regulated by gate.

Opening helps in scouring and removing the deposited silt from undersluiced pocket hence is

also called the scouring sluices. Gate-controlled undersluice helps regulating flow in intake at

the dry weather flow and low flow and periodic flushing.

Spillway is a structure constructed at the weir side to dispose surplus water from u/s to d/s

channel. It doesn’t let the water rise above maximum reservoir level and are provided as a

safety measure against overtopping and the consequent damages and failure. The spillway

must have adequate discharge capacity to pass the maximum flood d/s without causing any

damage to weir and at the same time, not letting the reservoir level to rise above the

maximum water level. Spillway is essentially a safety value for weir. Types of spillway

according to location, operation, structures etc. are Straight drop, Overflow or Ogee, Chute,

Side Channel, Shaft, Siphon, Orifice, gated etc.

Ogee Spillway is an improvement upon the free over fall spillway and is widely used with

concrete, masonry, arch and buttress dams. Ogee spillway works effectively only on one

particular head called designed head.

2.8.1.2 Design consideration of Diversion weir

The design of weir includes computing the elevation of weir crest, length of weir, computing

the forces acting on the weir and checking the safety of the weir from all aspects like

overturning, sliding, crushing etc. they are explained as follows:

2.8.1.2.1 Elevation of Weir crest

There are various factors that affect the elevation of the crest, but in our case, diversion

of water is the purpose and the height should be sufficient to pond the water at a level that

can facilitate design flow in the intake. The height of the weir is governed by the height

of intake sill, depth of intake orifice and depth of the river at the intake site. Four other

important considerations to be considered for fixing the crest level of the weir are as follows:

The elevation of the weir crest has to be fixed such that the design flood is safely

discharged to the downstream without severe damage to the downstream.


The height of the crest affects the discharge coefficient and consequently the water

head above the weir as well as the back water curve.

The elevation of the weir determines the head of the power production.

The height of the weir affects the discharge that can be diverted into the canal.

The height of the weir crest affects the shape and location of the jump and design of

the basin.

The bed level of the river at the headwork is 1270m. The crest level of weir provided is

1275m and undersluice crest level is 1270m.

2.8.1.2.2 Length of Weir and Undersluice

The length of the weir depends upon the width of the waterway at the intake site. Crest length

should be taken as the average wetted width during the flood. The upstream and downstream

should be properly examined for the protection consideration.

Rise in water level on the upstream of the structures after construction of the weir is called

afflux. Fixation of afflux depends on the topographic and geomorphologic factors. A high

afflux shortens the length of the weir but increases the cost of the river training and river

protection works. For alluvial reaches it is generally restricted to 1m but for mountainous

region it may be high. The water way must be sufficient to pass high floods with desired

afflux. A weir with crest length smaller than the natural river width can severely interfere the

natural regime of flow thus altering the hydraulic as well as the sediment carrying

characteristics of the river.

Generally, the spillway and undersluice lengths are designed so as to safely pass 80 % and

20% of the design flood respectively. In our particular design, the spillway and undersluice is

so accommodated that from total water way, 7.5 m is given to undersluice and remaining

77.2m is given to spillway. The spillway is so designed that it can accommodate total flood

design. The undersluice portion is designed only for sluicing the bed load. Hence, the

undersluice is designed for 231.44m³/sec discharge as flood discharge. This will economize

in the construction of energy dissipaters.


2.8.1.2.3 Shape of Spillway

The spillway has been designed as free over fall Ogee shaped weir. The discharge capacity of

Ogee shaped spillway is maximum as compared to that of other type of weirs. Ogee shaped

weir increases hydraulic efficiency and prevent cavitations. The profile of the spillway is

made similar to the nape profile of the free overfall weir to ensure that there is minimum

possibility of negative pressure development along its length.

The provisions of the fore and rare apron have been designed considering various factors as

presented in the detailed design of the weir structure. The parameters under consideration

are:

Hydraulic jump characteristics

Length and the height of formation of jump

Seepage Pressure

2.8.1.2.4 Forces acting on Weir

The main forces acting on the weir when it is in operation are:

Water Pressure

Uplift Pressure

Weight of the weir

2.8.1.2.4.1 Water Pressure

It is the major external force acting on the weir. This is called hydrostatic pressure force and

acts perpendicular on the surface of the weir and its magnitude is given by:

P=0.5* g*H2

Where, g = Acceleration of gravity

H = Depth of water

This pressure force acts on H/3 from the base.

The calculation is provided in appendix B.


2.8.1.2.4.2 Uplift Pressure

The water enters the pores, cracks and fissures within the body of the weir and the foundation material. Because the water is under pressure, it creates uplift pressure on the weir. The pressure act on all directions but the pressure acting upward is important for the design of the weir, as it reduces the effective weight of the weir. Hence it acts against the dam stability. The magnitude of uplift pressure is given by:

U= w*H

Where, w = Unit weight of water

H = Depth of water


2.8.1.2.4.3 Weight of Weir

The weight of weir and its foundation is the major stabilizing/ resisting force. While calculating the weight, the cross section is split into rectangle and triangle. The weight of each along with their C.G. is determined. The resultant of all these forces will represent the total weight of dam acting at the C.G. of dam. Simply, when the sectional area of each part is multiplied by unit weight of concrete, weight of that part is obtained. The weir is designed with ogee profile for spilling over its length. Hence weight is calculated by knowing its section and multiplying by its unit weight.


2.8.1.2.5 Modes of failure and Criteria for structural stability

2.8.1.2.5.1 Overturning about toeThe weir may fail by overturning about its toe or about the downstream edge of any

horizontal plane within the weir. The overturning failure occurs when the resultant of all the

forces acting on the base passes outside the base. In other words, the weir will overturn if the

resultant strikes within the base and also within all other horizontal sections.

The factor of safety against overturning is given as:

Fo=∑MR/ ∑Mo

Where, ∑MR= Resisting moment


∑Mo= Overturning moment

This must be greater than 1.5 to be safe.


2.8.1.2.5.2 Compression or CrushingThis type of failure occurs when the compressive stress in the weir exceeds the safe limit.

While designing the weir section it should be so design that the resultant should pass through

middle 3rd part of the section to avoid the possible tension on the weir section. The section

should be totally in compression. So, weir should be checked against the failure by crushing

of its material. If the actual compressive stress may exceed the allowable stress, the dam

material may get crushed.

The vertical combine stress at the base is given by:

Ϭmax=∑V/B(1+(6e/B)) and Ϭmin=∑V/B(1-(6e/B))

Where, e=B/2-x=Eccentricity of the resultant force from the centre of the base.

x=M/∑V; M= Moment and ∑V= Total vertical force.

This must be less than 200 KN/m3.


2.8.1.2.5.3 SlidingSliding will occur when the net horizontal force above any plane in the weir or at the base of

the weir exceed the frictional resistance developed at that level. Factor of safety against the

sliding is measured as Shear Stability Factor (SSF) and is given by:

Fs= μ * ∑V/ ∑H

Where, μ= Coefficient of friction

∑H= Total horizontal force

∑V= Total vertical force


For safety against sliding, SSF should be greater than 3-5.


2.8.2 Intake Structure

2.8.2.1 General

Intake is a structure where the water to the power plant is abstracted or separated from the

river flow. An intake can be defined as a structure that diverts water from river or other

course to a conveyance system downstream of the intake. The intake structure is used to trap

the required amount of water for the specific purpose with or without storing. An intake

structure should control the flow of water and prevent the heavy sediment load of the river

from entering the conveyance system. For this purpose, proper selection and sitting of intakes

must be chosen to evacuate necessary amount of water at any regime to the channel. The

peak discharge must be safely evacuated without any damage. To achieve this, hydrological

data must be collected and evaluated and the structures should be designed accordingly.

Prerequisites of the location of intake structure:

The course of the river should be relatively permanent at the intake site, i.e. the river

should not change its course at the intake location at the time.

The river should not have a large gradient at the intake site.

In case there is a confluence of two rivers in the selected site, the intake should be

located downstream of the confluence to take advantage of the flow of both rivers.

Advantage should be taken of stable banks such as rock outcrops or armored boulder

banks to protect the intake from erosion.

The intake should be located at the outer bend where flow is deeper and clearer and

towards the downstream end of the bend where the effect of the secondary currents

has fully developed. This limits sediment deposition at the intake area and also

ensures the flow availability during the dry season.

The intake structure is designed for 30% more than design discharge, 15% for flushing in

gravel trap, 15% for settling basin i.e. Qdesign(intake)= 1.3*Qdesign.


The intake consists of trash rack, intake canal and two orifice opening each of width 2.6 m

and height of 1.5m which allows the design flow to pass through it under normal condition

but restricts higher flows during floods.

The detailed design is shown in the appendix B.

2.8.2.2 Design considerations of intake

For small hydropower projects it is general practice to use 100 years return period from

probabilistic analysis of flood. A simple and moderately priced construction should be used

to minimize maintenance and repairs. For the small projects with no automation facilities,

hydraulically controlled structures become more feasible than mechanically controlled units.

There must be adequate provision to remove the suspended and bed load deposited upstream

behind the weir. This may be done using intermittent flushing using sluice gates or allowing

some water to flush it continuously. It has been found that entry of bed load towards diverted

canal will be minimum if the intake is located just downstream of concave bank of the river

bend. It not only restricts the bed load, but also ensures sufficient water depth even at low

water condition. The intake shall ensure uninterrupted supply of the required quantity of

water into the water conveyance system at all times. This requirement shall particularly be

met during periods of floods when the large amounts of boulders, trash and debris carried by

Nepali rivers could block or choke the trash rack, thereby forcing reduction in power

generation. The intake water passages shall be hydraulically efficient to minimize head

losses. For this purpose, the forms and dimensions of the intake water passages and its other

components, including piers and trash racks, shall, as far as possible, ensure smooth and

streamlined flow hydraulics. The design shall aim at achieving gradual transformation of the

static head to the conduit velocity and preventing formation of air-entraining vortices under

pressure flow conditions.

Topography, geology, height of bank, ratio of water diverted to that available, channel width,

routing of diversion canal, ease of diversion of river during construction, stability of river

bank and sides, river protection works governs the selection of the intake location and type.

For steeper gradients with straight reaches of river bottom rack intake is more suitable. But in

rocky banks, winding river, considerable suspended load it is not desirable. The lateral side


intake functions well in such case. Intake sill with 2 m is used not to allow bed loads to enter

the canals. Trash rack is used to prevent the entry of tree branches, leaves and other coarse

materials in the canal. Head is extremely valuable in hydropower projects so that trash rack

should be designed with minimum head loss. Suitable factor of safety should be employed to

design height of intake sill, to ensure sufficient withdrawal capacity in the future.

2.8.3 Gravel Trap

2.8.3.1 GeneralThe gravel trap is a basin constructed close to the intake in order to prevent gravel from

getting into the approach channel. Main function of the gravel trap is to collect the bed load,

smaller than the trash-rack opening size, entering through it to the approach canal. Gravel

trap’s location is governed by the site conditions, availability of flushing head and gravel

carrying capacity of the approach canal. Its dimension depends on the flow velocity, gravel

size and specific density of the gravel and it should be sufficient to settle and flush gravels

passing from the coarse trash-rack. Gravel trap is generally designed to collect maximum of

12 hours gravel deposit. A flushing arrangement associated within the gravel trap is operated

to flush out the collected gravels to the river. Flushing frequency is less during the low flow

periods whereas continuous flushing is recommended during the monsoon. A gravel trap may

be equipped with overflow spillway.

The gravel trap is designed for maximum discharge of 6.032m3/s with intermittent flushing

of sediment of greater than or equal to 2mm through flushing orifice of size 0.75m *0.5m.the

flushing canal size is 0.75m *0.75m with flushing velocity of 2.4 m/s and slope of 1:30.The

design of gravel trap is provided in appendix B and the drawings are provided in appendix D.

2.8.3.2 Design ConsiderationThe main design principle for a gravel trap is that the velocity through it should be less than

required to move the smallest size of gravel to be removed. In general the gravel trap should

settle particles larger than 2mm diameter. Smaller sized particles will be removed by the

settling basin. Therefore, to be able to trap particles of diameter less than 2 mm, the velocity

in the gravel trap should be limited to 0.6 m/s. For the easiness in construction depth is

generally 3m, width is calculated to ensure desirable efficiency of settling. The gravel trap


designed is of hopper shaped and the floor is about 30º (1:1.7). This shape is recommended

for easy flushing.

2.8.4 Approach Canal

2.8.4.1 GeneralThe water diverted from the intake to the settling basin of inlet chamber through the

conveyance system is termed as headrace. A high head diversion plant is generally associated

with tunnel to divert water where as a medium head to low head diversion plants generally

employ canal diversion. Geology, topography and hydrology are major factors to select such

options. For small plants with low heads intra basin diversion having fairly straight reaches

of river, canal is the best option. Headrace has to convey extra discharge for continuously

flushing the settling basin.

The design is provided in appendix B and the drawings are provided in appendix D.

2.8.4.2 Design ConsiderationThe canals for hydropower projects are constructed mainly for the purpose to alter the

gradient of the river to benefit hydropower production. Two essential parts of the canal in a

hydropower system are (i) headrace or power canal and (ii) tailrace. Points to be considered

for canal alignment can be summarized as:

The canal alignment should be sufficiently diverted away from the river so that the

risk of flood damage is minimum.

The velocity of the water must be high enough to ensure that suspended solid

(sediments) do not settle on the bed of the channel and that plant growth is

discouraged.

The water velocity must be low enough to ensure that the channel walls are not

eroded by the flow.

The alignment should be along the level to slightly sloping ground, pass through

stable terrain and follow the shortest reasonable route with a minimum crossings and

a minimum of head loss and minimum seepage loss because loss in head or discharge

is the loss in power production.


From earthwork point of view, the alignment should be selected to balance cut and fill as far

as possible. But this does not mean to balance cut and fill even by using costly retaining

structures. Stability is also a major factor.

The canal passing through gravel trap to settling basin through is known as approach canal .

Its dimension and shape depend on the discharge to be conveyed, prevailing topography and

geology of the alignment. Approach canal has to convey extra discharge for continuously

flushing the settling basin. It should also be able to carry the design flow with adequate

freeboard. The velocity should be low enough to ensure that the bed and the walls of the

canal are not eroded. A minimum velocity of 0.4 m/s should be maintained to prevent the

growth of aquatic plants.

2.8.5 Settling Basin

Settling basin is located right after the approach canal. The design of the settling basin is

depended on the suspended material type, their characteristics and the observation made

during the site visit. Topography and geological conditions prevails the design and

arrangement of the settling basin. The criteria adopted for the design of the settling basin is

summarized herein:

Maximum sediment concentration of 5000 ppm,

Mineralogical analysis of sediments,

Particle size distribution,

Intermittent flushing system is used for flushing. Intermittent flushing basin are of much

simpler design and less susceptible to blockage clogging than other types of basin.

There will be two chambers of settling basin and each will be 5.0 m wide, 54 m long and 3.5

m average depth having invert level slope of 1:30.


2.8.5.1 Design Consideration

The settling basin is designed following standard practices. The geometry of inlet, the width

of basin and any curvature must be such as to cause minimum turbulence which might impair

the efficiency. Concentration approach is used to design it. Trap efficiency is obtained as


90% for removal of 0.2 mm sized sedimentary particles. Vetter's equation is used for

efficiency calculation. Hazen's equation and various charts are used to compute the transit

velocity and the settling velocity. Gated structures have been provided to control flow.

Upstream of gated structures, fine trash rack has been provided

2.8.5.2 Sediment Flushing System

Intermittent flushing system has been adopted for flushing. The sediments are flushed after

the opening of flushing gates at the downstream end of the basin and allowing the water level

to drop. This causes high velocities over the sediment deposits that turn erode the sediments

from the basin. At the end of flushing cycle, the inlet gate is closed to enable closing of

flushing gate. Once the flushing gates are closed, the inlet gates are reopened and the basin is

refilled. At the end of refilling cycle, when the water level in the basin is same as that in the

intake channel, the outlet gates are opened in the balanced condition.

2.8.6 Penstock pipe

2.8.6.1 General

The conveyance of water from intake to penstock is not much difficult but the passing of water

through penstock is the most challenging one. It is because the penstock should be safe as well

as economic. The pipe designed to carry water to the turbines with the least possible loss of

head consistent with the overall economy of the project is known as penstock pipe. These are

pressurized water conduits which convey water to the turbines from free water surfaces. The

water comes through either surge chamber or reservoirs or forebay. The most economical

penstock will be the one in which the annual value of the power lost in friction plus annual

charges such as interest, depreciation, maintenance will be a minimum. The penstock is usually

made of steel, although reinforced, concrete, GRP, HDP penstocks have also been built recently

in increasing numbers.

Support piers and anchor blocks are not needed for PVC penstocks of flexible and small

diameter. These are laid in ground covered with sand and gravel which acts as an insulation.

Except for rock excavation required, larger penstocks are usually buried. Before burying it the

penstocks should be painted properly and the coated. This should be such that the maintenance


is minimum and least cost. From the environmental point of view, the solution is optimal

because the ground can be returned to its original condition, and the penstock does not

constitute a barrier to the movement of wildlife.

The factors that creates problem are: (i) daily variation of flow through penstock (ii) estimated

load factor over a term of years, (iii) profile of penstock, (iv) number of penstocks, (v) type of

material used, (vi) diameter and thickness, (vii) value of power lost in friction, (viii) cost of

penstock installed, (ix) cost of piers and anchors, (x) total annual charges of penstock in place,

and (xi) maximum permissible velocity. It is extremely difficult to express these variables in a

comprehensive formula. Also the penstock should be safe enough to failure without loss of life

and property.

A penstock installed above ground can be designed with or without expansion joints. The

temperature variation should be considered when the turbine is continuously not working or

when the penstock is dewatered for maintenance because of thermal expansion and

contraction. The penstock is usually built in straight lines, with concrete anchor blocks at

each bend and with expansion joint between each set of anchors. The anchor blocks must

resist the thrust of the penstock plus the frictional forces caused by its expansion and

contraction, so when possible they should be founded on rock. If, due to the nature of the

ground, the anchor blocks require large volumes of concrete, thus becoming rather

expensive, an alternative solution is to eliminate every second anchor block and all the

expansion joints, leaving the bends free to move slightly.

In this case it is desirable to lay the straight sections of the penstock in steel saddles, made to

fit the contour of the pipe and generally covering 120 degrees of the invert. The saddles can

be made from steel plates and shapes, with graphite asbestos sheet packing placed between

saddle and pipe to reduce friction forces. The movement can be accommodated with

expansion joints, or by designing the pipe layout with bends free to move

It best suited for the range of pressure fluctuations met in the turbine operation because of the

strength and flexibility of steel. Present design standards and construction practices were

developed gradually, following the advent of welded construction, and are the result of

improvements in the manufacture of welding-quality steels, in welding processes and

procedures, and in inspection and testing of welds.



2.8.6.2 Design Considerations

2.8.6.2.1 Owner’s Requirement

The owner requirements must consider the following:

Preferred material and design type

Plant operation requirement

Annual cost of capital investment and cost of power and revenue loss

Inspection and maintenance provisions

Applicable internal and governmental guidelines, criteria, and design requirements

Legal and political issues, including environmental and licensing issues.

2.8.6.2.2 Choice of materials

Today there is a wide choice of materials for penstocks. Fabricated welded steel is best suited

for the larger heads and diameters. If available in the required sizes, spiral machine-welded

steel pipes can also be considered, due to their lower price. For high heads, steel or ductile

iron pipes are preferred, but at medium and low heads steel becomes less competitive,

because the internal and external corrosion protection layers do not decrease with the wall

thickness and because there is a minimum wall thickness for the pipe.

For smaller diameters, there is a choice between: manufactured steel pipe, supplied with

spigot and socket joints and rubber "O" gaskets, which eliminates field welding, or with

welded-on flanges, bolted on site; plain spun or pre-stressed concrete; ductile iron spigot and

socket pipes with gaskets; cement-asbestos; glass-reinforced plastic (GRP); and PVC or

polyethylene (PE) plastic pipes. Plastic pipe PE14 is a very attractive solution for medium

heads (a PVC pipe of 0.4 m diameter can be used up to a maximum head of 200 meters)

because it is often cheaper, lighter and more easily handled than steel and does not need

protection against corrosion. PVC15 pipes are easy to install because of the spigot and socket

joints provided with "O" ring gaskets. PVC pipes are usually installed underground with a

minimum cover of one meter. Due to their low resistance to UV radiation they cannot be

used on the surface unless painted, coated or wrapped. The minimum radius of curvature of a


PVC pipe is relatively large (100 times the pipe diameter) – and its coefficient of thermal

expansion is five times higher than that for steel. They are also rather brittle and unsuited to

rocky ground. Pipes of PE16– (high molecular weight polyethylene) can be laid on top of the

ground and can accommodate bends of 20-40 times the pipe diameter (for sharper bends,

special factory fittings are required). PE pipe floats on water and can be

dragged by cable in long sections but must be joined in the field by fusion welding, requiring

a special machine. PE pipes can withstand pipeline freeze up without damage, may be not

available in sizes over 300 mm diameter.

2.8.6.2.3 Site-Specific Requirements

The site specific requirements are also equally important due to environmental restraints,

limitations on size and weight, geological restraints, hydrologic considerations, and limitations

due to alignment and support to the penstock physical layout. The site specific conditions,

requirements and design and cost associated with layout are determined by the choice of type of

installations such as above ground or buried penstocks or tunnel liner. Therefore the following

points must be considered for site-specific requirements to be addressed:

Land ownership, right-of-way limitations, mineral rights, and limitations relating to

excavation/quarrying operations

Environmental restraints, including aesthetics, fish, game and wildlife preservation,

archaeological excavations, disposal of material, clearing and erosion

Terrain configuration

Site geology, hydrology (groundwater conditions) and soils

Applicable codes and mandatory requirements

Other site-specific considerations

2.8.6.2.4 Preliminary Study

The preliminary study phase is an important phase of the general design effort of the

experienced designer. The final penstock configuration, alignment, design, and requirements

and parameters must be determined during this study phase. The designer must investigate the

site conditions and make several layouts of various alignments. Many trials are done during this

stage, Terrain, geologic characteristics, and foundation conditions play important roles during


this study phase. Since the ultimate goal of this study phase is to determine the most economic

and implementable alignment, it is not necessary to approach the study in a great precision.

2.8.6.2.5 Type of installation

The type of installation selected should reflect the above consideration. Penstocks are classified

into different types depending on their general features. Three following types have been

designed and used in recent years:

Supported penstocks or Exposed Penstock: These are usually fabricated from steel,

plastic fibreglass or wooden-stave pipe. They can be located above the ground or in

none encased tunnel and are usually supported on either steel or concrete support

systems. Plastic or fibreglass penstocks should not be exposed to sunlight because

ultraviolet rays break down the material

Buried penstocks: These are usually fabricated from steel, concrete, plastic or fibreglass.

They can be either partially or fully buried.

Steel Tunnel Liner: These are located in a tunnel and fully encased in concrete or

encased in a portion of a dam. The type of installation selected should reflect the cost-

effective penstock system which should consider the technical, environmental,

economic and constructability factors.

Each penstock type has different associated design, material and construction costs.

2.8.6.2.6 Conditions for selection of Pipeline

When a hydro-electric power station is to be supplied with water through a tunnel, arrangement

most frequently adopted is to terminate the tunnel with the portal at a relatively high level on the

hillside and connect the portal to the power station by means of a steel pipeline. The alternative

to such a pipeline is to arrange the tunnel at a low level so that it connects direct to the turbine.

Whether a pipeline or a low-level tunnel is adopted is largely governed by the overall costs, and

many factors have to be taken into consideration, including the nature of the ground, whether

composed of sound rock or deposited material; the amount of rock cover above the tunnel; the

most desirable position of the portal having regard to the most suitable geology. Having decided

to adopt a pipeline and having provisionally located the centreline in plan and elevation, it is


necessary to determine the water pressures to which it will be subjected. It can be assumed that

the maximum pressure through the pipeline due to surge is equal to the head resulting from the

maximum level of water in the surge shaft. It should be noted that the water-hammer pressure

wave travels from the valve to the surge shaft in a few seconds. The pressure is maximum at the

turbine valve and decreases to zero at the free water surface in the surge shaft / tank.

2.8.6.2.7 Alignment

To determine the most economical alignment of a pipeline, the designer must investigate the site

and make various layouts on topographic maps. He must then estimate material quantities for

each layout and evaluate its constructability. When making these layouts, the penstock should

be located on stable foundation sites such as along a ridge or a bench that has been cut into the

mountainside, Avoiding of troublesome sites such as underground water courses, landfill, fault

zones and potential slide areas is quite important. Because low-head penstocks cost less than

high-head penstock, the pipeline at high elevations needs to be made as long as possible before

going down the mountainside into powerhouse. To minimize costly anchors and costly pipe

transition sections, vertical bends, horizontal bends, and changes in diameter should be

combined in a way to have them at the same location.

2.8.6.3 Economic Diameter

The economically justified diameter for a penstock required to carry a design flow is the one at

which annual cost due to the greater investment do not exceed the annual value of the resulting

incremental energy output. The governing criterion is thus to regain economically the last

incremental kilo-watt-hour made available by reducing the head-loss through using a larger

diameter.

Under average conditions and present day prices the most suitable diameter for pipeline is

frequently one which gives a maximum water velocity of approximately 5 m/s (15 ft. per sec.).

As the pressure head or the cost of the pipeline per ton increases, it is economical to reduce the

diameter of the pipeline; similarly, as the load factor on the station increases, the diameter

should be increased. For a particular station the only variable is the pressure head which

increases as the pipe runs downhill towards the station. Some pipelines are therefore reduced in

diameter at the lower levels.


In the early stages of a project it is necessary to determine the approximate diameter of a

pipeline for estimating costs or other purposes.

In schemes where there are a number of turbines a single pipeline to supply all the turbines will

involve the use of the least amount of steel. Making joints in thick plates and handling large

pipes, however, are difficult and costly. It is frequently desirable, therefore, to use a separate

pipeline for each turbine, at least for the part nearest the power station where the pressure is

greatest. When separate pipes are used portal valves can be introduced on each pipeline, thereby

enabling any branch pipeline to isolate for maintenance without affecting the operation of the

remaining turbines.

In order to determine the economic diameter for any particular pipeline with greater accuracy, it

is necessary to consider a number of alternative diameters for the pipeline, and then estimate for

each diameter the annual charges to cover the capital cost of construction and the annual value

of the electrical energy lost on account of the friction head in the pipeline. The diameter which

gives a minimum for the sum of these two quantities is the most economical diameter.

2.8.6.4 Determination of Economic Diameter or Optimizing Penstock Diameter

In additional to alignment and design head, it is important to know about plant operation and

other factors that determine the annual cost of constructing and operating a powerhouse

penstock. The two major cost items involved in the annual cost are (1) cost of capital investment

and (2) cost of energy revenue loss from frictional head loss.

Cost of capital investment (Ct): The initial investment (capital) cost must be paid off

over a period of years (project life) at a specified interest rate. When the project life

and interest rate known, the capital recovery factor (CRF) can be determined. By

multiplying the capital cost by the CRF, the annual cost of capital investment is

calculated.

Cost of energy revenue loss (Ce): The flow rate (Q), the cost of kilowatt hours

generated each year, and turbine-generator efficiency must be determined through

careful study and planning. In addition, head loss must be accurately determined.

When all these parameters are known, the annual cost of energy revenue loss can be

calculated.


The total annual cost is determined by adding the two major costs above. Finally, select a

diameter that minimizes the total annual cost. The shell thickness is usually governed by the

allowable stress.

The diameter is selected as the result of a trade-off between penstock cost and power losses.

The power available from the flow Q and head H is given by the equation:

P=QHɣɳ

Where, Q is the discharge in m3/s, H the net head in m,

The economic diameter of a penstock is a function of head loss, cost and the value of energy. A

first estimate can be obtained from the equation given below:

D = EP x P 0.43 x H -0.57

Where, Ep = 0.49

D = diameter in meter

P = turbine rated capacity (kW)

H = turbine rated head (m)

2.8.6.6 Economic Diameter Equations

The economic diameter equations for penstocks are developed for the Case 1 or Case 2. They

are as follows.

(1) Case 1 —Minimum thickness for shipping and handling

When the shell thickness (t) in millimetres is determined by D/288, the economic diameter (D)

is given as:

1429.03 )(9025.0

WCpwffhMEQD

When a specific value is used for t, the economic diameter is:

D=0.3867 [ fhmEQ3 (pwf )WCt ]

0.1667


(2) Case 2 –Internal pressure governs

The economic diameter (D) for a Case 2 penstock is given as:

D=0.5[ ShfMEQ3 ( pwf )WCH ]

0 .1429

Where,

f = friction factor

h = hours per year of operation

M = $/kWh, composite value of energy

E = turbine/generator efficiency in decimal form

i = interest rate

n = years, repayment period

Q = design flow

W = specific weight of steel

C = capital cost of penstock installed

pwf = present worth factor,{(i+1)n+1}/i(i+1)n

S = allowable stress

t = thickness, D/288

H = Design Head

It is very important to know, how the power plant will be operated when determining the

penstock diameter. Some of the parameter values, such as the competitive value of power and


the number of hours of power generation, will vary greatly for a base-load power plant

compared to a peaking load plant. Selecting the design flow (Q) is important because this term

is cubed in the diameter equations. Variations in the design flow value have a significant impact

on the resulting diameter calculations.

2.8.6.7 Water HammerWater hammer is the result of a change in flow velocity in a closed conduit causing elastic waves to travel upstream and downstream from the point of origin. The elastic waves, in turn, cause increase or decrease in pressure as they travel along the line, and these pressure changes are variously referred to as water hammer, surge or transient pressure. As the water-hammer pressure wave travels rapidly, the amplitude of the successive pressure waves quickly falls from a maximum to a negligible amount, and normally this latter stage is reached before the surge pressure attains its maximum value. A water-hammer pressure oscillates above and below the immediately previously existing water pressure line, the pipeline must be investigated to ensure that the water pressure does not fall below atmospheric pressure. This undesirable condition is most likely to occur where there is a sharp bend downwards, in the pipeline. The pressure occurring at this point should be determined for the conditions when the reservoir is at its lowest working level and a turbine has been started up thereby producing a down surge in the surge shaft. It will generally be found that the negative water hammer due to opening of the turbine valve is greater than the amplitude of the secondary water hammer oscillations due to closure.

2.8.6.8 Calculation of Head LossesHydraulic losses in a penstock reduce the effective head in proportion to the length of the penstock and approximately as the square of the water velocity. Accurate determination of losses is not possible, but estimates can be made on the basis of data obtained from pipe flow tests in laboratories and full-scale installations. The various head losses which occur in penstock are the friction, bend, gradual contraction, bifurcation, valve and others.

2.8.6.9 BifurcationThere are two major categories of bifurcating geometries:

The symmetrical wyes may be a single symmetric bifurcation or a series of bifurcations pipes in which the branch pipes are parallel to the direction of the main pipe.

Non-symmetrical wyes distribute several branch pipes in the same direction from the straight main pipe.

In the plants with two units mainly two type of bifurcation are used:

In high head plants, the spherical type wye branch is used. In the medium and low head plants, the wye branch with external stiffener type is used.


2.8.7 Anchor Block and Support Piers

2.8.7.1 General

An anchor block is and encasement of penstock designed to restrain the pipe movement and

to fix the pipe in place during installation and operation. Anchor blocks tend to prevent the

movement of the penstocks due to steady or transient forces including expansion and

contraction forces and water hammer pressures. They provide necessary reaction to the

dynamic forces at the bends. To provide the necessary degree of stability to the pipe

assembly, anchor blocks find their significance. Anchor blocks are provided at all horizontal

and vertical bends of the pipe. Slide blocks are used to support the pipes at intermediate

points so as to prevent excessive bending stresses in the pipe. They resist the weight of the

pipe and water and resist the lateral movement but allow the longitudinal movement of the

pipe. So, these blocks are lighter in weight than anchor blocks and save the overall cost of the

support action.


2.8.7.1.1 Location of Anchor Block

At vertical and horizontal bends of the penstock. A filled penstock exerts forces at

such bends and the pipe needs to be properly anchored.

Immediately upstream of the powerhouse which minimizes forces on the turbine

housing.

At sections of the penstock where the straight pipe length exceeds 30m. It is done to

limit the thermal expansion of the pipe since an expansion joint will be placed

downstream of the anchor block.

2.8.7.2 Design Considerations

It should be constructed of 1:3:6 concrete with 40% plums and nominal reinforcement. Plums

are boulders that are distributed evenly around the block such that they occupy about 40% of

the block volume. The boulders add weight to the block therefore increases the stability

while decreasing the volume required. Hoop reinforcement is required around the pipe to


resist cracking of the concrete due to tensile forces from the pipe. Foundation parts and the

central part of the block can be made of 1:1.5:3 reinforced concrete and outer portion can be

made of stone masonary in1:4.

Water flowing under pressure when diverted from straight path exerts pressure as the bends.

To resist various forces these blocks are designed. The blocks act as the massive structures

and work as the gravity dams. Sliding, Overturning, tension and crushing are to be checked

for the blocks.

Anchor blocks are the support of the penstock and are constructed to meet this purpose. As

the penstock is circular, the anchor blocks are made to fit the curve surface. Saddle supports

are used in it and a sufficient cover is provided above the pipe for adequate fixity.

2.8.7.3 Mode of failure and safety against

Anchor blocks are designed similar to the gravity dam. The blocks are to be designed to

resist overturning, sliding, crushing and tension failure. A firm foundation is required for the

blocks. The blocks should be prevented from gulley erosion due to rain water.

2.8.7.4 Support Piers or Side Blocks

Support piers are required along the straight sections of exposed penstock between anchor

blocks. Thin- walled plain pipe can buckle at the support piers with relatively short spans. In

this case permissible span can be increased by welding a wear plate to the pipe at each

support. Wear plate is also required where the pipe leaves an anchor block, if the span to the

first support pier exceeds that allowed for plain pipe. It is usually not economical to increase

the pipe wall thickness in order to increase the support spacing, but should be considered

where the cost of support piers is significant.

The support engages less than the full perimeter of the penstock, generally between 90 and

180 degrees of arc, and typically 120°. These are simpler to construct than full perimeter ring

girder supports, but generally are spaced closer together than the ring girders. It is usually

spaced between 6 to 8 m between the anchor blocks. It is constructed of concrete 1:3:6.

Design procedure is same as that of the anchor blocks but only the combination of load is

different.


2.7.7.5 Provision of Expansion joints

Mechanical joints either expansion joint or bolted sleeve type coupling is used in both

exposed and buried penstocks to accommodate the longitudinal movement caused by the

temperature changes and to facilitate the construction. The joints shall allow for movement

where differential settlement or deflections are anticipated.

Expansion joint permit only the longitudinal movements. The joints are used primarily with

above ground installations and are located between the supports at the points where the

penstock deflections are of equal magnitude and direction. These joints divide the barrel shell

into separate units, which are watertight, but structurally discontinuous. It should be provided

just below the anchor block. Length of the expansion joints = α∆tL

2.8.8 Turbine

2.8.8.1 General

Hydraulic turbines are machines which convert hydraulic energy into mechanical energy.

The mechanical energy developed by turbine is used in running an electric generator which is

directly coupled to the shaft of the turbine which in turns converts mechanical energy into

electrical energy. Based on the energy conversion, turbines are classified as Impulsive or

Active and Reactive Turbines.

Impulse Turbine: The turbine, in which pressure head or potential energy of water is

converted into the kinetic energy of water in the form of jet of water issuing from one

or more nozzles and hitting a series of buckets mounted on the periphery of the wheel,

at atmospheric pressure is called impulse turbine. It is used for high head and low

discharge. Pelton and Turgo turbines are the examples of the impulse turbine.

Reactive Turbine: The turbine, in which both kinetic energy and potential energy of

water is utilized to rotate the runner or the turbine is called the reactive turbine. The

water flows through the runner under kinetic and potential energy. The turbine runner

is submerged and water enters all around the periphery of the runner. Water is taken

up to the tailrace by means of a closed draft tube and thus whole passage of water is

totally enclosed. Francis, Kaplan, Propeller, Deriaz turbine etc are the examples of

reactive turbines.


2.8.8.2 Selection of turbine

Selection of suitable type of turbine for the project depends upon several factors like head,

discharge, power production, load condition and corresponding efficiency, quality of water,

tail water level, size, construction feasibility etc. Selection of turbine is essential for the

layout of the powerhouse, approaching and discharging pipes, conditions of construction and

exploitation and techno economic parameters.

2.8.8.2.1 Head and discharge:

High head and low discharge -Pelton turbine

Medium head and medium discharge - Francis turbine

Low head and high discharge – Kaplan turbine

2.8.8.2.2 Specific speed:

10 to 50 - Pelton turbine

80 to 400 - Francis

300 to 500 - Kaplan – Diagonal

450 to 1200 - Kaplan – Axial

For Tadi Small Hydropower Project, Francis Turbine is selected. The selection was made by

using the head vs discharge graph. Because of medium head of 77.7m, we have selected

Francis turbine as it has better efficiency than other in part load operation. Discharge

variations in the river would happen as per FDC. Due to this, we used two turbines of same

capacity so that one will be operated at part loads not by reducing the efficiency to practically

low level. Also, two sets of turbines increases the degree of reliability. In our project, two

Francis turbines are used with equal capacity. The runner diameter of the turbine is 0.5m.


2.8.9 Powerhouse

2.8.9.1 General

Power house is a massive structure which accommodates electrical as well as mechanical

components such as turbine, generator, switch gear, control room, engineer's room,

reception room and operator's accommodation. The main function of this building is to

protect the electro-mechanical equipments from the adverse weather as well as possible

mishandling by unauthorized persons. The power house should accommodate all the

equipments with enough space and should be easily accessible without any difficulty.

Basically flat terrain is best suitable for the construction of powerhouse. Generally, there are

two types of powerhouse. They are:

Surface Powerhouse

Underground Powerhouse

Surface power house is cost effective and is best suited when the power house is far away

from flood plain. On other hand, the underground powerhouse is located inside the rock

mass which makes it more stable against flood effects and other external forces. Due to

underground construction and high technological methods, the underground powerhouse is

highly costlier than surface ones. Some powerhouses are located as semi-underground

structures being partly on surface and partly underground. Therefore, on basis of cost

effectiveness, surface power house is preferred where as if the site is prone to flood as well

as other dangers, underground powerhouse is preferred.

2.8.9.2 Powerhouse Sizing

Turbine, generators, control room equipments are very massive and require lots of space in

powerhouse. Power house size mainly depends on the discharge, head, type of turbine and

generator, number of units and the general arrangement in the power house. The size of the

power house should be sufficient to house all the components. Enough clear space should be

available for installation of equipment as well as for proper maintenance.


2.8.9.3 Height of Powerhouse

Height of power house is done by the addition of dimensions of turbine block and its

superstructure. Height of the lower turbine block from the foundation to the floor of the

machine hall is to be determined by the dimensions of the turbine. The height should be

enough for the installation of turbine, generator and shaft, gear mechanism and the cranes.

There should be sufficient space for removal and overhaul of any of the components without

disturbing other components. Sufficient clear space is also provided for crane installation,

operation and maintenance without disturbing any other component in the powerhouse.

2.8.10 Tailrace

2.8.10.1 General

After passing through the turbine the water returns to the river trough a short canal called a

tailrace. If the power house is close to river, the outflow may be discharged directly into the

river. But when the river is far off from the power house, one may have to construct a

channel or pipes according to topography of the site between the power house and the river.

The tailrace should be designed and maintained properly so that excessive aggravation and

degradation is avoided. Impulse turbines can have relatively high exit velocities, so the

tailrace should be designed to ensure that the powerhouse would not be undermined.

Protection with rock riprap or concrete aprons should be provided between the powerhouse

and the stream. The design should also ensure that during relatively high flows the water in

the tailrace does not rise so far that it interferes with the turbine runner. With a reaction

turbine the level of the water in the tailrace influences the operation of the turbine and more

specifically the onset of cavitation. This level also determines the available net head and in

low head systems may have a decisive influence on the economic results.



Design of the tailrace is similar to that of headrace channel except that higher velocity can be

allowed in the design without caring for head loss in the channel. High grade of concrete is

required to resist erosion of tailrace channel due to higher velocity. The downstream end of


tailrace must be protected to prevent the river by erosion or by flow from the tailrace. The

discharge should be disposed off over rock or large boulders. If erodible slopes exist in the

vicinity, a stilling basin may be required to dissipate energy.

2.8.11 Transmission Line

2.8.11.1 General

The transmission system planning focuses on the establishment of necessary extensions to

the grid in order to connect the new generation plants and transfer the power from the plants

to the load centers in reliable as well as economic way. Transmission lines transmit bulk

electrical power from power stations to load centers in the form of either underground cables

or overhead lines. Transmission system of an area is known as grid. The different grids are

interconnected through tie lines to form a national grid. Transmission voltages in Nepal are

33 KV, 66 KV and 132 KV and planning to transmit at 220 KV. The high voltage

transmission lines transmit electrical power from the sending end sub-station (Power Station)

to the receiving end stations. The transmission facilities affect the cost and reliability of

energy supplied to the consumers to a great extent.


The choice of the most economical voltage for transmission line requires a detailed study of

many technical and economical factors. The power capacity and distance of transmission are

specified. The detail design includes the line voltage, size of phase conductor, span, spacing

and configuration of the conductors, numbers and size of earth wires, number of insulators,

clearance, sag under operating and erecting condition etc.

The transmission line for the purpose of economy is required to be constructed at lowest cost.

This is achieved by optimizing the tower height and the span length. This will reduce the

overall cost of line. While deciding the length various factors such as voltage, public safety

and Government's regulation must be considered.


2.8.11.3 Basic planning/rules for reliability

With this cost of energy not served (ENS) the following basic planning rules have been established:

(N-1)1 supply of areas currently supplied through one line should be established when the net load during peak exceeds approximately 50MW

In cases, where areas are supplied through a single circuit stung on a double circuit tower, the second circuit should be strung when the net load during peak exceeds approximately 35 MW

Transmission lines from power plants should not in general be designed to sustain single outages without loss of generation.

Transformers shall in general, comply with (N-1) criteria for the system but not necessarily in individual substations.

Transmission lines and transformers should be allowed 20% overload during emergency operation.

2.8.11.4 Voltage and Frequency for Power reliability

The most typical operating criteria used in other countries are given as:

Maximum allowable voltage variation in normal operation: 5% Maximum allowable voltage variation during emergencies: 10% Maximum allowable frequency variation during emergencies: 5%

Once these design features are available, the voltage regulation and efficiency can be calculated. In case these quantities are not within the prescribed limits, a revision of the design is necessary. Most of the parameters mentioned above are beyond the scope of this project work. The cost and performance of the line depend, to a great extent, on the line voltage. An empirical formula for the optimum voltage is; Where, V = Line voltage in KV; L = Distance in Km; P = Power in KW. A standard voltage nearest to this value should be adopted. The above formula gives only a preliminary estimate.


3. DESCRIPTION OF PROJECT

3.1 LOCATION OF PROJECT

The proposed project “Tadi” is located in Rautbeshi, Shikarbeshi and Ghyanphedi Village

Development Committees (VDCs) of Nuwakot district in the Central Development Region of

Nepal. The proposed site lies between 27°57’30”N to 27°57’54”N latitude and 85°24’04”E

to 85°25’00”E longitude. The elevation of the proposed site area is within 1270m –1792.3m.

Tadi khola is one of the snow fed river and there are large number of rounded boulders

deposited in either side of the bank of the proposed site. It finally merges to Trishuli River.

The catchment area of the river basin at intake site is approximately 105sq. km. The

hydraulic structures like intake, approach canal and power house is proposed to run through

the left bank of the river. The intake site is located at Majhuwa village and the powerhouse

site is located near the conjunction of Kuntung Khola and Tadi Khola.

The location of the project area is provided in the Appendix D.

3.2 ACCESSIBILITY

There is direct transportation from Kathmandu to Trishuli Bazaar which branches off from

Ganagate to the project site. There is a motorable road(earthen and partially graveled)

of about 24 km from Ganagate to the project site. It takes about 6 hours from Kathmandu and

about 3 hours from Trishuli to reach the project site.

3.3 TOPOGRAPHY AND PHYSIOGRAPHY

The Tadi khola catchment lies within the Gandaki river basin. About, 3% of the catchment is

covered by snow whereas 26% is covered by rock and meadow. Similarly, about 46% of the

area is of agriculture land whereas 25% of the catchment area is covered by forest. The Tadi

khola flows with an average river slope of about 1 in 33.

3.4 CLIMATE

The average annual rainfall at the region is about 2755 mm. The project area experiences hot

and humid climate during June to September and cold climate during November to January.

The mean monthly temperature varies from 14 °C to 25.4°C. The relative humidity varies

from 33% to 93% over the year.


3.5 AVAILABILITY OF CONSTRUCTION MATERIALS

Local construction materials like sand, stones, aggregates etc. are available on the

construction site. Other construction material like cement, steel can be brought from

Kathmandu.


4. HYDROLOGY AND GEOLOGY

4.1 HYDROLOGY

4.1.1 Introduction

Water resources are the most important natural resources because they are not only

renewable but also abundantly available in Nepal. River runoff is the most important

component of available water resources in Nepal. The importance of the available water was

realized and The Government of Nepal started hydrological survey in early 1960s.

Availability of water and the risk factors at a project site are the major concern for the

development of any water resources project. Data on hydrology for most of the major river

basins in Nepal are available for more than 45 years. It is also estimated that more than 6000

rivers and rivulets are available in the country and only about 280 gauging stations are

established. Estimation of hydrological extremes and flow during normal condition are

essential for designing hydraulic structures of any hydropower. Hydrological study is

required for pre feasibility and feasibility study stages for future water balance analysis of

concerned catchments. Precipitation, temperature and humidity data are other important data.

Most important type of Hydrological data require for hydropower study is a long term stream

flow record of the flow available for power production. Stream flow data is used to estimate

the average annual energy that can be produced from the basin of available head. The

information about the high floods are extremely important to design the structures and to

ensure the safety of the structures as well as resident of the vicinity. Idea of flow availability

during the low flow season and during historical low flow year is also needed to estimate the

dependable capacity. If the stream flow data of the required basin is not available then they

are obtained from indirect methods like empirical methods, correlation/regional regression of

the available data of the nearby basin having similar hydrological characteristics, drainage

area, soil, precipitation pattern etc. Long term availability of stream flow is important in case

of Small hydropower Project, which are designed as runoff river plants normally at a slight

decrease in design discharge during its operation.


4.1.2 Collection of hydrological data

Hydrology is of great importance throughout all the project phases: from the preliminary

planning to the technical design, to the final management. In each phase of the project the

hydrological contribution is never a standard approach, but is a result of a fine calibration of

methodologies according to the requested degree of approximation and the available data.

The longer the hydrological data the more reliable is the estimation of design parameter for

the project. The collection of hydrological data mainly includes:

Precipitation in the catchment area.

Stream flow measurement.

Analyses of hydrological records are important to establish following parameters of the river:

Flow Duration Curve of the watershed at the intake site which is useful to determine

the design discharge.

Flood Analysis which is expected in the future can be done which is useful to

determine the maximum design flood.

Low Flow statistics are essential to determine the minimum design flow.

Parameter such as annual hydrograph showing long term mean monthly flow which is

useful to determine the firm and secondary energy that can be produced.

Stage discharge relationship curves at the intake site and tailrace site.

Tadi Khola is of the main tributaries of Trisuli River. The catchment area of the river lies

mainly in dense mixed forest. The Tadi Khola is gauged river whose gauging station number

is 448 located at Tadipul, Belkot, Nuwakot. Since, the catchment area characteristics of the

intake site are more or less similar to the gauge station number 448. So the hydrological data

for the proposed hydropower station can be taken from the above station.

.


4.1.3 Precipitation

The record of precipitation is important to understand the nature of catchment and flow of the

stream. The precipitation can be measured by two types of Rain Gauge.

Recording Type Rain gauge

Non Recording Type Rain gauge.

The measurement of precipitation of Tadi khola was done by using Recording Type Rain

gauge.

4.1.4 Discharge and Water Level

4.1.4.1 Discharge

The various methods of measuring the discharge are as follows:

Direct Method

Velocity-Area Method

Dilution method

Electromagnetic method

Ultrasonic method

Indirect Method

Hydraulic structures such as weir, flume etc

Slope –Area method

4.1.4.2 Water level

The stage/water level is the elevation of the top water surface from an arbitrary datum.

The water level can be measured using following methods:

Manual gauging (staff gauge, wire gauge)

Automatic stage recorder

Float gauge recorder

Bubble gauge


The gauge discharge can be expressed by rating equation:

Q=Cr (G-α)β

Where, Q = Storm Discharge

G = Gauging Height

α= gauge reading at zero discharge

Cr and β are rating curve constant.

4.1.5 Estimation of High Flood Levels

Estimation of the high flood likely to occur in the river during the life of the project is

extremely important so as to facilitate safe passage of flood without causing any serious

damage to the project, the vicinity and the downstream. The flood flow value acts as a safety

measure for the design and location of hydraulic structure as well as superstructures

Probabilistic and regional methods can be used to calculate it. The more the frequency of the

flow, the larger the flood and hence, the more costly is the project. The selection of the

frequency depends upon the project risk and the economic condition. It is usually practiced to

adopt 100 years return period flow in the Small Hydropower Projects.

Among the various methods Gumbel method is very popular and is widely used. Log

Person’s method is also widely used method. These methods are used in case of gauged

stations while for the ungauged stations WECS and DHM is widely used. PCJ method, and

other Empirical methods are also used for flood calculation.

The annual maximum instantaneous peak flow of the Tadi khola for the period of 1969-2006

for station 448 Tadi Khola was obtained from Department of Hydrology and Metrology

(DHM) and those data are used to calculate flood frequency analysis for different return

period.

4.1.5.1 Frequency Method

Frequency analysis is used to calculate the peak flow of a stream for any number of return

periods. It is a statistical method which is used for prediction of peak flow.


4.1.5.1.1 Gumbel Method

This extreme value distribution was introduced by Gumbel in 1941 and is commonly known

as Gumbel’s distribution. It is one of the widely used probabilities – distribution function for

the extreme values in hydrologic and meteorological studies for prediction of peak floods,

maximum rainfall, maximum wind speed, etc.

Gumbel defined a flood as the largest of the 365 daily flow and the annual series of flood

flows constitute a series of largest values of flood. According to this theory of extreme

events, the probability of occurrence of an event equals to or larger than a value Xo is

P ( X≥ Xo) = 1-e-e^(-y)

In which y is dimensionless variable given by,

Y = α(x-a)

Where, a = ξ – 0.4

α= 1.2825/ ϭx

thus, y = ( X-ξ )/ ϭx + 0.577

where, ξ= mean and

ϭx = standard deviation of the variate X.

In practice, it is the value of X for a given P that is required and is

transposed as

Yp = -ln {-ln( 1-P)}

Noting that time period T =1/P and designating YT = the value of y, commonly called the

reduced variate, for a given T

YT = -{ ln.ln (T/(T-1))}

YT = - {.834 +2.303 loglog (T/(T-1))}

The value of the variate X with a return period T is,

XT = ξ +Kϭ

Where, K= (YT – 0.577)/1.2825

The above equations constitute the basic Gumbel’s Equation and are applicable ta an infinite

sample size. Since practical annual data series of extreme events such as floods, maximum

rainfall depth, etc all have finite lengths of records; the equation for K is modified to account

for finite N as given for practical use

XT = ξ + K *ϭn-1


Where ϭn-1 = standard deviation of the sample of size N

= Sqrt (∑ (X –ξ)2 /(N-1))

K= frequency factor expressed as ( YT – YN)/SN

In which, Yn = reduced mean, a function of sample size N and is given table

Sn = reduced standard deviation, a function of sample size N

These equations are used under following procedures to estimate the flood magnitude

corresponding to the given return period based on an annual flood series.

1. Assemble the discharge data and note the sample size N. here the annual flood value

is the variate x. Find ξ and ϭn-1 for the given data.

2. Using tables determine Yn and Sn appropriate to given N.

3. Find YT for the given T by using YT = -{ ln.ln (T/(T-1))}

4. Find K using K= ( YT – Yn)/Sn

5. Determine the flood discharge, XT = ξ + K *ϭn-1.

The calculation is provided in Appendix A-I.2.1, the 100 year flood being 237.60cumecs.

4.1.5.1.2 Log Pearson Type III method

In this method the variate is first transformed into logarithmic form (base 10) and the

transformed data is then analyzed. If X is variate of random hydrologic series, then the series

of z variate is

z = log x

For z series, for any recurrence interval T

zT= z ̅ +KZ ϭz

where, KZ = a frequency factor of recurrence interval t and coefficient of skew CS.

ϭz = Standard deviation of the z variate sample

ϭz = Sqrt{∑(z-z̅)2 / (N-1)}

CS = coefficient of skew of variate z

CS = {N∑(z-z̅)}/{(N-1)(N-2) ϭz3}


The variate of KZ = f (CS,T ) is given in table.

The corresponding value of xT = antilog (zT)

The calculation is provided in appendix A-I.2.2, the 100 year flood being 231.44cumecs.

4.1.5.2 Regional Regression Method

The regional regression method is region basis methods for the given area in which country

is divided into different regions depending on various characteristics such as rainfall

intensities, catchment area, etc. WECS/DHM is commonly used regional methods in context

of Nepal.

4.1.5.2.1 WECS and DHM

The WECS/DHM method was developed by WECS (1989) which estimates the

hydrological characteristics of ungauged sites in Nepal using a frequency distribution

parameter technique that is a variation of the multiple regression technique. In this method,

the independent variable that is most significant in the regression analysis is the area of the

basin below the 3000m elevation i.e. the area of the basin influenced by monsoon

precipitation. This method is not applicable to basins located entirely above 3000m and its

results for basin with a very small portion below the 3000m elevation are not particularly

reliable.

4.1.6 Recommended flood flow

Since the station 448 Tadi Khola is a gauged station, the flood of different return periods are

obtained by Gumbel’s Method and Log Pearson Type III Method only. They are plotted

using flood data of Tadi khola and it gives a straight line graph from different return periods.

We preferred the value obtained from Log Pearson Type III Method because for daily and

monthly data this method works better.


4.1.7 Establishment of design discharge foe power calculation

The major approaches for assessing water availability of hydropower projects are mean monthly flow and flow duration curve. These curves give realistic estimation of flow and ascertain economic viability of a project.

4.1.7.1 Mean monthly flow

Availability of adequate water flow for power generation is indicated by estimation of mean

flow. Mean annual flow gives the potential power of stream but stream flow is usually less

than this flow. To calculate mean monthly flow following methods can be used.

MIP

Catchment Correlation

HYDEST

Modified HYDEST

MIP, HYDEST and modified HYDEST methods are used for an ungauged station. So

catchment correlation method was used to calculate the mean monthly flow.

Catchment Correlation

The mean monthly flow at the proposed intake is derived using data obtained from gauge

station no 448 with catchment area is 653 km2. The catchment area of the intake site is 105

km2. So the mean monthly flow at intake is calculated using the following formula:

Q2 = (A2/A1) *Q1

Where, Q2= Known discharge of the basin 2.

Q1= Required discharge of the basin 1.

A1= Area of the basin 1

A2= Area of the basin 2

The driest monthly flow was obtained as 0.83 m3/s.

The correlated data, the mean monthly flow and the hydrograph are provided in Appendix

A-I.1.2, A-I.1.1 and A-I.1.3.


4.1.7.2 Flow Duration Curve

The flow duration curve is a probability discharge curve that shows the percentage of time a

particular flow is exceeded or equaled. In a runoff river hydropower project, it is useful to

know the variation of flow over the year so as to make ease to select the most appropriate

turbine configuration as well as for project optimization.

Flow duration Curve at different probability of exceedence is provided in Appendix A-I.1.1.

The exceedence discharge at 40 % is obtained as 4.64 m3/s.

4.1.8 Rating curve

Rating curve is a graph of discharge versus stage for a given point on a stream, usually

at gauging stations, where the stream discharge is measured across the stream channel. With

the help of rating curve, for any discharge the water level can be known easily. This is very

important for determination of weir height.

The rating curves for the upstream of weir and downstream of tailrace have been plotted and

are provided in the Appendix A-I.3.1 and A-I.3.2.

4.1.9 Suspended matter and bed load

4.1.9.1 General

The sediment transport in the river is a complex phenomenon. A careful study of the

sediment inflow and assessment of deposition is of major importance in planning of any

hydropower project. The mineralogical analysis of the sediment sample is necessary to

determine the presence of hard and soft material contents. The sediment collected from

samples of fine and coarse deposits are generally used for mineralogical analysis. The size of

the sediment greater than 100mm is taken as bed load. The sediment having size less than

100mm is taken as suspended matter. The major effects of sediment and minerals for run off

river projects are:

Serve abrasion, wear and tear of turbine depending on nature of sediment overtime.

Reduction of storing capacity of dam due to deposition of sediment.

Cost of construction and maintenance of overall project increases.


http://en.wikipedia.org/wiki/Gauging_station

http://en.wikipedia.org/wiki/Discharge_(hydrology)

Degradation of river downstream of the dam resulting in instability on either side of

banks.

The concentration of bed load for any hydropower plant is approximately taken as 30%

of the maximum discharge which is used for sluice gate design. Similarly, the concentration

of suspended matter is taken as 10-20% of the maximum discharge of the river which is used

for the design of settling basin. The realistic and objective assessment of sedimentation is

necessary for both project economic and environment consideration.

4.1.9.2 Morphological influence upon solid matter particle

The size of the sediment in the river system of our country usually varies from fine sand to

big boulders. Tadi khola is one of the snow fed river and there are large number of rounded

boulders deposited in either side of the bank of the proposed site. At the meandering section

of the Tadi khola, high deposition of sediments takes place on either side of the river. The

bed characteristic of the river is rocky and mobile. The slope of the river is relatively high as

it is in the hilly region and the sediments are transported to a larger distance.

4.1.10 Estimation of Downstream Water Rights

When dam, weir etc is constructed across the stream for different purpose, the flow on

downstream is blocked. This will affect the privilege of downstream. The advantages that are

taken from the stream are not only human but also the fishes, natural plants, domestic

animals, and other directly or indirectly related living beings. To analyze compensation flow,

the total population of the downstream basin should be estimated. The use of stream by

animals, fish’s population, etc should be estimated as well. The fail in analysis of species

composition has directly influence on population density, age structure and sediment

characteristics. Therefore, it is recommended that at least 10% of the discharge should be

released to downstream as downstream water right.


4.2 GEOLOGY

4.2.1 General

Middle Tadi hydroelectric project is Run-of-river type project situated at Rautbeshi,

Shikharbeshi and Ghyanphedi VDC in Nuwakot district. The project is a seasonal type

project which has its headworks located 7km upstream from Samundratar Bazaar whereas

powerhouse is planned to be constructed right across the Shikharbeshi Bazaar. The waterway

is envisaged to be of pressure penstock steel pipe.

The geological and geotechnical investigation is one of the major components for the

feasibility study of hydroelectric projects. Detailed engineering geological study is the basic

requirement for the construction of hydropower projects. It directly related with the sub

surface condition of the rock the soil and their engineering properties. It plays an important

role in understanding of ground through which the project is planned to align. It is even more

important for the projects that have underground structures. A small mistake in geo-technical

investigation can collapse the whole structure and hence carry great risk in construction.

Therefore, proper investigations are necessary to clarify the magnitude of risk and how they

can be minimized or managed. With this backdrop, the main objective of the study is set to

achieve required information and data on the following aspect of the project area:

To provide basic geological and geotechnical parameters for the environmental

study and also the design of hydraulic structures,

To study the geomorphology of the project area,

To find out major weakness zone, hazardous and non-hazardous area, degree of

stability,

To obtain information on regional geology of the project area and site specific

surface geology condition in order to assess the suitability and stability of

structures,

To study the Lithology of the project area and identify the type of earth materials,

To indentify the location of construction material sites and hence carry out

construction material survey,


The study abstracts a brief description of regional geology and detail engineering geological

condition of the project area, which provides an assessment of rock support of underground

works and foundation requirement of important structures for the feasibility of the MTKHEP.

This section of the report is based on several site visits findings and observation.

4.2.2 Geology of Nepal

Nepal occupies about 800km long Himalayan range in the central sector of the southwardly

convex Himalayan mountain arc. Nepal can be divided into the following five tectonic zones

(Hagen, 1969)

Tibetan-Tethys Himalaya Zone

Higher Himalaya Zone

Lesser Himalaya Zone

Sub- Himalaya (Siwalik) Zone

Terai Zone

4.2.2.1 Tibetan- Tethys Zone

It lies between the south Tibetan Detachment System in the south and the Indus-Tsangpo

Suture Zone in the north. This zone is the northernmost tectonic zone that comprises chiefly

of fossiliferous sedimentary rocks, such as shale, limestone and sandstone of age ranging

from lower Paleozoic to Paleocene. The rocks of this zone are well exposed and studied in

Thak Khola (Mustang), Manang, Dolpa, Mt. Everest, Mt. Makalu, Mt. Annapurna and Mt.

Dhaulagiri regions.

4.2.2.2 Higher Himalayan zone

This zone is tectonically still active and made up of metamorphic rocks. This zone is

geologically as well as morphologically well defined and consists of a huge pile (about

10km) of highly metamorphosed rocks. The Main Central Thrust (MCT) bounds this zone in

the southern and the South Tibetan Detachment System. The MCT zone is characterized by

inverted metamorphism. It has been observed that higher grade of metamorphic rocks lie

structurally and topographically above the low- grade rocks. Le Fort (1975 b) and Sharma


(1978) explain the inverted metamorphism in terms of thermal regime associated with MCT.

The Higher Himalayan Zone is composed of crystalline rocks. Bordet et al, (1972) divided

this zone into the following four main units:

Kyanite-Silliminite gneiss

Pyroxenic marble and gneiss

Banded gneiss

Augen gneiss

4.2.2.3 Lesser Himalayan Zone

The Lesser Himalayan Zone lies at the south of the Higher Himalayan Zone. It is bounded by

the Main Central Thrust (MCT) and Main Boundary Thrust (MBT) in the south. This Lesser

Himalayas of Nepal include both midlands and Mahabharat Range in the physiographic

division. The important valleys like Kathmandu and Pokhara lies within this zone. This zone

is composed of relatively high- grade meta-sedimentary rocks of Cambrian to Eocene age.

This zone is also characterized by the development of extensive thrust sheets and tectonic

windows. A great variation in the tectonic structure is found in the eastern and western sides.

4.2.2.4 Sub- Himalayan (Siwalik) Zone

It lies in the south of the Lesser Himalayan Zone. It is represented by the first low altitude

hills, bordering the plains of Terai. These ranges rise immediately to the north of the Terai

plain. The Siwaliks are bounded by the MBT on the north and the Main Frontal Thrust

(MFT) on the south. This zone exhibits a rugged topography characterized by steep hill

slopes and deep valleys with landslides and steep escarpments and runs along the entire

length of the country from east to west. The youngest mountain chain seems to be

tectonically active and still rising. The Siwaliks of Nepal are composed chiefly of fluvial

sediments like sand, shale, and pebble beds of Neogene age.

4.2.2.5 Terai Zone

It is the southernmost tectonic division of Nepal. It is part of the Indo-Gangetic Plain and

gently slopes towards the south. In the northern part, the MFT separated the Terai Plain from

the Sub-Himalayas. The alluvial deposits of Pleistocene to Recent age (Sharma 1990) cover


the Terai Plain. The average thickness of alluvium deposits is about 1500 m. The rivers

coming from the hills in the north bring these sediments.

4.2.3 Objective of Geological Study

The main objectives of the detailed geological and geo-technical investigation are as follows:

To obtain the required information about regional geology of the project area

and the site specific surface geological condition in order to assess the

stability and suitability of the particular structure;

To find out the rock mass condition of project area and geotechnical

condition, regional geology of the overall project;

To produce engineering geological maps, cross-section and profiles of the

major structures;

To assess the location of construction material sites and hence carries out

construction material survey.

4.2.4 Scope of geological study

The scope of this feasibility study comprises of the following works:

To collect and review the available literature, topographical and geological maps,

photographs and land satellite images;

To study the geological and geo-morphological information prior to previous

studies;

To conduct field survey to collect and verify geological information prior to

general and detail geological mapping of the project components and particular

structures;

To identify the geological and seismic hazards such as faults, thrusts and

landslides, etc;

To identify and assess construction material quarry sites, sources and their

quality.

4.2.5 Regional Geology

The project lies in the Nuwakot Complex of Lowe Nuwakot group of Kuncha Formation.

According to Brodet (1961), rock is described as “an enormous complex, a kind of flysh, a

silky luster, slightly metamorphic, of yellowish, blue grey and green grey color, and


extremely monotonous”. Particular characteristic of Kuncha formation are frequent

intercalation of phyllitic grit stones, consisting of detrial grains of mostly quartz, very

subordinately feldspar, tourmaline and other minerals, which are loosely disseminated in a

phyllitic matrix. Sericite and chlorite are usually the only metamorphic minerals recognizable

in the Kunch Formation, but an increase in metamorphic grade was locally seen in lower

parts of the formation, with appearance of chloritized biotite and Betrawati, and of biotite and

even small garmets near the confluence of Bhotekoshi and Sunkoshi.

A special noteworthy feature of the Kuncha formation is a strong lineaton, predominantly in

a N or N-NE direction, seen in nearly all outcrops. It is less distinct in the higher parts of the

Nuwakot Complex. This project lies in Higher Himalayan unit of the Central Nepal. It

consists of high grade metamorphic rocks such as gneiss, migamitte etc. The area lies in the

Gosainkund Crystalline nappe with para-gneiss as the main rock type. The geology of the

Central Nepal is summarized in Table below.

Complex Groups Formation Main Lithology Thickness, m

Age

Kat

hman

du C

ompl

ex

Phulchoki Group

Godawari Formation

Limestone, dolomite 300 Devonian

Chitlang Formation

Slate 1000 Silurian

Chandragiri lomestone

Limestone 2000 Cambro-Ordoviclan

Sopyang Formation

Slate, Calc-Phylite 200 Cambrian

Tistung Formation

Metasandstone, phylite

3000 Late Precambrian

Transitional Zone

Markhu Formation

Marble, Schist 1000 Precambrian


Kulekhani Formation

Quartzite, Schist 2000 Precambrian

Chisapani Quartzite

White Quartzite 400 Precambrian

Kalitar Formation Schist, Quartzite 2000 Precambrian

Bhaise Dobhan Marble

Marble 800 Precambrian

Raduwa Formation

Granetiferous 1000 Precambrian

Mahabharat Thrust

Nuw

akot

C o

mpl

ex

Upper Nuwakot Group

Robang Formation

Phyllite, Quartzite 1000 Paleozoic

Malekhu Limestone

Limestone, Dolomite 800 Paleozoic

Benighat Slate Slate, Argillaceous Dolomite

2000 Paleozoic

Erosional Unconformity

Lower Nuwakot

Dhading Dolomite

Stromatalitic Dolomite


Nourpul Formation

Phyllite, Quartzite, Dolomite


Dandagaon Phyllite

Phyllite 1000 Late Precambrian

Fagfog Quartzite White Quartzite 400 Late Precambrian

Kunchha Formation

Phyllite, Quartzite, Gritstone, Conglomerate

3000+ Late Precambrian

Main Boundary Thrust

Siwaliks Group


Table 3.1 Stratigraphic Subdivision of Central Nepal (after Stoldin and Bhattarai (1977) Stocklin (1980))

4.2.6 General geology and Geomorphology of the project area

Geologically, the MTHEP area lies in the Gosainkund Crystalline Nappe with para gneiss at

the main rock type and of Higher Himalayan Unit of the central Nepal. It consist of high

grade metamorphic rocks such as gneiss, migmatite etc.

Most of the project area lies in steep to gentle sloppy and flat area. Right bank of headworks

is lies in alluvium deposit whereas left bank lies in colluviums deposit. The river course is

covered with pebbles, cobbles and big boulder of up to about 5 m in diameter. The gravel

trap, approach cannel, settling basin, penstock pressure pipe passes steep topography to flat

area. In some locations of penstock alignment quartzite is exposed.

4.2.7 Soil Types

4.2.7.1 Colluvium Soil

Colluviums soil is commonly encountered in the project area. It is composed of light grey to

dark grey, angular to sub-angular pebbles, cobbles, boulders and gravel supported in the

clayey sandy matrix. It consists of about 65% coarse material and about 35% fine materials.

Fine material contains low to medium plastic sandy silt. The estimated thickness of the

colluviums varies from about 3 m to 9 m depending upon the nature of slope. Unconsolidated

soil is found in relatively flat and gently sloping areas and semi consolidated soil in

moderately steeper slopes.

4.2.7.2 Alluvium Soil

It covers maximum surface area of the project area. Recent and old alluvial deposits are

distributed at both banks of the Tadi Khola in headworks area, waterway and powerhouse

site and which could be around 5 to 15 m high from the existing riverbed level. The old river

alluvium is deposited over the bedrock in some stretches of these areas. The terrace consists

of sub-rounded to rounded boulder (max diameter > 2000 cm), cobble, pebble and gravel of

gneiss limestone slate dolomite etc supported by sandy and silty matrix. It is light grey in


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