Vol-II-Detail-Design-Report

TRISHULI JAL VIDHYUT COMPANY LIMITED
UPPER TRISHULI 3B HYDROELECTRIC
PROJECT (42 MW)
Powerhouse Site
Volume II
Detail Project Report
Prepared by:
Trishuli Jal Vidhyut Company Limited
Sohrakhutte, Kathmandu
Ph : 4363681, Fax No. 4363681, P.O Box 6464
Date: October 2013

Detail Project Report of UT3B HEP


Content of Reports, Drawings and Appendix
Volume 1: Executive Summary
Volume 2: Detail Project Report
Volume 3: Drawings ( Detail Project Report)
Volume 4: Drawing of Structural Design
Appendix A: Topographic Survey and Cadastral Mapping
Appendix B: Hydrology
Appendix C: Geological Study
Appendix D: Hydraulic Design
Appendix E: Rate Analysis
Appendix F: Cost Estimate
Appendix G: Structure Design Report
Engineering Study and Design Team:
S.N Name and Designation Signature
1 Er. Damodar Bhakta Shrestha
(CEO)
2 Er. Bishow Kumar Shrestha
(Structural Engineer)
3 Er. Sunil Basnet
(Hydropower Engineer)
4 Er. Deepak Pandey
(Contract Engineer)
5 Er. Rajesh Sharma
(Civil Engineer)
6 Er. Kalyan Khanal
(Civil Engineer)

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Table of Content
Chapter 1
Introduction
1.1 Study Background ...........................................................................................................................1-1
1.2 Previous Studies...............................................................................................................................1-2
1.3 Objectives and Scope of Work......................................................................................................1-2
1.4 Field Investigation Works...............................................................................................................1-3
1.4.1 Topographical Survey and Mapping ......................................................................................1-3
1.4.2 Geological and Geotechnical Investigation...........................................................................1-3
1.4.3 Project supports facilities.........................................................................................................1-4
1.5 Design Work.....................................................................................................................................1-4
Chapter 2
Description of Project Area
2.1 Location............................................................................................................................................2-1
2.2 Physical Features .............................................................................................................................2-2
2.3 Accessibility......................................................................................................................................2-3
Chapter 3
Field Investigation and Data Collection
3.1 Topographic Survey and Mapping ...............................................................................................3-1
3.1.1 Previous Study...........................................................................................................................3-1
3.1.2 Additional Topographic Mapping and Survey, Fiscal Year-2013.......................................3-1
3.1.3 Scope of works .......................................................................................................................3-1
3.1.4 Monumentation of Ground Control Points and Benchmarks ........................................3-3
3.1.5 Detail Topographical Survey ................................................................................................3-4
3.1.6 Cross- Section Survey ............................................................................................................3-4
3.1.8 Location of Bore Holes, Test Pits and Resistivity Line.....................................................3-6
3.2 Hydrological Investigations ...........................................................................................................3-7
3.2.1 Collection of Available Meteorological and Hydrological Data ......................................3-7
3.2.2 Establishment of Gauging Station ........................................................................................3-7
3.2.3 Water Level Recording and Flow Measurement.................................................................3-7
3.3 Geological and Geotechnical Investigations...............................................................................3-7
3.3.1 Previous Study ...........................................................................................................................3-8

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3.3.5 Field Investigation....................................................................................................................3-9
3.3.5.1 Core Drilling..................................................................................................................3-9
3.3.5.2 Geological Mapping .................................................................................................. 3-10
3.3.5.3 Seismic Refraction Survey ........................................................................................ 3-10
3.3.5.4 Construction Material Survey .................................................................................. 3-12
3.3.2 Additional geological geotechnical investigation, Fiscal Year-2013 ............................... 3-13
Chapter 4
Hydrology and Sediment Study
4.1 Introduction........................................................................................................................................4-1
4.2 Basin Characteristic ...........................................................................................................................4-2
4.3 Review of Catchment Area...............................................................................................................4-3
4.4 Climate Study......................................................................................................................................4-3
4.5 Available Hydrological Data.............................................................................................................4-4
4.5.1 Installation of Hydrometric Station ............................................................................................4-4
4.5.2 Hydrometric Stations ....................................................................................................................4-5
4.5.3 Discharge Measurement by DHM and NEA............................................................................4-5
4.6 Rating Curves .....................................................................................................................................4-7
4.7 Reference Hydrology.........................................................................................................................4-7
4.7.1 Mean Monthly Flow..................................................................................................................4-7
4.7.2 Long Term Trends in Flows....................................................................................................4-9
4.7.3 Correlation between Flows on Trishuli River at Upper Trisuli 3A dam site and Betrawati
Gauge station 447......................................................................................................................4-9
4.7.4 Flow Duration Curve..............................................................................................................4-10
4.7.5 Downstream Release Flow.....................................................................................................4-10
4.8 Flood Estimates ...............................................................................................................................4-10
4.8.1 Introduction .............................................................................................................................4-10
4.8.2 Flood Estimation by Regional Analysis ...............................................................................4-11
4.8.3 Flood Frequency Analysis ......................................................................................................4-13
4.8.4 Flood levels...............................................................................................................................4-15
4.8.5 Construction Flood.................................................................................................................4-15
4.9 Glacier Lake Outburst Floods (GLOF) .......................................................................................4-15
4.9.1 General......................................................................................................................................4-15
4.9.2 Historical Record of GLOF...................................................................................................4-16
4.9.3 GLOF Hazard..........................................................................................................................4-24

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4.9.4 Peak Flows from GLOFs.......................................................................................................4-24
4.9.5 Peak Flow Attenuation with Distance..................................................................................4-25
4.9.6 Longda Glacier Lakes (threat to dam site and powerhouse site)......................................4-26
4.10 Sediment Study.................................................................................................................................4-26
4.10.1 Sediment Data......................................................................................................................4-26
4.10.2 Methods of Estimating the Sediment Flow from the River..........................................4-26
4.10.3 Regional Analysis.................................................................................................................4-26
4.10.4 Estimate based on the Measured Data.............................................................................4-28
4.11 Conclusion ........................................................................................................................................4-33
4.12 Recommendation.............................................................................................................................4-33
Chapter 5
Geological and Geotechnical Studies
5.1 General ..............................................................................................................................................5-1
5.2 Geology of Project Area...............................................................................................................5-1
5.2.1 Intake portal..............................................................................................................................5-1
5.2.2 Headrace Tunnel........................................................................................................................5-2
5.2.3 Adit Portal Area.........................................................................................................................5-4
5.2.4 Surge Tank (Option I) ..............................................................................................................5-4
5.2.5 Powerhouse Site (Option I) .....................................................................................................5-5
5.2.6 Drop shaft/ Pressure tunnel Alignment ................................................................................5-6
5.2.7 Tailrace box Duct......................................................................................................................5-6
5.2.8 Conclusion and Recommendation..........................................................................................5-7
5.3 Seismicity ..........................................................................................................................................5-8
5.3.1 General.......................................................................................................................................5-8
5.3.2 Main Central Thrust (MCT)....................................................................................................5-8
5.3.3 Main Boundary Thrust (MBT) ...............................................................................................5-8
5.3.4 Himalayan Frontal Fault (HFF) .............................................................................................5-9
5.3.5 Seismicity Evaluation...............................................................................................................5-9
5.4 Core Drilling.................................................................................................................................5-15
5.4.1 Core Drilling during feasibility study, July 2007 .................................................................5-15
5.4.2 Drilling Works Result and Analysis ......................................................................................5-15
5.4.3 Core Drilling during Detail Design, June 2013...................................................................5-17
5.4.4 Drilling Works Result and Analyses .....................................................................................5-17
5.5 Construction Material Survey.....................................................................................................5-20

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5.5.1 Introduction .............................................................................................................................5-20
5.5.2 Field Exploration.....................................................................................................................5-20
5.5.3 Laboratory Test and Analysis ................................................................................................5-21
5.5.4 Granular Borrow area .............................................................................................................5-21
5.5.5 Quarry Site..................................................................................................................................5-22
5.5.6 Laboratory Test on Core Samples.........................................................................................5-23
5.5.7 Reserve Estimation of the Borrow Areas and Quarry areas.............................................5-23
5.5.8 Test summary...........................................................................................................................5-23
5.6 Geotechnical Design: rock support design of underground structure ................................5-28
5.6.1 Methods ....................................................................................................................................5-28
5.6.1.1 Empirical Method ...........................................................................................................5-28
5.6.1.2 Analytical Method ...........................................................................................................5-28
5.6.2 Analysis for support design....................................................................................................5-29
5.6.3 Design Criteria .........................................................................................................................5-30
5.6.3.1 Analysis using Rock Cover ............................................................................................5-30
5.6.3.2 Analysis using In Situ Stresses.......................................................................................5-30
5.6.3.3 Analysis using Elastic and Plastic Behavior.................................................................5-31
5.6.4 Failure Criteria..........................................................................................................................5-33
5.6.5 Estimation of In-Situ Deformation Modulus......................................................................5-35
5.6.6 Rock Mass Classification........................................................................................................5-36
5.6.8 Empirical Design According to NGI Method....................................................................5-37
5.6.9 Empirical Design Recommendation According to U.S Corps of Engineers .................5-41
5.6.10 Underground Wedge Stability Analysis............................................................................5-43
5.6.10.1 Methodology ........................................................................................................................5-43
5.6.10.2 Results of Analysis...........................................................................................................5-43
5.6.11 Finite Element Method ......................................................................................................5-46
5.6.11.1 Available Data ..................................................................................................................5-46
5.6.11.2 Result of Analysis.............................................................................................................5-47
5.6.12 Slope Stability.......................................................................................................................5-49
5.6.13 Conclusions and Recommendations ................................................................................5-50
5.6.14 Conclusions and Recommendations ...............................................................................5-54
Chapter 6
Layout Optimization
6.1 Introduction....................................................................................................................................6-1

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6.2 Study of Possible Alternative Layouts for the Project...............................................................6-2
6.2.1 Alternative-I ...........................................................................................................................6-3
6.2.2 Alternative-II..........................................................................................................................6-4
6.2.3 Alternative-III........................................................................................................................6-5
6.3 P r es entat i on of Recommended Layout..............................................................................6-6
Chapter 7
Project Design and Description
7.1 General............................................................................................................................................7-1
7.2 Design Basis.....................................................................................................................................7-1
7.3 Description of Project Components..............................................................................................7-2
7.3.1 Project Access ......................................................................................................................7-2
7.3.2 River Diversion ....................................................................................................................7-3
7.3.3 Headpond/Intake Portal ....................................................................................................7-3
7.3.4 Headrace Pipe....................................................................................................................7-5
7.3.5 Headrace Tunnel..................................................................................................................7-6
7.3.6 Surge Shaft/Tank.................................................................................................................7-8
7.3.7 Pressure Tunnel after Surge Tank .....................................................................................7-9
7.3.8 Drop Shaft and Horizontal Pressure Tunnel.................................................................7-10
7.3.9 Manifolds..........................................................................................................................7-11
7.3.10 Powerhouse......................................................................................................................7-11
7.3.11 Draft Tube........................................................................................................................7-15
7.3.12 Tailrace Conduit ..............................................................................................................7-15
7.3.13 Tailrace Outlet Pond.......................................................................................................7-16
7.3.14 Adit Tunnels.....................................................................................................................7-17
7.4 Generating Equipment.................................................................................................................7-17
7.4.1 Mechanical Equipment .....................................................................................................7-17
7.4.1.1 Initial Data ..........................................................................................................7-17
7.4.1.2 Turbine Selection...............................................................................................7-18
7.4.1.3 Unit Capacity......................................................................................................7-18
7.4.1.4 Turbine Speed ....................................................................................................7-18
7.4.1.5 Powerhouse Dimensions and Unit Parameters.............................................7-18
7.4.1.6 Turbine................................................................................................................7-19
7.4.1.7 Governor.............................................................................................................7-19
7.4.1.8 Inlet Valve...........................................................................................................7-20

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7.4.1.9 High Pressure Oil System.................................................................................7-20
7.4.1.10 Lubricating Oil System......................................................................................7-21
7.4.1.11 Cooling Water System.......................................................................................7-21
7.4.1.12 Drainage and Dewatering System....................................................................7-21
7.4.1.13 Compressed Air System....................................................................................7-22
7.4.1.14 Unit Breaking System........................................................................................7-22
7.4.1.15 Automatic Grease Lubrication System...........................................................7-23
7.4.1.16 Oil Handling System..........................................................................................7-23
7.4.1.17 Air Conditioning and Ventilation System ......................................................7-23
7.4.1.18 Fire Detection and Fire Fighting System........................................................7-24
7.4.1.19 Overhead Traveling Crane................................................................................7-24
7.4.1.20 Diesel Engine Generating Set..........................................................................7-24
7.4.1.21 Mechanical Workshop.......................................................................................7-25
7.4.2 Powerhouse Electrical Equipment..................................................................................7-25
7.4.2.1 Generator............................................................................................................7-25
7.4.2.2 Excitation System ..............................................................................................7-26
7.4.2.3 Main Power Transformer .................................................................................7-26
7.4.2.4 Station Service Transformer.............................................................................7-26
7.4.2.5 Medium Voltage Switchgear.............................................................................7-26
7.4.2.6 High Voltage Switchgear ..................................................................................7-26
7.4.2.7 Disconnecting Switch........................................................................................7-27
7.4.2.8 Control System...................................................................................................7-27
7.4.2.9 Protection System..............................................................................................7-28
7.4.2.10 Switchyard...........................................................................................................7-28
7.4.2.11 Communication System....................................................................................7-29
7.4.2.12 Battery and Battery Charger .............................................................................7-29
7.4.2.13 Grounding System.............................................................................................7-29
7.5 Transmission Line.........................................................................................................................7-30
Chapter 8
Power and Energy Generation
8.1 Background.........................................................................................................................................8-1
8.2 Dependable Flow...............................................................................................................................8-1
8.3 Gross Head & Net Head..................................................................................................................8-2
8.4 Overall Efficiency..........................................................................................................................8-3

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8.5 Ener g y Computation.................................................................................................................8-3
Chapter 9
Construction Planning and Schedule
9.1 General............................................................................................................................................9-1
9.2 Objective & Scope of work..........................................................................................................9-1
9.3 Site Condition.................................................................................................................................9-2
9.3.1 Topography and Land Use ..................................................................................................9-2
9.3.2 Climatic Conditions...............................................................................................................9-2
9.3.3 Telecommunication Facilities..............................................................................................9-2
9.4 Access to the Site...........................................................................................................................9-2
9.5 Basic Assumptions.........................................................................................................................9-3
9.6 Concreting Facilities......................................................................................................................9-4
9.7 Project Construction Work and Construction Planning..........................................................9-4
9.7.1 Construction Power, Camp and project road ...................................................................9-5
9.7.2 Headrace pipe ........................................................................................................................9-6
9.7.3 Surface head pond (intake of UT3B HEP) .......................................................................9-6
9.7.4 Headrace Tunnel ...................................................................................................................9-7
9.7.5 Adit Tunnels...........................................................................................................................9-8
9.7.6 Underground Surge tank/Shaft...........................................................................................9-8
9.7.7 Valve Chamber and Access to Valve Chamber ................................................................9-9
9.7.8 Pressure tunnel after Surge tank..........................................................................................9-9
9.7.9 Drop Shaft..............................................................................................................................9-9
9.7.10 Pressure Tunnel after Drop Shaft.......................................................................................9-9
9.7.11 Powerhouse..........................................................................................................................9-10
9.7.12 Tailrace conduit and Outlet Structure..............................................................................9-11
9.7.13 Electro-Mechanical Equipment.........................................................................................9-11
9.7.14 Switchyard, ancillary Buildings and transmission line....................................................9-11
9.7.15 Testing and Commissioning ..............................................................................................9-11
9.10 Construction Planning and Scheduling ................................................................................9-13
9.11 Key Dates .................................................................................................................................9-14
Chapter 10
Environmental Impact Assessment
10.1 Introduction..................................................................................................................................10-1
10.2 Project Description......................................................................................................................10-1

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10.3 Study Methodology......................................................................................................................10-2
10.4 Existing Environment Conditions ............................................................................................10-2
10.4.1 Physical Environment.........................................................................................................10-2
10.4.2 Biological Environment......................................................................................................10-3
10.4.3 Socio-economic and Culture Environment.....................................................................10-4
10.5 Impact Assessment......................................................................................................................10-6
10.5.1 Physical Environment........................................................................................................10-6
10.5.3 Socio-economic and Cultural Environment....................................................................10-7
10.6 Alternatives Study........................................................................................................................10-8
10.7 Mitigation Measures ....................................................................................................................10-9
10.7.1 Physical Environment.........................................................................................................10-9
10.7.3 Socio-economic and Cultural Environment................................................................. 10-10
10.8 Environmental Management Plan.......................................................................................... 10-11
10.10 Review of Plans/policies, acts, rules/regulation, guidelines, conventions strategies and
standards................................................................................................................................................. 10-12
10.11 Conclusion............................................................................................................................. 10-12
Chapter 11
Cost Estimate
11.1 General..........................................................................................................................................11-1
11.2 Criteria, Assumptions and Cost Components.........................................................................11-1
11.3 Estimating methodology.............................................................................................................11-1
11.4 Civil Works...................................................................................................................................11-2
11.5 Electro-Mechanical Equipment.................................................................................................11-3
11.6 Hydro-mechanical equipment....................................................................................................11-3
11.7 Resettlement, Land acquisition, and Environmental provisions ..........................................11-3
11.8 Contingencies ...............................................................................................................................11-3
11.9 Pre operating and management cost.........................................................................................11-4
11.10 Project Cost..............................................................................................................................11-4
Chapter 12
Project Evaluation
12.1 General......................................................................................................................................12-1
12.2 Methodology ............................................................................................................................12-2

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12.2.1 Estimation of Project Costs...............................................................................................12-2
12.2.2 Estimation of Project Benefits ..........................................................................................12-2
12.2.3 Construction Period............................................................................................................12-3
12.2.4 Calculation of Net Benefits................................................................................................12-4
12.3 Assumptions.............................................................................................................................12-5
12.3.1 Discount Rate ......................................................................................................................12-5
12.3.2 Cost Datum..........................................................................................................................12-5
12.3.3 Planning Horizon ................................................................................................................12-6
12.3.4 Operation and Maintenance Cost.....................................................................................12-6
12.3.5 Price Escalation ...................................................................................................................12-6
12.3.6 Taxes, Duties and VAT......................................................................................................12-6
12.3.7 Royalties................................................................................................................................12-6
12.3.8 Debt Equity..........................................................................................................................12-7
12.3.9 Interest Rate .........................................................................................................................12-7
12.3.10 Loan Repayment Period.................................................................................................12-7
12.3.11 Other Charges..................................................................................................................12-7
12.4 Economic Evaluation Result .................................................................................................12-8
12.5 Financial Evaluation.............................................................................................................12-11
Chapter 13
Conclusions and Recommendations..........................................................................................................13-1
List of the Table
Table 3.1: Co-ordinates and Elevation of Existing Control Points .........................................................3-3
Table 3.2: List of Co-ordinates and Elevations of Permanent Benchmarks ..........................................3-3
Table 3.3: List of borehole locations (core drilling works-August 2013)..............................................3-6
Table 3.4 : General Description of Drill Holes (Coordinates based on old survey reports).......... 3-10
Table 3.5: Brief Description of Seismic Refraction Survey.................................................................. 3-11
Table 3.6: A Brief Description of Test Pits............................................................................................. 3-13
Table 4.1: Average precipitation of the stations located near the project area......................................4-4
Table 4.2: Rainfall records available from China.......................................................................................4-4
Table 4.3: Discharge Measurements at Pairobesi Bridge..........................................................................4-5
Table 4.4: Hydrometric stations located in the Trishuli River Basin......................................................4-5
Table 4.5: Discharge measurement in Trishuli river at Gauge Station 447, Betrawati.........................4-6

x
Table 4.6: Discharge measurement in the tributaries of Trishuli River near project area ...................4-6
Table 4.7: Monthly mean flows (m3/s) for 1967-2005 on Upper Trishuli 3A Dam site ....................4-8
Table 4.8: Flow duration curve at dam site...............................................................................................4-10
Table 4.9: Floods and Regression Coefficient (Regional Analysis).......................................................4-13
Table 4.10: Instantaneous peak for the Flood Frequency Analysis ......................................................4-13
Table 4.11: Frequency Analysis by Theoretical Distribution.................................................................4-14
Table 4.12: Flood water level at different project components.............................................................4-15
Table 4.13: Historical GLOF events in Nepal and China (Tibet)........................................................4-18
Table 4.14: Summary of Sediment Concentration Data, Station 447...................................................4-29
Table 4.15: Comparison of Sediment Concentration 1977-1979..........................................................4-30
Table 4.16: Recommended Monthly Sediment Concentration .............................................................4-31
Table 4.17: Particle Size Distribution of Bucket Sampling ....................................................................4-32
Table 5.1: General Description of Boreholes...........................................................................................5-15
Table No. 5.2: Summary of borehole location, depth, direction and bedrock depth.........................5-17
Table 5.4: Summary of Pits and Sample Description..............................................................................5-21
Table 5.5: Reserve Estimation of Borrow Area.......................................................................................5-23
Table 5.6: Summary of Laboratory Test Results on Granular Material ...............................................5-24
Table 5.7: Summary of Laboratory Test Results on Quarry Material...................................................5-25
Table 5.8: Summary of Laboratory Test Results on Core Samples ......................................................5-25
Table 5.9: Summary of Laboratory Test Results on Core Samples ......................................................5-26
Table 5.10: Summary of Laboratory Test Results on Core Samples ....................................................5-26
Table 5.11: Point Load Test Results..........................................................................................................5-27
Table 5.12: Damage Index ..........................................................................................................................5-32
Table 5.13: Values of constant mi for Intact Rock by rock group........................................................5-34
Table 5.14: Estimation of In-Situ Modulus of Deformability ...............................................................5-35
Table 5.15: Rock Mass Strength Parameters ............................................................................................5-36
Table 5.16: Rock Mass Classification using Rock Mass Rating (RMR) system (Bieniawski, 1989)..5-36
Table 5.17: Rock Mass Classification from Rock Tunneling Quality Index, Q (Stillborg, 1994).....5-37
Table 5.18: Typical Design Recommendations after U.S. Corps of Engineers (1980) and Douglas
and Arthur (1983).........................................................................................................................................5-41
Table 5.19: Summary of Analysis for Headrace Tunnel (N256°)..........................................................5-44

xi
Table 5.24: Summary of Analysis for Horizontal Pressure Tunnel (N140°).......................................5-45
Table 5.25: Basic Design Parameters for Elasto - Plastic Analysis .......................................................5-48
Table 5.26: Summary of the result of analysis..........................................................................................5-49
Table 5.26: Rock Support Pattern for Upper Trishuli-3B Hydroelectric Project..............................5-51
Table 5.27: Chainage wise Support Class Headrace Tunnel ..................................................................5-52
Table 5.28: Geological & Geotechnical Evaluation of Option I & Option II Powerhouse Site .....5-53
Table 6-1: Flow Data Used for the Alternative Studies...........................................................................6-3
Table 6.2: summary of Cost Comparison of Different Layouts..............................................................6-6
Table 3: Details of Cost Comparison of different layouts .......................................................................6-7
Table 7.1: Bend Characteristics of Headrace Pressure Pipe.....................................................................7-6
Table 7.2: Lengths of different rock class in headrace tunnel .................................................................7-7
Table 7.3: Description of Headrace Tunnel before surge tank ...............................................................7-7
Table 7.4: Details of Horizontal bends for both alternatives ..................................................................7-8
Table 7.5: Description of designed surge tank...........................................................................................7-8
Table 7.6: Description of water conveyance after surge tank..................................................................-10
Table 7.7: Details of Pressure Shaft Bends (Vertical Shaft Option).....................................................7-10
Table 7.8: Design parameters for sizing of Powerhouse........................................................................7-12
Table 7.9: Design parameters for Draft tube ...........................................................................................7-15
Table 7.10: Design parameters for tailrace Outlet Pond ........................................................................7-16
Table 8.1: Average Head Loss for Design Discharge..............................................................................8-2
Table 8.2: Monthly Energy Generation from Upper Trishuli 3B HEP ..................................................8-4
Table 9.1: Estimate of construction power ................................................................................................9-5
Table11.1: summary of cost estimate ........................................................................................................11-6
Table 12.1: Result of Economic Analysis .................................................................................................12-8
Table 12.2: Result of Sensitivity analysis...................................................................................................12-8
Table 12.3: Economic Analysis Detail Table ...........................................................................................12-9
Table12.4: Financial Analysis Data and Result ......................................................................................12-12
List of the Figure
Figure 2.1: Physiographic location of the project......................................................................................2-1
Figure 2.2: Location of the Project..............................................................................................................2-2
Figure 5.1: Seismic Risk Map of Nepal .....................................................................................................5-11
Figure 5.2: Seismic Hazard Map of Nepal................................................................................................5-12

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Figure 5.3: Seismic Risk Map of India.......................................................................................................5-14
Figure 5.4: Estimated Support Categories based on the tunneling quality Index Q (After Grimstad &
Barton, 1993).................................................................................................................................................5-38
Figure 12-2: Interest Rate vs FIRR..........................................................................................................12-12

1-1
Trisuli Jalvidyut Company Limited
Chapter 1:
Introduction
1.1 Study Background
Nepal is entering a phase of rapid economic development and a major part of this
development is based on the tapping of its immense water resources potential. The total
hydroelectric potential of the country has been estimated at 83,000 MW of which approximately
42000 MW is considered to be economically feasible potential. A number of Hydroelectric schemes
like Modi (14 MW) HEP, Puwa(6.2 MW) HEP, Khimti (60 MW) HEP, Bhote Koshi (36 MW) HEP,
Kaligandaki – A (144 MW) HEP, Chilime (22 MW) HEP, Middel Marsyangdi (70 MW) HEP have
already been completed recently while other projects like Chameliya (30 MW HEP, Kulekhani III
(14 MW) HEP, Tama Koshi (456 MW) HEP, Mai Khola(22 MW) HEP, Lower Modi (20 MW)
HEP are under various stages of construction. The private sector has implemented projects
Khimti, Bhote Koshi, Mai Khola, Lower Modi and other small projects. The independent power
producer (IPP) have generated around 230.5 MW (F/Y 2012/13 NEA Report).
Harnessing of Nepal’s huge hydro-electric potential could not only fulfill much of the energy needs
but could also become the source of prosperity. Hydroelectricity can be the prime mover of
economic development of Nepal and hence deserve special importance. The main attraction of
Hydroelectric is that this clean source of energy does not require fuel cost and the electricity
generating costs decline over the life span of the venture.
The first hydro electric plant was installed in Pharping (500 KW) in 1911. At present, Nepal has an
installed capacity of 762 MW, out of this total capacity, 53.41 MW is generated through thermal
power plants and 7 0 8 .5 MW through hydro power projects under power purchase agreements
with the private sector. Only about 45 % of the country’s population is served by electricity which
shows a per capita consumption to be very low. Nepal has been experiencing load shedding since
the past few years (and the supply deficit is nearly 800 MW in the dry season). The demand
projection made by NEA indicates that the peak load demand for the years 2015 and 2020 will be
1510 MW and 2206 MW respectively. NEA, an undertaking of Government of Nepal has launched

1-2
a wide range of study programs aimed at identifying and studying a series of Hydroelectric
projects. The objective of the study program is to identify technically and economically feasible
projects for subsequent implementation.
1.2 Previous Studies
Upper Trisuli 3B HEP (37 MW) is a cascade project of Upper Trisuli 3A HEP and was identified by
NEA Engineering Services in 2004/05 as part of Project Identification Study. NEA has completed
the feasibility study in 2007/08. Four cascade schemes namely Upper Trishuli 1, 2, 3A and 3 B were
identified in the Upper Trishuli basin located between Syabrubesi and Betrawati which has a total
head of 750m. NEA has completed detailed project report study of the Upper Trishuli 3A which has
an installed capacity of 60 MW and is under construction. Upper Trishuli 3B HEP is a downstream
project which utilizes the discharge from the tailrace of Upper Trishuli 3A HEP.
1.3 Objectives and Scope of Work
Trisuli Jalvidyut Company Limited (TJCL) has carried out the review of the Trisuli 3B HEP and
carried out the site verification. The outcome of the review study is as follows:
a) It is urgent need to update the cost of the project according to the prevailing market rate.
b) During the site visit it is found the land slide occurred at the powerhouse location year
in the year 2011, therefore, it is necessary to locate the powerhouse at the alternative
place.
c) Carry out the cost comparison between different alternative layouts.
d) Since the access road is available at the intake area to powerhouse area, the cost of these
item has to reduce from the estimate.
The main objective of this study is to carry out a Detailed Project Report of the Upper
Trishuli 3 B Hydroelectric Project. This is being done by taking into consideration all the relevant
data and information collected from the previous studies, field surveys and investigations conducted
during the present study. The EIA study required to complete the Detailed Project Report is also a
part of the objectives of this study. The scope of work can broadly be divided into the field

1-3
investigation work and the design of the project.
1.4 Field Investigation Works
The following additional works were carried out in the design phase apart from the feasibility phase
of study.
1.4.1 Topographical Survey and Mapping
For detail engineering design, following topographical survey and mapping works has been carried
out by the TJCL:
i) Mapping in the dam site area at a scale of 1:500 and with a contour interval of 1 m.
ii) Mapping of the Powerhouse (alternative option and original option) area at a scale of
1:500 and a contour interval of 1m.
iii) Connection with the national grid.
iv) Cross section survey of the river.
v) Mapping of tunnel alignment area at scale of 1:5000.
vi) Cadastral mapping of the project for land acquisition of project
1.4.2 Geological and Geotechnical Investigation
The following geological investigation works were carried out for this phase of the study.
i) A total of 250 m of core drilling was completed at various locations during the
feasibility study. Additional 195 m drilling works were completed at the alternative
powerhouse option I the Fiscal Year 2069/70.
ii) A total of 11 test pits were completed at various locations in and around the project
area.
iii) Laboratory tests were conducted for the test pit samples.
iv) Surface geological mapping of the project were carried out during feasibility study.

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Apart from that, new surface geological mapping of the intake area, powerhouse area
and alternative powerhouse area were carried out at appropriate scales.
1.4.3 Project supports facilities
For the construction of the project, the planning will set according to the location of support
facilities such as quarry site, dumping site, muck disposal area, access road and adit at different
location. Therefore, during the detail design, the site visit has been done to locate all these support
facilities.
a) Location of muck disposal area has been identified based on the adit tunnel. For
this purpose most of those places are near the river bank and government land.
b) Location of Quarry site are done based on the availability of construction material
such as sand and gravel.
c) Contractor’s construction camp are located based on the availability of land at the
site. They have been identified near the powerhouse area.
d) Most of the access road has been constructed, the project road is required for the
surge tank access and powerhouse area only. A portion of road from New Bridge
(the Belly Bridge constructed by Trisuli 3A HEP) to Tupche (near the pressure
tunnel alignment) has to be relocated and cost estimate has been done for these
item separately.
e) The construction camps for the company office are designed by the team of TJCL
engineer.
1.5 Design Work
The main part of the design consisted of the alternative layout of the powerhouse and carry out
the hydraulic design and structural design of the different structures. The main works consisted of
the following:
i) Review of available information (feasibility Study);
ii) Collection of basic information/data through field surveys, investigations and

1-5
laboratory tests;
iii) Preparation of design drawings;
iv) Alternative studies of powerhouse location;
v) Detail design of the following structures:
• Project road
• Headponds at the outlet of Trisuli 3A HEP tailrace
• Adit tunnel at different location
• Conveyance system including headrace pipe, headrace tunnel, surge tank, drop
shaft
• Surface powerhouse
• Tailrace duct
• Electromechanical Facilities
vii) Computation of Project Energy Outputs and Related Benefits;
viii) Construction Planning in Detail;
ix) Detail Quantity Cost Estimate;
x) Disbursement Schedule;
xi) Project Evaluation for finance.

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Chapter 2:
Description of Project Area
2.1 Location
Nepal lies in the foothills of the highest areas of the Great Himalayan Range. It extends from the
Republic of India in the south to the high Tibetan Plateau of the People’s Republic of China in the
north. It is roughly rectangular in shape. Nepal embraces within itself a unique variety of
geographical settings ranging from the southern lowlands at approximately 60 masl to the highest
peaks in the world in its northern parts. Between these marginal zones there are three richly varied
regions, namely, the Terai Region in the south, the Middle Hilly Region in between and the Trans
Himalayan Region in the north. Physiographically, the project is located at Middle Mountains as
shown in Figure 2.1.
Figure 2.1: Physiographic location of the project
Terai
Siwaliks
Middle Mountains High Mountains High Himalaya
Shale
Alluvium
Conglomertate
Sandstone
Granite
Schist
Limestone
Metamorphosed
Argillaceous
Rocks
Gneiss
Schist
Granite
Tibetan
Sediments
Physiographic Region of Nepal
Project Location

2-2
The Upper Trishuli 3B Hydroelectric Project is located in Nuwakot and Rasuwa District of the
Central Development Region between longitudes of 85O
10’11” and 85O
12’01”and between latitudes
of 27O
59'12” and 28O
01'54”. The project lies in the Trishuli River of the Middle Hilly Region which
constitutes a broad complex of hills and valleys. It is a major river of the Gandaki Basin. Rugged
landscapes with a generally north to south flowing rivers like Sapta Gandaki characterizes the
Gandaki Basin. The area of the intake site is located about 5 km upstream from the confluence of
the Salankhu Khola and Trishuli while the powerhouse site is located approximately 0.5 kilometers
upstream from the confluence of Salankhu Khola and Trishuli River. The project location map is
given in Figure 2.2 and DWG No UT-3B HEP 01.
Figure 2.2: Location of the Project
2.2 Physical Features
Owing to the three richly varied regions, Nepal lies in an area with a great difference in elevation
from the north to the south. As a result, Nepal experiences an exceptional variation in climate. From
south to north, five defined climatic zones exist in the country, these are:
Project Location

2-3
• Tropical
• Subtropical
• Temperate
• Alpine
• Sub Arctic
The dominant climatic influence is that of the south east monsoon. The climate of the
Gandaki Basin is influenced by the physiography of the region. The difference between the warm
humid summer and the severe cold winter becomes more marked with the increase in altitude.
The south east monsoon is responsible for almost all of the rainfall in the basin. The monsoon
starts in mid June and continues until late September. This is followed by a dry period and the
winter, which starts in November and lasts until February. A short winter rainfall characterizes the
winter. The climate becomes progressively warmer from March until the beginning of the next
monsoon.
2.3 Accessibility
The project site is located about 12 km from Trishuli Bajaar and the existing Trishuli
Hydroelectric project (24 MW), which is the nearest town. The nearest airport is located in
Kathmandu which is approximately 84 km from the project site.
Access conditions to the site are excellent. There is a blacktopped road from Kathmandu to Trishuli
Bajaar which is approximately 72 km long. The black topped road from Trisuli Bazar to Dhunche
highway passes through the Betrawati Bazar at about 10 km from Trisuli Bazar. A graveled road
exists from Betrawati Bajaar to the powerhouse site of the project and it is approximately 2
km long. This gravel road passes through the headworks area of Upper Trisuli 3B Hydroelectric
Project. The distance between powerhouse to headworks area is about 4 km.
It is therefore obvious that the project is accessible by the gravel road. During the construction, the
project has to build the road to powerhouse and road to surge tank adit, this shall be about 0.8 km
long.

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Chapter 3:
Field Investigation and Data Collection
3.1 Topographic Survey and Mapping
3.1.1 Previous Study
The overall survey works for the proposed project were conducted in two phases. The first phase
lasted from November end to December end of the year 2006 while the second phase survey was
carried out from first February to last February 2006. The first phase survey works were carried
out to map the project area as a whole including headworks, intake area, surge shaft and
powerhouse area. The second phase of survey works included additional mapping for the
alternate powerhouse location. The details are given in the Detail Project Report, Volume-1 of
Upper Trisuli 3B Hydroelectric Project.
3.1.2 Additional Topographic Mapping and Survey, Fiscal Year-2013
Proper survey and leveling works are necessary to design the components, to prepare drawings and
to calculate the quantities of the project components. The survey data greatly influences the
accuracy of design and quantity take offs. All the survey works were carried out precisely and
correctly again. Therefore, the company TJCL has carried out the detail topographic survey and
mapping for the detail design and construction purpose.
The new topographic mapping covers the survey of alternative location of powerhouse site. Since
the project is cascade development of Upper Trisuli 3A HEP, the ground control points are taken
from the same projects. The detail reports of survey are given in “ Detail Topographic Survey of
Upper Trisuli 3B Hydroelectric Project-February 2013.
3.1.3 Scope of works
a. Review of the topographical map of feasibility study of the project, based on the

3-2
available maps of the project area.
b. Finalization of the methodology of survey and plan
c. Interconnection of the Ground Control Points (GCPs) of project area with respect to
the National Grid Co-ordinate System of Nepal.
d. Co-ordinates for Planimetric Control Points can be transferred from Upper Trishuli
“3A”, however verification is required before topographic survey and mapping.
e. Establishment of Benchmarks at various locations in the project area for the marks
required but not limited to are as shown below:
i. Headwork area 6 nos.
ii. Tunnel Adit area 2 nos.
iii. Surge Tank area 3 nos.
iv. Powerhouse area 6 nos.
v. Camp Site area 2 nos.
f. Detail topographical survey of Headwork, Tunnel alignment, Intake, Adit, Surge Tank,
Penstock Pipe/Dropshaft and Powerhouse area (including alternative powerhouse site)
at Scale 1:500. This shall be working drawing at contour interval 1m.
g. Overlay of Topographic Survey Map in GIS database of NGIIP of Nepal.
h. Access Road to the surge tank, the mapping of the access road is to be carried out if
necessary.
i. Strip Mapping of Tunnel alignment covering alternative-I and alternative-II in 1:5,000
Scale.
j. Cross Section survey at Trishuli River along Head pond and Powerhouse area (
Alternative powerhouse site shall be included )
k. The Topographic Map shall include but not limited to :
- Demarcation of road, forest land, agriculture land, barren land, rock cliff, bush and,
land slide area, rivulets and big boulder if any in the topographic mapping. The
verification shall be carried out at the site after draft survey report submission.
- Exact location of manmade structures such as houses, temples, bridges, canals, walls
and etc are to be shown in the topographic mapping and drawings. Such structures
shall be documented by the photographs.

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3.1.4 Monumentation of Ground Control Points and Benchmarks
List of Co-ordinates and Elevations of Existing Permanent Points provided by Upper Trishuli-3A
Hydroelectric Project.
Table 3.1: Co-ordinates and Elevation of Existing Control Points
Point No. Easting (m.) Northing (m.) Elevations (m.)
DX 18 617090.576 3101331.156 734.409
DX 19 616865.863 3101139.600 725.862
Monuments made of concrete pillars have been fixed on the strategic locations from where the detail
survey longitudinal sectioning and cross sectioning and setting out of the project components can be
carried out. Some benchmarks have been established on the stable boulders or on manmade
permanent structures which were available in the vicinity of survey area. The List of Co-ordinates of
established control points are given in Table 3:2
Table 3.2: List of Co-ordinates and Elevations of Permanent Benchmarks
S.
No.
Point
Name
Easting
(m.)
Northing
(m.)
Elevations
(m.)
Remarks
1
DX 18 617090.576 3101331.156 734.409 Existing point Fixed on
Concrete Pillar
2 DX 19 616865.863 3101139.600 725.862 “ “
3 BM-1 616058.861 3096433.271 632.334 Fixed on Concrete Pillar
4 BM-2 615909.991 3096472.042 640.407 Fixed on Boulder
6 BM-4 616015.244 3096722.002 749.960 “ “
9 BM-7 616556.547 3100813.820 786.142 “ “
10 BM-8 616850.989 3100640.112 724.497 “ “
11 BM-9 616675.455 3100636.592 724.497 “ “

3-4
17 BM-15 616460.537 3097274.502 647.795 “ “
18 BM-16 616289.996 3097599.897 777.605 “ “
19 BM-17 616273.929 3097611.528 782.370 “ “
3.1.5 Detail Topographical Survey
The detail topographical survey has been carried out by using TOPCON Total Stations Survey
instrument with the least count as 5 seconds. The survey has been carried to depict all natural and
manmade features in the study area in order to prepare the topographical map in 1:5,00 scale with 1.0
m contour interval. The topographical survey has been carried out by covering approximately 60 ha.
of land including headwork area, along tunnel alignment, Adit areas, surge tank and powerhouse
areas.
3.1.6 Cross- Section Survey
The Cross-Sections at Trishuli River have been taken at 50m intervals at alternative powerhouse
sites. The spot levels along the cross-section have been taken as per change of ground level to
prepare correct profile along the cross-section line which represents the existing shape. The details of
existing structures those falling along the line of cross-section have been taken properly.
3.1.7 Preparation of maps profiles and reports
Based on the data from the field survey, the topographical maps cross-sections have been prepared
by using the AutoCAD Land Development Software. The complete report and drawings have been
prepared.
(i) A Reference Plan of the Project area in scale as shown in the Bar Scale.
(ii) Detail Topographical Maps of Headwork, Adits and Powerhouse areas in scale 1:500

3-5
with contour interval 1 metre.
(iii) Detail Topographical Maps along the strip of Tunnel alignment in scale 1:5,000 with
contour interval 5 metres.
(iv) Cross-Sections drawings
(v) A complete report consisting of survey methodology, outputs of the work, D-Cards
etc.
In general, the maps, other drawings and reports have been prepared as below:
(i) A General Reference Map of the Project Area
In order to prepare the General Reference Map, GIS database of Topographical Map Sheet
No. 2885-13 and 2785-01B were collected from NGIIP, Survey Department of Nepal. By
using ArcGIS 9.2 Software, the data of the project area and its vicinity was selected from the
above mentioned GIS data. Then a Digital Terrain Model (DTM) was created, which consists
of relief model and site model having X, Y, Z Co-ordinates of each point. All the features
were then transferred to the plan and finally the Reference Map has been prepared.
(ii) Detail Topographical Maps
All existing physical and manmade features on the ground; such as structures, utilities features
and the land use information have been shown in the maps. The topographical maps have
been plotted in the scale: 1: 500 with counter interval 1m and 1:5,000 scale with 5 m. interval.
The maps have been prepared to produce DTMs to be enabling direct use to design.
(iii) Cross- Section Drawings
The cross-sections have been drawn and prepared in H = V 1:500 . The drawings have been
prepared in A1 size with a 25 mm border on the left and 10 mm border on three sides.

3-6
(iv) Reports
In general, the main report is prepared by incorporating the general approach and
methodology, and other general matters relating to the objective of the work. The secondary
data which would be useful later are annexed with the report. But the whole report is
managed in volume one. The annexure (Detail Topographic Survey-February 2013) which
are attached with the report are as follows:
● Location Map
● General Reference Map of the Project area
● Traverse Chart
● D-Cards of Permanent Benchmarks/Survey Stations
● List of Co-ordinates and Elevations of Existing Permanent Points provided
by Upper Trishuli-3A Hydroelectric Project.
3.1.8 Location of Bore Holes, Test Pits and Resistivity Line
During the feasibility study of Upper Trisuli 3B HEP, Number of bore holes, test pits and Resistivity
line survey were carried out. They are given in the report of “ Upper Trisuli 3B Hydroelectric
Project, Detail Project Report, Volume 1-year 2008”.
During detail design phase, A total of 4 boreholes were located on the ground at the powerhouse
site and surge tank area with given coordinates and elevation. The coordinates and elevation of
all the boreholes are given in Table 3.3.
Table 3.3: List of borehole locations (core drilling works-August 2013)
S. No. Bore Hole Northing Easting Elevation Location
1 DST-1 616196.445 3097625.756 813.15 Surge shaft
2 DPA-1 616353.178 3097447.957 683.07 Penstock alignment
3 DPH-1 616434.629 3097359.831 639.90 Powerhouse Site
4 DPH-2 616397.42 3097410.45 665.545 Powerhouse Site

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3.2 Hydrological Investigations
3.2.1 Collection of Available Meteorological and Hydrological Data
The meteorological and hydrological data for the project was obtained from Government of
Nepal, Department of Meteorology and Hydrology. The main data obtained were the
precipitation records, temperature and discharge measurements at available stations. The
details for the available data are given in the following sections and also in chapter 4.
3.2.2 Establishment of Gauging Station
A hydrological team visited the site in the month of January 2006. A total of 5 staff gauges
were installed during the field visit near the Headworks site and Powerhouse site on Trishuli 3B
Khola, and a staff gauge was installed in Salakhu Khola a tributary of Trishuli River at
Pairobesi, Champani and Sole village of Rasuwa and Nuwakot District.
During the site visit the river was traversed along its bank to locate the best possible site for the
staff gauge. The selected site was considered as the best location for the staff gauge as it had a
straight reach and a pool of water near the gauge site.
3.2.3 Water Level Recording and Flow Measurement
During the time of staff gauge installation, discharge measurements were carried out. Average
discharges on 3rd January 2007 were 28.715 m3
/s in Trishuli River at Pairobesi and 0.611
m3
/s in Salankhu Khola at Solye. Detailed discharge measurement sheets are attached herewith.
3.3 Geological and Geotechnical Investigations
NEA has carried out a lot of geotechnical investigation during the feasibility study of the project for
the given site conditions. They are given in the “Upper Trisuli-3B Hydroelectric Project, feasibility
study, Geology and Geotechnical Study (Appendix B, Year 2007) in detail. Since the proposed
powerhouse site has felt huge land slide in the year 2011, it is forced to see the alternative

3-8
powerhouse location. Therefore, the company has carried out new surface and subsurface geological
investigation in the year 2013. The results obtained from the investigation work will be used to
assess the technical viability of the project for the Detailed Design of the project.
3.3.1 Previous Study
Medium Hydro Power Study Project, NEA (1998) had carried out the reconnaissance study of
Upper Trishuli - 3 (UT-3) which is named as Gogane to Betrawati Hydroelectric Project and Upper
Trishuli -3B (UT-3B) is mutually included in UT-3 Project.
Department of Mines and Geology has also prepared and compiled regional geological map
including the project area in the scale of 1:1,000,000 (1994).
During the feasibility study of the project, the field investigation work is carried out to find out the
surface and sub- surface geological condition of the project area, to design the support
pattern for the underground structures and to confirm the availability of the construction materials
in terms of quality and quantity.
3.3.2 Scope of Work
The main scope of work in this phase of study is to assess the rock mass condition of the
project area by means of detailed geological mapping, core drilling and geophysical survey and to
produce engineering geological maps, cross-sections and profiles at various scales as deemed
necessary to provide information required for the engineering designs and underground
excavation.
The scope of work in geological mapping is to produce engineering geological maps of the
powerhouse site and the headworks site in the scale of 1:1,000 and 1:1,000 respectively and
engineering geological map of tunnel alignment area in the scale of 1:10,000.
The scope of work for the core drilling includes the assessment of sub-surface geological
condition including rock quality, rock type, joint characteristics and permeability condition of the

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rock mass.
Another main scope of work is geophysical investigation for the assessment of sub-surface
geological condition of the major structures during the present investigation.
The scope of work also includes the preliminary geotechnical design including stability
analysis and rock support classification of underground structures.
The scope of work for the construction material investigation includes the assessment for the
quality and quantity of construction material available within the easy haulage distance from the
project area.
3.3.5 Field Investigation
The following geological field investigation works have been carried out to assess the
geological and geotechnical condition of the project area. Geological mapping, core drilling, seismic
refraction survey and construction material investigations are the main activities which have been
carried out during the present study.
3.3.5.1 Core Drilling
A total of 250.00 m of linear core drilling has been carried out during the present investigation.
One bore hole DHP-1 has been drilled in the intake portal, three namely DP-1, DP-2, DP-4
have been drilled in the Powerhouse area and one DP-3 has been drilled in Surge Tank area.
Similarly, a Drill hole DHA-1 has been drilled at Andheri Khola to know the rock cover at headrace
tunnel alignment. The location of drill holes are shown in Drawing No.-6.1,6.2 and 6.3. The
general description of the bore holes are shown in Table No. 3.4.

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Table 3.4 : General Description of Drill Holes (Coordinates based on old survey reports)
Drill Hole
No.
Drilling
Machine
Inclination
& Direction
Location Length
(m)
Co-ordinates
X Y Z
DP-1
DP-2
DP-4
DHP-1
DHA-1
DP-3
Acker ‘Ace’
Acker ‘Ace’
Acker ‘Ace’
Tone UD-5
Tone UD-5
Acker 'Ace'
Vertical
Vertical
60°/285°
60°/275°
Vertical
Vertical
Powerhouse
Power house
Powerhouse
Intake Tunnel
Alignment Surge
tank
50.00
30.00
35.00
35.00
50.00
50.00
3097872.018
3097898.200
3097891.240
3100866.415
3100745.980
3097967.715
616658.991
616565.300
616590.128
616665.250
616228.730
616467.863
649.188
655.300
652.430
736.000
814.200
763.865
Total 250. m
3.3.5.2 Geological Mapping
Detailed engineering geological maps of the powerhouse site and headworks site have been
prepared in the scale of 1:1,000. While the engineering geological map of tunnel alignment has
been prepared in the scale of 1:10,000. Detailed joint survey was carried out at each hydraulic
structure site for engineering classification of rock mass. Both RMR and NGI ‘Q’ systems were
used for rock mass classification.
3.3.5.3 Seismic Refraction Survey
A total of 2180.00m of seismic refraction survey has been carried out at major hydraulic
structure sites. Altogether 26 seismic lines were executed for this purpose. The objective of the
survey was to determine the overburden thickness, bedrock quality, thickness of weathered zone
and degree of fracturing in the bedrock. The hammering method was used for the seismic refraction
survey. The result showed mainly three velocity layers which ranges from 400 - 600 m/s, 800 - 1000
m/s and 1400 - 2400 m/s. The bedrock and the compact overburden deposit consisting of large
boulders have shown the velocity in the range of 2200 - 2400 m/s. The details of seismic
refraction survey including investigation results are presented in Annex-B3. The brief description
of seismic refraction survey is shown in Table No. 3.5.

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Table 3.5: Brief Description of Seismic Refraction Survey
SN Location Seismic Line Length (m)
1 Headworks Site SLD – 1 115
Total 390
7 Tunnel Alignment SLT – 1 340
Total 675
13 Powerhouse site SLP – 1 235
Total 1115
Grand Total 2180

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3.3.5.4 Construction Material Survey
• General
The construction material investigation includes mainly the identification of borrow areas, test
pitting, sample collection and laboratory testing. The investigation has been carried out to
assess the availability of required volume of different construction materials such as
impervious core material, coarse and fine aggregates, rip-rap in different borrow areas and
quarry sites within the haulage distance of about 5 km from the project site. The laboratory
tests and analysis of collected samples were also carried out according to ASTM and AASTHO
standards.
Different locations for the construction materials such as cohesive material, fine and coarse
aggregates, fine sand and granular materials are identified within the permissible haulage
distance from the project area. The borrow areas are investigated by digging the test pits.
Two borrow areas for the granular material has been identified in the vicinity of the project
area. Similarly, two quarry sites for granular materials have been also identified during the
present investigation. The borrow areas are located at Trishuli River bed and Salankhu Khola
river bed and quarry sites are located at left bank of Trishuli River which is close to proposed
powerhouse site and another quarry site has been identified at Trishuli River bed deposit in the
vicinity of the project area.
The riverbed material can be used to produce concrete aggregates such as fine and coarse (sand and
gravel) after washing out the fines (No. 2000 sieve). Fine aggregate for concrete can also be
obtained by crushing the oversize material from riverbed (+56 mm)
The field exploration was conducted by pitting method in which test pits of depth up to 3m
were excavated manually with the help of hand shovel. The size of test pits were generally
2.0m x 2.0m. Different samples were collected for different types of soil encountered in a test pit.
The fraction passing 80 mm sieve was collected to carry out the laboratory tests such as Grain
Size Analysis, Index Properties, Specific Gravity, Los Angles Abrasion, Sulfate Soundness.

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A total of 11 test pits were excavated during the present field investigation. Out of which 5 test
pits were excavated at Salankhu Khola River Bed and remaining 6 test pits were excavated at
river bed deposit of Trishuli River.
Table 3.6: A Brief Description of Test Pits
Name of the
borrow/quarry area
Location Number of
test pit
No. of
sample
Remarks
GA Saletar 6 12 Weir site
GB Simle bagar 6 13 PH site
GC Andheri Khola bagar 4 9 Andheri Khola
CA Ratamate danda 5 10 Archale VDC
QA Headworks site 1 L/B Trishuli River
QB headworks site 1 R/B Trishuli River
QC Andheri Khola 3 Andheri Khola
3.3.2 Additional geological geotechnical investigation, Fiscal Year-2013
Details of new investigation are presented in the report “ Upper Trisuli-3B Hydroelectric Project, a)
Surface Geological Mapping, Year 2013 May, and b) Core Drilling, Year 2013 August”.

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Chapter 4:
Hydrology and Sediment Study
Preamble
The project under study is in the Trisuli River. The headworks is located at 500 m upstream of
the Andheri Khola. The powerhouse is located at 500 m upstream of the Salankhu Khola and
Trisuli River confluence. This is the run of the river cascade scheme with Upper Trisuli 3A
Hydroelectric Project (installed capacity 60 MW). The reference hydrology, basically a monthly
flow, are same in Upper Trisuli 3A and 3B. The Trishuli River is originated from China (Tibet)
and the major portion (80 %) of the catchment area lies in China. This study covers the field
investigation, hydrological data collection and hydrological analysis required for the project
design.
4.1 Introduction
Hydrological study of this project comprises of extensive data collection at the site for discharge
& sediment measurement and their analysis. Field investigation was carried out by establishing
several new Staff Gauge stations in the Trishuli River near the project site. Moreover, an
endeavour has been made to measure the precise catchment area of Trishuli River and its
tributaries located near the project site with the help of Satellite Image and Maps available.
Furthermore, a long term flow at the intake site has been produced by correlating with the long
term observation from the down stream gauge station 447 of the same river situated at Betrawati.
Hydrology, sediment and hydraulic study of the project were carried out to estimate the pertinent
design parameters. These parameters are (a) design flood (b) diversion flood (c) monthly flow (d)
rating curves (e) downstream release (f) sediment inflow (g) GLOF. While, establishing these
parameters, standard software and simple spread sheet have been used. The primary data for the
analysis have taken from “Department of Hydrology and Meteorology (DHM)”, and the related
reports from the other hydropower projects. Besides that the extensive field study were carried
out by the developer.
The major portion of the catchment lies in the China, the physiographic data as well as
precipitation data are not available, therefore, the average basin precipitation study is out of
scope. The hydrological study has been based on the Gauge Station 447 at Betrawati, Trisuli

4-2
River. Besides that the NEA has also established the Hydrological gauge station on the Trisuli
River at Pairobesi village to monitor the river flow.
4.2 Basin Characteristic
The head works of Upper Trisuli-3B Hydroelectric Project is on the Trisuli River located 6.5 km
downstream from the confluence of Mailun Khola and Trisuli River, whereas the powerhouse is
located at 500 m upstream from the Salanku Khola and Trisuli river confluence. (right bank of
Trisuli River).
Trishuli is one of the major tributaries of Sapta Gandaki river system. The river flows almost
North-South from Tibet to Nepal. The main source of Trishuli River discharge is the snow and
glacier melt from the higher Himalayas. Langtang Himal is one of the major mountain range in
the basin. The total area of Trishuli River basin up to intake site is 4577 km2
(intake site of Upper
Trisuli 3A HEP) and that of the power house site is 4605 km2
. The catchment area in Nepal
covers only 20 % of the total catchment area 4577 km2
. 'Inventory of Glacier lakes 2002'
published by ICIMOD have identified about 117 numbers of glacier lakes with total area of 2.03
(km2
) and 74 numbers of glacier rivers with total area of 246.65 (km2
) inside the Trishuli river
catchment in Nepal. This study have further identified that the ice reserve is 27.47 km3
. The
major tributaries of Trishuli River upstream of proposed Dam site are Chilime, Langtang and
Dhunche Trishuli. The Trisuli River basin within the Nepal is shown in Figure 4.1. The Trisuli
River basin including China and Nepal combined is shown in Figure 4.2.
Physiographically, Trisuli River basin upstream of dam site lies in the High Mountain and High
Himalayas. The High Himalayan region is constituted by the extremely high peaks. Some of
those major peaks are highlighted below.
Ganesh Himal (Nepal side) Altitude 7406 m
Lapsang Karubo (Nepal Side) Altitude 7150 m
Lantang Ri (Nepal Side) Altitude 7232 m
Langtang Lirung (Nepal Side) Altitude 7246 m
Gang Benchnen (China Side) Altitude 7211 m

4-3
4.3 Review of Catchment Area
The catchment area of the Trisuli river basin upstream of the gauging station 447 has been
revised by different agencies. The previous records of Catchment area of Trishuli River at
Betrawati 447 station from Department of Hydrology and Meteorology (DHM) published in
1998 shows that the area is only 4110 square km. Whereas, the Catchment area indicated by
WECS in 1990 shows as 4640 square km. During the feasibility study of Upper Tama Koshi
HEP, “NEA and Norconsult” has estimated the catchment area of the Trishuli basin upstream
of the Betrawati station 447 as 4850 km2
. In this study, this final figure 4850 km2
has been
recommended as the catchment area upstream of the Betrawati Gauge station.
4.4 Climate Study
Since the catchment of this river lies in the High Himalayas and the High Mountain region, the
physiographic characteristic influences the climate in this region. The Climatic condition varies
with respect to the altitude. The catchment area experiences severe cold, subtropical to
temperate climate. The southwest monsoon is dominant from June to the end of September in
the catchment as other parts of Nepal. The region receives approximately 80 % of the annual
rainfall during the Monsoon period. Rainfall intensities vary throughout the basin with maximum
intensity occurring on the south facing slopes. During the monsoon period, relative humidity
reaches at their maximum and the temperatures are lower compared to the pre-monsoon period.
The precipitation on the basin determines the average basin precipitation and flood generation.
The meteorological stations near the project area are tabulated in Table 4.1. It is noticed the
meteorological station Index Nos. 1005 and 1057 are the closest to the project area. The location
of the precipitation stations are shown in Figure 4.3.The precipitation record in the China (Tibet)
catchment area is not known. A short precipitation records of Tingri and Nyalum (Precipitation
station in Tibet) is available and shown in the Table 4.2. The annual precipitations in these
stations are below 800 mm. The mean annual precipitation map of the country shows that the
annual precipitation at the Nepal side lies below the range of 2000mm.

4-4
Table 4.1: Average precipitation of the stations located near the project area
Index
No.
Station
Name
Elevation
(m amsl)
Lat. /Long. Year of
Records
Annual Mean
Precipitation (mm)
1001 Timure 1900 27°14'/85°25' 1957-94 950
1004 Nuwakot 1003 27°55'/85°10' 1956-94 1870
1005 Dhading 1427 27°52'/84°56' 1956-94 2195
1015 Thankot 1631 27°41'/85°12' 1967-94 2000
1054 Thamchi 1847 28°10'/85°19' 1972-94 1039
1055 Dhunche 1982 28°06'/85°18' 1972-94 1863
1057 Pansaya Khola 1240 28°01'/85°07' 1973-94 3040
1058 Tarke Ghyang 2480 28°00'/85°33' 1974-94 2859
Table 4.2: Rainfall records available from China
Station Longitude Latitude Altitude
(m)
River
Basin
Time
Interval
Period Mean Annual
Rainfall (mm)
Nyalam N/A N/A N/A Bhote
Koshi
monthly 1966-75 627
Monthly 1976-86 717
Tingri 28O 36’ N 87O 06’ E 4302 Arun
River
Monthly 1960-86, excl
1969-70
285
3.5 Available Hydrological Data
3.5.1 Installation of Hydrometric Station
NEA has installed the Hydrometric Station on Trisuli at Pairobesi Bridge at Manakaman VDC
from 19th
Paush 2063. The gauge station is 1500 m downstream of the headworks site of the
Upper Trisuli-3B Hydroelectric Project. Staff gauge reading from this gauging station is
continuously being measured. Gauge readers have been recruited to read the water level thrice a
day at 8:00 hour, 12 hour and 16:00 hour. The location of the staff gauge installation is shown in
Figure 4.4. The summary of discharge measurements at different period is given below.

4-5
Table 4.3: Discharge Measurements at Pairobesi Bridge
S. No Date Time Discharge (m3
/sec) Gauge Height(m)
1 2063-9-19 11:00 AM 48.384 0.32
2 2064-02-11 10:3 AM 221.488 0.89
3 2064-02-12 10:30 AM 196.64 0.87
4 2064-07-18 7:55 PM 117.702 0.50
4.5.2 Hydrometric Stations
Besides the gauging station installed by the project, there exist the hydrometric stations operated
by Department of Hydrology and meteorology (DHM) located in the Trishuli River basin. Most
of these gauging stations have daily water level recording facilities. They are shown in the Table
4.4.
Table 4.4: Hydrometric stations located in the Trishuli River Basin
S.
No
Gauge
Station
Type of
Station
Name of River Location Comments
1 447 Cable way,
Water level
Trishuli Betrawati. Located at 12
km d/s of Intake.
Established in
1967.
2 446.7 Water level Phalakhu (Tributary of
Trishuli River)
d/s of TOL and u/s of
Betrawati and about
200m u/s of Phalakhu
446.8
Data used in
present study
3 446.8 Water level Phalakhu (Tributary of
Trishuli River at
Betrawati.)
d/s of TOL and u/s of
Betrawati at confluence
with Trishuli
Data used in
present study
4 446.3 Water level Dhunche Trishuli u/s of Intake Data not used in
present study
5 446.2 Water level Langtang Khola u/s of Intake Data not used in
present study
6 446.25 Water level Bhote Koshi u/s of Intake Data not used in
present study
Out of these measuring stations, the station No 447 has been used in the present detail design
study for generating long term daily flow. The gauge station No 447 on the Trishuli River is
located at Betrawati which is about 16 km downstream of Intake site of this project. It is noticed
the station 447 has been operated by DHM since 1967.

4-6
3.5.3 Discharge Measurement by DHM and NEA
The discharge of Trishuli River has been measured at the nearest station 447 Betrawati
established by Department of Hydrology. This station is located about 16 km downstream of
intake site. There exist three tributaries in between tailrace outlet and Betrawati station no. 447.
These tributaries are Andheri Khola, Salakhu and Phalakhu Khola. Among these three the
Andheri Khola has drainage area of only 4.5 sq. km and the surface flow is not visible during dry
season. Therefore, latter two tributaries are the major tributaries in between tailrace outlet and
Station no. 447-Betrawati. There exist two staff gauge stations in Phalakhu Khola (446.7 and
446.8). However, the daily flow records in these tributaries are available only for the five years
from 1985 to 1986 and from 1988 to 1990 respectively. There exist no daily flow records in
Salakhu Khola. The measured discharge records are illustrated in the following Table 4.5 and
Table 4.6.
Table 4.5: Discharge measurement in Trishuli river at Gauge Station 447, Betrawati
S. No. Date Time Discharge
(m3
/sec)
Gauge
Height(m)
Method Agency
1 8-Oct-05 496 2.6 CM DHM
2 24-Feb-06 13:00 44.33 0.76 CM DHM/NEA
3 24-Feb-06 14:44 43 0.75 CM DHM/NEA
4 12-May-06 8:00 96.03 1.52 CM DHM/NEA
5 12-May-06 16:00 87.72 1.42 CM DHM/NEA
Note: CM= Current Meter
Table 4.6: Discharge measurement in the tributaries of Trishuli River near project area
S.
No
Date Time Tributary
Name
Discharge
(m3
/sec)
Gauge
Height
(m)
Method Agency
1 25-Dec-05 16:25 Mailung 2.695 CM NEA
1 25-Dec-05 10:15 Salakhu 1.134 CM NEA
2 24-Feb-06 16:00 Salakhu 0.553 CM DHM/NEA
3 11-May-06 16:00 Salakhu 0.709 CM DHM/NEA
4 12-May-06 10:30 Salakhu 1.057 CM DHM/NEA

4-7
S.
No
Date Time Tributary
Name
Discharge
(m3
/sec)
Gauge
Height
(m)
Method Agency
1 24-Feb-06 8:25 Phalakhu 446.7 1.247 3.4 CM DHM/NEA
4 11-May-06 15:00 Phalakhu 446.8 3.24 0.52 CM DHM/NEA
5 12-May-06 8:20 Phalakhu 446.8 3.12 0.49 CM DHM/NEA
4.6 Rating Curves
The rating curves at the different site of interest of the project were developed using Manning’s
equation. The rating curve for the tailrace outlet of Upper Trisuli-3A HEP and intake area of
Trsisuli 3B HEP and tailrace outlet of Upper Trisuli 3B HEP was developed. The Manning’s “n”
for the development of rating curve assumed is 0.035.
The rating curve at the proposed intake site (that is, outlet portal of Upper Trisuli 3A HEP) is
shown in the Figure 4.5. Similarly, the rating curve at the inlet portal of tunnel (near the section
PX-15) was developed and shown in the Figure 4.6. Similarly, the rating curve at tailrace outlet of
Upper Trisuli 3B HEP is shown in Figure 4.7.
4.7 Reference Hydrology
3.7.1 Mean Monthly Flow
Since the daily mean discharge at the dam axis of Upper Trsiuli-3A Hydroelectric Project is not
available, the reference hydrology has been derived from the gauging station 447 at Betrawati.
The number of years of data availability in this station is 1967 to 2005. The flow data at the
gauging station 447 were closely examined and found consistent. Therefore, the catchment area
ratio is used to generate the flow at the dam site of the Project. The equation that has been used
in data generation is

4-8
QIntake = (AIntake / Aknown)* Q known
Where,
QIntake = Flow at Intake site (Intake site of Upper Trisuli 3A HEP, 60 MW)
Q known = Flow at known site
A Intake = Area upstream of Intake site
Aknown = Area upstream of known site
The summaries of the mean monthly flow generated are shown in the Table 4.7. The variations
of the monthly flow are depicted in Figure 4.8. The annual mean at intake of Upper Trisuli 3A
HEP is found to be 192.0 m3
/s. The minimum monthly flow occurs in the February. The flow
gradually increases from April as the snow in the high mountain start melting. The maximum
monthly flow occurs mostly in August which lies in the monsoon period.
Table 4.7: Monthly mean flows (m3
/s) for 1967-2005 on Upper Trishuli 3A Dam site
Year Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
1967 44.5 35.9 33.6 38.8 60.1 129.9 405.9 489.2 308.0 112.3 63.1 45.5
1968 35.7 30.2 29.2 36.5 61.2 207.8 458.2 452.4 265.2 160.0 71.5 48.1
1969 38.2 33.5 31.2 35.9 58.8 125.8 375.7 425.7 316.2 118.7 63.5 44.8
1970 34.6 30.1 28.2 38.3 61.6 153.1 441.8 482.7 274.1 143.0 78.9 54.7
1971 42.5 36.5 34.8 43.8 61.4 328.4 422.7 518.0 302.0 145.0 76.9 51.7
1972 40.6 35.2 36.7 40.5 95.4 153.5 406.4 448.4 266.7 99.6 59.0 40.6
1973 35.2 34.7 37.9 57.0 91.3 345.6 481.1 625.2 495.6 271.8 94.3 62.0
1974 47.9 37.5 34.2 50.8 77.6 188.7 515.5 603.8 374.1 175.8 81.5 57.2
1975 48.3 43.6 41.8 56.8 86.4 248.8 517.5 529.3 486.8 209.8 104.2 65.8
1976 46.5 39.5 38.0 44.0 80.3 195.6 346.2 459.8 351.4 155.5 93.8 61.8
1977 45.4 43.9 47.0 51.8 73.4 181.5 557.9 574.3 339.7 154.5 88.7 58.2
1978 43.9 41.6 42.8 54.1 142.2 316.0 490.8 589.8 313.0 202.8 101.9 66.1
1979 48.4 41.1 41.4 49.4 86.7 175.0 441.3 475.8 264.2 129.0 78.3 52.5
1980 41.1 38.0 38.5 56.1 76.0 260.4 625.8 640.0 368.0 153.2 86.0 55.6
1981 40.4 34.4 35.1 47.1 80.2 274.3 673.7 584.7 348.7 132.6 82.2 52.8
1982 40.8 37.6 52.9 70.4 76.8 200.2 384.4 562.1 371.0 113.6 73.1 51.0
1983 37.8 32.8 34.3 36.4 66.0 152.1 355.7 477.9 413.8 190.6 89.5 57.0
1984 44.0 31.5 32.3 32.6 100.8 281.6 584.5 487.7 394.1 110.7 65.6 46.2
1985 33.6 31.9 39.5 43.7 51.5 147.7 458.9 407.7 348.4 189.2 86.5 65.2
1986 52.0 51.4 50.9 61.0 72.8 300.9 655.1 561.6 428.5 159.7 91.0 64.1
1987 51.2 48.3 N.A. 48.9 55.1 N.A. N.A. N.A. 178.2 110.0 74.3 58.3
1988 49.3 45.8 46.5 56.4 81.4 167.9 460.1 534.3 245.2 102.8 67.8 55.5
1989 50.8 44.8 45.7 54.0 99.0 177.3 335.6 416.6 266.0 112.8 61.4 45.9
1990 39.2 35.0 33.8 45.2 86.1 297.2 769.3 592.8 427.0 157.5 72.8 46.3
1991 36.4 30.7 30.7 35.9 81.5 198.3 460.2 756.4 618.0 N.A. 55.3 42.5
1992 32.5 27.4 27.0 32.6 40.7 114.8 306.6 668.9 386.8 132.0 62.8 39.4

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