aaratipower.com...Upper Irkhuwa Khola Hydropower Project Feasibility Study Report i Salient Features of Upper Irkhuwa Khola Hydropower Project 1. Project name : Upper Irkhuwa Khola

Upper Irkhuwa Khola Hydropower Project Feasibility Study Report

i

Salient Features of Upper Irkhuwa Khola Hydropower Project

1. Project name : Upper Irkhuwa Khola Hydropower

Project

2. Location : Dobhane, Khatama & Kudakaule VDCs

of Bhojpur District

Co-ordinates of Project Area : 27o22’58” E and 27 o24’17” N

: 87o01’33” E and 87 o03’51” N

3. Type of project : Run-of-the-river

4. Hydrology at intake

Catchment area

Phedi Headworks

Thumlung Headworks

Total

:

:

:

74.17 km2

63.18 km2

137.35 km2

Maximum design flood (Q100)

Phedi Headworks

Thumlung Headworks

:

:

191.63 m3/s

181.56 m3/s

Probable maximum flood (Q1000)

Phedi Headworks

Thumlung Headworks

:

:

267.69 m3/s

252.61 m3/s

Mean monthly flow

Phedi Khola

Thumlung Khola

Total

:

:

:

7.74 m3/s

6.81 m3/s

14.55 m3/s

Design Flow (Q45) : 7.80 m3/s

5. Headworks

Type of weir (Both Headworks) : Ogee shaped concrete gravity weir

Length of weir (Both Headworks) : 20 m

Weir height

Phedi Headworks

Thumlung Headworks

:

:

2 m

3 m

Weir crest elevation

Phedi Headworks

:

927 masl


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Thumlung Headworks : 923 masl

Intake type (Both Headworks) : Side intake, orifice type

6. Approach canal and Settling

Basin

Type : Surface

Length of approach canal : 20 m

Total length of Settling Basin : 90.85 m

Length of effective section : 60 m

Width of uniform section : 8 m

No. of bays : 2

7. Headrace Pipe

Steel type : SM400B

Length : 375 m

Diameter : 1.50 m

Thickness : 10 mm

8. Headrace tunnel

Shape : Inverted D shaped (W = 3.5 m, H=3.5m)

Area = 10.94 m2)

Length : 3720 m

9. Surge shaft

Type : Simple Orifice type

Internal diameter : 5.0 m

Height : 25.0 m

10. Penstock pipe

Steel type : SM400B

Length : 375 m

Diameter : 1.85 m

Thickness : Varies(10 mm-24 mm)

11. Powerhouse

Type : Surface

Size : 30.25 m x 10 m x 10 m (L x B x H)


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Turbine axis elevation : 701.50 masl

12. Tailrace

Length : 27 m

Shape Rectangular

Dimension (B x H) 2.6 m x 1.8 m

13. Turbine

Type : Horizontal axis Pelton Turbine

Speed : 300 rpm

Capacity : 2 x 7.25 MW

Design discharge : 7.80 m3/s

14. Generator

Type : Synchronouos, 3-phase

Specification : 50 Hz, 0.8 power factor, 9.965 kVA x 2

Nos.

15. Power and energy

Gross head : 221.50 m

Net head at design discharge : 217.85 m

Installed capacity : 14.50 MW

Efficiency : 92%, 96% and 99% (turbine, generator

and

transformer)

Dry energy : 30.18 GWh/yr

Wet energy : 60.39 GWh/yr

Total energy : 90.57 GWh/yr

Annual firm power : 48.66 GWh

Annual firm energy : 41.91 GWh

16. Transmission line

Substation Location :

Shitalpati

Length : 8 km

Voltage : Double circuit 33 kV level

TL (Alternate option)


iv

Substation Location : Tumlingtar

Length : 13 km

Voltage : 132 kV

17. Access road and project road

Road Head : Dobhane

Length : 3 km for the alignment

18. Project cost

Reference year (exchange rate) : April 2017

Civil works : 1,500,47,000 NRs.

Electro-mechanical works : 518,375,000 NRs.

Hydro-mechanical works : 129,838,000 NRs.

Transmission line : 85,000,000 NRs.

Road and Infrastructures : 9,100,000 NRs.

Total financial cost : 2,602,271,000 NRs. (at the end of

construction period)

Specific cost per kW : 179,467 NRs.

19. Financial indicators

Project cost : 2,602,271,000 NRs.

Interest rate : 10%

IRR : 14.98%

NPV : 1,179.3 million NRs.

B/C : 1.45

Simple Payback Period : 6.78 Years

Discounted Payback Period : 11.17 Years

Return on Equity (RoE) : 29


v

Abbreviations and Acronyms

ARI : Acute Respiratory Infection

B : Breadth

B/C : Benefit-Cost Ratio

BoQ : Bill of Quantities

CPM : Critical Path Method

CBR : California Bearing Ratio

CBS : Central Bureau of Statistics

DDC : District Development Committee

DHM : Department of Hydrology & Meteorology

DMG : Department of Mines & Geology

DoED : Department of Electricity Development

d/s : Downstream

E : East

EA : Environmental Assessment

EIA : Environmental Impact Assessment

EMU : Environmental Management Unit

EPR : Environment Protection Rules

ERT : Electrical Resistivity Tomography

FIDIC : International Federation of Consulting Engineers

FINNIDA : Finnish International Development Agency

GIS : Geographic Information System

GLOF : Glacier Lake Outburst Flood

GoN : Government of Nepal

GPS : Global Positioning System


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GWh : Giga Watt-Hour

H : Height

ha : Hectares

HFL : High Flood Level

HFT : Himalayan Frontal Thrust

IEE : Initial Environmental Examination

INPS : Integrated Nepal Power System

UIKHP : Upper Irkhuwa Khola Hydropower Project

IRR : Internal Rate of Return

IS : Indian Standards

J/V : Joint Venture

km : Kilometer

kV : Kilo Volt

kW : Kilo Watt

kWh : Kilo Watt-Hour

L : Length

LS : Lump Sum

m : Meter

masl : Meters above Sea Level

MBT : Main Boundary Thrust

MCT : Main Central Thrust

mm : Millimeter

MoEn : Ministry of Energy

MoSTE : Ministry of Science, Technology and Environment


vii

MW : Mega Watt

N : North

NCS : National Conservation Strategy

NEA : Nepal Electricity Authority

NPHC : National Population and Housing Census

PAFs : Project Affected Families

NPV : Net Present Value

NRs. : Nepalese Rupees

PERT : Program Evaluation and Review Technique

Q : River Discharge

QCBS : Quality and Cost-Based Selection

RoR : Run-of-the-River

rpm : Revolutions per Minute

s : Second

S : South

SD : Scoping Document

SPAFs : Seriously Project Affected Families

TL : Transmission Line

ToR : Terms of Reference

u/s : Upstream

US$ : United States Dollars

VDC : Village Development Committee

W : West

WECS : Water and Energy Commission Secretariat

yr : Year


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Table of Contents

SALIENT FEATURES OF UPPER IRKHUWA KHOLA HYDROPOWER PROJECT .............................................. I

ABBREVIATIONS AND ACRONYMS ......................................................................................................... V

TABLE OF CONTENTS ........................................................................................................................... VIII

LIST OF TABLES .................................................................................................................................. XVIII

LIST OF FIGURES ................................................................................................................................... XX

LIST OF PHOTOS ................................................................................. ERROR! BOOKMARK NOT DEFINED.

1. BACKGROUND AND INTRODUCTION ..................................................................................... 1-1

1.1. BACKGROUND ....................................................................................................................... 1-1

1.2. THE PROJECT ......................................................................................................................... 1-1

1.3. LOCATION .............................................................................................................................. 1-2

1.4. ACCESSIBILITY ........................................................................................................................ 1-2

1.5. TRANSMISSION LINE .............................................................................................................. 1-3

1.6. OBJECTIVES OF THE STUDY .................................................................................................... 1-3

1.7. ORGANIZATION OF THE REPORT ........................................................................................... 1-4

2. TOPOGRAPHICAL SURVEY ..................................................................................................... 2-1

2.1. INTRODUCTION ..................................................................................................................... 2-1

2.2. COLLECTION OF AVAILABLE INFORMATION AND DATA ......................................................... 2-1

2.3. SCOPE OF WORKS .................................................................................................................. 2-1

2.4. DESK STUDY........................................................................................................................... 2-2

2.5. PROJECT SITE VISIT ................................................................................................................ 2-2

2.6. SURVEY METHODOLOGY ....................................................................................................... 2-2

2.7. TOPOGRAPHY OF THE SITE .................................................................................................... 2-2

2.8. SURVEY METHODOLOGY OF THE PROJECT WORKS ................................................................ 2-2

2.8.1. DETAIL SURVEY ...................................................................................................................... 2-3

2.8.2. CONTROL TRAVERSING .......................................................................................................... 2-3

2.8.3. HORIZONTAL AND VERTICAL CONTROL ................................................................................. 2-5

2.8.4. ACCURACY ............................................................................................................................. 2-6

2.8.5. DETAIL TOPOGRAPHICAL SURVEY .......................................................................................... 2-6

2.8.6. MAPPING .............................................................................................................................. 2-6

2.8.7. RIVER CROSS SECTION AND PROFILE ..................................................................................... 2-6

2.8.8. ESTABLISHMENT OF CONTROL POINTS .................................................................................. 2-6


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2.8.9. DESIGN DATA ........................................................................................................................ 2-7

3. HYDROLOGICAL STUDY .......................................................................................................... 3-1

3.1. GENERAL ............................................................................................................................... 3-1

3.2. IRKHUWA KHOLA CATCHMENT CHARACTERISTICS ................................................................ 3-1

3.2.1. CATCHMENT PHYSIOGRAPHY ................................................................................................ 3-1

3.2.2. WATER SHARING ISSUES ....................................................................................................... 3-3

3.3. REFERENCE HYDROLOGY AND AVAILABLE DATA ................................................................... 3-3

3.3.1. STREAM GAUGING ................................................................................................................ 3-3

3.3.2. LONG TERM MEAN MONTHLY FLOW AND FLOW DURATION CURVE ..................................... 3-3

3.3.3. WECS/DHM METHOD ............................................................................................................ 3-4

3.3.4. MHSP METHOD ..................................................................................................................... 3-4

3.3.5. CATCHMENT AREA RATIO (CAR) METHOD ............................................................................. 3-5

3.3.6. ADOPTION OF DESIGN DISCHARGE AND FLOW DURATION CURVE ........................................ 3-6

3.3.7. RIPARIAN RELEASE ................................................................................................................ 3-9

3.4. FLOOD HYDROLOGY .............................................................................................................. 3-9

3.4.1. DESIGN HIGH FLOODS ........................................................................................................... 3-9

3.4.2. DRY SEASON FLOODS .......................................................................................................... 3-15

3.5. LOW FLOW ANALYSIS .......................................................................................................... 3-16

3.6. SEDIMENT ANALYSIS ........................................................................................................... 3-16

3.6.1. GENERAL ............................................................................................................................. 3-16

3.6.2. SOURCES OF SEDIMENT ....................................................................................................... 3-17

3.6.3. ESTIMATION OF SEDIMENT YIELD ........................................................................................ 3-17

3.7. CONCLUSION AND RECOMMENDATION .............................................................................. 3-18

3.7.1. CONCLUSION ....................................................................................................................... 3-18

3.7.2. RECOMMENDATION ............................................................................................................ 3-18

4. GEOLOGICAL STUDY OF THE PROJECT .................................................................................... 4-1

4.1. INTRODUCTION ..................................................................................................................... 4-1

4.2. OBJECTIVES ........................................................................................................................... 4-2

4.3. SCOPE OF WORKS .................................................................................................................. 4-2

4.4. METHODOLOGY .................................................................................................................... 4-3

4.4.1. DESK STUDY........................................................................................................................... 4-3

4.4.2. DATA COLLECTION AND FIELD WORKS .................................................................................. 4-3

4.4.3. DATA INTERPRETATION AND REPORT WRITING .................................................................... 4-3

4.4.4. BACKGROUND INFORMATION ............................................................................................... 4-3

4.4.5. PRESENT INVESTIGATION ...................................................................................................... 4-4


x

4.4.5.1 GEOLOGICAL MAPPING ......................................................................................................... 4-4

4.4.5.2 GEOTECHNICAL INVESTIGATION ............................................................................................ 4-4

4.4.6. CONSTRUCTION MATERIAL SURVEY ...................................................................................... 4-4

4.5. HIMALAYA IN GENERAL ......................................................................................................... 4-5

4.5.1. PUNJAB HIMALAYA ............................................................................................................... 4-5

4.5.2. KUMAON HIMALAYA ............................................................................................................. 4-5

4.5.3. NEPAL HIMALAYA .................................................................................................................. 4-5

4.5.4. SIKKIM-BHUTAN HIMALAYA .................................................................................................. 4-5

4.5.5. NEFA (NORTH EAST FRONTIER AGENCY) HIMALAYA .............................................................. 4-5

4.6. GEOLOGY OF THE NEPAL HIMALAYA ..................................................................................... 4-6

4.6.1. INDO-GANGETIC PLAIN (TERAI) ............................................................................................. 4-6

4.6.2. SUB-HIMALAYA (SIWALIKS OR CHURIA GROUP) .................................................................... 4-6

4.6.3. LESSER HIMALAYA ................................................................................................................. 4-7

4.6.4. HIGHER HIMALAYA ................................................................................................................ 4-7

4.6.5. TIBETAN-TETHYS HIMALAYA.................................................................................................. 4-8

4.6.6. PHYSIOGRAPHY OF NEPAL ..................................................................................................... 4-8

4.6.6.1 MAHABHARAT RANGE........................................................................................................... 4-8

4.6.6.2 MIDLANDS ............................................................................................................................. 4-9

4.6.6.3 FORE HIMALAYA .................................................................................................................... 4-9

4.7. REGIONAL GEOLOGY OF THE PROJECT AREA ....................................................................... 4-11

4.7.1. LESSER HIMALAYA ............................................................................................................... 4-12

4.7.2. THRUSTS .............................................................................................................................. 4-13

4.7.2.1 BARUN THRUST (BT) OR MAIN CENTRAL THRUST (MCT) ..................................................... 4-13

4.7.2.2 ARUN THRUST (AT) .............................................................................................................. 4-14

4.7.3. FOLD AND FOLIATION .......................................................................................................... 4-14

4.7.3.1 FOLD .................................................................................................................................... 4-14

4.7.3.2 FOLIATION ........................................................................................................................... 4-14

4.7.3.3 JOINTS ................................................................................................................................. 4-15

4.7.4. PREVIOUS STUDIES .............................................................................................................. 4-15

4.8. GEOLOGICAL AND ENGINNERING GEOLOGICAL CONDITION OF THE PROJECT AREA ............ 4-16

4.8.1. DIVERSION WEIR AXIS AREA ................................................................................................ 4-16

4.8.2. DESANDER BASIN AND APPROACH WATERWAYS ALIGNMENT AREA .................................. 4-17

4.8.3. INLET PORTAL AREA ............................................................................................................ 4-18

4.8.4. TUNNEL ALIGNMENT AREA .................................................................................................. 4-18

4.8.5. SURGE TANK AND PENSTOCK ALIGNMENT AREA................................................................. 4-18


xi

4.8.6. POWERHOUSE AND TAILRACE AREA.................................................................................... 4-19

4.8.7. GEOMORPHOLOGY .............................................................................................................. 4-19

4.9. GEOTECHNICAL STUDIES OF THE PROJECT AREA ................................................................. 4-19

4.9.1. GNEISS/ SCHIST ................................................................................................................... 4-20

4.9.2. COLLUVIAL AND RESIDUAL SOIL DEPOSITS .......................................................................... 4-20

4.9.3. ALLUVIAL DEPOSITS OF RECENT RIVER TERRACE ................................................................. 4-20

4.9.4. DESCRIPTION OF PROPOSED STRUCTURES .......................................................................... 4-21

4.9.4.1 DIVERSION WEIR AXIS AND INTAKE AREA ........................................................................... 4-21

4.9.4.2 DESANDER BASIN AND APPROACH WATERWAY ALIGNMENT ............................................. 4-24

4.9.4.3 INLET PORTAL AREA ............................................................................................................ 4-26

4.9.4.4 TUNNEL ALIGNMENT AREA .................................................................................................. 4-28

4.9.4.5 SURGE TANK AND PENSTOCK ALIGNMENT AREA................................................................. 4-39

4.9.4.6 POWERHOUSE AND TAILRACE AREA.................................................................................... 4-41

4.10. SEISMICITY .......................................................................................................................... 4-42

4.10.1. SEISMO-TECTONIC MODEL .................................................................................................. 4-43

4.10.1.1 DETERMINISTIC ASSESSMENT .............................................................................................. 4-43

4.10.2. HORIZONTAL ACCELERATION .............................................................................................. 4-44

4.10.2.1 DETERMINISTIC APPROACH ................................................................................................. 4-44

4.10.2.2 PROBABILISTIC APPROACH .................................................................................................. 4-44

4.10.2.3 RECURRENCE PERIOD .......................................................................................................... 4-45

4.10.3. HISTORICAL SEISMIC ACTIVITY ............................................................................................. 4-47

4.10.4. EARTHQUAKE CATALOGUE .................................................................................................. 4-48

4.10.5. NEPALESE STANDARD .......................................................................................................... 4-49

4.10.6. INDIAN STANDARD .............................................................................................................. 4-51

4.10.7. SEISMIC ZONING .................................................................................................................. 4-52

4.10.7.1 SEISMIC DESIGN ACCELERATION COEFFICIENT ..................................................................... 4-52

4.11. CONSTRUCTION MATERIALS SURVEY AND TESTS ................................................................ 4-54

4.11.1. BORROW AREA .................................................................................................................... 4-54

4.11.2. COARSE AND FINE AGGREGATES ......................................................................................... 4-54

4.11.3. LABORATORY TEST OF THE CONSTRUCTION MATERIALS ..................................................... 4-56

4.11.3.1 COARSE AGGREGATE ........................................................................................................... 4-56

4.11.3.2 FINE AGGREGATE ................................................................................................................ 4-56

4.11.3.3 SIEVE ANALYSIS ................................................................................................................... 4-57

4.11.3.4 SPECIFIC GRAVITY AND ABSORPTION TEST .......................................................................... 4-57

4.11.3.5 LOS ANGELES ABRASION TEST ............................................................................................. 4-57


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4.11.3.6 SULPHATE SOUNDNESS TEST ............................................................................................... 4-57

4.11.3.7 LOOSE DENSITY DETERMINATION ....................................................................................... 4-58

4.11.3.8 COMPACTION TEST .............................................................................................................. 4-58

4.11.3.9 POINT LOAD TEST ................................................................................................................ 4-58

4.11.3.10 CRUSHING VALUE .......................................................................................................... 4-58

4.11.3.11 FLAKINESS INDEX ........................................................................................................... 4-58

4.11.3.12 ELONGATION INDEX ...................................................................................................... 4-58

4.11.4. RESULTS AND DISCUSSIONS ................................................................................................ 4-59

4.11.5. GEOPHYSICAL INVESTIGATION ............................................................................................ 4-60

ERT-1, RIGHT BANK OF WEIR AXIS (FIGURE 4 A AND 4B OF ANNEX) .................................... 4-61

ERT-2, LEFT BANK OF WEIR AXIS FIGURE 5 A AND 5B OF ANNEX ......................................... 4-61

ERT-3, ALONG WEIR AXIS FIGURE: 6 A AND 6B OF ANNEX ................................................... 4-62

ERT-4, DESANDER ALONG RIVER FIGURE 7 A AND 7B .......................................................... 4-62

ERT-5, ACROSS DESANDER/RIVER (FAR FROM RIVER) FIGURE 8 A AND 8B .......................... 4-62

ERT-6 ALONG HRT ALIGNMENT FIGURE 9A AND 9B ............................................................. 4-62

ERT- 9, 10, 11, 12, POWER HOUSE FIGURES 9A, 9B, 10A, 10B, 11A, 11B, 12A, AND 12B ....... 4-62

4.12. MUCK DISPOSAL AREA ........................................................................................................ 4-63

4.13. CONCLUSIONS AND RECOMMENDATIONS .......................................................................... 4-63

4.13.1. CONCLUSIONS ..................................................................................................................... 4-63

4.13.2. RECOMMENDATIONS .......................................................................................................... 4-64

5. ALTERNATIVE LAYOUTS AND RECOMMENDED PROJECT LAYOUT .......................................... 5-1

5.1. STUDY OF POSSIBLE ALTERNATIVE LAYOUTS FOR THE PROJECT ............................................ 5-1

5.2. PRESENTATION OF RECOMMENDED LAYOUT ........................................................................ 5-2

6. PROJECT OPTIMIZATION ........................................................................................................ 6-1

6.1. INTRODUCTION ..................................................................................................................... 6-1

6.2. OBJECTIVES AND GENERAL APPROACH ................................................................................. 6-1

6.3. HYDROLOGY .......................................................................................................................... 6-3

6.4. CONCEPTUAL LAYOUT AND COST COMPARISON ................................................................... 6-4

6.5. RANGE OF OPTIONS AND ENERGY PRODUCTION................................................................... 6-5

6.6. RESULT OF FINANCIAL ANALYSIS ........................................................................................... 6-6

6.7. CONCLUSIONS ....................................................................................................................... 6-7

7. PROJECT DESCRIPTION AND DESIGN ..................................................................................... 7-1

7.1. INTRODUCTION ..................................................................................................................... 7-1

7.2. HEADWORKS ......................................................................................................................... 7-1

7.2.1. GENERAL ............................................................................................................................... 7-1


xiii

7.2.2. FUNCTION OF HEADWORKS .................................................................................................. 7-2

7.2.3. DIVERSION WEIR ................................................................................................................... 7-3

7.2.4. INTAKE .................................................................................................................................. 7-4

7.2.5. UNDERSLUICE ........................................................................................................................ 7-4

7.2.6. STILLING BASIN ...................................................................................................................... 7-5

7.2.7. COARSE TRASHRACK, GRAVEL TRAP AND SPILLWAY ............................................................. 7-5

7.2.8. APPROACH CANAL ................................................................................................................. 7-5

7.2.9. SETTLING BASIN AND SEDIMENT FLUSHING CHANNEL .......................................................... 7-6

7.3. HEADRACE TUNNEL ............................................................................................................... 7-7

7.3.1. GENERAL ............................................................................................................................... 7-7

7.3.2. DESIGN CRITERIA ................................................................................................................... 7-7

7.3.3. HEADPOND ............................................................................................................................ 7-7

7.3.4. HEADRACE TUNNEL ............................................................................................................... 7-7

7.3.5. ANCHOR BLOCK AND SUPPORT PIERS ................................................................................... 7-7

7.3.6. EXPANSION JOINTS................................................................................................................ 7-8

7.4. SURGE SHAFT ........................................................................................................................ 7-8

7.5. PENSTOCK ............................................................................................................................. 7-9

7.5.1. GENERAL ............................................................................................................................... 7-9

7.5.2. DESIGN CONDITIONS ........................................................................................................... 7-10

7.5.3. DESIGN STRESSES ................................................................................................................ 7-11

7.5.3.1 STEEL PLATES AND STRUCTURAL STEELS .............................................................................. 7-11

7.5.3.2 ALLOWABLE STRESSES ......................................................................................................... 7-12

7.5.3.3 ASSUMPTIONS ..................................................................................................................... 7-13

7.5.4. EXPANSION JOINTS.............................................................................................................. 7-13

7.5.5. ANCHOR BLOCKS AND SUPPORT PIERS ................................................................................ 7-14

7.6. POWERHOUSE ..................................................................................................................... 7-14

7.6.1. GENERAL ............................................................................................................................. 7-14

7.6.2. POWERHOUSE MAIN FLOOR................................................................................................ 7-14

7.6.3. CONTROL ROOM AND OTHER UTILITY SPACES .................................................................... 7-14

7.6.4. SWITCHYARD AREA ............................................................................................................. 7-15

7.7. TAILRACE CANAL ................................................................................................................. 7-15

7.8. HYDRO-MECHANICAL EQUIPMENT ...................................................................................... 7-15

7.8.1. STOPLOGS ........................................................................................................................... 7-15

7.8.2. INTAKE GATES ..................................................................................................................... 7-16

7.8.3. TRASHRACKS ....................................................................................................................... 7-16


xiv

7.8.3.1 COARSE TRASHRACK ........................................................................................................... 7-16

7.8.3.2 FINE TRASHRACK ................................................................................................................. 7-17

7.8.4. UNDERSLUICE GATE ............................................................................................................. 7-17

7.8.5. SETTLING BASIN INLET GATE................................................................................................ 7-18

7.8.6. SETTLING BASIN FLUSHING .................................................................................................. 7-19

7.8.7. PENSTOCK VALVE ................................................................................................................ 7-19

7.9. ELECTRO-MECHANICAL EQUIPMENT ................................................................................... 7-19

7.9.1. GENERAL ............................................................................................................................. 7-19

7.9.2. POWERHOUSE MECHANICAL EQUIPMENT .......................................................................... 7-20

7.9.3. TURBINE .............................................................................................................................. 7-21

7.9.3.1 TURBINE SPEED ................................................................................................................... 7-23

7.9.3.2 RUNNER .............................................................................................................................. 7-23

7.9.3.3 SHAFT .................................................................................................................................. 7-24

7.9.3.4 GUIDE BEARING ................................................................................................................... 7-24

7.9.3.5 SPIRAL CASE AND STAY RING ............................................................................................... 7-24

7.9.3.6 WICKET GATES ..................................................................................................................... 7-24

7.9.3.7 DRAFT TUBE ........................................................................................................................ 7-25

7.9.4. GOVERNOR .......................................................................................................................... 7-25

7.9.5. INLET VALVE ........................................................................................................................ 7-27

7.9.6. COOLING WATER AND WATER SUPPLY SYSTEM .................................................................. 7-28

7.9.7. DRAINAGE AND DEWATERING SYSTEM ............................................................................... 7-28

7.9.8. PRESSURE OIL SYSTEM ........................................................................................................ 7-29

7.9.9. VENTILATION AND AIR CONDITIONING SYSTEM .................................................................. 7-29

7.9.10. FIRE PROTECTION SYSTEM ................................................................................................... 7-30

7.9.11. MECHANICAL WORKSHOP AND EQUIPMENT....................................................................... 7-30

7.9.12. POWERHOUSE OVERHEAD TRAVELLING CRANE .................................................................. 7-31

7.9.13. POWERHOUSE ELECTRICAL EQUIPMENT.............................................................................. 7-31

7.9.13.1 GENERATOR ........................................................................................................................ 7-32

7.9.13.2 EXCITATION SYSTEM AND AUTOMATIC VOLTAGE REGULATOR ........................................... 7-35

7.9.13.3 POWER TRANSFORMER ....................................................................................................... 7-36

7.9.13.4 STATION SUPPLY TRANSFORMER ........................................................................................ 7-37

7.9.13.5 11 KV PROTECTION AND MEASURING EQUIPMENT ............................................................. 7-38

7.9.13.6 AIR CIRCUIT BREAKER .......................................................................................................... 7-39

7.9.13.7 DIESEL GENERATOR ............................................................................................................. 7-40

7.9.13.8 MOTOR CONTROL CENTRE .................................................................................................. 7-40


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7.9.13.9 DC POWER SUPPLY .............................................................................................................. 7-40

7.9.13.10 GROUNDING/EARTHING SYSTEM .................................................................................. 7-41

7.9.13.11 BLACK START/ISLAND MODE OPERATION ..................................................................... 7-41

7.9.13.12 COMMUNICATION SYSTEM ........................................................................................... 7-42

7.9.13.13 CONTROL AND SCADA SYSTEM ...................................................................................... 7-42

7.9.14. INTERCONNECTION POINT AND SWITCHYARD .................................................................... 7-43

7.9.14.1 HIGH VOLTAGE SWITCHYARD .............................................................................................. 7-43

7.9.14.2 132 KV MEASURING AND PROTECTING EQUIPMENTS ......................................................... 7-44

7.9.14.3 POWER EVACUATION .......................................................................................................... 7-45

7.9.15. CONSTRUCTION POWER ...................................................................................................... 7-45

7.9.16. ELECTRO-MECHANICAL WORKS COST .................................................................................. 7-45

8. POWER AND ENERGY ............................................................................................................ 8-1

8.1. INTRODUCTION ..................................................................................................................... 8-1

8.2. INTEGRATED NEPAL POWER SYSTEM .................................................................................... 8-1

8.2.1. LOAD FORECAST .................................................................................................................... 8-2

8.2.2. COMMITTED GENERATION FOR INPS..................................................................................... 8-3

8.3. ENERGY DEFINITIONS ............................................................................................................ 8-3

8.4. POWER AND ENERGY GENERATION ....................................................................................... 8-4

8.5. POWER AND ENERGY BENEFITS ............................................................................................. 8-6

8.6. POWER EVACUATION ............................................................................................................ 8-6

8.7. CONCLUSIONS AND RECOMMENDATIONS ............................................................................ 8-7

9. CONSTRUCTION PLANNING AND SCHEDULING ...................................................................... 9-1

9.1. GENERAL ............................................................................................................................... 9-1

9.2. PREPARATORY WORKS .......................................................................................................... 9-2

9.2.1. ACCESS AND PROJECT ROAD ................................................................................................. 9-2

9.2.2. CONSTRUCTION POWER ........................................................................................................ 9-2

9.2.3. CONSTRUCTION CAMPS ........................................................................................................ 9-3

9.2.4. WATER SUPPLY SYSTEM ........................................................................................................ 9-3

9.3. CONSTRUCTION SCHEDULING OF INDIVIDUAL STRUCTURES ................................................. 9-4

9.3.1. RIVER DIVERSION AND CONSTRUCTION OF WEIR AND INTAKE STRUCTURES ........................ 9-4

9.3.2. DESANDING BASIN AND TUNNEL INLET PORTAL .................................................................... 9-5

9.3.3. HEADRACE TUNNEL ............................................................................................................... 9-5

9.3.4. SURGE TANK .......................................................................................................................... 9-5

9.3.5. PENSTOCK INSTALLATION ...................................................................................................... 9-6

9.3.6. POWERHOUSE& TAILRACE .................................................................................................... 9-6


xvi

9.3.7. TURBINE AND GENERATOR INSTALLATION ............................................................................ 9-6

9.3.8. TRANSMISSION LINE AND SUB-STATION ............................................................................... 9-6

9.4. MATERIALS HANDLING .......................................................................................................... 9-7

9.4.1. HANDLING OF CONSTRUCTION MATERIALS ........................................................................... 9-7

9.4.2. LOCAL CONSTRUCTION MATERIALS ....................................................................................... 9-7

9.4.2.1 SAND ..................................................................................................................................... 9-7

9.4.2.2 GRAVEL ................................................................................................................................. 9-7

9.4.2.3 RUBBLE STONE ...................................................................................................................... 9-7

9.4.3. OTHER CONSTRUCTION MATERIALS ...................................................................................... 9-8

9.4.3.1 CEMENT ................................................................................................................................. 9-8

9.4.3.2 REINFORCEMENT STEEL ......................................................................................................... 9-8

9.4.3.3 EXPLOSIVES ........................................................................................................................... 9-8

9.4.4. SPOIL MATERIALS HANDLING ................................................................................................ 9-8

9.5. CONTRACT PACKAGES ........................................................................................................... 9-8

9.5.1. LOT 1 - INFRASTRUCTURE WORKS ......................................................................................... 9-8

9.5.2. LOT 2 - CIVIL WORKS .............................................................................................................. 9-8

9.5.3. LOT 3 - HYDRO-MECHANICAL WORKS .................................................................................... 9-9

9.5.4. LOT 4 - ELECTRO-MECHANICAL WORKS ................................................................................. 9-9

9.5.5. LOT 5 - TRANSMISSION LINE .................................................................................................. 9-9

9.6. OVERALL DURATION OF PROJECT CONSTRUCTION ................................................................ 9-9

10. PROJECT COST AND REVENUE ............................................................................................. 10-1

10.1. PROJECT COST ..................................................................................................................... 10-1

10.2. ASSUMED CONDITIONS & SEQUENTIAL EXECUTION. ........................................................... 10-1

10.3. TOTAL PROJECT COST .......................................................................................................... 10-2

10.3.1. PRELIMINARY EXPENSES ...................................................................................................... 10-3

10.3.2. LAND PROCUREMENT .......................................................................................................... 10-4

10.3.3. INFRASTRUCTURES DEVELOPMENT ..................................................................................... 10-4

10.3.4. SITE OFFICE & CAMPING FACILITIES CONSTRUCTION ........................................................... 10-4

10.3.5. CONSTRUCTION DESIGN & BOQ PREPARATION ................................................................... 10-4

10.3.6. CIVIL CONSTRUCTION WORKS ............................................................................................. 10-4

10.3.7. METAL WORKS .................................................................................................................... 10-4

10.3.8. ELECTRO-MECHANICAL PLANTS & MACHINERY ................................................................... 10-4

10.3.9. TRANSMISSION LINE & SWITCHYARD .................................................................................. 10-5

10.3.10. PROJECT MANAGEMENT & SUPERVISION ........................................................................... 10-5

10.3.11. OFFICE EQUIPMENT & VEHICLE ........................................................................................... 10-5


xvii

10.3.12. MISCELLANEOUS ................................................................................................................. 10-5

10.3.13. INTEREST DURING CONSTRUCTION ..................................................................................... 10-5

10.4. ENERGY GENERATION ......................................................................................................... 10-5

10.4.1. REVENUE POTENTIAL ........................................................................................................... 10-6

10.4.2. YEARLY REVENUE ................................................................................................................ 10-7

11. PROJECT FINANCING & PROJECTIONS.................................................................................. 11-1

11.1. INVESTMENT STRUCTURE .................................................................................................... 11-1

11.2. PROJECTED FINANCIAL STATEMENTS .................................................................................. 11-1

11.2.1. SALES ................................................................................................................................... 11-1

11.2.2. GOVERNMENT SUBSIDY ...................................................................................................... 11-1

11.2.3. OPERATION AND MAINTENANCE COST ............................................................................... 11-2

11.2.4. ROYALTY .............................................................................................................................. 11-2

11.2.5. EMPLOYEES’ BONUS ............................................................................................................ 11-2

11.2.6. DEPRECIATION .................................................................................................................... 11-2

11.2.7. AMORTIZATION ................................................................................................................... 11-2

11.2.8. TAX ...................................................................................................................................... 11-2

11.2.9. E&M REPLACEMENT ............................................................................................................ 11-2

11.2.10. BANK LOANS AND INTEREST REPAYMENT ........................................................................... 11-3

11.2.11. AGENCY FEE ......................................................................................................................... 11-3

12. PROJECT EVALUATION ......................................................................................................... 12-1

12.1. PARAMETERS AND ASSUMPTIONS ...................................................................................... 12-1

12.2. FINANCIAL ANALYSIS ........................................................................................................... 12-2

12.2.1. ANNUITY ............................................................................................................................. 12-3

12.2.2. TIME VALUE OF MONEY ...................................................................................................... 12-4

12.3. PLANT FACTOR .................................................................................................................... 12-8

12.4. UNIT ENERGY COST ............................................................................................................. 12-9

12.5. DEBT SERVICE COVERAGE RATIO ......................................................................................... 12-9

12.6. SENSITIVITY ANALYSIS ........................................................................................................ 12-10

13. CONCLUSIONS AND RECOMMENDATIONS .......................................................................... 13-1

13.1. CONCLUSIONS ..................................................................................................................... 13-1

13.2. RECOMMENDATIONS .......................................................................................................... 13-1

REFERENCES ........................................................................................................................................... B

ANNEX I – PHOTOGRAPHS ...................................................................................................................... I


xviii

List of Tables

Table 2-1: Corrected coordinates of Traverse points of National Control Points (for reference) . 2-

3

Table 2-2: Corrected coordinates of Bench marks established for the Topograhic survey at

Irkhuwa Khola Site .......................................................................................................... 2-3

Table 3-1: Characteristics of Irkhuwa Khola catchment at the various sites .............................. 3-2

Table 3-2:: Representative discharge measurements at Upper Irkhuwa Intake site .................. 3-3

Table 3-3: Mean monthly flow (m3/s) at headworks site by WECS/DHM & modified HYDEST

methods .......................................................................................................................... 3-4

Table 3-4: Mean monthly flow (m3/s) at headworks site by MHSP method ............................. 3-4

Table 3-5: Mean monthly flow (m3/s) at headworks site by CAR method ................................ 3-5

Table 3-6: Mean monthly flow (m3/s) at headworks site by various methods .......................... 3-6

Table 3-7: Adopted long-term mean monthly flows (m3/s) at Upper Irkhuwa headworks site . 3-7

Table 3-8: Adopted percentile dependable flows at headworks site (m3/s) ............................. 3-8

Table 3-9: Estimated instantaneous high floods by WECS/DHM method ............................... 3-10

Table 3-10(a): Estimated instantaneous high floods by frequency analysis of Sabhaya river at

Phedi intake site ............................................................................................................ 3-14

Table 3-10(b): Estimated instantaneous high floods by frequency analysis of Sabhaya river at

Thumlung intake site .................................................................................................... 3-14

Table 3-11: Estimated instantaneous high floods by frequency analysis of Sabhaya river at

powerhouse site ........................................................................................................... 3-14

Table 3-12: Estimated floods for dry season............................................................................ 3-15

Table 3-13: Low flow frequency analysis at Upper Irkhuwaheadworks site ........................... 3-16

Table 4-1: Geomorphic Units of Nepal ..................................................................................... 4-10

Table 4-2: Lithostratigraphy of lesser Himalaya, Eastern Nepal (after Hashimoto et al. 1973) .. 4-

12

Table 4-3: Rock Mass Classification ......................................................................................... 4-20

Table 4-4: Attitudes of Rock Mass (Dip Direction / Dip Amount) ............................................ 4-21

Table 4-5: Rock Mass Rating (RMR) of the Project Area .......................................................... 4-22

Table 4-6: Geochemcial Parameters of Rock Mass of the Project Area .................................. 4-24

Table 4-7: Stability Condition of the Project Area ................................................................... 4-25

Table 4-8: NGI Tunnelling Index ‘Q’ values of the Tunnel Alignment Area ............................. 4-29

Table 4-9: Designed Tunnel Rock Support Class and Respective Rock Support ...................... 4-31

Table 4-10: Assigned Rock Support in respect with rockmass and Rock Support Class .......... 4-32

Table 4-11: Summary of the Support system of the Tunnel Alignment .................................. 4-33

Table 4-12: Larger Magnitude of Earthquake occurred in Nepal Himalaya............................. 4-47

Table 4-13: Instrumentally Recorded Earthquake ................................................................... 4-48

Table 4-14: Design Earthquake Acceleration Coefficients ....................................................... 4-52

Table 4-15: Recommended Seismic Coefficient for Various Projects ...................................... 4-53

Table 4-16: Volume and Location of the Construction Materials ............................................ 4-55

Table 4-17: Laboratory test details for Fine aggregates .......................................................... 4-56

Table 4-18: Summary of the Results for Material Tests ........................................................... 4-59

Table 4-19: Proposed Core drilling locations and respective depths ...................................... 4-60


xix

Table 4-20: Conducted ERT Locations and details (Geophysical Investigations) ..................... 4-60

Table 6-1: Average Monthly flows ............................................................................................... 6-3

Table 6-2:Flow exceedence discharge .......................................................................................... 6-3

Table 6-3:Summary for different option ...................................................................................... 6-5

Table 6-4:Summary for Economic analysis of different option .................................................... 6-6

Table 7-1: Thickness of penstock pipe for different head ......................................................... 7-10

Table 7-2: Parameters of Francis Turbine .................................................................................. 7-23

Table 7-3: Details of powerhouse crane .................................................................................... 7-31

Table 7-4: Details of Generator.................................................................................................. 7-32

Table 7-5: Details of Power Transformer ................................................................................... 7-36

Table 7-6: Details of Station Auxiliary Transformer ................................................................... 7-37

Table 7-7: Details of VCB ........................................................................................................... 7-38

Table 7-8: Details of 11kV Potential Transformer ..................................................................... 7-39

Table 7-9: Details of 11kV Lightning Arrestor ........................................................................... 7-39

Table 7-10: Details of Air Circuit Breaker .................................................................................. 7-39

Table 7-11: Details of 132kV SF6 Breaker .................................................................................. 7-44

Table 7-12: Details of CT on 132kV side ..................................................................................... 7-44

Table 7-13: Details of PT on 132kV side .................................................................................... 7-45

Table 7-14: Power Requirement for Construction Purpose ...................................................... 7-45

Table 8-1: National power scenario from different options ........................................................ 8-1

Table 8-2: Load and energy forecast............................................................................................ 8-2

Table 8-3: Input parameters and assumptions ............................................................................ 8-4

Table 8-4: Monthly power and energy generation ...................................................................... 8-4

Table 8-5: Energy rate for the projects bigger than 25 MW ........................................................ 8-6

Table 10-1: Detail Breakdown of the Project Cost ..................................................................... 10-2

Table 10-14: Energy Generation ................................................................................................ 10-6

Table 10-15: Revenue Generation ............................................................................................. 10-6

Table 11-1: Investment structure ............................................................................................. 11-1

Table 11-2: Bank loan repayment plan ...................................................................................... 11-3

Table 12-1: Parameters and Assumptions ................................................................................ 12-1

Table 12-2: Benefit cost ratio at different discount rates......................................................... 12-7

Table 12-3: Results for Sensitivity Analysis .............................................................................. 12-10


xx

List of Figures

Figure 1-1: Map of Nepal showing the Irkhuwa Khola B Hydropower Project site ..................... 1-5

Figure 1-2: Location of the Project area in Bhojpur district Map ................................................ 1-6

Figure 3-1: Catchment areas at proposed intake and tailrace sites ............................................ 3-2

Figure 3-2: Flow duration curve of Upper Irkhuwa Khola at proposed headworks site .............. 3-8

Figure 4-1: Location Map of Project area .................................................................................... 4-1

Figure 4-2: Physiographic Subdivision of the Himalayan Arc (After Gansser, 1964) ................... 4-5

Figure 4-3: Geological Map of the Nepal Himalaya (After Upreti and Le Fort, 1999) ................. 4-7

Figure 4-4: Physiographic Map of Nepal .................................................................................... 4-11

Figure 4-5: Regional Geological Map of Irkhuwa Khola Area (Hashimoto et at., 1973) ............ 4-13

Figure 4-6: Regional Geological Map of Irkhuwa Khola Area (Box with dark line represents the

Project area, ICN – Irkhuwa Crystalling Nappe) ............................................................ 4-14

Figure 4-7: Structural Map of the Project Area ......................................................................... 4-16

Figure 4-8: Stereographic Projection of the Rock Mass at Right Bank of Weir Axis Area ......... 4-23

Figure 4-9: Stereographic Projection of the rockmass of the Approach Canal Alignment Area 4-26

Figure 4-10: Stereographic Project of the Inlet Portal Area ...................................................... 4-28

Figure 4-11: Stereographic Projection of the Rockmass of the waterways alignment (ch 0+620 to

0+980) ........................................................................................................................... 4-34


1+200) ........................................................................................................................... 4-35


1+600) ........................................................................................................................... 4-36


2+930) ........................................................................................................................... 4-37


3+300) ........................................................................................................................... 4-38


3+800) ........................................................................................................................... 4-39

Figure 4-17: Stereographic Projection of the Rockmass of the Surge Tank and Penstock Alignment

...................................................................................................................................... 4-41

Figure 4-18: Stereographic Projection of the Rockmass of the Powrhouse Area ..................... 4-42

Figure 4-19: Epicenter of the Earthquke in Nepal Himalaya ..................................................... 4-46

Figure 4-20: Probabilistic Seismic Hazard Assessment Map of the Nepal Himalaya ................. 4-46

Figure 4-21: Seismic Zonation Map of the Nepal Himalaya ....................................................... 4-47

Figure 4-22: Seismic Risk Map of India ...................................................................................... 4-51

Figure 6-1:Variation of NPV with different discharge .................................................................. 6-5

Figure 6-2:Return on equity with different discharges ................................................................ 6-6

Figure 6-3:Specific Energy cost for different installed Capacity ................................................... 6-7

Figure 7-1: Turbine Selection Chart ..................................................................................... 7-22

Figure 8-1: Load forecast for next 15 years ................................................................................. 8-3

Figure 8-2: Mean monthly energy generation ............................................................................. 8-5

Figure 9-1: Implementation schedule of Irkhuwa Khola Hydropower Project .......................... 9-10

Figure 10-1: Classification of Total Cost ..................................................................................... 10-3


xxi

List of Photos

Photo P-1: Headworks Site for Upper Irkhuwa Khola Hydropower Project .................................... I

Photo P-2:Powerhouse location for Upper Irkhuwa Khola Hydropower Project ............................ I

Photo P-3: Survey work in the headworks area before disturbance by local community ............. II

Photo P-4: Discharge Measurement at Irkhuwa Khola ................................................................... II

Photo P-5: Gauge Station fixed at Irkhuwa Khola .......................................................................... III

Photo P-6: Map study by the experts during site visit ................................................................... III

Photo P-7: Discussion with the community in Headworks area .......Error! Bookmark not defined.

Photo P-8:Mass meeting with all landowner of the alignment which made agreement for mutual

cooperation ..........................................................................Error! Bookmark not defined.


1-1

1. BACKGROUND AND INTRODUCTION

1.1. Background

Nepal has more than six thousand small and big rivers running down from the Himalayas and

high mountains covered with snow towards the plain of Terai. The gross hydropower potential

of these rivers is estimated to be about 83’000 MW. Out of which 42’000 MW is considered to

be technically and economically feasible for the hydropower generation. The present peak

power demand in the country is more than 1350 MW and it is increasing by around ten percent

per annum whereas the total installed capacity in the Integrated Nepal Power System (INPS) of

the country is about 850 MW, including solar and thermal power (Nepal Electricity Authority

(NEA): A Year in Review; August 2016).

Due to the typical hydrological nature of Nepalese rivers having considerably low discharge

during four months in winter season, present power supply is in acute scarcity leading to severe

load-shedding hours during the dry months till last year. Even with the thermal plants generating

the deficit portion of power and big portion being imported from India, load-shedding during the

four winter months is hardly managed from this year and this situation will continue for some

years to come, till sufficient hydropower is generated in the country to meet the growing

demand.

To attract private investors towards the development of Small hydropower projects,

Government of Nepal has adopted a liberal policy since 1990. The Nepal Electricity Authority

(NEA) has also announced its policy to purchase power generated by the independent power

producers (IPPs) up to 25 MW capacity and two distinct prices for electricity is fixed for both dry

and wet seasons - NRs. 4.80 for the wet season and NRs. 8.40 for the dry season. In addition, an

IPP can profit of a yearly escalation in this price by 5% up to five years starting its first commercial

generation. The power purchase agreement (PPA) shall be valid for 30 years. Banks and financial

institutions have also shown their interest to invest in hydropower projects as priority sector

investment. This scenario has encouraged the private investors to promote hydropower projects

in Nepal.

1.2. The Project

The site for proposed Upper Irkhuwa Khola Hydropower Project (hereinafter called ‘the Project’)

was first identified by a group of experts on behalf of Aarati Power Company Ltd. Then, a team

of professionals comprising of a hydropower engineer, an engineering geologist, a hydrologist,

and an environmental expert was deployed to the Project site to carry out necessary field

investigations needed for present desk study.


1-2

Upper Irkhuwa Khola Hydropower Project lies in Bhojpur District of eastern development region

of Nepal and uses the water from Irkhuwa Khola, a tributary of Arun river, which, ultimately

merges with Koshi River, the biggest river of Nepal (Figure 1-1 and Figure 1-2). Irkhuwa Khola,

within the Project area, flows towards eastern direction.

1.3. Location

The Project area is approximately 12 kilometres south east from Dingla, one of the major

historical town of Bhojpur. Irkhuwa Khola, within the Project area, lies entirely within Dobhane,

Khatama and Kuda kaule Village Development Committees (VDCs). The headworks site has been

proposed very close to the confluence between Phedi Khola and Thumlung Khola whereas the

proposed powerhouse site is located about 200 m upstream from the confluence of Irkhuwa

Khola and Benkhuwa Khola which lies in Kuda Kaule VDC.

Geographically, the licensed co-ordinates of the Project area spreads between 87o01’33” to

87o03’51” longitudes and 27o22’58” to 27o24’17” latitudes. The proposed intake site at Irkhuwa

Khola is located at 87o01’38” longitude and 27o23’12” latitude for Phedi Intake and 87o01’40”

longitude and 27o23’06” for Thumlung Intake. Around 3.72 km long water conveyance has been

proposed from intake up to the powerhouse site. The proposed powerhouse site is located at

87o03’41” longitude and 27o23’55” latitude (Figure 1-1).

1.4. Accessibility

The proposed project site can be accessed by three different alternatives.

Route 1: Tumlingtar-Satighat-Chirkhuwa-Nepaledanda-Tamutar- Phedi -Headworks site

Route 2: Tumlingtar-Satighat-Chirkhuwa-Gahate-Majuwa beshi – Tintama-Gothe bazaar – Phedi

– Headworks site

Route 3: Bhojpur-Dingla-Chirkhuwa-Route1/Route 2

Route 4: Khadbari-Heluwa beshi-Majuwa beshi-Route 2

Tumlingtar in sankhuwasabha district has all weather motorable roads as well as airport with

black topped pitch. For the Route 1, there is bridge underconstruction in Satighat for Arun River.

It needs to cross Chirkhuwa to access project all round the year. The track opening for the Route

1 is ongoing and about 4 km is being built to reach headworks site. Similar is the case for Route

2, there is necessity of track opening about 200m in the right bank of Irkhuwa Khola near the

confluence with Sisne Khola. For Route 4, there is public taxi servie up to Heluwa beshi and there

is bridge proposed in Arun River. For Route 3, there is public service up to Dingla bazaar and


1-3

tractor is running from Dingla to Chirkhuwa. From Chirkhuwa it can be extended towards the

project site either by Route 1 or Route 2. These alternate routes are shown in Annex I.

1.5. Transmission Line

There is proposed substation at Sitapati in Sankhuwasabha district, which is about 8 km distance

from the proposed powerhouse. The generated power can be evacuated on the proposed

substation with 33 kV double circuit line. Alternately, the power can be evacuated to Tumlingtar

substation with 13 km long transmission line from the proposed powerhouse. For the

construction power supply, it is purposed to construct 11 kV transmission line from existing

national grid from Khadbari or Tumlingtar.

1.6. Objectives of the Study

The main objective of this study is to carry out the Feasibility Study of Upper Irkhuwa Khola

Hydropower Project to determine whether the Project is feasible or not, both technically and

financially. The Feasibility Study Report of the Project, hereinafter termed as “the Report”, will

serve the Company as basic documentation for obtaining the license for the construction of the

Project from the Department of Electricity Development (DoED), and as a close guideline

regarding financial resources necessary for the development of the Project.

The Feasibility Study of Upper Irkhuwa Khola Hydropower Project has been carried out using all

data and information collected from field survey and investigations. The Consultant conducted

the Feasibility Study of the Project pertaining to the requirements as per national standards and

standard engineering norms. Main objectives and scopes of work include, but not limited to, the

followings:

Review of available literatures and other information regarding hydropower

projects including current legislation

Collection of necessary information and data regarding the Project through field

survey and investigations

Carry out topographical survey and preparation of necessary topographical maps

of the project area

Carry out hydrological study of Irkhuwa Khola at the project site

Conducting geological investigations of the project area and preparation of

geological maps

Determination of optimum installed capacity and finalizing the project layout

Preparation of conceptual design and drawings


1-4

Cost estimate of the project

Preparation of construction plan and project implementation schedule

Conducting economic and financial evaluation

Preparation of Feasibility Study Report adhering to the national standards.

1.7. Organization of the Report

This Feasibility Study Report describes the findings, results and conclusions of the

feasibility study of Upper Irkhuwa Khola Hydropower Project. The report is presented in

three different volumes namely:

Volume I : Main Report

Volume II : Drawings

Volume III : Appendices

‘Volume I: Main Report’ (the present report) presents in a systematic order all the

findings, analyses, conclusions made during the feasibility study. ‘Volume III : Drawings’

contains the design drawings and maps of the Project and the investigation data,

calculations and other arithmetic are presented in ‘Volume III : Appendices’.


1. Progress Report 1-5

Figure 1-1: Map of Nepal showing the Irkhuwa Khola B Hydropower Project site

Project Area


Feasibility Study Report 1-6

Figure 1-2: Location of the Project area in Bhojpur district Map


1-1

2. TOPOGRAPHICAL SURVEY

2.1. Introduction

The survey works for the feasibility study of the proposed project were conducted from April to

May 2016. Survey and leveling works are necessary to design the components, to prepare

drawings and to calculate the quantities of the project structures. The collected data pertinent

to surveying and topographical mapping are included in this chapter. The scope of works,

methodology adopted, equipment used and manpower deployed for conduct of survey are also

described in the subsequent sections.

2.2. Collection of Available information and Data

The following information/data available for carrying out the feasibility study of the Upper Irkhuwa Khola Hydropower Project were collected.

i. Topographical maps from the Department of Survey.

Scale 1:25,000

Sheet No. 2787 09A

Contour interval 20m

ii. Feasibility Study report of Irkhuwa Khola B Small Hydropower Project by DK Consult (P.) Ltd.

iii. Desk Study Report of Upper Irkhuwa Khola Small Hydropower Project prepared by DK Consult (P.) Ltd.

iv. District Map of Bhojpur district.

2.3. Scope of Works

The survey work was carried out with the objective of preparing topographic maps of entire

project area in appropriate scale and to select the proper location of project components like

Headworks (diversion, intake, and desander), water conveyance, forebay tank, Powerhouse and

Tailrace. The following survey works have been included in the scope of the works:

Establishing traverse enclosing the project area

Establishing control points and permanent benchmarks for construction purposes


1-2

Measuring longitudinal and cross sections of river

Preparation of topographical map

Selection of appropriate alignment and position of project components in prepared

topographical map

Preparation of survey report of the project

2.4. Desk Study

Prior to the field survey, desk study was carried out by using topographical map (scale 1:25,000)

published by Government of Nepal, Survey Department. With the team of hydro experts detail

information about the project area for the survey work was received and noted. Approximate

location, sketches of plan in the topographical map were prepared.

2.5. Project Site Visit

A team consists of Hydropower engineer, Civil engineer, Geologist and a Senior Surveyor with

representative of developer were mobilized for field visit. After finalizing the project site and

before the detail survey work, a brief reconnaissance survey was carried out around the entire

project area to be mapped. A group of multi-disciplinary experts had conducted reconnaissance

site visit from March 2016.

2.6. Survey Methodology

As per the scope of works, the methodology for survey was developed which comprises the desk

study, reconnaissance survey, detail topographical survey and mapping of the project located in

Dobhane, Khatama and Kudakaule VDCs.

2.7. Topography of the Site

The project site is located in hilly range. Most of the project areas are in forest and bushy area

with some in cultivated land. No dense jungle is found within entire project area.

2.8. Survey Methodology of the Project Works

The principle of surveying ‘Working from whole to part’ was introduced for the survey of the

project. A closed loop was carried out first covering the project boundary establishing the

different traversing points in different position. The loop was computed and corrected by

Bowditch’s rule and the position of spot detailing was taken by means of traverse points as well

as offsets points set from them. Also the detail data was recorded in the ‘Topcon Total Station’


1-3

and physical features like river line, cliff, water level, road, foot trail, bridges etc. were clearly

mentioned in the remarks.

2.8.1. Detail Survey

In the detail survey, the data necessary to prepare maps were taken of the entire project area.

The following ground information were collected,

Rivers and drainages

Temporary suspension bridges

Houses temples and monasteries

Road and tracks

Agricultural field boundaries

Forestry boundaries

River water level at different points

Rock exposed areas

Landslides in different areas

2.8.2. Control Traversing

A closed traverse was carried out at the headwork site and powerhouse site and was finally

connected to National Grid System. Additional offset points were also established conventionally

to cover entire area.

The traverse legs were made as long as possible and a fixed tripod system was used for all

reflecting prisms to achieve better accuracy. The list of traverse points and their corrected co-

ordinates are presented in Error! Reference source not found. and Error! Reference source not

found.as follows:

Table 2-1: Corrected coordinates of Traverse points of National Control Points (for reference)

PT # Northing Easting Elevation Remarks

1305 3030175.349

503633.761 858.74 Boulder BM

1307 3030159.480

503625.121 858.798 Boulder BM

Table 2-2: Corrected coordinates of Bench marks established for the Topograhic survey at Irkhuwa Khola Site

Pcode Point # Easting(m) Northing(m) Elevation (m) Remarks

TP21,TP22 1 505456.673 3030977.429 734.813 Boulder

TPA 2 505344.000 3030919.273 737.257 Boulder

TP22,TPB 3 505239.102 3030894.481 748.380 Boulder

TPB 4 505239.094 3030894.474 748.357 Boulder


1-4

TPC 5 505017.536 3030740.199 761.707 Boulder

TPD 6 504797.147 3030467.392 793.587 Boulder

TPE 7 504655.856 3030296.762 800.582 Boulder

TPF 8 504518.622 3030272.341 806.593 Boulder

TPG 9 504410.893 3030250.506 817.968 Boulder

TP1 10 504397.128 3030248.978 822.431 Boulder

TP2 11 504350.861 3030259.097 822.257 Boulder

TP3 12 504331.630 3030265.624 822.664 Boulder

TP4 13 504275.427 3030264.403 826.173 Boulder

TP5 14 504192.623 3030267.366 832.058 Boulder

TP6 15 504161.215 3030251.480 842.420 Boulder

TP7 16 504072.179 3030273.250 834.076 Boulder

TP8 17 503997.062 3030275.600 840.122 Boulder

TP9 18 503961.149 3030272.803 843.132 Boulder

TP10 19 503876.847 3030216.299 857.618 Boulder

TP11 20 503848.558 3030207.595 863.571 Boulder

TP12 21 503788.366 3030154.773 874.457 Boulder

TP13 22 503765.659 3030177.651 871.135 Boulder

TP14 23 503673.854 3030170.689 864.662 Boulder

TP15 24 503617.371 3030145.024 860.346 Boulder

TP16 25 503596.087 3030101.146 866.410 Boulder

TP17 26 503530.109 3030041.077 872.268 Boulder

TP18 27 503482.455 3030034.317 869.570 Boulder

TP19,TP29 28 503406.950 3029941.371 875.553 Boulder

TP20 29 503315.370 3029899.025 878.957 Boulder

TP21 30 503282.552 3029891.683 884.717 Boulder

TP22 31 503249.053 3029854.254 890.019 Boulder

TP23 32 503225.984 3029823.097 887.818 Boulder

TP24 33 503146.320 3029815.712 892.406 Boulder

TP25 34 503011.458 3029816.699 910.172 Boulder

TP26 35 502921.519 3029820.252 918.481 Boulder

TP27 36 502876.522 3029828.198 922.012 Boulder

TP28 37 502880.357 3029876.972 915.816 Boulder

TP29 38 502965.413 3029829.127 909.666 Boulder

TP30 39 503004.980 3029893.590 903.216 Boulder

TP31 40 503191.251 3029925.489 890.566 Boulder

TP32 41 503264.087 3029953.913 889.868 Boulder

TP33 42 503334.782 3030019.815 885.648 Boulder

TP34 43 503426.763 3030088.357 876.633 Boulder

TP35 44 503471.261 3030107.289 870.921 Boulder

TP35,TP36 45 503552.015 3030175.882 857.146 Boulder

TP36,TP37 46 503624.002 3030227.863 851.824 Boulder

TP38 47 503720.707 3030294.720 847.483 Boulder

TP39 48 503725.992 3030260.326 852.994 Boulder


1-5

TP40 49 503840.595 3030290.234 842.260 Boulder

TP41 50 503935.634 3030302.407 835.861 Boulder

TP42 51 504007.953 3030313.235 834.831 Boulder

TP43 52 504121.034 3030332.743 823.412 Boulder

TP44 53 504230.674 3030357.787 816.512 Boulder

TP45 54 504306.871 3030341.850 813.691 Boulder

TP46 55 504384.642 3030290.931 810.873 Boulder

TP1 56 504395.983 3030252.552 821.151 Boulder

TP47 57 504400.659 3030255.802 817.862 Boulder

TP48 58 504409.554 3030254.452 816.625 Boulder

TP48,TP4 59 504396.009 3030252.542 821.088 Boulder

BM-8 1305 503633.761 3030175.349 858.740 Boulder

BM-7 1307 503625.121 3030159.480 858.798 Boulder

BM-6 2017 503061.253 3029883.524 907.727 Boulder

BM-5 2019 503011.372 3029818.626 910.412 Boulder

TPI,BM B 4691 506929.087 3031576.613 660.478 Boulder

BM-1 5459 506072.616 3031328.326 698.382 Boulder

BM-2 5525 506089.613 3031258.793 700.996 Boulder

BM3 6299 505453.026 3030990.901 735.668 Boulder

BM4 6303 505428.300 3030982.841 737.720 Boulder

All offsets and benchmarks were established from two control points wherever necessary.

2.8.3. Horizontal and Vertical Control

The control points were established by the traverse method. The traverse was conducted along

right bank of the Irkhuwa Khola and was then closed to the same station covering the required

area along right bank including headwork site and powerhouse site.

Total Station with a least count of 5” was used for measuring horizontal and vertical angles. One

complete set of horizontal and vertical angles were observed during the traversing.

Distance was measured in fore and back sight directions and then mean distance was taken.

Distance measurement was performed by Total Station with standard reflecting Prism.

For horizontal control, the following measurements were taken:

Mean angle and distance computation was checked precisely.

Angular closure was checked between traverse points.

Angular disclosures were adjusted.

∆E and ∆N were computed.

Closing error was distributed according to the common survey standards.


1-6

For vertical control, the following measurements were taken:

∆h in closed traverse was computed.

Error in height was distributed according to the common survey standards.

2.8.4. Accuracy

The closing errors were distributed according to common survey standards. In all the survey

works high accuracy survey instruments ‘Total Station GTS 230’ with a list count of 5” was used.

2.8.5. Detail Topographical Survey

The features of terrain were surveyed by means of spot surveying. Spot positions were taken by

the Total Stations from different point of traverse and offset points.

Features such as riverbanks, high flood level, cliff, house, earthen road, bridges, boulders, and

rock exposure were recorded during survey.

The survey works were carried out for headworks area, desander, surge tank, penstock,

powerhouse area and tailrace area.

2.8.6. Mapping

Land Development 2004” was used for preparing topographic map. The detail topographic map

of different component of the project such as: Headwork, Desander, Water Conveyance

alignment, Penstock alignment, Surge Shaft, Powerhouse and Tailrace area were prepared in the

following scale:

Proposed Headwork site Scale 1:1000

Proposed Powerhouse site Scale 1:1000

All the topographical maps are presented in annex

2.8.7. River Cross Section and Profile

Several cross-sections were taken for calculating the discharges rating curves at headwork and

powerhouse site. The sections were taken from weir axis at an interval of 25 m c/c in upstream

direction up to 100 m and in downstream direction at least up to desander area.

2.8.8. Establishment of Control Points

Some control points and bench marks were fixed in the field. Altogether 68 control points/

benchmarks for traversing and detailing were fixed in the project area. They were made

noticeable by cross marking on boulder with red enamel paint.


1-7

Altogether 2 benchmarks were fixed at the headworks site, which were designated as BM5 and

BM6. Similarly 4 benchmarks were fixed along the river alignment between headworks and

powerhouse sites which were designated as BM3, BM4, BM7 and BM8 and 2 benchmarks were

fixed as well at the powerhouse site which were designated as BM1 and BM2.

2.8.9. Design Data

The surveyed data recorded in total stations, were downloaded and processed to build the map.

The checking for the errors and uncovered areas were done. The closed loop was calculated and

checked in site for avoiding the errors. Final processing and preparation of map was executed in

Kathmandu office. The horizontal distances and elevations were calculated reciprocally.

Coordinates of each points was then computed with respect to given UTM coordinates and

elevation of control points. Mapping software Land Development 2004 was used to prepare map

after the all data checking completely. Finally the topographic map was converted into AutoCAD

2006 format.


3-1

3. HYDROLOGICAL STUDY

3.1. General

This section of report contains an overview of the hydrology of the Irkhuwa Khola catchment at

the proposed headworks site. The main objective of the hydrological study is to study rainfall

pattern, to pertain discharging capacity of catchment, generate mean monthly flow and to

predict design discharge, flood flow and low flow of the river. The overall aim of the hydrological

and meteorological study of the project is to estimate the design flow for the required capacity

of the hydroelectric power plant.

An accurate assessment of long-term hydrology is essential to any hydropower project. The

longer the hydrological record, more reliable is the estimation of design parameters for the

project. In the case of ungauged (i.e. either limited or no stream flow records) river, direct

measurements of hydrological parameters are not available.

The hydrological study of the project area thus comprises the field investigation including desk

study, collection of meteorological data and various literature reviews. Briefly the methodology

of hydrological study is stated below:

Direct measurement of discharge and estimation of annual flow

WECS Method of discharge estimation

Development of rating curve at headworks and powerhouse site.

Adoption of flow duration curve for fixation of design flow

During the feasibility level of study, the Irkhuwa Khola catchment was studied from the available

topographical maps.

3.2. Irkhuwa Khola Catchment Characteristics

3.2.1. Catchment Physiography

Irkhuwa Khola, formed by the confluence of two streams Phedi Khola and Thumlung Khola, is

one of the tributaries of Arun River which ultimately merges with Saptakoshi River, the biggest

river of Nepal. Irkhuwa Khola is a perennial river even though not snow-fed, and has a total

catchment area of 137.35 km2 at proposed intake site of the project out of which Phedi Khola

has catchment area of 74.17 km2 and Thumlung Khola has catchment area of 61.18 km2 at


3-2

respective intake sites. The flow of Irkhuwa Khola is originated from middle mountains with the

highest peak at an elevation of 4100 masl.

The proposed headworks site on Phedi Khola lies at about 700 m upstream along the river from

the its confluence with Thumlung Khola while the head works site on Thumlung Khola lies at

about 640 m upstream along the river from its confluence with Phedi Khola. The proposed

powerhouse site of Irkhuwa Khola, A Small Hydropower Project is located at around 800m

upstream of confluence with Benkhuwa Khola. The total catchment area at proposed

powerhouse site is 165.00 km2. Catchment area at various locations is presented below in Error!

Reference source not found..

Figure 0-1: Catchment areas at proposed intake and tailrace sites

The average gradient of Irkhuwa Khola in between the headworks site and tailrace site is about

10%. The Irkhuwa Khola basin drains towards east direction. The basin shape is roughly

equilateral triangular having average length of 20 km. Irkhuwa Khola basin is mainly covered with

moderately dense mixed forest. Agricultural field on terraces and scattered settlements

dominate in the catchment area lying below 2’500 masl.

The information regarding the Irkhuwa Khola drainage area has been obtained based on the

topographical maps of 1:50,000 scale complied from arial photographs of 1996 published by the

Survey Department of the GoN and further information was collected from in-site observations

and interviews with local people.

The characteristics of Irkhuwa Khola catchments at various sites have been presented in Error!

Reference source not found. below.

Table 0-1: Characteristics of Irkhuwa Khola catchment at the various sites

Catchment Areas (km2)

Catchment area:

Phedi Khola Intake

Total area: 74.17 km2

Below 3000m: 61.75 km2

Thumlung Khola Intake

Total Area: 63.18 km2

Below 3000m: 57.72 km2

So,

Total area at intake: 137.35 km2

Area below 3000m: 119.47 km2

At Powerhouse:

Total area: 165.00 km2

Below 3000m: 147.13 km2


3-3

Elevation (amsl)

Intake at Phedi Khola

Intake at Thumlung

Khola

Tailrace at Irkhuwa

Khola

>3000 12.42 5.46 17.87

<3000 61.75 57.72 147.13

Total 137.35 165.00

Mostly the catchment area is covered with dense forest and the slope is steep on the both banks.

Both banks of the Irkhuwa Khola mostly are forest region and some cultivated land and irrigation

water is available from tributaries.

3.2.2. Water Sharing Issues

There are few water ghattas (water mills) which are using the water from Irkhuwa Khola

downstream of proposed intake area.

3.3. Reference Hydrology and Available Data

3.3.1. Stream Gauging

Irkhuwa Khola being an ungauged river, discharge measurements were made at the proposed

Project site for the purpose of the present study on various dates. Table 0-2 shows

representative field discharge measurements used for further hydrological analysis selected out

of numerous field measurements. A permanent discharge gauging station has to be established

in the vicinity of proposed intake site to measure the regular dry and flood flows of Irkhuwa

Khola.

Table 0-2:: Representative discharge measurements at Upper Irkhuwa Intake site

SN Date Discharge (m3/s)

1 February 14, 2016 2.827 (intake)

2 March 21, 2016 2.793 (intake)

3 May 2, 2016 1.852 (intake)

4 November 23, 2016 6.594 (Intake)

5 December 27, 2016 5.339 (Intake)

6 January 1, 2017 3.625 (Intake)

3.3.2. Long term mean monthly flow and flow duration curve

Long term mean monthly flows or hydrograph are quite useful for assessing the design flow and

monthly generation of energy from a hydropower project. A flow duration curve (FDC) showing


3-4

the percentage of time a particular flow is equaled or exceeded for Upper Irkhuwa Khola

Hydroelectric Project headworks site have been developed from various independent methods

which are explained below under subsequent headings.

3.3.3. WECS/DHM Method

A study on methodologies for Engineering Hydrologic Characteristics of ungauged locations in

Nepal was published out by WECS and DHM in July 1990. This study uses the approach of multiple

regression equations relating the physiographic and climatologic characteristics of the selected

basins to the average monthly flow values. Altogether twelve individual monthly regression

equations are developed.

Catchment area of Irkhuwa Khola at the proposed headworks site is 137.35 km2 with the

catchment area lying below 3000m elevation being 119.48 km2. Monsoon wetness index at the

catchment centroid has been adopted from the published data of Aiselukharka (St.1204),

Bhojpur (St.1324) and Dingla (St. 1325) rain gauge stations which comes out to be 1534 mm,

total rainfall during four monsoon months from June to September.

Alternately, modified HYDEST method has been used as a comparative approach for estimation

of mean monthly discharge at the headworks site of Irkhuwa Khola. Average altitude of the

Irkhuwa Khola catchment at proposed intake site has been taken to be 2510 m for this study.

The following Table 0-3 shows the results from WECS/DHM and modified HYDEST.

Table 0-3: Mean monthly flow (m3/s) at headworks site by WECS/DHM & modified HYDEST methods

Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Avg.

WECS/D

HM 1.76 1.50 1.35 1.37 1.82 6.37 19.57 23.65 18.18 7.98 3.50 2.29 7.45

Modified

HYDEST 3.73 3.17 2.10 1.96 2.54 11.88 28.77 41.91 28.81 13.73 6.55 4.53 12.47

3.3.4. MHSP Method

Nepal Electricity Authority (NEA) in 1997 developed a method to predict long-term flows, flood

flows and flow duration curves at ungauged sites through regional regression technique. This

approach uses both monsoon wetness index and average precipitation of the area along with

catchment area of the river. With all other input parameters as previously adopted in

WECS/DHM method and average precipitation obtained at Irkhuwa Khola as 2012 mm, the

results from MHSP method are presented below in Table 0-4.

Table 0-4: Mean monthly flow (m3/s) at headworks site by MHSP method



3-5

Q (m3/s) 2.20 1.80 1.64 1.97 2.24 7.45 22.53 26.86 21.01 9.85 4.73 3.05 8.78

3.3.5. Catchment Area Ratio (CAR) Method

There are four key stream gauging stations in the vicinity of the Project area, Hinwa Khola at

Pipletar (Index No. 602.5), Sabhaya Khola at Tumlingtar (Index No. 602), Likhu Khola at

Sangutar(Index No. 660) and Khimti Khola at Rasnalu Village (Index No. 650). These station’s data

have been analyzed for the stream flow analysis of Irkhuwa Khola. Because of the non-availability

of long-term discharge data for Irkhuwa Khola, an attempt has been made to derive the

reference hydrology from the gauging station at these three reference stations.

Considering the physiographic conditions and geographical proximity of Irkhuwa Khola from the

gauging stations, it is appropriate to use the discharge data from Hinwa Khola at Pipletar

(watershed area: 148.4 sq.km), Sabhaya Khola at Tumlingtar (watershed area: 393.66 sq.km),

Likhu Khola at Sangutar (watershed area: 856.14 sq.km) and Khimti Khola at Rasnalu Village

(watershed area: 313.00 sq.km), for deriving the stream flow at the headworks site of the

Project. The Area Coefficient for the calculation has been taken 0.8. The results from CAR method

are presented below in Table 0-5.

Table 0-5: Mean monthly flow (m3/s) at headworks site by CAR method

Month

Design(m3/s)

CAR-Hinwa CAR-Sabhaya CAR-Likhu CAR-Khimti

January 2.44 3.12 3.87 3.30

February 2.07 2.63 3.20 2.86

March 1.80 2.42 2.99 2.57

April 2.63 3.24 3.30 2.67

May 5.64 7.98 4.87 4.81

June 10.91 16.69 13.41 19.47

July 16.45 25.25 38.16 50.25

August 17.92 26.29 43.54 51.11

September 14.85 23.91 31.81 31.28

October 9.64 12.80 15.95 14.34

November 5.58 6.44 8.19 7.01

December 3.60 4.12 5.36 4.76

Average 7.79 11.24 14.55 16.20


3-6

3.3.6. Adoption of Design discharge and Flow Duration Curve

Table 3-7 below shows the results derived for long-term mean monthly flows at the proposed intake site from various methods for comparative study.

Table 0-6: Mean monthly flow (m3/s) at headworks site by various methods


MIP- 14 Feb 3.87 2.84 2.05 1.83 3.69 8.44 22.01 34.75 27.49 14.59 7.47 5.20 11.19

MIP -21 March 5.59 4.10 2.96 2.64 5.32 12.19 31.80 50.20 39.72 21.08 10.80 7.52 16.16

MIP 2 May 2.77 2.03 1.47 1.31 2.64 6.05 15.77 24.90 19.70 10.46 5.36 3.73 8.01

MIP- 23 Nov 3.95 2.90 2.10 1.87 3.77 8.63 22.51 35.54 28.11 14.92 7.64 5.32 11.44

MIP- 27 Dec 4.41 3.23 2.34 2.08 4.20 9.62 25.08 39.60 31.33 16.63 8.52 5.93 12.75

MIP- 25 Jan 3.98 2.91 2.11 1.88 3.79 8.68 22.62 35.72 28.26 15.00 7.68 5.35 11.50

Hydest 1.76 1.50 1.35 1.37 1.82 6.37 19.57 23.65 18.18 7.98 3.50 2.29 7.45

Modified Hydest 3.73 3.17 2.10 1.96 2.54 11.88 28.77 41.91 28.81 13.73 6.55 4.53 12.47

MSHP 2.20 1.80 1.64 1.97 2.24 7.45 22.53 26.86 21.01 9.85 4.73 3.05 8.78

CAR- Hinwa 2.44 2.07 1.80 2.63 5.64 10.91 16.45 17.92 14.85 9.64 5.58 3.60 7.79

CAR-Sabaya 3.12 2.63 2.42 3.24 7.98 16.69 25.25 26.29 23.91 12.80 6.44 4.12 11.24

CAR-Likhu 3.87 3.20 2.99 3.30 4.87 13.41 38.16 43.54 31.81 15.95 8.19 5.36 14.55

CAR-Khimti 3.30 2.86 2.57 2.67 4.81 19.47 50.25 51.11 31.28 14.34 7.01 4.76 16.20

The table shows that the derived long-term mean monthly flows at the intake site from various

methods are quite comparable. There is not a proven statistical tool to interpret the river specific

annual discharge variation pattern of Irkhuwa Khola. The best method to analyze the Irkhuwa

Khola hydrology is to establish a permanent gauging station and get a long-term daily discharge

data for sufficiently long period.

The MIP method, as is based in regional hydrograph of the locality, trends to deliver traditional

results yielding an absolute minimum flow during the month of April. The field discharge

measurements and interviews with local people show the driest period to take place somewhere

in March with gradual reduction in discharge between the months November to March. With

the onset of monsoon in June/July, once the spring sources are recharged, the discharge of

Irkhuwa Khola goes up smoothly till the month of September, with an instantaneous peak during


3-7

the monsoon month of August. WECS/DHM method and MHSP methods give reliable estimates

of monthly flows compared to the measured values, though they give comparatively lower

values. Similarly, CAR method generates the data on the higher side in all of the cases except for

Hinwa.

Hence, a cognitive approach has been applied in deriving the long-term average monthly flows

of Irkhuwa Khola by considering the measured discharge values during the dry season as the

reference values and comparing the results with other methods. The MIP method based on

measurement done in the dry month of March gives the higher average monthly flow values.

The results obtained from the WECS/DHM, MHSP are on lower sides whereas Modified HYDEST

method gives relatively higher values of discharge giving overestimated design discharge value.

After due consideration to the results from various methods, the results obtained from CAR

method for Likhu Khola has been adopted to compute the long-term mean monthly flows of

Irkhuwa Khola used for the purpose of this feasibility study. This is done as the flow pattern has

similarity to the discharge values noted at the intake site at various dry months and since this

analysis uses the mean monthly discharges of the stations which are similar to our site. The

adopted long-term mean monthly flows used for the design purpose are presented below in

Table 0-7.

Table 0-7: Adopted long-term mean monthly flows (m3/s) at Upper Irkhuwa headworks site


Phedi

Discharge

(m3/s)

2.06 1.70 1.59 1.76 2.59 7.13 20.30 23.17 16.92 8.49 4.36 2.85 7.74

Thumlung

Discharge

(m3/s)

1.81 1.50 1.40 1.55 2.28 6.27 17.86 20.38 14.88 7.47 3.83 2.51 6.81

Total

Discharge

(m3/s)

3.87 3.20 2.99 3.30 4.87 13.41 38.16 43.54 31.81 15.95 8.19 5.36 14.55

Flow duration curve of Irkhuwa Khola at proposed headworksite is shown below in Figure 0-2

based on adopted long-term monthly average flows. The horizontal dark line represents the

design discharge generally adopted for hydropower generation purpose in Nepal corresponding

to 45% probability of exceedance.


3-8

Figure 0-2: Flow duration curve of Upper Irkhuwa Khola at proposed headworks site

Discharge values at an interval of 5% probability of exceedance derived from the curve are shown in Table 3-8 below.

Table 0-8: Adopted percentile dependable flows at headworks site (m3/s)

Probability of Exceedence

(%)

Days per year

Discharge (m3/s)

Probability of Exceedence

(%)

Days per year

Discharge (m3/s)

5% 18 44.05 55% 201 5.62

10% 37 41.48 60% 219 5.09

15% 55 36.08 65% 237 4.19

20% 73 31.66 70% 256 3.88

25% 91 24.27 75% 274 3.55

30% 110 17.96 80% 292 3.33

35% 128 13.13 85% 310 3.19

40% 146 9.83 90% 329 3.08

45% 164 7.80 95% 347 2.97

50% 183 6.44 99.7% 364 2.89


3-9

3.3.7. Riparian Release

The long-term mean monthly flow at the proposed intake site of Upper Irkhuwa Khola for the

driest month March as per Table 3-8 is 2.99 m3/sec. A flow equivalent to 10% of the driest flow,

i.e. 299 lps will be released downstream at all the times as the riparian release for downstream

riverine habitants for fulfilling environmental protection requirements.

3.4. Flood Hydrology

In hydropower projects, high floods are required to be computed for designing the headworks

structures as well as the powerhouse complex. It has been a common practice to analyse the

flood events that might occur during the driest periods for the purpose of the construction of

diversion headworks structures. Flood hydrology has been analysed in two parts - design high

floods for the design of headworks, powerhouse, and other hydraulic structures; and dry season

floods for the construction of river diversion structures.

3.4.1. Design High Floods

1) WECS/DHM Method

The study on ‘methodologies for estimating hydrological characteristics of ungauged locations

in Nepal (July 1990)’ published by WECS/DHM uses the approach of regional flood frequency

analysis. The results of this study are used for estimation of flood discharges at the proposed

headworks site as well as the powerhouse site, when no measured flood discharges are available.

The study shows the results from the frequency distribution parameter prediction method,

which is a variation of the multiple regression method. The independent variable that is found

to be the most significant in all the of the regression analyses is the area of the basin below 3000

m elevation. This area represents the portion of the basin that is influenced by the monsoon

precipitation. In addition, ‘Hydrological Studies of Nepal (1982)’ published by WECS uses the

same parameter.

The study shows that the prediction regression equation for an instantaneous flood peak with 2-

year return period is:

Q2(instantaneous)= 1.8767(A3000+1)0.8783

Similarly, the prediction regression equation for an instantaneous flood peak with 100-year

return period is given by:

Q100 (instantaneous)= 14.63(A3000+1)0.7342

In these equations, the area of the basin below 3000m, A3000, is to be expressed in square

kilometres to get the flood discharge in cumec.


3-10

Instantaneous peak floods with any other return period ‘R-years’ QR (Instantaneous), can be calculated

using the following formulae:

QR (Instantaneous)=Exp (In Q2 (Instantaneous) +s)

s = standardized normal variant as listed below:

Return Period, 'R-years’ s

5 0.842

10 1.282

20 1.645

50 2.054

200 2.576

500 2.878

1’000 3.090

10’000 3.719

=standard deviation of the natural logarithms of annual floods

= ln (Q100/Q2)/2.326)

The catchment area below 3000 m elevation at headworks site of Phedi Khola and Thumlung

Khola are 61.75 km2 and 57.72 km2 respectively and at the powerhouse site of the Upper Irkhuwa

Khola Hydropower Project is 147.13 km2. The results of the flood estimates from this regional

frequency analysis are presented in Error! Reference source not found.:

Table 0-9: Estimated instantaneous high floods by WECS/DHM method

Return Period (Years)

Flood Dishcarge(m3/s)

Headworks Site at Phedi

Headworks Site at

Thumlung

Powerhouse Site

2 71.16 67.13 151.3

5 120.60 114.16 245.2

10 158.87 150.66 315.5

20 199.43 189.41 388.5

50 257.68 245.13 491.2

100 305.54 291.00 574.0

200 357.34 340.68 662.5

500 431.77 412.15 787.7


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1000 493.09 471.09 889.5

2) Gumbel Method

According to this theory of extreme events, the probability of occurrence of an event equal to or

larger than a value x0 is

P(X>=��) =1-��

...................................................................................... (1)

In which y is a dimensionless variable given by

y=α(x-a) a=�-̅0.45005�� α=1.2825/�� Thus

y=�.��(��)̅

��+0.577............................................................................................ (2)

Where �=̅mean and ��=standard deviation of the variate X.in practice it is the value of X for a

given P that is required and as such (1) is transposed as

��=-ln[-ln(1-P)]……………………………………………………………………

Noting that return period T=1/P and designating

��= -[ln*ln�

��]

Now rearranging eq. (2), the value of variate X with a return period T is

��=�+̅K��

K= (��.��)

�.��

The results of the flood estimates from this regional frequency analysis are presented in Table 3-

11:

3) Log Pearson Type III Distribution

The Log-Pearson Type- III distribution is extensively used in USA for projects sponsored by

the US Government. In this distribution, the variate is first transformed into logarithmic form

(base 10) and then this transformed data is analyzed. If X is the variate of a random hydrologic

series, then the series of Z variate where

Z=logx


3-12

are first obtained. For this Z series, for any recurrence interval T, the value of zt can be obtained

as

��=�+̅��

Where Kz=a frequency factor which is a function of recurrence interval T and the

coefficient of skew Cs,

��=standard deviation of the Z variate sample

=�∑(��)̅�

� ��

Cs=coefficient of skew Variate Z

= N∑(��)̅�

(� ��)(� ��)(��)�

Where � ̅=Mean of the z values

N= Sample size=number of years of record

Kz= f (Cs, T)

After finding the value of zt, the corresponding value of xt is also obtained by the

equation:

xt= antilog(zt)

Although not considered under the standard procedure, the coefficient of skew Cs can

also be adjusted to account the size of the sample by using the following relation

(proposed by Hazen in 1930)

��s=Cs (��.�

�)

Where ��s=adjusted coefficient of skew.

If the value of coefficient of skew Cs=0,log Pearson type III distribution is reduced to log normal

distribution which plots as a straight line on logarithmic probability paper.


3-13

The transposed annual flows from Sabhaya Khola were employed to compute flood flows using frequency analysis. The results of the flood estimates from this regional frequency analysis are presented in Table 0-10(a): Estimated instantaneous high

floods by frequency analysis of Sabhaya river at Phedi intake site

Return Period

Frequency Analysis

Gumbel's Method (Below 3000 m)

Log Pearson Type III (Below 3000 m)

Log Normal (Below 3000 m)

2 52.07 46.46 48.96

5 89.44 76.88 78.60

10 114.18 103.18 100.65

25 145.43 144.78 131.01

50 168.62 182.64 155.33

100 191.63 227.23 180.99

200 214.57 279.64 208.30

1000 267.69 440.65 278.08

Table 0-11(b): Estimated instantaneous high floods by frequency analysis of Sabhaya river at Thumlung intake site

Return Period

Frequency Analysis




2 49.34 44.02 46.39

5 84.73 72.84 74.46

10 108.17 97.76 95.36

25 137.78 137.17 124.12

50 159.75 173.04 147.17

100 181.56 215.29 171.48

200 203.28 264.95 197.35

1000 253.61 417.49 263.46

Table 0-12: Estimated instantaneous high floods by frequency analysis of Sabhaya river at powerhouse site

Return Period

Frequency Analysis




2 104.29 93.05 98.06

5 179.12 153.99 157.42

10 228.67 206.66 201.59

25 291.26 289.97 262.39

50 337.70 365.81 311.11

100 383.80 455.11 362.51

200 429.73 560.09 417.20

1000 536.11 882.57 556.95

:


3-14

Table 0-10(a): Estimated instantaneous high floods by frequency analysis of Sabhaya river at Phedi intake site

Return Period

Frequency Analysis




2 52.07 46.46 48.96

5 89.44 76.88 78.60

10 114.18 103.18 100.65

25 145.43 144.78 131.01

50 168.62 182.64 155.33

100 191.63 227.23 180.99

200 214.57 279.64 208.30

1000 267.69 440.65 278.08

Table 0-11(b): Estimated instantaneous high floods by frequency analysis of Sabhaya river at Thumlung intake site

Return Period

Frequency Analysis




2 49.34 44.02 46.39

5 84.73 72.84 74.46

10 108.17 97.76 95.36

25 137.78 137.17 124.12

50 159.75 173.04 147.17

100 181.56 215.29 171.48

200 203.28 264.95 197.35

1000 253.61 417.49 263.46

Table 0-12: Estimated instantaneous high floods by frequency analysis of Sabhaya river at powerhouse site

Return Period

Frequency Analysis




2 104.29 93.05 98.06

5 179.12 153.99 157.42

10 228.67 206.66 201.59

25 291.26 289.97 262.39

50 337.70 365.81 311.11

100 383.80 455.11 362.51

200 429.73 560.09 417.20

1000 536.11 882.57 556.95

Due to the non-availability of the flood discharge data of Irkhuwa Khola itself, the results

from Gumbel frequency analysis method have been adopted for the purpose of this study

based on the catchment area, elevation of catchment zones, precipitation at the stations,


3-15

etc. As a general practice, instantaneous peak flood with return period of 100 years is

adopted as the design flood. Hence, for the hydraulic designs, the corresponding adopted

design floods are – 191.63 for Phedi headworks, 181.56 m3/s for Thumlung Headworks

and 383.80 m3/s for tailrace structures respectively as shown in Table 3-10 and Table 3-

11.

3.4.2. Dry Season Floods

Generally, the headworks structures are constructed during the dry months of year due to low

flow in the river resulting in low cost of river diversion structures. For the river diversion during

dry season, it will be crucial to come to a common understanding as for the commencement of

this season. For Upper Irkhuwa Small Hydropower Project, the period from December to May

has been envisaged as the dry season period for river diversion.

Different types of frequency distribution functions were fitted to the sample flood data. There were very little real differences among the results from various distributions. The results of the Gumbel distribution of Sabhaya River were adopted and are

given below in Table 0-13: Estimated floods for dry season


Dry Flood (m3/s)

Phedi Intake

Thumlng Intake

2 9.10 7.75

5 16.17 13.78

10 20.85 17.76

20 25.35 21.59

The design dry season flood for the construction of diversion headworks structures is taken as 1

in 5 year flood, i.e. 29.64 m3/s.

.

Table 0-13: Estimated floods for dry season


Dry Flood (m3/s)

Phedi Intake

Thumlng Intake

2 9.10 7.75

5 16.17 13.78

10 20.85 17.76

20 25.35 21.59

The design dry season flood for the construction of diversion headworks structures is taken as 1

in 5 year flood, i.e. 29.64 m3/s.


3-16

3.5. Low Flow Analysis

The duration curve of long-term inflow series predicts the flow duration for an average

hydrological year. Individual dry and wet years would display different flow duration

characteristics. For a hydroelectric plant, sustained low flows experienced in dry years are critical

to the operation resulting in nil energy generation when the flow decreases below the minimum

permissible limit.

The low flow discharge values, in hydropower projects, not only decide the design flow to be

diverted but also serve for environmental purposes as to how much water must be left in the

river system for the survival of the downstream aquatic flora and fauna.

In order to predict the likelihood of this occurring, a probabilistic low flow analysis is carried out using the methodology by WECS/DHM for ungauged river basins. The results of the low flow analysis are given in Table 0-14: Low flow frequency

analysis at Upper Irkhuwaheadworks site


Low Flow (m3/s)

Phedi Thumlung

Daily Weekly Monthly Daily Weekly Monthly

2 0.54 0.57 0.80 0.46 0.49 0.70

10 0.26 0.31 0.53 0.20 0.25 0.45

20 0.19 0.26 0.47 0.15 0.21 0.40

below.

Table 0-14: Low flow frequency analysis at Upper Irkhuwaheadworks site


Low Flow (m3/s)

Phedi Thumlung

Daily Weekly Monthly Daily Weekly Monthly

2 0.54 0.57 0.80 0.46 0.49 0.70

10 0.26 0.31 0.53 0.20 0.25 0.45

20 0.19 0.26 0.47 0.15 0.21 0.40

3.6. Sediment Analysis

3.6.1. General

Sediment transport in Himalayan Rivers is a natural and complex phenomenon and Irkhuwa

Khola is no exception. Particle size may range from fine sand to big boulders. Prior to this study,

there were no data on suspended sediment load of Irkhuwa Khola. However, it is expected to

follow certain characteristics which are common to Himalayan Rivers.

Sediment load in the river may vary from year to year. Therefore, for design purpose a long-term

data base is required. Fluctuations in the annual sediment load are usually much larger than flow

variations. Larger seasonal variations are usually seen in the sediment load. Most of the sediment


3-17

transport takes place during the monsoon season (usually assumed to be 80% to 90%). High

sediment concentrations can, however, is expected during relatively small pre-monsoon floods.

Removal of sediments from the diverted water is very important for any hydropower plant.

Suspended sediment particles cause severe abrasion to the runner and other mechanical parts

of a turbine and thus drastically decrease its life and efficiency. The abrasion of hydro-mechanical

components due to suspended sediment largely depends upon factors like the hardness, shape

and size of mineral, hardness of substrate material, impingement angle and relative velocity with

which the particle strikes the substrate material. To estimate the amount of wear, collection,

study and analysis of these aspects is therefore imperative.

3.6.2. Sources of Sediment

The basin area of Irkhuwa Khola is mainly covered with sub-tropical forest. Sediment generation

in forest area is relatively small. Landslides of significant scale are not available within the

catchment area of the project. Debris flow is also not so frequent. It is a comparatively stable

river with little meandering. So there is not vulnerable sediment problem in the river. But due to

the steepness of the river, the river scours its side and bed which is the main source of sediment.

3.6.3. Estimation of Sediment Yield

Sediment measurement and sampling was not carried out in Irkhuwa Khola. Thus, indirect

method of sediment yield was adopted to compute sediment volume and sediment

concentration. During the identification visit river deposits are observed and found the

possibility of transporting up to 500 mm diameter sediment particle in yearly flood. Cobble,

pebble, gravel, sand and silt are predominant sediment of the river. Quartz, feldspar, mica are

the predominant mineral of the sediment.

The sediment yield equation adopted in Nepal for catchment area below 150 km2:

Y=0.395/A0.311

And sediment concentration by mass

C = Tm/Qm

Where,

Y = Sediment Yield (Mm3/100 km2 / year)

A = Catchment area (km2)

C= Sediment concentration (tons/m3)

Tm = Mass of sediment carried in three months (tons)

Qm = Water volume during three months (m3)


3-18

The sediment concentration is worked out as 2000 mg/litre assuming the density of sediment 2

tons/m3, mean monsoon discharge 1.00 m3/s and 60 % sediment is transported within three

months period. This is an average sediment concentration in river during monsoon season. Peak

sediment concentration can be more than three times of the above values but all the sediment

at the river may not enter into the intake. Some of the sediment can be excluded from gravel

trap, some from settling basin. For the purpose of settling basin design about 1.5 times of the

average sediment concentration (3000 ppm approximately) is assumed for sediment storage

volume calculation and flushing frequency computation.

3.7. Conclusion and Recommendation

3.7.1. Conclusion

Following conclusions have been drawn at the end of the hydrological studies performed under

this chapter:

The 100-years’ return period design flood is 191.63 m3/s at the proposed headworks site

of Phedi Khola and 181.56 m3/s at the proposed headworks site of Thumlung Khola.

Similarly the 100-years’ return period flood is 383.80 m3/s at the proposed powerhouse

site.

The design 5-years construction flood is 16.17 m3/s at the proposed headworks site of

Phedi Khola and 13.78 m3/s at the proposed headworks site of Thumlung Khola.

The adopted design discharge is 7.80 m3/s out of which 4.15 m3/s is obtained from Phedi

Khola and 3.65 m3/s is obtained from Thumlung Khola (corresponding to 45%

dependable flow).

The 20 years’ monthly low flow is 0.47 m3/s at the proposed headworks site of Phedi

Khola and 0.40 m3/s at the proposed headworks site of Thumlung Khola.

The mandatory compensation flow in Phedi Khola downstream of the proposed weir axis

is 0.159 and in Thumlung Khola downstream of proposed headworks site is 0.14 m3/s.

3.7.2. Recommendation

Based on the conclusions drawn above, it is recommended that daily staff gauge readings of

Irkhuwa Khola at the proposed intake sites and tailrace site shall be done till the start of the

implementation of the project.River discharge measurements should also be taken at various

gauge height so as to develop reliable rating curves at both the sites.


4-1

4. GEOLOGICAL STUDY OF THE PROJECT

4.1. Introduction

The proposed Upper Irkhuwa Khola Hydropower Project (UIKHP) is located towards north of

Tumlingtar between the Dobhan village and Gothe Bazaar, Bhojpur District, Koshi Zone, Eastern

Development Region, Nepal (Figure 4-1). The project covers the area between Gothe Bazaar

village just upstream from the confluence between the Irkhuwa Khola and Benkhuwa Khola) at

Dobhan village and about 600 m upstream from the confluence between Phedi Khola and

Thumlung Khola. The entire project components follow the right bank of the Irkhuwa Khola

passing through Nagdanda and Dobhan villages. The Irkhuwa Khola is one of the minor

tributaries of the Arun River originates from the Makalu Himalayan Region of the Higher

Himalaya. The project area is located about 20 km northwest of Tumlingtar.

A diversion weir is proposed at about 600 m upstream from the confluence of Thumlung Khola

and Phedi Khola at Dobhan village. The Irkhuwa Khola is named after junction of Thumlung Khola

and Phedi Khola. The powerhouse is proposed at about 250 m upstream from the confluence

between the Irkhuwa Khola and Thado Khola on left bank of the Irkhuwa Khola at Gothe Bazaar.

The nearest airport is Tumlingtar situated approximately 20 km south of the project area. The

project area is connected to Kathmandu, capital city of Nepal via Prithvi Highway and East-West

Highway at Itahari about 500 km in length. Irkhuwa Khola is a rain fed river and is a minor

tributary of the Arun River of the Koshi basin. Irkhuwa Khola is originated from southern flank of

the Makalu Himalayan Range.

Figure 4-1: Location Map of Project area

Proposed IKHEP Area

Proposed UIKHEP Area


4-2

Proposed Upper Irkhuwa Khola Hydropower Project is a run-of-the-river type scheme. Water

diverted into the tunnel alignment from the inlet portal is conveyed upto the proposed

powerhouse to generate 14.5 MW power. Related all structures are located along the right bank

of Irkhuwa Khola on bedrocks as well as alluvial, residual and colluvial soil deposits.

4.2. Objectives

The main objectives of the present geological study are as follows:

To obtain information on regional geology of the project area.

To study detail geological condition at the locations of proposed project structures.

To prepare detailed engineering geological map (1:1,000), geological cross-sections of the

locations of major project structures like the dam axis and intake and powerhouse and

tailrace areas, engineering geological map of proposed tunnel alignment area and cross-

section in 1:1,000 scale,

To identify geomorphologic condition of the project area.

To collect the data of the discontinuities for stability analysis of the tunnel alignment.

To carry out Rock Mass Classification using “RMR” and “Q” systems of the tunnel for the

design of the structures,

To carry out construction material survey and tests.

To locate the mucking areas for the project.

To propose the geophysical investigation (Electrical Resistivity Tomogram, ERT) of the

subsurface condition of the project area.

4.3. Scope of Works

The present study comprises of the following works:

Collect and review available literatures, topographical and geological maps, photographs

and landsat images

Collection and study of geological and geomorphologic information of previous studies

Conduct field survey to collect and verify geological information prior to general and detail

geological mapping, engineering geological mapping of project components and particular

structures.


4-3

Identify geological and seismic hazards such as faults, thrusts and landslides.

Measurement of discontinuities to analyze slope stability.

Prepare maps (engineering geological map) at the scale mentioned in DoED’s guidelines.

4.4. Methodology

To accomplish the objectives and scope of work, desk study, field visit and field data analysis

have been carried out, the details of which have been outlined below.

4.4.1. Desk Study

During the desk study, available geological information and geological maps of the Irkhuwa

Khola-Arun River around Tumlingtar section of eastern Nepal relevant to the project area was

thoroughly studied.

4.4.2. Data Collection and Field Works

After the desk study, the field visit to the project was conducted. During the field visit, geological

as well as the engineering geological mapping and discontinuity survey of the project area has

been done. Detailed geological information of diversion weir axis, desander basin area, inlet

portal, tunnel alignment, surge tank, penstock alignment, powerhouse and tailrace areas were

collected. The instability and mass wasting area and necessary geological data were also

collected.

4.4.3. Data Interpretation and Report Writing

After field observation, the detail analysis of geological data was carried out which includes

graphical analysis, slope stability analysis of the project area. Calculation of the data of the tunnel

alignment was also done for the rock mass classification. All the analyzed data has been

incorporated in the report.

4.4.4. Background Information

Eastern Region of Nepal within varied geomorphic scenario and with complex geological set up

offers immense scope for utilization of water resources. The water resources of the Irkhuwa

Khola which ultimately drains into the Arun River and finally drains out into the Koshi River Basin,

still remains unutilized. The Irkhuwa Khola is a tributary of the Arun River and the Arun River is

a main tributary of the Koshi River basin. These rivers are perennial and carry huge quantity of

water that flows down with a rapid fall. Since the rainfall of the catchment area is very high,

these exists a steady discharge of water in these rivers throughout the year making them ideal

for hydropower development in tandem. In view of above, number of hydropower projects were

identified and awarded to Private Developers by the Government of Nepal to harness these vast


4-4

natural resources for the hydropower generation. The proposed Upper Irkhuwa Khola

Hydropower Project is a self identified project which has been awarded to Aarati Hydropower

Limited by the Department of Electricity Development (DoED) under the Ministry of Energy,

Government of Nepal. The Aarati Hydropower Limited intends to develop the hydropower

project through construction of a 14.5 MW hydroelectric plant utilizing the water resources of

the Irkhuwa Khola in Bhojpur District, Koshi Zone, Eastern Development Region of Nepal.

Installed capacity has been worked out as a run-of-the-river scheme.

4.4.5. Present Investigation

In order to fulfill the objectives and scope of work, the present studies were focused mainly on

general and detailed geological/ engineering geological mapping and subsurface explorations.

The main activities performed during the present investigation include the following:

4.4.5.1 Geological Mapping

General geological and engineering geological mapping of the project area in 1:1,000 scale.

Detailed geological and engineering geological mapping of the headworks and powerhouse

areas in 1:1,000 scale.

Geological section of the tunnel alignment on 1:5,000 scale.

Mapping of the mucking area in 1:50,000 scale.

Source of the construction materials in 1:50,000 scale and collection of the materials for

testing of the physicochemical properties of the materials.

4.4.5.2 Geotechnical Investigation

Construction material survey and laboratory testing.

Stereographic projection of major discontinuities of the rock of the project area.

4.4.6. Construction Material Survey

The construction material survey is comprised of identification of the prospective reserves of

different varieties of construction material required for the construction of hydropower project,

excavation of test pits at the identified borrow areas and prospective locations, collection of

samples from the test pits and identified borrow areas, testing of rock and soil samples in the

laboratory and analysis of laboratory test data. Two samples (sand and aggregate) were collected

for the test of the physiochemical and mechanical properties of the deposits from two locations.


4-5

4.5. Himalaya in General

The Himalaya is the largest mountain range of the world, which extends for a total length of

about 2,400 km. This lengthy mountain chain is geologically divided into five sections from west

to east (Figure 4-2, Gansser, 1964). The brief descriptions are as follow:

4.5.1. Punjab Himalaya

The Punjab Himalaya (about 550 km) lies between the Indus River in the west and Sutlej River in

the east.

4.5.2. Kumaon Himalaya

It borders the Sutlej River in the west and the Mahakali River in the east and extends about 320

km.

4.5.3. Nepal Himalaya

The Nepal Himalaya (800 km) lies between the Mahakali River in the west and the Mechi River

in the east.

4.5.4. Sikkim-Bhutan Himalaya

It starts from the Mechi River and extends along Sikkim and Bhutan for a length of 400 km.

4.5.5. NEFA (North East Frontier Agency) Himalaya

It stretches for 440 km from eastern boundary of Bhutan to the Tsangpo River in the east.

Figure 4-2: Physiographic Subdivision of the Himalayan Arc (After Gansser, 1964)


4-6

4.6. Geology of the Nepal Himalaya

The Nepal Himalaya is situated in the central part of the Himalayan arc and has covered about

one third part (about 800 km in length). The Nepal Himalaya is located between the Kumaon

Himalaya in the west and the Sikkim-Bhutan Himalaya in the east. The Nepal Himalaya is

subdivided into the following five major tectonic zones from south to north (Figure 4-3, Upreti

and Le Fort, 1999).

Indo-Gangetic Plain (Terai) ---- Himalayan Frontal Thrust (HFT) ----

Sub-Himalaya (Siwalik or Churia Group) ---- Main Boundary Thrust (MBT) ----

Lesser Himalaya ---- Main Central Thrust (MCT) ----

Higher Himalaya ---- South Tibetan Detachment System (STDS) ----

Tibetan-Tethys Himalaya

4.6.1. Indo-Gangetic Plain (Terai)

This zone represents the northern edge of the Indo-Gangetic Plain and forms the southernmost

tectonic division of the Himalaya, represents Pleistocene to Recent in age and has an average

thickness of about 1,500 m. This zone lies in southern part of the Himalaya, basically composed

of the clay to boulder. The uppermost part of the Indo-Gangetic Plain is the Bhabhar zone and it

comprises of boulder to pebble. The Middle part (Marshy zone) is composed of sands whereas

the clays are dominant in the southern Terai.

4.6.2. Sub-Himalaya (Siwaliks or Churia Group)

The Sub-Himalaya (Siwaliks or Churia Group) is developed in the southern part of the country

and is represented by low hills of the Churia Range. The Siwalik Group of Nepal is composed of

5-6 km thick fluvial sediments of the middle Miocene to early Pleistocene age. The sediments

are generally layers of mudstone, sandstone and conglomerate. The Siwalik Group is divided into

the Lower, Middle and Upper Siwaliks in ascending order based on lithology and increasing grain

size. The Lower Siwalik is comprised of mudstone and sandstone, whereas the Middle Siwalik

represented by thick-bedded, coarse-grained, "pepper and salt" appearance sandstone. The

Upper Siwalik is identified with the presence of conglomerate with lenses of muds and sands.


4-7

Figure 4-3: Geological Map of the Nepal Himalaya (After Upreti and Le Fort, 1999)

4.6.3. Lesser Himalaya

The Lesser Himalaya lies in between the Sub-Himalaya (Siwalik Group) in the south and Higher

Himalaya in the north. Both the southern and northern limits of this zone are represented by

thrusts, the Main Boundary Thrust (MBT) and the Main Central Thrust (MCT), respectively.

Tectonically, the entire Lesser Himalaya consists of allochthonous and para-autochthonous

rocks. Rock sequences have developed with nappes, klippes and tectonic windows, which have

complicated the geology. The Lesser Himalaya is made up of mostly the unfossiliferous

sedimentary and metasedimentary rocks, consisting of quartzite, phyllite, slate and limestone

ranging in age from Pre-Cambrian to Miocene. Generally the high-grade metamorphic rocks are

very rare in Lesser Himalaya but augen gneiss can be seen.

4.6.4. Higher Himalaya

This zone is geologically as well as morphologically well defined, and consists of a huge pile of

highly metamorphosed rocks. It is situated between the fossiliferous sedimentary zone (the

Tibetan-Tethys Himalaya in the north, separated by STDS and the Lesser Himalaya, separated by

the MCT in the south. This zone has made up of the oldest rocks of Pre-Cambriam metamorphic

and granitic gneiss. The north-south width of the unit varies from place to place. This zone

consists of almost 10 km thick succession of the crystalline rocks also known as the Tibetan Slab

Proposed UIKKHP Area


4-8

(Le Fort, 1975). This sequence can be divided into four main units. From bottom to top these

units are: Kyanite-sillimanite gneiss (Formation I), Pyroxene, marble and banded gneiss

(Formation II) and Augen gneiss (Formation III).

4.6.5. Tibetan-Tethys Himalaya

Rocks of the Tibetan-Tethys Himalaya zone are made up of thick pile of richly fossiliferous

sediments and their age ranges from early Paleozoic to middle Cretaceous. This zone is about 40

km wide and composed of sedimentary rocks such as shale, limestone and sandstone. In Nepal,

these fossiliferous rocks of the Tibetan-Tethys Himalaya are well developed in the Thak Khola

(Mustang), Manang and Dolpa as well as in Saipal area Nepal.

The proposed Upper Irkhuwa Khola Hydropower Project belongs to the rocks of the Lesser

Himalaya, Eastern Nepal, and south of the Main Central Thrust (MCT) or Barun Thrust (BT). The

area is mainly composed of intercalation of gneiss/ augen gneiss and schist. The proportion as

well as thickness of gneiss is greater than schist.

4.6.6. Physiography of Nepal

Physiographically, the project area falls in the Lesser (Mahabharat and Midland) and Trans Himalayas. The elevation of the Trans Himalaya ranges from 1,000 to 4,500 m and composed of

quartzite, slate, phyllite and limestone as well as gneiss and schist (Figure 4-4,

Table 4-1).

4.6.6.1 Mahabharat Range

The Mahabharat Range derives its name from the famous Hindu epic the Mahabharat. It rises up to 3,000 m and extends throughout the length of the country (Figure 4-4,

Table 4-1). The range rises high among the surroundings of the Churia Hills and the Midlands and

significantly controls the climate of the region. At a few places the Mahabharat Range is

intersected by the major rivers of the country through which all the waters of Nepal originating

north of the Mahabharat Range is drained off to the south. In contrast to the Churia Hills and the

Midlands, the Mahabharat Range is topographically distinct with its towering height, rugged

nature, sharp crests and steep southern slopes. The Mahabharat Range is characterized by the

concentration of the population along the ridge and the gently dipping northern slopes. There

are degraded forests and pasture lands.


4-9

4.6.6.2 Midlands

The Midlands (Figure 4-4,

Table 4-1) are bounded by the towering snow-clad Great Himalayan Ranges on the north and the

Mahabharat Range on the south. The Midland Zone has an average width of 60 km and ranges

in elevation between 200 and 3,000 m. The Midlands consisting of low hills, river valleys, and

tectonic basins form the most important physiographic province of Nepal. This zone, in contrast

to other physiographic divisions, exhibits a mature landscape. Within the midlands are the large

valleys of Kathmandu, Banepa, Panchkhal in Central Nepal, Pokhara and Mariphant in Western

Nepal and Patan in Far Western Nepal.

It is drained by a network of large number of rivers and streams with predominantly N-S and E-

W trending valleys. The larger rivers with their predominantly N-S course, when reach the

northern slope of the Mahabharat Range, suddenly deflect making right angle bends and flow

along E-W direction for a long distances collecting waters of many other N-S flowing rivers and

streams on their way. The rivers breach the barrier of the Mahabharat Range only at a few places.

The major rivers flowing through the Midlands have very low gradient and form extensive

Quaternary terraces along their courses.

The Midlands are marked by the diversity in the land use and land systems. The soil ranges from

the ancient river terrace to the deeply weathered residual soil. The river valleys are densely

populated and cultivated. On the other hand, some of the valleys are filled up by the lacustrine

deposits. Cultivated wetlands are found either on the river terraces or on the gently dipping

slopes with colluvial and residual soils. The dry cultivated land is found along the ridges and spurs

of the hills. The Midland Zone is densely populated comprising nearly half of the country's

population.

4.6.6.3 Fore Himalaya

Hagen (1969) defined a separate physiographic unit intermediate between the Midland and the Great Himalayan Ranges and named it as the Fore Himalaya (Figure 4-4,

Table 4-1). The Fore Himalayan Zone is 10 to 50 km wide with the altitude generally more than

3,000 m. Solukhumbu in Eastern Nepal and Dhorpatan and Jumla in the Western Nepal belong

to this zone. The Fore Himalaya is generally covered by forest with sparse population. The

population is concentrated on the river valleys.


4-10

Table 4-1: Geomorphic Units of Nepal

S N Geomorphic

Unit

Width

(km)

Altitude

(m) Main Rock Types Age

1. Terai

(Northern edge

of the Gangetic

Plain)

20-50 100-200 Alluvium (gravels in the north near the foot of

the mountain, and gradually becomes finer

southward

Recent

2. Churia Hills

(Siwaliks)

10-50 200-

1,300

Sandstone, mudstone and conglomerate. Mid-

Miocene to

Pleistocen

e

Dun Valleys 5-30 200-300 Valleys develop within Siwaliks and filled with

alluvial sediments

Recent

3. Mahabharat

Range

10-35 1000-

3,000

Schist, phyllite, quartzite, granite, limestone

belonging to Lesser Himalayan Zone

Pre-

Cambrian

and

Palaeozoic

4. Midland 40-60 200-

2,000

Schist, phyllite, gneiss, quartzite, granite,

limestone geologically belonging to the Lesser

Himalayan Zone

5. Fore Himalaya 20-70 2,000-

5,000

Gneiss, schist and marble

Pre-

Cambrian 6.

Higher Himalaya 10-60 >5,000 Gneisses schist and marbles belonging to Higher

Himalayan Zone

7. Trans

Himalayan and

Inner Himalayan

Valleys

2,500-

4,300

Tethyan sediments (limestone, shale,

sandstone) belonging to Tibetan-Tethys Zone

Cambrian

to

Cretaceous


4-11

Figure 4-4: Physiographic Map of Nepal

4.7. Regional Geology of the Project Area

The project area lies about 200 m downstream from junction between the junction between the Phunglung Khola and Phedi Khola and 100 m upstream from junction between the Irkhuwa

Khola and Thado Khola at Gothe Bazaar along the Irkhuwa Khola. The area is located geologically in the Lesser Himalaya, Eastern Nepal, consists of low- to high-grade metamorphic rock e.g., intercalation of grey, coarse-grained gneiss and grey schist as well as quartzite (Figure

4-5, Figure 4-6 and

Figure 4-7). Majority of the area is covered by gneiss of the Lesser Himalaya. The ratio of gneiss is greater than schist in general can be seen in the project area. Structurally, the Barun Thrust

(BT) or Main Central Thrust (MCT) is located in the north of the project area. The Barun Thrust is correlated to the Main Central Thrust (MCT) situated about 6 km north from the project

area. The lithostratigraphy the Lesser Himalaya of the area has been given in Figure 4-5, Figure 4-6 and

Table 4-2. The augen gneiss of the Lesser Himalaya is evolved due to metamorphism of the granite

of early Paleozoic. So, augen gneiss can be seen in the Lesser Himalaya.

Project Area


4-12

Table 4-2: Lithostratigraphy of lesser Himalaya, Eastern Nepal (after Hashimoto et al. 1973)

Zone Tectonic Rock Types

Tibetan Zone Tibetan-Tethys Sediment

Zone

Makalu

Granite

Limestone, Sandstone,

Shale

Basement Gneiss

Zone, Higher

Himalaya

Chamlang Migmatite

Schuppen

Barun Gneiss Zone Khumbu

Thrust

Barun I Thrust (Main Central Thrust)

Lesser Himalaya

Midland Zone

Barun Phyllite Schuppen Garnet Biotite gGeiss

Irkhua Crystalline Nappe

(Ulleri Formation)

Irkhua Thrust Garnet Gneiss and Schist

Gudel Phyllite Schuppen Gudel Thrust Phylite, Marble,

Amphibolite

Augen Gneiss Schuppen Midland

Thrsut

Biotite Gneiss

Lesser Himalaya

Midland

Authochthonous

Dudh Kosi Dome Zone Yaku Bitle

Thrust

Tumlingtar

Authochthonous Zone

Dhankuta

Thrust

Dhankuta Authochthonous

Zone

Mulghat Fault

Mulghat Authochthonous

Zone

4.7.1. Lesser Himalaya

The Lesser Himalaya Has been subdivided into the Midland authochthonous and Midland groups.

The Midlland authchthonous Group is subdivided into the Mulghat autochthonous, Dhankuta

autochthonous zone, Tumlingtar autochthonous zone, Dudh Kosi Dome zone in ascending order.

The Midland Group is subdivided into the Aguen Gneiss schuppen, Gudel Phyllite schuppen,

Irkhuwa Crystalline schuppen and Barun Phyllite schuppen zones in ascending order.

The Gudel Phyllite Schuppen is composed of slate, limestone whereas the Irkhuwa Cystalline

Nappe is composed of biotite-garnet bearing gneiss and schist. The Barun Phyllite Schuppen

contents of quartzite and mica schist.


4-13

4.7.2. Thrusts

4.7.2.1 Barun Thrust (BT) or Main Central Thrust (MCT)

The Barun Thrust extends from northeast to southwest direction and separates rocks of Irkhuwa

Crystalline Nappe in south and Barun Phyllite Schuppen in north. The Barun Thrust or Main

Central Thrust is located at about 6 km south of the project area.

Figure 4-5: Regional Geological Map of Irkhuwa Khola Area (Hashimoto et at., 1973)

Irkhu


4-14

Figure 4-6: Regional Geological Map of Irkhuwa Khola Area (Box with dark line represents the Project area, ICN – Irkhuwa Crystalling Nappe)

4.7.2.2 Arun Thrust (AT)

The thrust extends nearly in north-south direction that cuts along the elongation axis of the

Tumlingtar window.

It is considered that these thrusts have nominal effect to the project.

4.7.3. Fold and Foliation

4.7.3.1 Fold

Around the project area, regional folds are not reported and minor and micro folds can be seen.

The micro folds developed in the intercalation of quartzite and phyllite and not directly affect to

the project structures especially along the waterways alignment.

4.7.3.2 Foliation

Foliation is another most important geological structures observed in the project area.

The foliation is dipping towards southwest with amount in average 50°. There is

no any change in the orientation of the foliation plane around the project area

deviation range within 10°. It indicates that there is no any geological disturbance

Irkhu


4-15

within the project area. The trends of the foliation plane of the project area are

northeast (230° to 240°) dipping towards south (45° to 70°). The strike of the

foliation plane is southeast to northwest in direction 330° to 340° and dipping

towards south (50° S;

Figure 4-7).

4.7.3.3 Joints

Two to three sets of the joints are common in the project area but major two sets of the joint

are predominant. Densities of the joints are less in the rocks of gneiss. Major joint planes are

directed southwest (J1) and minor joints are directed towards northwest and northeast (J2 and

J3) whereas the foliation plane is directed towards northeast. Along the waterways area, the low

spaced joints directed to the southwest can be found.

More or less the tends of the joints are same entire the project area. Some of the area is covered

with superficially fractured rocks.

The proposed project area lies in the rocks of the Irkhuwa Crystalline Nappe (Hashimaoto et al.,

1973) or Ulleri Formation (DMG, 1987), Lesser Himalaya which is composed of gneiss schist.

Structurally, the Barun Thrust (BT) lies 4 km north from the headworks area. There are no

remarkable regional folds. It is expected that there will be very minimal effect of the thrust

activities in the project area.

4.7.4. Previous Studies

The geology of eastern Nepal in the northern part remained less known for a long time, and even

today it is the least studied part of Nepal. Gansser (1964) in his compiled geological map of the

Himalaya shows the major lithological units of Kumaon to continue into Nepal. Hagen (1969)

worked in the fifties in this area and gave a somewhat different tectonic interpretation than that

of Gansser (1964). Some pioneer work has been done by Hashimoto et al (1973). In this report,

the study follows the report of Hashimoto et al (1973).


4-16

Figure 4-7: Structural Map of the Project Area

4.8. Geological and Enginnering Geological Condition of the project area

Based on the field visit, surface geological map and engineering geological map of the project

area has been prepared (Volume II: Drawings no UIKHP-GM-01 to UIKHP-GM-15) in 1:1,000 scale.

The project layout map also represents engineering geological map of the project area presented

in Volume II Drawings of the report. The project area is composed of rock from the Irkhuwa

Crystalline Nappe or Ulleri Formation (Lesser Himalaya), Eastern Nepal. Generally, the rocks are

dipping towards southwest direction in the project area. Three sets of the joints are very rare

found in the exposed rocks of the project area but two sets of joints are prominent but random

joints are also seen on surface. Density of the joints is low in the rock mass. They are rough to

planar and stepped. These data have also been used in rock mass classification for waterways

alignment. More than 50 discontinuities were measured during the field visit. The dip directions

of foliation plane range from 2300 to 2400 and dipping towards north (500 to 700). The project

area superficially covered with old alluvial and colluvial deposits in the powerhouse as well as

tunnel alignment area which is expected more than 5 m in thickness. Details of discontinuities

present in the rock mass were measured for the analysis of slope and waterways stability.

4.8.1. Diversion Weir Axis Area

The proposed Diversion Weir Axis area of Phunglung Khola (Volume II: Drawings no UIKHP-GM-

01 & UIKHP-GM-02) is located about 200 m upstream from the confluence between the


4-17

Phunglung Khola and weir axis at Phedi Khola about 600 m upstream from the confluence

between the Phunglung Khola and Phedi Khola at Dobhan village. The area belongs to

geologically the rocks of the Irkhuwa Crystalline Nappe, Lesser Himalaya. The rock unit is

composed of thick bedded, grey, coarse-grained, two mica bearing gneiss and contents of

partings of highly foliated schist. The bedrocks of the Irkhuwa Crystalline Nappe are well exposed

on the right bank (gentle sloped cliff) of the Irkhuwa Khola. But, the left bank comprises old and

recent alluvial deposits. The deposits are composed of thick boulder beds (> 90% boulders of

gneiss and schist).

Thickness of individual beds of gneiss range from 2 to 3 m whereas schist has less than 0.2 m in

thickness. The exposed rocks are moderately weathered on the right bank of the Irkhuwa Khola

at the proposed area. More than 10 m thick recent and old alluvial deposits are seen on the left

bank of the Irkhuwa Khola. Land use pattern of the proposed area is barren to forest on right

bank whereas on the left bank has cultivated land.

4.8.2. Desander Basin and Approach Waterways Alignment Area

The proposed desander basin and approach waterway alignment follow the right bank of

Irkhuwa Khola, located at Dobhan village 200 m downstream from proposed headworks area.

Geologically, the proposed area belongs to the rocks of the Irkhuwa Crystalline Nappe. But,

superficially the area is covered by thick residual soil and alluvial deposits. Thickness of the

boulder mixed soil is considered as more than 10 m. Uphill side of the proposed desander basin

is covered by colluvial deposits on the bedrocks of gneiss. Hill slope is less than 30 degree. Uphill

side is covered by forest and barren land.

The approach waterway alignment which connects the desander basin and the intake or

headworks area passes through the boulder mixed soil of the recent alluvial deposits as well as

bedrocks of the gneiss. The rocks of the Irkhuwa Crystalline Nappe are exposed on the hill slope

along the approach waterway alignment. The exposed rocks are characterized by thick bedded,

coarse-grained, two mica bearing gneiss with thinly foliated schist. Bedrocks are well exposed on

the left bank also, hill slope of the Irkhuwa Khola. Thickness of individual beds of the gneiss

ranges from 2 to 5 m.


4-18

4.8.3. Inlet Portal Area

The proposed portal inlet area follows the right bank of Irkhuwa Khola, at about 200 m

downstream from the proposed weir axis area. Geologically, the proposed area belongs to the

rocks of the Irkhuwa Crystalline Nappe. But, superficially the area is covered by bedrocks of fresh

to slightly weathered gneiss. The rocks of the Irkhuwa Crystalline Nappe are exposed on the hill

slope. The exposed rocks are characterized by thick bedded, coarse-grained, two mica bearing

gneiss. Bedrocks are well exposed on the right bank, hill slope of the Irkhuwa Khola. Thickness

of beds range from 2 to 3 m.

4.8.4. Tunnel Alignment Area

The waterways alignment as tunnel alignment follows the right bank of Irkhuwa Khola.

Geologically, the alignment passes in the rocks of the Irkhuwa Crystalline Nappe (Volume II:

Drawings no UIKHP-GM-03 to UIKHP-GM-14). The litho unit is composed of thick bedded, coarse-

grained, two mica bearing gneiss and intercalation of schist. Thickness of the individual beds are

more than 2 m are found in the tunnel alignment. Thick beds colluvial and residual soil deposits

are exposed along the proposed headrace tunnel alignment on the bedrocks of the Irkhuwa

Crystalline Nappe. The tunnel alignment crosses a major crossing the Gurung Khola. The tunnel

alignment superficially covered by forest as land use pattern.

4.8.5. Surge Tank and Penstock Alignment Area

The proposed area for the surge tank and penstock alignment is located on the right bank of the

Irkhuwa Khola. The proposed surge tank is located just opposite to Gothe Bazaar village.

Geologically, the proposed structures lie on the rocks of the Irkhuwa Crystalline Nappe (Volume

II: Drawings no UIKHP-GM-04 & UIKHP-GM-15). The Irkhuwa Crystalline Nappe is comprised of

thick bedded, coarse-grained, grey gneiss and schist. Thin to thick beds are seen along the

proposed surge tank and penstock alignment area. But the proposed structural area including

penstock alignment is covered by thick colluvial along with residual soil deposits. Thickness of

the bedrocks are more than 2 m.

The area is covered with colluvial and residual soil deposits. Thickness of the soil along the

penstock alignment is more than 5 m along the penstock alignment. Landuse pattern of the area

is cultivated land and forest along the penstock alignment whereas the surge tank area has

covered by barren to forest area.


4-19

4.8.6. Powerhouse and Tailrace Area

The powerhouse area is located on the right bank of Irkhuwa Khola about 100 m upstream from

the junction of Irkhuwa Khola and Thado Khola at Gothe Bazaar (Volume II: Drawings no UIKHP-

GM-15). The proposed structure lies on the rocks of the Irkhuwa Crystalline Nappe. The Irkhuwa

Crystalline Nappe is comprised of thick bedded, coarse-grained, grey gneisses and schist.

Superficially the proposed area is covered by thick alluvial deposits. Thickness of the alluvial

deposits is considered as more than 10 m. The alluvial deposits are composed of loose boulder

mixed soil.

4.8.7. Geomorphology

Irkhuwa Khola is one of the minor tributaries of the Arun River (a major tributary of the Saptkoshi

River basin) in the eastern Nepal and originates from the Makalu Himalayan Range. The

catchment area of the river is characterized by very rugged topography, which was resulted by

the upliftment of the Himalayan range. It is mainly composed of sharp crested ridges, medium

to very steep slopes and very little spaces are left for gently sloping lowlands in the valley.

Majority of catchment lies in the slopes (90%), lowlands less than 10 % and ridge areas are less

than here are a number of old as well as active landslides, within their catchments because of

thrust activities.

The headworks area has very gentle slope on both banks of the Ikhuwa Khola. The waterways

alignment has gentle slope and fore bay and penstock alignment area as well as powerhouse has

gentle slope.

4.9. Geotechnical Studies of the Project Area

Rock mass classification was carried out based on the NGI “Q” and CSIR “RMR” system. Based on

the computed “Q” and “RMR” values the rock mass could be classified into very good to

excellent, good, fair to good, poor and very poor, extremely poor and exceptionally poor rock

zones. Classified rock masses are given in Table 4-3. The calculated values can be used for rock

support in headrace tunnel alignment as well as the underground structures of the project

components.


4-20

4.9.1. Gneiss/ Schist

Coarse-grained, fresh to slightly weathered in nature and seen in the headwork area as well as

along the proposed Hydraulic area. The beds are thick and consist of feldspar, quartzite and mica.

The gneiss belongs to the rocks of Irkhuwa Crystalline Nappe or Ulleri Formation, Lesser

Himalaya. Generally, the rocks of the gneiss and schist are seen in the headworks area as well as

in the tunnel alignment area also.

4.9.2. Colluvial and Residual Soil Deposits

The colluvial deposits are the loose slope debris deposit of the eroded mass and landslide

materials as well as accumulated weathered rock fragments. The clasts are angular to sub-

angular gravel, pebble, cobble and boulder of gneisses. The boulders are more than 5 m in

diameters. Residual soil is composed of silty sands and sands, originated from the weathering of

the parent rock gneiss. The area with residual soil dominance has gentle slope.

4.9.3. Alluvial Deposits of Recent River Terrace

It is unconsolidated low-level flood plain terrace deposits are found along the Irkhuwa Khola.

The sediments are of different sizes ranging from sands to boulder of mainly gneiss and other

derived from the Higher Himalayan range as well as from the Irkhuwa Crystalline Nappe. The

thicknesses of deposits above the bedrock are more than 4 m. Thick alluvial deposits are found

in the headworks area. The alluvial deposits are composed of boulder beds of gneiss. Diameter

of the boulders ranges from 2 to 5 m. The detailed surface geological and engineering geological

condition is described in below in Table 4-3.

Table 4-3: Rock Mass Classification

44ln9 QRMR (Bieniawaski, 1989); 50log15 QRMR (Barton, 1995)

Descriptions Range of Q-values Range of RMR-values

Rock Class Quality descriptions Minimum Maximum Minimum Maximum

Class I Very good to excellent 100 1000 85 100

Class II Good 10 100 65 85

Class III Fair to good 4 10 56 65

Class IV Poor 1 4 44 56

Class V Very poor 0.1 1 35 44

Class VI Extremely poor 0.01 0.1 20 35

Class VII Exceptionally poor 0.001 0.01 5 20


4-21

4.9.4. Description of Proposed Structures

4.9.4.1 Diversion Weir Axis and Intake Area

The proposed diversion weir site and intake area belongs to the rocks of the Irkhuwa Crystalline

Nappe and the area is comprised of thick gneiss and parting of the schist. On right bank of the

Irkhuwa Khola, the bedrock of gneiss which is characterized by thick bedded, long spacing and

fresh nature. Thickness of the bed ranges from 2 to 3 m and represents blocky nature. It is

considered that the rock has the RQD values of about 85%. Along the riverbed thick alluvial

deposits can be seen. The alluvial deposits are composed of boulder of gneiss. 30% boulder, 60%

cobble and 10% fine materials are found. The area is presently covered by forest and barren land.

The diversion weir axis area of the proposed Upper Irkhuwa Khola Hydropower Project is located

superficially on thick alluvial deposits and intake area falls on the bedrocks. The hill slope starts

abruptly with an average slope of 30 degrees on the right bank and increasing of up to 40 degrees

in the upper hill slope on right bank whereas the gradient is abruptly change into 10 to 15 at

lower part of the proposed area on the left bank. More than 50 discontinuities were measured

in the proposed intake and weir axis area. The bedrock exposed at the site has average foliation

attitude on right bank (Dip Direction/Dip Amount) of 221/74 and one major (084/53) and

other minor joint systems (142/44) on right bank are described in Table 4-4. The counter

densities of the measured discontinuities are shown in Figure 4-8.

Table 4-4: Attitudes of Rock Mass (Dip Direction / Dip Amount)

Locations

Natural Hill

Slope Foliation Joint (J1) Joint (J2) Joint (J3)

Strike and Dip

amount

Diversion Weir Axis Area

Right Bank 334/35 221/74 083/54 030/64 311-131/74S

Desander Basin Area 113/43 219/69 143/43 091/43 309-129/43S

Inlet Portal Area

Right Bank 113/43 219/69 143/43 091/43 309-129/43S

Tunnel Alignment Area

Ch. 0+600- Ch 0+980 - 215/43 322/24 125/79 045/08 305-125/43S

Ch. 0+980-Ch. 1+200 222/40 130/79 275/75 042/49 312-132/40S


4-22

Ch. 1+200-Ch. 1+600 231/28 223/78 143/44 041/44 321-141/28S

Ch. 1+600- Ch. 2+930 284/44 125/45 067/74 014-194/44N

Ch. 2+930-Ch.3+300 302/18 140/76 209/64 350/65 032-202/18N

Ch. 3+300-Ch. 3+800 292/43 312/45 105/24 235/50 022-202/43N

Surge Tank and Penstock Alignment Area

Right Bank 337/60 247/44 073/80 170/53 337-157/44S

Powerhouse and Tailrace Area

Right Bank 329/38 257/35 173/35 058/74 347-167/36S

Rock Classification

Geomechanical classification for jointed rock mass of the headworks in weir axis area using CSIR

classification was carried out based on the detailed surface discontinuity. Most of the Rock Mass

Rating (RMR) of the headwork area falls in the range of 57 and it indicates that the rock mass of

headworks site is categorized as a Class III type, which is defined as the fair to good Rock (Table

4-5). The calculation of the rock mass is based only on the vision of the surface geology.

Table 4-5: Rock Mass Rating (RMR) of the Project Area

Weathering and Strength

Rock mass in the intake and weir axis area on the right bank is fresh to slightly weathered on

surface (Table 4-6) on surface but hope to find the fresh and intact rock at shallow depth.

Generally, the rocks along riverbank are fresh rock and slightly to moderately weathered at

higher hill slope. At some places of the proposed structure area intercalations of gneiss and schist

are found. Gneiss is strong and competent rocks.

Slope Stability Condition

To clarify the slope stability in the rock mass, some remarkable discontinuities were measured

in the field visit. Because of the lack of the exposure along the riverbed only a few area is possible


4-23

to measure the representative discontinuities in this report. The slope stability assessment

analysis of the right bank hill slope was carried out on the basis of aerial photos interpretation

and geological observations. An analysis of foliations to determine the stability of the rock mass

due to the presence and orientations of the foliations in the rock mass at the weir axis site was

done using Lower Hemisphere Projection of the foliation planes in Schmidt’s equal area net. The

wedges formed by the planes (joints and foliation) were then analyzed with respect to the hill

slope surface using computer software Dips 5.1. The dipping of the foliation plane is favorable

to the natural hill slope and the relation between them is oblique so less possibility to occur

failure. The wedge formed by the intersection of the joints (J1 and F) seems to be stable because

of the wedge formed in opposite direction to the natural hill slope. Thickness of colluvial deposits

in the hill surface exceeds 1 m at most places. The slope stability condition of the rock mass is

presented in Figure 4-8.

.

Figure 4-8: Stereographic Projection of the Rock Mass at Right Bank of Weir Axis Area


4-24

4.9.4.2 Desander Basin and Approach Waterway Alignment

The basin is located on the right bank of the Irkhuwa Khola about 200 m downstream from the

weir axis area at Dobhan and geologically belongs to the rocks of the Irkhuwa Crystalline Nappe.

This litho unit is comprised of thick bedded, grey, coarse-grained gneiss and intercalated with

foliated schist. The bedrocks are exposed on the hill side as well as along the left bank of Irkhuwa

Khola. Thickness of the gneiss ranges from 0.5 to 3 m. The proposed area is covered by bushes

and cultivated land. The topography of the hill slope on the left bank of the Irkhuwa Khola is

gentle. The RQD value is assumed to be more than 90%. Density of the joints in the rocks is found

very less. The bedrocks show long spacing same as in the rock exposed in the weir axis. Thick

colluvial/alluvial deposits can be found on the bedrock (boulder 50%, cobble 10% and fine 45%).

Thickness of colluvial/alluvial deposits are more than 10 m. The deposits are composed of gneiss

and schist.

The proposed is located on the right bank of the Irkhuwa Khola and faces 113/43. The hill slope

of proposed desander basin area is steep but proposed area has gentle topography. The exposed

rock beds are competent and are favourably dipping against slope face direction. The attitude of

the bedrock is 219/69 (dip/direction dip). One major (143/43) and other minor joint sets

(091/43) are observed in the exposed area. The exposed rock is fresh to slightly weathered

with average joint spacing more than 5 m. The joint surfaces are rough and have some silty sand

fillings in the exposed areas. The measured discontinuities are given in Table 4-4.

Table 4-6: Geochemcial Parameters of Rock Mass of the Project Area


4-25

Table 4-7: Stability Condition of the Project Area

Location HS and F F and J1 F and J2 J1 and J2 Remarks

Powerhouse and Tailrace Area

Powerhou

se

Stable Unstable Stable Stable

Surge Tank and Vertical Shaft Area

Surge

tank and

c’

Stable Stable Highly

unstable

Stable

Tunnel Alignment Area

Ch. 0+600- Ch 0+980 Generally stable wedge formed by J1 and F is unstable

Ch. 0+980-Ch. 1+200 Generally stable wedge formed by F and J1 is critical

Ch. 1+200-Ch. 1+600 Generally stable, wedge formed by J2 and J1, F and J1 are unstable

Ch. 1+600- Ch. 2+930 Generally stable, wedge formed by J2 and J1 is unstable

Ch. 2+930-Ch.3+300 Generally stable, wedge formed by J2 and J1 and F are unstable

Ch. 3+300-Ch. 3+800 Generally stable, wedge formed by J2 and J1 and F are unstable

Desander Basin/Portal Inlet Area

Right

Bank

Stable Stable Less

stable

Stable

HS-Hill Slope; F-Foliation; J-Joint; PL-Plane Failure; TP-Toppling Failure


Rock mass is fresh to slightly weathered and hope to find the fresh and intact rocks at shallow

depth (Table 4-6). The rock mass in the area is strong and competent.


The proposed area for the basin area seems to be unstable. Analysis has been done with the

frictional angle of the rock gneiss. Most of the wedges are unstable (Figure 4-9). The wedge

formed by intersection of the F and Joint (J1) as well as J1 and J2 are stable; there is less

possibility of occurring failure. But there is high possibility of occurring toppling failures.

Trimming of the slope is the best option.


4-26

Figure 4-9: Stereographic Projection of the rockmass of the Approach Canal Alignment Area

4.9.4.3 Inlet Portal Area

This structure is proposed on the right bank of the Irkhuwa Khola and belongs to the rocks of the

Irkhuwa Crystalline Nappe about 200 m downstream from the desandser basin. This litho unit is

comprised of thick bedded, grey, coarse-grained gneiss and intercalated with foliated schist. The

bedrocks are exposed on the hill side as well as along the left bank of Irkhuwa Khola. Thickness

of the gneiss ranges from 1 to 3 m. The proposed area is covered by forest and barren land. The

topography of the hill slope on the left bank of the Irkhuwa Khola is steep. The RQD value is

assumed to be more than 80%. Density of the joints in the rocks is found comparatively greater

than the weir axis area. The bedrocks show moderate spacing.

The proposed is located on the left bank of the Irkhuwa Khola and faces 113/43. The exposed

rock beds are competent and are favourably dipping against slope face direction. The attitude of


4-27

the bedrock is 219/69 (dip/direction dip). One major (143/43) and two other minor joint sets

(091/43) are observed in the exposed area. The exposed rock is fresh with average joint spacing

more than 1 m. The joint surfaces are rough and have some silty sand fillings in the exposed

areas. The measured discontinuities are shown in Figure 4-10 and Table 4-4.

Rock Classification

Geomechanical classification for jointed rock mass of the portal inlet area using CSIR



inlet portal site is categorized as a Class III type, which is defined as the good to fair Rock (Table

6.3). But it is also hoped that the fresh and less fractured rocks can be found at shallow depth.

The calculation of the rock mass is based only on the vision of the surface geology. Superficially,

the rocks are moderately fractured and moderately spacing. Situation shall be changed when

the drifting of the weir axis shall be done. .


Rock mass is fresh and hope to find the fresh and intact rocks (Table 4-6). The rock mass in the

area is strong and competent.


The proposed area for the basin area seems to be stable on hill slope. There is no any types of

the failure. Analysis has been done with relation between the hill slope and dip direction of the

foliation plane. Most of the wedges are unstable (Figure 4-10). The wedge formed by intersection

of the F and Joint (J1) as well as J1 and J2 are critical; there is possibility of occurring failure. The

relation of the hill slope and foliation plane is good.


4-28

Figure 4-10: Stereographic Project of the Inlet Portal Area

4.9.4.4 Tunnel Alignment Area

The conveyance of water is proposed to be done by underground waterways. This has been

proposed considering the following aspects: a) the morphological conditions of the alignment

route, b) surface slope stability conditions, c) rock mass property observations, and d)

economical aspects.

The proposed tunnel alignment is passes on the rocks of the Irkhuwa Crystalline Nappe and

follows the right bank of the Irkhuwa Khola. On surface thick colluvial and residual soil deposits

can be seen. Thickness of the soil deposits along the waterways alignment is considered as more

than 10 m. Because of the mineral composition of the rock, there is chance to meet thick residual

soil deposits. Along the tunnel alignment, more than 90% length of alignment passes in the rocks

are fresh to slightly weathered and are containing of thick-bedded gneiss (0.5 to 4.0 m). The rock


4-29

mass consists of three sets of joint and show large spacing. The alignment follows on the

cultivated land (colluvial and residual soil deposits) with gentle slope.

The slope along the proposed waterways alignment is generally favourable and stable. The

foundation of the tunnel alignemnt is on the bedrock. Most of the alignment is on gneiss and

schist bedrock of the Irkhuwa Crystalline Nappe, Lesser Himalaya and is over moderate steep to

steep hill slope. The hill slope starts abruptly with an average slope of more than 60 degrees. The

attitude of foliation of the rock mass, major and minor joint sets are shown in Table 4-4. The

exposed has average joint spacing of 1 to more than 5 m (Table 4-6). The joint surfaces are rough

and steeped; and have some silty sand fillings in the exposed areas. Along the waterways

alignment some of the area has joint has wide space.

Rock Classification



Rating (RMR) of the headwork area falls in the range of 39 to 67 and it indicates that the rock

mass of tunnel alignment area is categorized as a Class II to IV types, which is defined as the good

rock to poor rocks (Table 4-5). But it is also hoped that the fresh and less fractured rocks can be

found at shallow depth.


Rock mass is fresh and hope to find the fresh and intact rocks (Table 4-6). The rock mass in the

area is strong and competent.

Table 4-8: NGI Tunnelling Index ‘Q’ values of the Tunnel Alignment Area

Assessment of Initial Support Requirement for Tunnel Alignment


4-30

Empirical Method

Empirical assessment of rock enforcement requirement for the tunnel has been empirically

assessed based on the rock mass classification and stability analysis carried out based on

assumed/extrapolated data. Once the excavation begins, the parameters used to determine the

rock mass quality must be re-evaluated continuously.

These parameters include:

Number of joints per unit volume and their orientations

Joint conditions such as tightness, loose openings and in-fill materials

Continuity of joints

Joint surface conditions such as roughness, degree of weathering and coatings.

Joint water conditions

Presence and orientation of shear zones, clay seams or loose open joints crossing the

tunnel excavation or the presence of squeezing of swelling rock

The rock strength with ratio to the major principal rock stress expected at the tunnel

periphery.

Estimated Rock Support

Rock support in the tunnel and underground cavern is provided to improve the stability and to

safeguard the opening with respect to safety of the working crew. The guiding principle of rock

support design is that it is capable to response the actual ground conditions that is encountered

in the tunnel and the safety requirement at the tunnel face is met. The calculated values of the

RMR and Q are given in the Table 4-8 and Table 4-10 by empirical Method. This requires provision

of flexible rock support methods that can be quickly adjusted to meet continuously changing

heterogeneous rock mass (Table 4-9). The best way to achieve such flexibility is the use of rock

bolts, steel fiber shotcrete, pre-injection grouting, and the use of steel ribs.

The rock support in the tunnel is normally carried out in two main stages:

The initial support, which is installed immediately after the excavation of the tunnel to

secure safe working conditions to the tunnelling crew working at tunnel face. At this

stage, the type and methods of rock support should be decided in accordance with the

quality of rock mass. More importantly, the initial support should be designed as such

that this will be converted as a part of the permanent rock support.


4-31

The permanent support, which is installed to meet long term stability requirements of

the tunnel opening that guarantees satisfactory functioning of the opening during its life

time operation. Largely the extent of permanent rock support depends on the purpose

and type of tunnels.

In general, Himalayan rock mass are influenced by the tectonic processes and as a result of this

the rock mass are highly fractured and sheared. There are also chances to meet the shear zone

a lot. Superficially the alignment area is covered by the forest and colluvial deposits so cannot

recognised. Such rock mass always demand more tunnel rock support during excavation to

safeguard immediate tunnel collapse (stability) and the safety requirement of the tunnelling

crew. Initial flexible rock support and final concrete lining as permanent support will make

projects economically unfeasible. Hence, the best approach would be to use initial rock support

as a part of permanent rock support. The applied rock support for water conveying tunnel must

be sufficient to withstand long term stability as well as should be to extent water tight. The final

concrete lining should be provisioned only in the required segments of the underground opening

with respect to stability and hydraulic requirement.

Hence, special attention has been made while designing the rock support to make underground

opening safe with respect to stability. The concept of pre-injection grouting has been introduced

to control unwanted leakage from headrace tunnel. The flexible rock support comprising steel

fibre shotcrete and systematic bolting and steel arch ribs have been provisioned to control

excessive plastic deformation (squeezing). The designed rock support class for respective rock

mass quality is given in Table 4-9.

Table 4-9: Designed Tunnel Rock Support Class and Respective Rock Support

Rock Mass Quality

Description

Rock

Support

(RS) Class

Assigned Tunnel Rock Support

Very good to

excellent

RSI 25 mm diameter 1.5 m long systematic grouted rock bolts at a

spacing of 3.0 m x 3.0 m and 10 cm thick steel fiber shotcrete

Good Rock RS II 25 mm diameter 1.5 m long systematic grouted rock bolts at a


Fair to good rock

mass

RS III 25 mm diameter 1.5 m long systematic grouted rock bolts at a


Poor rock mass RS IV 25 mm diameter 1.5 m long systematic grouted rock bolts at a

spacing of 1.3 m x 1.5 m and 20 cm thick steel fiber shotcrete.


4-32

Advance pre-injection grouting to control water inflow into the

tunnel.

Very poor rock

mass

RS V 25 mm diameter 1.5 m long systematic grouted rock bolts at a


Extremely poor

rock mass

RS VI 25mm diameter 1.5 m long systematic grouted rock bolts at a


Steel ribs at a spacing of 1 meter to control plastic

deformation. Advance pre-injection grouting is provisioned to

control water inflow into the tunnel.

Exceptionally poor

rock mass

RS VII 25 mm diameter 1.5 m long systematic grouted rock bolts at a


Steel ribs at a spacing of 1 meter to control plastic

deformation.

Table 4-10: Assigned Rock Support in respect with rockmass and Rock Support Class

Location

Rock

Mass

Class

Rock

Support

Class

Assigned rock support measures

Ch.0+600- Ch.0+980

Class II RS II

25 mm diameter 1.5 m long systematic grouted

rock bolts at a spacing of 2.0 m x 2.0 m and 10 cm

thick steel fiber shotcrete

Ch.0+980- Ch.1+200

Class IV RS IV



thick steel fiber shotcrete. Advance pre-injection

grouting to control water inflow into the tunnel.

Ch.1+200-Ch.1+600

Class III RS III




Ch.1+600- Ch.2+930 Class IV RS IV





Ch. 2+930- Ch.3+300

Class III RS III




Ch.3+300-Ch.3+800 Class IV RS IV

25 mm diameter 3 m long systematic grouted



4-33



The rock mass (Table 4-10) from Ch. 0+600 to Ch. 0+980 (0.38 km) requires the II support type

whereas of tunnel from Ch. 0+980 to 1+200 (0.22 km) requires the IV. Then, from Ch. 1+200 to

Ch. 1+600 (0.40km) needs of III support types (Table 4-9 and Table 4-10). Similarly, from Ch. 1+600

to 2+930 requires the support of IV and from Ch. 2+930-3+300 needs of support of III whereas

the last part of the tunnel requires of 3+300-3+800 requires of support types of IV (Table 4-11).

Table 4-11: Summary of the Support system of the Tunnel Alignment

Ground Water Effect along the Tunnel Alignment Area

The most critical area with respect to groundwater is the weakness zone like the thrust and fault

area. Since the weathering depth at this headrace tailrace tunnel segment is not deep can be

seen where sufficient rock cover is available. The mapping carried out at surface indicated that

the weathering depth is high and jointed rocks are prominent. So, there may affect the

groundwater problem along the tunnel alignment.

Potential Rock Squeezing along the Headrace Tunnel

The headrace tunnel passes through rocks of gneiss, augen gneiss and banded gneiss as well as

schist. Because of presence of thick bedded gneiss rocks there is less chances to occur the

squeezing in rock even there is more than sufficient coverage. Tunnelling through this rock mass

is relatively critical and special attention must be taken while tunnelling in thick schist. The rock

mass will be of weak quality and will have very low stand up time.

The headrace tunnel will be in hydrostatic condition during its operation. Since the designed rock

support in the table is not water tight, the concept of pre-injection grouting should be applied at

the required length of headrace tunnel to control possible water leakage during operation. In

Table 6.8, the rock support assigned for headrace tunnel has been presented since the ground

condition changes at different tunnel segment.


4-34


In general, the stability condition is fair to good to poor along the proposed tunnel alignment

(Figure 4-11 to Figure 4-16). The analyzed data of the discontinuities are based on the friction

angle of the rocks. The angle of friction of the rock has been considered to be 30 degrees. The

wedged formed by the intersection of the joints and foliation plane are very critical.

Figure 4-11: Stereographic Projection of the Rockmass of the waterways alignment (ch 0+620 to 0+980)


4-35



4-36



4-37



4-38



4-39


Generally, the slope stability condition is stable except some wedges formed by the joints might

be unstable. The stability condition is shown in Figure 4-11 to Figure 4-16.

4.9.4.5 Surge tank and Penstock Alignment Area

The proposed surge tank and penstock alignment area is located on thick to thin layers of the

residual soil deposits. Bedrocks are exposed in these structural areas and thick layer covered by

soils. But there is high possibility to find bedrock in shallow depth in accordance to the

orientation of the foliation plane. The deposited soil is considered to be more than 5 m,

composed of gneiss clasts and sandy silt. Presently the alignment and proposed surge tank area

is covered by cultivated land and forest.

Surge tank area is geologically located on rocks of gneiss and the area is covered by colluvial

deposits. The colluvial deposits are composed of 20% cobble and pebble and 80% fine. These


4-40

soils are derived from the weathering product of the gneiss. Topographically, the area has gentle

slope and covered presently by bushy land. Thickness of colluvial deposits are considered as

more than 40 m. The penstock alignment is passes forest and busy area. The slope of the

penstock alignment is between 30-40 degrees.

The surge tank and penstock alignment are located at on the left bank of the Irkhuwa Khola and

faces less than 50. The hill slope of surge tank face is gentle to steep. The exposed rock beds are

competent and are favourably dipping against slope face direction. The attitude of the bedrock

is 247/44 (dip direction/ dip). One major (073/80) and other minor joint set (170/53) are

observed in the exposed area. The surge tank as well as the penstock alignment passes though

intercalation of gneiss and schist, Lesser Himalaya. Ratio of the gneiss is greater than schist. The

joint surfaces are slightly to moderately altered with average joint spacing of 0.5 to 3 m. The joint

surfaces are rough and have silty clay fillings in the exposed areas. The measured discontinuities

are given in Table 6.4.

Rock Classification




headworks site is categorized as a Class III type, which is defined as the good to fair Rock (Table

6.3). But it is also hoped that the fresh and less fractured rocks can be found at shallow depth.

The calculation of the rock mass is based only on the vision of the surface geology. Superficially,

the rocks are moderately fractured and moderately spacing. Situation shall be changed when the

drifting of the weir axis shall be done.


Rock mass is fresh to slightly weathered, with some fresh to slightly weathered rock exposed.


The slope stability condition in the soil around the proposed surge tank and penstock alignment

area is found to be stable. The rocks are well exposed along the penstock alignment. But, the

collected data of the discontinuities show that there is high possibility to occur wedge failure

which might be critical (Figure 4-17).


4-41

Figure 4-17: Stereographic Projection of the Rockmass of the Surge Tank and Penstock Alignment

4.9.4.6 Powerhouse and Tailrace Area

The proposed area is covered by thick alluvial deposits and high possibility to find the bedrocks

in shallow depth. Presently, the proposed area is covered by barren on top. Thicknesses of the

alluvial deposits are considered as more than 10 m. The bedrocks are covered by alluvial

deposits. Topography of the area is nearly flat. Soil is composed of 15% boulder.


Stability condition is good in the soil exposed on the hill slope. The stability condition at

Powrhouse and Tailrace area is shown in Figure 4-18.


4-42

Figure 4-18: Stereographic Projection of the Rockmass of the Powrhouse Area

4.10. Seismicity

The seismicity deals with the preliminary investigation of maximum credible earthquake and

peak ground acceleration for an assessment of the Upper Irkhuwa Khola Hydropower Project.

The analysis is basically made by deterministic evaluation of earthquake sources in the vicinity

with the state of art consideration of attenuation for the Himalayan terrain. It should be

acknowledged that the problems of seismo-tectonic events of Himalaya are not fully understood

and the knowledge is increasing with more and more accumulation of research results and data

analysis. The study has considered the latest results of seismo-tectonic study of the Himalaya

and the vicinity. For comparison purpose, both deterministic and probabilistic assessments of

seismic hazards have been considered.


4-43

4.10.1. Seismo-tectonic Model

The Himalaya seismicity, in general, owes its origin to the continued northward movement of

Indian plate after the continental collision between Indian plate and Eurasian plate. The

magnitude, recurrence and the mechanism of continental collision depend upon the geometry

and plate velocity of Indian plate in relation to southern Tibet (Eurasian Plate). Recent results

suggest that the convergence rate is about 20 mm / year and the Indian plate is sub-horizontal

below the Sub- Himalaya and the Lesser Himalaya.

The result of micro seismic investigation, geodetic monitoring and morphotectonic study of the

Central Nepal has depicted that the more frequent medium sized earthquakes of 6 to 7

magnitude are confined either to flat decollment beneath the Lesser Himalaya or the upper part

of the middle crustal ramp. The ramp is occurring at about 15 km depth below the foothills of

the Higher Himalaya in the south of MCT surface exposures. Big events of magnitude greater

than eight are nucleated near the ramp flat transition and ruptures the whole ramp-flat system

up to the blind thrust (MBT) of the Sub-Himalaya (Pandey et. Al., 1995).

This general model worked out for the Central Nepal can be applied to other parts of the

Himalaya with the evaluation of further subsequent ramping towards more south in the Lesser

Himalaya and the associated seismicity. This structural variation along Himalayan arc is

responsible for the segmentation of potential ruptures along the arc i.e. along the longitudinal

direction.

4.10.1.1 Deterministic Assessment

Considering the above interpretation, the deterministic design earthquake can be taken as a sub-

horizontal thrust of rupture extent of about 30 km occurring at a depth of 15 km within a plan

distance of a few km, (e.g., 5 km) from the site. The width of the rupture is proposed to be about

25 km. A magnitude of 7.0 is estimated from rupture area of 750 km2 with Ms = 4.15 + log A

(Wyss, 1979). Actually there has been an earthquake of M = 7 at a distance of about 15 km from

the site in 27 May 1936. However the epicenter may be closed to the site considering the

uncertainty of location. It should be noted that a similar environment exists in the Uttarkashi

area of Garhawal Himalaya where an event of magnitude Mb 6.5, Ms 7.1 occurred in 19 October

1991. Its moment magnitude was Mw 6.8 with moment equal to (0.8- 1.8)* 10 E 19 N-m. and


4-44

the mechanism was a low angle thrust. The rupture length is reported to be about 25 km with

maximum slip of 2.5 m.

The deterministic assessment of maximum credible earthquake can be considered to be the big

earthquake rupturing the entire detachment of the Indian plate as discussed in the model and

therefore considered to be of magnitude of 8.3-8.6 like other great earthquakes of the Himalaya.

4.10.2. Horizontal Acceleration

4.10.2.1 Deterministic Approach

Evaluation of peak ground acceleration is carried out by applying the mostly used formula of

McGuire (1968), Katayama (1975), Oliveira (1984) and Kawashima (1984) for the above

earthquakes concluded deterministically from seismo-tectonic models.

Log A = 3.090 + 0.347 M -2 lag (R + 25) (C. Oliveira)

Log A = 2.308 + 0.411 M- 1.637lag-(R + 30) (T. Katayama)

Log A = 2.674 +0.278 M – 1.30 1 log (R + 25) (R. K. McGuire)

A = 1.006* 10E (0.216*M)*(R+30) E-l.218 (Kawashima)

R = hypo central distance in 4-44picenter

The recorded peak acceleration data in Uttarkashi earthquake of Ms = 7.1 of 1991 is 0.219 at a

distance of about 28 km. from the 4-44picenter. Katayama’s relation gives an estimate of 0.20g;

Kawashima’s estimate is 0.23g while McGuire’s relation estimates as 0.24g. Oliveira’s relation

underestimates the acceleration.

4.10.2.2 Probabilistic Approach

Preliminary seismic hazard assessment of the country using Gumbel’s third asymptotic extremes

with the instrumental seismicity database of ISC is carried out by Bajracharya (1994) for different

return periods 50, 100, 200 and 300 years. Attenuation model with mean value of “McGuire and

Oliveira” (see above) is used for horizontal acceleration. Figure 4-19 and Figure 4-20 shows the

seismic hazard and the epicenters of the earthquake in Nepal Himalaya and related to the Project

area.

Return period (years) Peak horizontal acceleration (g)


4-45

50 0.10

100 0.15

200 0.20

300 0.25

4.10.2.3 Recurrence Period

The best estimate of ‘b’ value for the Project area is 0.84 as shown by the analysis of micro

seismic events. The 1991 event of Uttarkashi is considered by many investigators to be the

repetition of 1833 event, which gives a basis for a recurrence of 158 years for 7.1 magnitude

event in similar geological setting. Moreover the observed slip of about 2.5m in Uttarkashi

earthquake also is consistent with 178 years of recurrence considering 70% contribution of 20

mm/year plate convergence rate to seismic strain.

The design earthquake for the Project is consistent with an Ms = 7.0 earthquake, the

4-45picenter of which is located within 5 km from the project site and at a depth of 15

km. The event is similar to Uttarkashi event of Garhwal Himalaya of Magnitude 7.1 which

occurred in 20 October 1991.

Estimate of peak ground acceleration due to the event at the Project site is 0.10-0.15g.

This value is based on the return period of the big earthquake and also the west central

part of the Nepal Himalaya is seismic gap area.


4-46

Figure 4-19: Epicenter of the Earthquke in Nepal Himalaya

Figure 4-20: Probabilistic Seismic Hazard Assessment Map of the Nepal Himalaya


4-47

Figure 4-21: Seismic Zonation Map of the Nepal Himalaya

The proposed area falls in the seismic Zonation 2 of the Nepal Himalaya.

4.10.3. Historical Seismic Activity

The Nepal Himalaya has experienced several large earthquakes over the past centuries. The

earthquakes of larger magnitudes that have occurred in Nepal Himalaya imalayaHhare

summarized below in Table 4-12.

Table 4-12: Larger Magnitude of Earthquake occurred in Nepal Himalaya

S. N. Location of Earthquake Year Magnitudes

1 Udayapur, Eastern Nepal 1988 6.6

2 Chainpur, Eastern Nepal 1934 8.3

3 Dolakha, Central Nepal 1934 8.0

4 Sindhupalchowk, Central Nepal 1833 8.0

5 Kaski, Central Nepal 1954 6.4

6 Myagdi, Central Nepal 1936 7.0

7 Bajhang, Far Central Nepal 1980 6.5

8 Dharchula, Far Central Nepal 1966 6.1



11 Gorkha, Central Nepal 2015 7.9


4-48

S. N. Location of Earthquake Year Magnitudes

12 Dolkha, Central Nepal 2015 6.9

4.10.4. Earthquake Catalogue

The National Building Code Development Project (BCDP, 1994) has developed an earthquake

catalogue using earthquake data catalogues of the US Geological Survey, The National

Earthquake Information Center (NEIC), National Oceanic and Atmospheric Administration and

National Geological Data Center (NGDC). The complete earthquake catalogue for the magnitudes

M 4.5 and greater is given in Table 4-13.

Table 4-13: Instrumentally Recorded Earthquake

S. N. Magnitudes Catalogue Year

1 M 6.0 and greater than M 6.0 Catalogue complete for the period 1911 to 1992

2 M 5.5 and greater than M 5.5 Catalogue complete for the period 1925 to 1992

3 M 5.9 and greater than M 5.9 Catalogue complete for the period early 1960 to 1992

4 M 4.5 and greater than M 4.5 Catalogue complete for the period late 1970 to 1980s

The largest event reported in the catalogue is the magnitude 8.3 Bihar–Nepal earthquake

(Chainpur), which appears to have occurred in 1934.

Several seismicity studies have been carried out for the various projects in the country during

the engineering design phase and seismic design coefficients have been derived for the project.

There are several method to convert the maximum acceleration of the earthquake motion into

the design seismic coefficient. Generally three methods are commonly used to establish the

seismic coefficient. These are:

The Simplest Method

The Empirical Method

The Dynamic Analysis Method using Dynamic Model

The effective design seismic coefficient is determined by using the simplest method, the

following equation:

Aeff=R*Amax/980

Where, Aeff is effective design seismic coefficient


4-49

R=Reduction factor (empirical value R=0.50-0.65).

The result obtained from this method is found to be similar in the recent studies carried out by

using the dynamic analysis and the static analysis. Therefore, this method is considered to be the

most common method to establish the design seismic coefficient at present.

The third method is the Dynamic Analysis Method using the dynamic model. This method is

considered to be te most reasonable method at present. However, to apply the this method

parameters like the design input motion, the soil structure model, the properties of the rock

materials have to be known, and therefore, it means that a detailed study is required to use this

method. Therefore, the Empirical Method is considered to be the best to establish the design

seismic coefficient for this level of the study.

A project specific seismicity study has already carried out for the Budhigandaki Hydropower

Project and Middle Marshyangdi Hydropower Project, and recommended design seismic

coefficient for the probable earthquake of VIII intensity MM. The Budhigandaki and Marshyangdi

Hydropower Project are located in different Himalayan terrain than the present project area.

The project area is located about 500 km aerial distance from the Budhigandaki Hydropower

Project. The area is about 6 km south from the Barun Thrust. So, the design seismic coefficient

for the Irkhuwa Khola Hydropower Project has been derived on the basis of the above empirical

method.

The evaluation of seismic coefficient for the Irkhuwa Khola Hydropower Project was based on

both the Nepalese and Indian Standard. The activation of the Barun Thrust (equivalent to Main

Central Thrust) is passive because frequencies of the landslides are very low so the activation of

the major thrust like Barun Thrust is considered as low. The Barun Thrust is about 10 km north

from the project area.

4.10.5. Nepalese Standard

In order to determine the seismic coefficient a seismic design code for Nepal has been prepared.

The country is derived into the three seismic zones based on allowable bearing capacity of three

types of the soil formation. The proposed Irkhuwa Khola Hydropower Project lies in the seismic

zone 2 of the Nepal Himalaya. The soil of the foundation at the dam site belongs to average soil

type is quartzite. Therefore, the basic horizontal seismic coefficient is considered to be 0.50. By


4-50

using the above empirical method, the effective design coefficient according to the seismic

design code of Nepal is given by the equation:

Aeff = R*Amax/980

Where, Aeff is effective design seismic coefficient

R = Reduction factor (empirical value R=0.50-0.65)

For the minimum acceleration of 250 gal (Figure 4-21 ), reduction factor of 0.50 the calculated

effective design seismic coefficient is approximately 0.13.

For the maximum acceleration of 300 gal (Figure 4-20 and Figure 4-21), reduction factor of 0.50

the calculated effective design seismic coefficient is approximately 0.15.

Hence, the design horizontal seismic coefficient ranges from 0.13 to 0.15 (calculated values).

Based on above results the design seismic coefficient for the Project can be taken in the range

of 0.13 to 0.15 which is more or less same value represented from the return period of the

earthquake. If the structures fall on the different types of the soil (residual, colluvial and alluvial

soil), the recommended values of the PGA can be increased by 20%.


4-51

Figure 4-22: Seismic Risk Map of India

4.10.6. Indian Standard

In order to design horizontal coefficient, a seismic risk map for India has been prepared. The map

is published in the Indian Criteria for Earthquake Resistant Design of the structures. The country

is divided into five seismic risk zones in the India (Figure 4-22) Standard. When the seismic risk

map of Nepal is compared with the Indian map it can be concluded that the seismic rick zone 2

of the Nepal is equivalent to the forth seismic risk zone of the India (zone IV). Therefore, it can

be considered the the proposed project can be considered located in the seismic zone 4 of India.

The horizontal seismic coefficient (αo) can be taken as 0.05.

The design horizontal seismic coefficient in the Indian Standard is defined by the equation:

αh- β * l * α0


4-52

Where, α0 = Design Horizontal seismic coefficient

β = Soil foundation factor (1 for dam)

l = Importance factor (4 for dam)

α0 = Basic horizontal seismic coefficient

Therefore, the design seismic coefficient for the proposed HEP is 0.15 according to Indian

Standard.

By comparing all above evaluations and the recommended seismic coefficients, the design

horizontal seismic coefficient for Irkhuwa Khola Hydropower Project can be taken as 0.15 for

present level of the study. However, this value is to be checked by carrying out a detailed project

specific seismicity study using dynamic analysis with model the detailed engineering study phase.

4.10.7. Seismic Zoning

The Seismic Hazard Mapping and Risk Assessment component of the NBCDP carried out detailed

analysis of the earth activity and the tectonic structure of Nepal, and had identified groups of

earthquakes with major tectonic features leading to the identification of seismic zones of

assumed uniform seismicity. The three seismic zones thus identified in Nepal are shown in Figure

4-22.

4.10.7.1 Seismic Design Acceleration Coefficient

On the basis of the MHSP studies on Seismic Hazard Assessment and the derivation of the basic

design earthquake accelerations, and on the basis of the earthquake design coefficient used in

other major hydroelectric projects in Nepal, e.g. the Kali Gandaki ”A” Hydroelectric Project and

the Arun-III Hydroelectric Project, the following earthquake coefficients were recommended and

used in the design of major and minor structures of the LIVHEP are as given in Table 4-14.

Table 4-14: Design Earthquake Acceleration Coefficients

S. N. Structure Basic Horizontal Acceleration

Coefficient (αH)

Vertical Acceleration

Coefficient (αv)

1 Major Structure 0.25 67% of(αH)

2 Minor Structure 0.20 67% of(αH)


4-53

The seismic coefficients based on deterministic approach and probabilistic approaches for the

different projects in Nepal Himalaya are given in Table 4-15.

Table 4-15: Recommended Seismic Coefficient for Various Projects

Project Name Study Agency Recommended Seismic

coefficient

Arun-3 JICA 0.12g

Upper Arun MKE, Lahmeyer, TEPSCO, NEPECON 0.12g

Tamor-Mewa MHSP, CIWEC 0.15-0.25g

Marsyangdi KOIKA, Hyundai Engineering Co. Korea 0.15g

Middle Marshyangdi Lahmeyer International, METCON, Nepal

Consultant, Shah Consult

0.10-0.16g

Lower Modi Water Resource Consult (WRC) 0.25g

Kabeli-A Nepal Consult, Hydro Engineering Service

(HES)

0.25g

The historic earthquake catalog of the far western Nepal and adjoining area shows occurrence

of magnitude 6 Richter scale occurred in Chainpur, Bajhang in 1980 at 30 km south east from

Project area. The Peak Ground Acceleration (PGA) value of this earthquake at the project area

from Young’s relation (Young et al., 1997) is 0.1079g.

Thus, from the above discussion and the case of histories and relation to the Indian standard and

the using empirical method the seismic coefficient for the proposed Irkhuwa Khola Hydropower

Project is recommended as 0.15g. The report prepared by JICA has calculated the seismic

coefficient values of 0.12g in the Upper Arun-3 Hydroelectric Project and in the Upper Arun HEP

by MKE, Lahmeyer, TEPSCO, NEPECON. The both areas are very near to the proposed Irkhuwa

Khola HEP.


4-54

4.11. Construction Materials Survey and Tests

A construction material investigation was conducted in the vicinity of the headwork and

powerhouse sites along the Irkhuwa Khola as well as along the Arun River in the project area.

The investigation is focused on locating prospective borrows areas of non-cohesive materials,

which are to be used mainly as an ingredient of concrete. The prospective borrow sites were

identified as sources of coarse aggregates.

The construction material survey was carried out for the following purposes:

Identification of the location, estimation of quantity of sand and other possible

construction material in and around the construction site.

Site identification and determination of relevant materials available along riverbeds that

can be used as concrete aggregates.

4.11.1. Borrow Area

The field investigation comprises of test pitting, sampling in the proposed area and study and

collection of river bed materials to determine their suitability as concrete aggregates from the

Irkhuwa Khola and Arun River sections. The borrow area is located along the riverbed.

In total two test pits were excavated to collect representative samples for determination of the

different material resources from the Irkhuwa Khola and Arun River. The activity includes manual

excavation of pits at the headworks site, nearby powerhouse site. On the basis of the site

investigation; the sources of different construction materials are described in the following

headings.

4.11.2. Coarse and Fine Aggregates

The Irkhuwa Khola is the high gradient, steep sided river in the project area. Gravels and boulders

are the dominant materials available in the Irkhuwa Khola. Boulders, gravels and very little

quantity of sand are available on the Irkhuwa Khola and Arun River riverbed and river terraces.

The river terrace consists of sun-angular to well rounded sandy gravels with some boulders. The

composition of gravels and boulders available in the Irkhuwa Khola and Arun River are quartzite,

gneiss and schist. The percentage of boulder materials is 60-70%, that of gravels is 20-30% and

fines up to 10%. These construction materials are available within short haulage distance. Since

sufficient amount of coarse materials are available around the project areas like boulders and


4-55

gravels. But sand size materials are not available in sufficient quantity. Sands can be extracted

either from the Arun River or crushing of the gneiss excavation from the waterways. For these

sand size materials, crushers should be installed in the suitable sites.

The requisite quantities of construction material like boulders, cobble, gravel and sand are

generally available in and around the project. Point bar deposits of the Irkhuwa Khola and Arun

River and excavated materials from the waterways alignment are the main source of

construction material because the alignment passes through the highly competent rocks. These

deposits predominantly consist of gneiss and schist boulder, cobble and gravel including some

quartzite. The boulder, gravel and sand deposits in the point bars in and around the powerhouse

site along the Arun River can be used as construction material. Crushing of the gneiss is best

option for the materials. Sands are found as pocket area along the riverbed as well as old alluvial

deposited area and huge quantity of the sands area not available along the river valley because

the river has high gradient so sands wash out.

The location as well as the expected volume and composition and list of the laboratory tests the

materials are presented in Table 4-16.

Table 4-16: Volume and Location of the Construction Materials

S

N

Location Percentage

of clasts

Volume

(m3)

Composition Stability

condition

Source of

sediments

Land Use

1 Irkhuwa

Khola#

Boulder-

60%,

Cobble and

pebble

30%,

sands-10%

200x10x5 Gneiss (60%),

quartzite

(20%), schist

(10%) and

limestone 10%

Stable River bed Barren

2 Arun

River#

Boulder-

40%,

Cobble and

pebble

50%,

sands-10%

200x15x5 Gneiss (60%),

quartzite

(20%), schist

(10%) and

limestone 10%

Stable River bed Barren

3 Waterways

Alignment#

Gneiss Unlimited Gneiss 100% Stable Terrace/waterways

# Sample not collected


4-56

4.11.3. Laboratory Test of the Construction Materials

All laboratory tests were carried out at well equipped laboratory - Material Test (P.) Ltd., Mid

Baneshwor in Kathmandu.

4.11.3.1 Coarse Aggregate

The following tests are carried out to test the material for use as coarse aggregate:

S. N. Name of Test Reference Standard

to be Followed

1 Specific Gravity IS: 2386 (Part 3)-1963

2 Water Absorption IS: 2386 (Part 3)-1963

3 Aggregate Abrasion Value (Los-Angeles) IS: 2386 (Part 4)-1963

4 Aggregate Crushing Value IS: 2386 (Part 4)-1963

5 Soundness ( 5 cycles) (Sodium Sulphate) IS: 2386 (Part 5)-1963

6 Flakiness Index IS: 2386 (Part 1)-1963

7 Elongation Index IS: 2386 (Part 1)-1963

8 Petrographic Examination IS: 2386 (Part 8)-1963

9 Alkali Aggregate Reactivity by Mortar Bar Method

(Accelerated Technique) ASTM Designation: C 1260-01

10 Point Load Test ASTM D5731 – 08

11 Unit weight ASTM C-36

4.11.3.2 Fine Aggregate

The following tests as shown in Table 4-17 are carried out to test the material for use as fine

aggregate:

Table 4-17: Laboratory test details for Fine aggregates

S.N. Name of Test Reference Standard

to be Followed

1 Gradation and Fineness Modulus IS: 2386 (Part 1)-1963

2 Natural Moisture Content IS: 2386 (Part 2)-1963

3 Specific Gravity IS: 2386 (Part 3)-1963

4 Organic Impurities IS: 2386 (Part 2)-1963


4-57

S.N. Name of Test Reference Standard

to be Followed

5 Mortar making properties (7 & 28 days) IS: 2386 (Part 6)-1963

6 Water absorption IS 2386 ( Part 3) - 1963

7 Atterberg Limit ASTM

8 Density ASTM

9 Compaction IS 2720 (part VIII 1983

4.11.3.3 Sieve Analysis

The grain size analysis (gradation test) was carried out according to AASHTO T 27–82 standard

procedures by receiving the sample through a stack of sieve from 75mm to 0.075mm in

diameter. The mass of material retained in each individual sieve was determined and the

cumulative percentage was calculated. The grain size curve was plotted on the basis of obtained

data.

4.11.3.4 Specific Gravity and Absorption Test

The specific gravity and absorption test were carried out for fine and coarse aggregate in

accordance to BS 812: Part 2: 1975 standard. Usually aggregate with absorption value of greater

than 2% are considered as unsuitable for construction material.

4.11.3.5 Los Angeles Abrasion Test

The Los Angeles Abrasion test was carried out according to the standard procedures outlined by

AASHTO T 96 – 77 (1982). The percentage of abrasion was calculated on the basis of the tests.

Samples collected for construction material were subjected to the Los Angeles Abrasion Test.

The range of the values of LAA is less than 45%. The values is if less than 45% that sample is good

for construction materials.

4.11.3.6 Sulphate Soundness Test

The soundness test was carried out on the construction material to determine the durability of

aggregates against physical weathering. The test was done as per the standard procedures of

determining the sulphate soundness of aggregates as recommended by AASHTO T 104 – 77


4-58

(1982). The sulphate soundness tests were performed on the samples. The test results indicate

that the value obtained does not exceed the limiting value of 10%.

4.11.3.7 Loose Density Determination

The loose density determination test was carried out on foundation materials as per the standard

procedures outlined by the AASHTO T 19 – 80.

4.11.3.8 Compaction Test

The Compaction test namely, the moisture/density relationship were determined according to

the standard procedure outlined in IS 2720 (part VIII 1983).

4.11.3.9 Point Load Test

The point load test was carried out on the core sample collected from the bore hole according

to the suggested method for determining load strength by point load tester model PIL – 5 of rock

test.

4.11.3.10 Crushing Value

The aggregate crushing test was carried out according to British Standard of BS 812: Part 110:

1990. The test results indicate that the value obtained does not exceed the limiting value of 25%.

4.11.3.11 Flakiness Index

Flakiness Index is the percentage by weight of particles in it, whose least dimension (i.e.

thickness) is less than three-fifths of its mean dimension. Elongation Index is the percentage by

weight of particles in it, whose largest dimension (i.e. length) is greater than one and four-fifths

times its mean dimension. The maximum value in accordance 13 S 812P-105.1 less than 25% can

be achieved to meet specific client requirement.

4.11.3.12 Elongation Index

The elongation index of an aggregate is the percentage by weight of particles whose greatest

dimension (length) is greater than one and four fifth times (1.8 times) their mean dimension. The

elongation test is not applicable to sizes smaller than 6.3 mm.


4-59

The test pit samples, collected from different locations are subjected to different laboratory tests

in order to determine its suitability for construction purpose. Laboratory tests were performed

in accordance with the standard procedures recommended by ASTM, AASHTO, BS or IS. Test

method codes are presented in all test results for reference.

Different laboratory tests like sieve analysis, abrasion test, specific gravity and absorption test,

rodded density determination test, sulphate soundness test etc were performed in order to

assure the quality of material collected for construction purpose.

4.11.4. Results and Discussions

The results of laboratory tests of the construction materials are given in Investigation report of

Volume III and summary of the results of the construction materials are given in Table 4-18.

Altogether four samples for construction materials and two rock samples were collected from

different locations along the Irkhuwa Khola and Arun River. The tested values of the construction

materials fall within the standard values. However, the materials along the river beds are good

for use as the construction materials.

Table 4-18: Summary of the Results for Material Tests

Pit No.

Alkali

React

ivity

Sulphat

e

Soundn

ess

Aggreg

ate

Crushin

g Value

Unit

Weig

ht

Grain

Size

Analy

sis

Orga

nic

Impu

rities

Cont

ent

Flacki

ness

Indes

Sp. Gr.

and

Absorpt

ion

LAA

Tes

t

Elo

nga

tion

Ind

ex

Natur

al

Moist

ure

Conte

nt

Aggre

gate

Impac

t

Value

s

SANDS AND AGGREGATE

Sands Fine

sand

0.14 2.65 7.54

Aggre

gate

38.30 2.24 24.30 1.76 24.41 2.67/0.

02

32.

36

24.

95

23.81

The materials are sufficiently available along the riverbed of the Irkhuwa Khola. The materials

can also be taken from the Arun River but it needs to take permission or mutual relationship

between Irkhuwa Khola Hydropower Project and Arun-3 HEP to extract the construction

materials from the Arun River because of out of boundary of the Project area.


4-60

4.11.5. Geophysical Investigation

Subsurface condition of the project area is determined by the geophycal methods either by using

Electrical Resistivity Tomogram (ERT) and Seismic Refraction method. Only the ERT is conducted

in the project area. After comletion of the ERT, the locaition of the drilling shall be done. The

proposed location of the core drilling area is shown in Table 4-19.

Table 4-19: Proposed Core drilling locations and respective depths

Location Depth Geology

DH-1 right bank of the weir axis 15 m Rock

DH-2 left bank of the weir axis 25 m Alluvial deposits

DH-3 Desander basin 15 m Alluvial deposits

DH-4 Portal Inlet area 15 m Rock

DH-5Surge tank area 50 m Rock/residual soil

DH-6 Powerhouse 15 m Rock/alluvial deposits

Dh-7 Powerhouse 15 m

Total 150 m

The core drilling shall be conducted in preparation of the DPR.

The geophysical investigation of the ERT has been done in ten lines from ERT-1 to ERT-12 (Table

4-20). The detailed findings are presented in the Investigatin report. The findings of the ERT is

described in below.

Table 4-20: Conducted ERT Locations and details (Geophysical Investigations)

S.N. Profile

Nos

Location Length

(m)

Starting Point End Point

1 ERT-1 Right Bank of Weir

Axis

150 503484 3030084 503273 3029977

2 ERT-2 Left Bank of Weir

Axis

150 503492 3029994 503287 3029851

3 ERT-3 Along Weir axis 150 503302 3029893 503438 3030010


4-61

4 ERT-4 Desander along

river

150 503523 3030058 503708 3030255

5 ERT-5 Desander far from

river

150 503805 3030100 503564 3030194

6 ERT-6 HRT Alignment 150 505056 3030395 504906 3030354

7 ERT-9 Powerhouse 150 505980 3031214 506141 3031284

8 ERT-10 Powerhouse 150 505940 3031193 506092 3031285

9 ERT-11 Powerhouse 150 505929 3031157 506061 3031292

10 ERT-12 Powerhouse 150 505911 3031161 505996 3031304

Total surface

length

1500

ERT-1, Right bank of weir axis (Figure 4 A and 4B of Annex)

The resistivity tomogram indicate that the subsurface information can be interpreted as two

layered geology. The first layer is overburden and the second layer is bedrock. The first layer is

made of alluvium deposit predominated by boulders. The first overburden layer can be divided

in to two layers. One is dry alluvium layer at the surface and second is wet alluvium layer below

the first layer. The base of the first layer may also include open jointed rock mass. Due to higher

moisture content lower portion of the overburden has low resistivity. Low resistivity zones within

the bedrock are due to the presence of jointed rock mass. Depth to bedrock varies between 10

m to 20 m along the profile

ERT-2, Left bank of weir axis Figure 5 A and 5B of Annex

Interpretation of this profile is similar to previous profile. First layer is interpreted as dry

overburden and the second layer is interpreted as weathered bedrock. The first layer is

predominated by boulders. In some parts at the surface the weathered bed rock can be

observed. The depth to bedrock varies between 5m to 20 m.


4-62

ERT-3, Along weir axis Figure: 6 A and 6B of Annex

The interpretation is similar to previous two profiles. As indicated by the resistivity tomogram

the bedrock is observed at the right bank about 7m depth. There is dry flood plain at the surface

and saturated alluvium about 20m depth on left bank.

ERT-4, Desander along river Figure 7 A and 7B

The Resistivity tomogram along desander basin, it is indicated that there are clearly two kind of

geology. First layer consists of dry alluvial deposit has high electrical resistivity and wet alluvial

deposits has low electrical resistivity as presented in the figure 7B. The depth of bed rock is about

20 m from the surface

ERT-5, Across Desander/river (far from river) Figure 8 A and 8B

ERT profile no. 5 across the desander basin shows the depth of bed rock is varied between 7 m

to 25m along the profile. Overburden soil and dry alluvial is present at the surface as presented

in the figure 8B. Saturated alluvium is presented near the river just below the dry alluvium

whereas the weathered and jointed rock mass is observed at the center of the profile just below

the dry alluvium.

ERT-6 along HRT alignment Figure 9A and 9B

This profile is runs along the head race tunnel. ERT-6 indicates that the subsurface geology has

bed rock which is exposed at the surface in certain section of the profile. A big sliding mass

(colluvium) is observed which has high resistivity because of dry condition. Thick (about 10 m)

dry colluvium covers the bed rock.

ERT- 9, 10, 11, 12, Power house Figures 9A, 9B, 10A, 10B, 11A, 11B, 12A, and 12B

The profiles 9, 10, 11 and 12 are lies at the power house area. The overburden material is

cultivated terrace land about 5-7 m thick from the surface. Therefore, bed rock can be obtained

in shallow depth as shown in the figures 9A, 9B, 10A, 10B, 11A, 11B, 12A, and 12B.


4-63

4.12. Muck Disposal Area

The materials come out from the tunnel can be deposited along the Irkhuwa Khola bank at open

spaced area. Most of the materials can be used as the construction materials as the sources of

the sands.

4.13. Conclusions and Recommendations

4.13.1. Conclusions

Geologically, the proposed Upper Irkhuwa Khola Hydropower Project lies in the rocks of

the Irkhuwa Crystalline Nappe, Lesser Himalaya. The main rock is composed of gneiss and

schist. The Irkhuwa Crystalline Nappe is equivalent to the rocks of the Ulleri Formation of

the Eastern Nepal.

Structurally, the proposed are lies in south of the Barun Thrust (BT). This thrust is

considered as the main Central Thrust (MCT). The thrust is located about 10 km north

from the project area. Activation of the thrust is considered as minimal.

The slope stability condition along the tunnel alignment and project area is good to fair

in general on the right bank of the Irkhuwa Khola. Other hydraulic components has stable

stability.

More than sufficient quantity of the construction materials mainly the sands along the

Arun River as well as from the Irkhuwa Khola.

The proposed surge tank area and penstock alignment area lies in the soil covered area

and seems to be stable area. There is high possibility to see the bedrocks at shallow

depth.

Powerhouse and tailrace, waterways alignment passes though the bedrocks of the

Irkhuwa Crystalline Nappe basically composed of thick gneiss.

The support system of the waterways alignment needs to apply RS III and RS IV. But

during the excavation time there is considered as finding fair to good rock 25.62%, poor

rock can be found less than 62.50% and good rock 11.88%. The rock mass of the

headworks, inlet portal and surge tank has more or less same characteristic rock so the

area is covered by good rock and fair to good rock mass, respectively.


4-64

The calculated values of the seismic coefficient are considered as 0.15g. if the structures

founded on the soil the PGA value requires to increase by 20% of the recommended

value.

The tested materials falls in the standard values of the materials norms.

The core drilling has proposed 175 m in six locations. The core drill has not conducted in

the feasibility report.

4.13.2. Recommendations

150 m core drillings are required to find the sub-surface condition of the project area

The hydraulic structures should be recommended to construct with recommended values

of the PGA values. If the structures founded on the soil the PGA value requires increasing

by 20% of the recommended value.


5-1

5. ALTERNATIVE LAYOUTS AND RECOMMENDED PROJECT LAYOUT

5.1. Study of Possible Alternative Layouts for the Project

Proposed Upper Irkhuwa Khola Hydropower Project is a run-of-river type project. It utilizes water

of Irkhuwa Khola. The major structural components of the project are 20m long diversion weir,

5.2m wide intake, 3m wide undersluice, 24m long approach canal, 90m long Desilting basin

(effective length of 60m), 3720m long headrace tunnel of 3.5m internal diameter& inverted D

shape, 5m diameter surge shaft, 375m long penstock pipe, 30.25 m by 10 m power house, and

27 m long tailrace canal.

The headworks of the project has been fixed at about 600 m upstream of the confluence

between Thumlung Khola and Irkhuwa Khola. Right bank at the headworks area lies at Kudakaule

VDC whereas the left bank is at Dobhane VDC. The project has been optimized to generate

14,500 kW electricity. The design discharge has been fixed at 7.8 m3/s. Considering the

headworks site, fixed installed capacity, hydrology of the river, and topographical constraints,

the powerhouse site has been fixed about 3720 m downstream of the intake site with two

alternate possible options. In both cases, powerhouse site is located in Kudakaule VDC, about

250m upstream of Irkhuwa khola confluence with Benkhuwa Khola in the right bank. After fixing

the intake, connecting canal, desanding basin and powerhouse sites, there would be different

alternative options in the conveyance of water from desanding basin up to powerhouse site. The

possible alternative options for water conveyance might be tunnel, pressure canal, or steel

penstock pipe alignment or the combination between all alternatives. Both advantages and

drawbacks for all options are discussed briefly below.

Following reasons are considered for the choice of headworks and powerhouse for the studied

option.

The weir axis as well as headworks is located upstream of the confluence between

Thumlung Khola and Irkhuwa Khola. The location itself should be safe from possible high

flood of Thumlung Khola.

The location of Headworks is fixed considering suitable for the access road connection

from proposed road Nepal danda –Gothe Bazaar-Dobhane.

The inner location and upstream of the confluence between Benkhuwa Khola and

Irkhuwa Khola ie. cultivated land is suitable for the powerhouse for Upper Irkhuwa Khola

Hydropower Project. The safety and cost of the proposed structures needs to be assessed

before the final decision.

The geology seems very stable in the proposed surface powerhouse option.


5-2

With the two options- between the canal option and tunnel option, the tunnel option is

proposed having taken into consideration the following factors:

Head loss will be reduced and hence net head will be increased during dry months in the

tunnel option for the same gross head of canal option,

As per site topography, introduction of tunnel has less impacts on the surface compared

to the construction of canal,

As the canal alignment follows steep terrain or rocky area at few places, the safety of the

project will be uncertain due to possible slope failure and necessity of more protection &

mitigation works.

Tunnel option avoids the problems of sedimentation due to land erosion during water

conveyance as in the case of canal option,

The seepage loss can be controlled in the Tunnel option,

The adverse environmental impacts of tunnel option will be minimum compared to that

of canal option,

In Tunnel option, all the alignments are underground thus preventing the encroachment

of fertile land.

Though both options have limitations and advantages, the tunnel option should be best possible

alternative for the provided hydrology and topography of the project. For the economic and

financial analysis purpose, low pressure tunnel option has been discussed more detail in

following chapters for Irkhuwa Khola B Hydropower Project.

5.2. Presentation of Recommended Layout

The headworks at the first alternative, water way as tunnel and surface powerhouse is

recommended at this stage of study. The layout for the recommended options has been

presented in Volume-IIof this report.


6-1

6. PROJECT OPTIMIZATION

6.1. Introduction

This chapter presents the methodology and assumptions considered for the optimization of the

project to determine the optimum cost effective project size i.e. the Optimum Plant Capacity.

The optimization study is conducted to determine the optimum plant capacity.

The optimization study is carried out taking a range of technically viable alternative plant

capacities. As per available mean monthly river discharge data and available head, energy

calculated at different plant capacities. Project cost at different capacity is derived by calculating

the cost of major items of different structures involved in the project such as diversion weir,

settling basin, water conveyance system, powerhouse and tailrace. Optimization study includes

the cost of different alternatives and their financial parameters. The alternative with minimum

generation cost has been selected as the optimum project size.

6.2. Objectives and General Approach

The objective of the optimization study is to determine a technically most feasible project

capacity, which will produce the energy at minimum cost. As such, the derivation of project cost

and its benefits in terms of energy produced will be required to form a matrix of different

alternatives from which the optimum project capacity could be selected. The study would also

require determination of optimum dimensions of various project structures or components like

water conveyance system, penstock and water level at headwork. These studies are based on

available hydrological, topographical and geological data, which indicated that an installed

capacity in the range of 14.5 MW would be most feasible at the proposed site.

The optimization process is undertaken as a financial analysis with results expressed as financial

costs and benefits. Conceptual layouts are developed for each alternative from which cost

estimates are prepared. The power benefits are determined for each alternative and compared

with costs.

The objective is to determine the element size, which maximizes the benefits of power supply.

The optimization procedure in this study follows the general procedure outlined below.

Selection of the procedures to be optimized and their range and thus establishing

series of alternatives.

For each alternative, carrying out the conceptual design and produce cost

estimate.

For each alternative, assessment of its performance and estimate its benefits;

Comparison of the costs and benefits and carrying out economic analysis.


6-2

For each case of the installed capacity, a preliminary layout on the available topographical map

was carried out and preliminary cost estimate is derived including electro-mechanical costs.

Common costs like cost for environmental mitigation, access road and transmission line are not

considered in this study. For each case, energy calculation depending on the available

hydrological data was carried out to determine the dry and wet energy.

The major project structures which differ from one case to another with different installed

capacity are listed below.

Overflow weir & Undersluice

Intake & Desanding basin

Headrace tunnel

Surge tank & Penstock

Powerhouse and tailrace

Hydro-mechanical structures like gates and trash-racks

Electro-mechanical equipment like turbine, generator, power transformer and

valves etc.

Quantity estimate and tentative costs are calculated for each of these structures. Water

conveyance system is the major variable in the cost of different alternatives and is optimum for

the given head and discharge characteristics of the installed capacity. For electro-mechanical

costs supplier’s quotations of various recent projects in Nepal is based on per kilowatt cost of

equipment on “water to wire basis”. Since detailed rate analysis were not carried out, the unit

rates for various works based on the projects of similar nature is considered.

The following assumptions are made for the optimization studies.

Discount rate is taken as 10%.

Financial analysis is carried out for 30 years.

Operation and maintenance cost is assumed to be about 1.5% of the total financial

cost.

The construction period of the project is assumed to be 3 years with cost distribution

of 25%, 50%, 25% the first, second and third year.

The price of energy generated and supplied to the NEA grid has been taken from the

average of the negotiated rates with NEA by the developer with capacity less than

25 MW capacity. The initial average energy price is average of dry and wet season

energy price adopted by NEA. An annual increment of 3% for first 6 years is

considered.

Efficiency of turbine, generators and transformers considered are 92%, 96% and

99% respectively.

Financial evaluation was carried out using discounted cash flow techniques for each case to

determine economic indicators like benefit-cost (B/C) ratio, internal rate of return (EIRR), specific


6-3

energy cost and net present value (NPV) of the project. The economic indicators for all the cases

were tabulated and appropriate charts drawn. The case producing the maximum RoE, B/C ratio

and minimum specific energy cost was then selected as the optimum and detailed studies should

be carried out for this option.

6.3. Hydrology

The capacity and energy potential of a particular option is dependent on the river flows. The long

term mean monthly flows at the intake site of the project are derived from hydrological analysis

carried out in detail for this project. The mean monthly flow series is shown in Table 6-1.

Table 6-1: Average Monthly flows

Month Discharge (m3/s)

January 3.30

February 2.86

March 2.57

April 2.67

May 4.81

June 19.47

July 50.25

August 51.11

September 31.28

October 14.34

November 7.01

December 4.76

These flows have been used in the computations of dry and wet energies and the capacity

potential for project optimization

To maintain the aquatic life in the dewatered reach of the river, 10% of the minimum monthly

flow, i.e., 0.257 m3/s will be released from the headworks. The percentage flow equaled or

exceeded of the project is presented in Table 6-2 below.

Table 6-2:Flow exceedence discharge

Time of exceedence (%) Discharge (m3/s)


6-4

5 44.05

20 31.66

25 24.27

35 13.13

45 7.80

55 5.62

65 4.19

70 3.88

80 3.33

90 3.08

100 2.89

6.4. Conceptual layout and cost Comparison

The layout of the project components consist of overflow weir with side intake in the Irkhuwa

Khola. The water drawn from intake passes towards connecting canal and desanding basin. Just

after settling basin, a low pressure tunnel will join the surge tank. The water conveyance from

the Desanding basin to the powerhouse consists of headrace tunnel, surge shaft and penstock

pipe.

The sizes of all individual structures for each capacity option were computed to determine the

respective cost of the structure for the purpose of optimization. As the flood hydrology does not

change for the different cases, the design of overflow weir and undersluice has been kept

constant. However, change in the installed capacity changes the design discharge; accordingly,

the sizes of settling basin and mainly the penstock pipe cost were adjusted. The diameters of the

penstock are designed based on the annual costs and benefits. Powerhouse size is also changed

inconsideration to the equipment capacity.

Preliminary quantity and cost estimates were developed for all the cases considered. Only the

major items were computed in detail, while minor items were estimated based on the rates and

data of similar structures of other projects. As the optimization is a relative process, it was

considered sufficiently reliable for comparison purposes. Unit rates were derived from

completed projects in Nepal of this range of capacity of recent projects undertaken by NEA and

other private developers with some modifications. Electro-mechanical equipment costs have

been estimated with reference to similar size of projects and from quotations of different

suppliers and manufacturers and also based on the recent projects by private developers. The

cost estimates also considered the costs for access roads, infrastructure development and


6-5

environmental mitigation costs. Technical contingencies have been taken into account for

obtaining the total implementation cost of the alternative.

6.5. Range of Options and Energy Production

In order to determine the optimum installed capacity of the project, a total of five alternatives

ranging from 7.74 MW to 23.94 MW with varying exceedence flows ranging from 35% to 65%

flow exceedence were considered to derive the optimum plant capacity. Different alternative

capacity and corresponding energy generation capacity have been calculated.

As the project is run-of-river scheme, energy productions were calculated for all alternatives

considering average monthly flows as given in Table 6-1. The energy produced is categorized into

dry and wet energy. The design discharge given above were derived for each of the flows

assuming an overall efficiency of turbine, generator and transformer as 87.4 % and the headloss

for each design flow is calculated in the water conveyance system. Gross head is calculated from

the water level at the surge tank to the normal level of tailrace. The summary of range of options

and various types of energy produced are given in Table 6-3 and Figure 6-1.

Table 6-3:Summary for different option

%

Exceedence

Discharge

(m3/s)

Power

(MW)

Energy

(GWh)

Financial Cost

(Mill. NRs)

35 13.69 23.94 123.03 4439.01

45 7.8 14.5 90.58 2602.27

55 5.10 10.22 69.21 2140.97

66 4.23 7.74 56.99 1997.78

Figure 6-1:Variation of NPV with different discharge

-

200

400

600

800

1,000

1,200

1,400

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

NP

V (

'000)

Discharge (m3/s)

NPV


6-6

6.6. Result of Financial Analysis

The financial analysis of the different alternatives was carried out by comparing the project cost

in each case, the implementation cost and operation costs with accrued benefits due to energy

production. Financial analysis was carried out to determine the basic economic parameters like

net present value (NPV), economic internal rate of return (EIRR), benefit-cost ratio (B/C) and

specific energy cost. The results of the economic analysis for all the cases are summarized in

Table 6-4 and Figure 6-1, Figure 6-2 and Figure 6-3.

Table 6-4:Summary for Economic analysis of different option

From the above table, it is evident that the economic parameters like B/C ratio and RoE are

maximum and the levelized cost of energy is minimum for plant capacity at 14.5 MW as shown

in Figure 6-2 and Figure 6-3.

Figure 6-2:Return on equity with different discharges

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Retu

rn o

n e

quity

(%)

Discharge (m3/s)

Return on equity

Power

(MW)

B/C Ratio RoE (%) NPV

(Mill NRs)

Specific Energy

Cost (Cents/kWh)

24.97 1.04 14.36 198.2 5.03

14.5 1.45 29.00 1179.3 4.45

9.28 1.32 23.4 681.7 4.95

7.82 1.13 16.15 264.3 5.63


6-7

Figure 6-3:Specific Energy cost for different installed Capacity

6.7. Conclusions

The studies undertaken revealed that the installed capacity could be in the range of 14.5 MW as

this gave the maximum values of economic indicators. With respect to B/C ratio, internal rate of

return and the specific energy cost (economic and financial both) the optimum installed capacity

is determined as 14.5 MW. Being a run-of-river project lower installation is preferred as the

higher installation will only increase the production of secondary energy in the wet season, which

is very hard to realize in the Nepal Power system. Hence, plant capacity of 14.5MW is selected

as the optimum case and recommended for the detail engineering of the project. The optimum

plant capacity of 14.5 MW corresponds to the design discharge of 7.8 m3/s which is 45% of flow

exceedence of source river Irkhuwa Khola.

2.00

2.50

3.00

3.50

4.00

4.50

5.00

5.50

6.00

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Specific

Energ

y c

ost(

NR

s./kW

h)

Discharge (m3/s)

Sp Energy Cost


7-1

7. PROJECT DESCRIPTION AND DESIGN

7.1. Introduction

Proposed Upper Irkhuwa Khola Hydropower Project (UIKHP) is a run-of-the-river type project.

The proposed system of the power plant will be run at its full capacity of 14.5 MW for about

6 months of a year. The design discharge of the proposed plant is 7.8 m3/s and has about 45-

percentile probability of exceedance. The river gradient is quite steep with 221.5 m of gross

head available for the project in about 4000 m downstream of headworks. The proposed project

layout is the best option selected amongst the various alternatives during the study. The project

layout is finalized based on the findings of the site visits.

7.2. Headworks

7.2.1. General

Based on the scheme optimization, installed capacity of 14.5 MW has been found optimum. The

design discharge for the optimum capacity is 7.8 m3/s which has 45-percentile probability of

exceedance. In addition to the design discharge, the headworks is also capable to divert 30%

more of the design discharge for sediment flushing from settling basin.

The major components of the headworks are diversion weir, under sluice, orifice type side

intake, approach canal and settling basin with flushing canal.

The design of the headworks is based on the following design criteria:

Structures should not be vulnerable to hazard floods, i. e., free overflow weir is

required.

All the bed load of the river must pass through the undersluice without any build

up at intake opening site.

Floating debris must not cause blockage at the intake openings.

100-year return period flood has been considered to calculate height of the flood

walls.

Bottom of the intake orifice is 1.25 m above river bed level so larger gravel size

are not expected to enter into the intake. Design discharge is 7.8 m3/s and

additional flow equal to 20% of the design discharge for settling basin has been

considered.


7-2

Sediment exclusion for 90% of 0.2 mm or greater sized particles from the settling

basin has been considered. All suspended sediment larger than 0.2 mm shall be

flushed back to the river.

Conventional hydraulic flushing has been adopted.

All components must be hydraulically, geotechnically and structurally stable.

The head loss is a major concern, and thus the hydraulic parameters were checked in design

water conveyance system to ensure a safe passage of design flow with minimum head loss. The

head losses in the different components of the headworks have been calculated to arrive at total

head loss in the system.

A brief description of all headworks components are discussed in the subsequent sections and

the drawings of the structures are shown in Volume - II (Drawings).

7.2.2. Function of Headworks

During normal flow, the level of water will be maintained at crest level 923.0 masl. In order to

maintain downstream environmental release, 10% of the driest mean monthly flow will be

released at the downstream of river throughout the year. During dry season, all gates (gates of

gravel trap and undersluice) will be kept closed.

During high flood, excess flow will be spilled through the weir. Depending upon head over weir

crest, flow through orifice will be pressurized. In this condition, flow is regulated by means of

undersluice gates, the gates at the beginning of the approach canal. The approach canal will

convey the flow required for settling basin flushing and design discharge. During operation, the

flow will be controlled by gates located at the intake and spillway proposed in transition canal.

Regarding sediment control, small sized sediments i.e. particle size greater than or equal to 2mm

will be trapped in the gravel trap and will be flushed through gravel flush while smaller sized

sediments will be trapped in settling basin whereas bigger sized boulders and debris will be

flushed through the under sluice provided just front of intake. In order to ensure diversion and

safe passage of bed load and prevent excessive sediment entering into the intake, guide/ divide

wall is proposed between sluiceway and weir. To control the flow regime in the headworks area,

flood protection wall has been proposed on both banks on the upstream and downstream area

of the weir. The top level of flood protection wall is maintained at 926.3 masl for 100-year flood

with freeboard of 0.96 m. It is considered that during higher floods, there will be some damages

though of repairable nature.


7-3

7.2.3. Diversion Weir

The proposed diversion weir is located at about 600 m upstream from the confluence of Phedi

Khola and Thumlung Khola, at Thumlung Khola. The sediment transport in Irkhuwa Khola is high

during the monsoon season with the particle size ranging from sand particles to big boulders. At

the other hand during dry season sediment transportation is nearly nil. The diversion weir shall

not disturb the sediment transport pattern in the river. Total catchment area of the project is

137.35 km2, among them 17.88km2 lies above 3’000 masl and remaining 119.47 km2 lies below

the 3’000 masl. Although there are GLOF risks in Arun River and its tributary like Barun, that will

not affect the Irkhuwa khola as its powerhouse location is much higher from the Arun River and

Irkhuwa Khola confluence. Hence, it does not include any glacial lakes thereby no possibility of a

GLOF. To prevent large damages during the probable maximum flood, a simple uncontrolled free

overflow diversion weir of concrete is proposed with a provision of under sluice on the right

bank. There will be two hydraulic operated lift gates to control the flow and bed load deposition

in front of the intake. The diversion weir is designed to maintain water level to divert 7.80 m3/s

discharge. It will generate 14.5 MW of power using 221.5 m of gross head. The operation level

of water at intake is maintained at 923.0 masl during normal flow. In addition, the weir facilitates

safe overflow of 100-year flood flow of 181.56 m3/s. With the assumptions of severe conditions,

the operating platform level has been set at 926.30 masl elevation considering 100-year flood.

The river bed consists of exposed bed rock. Natural river fall is present at downstream of the

weir axis. To completely dissipate the energy while flowing through the ogee type glacis, stilling

basin has been designed downstream of the weir to accommodate the entire jump length

considering 100-year flood flow. The scour depth has been determined using the Lacey’s theory

and the length of the floor has been checked to minimize the scour.

One of the critical design parameters for the intake orifice and weir is the elevation of the crest.

If the crest level is too high, not only increases the submergence area and cost of construction

but also increases the risk of seepage under the weir and scour at the downstream toe. Too low

a crest level makes the intake sill to be seated near to the riverbed causing problem of bed load

and sediment load. Flushing head at the settling basin will also be insufficient if the weir height

is not sufficiently high. After assessment of these factors, the proposed weir crest level has been

set at a level of 923 masl.

The upstream side of the weir is vertical and the downstream profile is parabolic and slope in

average is 1:1 (V: H). Boulder riprap at upstream of weir is provided for the stability of riverbed

as well as to protect the intake site.

To prevent the off tracking of the river due to the construction of diversion weir, bank protection

is provided on both banks. The flood protection wall is designed for flood of 100 years’ return

period. Both banks consist of exposed steep rock slope.


7-4

7.2.4. Intake

According to the river characteristics at the headworks area, orifice type side intake is the best

alternative. The top of the orifice is kept below the weir crest level. Such arrangement has the

following advantages:

Side intake is simpler and less expensive than other types of intake from

construction, operation and maintenance point of view.

Side intake does not allow excessive flow into the intake during floods, minimizing

associated bed load handling problem.

It will minimize entry of bed load.

It also helps to minimize entry of floating debris.

The intake consists of two orifices of size 2.8 m x 1.75 m (BxH) each, on the intake right bank

headwall. The sill level of the intake opening is set at an elevation of 920.75 masl. The entrance

velocity through the opening is calculated as 0.96 m/s during normal flow. During the flood of

100 yrs’ return period, 23.84 m3/s of water will enter through the orifice.

It is assumed that the bed load up to 50 mm diameter will pass through the intake orifice and

will be conveyed through gravel trap flushing and the settling basin flushing to downstream of

the weir. Intake platform is fixed at elevation 926.3 masl for the gate operation, with the level

fixed for 100-year flood with free board of about 0.96 m. A ladder will be placed over the intake

culvert as an access to the platform.

7.2.5. Undersluice

The proposed undersluice is located on the right side of the diversion weir and is basically

proposed for the prevention of the large amount of sediment from entering in to the intake and

in addition to pass a portion of high flood discharge and bed load in the river downstream.

However, during the low flow season the design discharge shall be allowed to flow through the

intake by closing the sluice gate. The width of undersluice is 3m and floor of the sluice is 3.5 m

below the crest elevation of the weir i.e. at an elevation of 919.50 masl.

One steel lift gate of 3.0 m overall span and 2.0 m height, have been provided on the sluiceway

opening. Besides, stop-log has been provided in front of the gate for repair and maintenance of

the working gate. When water rises to the design flood level of 925.34 m, the discharge through

the undersluice, with gates fully opened, would be about 38.52 m3/sec.

During normal condition, the gate of the undersluice remains closed so as to ensure available

flow into the waterways. During flood flow, the regime inside the undersluice will be pressurized

and boulders will be flushed out downstream of the weir. Hence, hard stone lining is proposed


7-5

to prevent bed scouring. Boulders bigger than the size which cannot be dragged by the pressure

head will be taken out during regular maintenance.

7.2.6. Stilling Basin

Stilling basin has been proposed at downstream of weir and undersluice, respectively, to

dissipate the energy of upstream water. Length of the stilling basin depends on the length of

hydraulic jump whereas length of jump depends on the sequent depths. Thickness of the stilling

basin has been calculated from seepage analysis. Design of stilling basin is carried out based on

“Hydraulic Design of Stilling Basins and Energy Dissipaters” published by the United States

Department of the Interior Bureau of Reclamation.

Froude numbers before and after jump are found to be 5.30 and 0.29 respectively. Since the

Froude number before the hydraulic jump is greater than 4.5, Type II stilling basin has been

proposed. Expected energy loss in the stilling basin is 51.48 % of the initial energy. Bed level of

stilling basin has been kept at 916.42 masl. Total Length of the stilling basin has been proposed

as 18.2 m. Two cut-offs are provided at upstream and downstream of weir and undersluice

portion to reduce the seepage flow. Depth of two cut-offs at start and end are 3.5 m and 5 m

depth respectively.

7.2.7. Coarse Trashrack, Gravel Trap and Spillway

A coarse trashrack is provided just before the intake orifice. A Gravel Trap of size 15m x 6.4 m x

3.0 m (LxBxH) is introduced after intake portion with 5m outlet transition followed by approach

canal of length 20 m. Gravel trap accommodates a spillway of length 15 m which is provided to

spill the flood water entering through the intake. The Gravel trap traps the sediment of sizes

greater than or equal to 2mm and flushes them along the gravel flush. The water spilled along

the spillway canal and the sediments flushed through the gravel trap is discharged at the

downstream of the weir at the stilling basin.

7.2.8. Approach Canal

Two approach have been provided. Total length of each approach canal is 20 m. The water

passed through the gravel trap and the transition canal gets conveyed to the settling basin

through two approach canal. Flow in this canal will be open channel flow. The cross-section of

each approach canal is 2.0 m x 1.65 m. Depth of the water for design discharge will be 1.11 m.

During the normal operation, the velocity in approach canal will be 1.96 m/s. Flow in the

approach canal will be controlled by the gates provided at the intake which are accessible during

floods and for maintenance purpose.


7-6

7.2.9. Settling Basin and Sediment Flushing Channel

The objective of the settling basin is to allow suspended sediment particles to settle down within

the basin by reducing the turbulence level and to be deposited at the bottom of the basin. The

deposits are then removed through a flushing culvert located at the end of the settling basin.

Settling conditions are obtained by reducing the transit velocity of the water so the effect of

gravity increases relative to the effect of the turbulence. The suspended particles will not follow

the movement of the water because the fall velocity of the particles will create a flux of

sediments downwards. The transit velocity in the settling basin will normally be in the range of

0.1 to 0.4 m/s, depending on the design criteria for particle size and to some extent on the size

and shape of the area available for settling basins. At this stage of planning, a transit velocity of

0.2 m/s within effective cross-sectional area of flow is adopted.

The performance of a settling basin is guided by its ability to trap suspended sediments and its

ability to remove the trapped deposits from the settling basins, i.e., the qualities of the adopted

sediment flushing system.

Considering the availability of water for flushing settling basin is designed for continuous flushing

during flood and intermittent flushing during dry season, so additional 10% of the design

discharge is also considered for the design. A hopper type basin with continuous flushing is found

cheaper, gives the best settling performance and has excellent reliability. Two chambers are

proposed in the settling basin considering the site conditions and also to ensure continuous

supply of flow for power production when one settling basin chamber will be closed for

maintenance.

The settling basin is designed to trap 90% of 0.2 mm particles sized sediment. It will have two

equal settling chambers in series, each 60 m long and 8 m wide. Total length of the settling basin

is 90.85 m. The maximum flow velocity in main settling zone is 0.18 m/s. 14m long inlet transition

zone has horizontal and vertical transition slope of about 1:5 and 1:4 respectively. The flushing

culvert of the settling basin has a slope of 1 in 100. The top of the settling basin wall is fixed at

923.33 masl. From the settling basin the water will pass to headpond and then through headrace

tunnel.

The flushing system is designed as an intermittent type during dry season (or low flow season),

though there is provision of continuous flushing during high flood period. The settling basin

bottom flushing channels are connected with flushing canal of size 2.6 m x 2.0 m which convey

the deposited sediment into the downstream river course through 5.10 m long flushing canal.


7-7

7.3. Headrace Tunnel

7.3.1. General

Right bank is selected as suitable alignment for headrace waterways of the project to convey the

flow from the settling basin to the penstock. Total length of the headrace tunnel is around 3720

m.

7.3.2. Design Criteria

The design of the headrace has been based on the following criteria:

The maximum design discharge is 7.8 m3/s.

The flow is assumed to be pressurized flow for the design of headrace tunnel.

7.3.3. Headpond

Headpond is located on the right bank of Irkhuwa Khola at the end of settling basin. The purpose

of the intake is to draw water into headrace tunnel. An arrangement to prevent debris flow

inside the headrace pipe is provided by a fine trashrack in front of the headpond. The headrace

tunnel entrance is lowered by 5.5 m to prevent vortex. The size of the headpond is 3.5m x 5.5m

(BxH).

7.3.4. Headrace Tunnel

The headrace tunnel conveys the flow to the surge shaft and thereby to the turbines through

penstock pipe. Design flow of 7.8 m3/s will be conveyed through the headrace tunnel. The sizing

of headrace tunnel is done by optimization. Spreadsheets were prepared to carry out the

optimization. The Headrace tunnel has an inverted D shape at top with radius of 1.75 m and the

bottom rectangular portion has sizing 3.5 mx1.75 m (BxH).The velocity of flow inside the tunnel

is 0.71 m/s. The total length of the tunnel from the headpond to the penstock pipe inlet is around

3720 m.

7.3.5. Anchor Block and Support Piers

An anchor block is a mass of concrete fixed into the ground which holds the penstock and restrain

its movements. Movement of the penstock occurs due to various forces. These forces include

forces due to dead weight of penstock and water being carried, expansion and contraction

forces, water hammer pressure and forces on the bends. A total of 6 Anchor blocks are required

to accommodate the horizontal and the vertical bends of the headrace pipe alignment and to

provide the necessary degree of stability to the pipe assembly. The sizing of the blocks are done

as per the nature of bends in the pipe and also the considerations on the safety against

overturning, safety against bearing capacity and safety against sliding.


7-8

7.3.6. Expansion Joints

Expansion joints are provided to accommodate the stresses occurring due to thermal expansion.

A thermal expansion adds stresses on the penstock pipe which can cause buckling of the pipe.

So, provision must be made for the penstock pipe to expand and contract, by installing an

expansion joint in a penstock pipe section between two anchor blocks. Mechanical joints either

expansion joint or bolted sleeve type coupling is used in both exposed and buried penstocks to

accommodate the longitudinal movement caused by the temperature changes and to facilitate

the construction. It should be provided just below the anchor block. The provision of the

expansion joints helps to decrease the size of the anchor block since they will not need to

withstand forces due to pipe expansion and also accommodate slight angular pipe misalignment.

7.4. Surge Shaft

The surge analysis of the proposed surge tank has been conducted as per Thoma’s Equation

which allows us to calculate the minimum required area of the surge tank and thus allowing us

to determine the diameter of the surge tank.

The critical section for stability is given by Thoma’s Equation,

�� =��

2�∗

�� ∗��

ℎ� ∗(� − ℎ�)

Where,

�� = minimum cross sectional area of surge tank, m2

� = velocity in pipe, m/s

�� = cross sectional area of pipe

�� = length of headrace pipe

ℎ� = headloss in pipe

� = gross head

For a sudden 100% load rejection,

�� = 1 −�

�� +

�

��*��

And for 100% load acceptance,

�� = (1 − 2��)∗��


7-9

Where,

�� =��

��∗�

�� ∗��

� ∗��

�� =ℎ�

��

Where, �� and �� are maximum upsurge and maximum downsurge respectively.

As per the calcualtions, a cylindrical simple orifice type surge shaft with 5 m diameter is proposed

for the stability of the surges. This analysis showed that the downsurge reaches to 914.75 masl

and the upsurge reaches to 931.59 masl. But the top level of the surge tank is fixed to 933.60

masl as per topographic condition which is very safe so that the water will not get spilled even

in worst case of upsurge. A steel wire mesh manhole on top of the surge tank is provided for

access during maintenance.

Based on the calculations, the study came to propose the surge tank with following features:

Type : Simple orifice type

Shape of surge shaft : Cylindrical

Diameter : 5 m

Height : 25.0 m

Static water level : 920.18 masl

Maximum upsurge level : 931.59 masl

Minimum down surge level : 914.75 masl

7.5. Penstock

7.5.1. General

Steel penstock pipe is provided to convey water from surge shaft under pressure to turbine.

From the optimization the internal diameter of penstock is 1.85 m before bifurcation & 1.35 m

after bifurcation. The wall thickness of penstock pipe varies from 10 mm to 24 mm. The pipe will

be manufactured from Plate of Standard SM400B or equivalent. The thickness was calculated by

taking the effect of water hammer by 40% along with the 2 mm corrosion allowance. The total

length of the penstock is about 375 m including the penstock pipe length after bifurcation. The

design flow velocity in the main penstock pipe is 2.9 m/sec.


7-10

The penstock starts from surge shaft at an elevation of 910.41 masl. During this study, the pipe

thickness has been varied in five stretches as per the design criteria that show the thickness of

the pipe for different gross heads. Thickness transition in accordance with internal pressure

criteria shall be reduced at the time of detailed design and material procurement. The

optimization study of penstock pipe for different arrangement and different operating modes

are carried out and presented in Error! Reference source not found..

Table 7-1: Thickness of penstock pipe for different head

S N Section Internal diameter (mm) Thickness (mm)

1 Head 9.77m to 32.11 m 1850 10

2 Head 32.11m to 62.92 m 1850 12

3 Head 62.92m to 119.64 m 1850 26

4 Head 119.64m to 147.81m 1850 18

5 Head 147.81m to 220.18m 1850 24

7.5.2. Design Conditions

The steel penstock pipe is designed for the following conditions:

(a)To resist the internal pressure, the internal pressure is of the sum of the static head and the

pressure rise due to water hammer plus high surge water level, which are defined as follows:

(i) Static head is the difference between the elevation of the turbine axis and weir crest level.

Where,

Weir crest level = EL 923.00 m

Tailrace water level = EL 701.50 m

(ii) Pressure rise due to water hammer

The maximum water hammer pressure is 10% of gross head.

(iii) The maximum water level at the Surge Tank is at elevation of 931.59 m.

(b) To resist the external pressures

The penstock pipe if encased in concrete is capable of resisting the following external pressure

when the penstock is empty. The factor of safety for pipe shall against buckling under the

external pressure is not less than 1.5.


7-11

The external pressure at the embedded portion of the penstock pipe is assumed to be as a water

head equivalent to the difference between the centerline of the penstock pipe and the elevation

of the ground surface.

The thickness of the penstock pipe shell required to withstand the external pressure shall not be

less than that required by Amstutz’s formula for embedded pipe.

The external design pressure of the penstock pipe is a water head of 3 m during dewatering

operation for the surface penstock and head of ground surface to the centerline of penstock for

embedded type Penstock. The penstock where embedded in all the horizontal portions is

capable of resisting the external pressure due to contact grouting between the pipe shells and

secondary concrete. The grouting pressure for designing the penstock pipe is 3 kgf/cm2.

(c) To resist the axial forces

The penstock pipe is capable of resisting the axial forces. The considerable axial forces are as

follows:

(i) Bending stress due to restraining the pipe shell expansion by the stiffener rings.

(ii) Stress due to the weight of the penstock steel pipe at the inclined portions.

(iii) Stress due to axial component of internal pressure acting on the reducing pipes.

(iv) Stress due to temperature variation of the penstock during water filling.

(v) Stress due to Poisson's effect.

(d) To resist the loads due to handling during fabrication, transportation and field erection.

(e)To reduce hydraulic frication losses in the penstock to a minimum

The maximum deflection angle between segments of a bend is 7.5 degrees. Under such

inevitable cases as right angle bend pipes, bifurcating pipes, and the like, the radius of curvatures

of the pipes may be equal or greater than, 3 times of the inside diameter of the pipe.

7.5.3. Design Stresses

7.5.3.1 Steel Plates and Structural Steels

The stresses of steel plates and structural steels, for SM490B or equivalent steel, are as given

below:


7-12

Stress Thickness ≤ 16

mm

Thickness ≥ 16 to ≤ 40

mm Thickness ≥ 40

Yield Point Stress 365 MPa 355 MPa 335 MPa

Ultimate Tensile

Stress

490 to 610 MPa

7.5.3.2 Allowable Stresses

(i) Ample factors of safety are used throughout the design of the equipment, especially in the

design of parts and components subject to alternating stresses, vibration, impact or shock.

Under maximum normal operating conditions and hydrostatic pressure test conditions

respectively, the unit stress in the material shall not exceed the following values:

Parts under static stress 50% of the yield strength

Parts under dynamic, alternating stresses and rotating

parts

35% of the yield strength

Parts under hydrostatic test pressures 70% of the yield strength (during

tests)

Rotating parts under maximum runaway conditions 75% of the yield strength

The design assumes full responsibility for an adequate design and shall use lower stresses

wherever necessary (conforming to accepted good engineering practice).

(ii) Under the loading condition of fully filled with water in the penstock steel pipe, the circular

stress, axial stress and the shearing stress acting perpendicular to the axis of the pipe and the

combined stress, is less than the allowable stresses specified under clause (i). However, the

allowable stress may be increased by 1.35 times the above allowable stresses when the bending

stress in the pipe shell due to restraining the pipe shell expansion by the stiffener ring has been

considered.

The combined stress is calculated by the following formula as developed by Mises Hencky Huber:

221

2

2

2

1 3 g

Where,

g : Combined stress


7-13

1 : Circular stress (tension is considered as positive)

2 : Axial stress acting perpendicular to axis of 1

(Tension is considered as positive)

: Shearing stress

(iii) Allowable stresses for circular bending stress imposed in penstock shell during water filling

operation into the penstock steel pipe may be 50 per cent higher than those specified under

clause (i). In no case, however, shall any stresses exceed 90% of the minimum elastic limit of the

material used.

(iv) When other steel material than those mentioned in clause (i) is used, its allowable stresses

is determined based on the yield stresses of the steel materials to be used according to the ratio

of the allowable stresses and steel materials specified under clause (i).

7.5.3.3 Assumptions

The pipe thickness design is based on the following data and assumptions:

Design flow (Q) : 7.80 m3/s

Static Head : 221.5 m

Unit weight of steel : 7850.0 Kg/m3

Material Specification : SM400B

Young’s modulus of steel : 200,000 N/mm2

Corrosion allowance : 2.0 mm

Welding efficiency (ηw) : 90 %

Surge head (Hs) : 10% of static head

Factor of safety (FOS) : 2.5

7.5.4. Expansion Joints

There are 4 numbers of expansion joints in the penstock line. The suitable expansion joints are

designed and fabricated to absorb the thermal stresses due to temperature difference in

penstock. The expansion joints aredesigned to withstand the 1.5 times of design pressure. The


7-14

expansion joints are designed with 100% water tight. The internal diameter of expansion joints

are 1.85m.

7.5.5. Anchor Blocks and Support Piers

Six anchor blocks for exposed part of the penstock have been proposed for this project with two

extra blocks for bifurcated pipes. Anchor blocks are of C25 concrete with 40% plums and

nominal/ temperature reinforcement to avoid uneven settlement & cracking. The blocks have

been designed to provide stability against sliding, overturning and bearing pressure.

7.6. Powerhouse

7.6.1. General

The proposed powerhouse is located at Kuda Kaule VDC on the right bank of Irkhuwa River. It is

located at downhill of the Dhopichaur village and about 250 m upstream of the confluence of

Irkhuwa River and Benkhuwa River. The powerhouse is surface type with two units of horizontal

axis Pelton turbine, each of 7.25 MW generating capacity. The centerline of turbine axis is fixed

at 701.5 masl. Overall size of powerhouse is about 30.25 m long and 10 m wide.

Powerhouse complex contains inlet valve, turbines, generators and electro-mechanical

accessories. The proposed size of powerhouse is selected based on size and number of

electromechanical component.

7.6.2. Powerhouse Main Floor

The powerhouse main floor consists of:

Machine hall

Erection bay

Workshop, store, rest room and a common room

The machine floor of the powerhouse is 19.5 m long and 9.5 m wide. It contains two units of

horizontal axis Pelton turbine. The center line of the turbine and generator is at 700 masl

elevation. A 32-ton bridge crane will run on two parallel crane beams supported on a series of

concrete columns along the long sides of the powerhouse.

7.6.3. Control Room and Other Utility Spaces

The control building is one story building above 701.5 masl. Floor area is 3.6 m x 12.75 m. High

voltage switchgear room, maintenance and tools room and office facilities are provided at the

ground floors. The control room is located on surface and contains all necessary equipment

required to control the powerhouse operation and monitor the operation of headwork structure.


7-15

7.6.4. Switchyard Area

The proposed outdoor switchyard area is located close to entrance of the powerhouse. The

switchyard covers 15 m x 9.5 m area at the right bank of Irkhuwa Khola at an elevation of 700

masl. A security fence with an entrance gate will be built in the switchyard area to prevent

unauthorized access.

7.7. Tailrace Canal

The tailrace canal is designed as a non-pressure flow. The tailrace canal would discharge water

from the turbine into the Irkhuwa River. The size of the proposed tailrace canal is 2.6 m wide,

1.8 m high and 27 m long.

1 in 470 bed slope of the channel has been set to correspond the flow of water. The selection of

the invert level at the discharge point is based on flood levels in the river. At full flow (7.8 m3/s),

the depth of the water in the channel will be 1.3 m.

7.8. Hydro-Mechanical Equipment

The hydro-mechanical components of the Project will consist of the following items:

7.8.1. Stoplogs

Two sets of vertical lift fixed wheel stoplog, electric chain pulley operated hoisting with its guide

frame, lifting beam, four-way sealing arrangement, steel support, roof truss, purlin, CGI Sheet,

Ladder & other materials for hoisting Shed, embedded parts and dogging device with handling

tools complete with necessary accessories is designed in the Undersluice.

The stoplog is designed in the conditions that thickness of 2.0 mm shall added as corrosion

allowance to the calculated thickness of all steel plates for all exposed surfaces in water.

(i) Design Data:

Gate Width (w) = 3.0 m

Gate Height (h) = 2.0 m

Sill Elevation = 919.50 masl

Quantity = 1 Set

Hoisting Type = Electric Chain Pulley Operated

Water Seal = Downstream, Four-way

(ii) Assumptions for Design:


7-16

Material: = IS 2062:1999 Grade ‘B’

Allowable Bending stress ≤ 120 N/ mm2

Allowable Shear Stress ≤ 70 N/ mm2

Deflection Ratio (L / ymax) ≥ 800

Effective Width of Roller ≥ 60 mm

Roller Material = Cast Steel

Roller Brinell Hardness (BHN) = 217kgf /cm2

7.8.2. Intake Gates

For the sake of regulating the inflow as well as repair and maintenance works, two sets

manually operated vertical mild steel lift gate of 2.6m x 2.25m (W x H) and 2.8m x 2.25m

(W x H) is proposed at the intake of Phedi and Thumlung Khola Respectively. For the ease

of operating manually, it will be of spindle type.

7.8.3. Trashracks

The trashracks are designed to prevent debris and others matters injurious to the water turbines

and to adequately withstand the static load, impact load, and vibration phenomenon which are

likely to occur due to flow of water passing through the trashrack.

7.8.3.1 Coarse Trashrack

(i) Design Data

Trashrack Width (w) = 2.8 m

Trashrack Height (h) = 2.80 m


Inclination = 70 Degree

Quantity = 2 Sets

Clear Bar Spacing = 50 mm

(ii) Assumptions for Design


Bending stress ≤ 0.66 x (Yield Stress) x (1.23 -0.015L/t)

L/t ≤ 70

d/t ≤ 12


7-17

L : Laterally unsupported length of bar

t : Thickness of bar

d : Depth of bar

(iii) Trashrack Body

Plate thickness ≥ 10 mm


7.8.3.2 Fine Trashrack

(i) Design Data

Trashrack Width (w) = 3.5 m

Trashrack Height (h) = 1.87m


Inclination = 70 Degree

Quantity = 1 Set

Clear Bar Spacing = 25 mm



Bending stress ≤ 0.66 x (Yield Stress) x (1.23 -0.015L/t)

L/t ≤ 70

d/t ≤ 12

L : Laterally unsupported length of bar

t : Thickness of bar

d : Depth of bar

7.8.4. Undersluice Gate

Two sets of vertical lift gate, rope drum operated hoisting with its guide frame, control system,

control cabinet, upstream four-way sealing arrangement, steel support, roof truss, purlin, CGI

Sheet, Ladder & other materials for hoisting Shed, embedded parts and dogging device with

handling tools are proposed in the Undersluice.

The gate is designed in the conditions that thickness of 2.0 mm shall added as corrosion



7-18

(i) Design Data




Quantity = 1 Set

Hoisting Type = Rope Drum Operated

Water Seal = Upstream, Four-way






Effective Width ≥ 60 mm


Brinell Hardness (BHN) = 217kgf/cm2

7.8.5. Settling Basin Inlet Gate

Two sets of vertical lift electric chain pulley, fixed wheel gate with its guide frame, Upstream

three-way sealing arrangement, steel support, roof truss, purlin, CGI Sheet, Ladder & other

materials for hoisting Shed, embedded parts and dogging device with handling tools complete

with necessary accessories is designed in the settling basin.

The gate is designed in the conditions that thickness of 2.0 mm shall added as corrosion


(i) Design Data




Quantity = 2 Sets

Hoisting Type = Electric Chain Pulley Operated

Water Seal = Upstream, Three-way


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Roller Effective Width ≥ 60 mm


Brinell Hardness (BHN) = 217 kgf/cm2

7.8.6. Settling Basin Flushing

Two sets of exit gate are provided at the end of flushing channel for flushing the sediment

deposited.

7.8.7. Penstock Valve

One set of penstock valve butterfly type, internal diameter 2.3 m with accessories is designed in

the penstock pipe after surge shaft. The design head for the butterfly valve is 22 m WC.

One (1) set of butterfly valve complete with bypass valve complete with:

Service seal arrangement

Maintenance Seal arrangement

Operating mechanism and instrumentation

Bypass line and appurtenances

Foundation plates, complete with back holders, anchor bolts, nuts, washers, etc.

Control devices, control cables, control cabinet, power cables etc.

One (1) set of Gantry crane

7.9. Electro-Mechanical Equipment

7.9.1. General

Hydroelectric power generation involves conversion of hydraulic energy into mechanical energy

by the hydraulic turbine, and conversion of mechanical energy into electrical energy by an

electric generator. The generating equipments housed in power house is divided into

mechanical generating equipments, comprising of turbines, inlet valves, governor, cooling water


7-20

supply, etc. and electrical equipments comprising of generator, excitation system, breakers,

metering, protection and control equipments, etc. The generating units with high efficiency build

from modern state of the art technology and the best one that can be realized in practice are

considered in Upper Irkhuwa Khola Hydropower Project. Both the equipments are discussed in

detail in upcoming section.

The general design and performance specification for the electrical and mechanical equipment

are based on the latest standards issued by IEC and/or equivalent standards.

7.9.2. Powerhouse Mechanical Equipment

The study reveals that the installation of two turbine-generator units will be more economical

for the following reasons:

The reliability of the plant during the operation

To avoid turbine to run in partial flow condition

Annual maintenance of the turbine-generator units during the dry season without

losing the available discharge

The powerhouse mechanical equipment of the Project mainly consists of the followings:

Turbine

Governor

Turbine inlet valve

Fly wheel

Cooling water supply system

Drainage and dewatering system

Compressed air system

Lubricating system

Oil handling system

Ventilation and air conditioning system

Emergency diesel generating set

Fire protection system

Mechanical workshop and equipment


7-21

Powerhouse overhead travelling crane

7.9.3. Turbine

The selection of type of turbine primarily depends upon the net lead available and design

discharge. For the rated net head of 217.85 meter and unit design discharge of 7.80 m3/s, Pelton

Turbine having horizontal shaft arrangement is the choice of the turbine.

The selection of Turbine is carried out considering both the 2 units and 3 units option. The rated

discharge for two unit and three unit option is 3.9 m3/s and 2.6 m3/s respectively. With both the

options the turbine for Upper Irkhuwa Khola Small Hydropower Project, horizontal Pelton

turbine is selected as shown Error! Reference source not found..

The selection of number of units is based on the assumption that minimum number of units

could be installed for the more economic development of the project, reliability of generation,

and minimum loss of power during maintenance and operation at difference stage of time. Unit

capacity is generally determined by considering the available discharge throughout the seasons,

load demand, type of operations, efficiency of the machine, etc. Single unit is not preferred due

to the fact that total generation loss will occur in time of the unit breakdown and hence two or

three units will be suitable for the Project.

So, for a given design discharge and net head available at powerhouse, 7.80 m3/s and 219.01m

respectively, two units horizontal axis Pelton turbine is selected considering the EM cost,

increase in operation cost with the increase in number of units and increase in power house size

with the increase in number of units; and succeeding discussions are based on two unit options.


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Figure 7-1: Turbine Selection Chart

Each turbine shall be capable of handling 3.90 m3/s discharge (design) at a rated net head of

219.01 m, which result in the turbine shaft power of 7.25 MW at a maximum efficiency of 0.92.

The size and speed of the turbine is such that the total costs of civil, electrical and mechanical

works will be minimized.

Further detailed information about the turbine operation during flood periods and part load will

be studied in the next phase of the study.

The Francis runner will be coupled to the generators by turbine shaft or by intermediate shaft, if

required for sideways dismantling, as will be addressed in detailed design. Both couplings of the

shaft will be bolted flanges.

The parameters of the turbine is given in Error! Reference source not found. below


7-23

Table 7-2: Parameters of Francis Turbine

Description Parameters

Turbine rated output, P 2x 7250kW

Rated net head, Hn 217.85

Rated water flow, Q 3.90 m3/s x 2

Efficiency, η 92%

7.9.3.1 Turbine Speed

Speeds for modern Francis turbines are represented by the equation

Trial Specific Speed ns’ = 3470/H0.625

= 151.659

Trial Synchronous Speed

= 695.92

Number of pair of poles = 60*50/n’ = 4.31

Hence, the calculated turbine speed comes out to be 750 rpm.

7.9.3.2 Runner

The shape of runner vanes will be designed to obtain the best possible results taking into

consideration Cavitation and efficiency. The runner will be free of cracks, porosities and

inclusions and will be machined/polished to a perfect finish, dynamically and statically balanced

and heat treated for stress relieving.

The runner will be of integrally solid casting or welded steel of minimum 13% Cr and 4% Ni. The

runner will be designed and constructed to safely withstand the stresses due to operation at

runway speed and under the most severe conditions. All surfaces of the runner exposed to water

will be furnished smooth and polished.

Inlet edges of guide vanes and discharge openings between adjacent vanes will be uniformed

and properly shaped. The runner will be interchangeable. Bolted connection will be provided for

attaching the runner to the turbine shaft. The bolts shall be locked in position to prevent

loosening during operation.


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7.9.3.3 Shaft

The turbine shaft will be made of forged steel with properly heat treated. It will be designed to

operate safely in combination with the generator shaft at any speed up to the maximum runway

speed without detrimental vibration or distortion.

The shaft will have an integrally forged flanged half-coupling on its Generator side end for

connection with a coupling flange on the generator shaft. The runner side shaft flange will be

provided with necessary arrangement for attachment of the runner removal device. The shaft

alignment of both turbine and generator will be carried out as per NEMA standard.

7.9.3.4 Guide Bearing

The turbine will be equipped with a self-lubricating oil type guide bearing. The bearing will

consist of support or housing and a removable bearing sheet. The guide bearing will be of self-

lubricated and water cooled and complete with oil reservoir and water cooling coil.

7.9.3.5 Spiral Case and Stay Ring

The spiral casing and stay ring will be designed without considering support from the surrounding

concrete. The resulting forces shall be transferred through amply dimensioned anchors into the

concrete foundations. The stay vanes and stay rings will be of welded construction, or cast steel.

The stay vanes will have a favorable hydraulic profile.

The spiral casing will be made from steel plate sections as a welded construction. The number of

sections shall be suitably chosen so that the water does not abruptly change its flow direction.

The spiral casing shall have a manhole not less than 600 mm in diameter complete with cover,

bolts and O-ring and seal. The inside surface of the cover will be flush with the inside surface of

the spiral casing.

The spiral case will be constructed with sufficient strength to withstand the maximum hydraulic

pressure.

7.9.3.6 Wicket Gates

The wicket gates will be of stainless steel, cast or forged, material quality 13/4 Cr/Ni or similar.

Levers, links and regulating ring will be made of cast or welded steel. Breaking, bending or friction

links will be use.

A protective device will be furnished for each wicket gate so that a vane with broken or displaced

link will have a stable hydraulic position and will not be allowed to touch the runner or to cause

cascading failure of the other wicket gates.


7-25

The wicket gate operating mechanism, including the vanes, will be designed to withstand the

maximum load under the most severe operating conditions. The number of vanes will be

selected so that no vibration or resonance between runner and vanes will occur. The wicket gates

will be machined to a perfect shape and smoothness and be interchangeable.

7.9.3.7 Draft Tube

The draft tube will be designed for an efficient pressure recovery at all load conditions. It will be

dimensioned to withstand the worst possible transient conditions without undue stresses or

deformations. It will also withstand the outer force by the grouting when it is un-watered for the

installation at site.

The draft tube will be of elbow type and made of welded steel plate not less than 12 mm in

thickness using rolled steel for general structure. The draft tube will include the following parts:

Removable Cone with manhole of size 600 mm dia, which will be flanged and bolted to the

discharge ring.

Lower Draft Tube Liner which will be the embedded parts of the draft tube with bend and

diverging part, with flanged inlet. The downstream end will end up in a rectangular cross section.

The structure will be made from steel plates of minimum 12 mm thickness. All sections will have

sufficient ribs and anchors for safe embedding in concrete.

Steel props and foundation lugs for convenient installation and assembly, and suspension hooks

for hauling will be provided. A sufficient number of leveling screws or jacks and anchor rods with

turnbuckles will be provided for centering, leveling, and securely holding the liner in correct

position both vertically and laterally during erection, concreting and grouting.

The draft tube will be divided into sections suitable for the transportation limitation and will be

then assembled at the site by welding.

7.9.4. Governor

Each turbine unit will be provided with an efficient automatic governing system of adequate

capacity to control the turbine under all conditions. Control and operation of the turbines will

be possible either from the station control room or from the local unit control panel for the

purpose of commissioning and testing.

Control of the turbine will be accomplished by controlling the opening of the guide vanes, with

minimum loss of water so that pressure in the penstock never exceed given limit. The governors

will be designed and equipped for taking the unit automatically to the rated speed at no-load

operation. When the generator is connected to the grid, the regulating parameters will be

changed and load setting will be possible. The governors will allow proper sharing of load


7-26

between the two units under any condition of load and speed without hunting. When the power

house is interconnected with the existing power system, the units will be capable of

synchronising with the other power stations in the system.

Each unit will consists of a Digital Electronic Governor with Proportional Integral Derivative (PID)

action while running on isolated as well as on Load Sharing Module.

The governor will control the speed of the turbine via modulation of the guide vanes. The

governing system should be highly accurate and rugged.

The turbine governor system shall include following control functions:

Manual Start-up by sequences of linked control actions,

Semi-automatic start up by sequences of linked control actions,

Full automatic start-up,

Operation with automatic power limitations, with power feedback,

Control of turbine output when the two units are operating in parallel,

Frequency control,

Load sharing between the units,

Rated speed no-load control,

Normal shut down,

Emergency shutdown, and

Provide oil pressure to control the main inlet valve.

The governor system will consist of the following main units:

Electronic speed governor,

Speed monitoring system,

Oil pressure system,

Oil pressure accumulator system,

Hydraulic actuator control unit,


7-27

Mechanical hydraulic over-speed device,

Servomotor feed-back system,

Instrumentation, alarm and safety devices and

Speed signal generator

The governor regulation data shall be as follows:

Speed rise during full load rejection : ≤ 30%

Pressure rise during full load rejection : ≤ 40%

Inlet Valve Closing Time : ≤ 65 seconds

Guide Vane closing time : 4 to 16 seconds

7.9.5. Inlet Valve

Flow is distributed to the turbines through a common penstock pipe. Therefore in order to isolate

any unit for inspection and maintenance without disrupting flow to the remaining units, it is

necessary to provide a main inlet valve (MIV) for each unit.

For the gross head of 221.5 m at the plant, a Butterfly Valve will be appropriate.

Depending on the concentration of sediment passing into the power waterway, the butterfly

valve blade may suffer erosion damage, which could affect sealing. Providing all seals are

removable, adjustable and made of high performance rubber, this should not be a major

problem. The inlet valve is located inside the powerhouse immediately upstream of the spiral

case, thus facilitating its installation and maintenance handling using the powerhouse overhead

crane. The valves are specifically designed;

To withstand the maximum operating pressure including water hammer;

To be able to close safe and reliable under flow conditions, i.e. against the

maximum turbine flow;

To open under nearly balanced pressure conditions on the upstream and

downstream valve side, achieved by means of an automatic bypass system;

For reliable sealing (drop tight) in closed condition


7-28

Opening of the valve is controlled by oil operated, single acting servomotor and closure of the

valve is by counterweight. The servomotor is supported on fixed base plates or directly on the

valve body. Necessary connection linkages will be provided.

7.9.6. Cooling Water and Water Supply System

Open circuit cooling water system with adequate capacity of pump shall be provided.

Cooling water system of one set common for all units shall comprise of the following:

Two Nos. of submersible pumps complete with motors, starters, base plates etc.,

One No. of flow meter, flow switches etc., One set of strainers.

Design of the cooling water system shall be such that one pump can meet the

requirements of cooling water for one unit. The whole system shall be designed

in such a way, that any pump can be operated for supply of cooling water to that

particular unit. Necessary sectionalizing valve shall be provided.

The cooling water shall be used for generator bearing lubricating oil system heat

exchanger and shaft sleeve (If applicable)

This circuit shall be equipped with, flow indicators, piping and valves etc. Return

lines from heat exchanger shall be discharged to tailrace.

7.9.7. Drainage and Dewatering System

Drainage and dewatering systems for the project are provided as follows:

(a) Station Drainage

Drainage water from different parts of the power station is collected in a deep drainage sump.

The drainage water from the sump is removed by two submersible water pumps to the tailrace.

(b) Unit Dewatering System

The dewatering system is designed to collect the water drained out from draft tube, turbine

space & spiral case into the dewatering pit and then this water is pumped out from dewatering

pit with the help of submersible pumps into the tailrace channel.

Suitable size pump is provided to pump out the drained water from dewatering pit to tailrace.

The pumps are submersible type and when dewatering is required, the pumps are lowered into

the dewatering pit using chain pulley block. The pumps are operated using a local electrical

control panel near the pit in manual mode.


7-29

7.9.8. Pressure Oil System

Pressurized oil is to be used for control the following:

a) Two nos. (Single acting) wicket gate servomotor (Open by oil pressure & close by

spring action).

b) One no. (Single acting) butterfly valve servomotor (Open by oil pressure and close

by counter weight).

c) Hydraulic Brake of Generator.

For application stated above, pressurized oil is required. Two nos. of Gear pumps, one as main

& other as stand-by which driven by electrical motors, supply oil to the system. Loading /

unloading of the pumps shall be made by the signals given from pressure switch provided at oil

pressure line. The standard oil pressure unit operates under a pressure of 64 bars, however the

normal operating pressure of 100-120 kg/cm2 is recommended. The high pressure units are

advantageous because they require smaller servomotors and associated parts. In addition, they

use bladder accumulators (viz. Nitrogen), thus eliminating the need for a separate high

compressed air station.

A common accumulator (bladder type) is provided for MIV & Turbine wicket gate, which

maintain the required pressure in the system and also shall use for pressure oil supply during

emergency operation or pump failure. The capacity of the accumulator shall be sufficient to meet

the pressure oil requirements.

7.9.9. Ventilation and Air Conditioning System

This system provides the fresh air to working personnel and removes the heat generated

by mechanical and electrical equipment. It also provides the smoke exhaust ventilation in case

of fire to minimize the circulation of smoke and production of combustion. Ventilation and air

conditioning system consists of fresh air handling unit and air conditioning unit.

The fresh air handling unit is installed inside the ventilation room and consists of air filters and

three air admission fans, two “on duty” and one “stand by”. The unit sucks air from outside and

distributes it via appropriate ducting to different locations of machine hall floor, generator floor,

turbine floor or other places such as control room.

The ventilation system will mainly consists of necessary numbers of axial ventilation fans

installed in appropriate locations. The various powerhouse rooms and areas like switchgear

room, office floor, machine hall floor whose ambient are not air conditioned are continuously

supplied with fresh filtered outside air.


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7.9.10. Fire Protection System

The Fire Fighting System is designed to safe guard equipment installed in the powerhouse &

switchyard area. The fire protection system shall comprise of following main parts;

1. Fire Hydrant System for Power House & switchyard and Pump House Equipment

The Hydrant system consists of over ground piping network, which is fed by 2 Nos. of horizontal

centrifugal pumps to be installed in Powerhouse. The Hydrant valves are installed on the stand

post, which is connected to the main header pipe and each hydrant valve is strategically located

around Power House equipment.

In the event of fire, with the rapid fall in header pressure due to opening of hydrant valve the

common fire pump shall start automatically. In case of failure of main fire pump the standby fire

pump will come into operation at a time.

2. Water Spray System for protection of Generators and Transformers

Automatic High Velocity Water Spray System will be used to protect generators and generating

Transformers located in powerhouse and switchyard area respectively. The generators and

transformer will be surrounded by a ring fitted with open high velocity spray nozzles. The ring

main will be connected to the spray system header through a wet pilot deluge valve fitted with

water motor gong and with upstream and downstream Gate Valves. The header will remain

charged with water under pressure up (7.0 bar) to the inlet of the deluge valve.

3. Portable fire extinguishers

Following portable fire extinguishers will also be provided for protection against fire at

powerhouse and switchyard area.

a) Dry Powder type fire extinguishers (4.5 kg)

b) CO2 type fire extinguishers (4.5 kg)

c) Foam type extinguisher (9 lts.)

d) Fire Bucket

7.9.11. Mechanical Workshop and Equipment

A mechanical workshop will be equipped with machine tools and devices appropriate for the

maintenance and repair of all mechanical components and machining of the smaller components

of the mechanical electrical equipment and hydraulic steel structures.


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7.9.12. Powerhouse Overhead Travelling Crane

A double girder Electric Overhead Travelling (EOT) crane having main hook capacity of 25 tons

will be installed inside the powerhouse. It will be used for lifting and handling any equipment

during installation, maintenance, and operation of the plant. Basic data and governing

dimensions of the powerhouse crane are given below in Error! Reference source not found..

The crane shall be complete in shape conforming to the standards of the Power House service.

Supply shall include current collector, down shop angle conductor with bracket, insulator.

The LT rails shall be supplied long with the crane.

Table 7-3: Details of powerhouse crane

Description Unit Quantity

Main Hook capacity Tons 22

Auxiliary Hook capacity Tons 5

Heaviest part to be lifted

(Generator Rotor)-

Approximately

Tons 18

Voltage 3 Phase, 400V, 50Hz

7.9.13. Powerhouse Electrical Equipment

The major electrical equipment will comprise of the following equipments:

1) Generator

2) Excitation and Automatic Voltage Regulator

3) Power Transformer

4) Station Auxiliary Transformer

5) 11kV Protection and Measuring Equipment

6) Air Circuit Breaker

7) Diesel Generator

8) Motor Control Centre

9) DC Power Supply


7-32

10) Grounding/Earthing System

11) Communication System

7.9.13.1 Generator

Self-excited, self-regulated, vertical axis, three phase, salient pole, synchronous generators built

in accordance with IEC standard is proposed to be used.

The generators will have capacity to incorporate sufficient flywheel inertia to achieve stable

frequency control when running in isolated mode. The generator shall have antifriction / sleeve

bearing.

The stator winding of the generator will be made of individually insulated stranded copper

conductors, stacked and form pressed to constitute coils or half coils with the design cross

section. Each coil will be insulated for the full generator voltage.

The rotor will be of the salient pole type and built in accordance with the best practice and

designed to withstand safely all overloads and other stresses encountered during abnormal

operating or runaway speed conditions. The poles will be built of thin steel laminations, bolted

under high pressure and furnished with dovetails for fastening to the rotor rim. Rotor will be

designed so as to allow dismantling of the poles without excessive disassembly of the stator or

rotor. The damper winding will be installed on pole faces with interconnecting type windings in

order to maintain the stable operation of the generator.

The generator will be capable of withstanding, without damage, a 30 second, 3 phase short

circuit at its terminal when operating at rated MVA, at rated power factor and at 5% over voltage

with fixed excitation.

The generators will have enough electric heaters and dehumidifiers and arranged in fan shield

of generator to protect it from moisture during shut down and to enable a start up at any time

without drying procedure. Insulation and other parts of the generator will not be damaged when

electric heater runs.

Resistance type temperature detectors of simplex / duplex type shall be arranged symmetrically

in the stator winding to indicate the temperature obtained during operation. An Auxiliary

Terminal box having suitable terminal blocks shall be mounted on the generator frame to

terminate the resistor element connections. The temperature detectors leads shall be kept

flexible to facilitate disconnecting them without breakage.

The generator details are given below in Error! Reference source not found..

Table 7-4: Details of Generator


7-33


Type Salient pole, synchronous

Number of units Two (2)

Capacity 9.965 kVA per unit

Excitation system type Brushless

Number of Poles 8

Synchronous Speed 750

Power Factor 0.85

Frequency 50 Hz

Class of Insulation F

Protection IP54

Efficiency 96.5%

Heating class B

The generator shall have following major protection system:

a) Reverse power Relay,

b) Loss of field relay,

c) High speed trip relay,

d) Generator differential protection,

e) Under and over frequency,

f) Loss of synchronization relay,

g) Field ground detect relay,

h) Negative phase sequence relay,

i) Overvoltage relay, and

j) Stator earth fault relay.

A. Generator Braking

Generator shall be provided with Hydraulic operated brakes of sufficient capacity to bring

rotating parts of generator and turbine to stop from 30 % of rated speed.


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B. Generation Voltage Level

As per IEC 60034-1, the rated voltage of generator with rated output of above 2500kVA lies

between 11kV<Un<15kV. Hence, considering the size of the generator, insulation problem,

switchgear connection and common practice, the generator voltage of 11kV is selected.

The switchgear panels will have inbuilt bus bar cabinets housed in its back. Each generator’s

output terminals shall be connected to 11kV unit circuit breaker with XLPE cable of adequate

size. The switchgears and other protection and control components will accompany them in the

switchgear panel to complete the incoming generation power circuit. Individual switchgear

panels for each generator incoming and outgoing will be provided to complete the generation

level switchgear system. This switchgear system will work in co-ordination with the control

panels accommodated in the control room.

C. Generator Grounding

The generator neutral grounding will be through resistance on secondary side of grounding

transformer.

Grounding resistor shall be mounted on a separate panel near each generator.

D. Generator Fire Protection

Generator fire protection will be provided by a CO2 deluge system. The activation of CO2 fire

protection system will be conditional to the operation of the flame or smoke detectors in the

generator pit combined with the operation of the generator differential protection. The

extinguisher release will only be initiated after a preset time delay and confirmation by operators

in order to allow evacuation of the personnel in the hall at that moment. The extinguisher release

will first initiate Unit shutdown procedures by opening circuit breaker and excitation system

before release.

E. Shaft Arrangement

The Generator will be coupled to the turbine runner through an intermediate coupling shaft.

Generator shaft shall have maximum rigidity and strength so as to guarantee no abnormal

deformation and vibration at various speeds (including maximum runaway speed) when run

together with the turbine. The generator shaft shall be made of a high quality medium carbon

steel, properly heat treated and accurately machined all over and polished at the bearing surface

sand at all accessible points for alignment checks. A complete set of test reports covering

metallurgical strength, & ultrasonic tests performed on each shaft shall be furnished.


7-35

F. Cooling of the Generator

Enclosed air housing with a recirculated air cooling system with air/water heat exchangers will

be selected as generator cooling system. The windings will be directly cooled by air as the

primary coolant and water as secondary coolant from the cooling water system.

7.9.13.2 Excitation System and Automatic Voltage Regulator

Brushless excitation has been selected for Upper Irkhuwa Khola Hydropower Project.

Brushless excitation system for generators consists of an A.C. exciter, rotating high power silicon

diodes.

The A.C. exciter is a 3-phase alternator. The A.C. generated on the rotor is fed to the rectifier

system which is also mounted on the rotor itself. Thus, D.C. voltage is available which is directly

fed to the generator field. For the purpose of making the assembly simpler and compact the A.C.

exciter, the rectifier system and the protection system devices shall be mounted on the same

shaft of the synchronous generator and shall be placed on the overhang portion of the non-

driving end bearing.

The DC voltage of exciter stator shall be fed from excitation panel placed in control room. The

features of excitation and AVR shall be

- Auto channel

- Manual channel

- Compounding for parallel operation.

- Follow up to match Auto and Manual channel out-put.

- Auto over fluxing feature.

- Under / over excitation protection.

- Under excited MVAR limiter.

- Power factor controller.

- Auto control on push-button.

- Manual control on push-button.

- Lamp test push-button.

- Auto voltage Raise / Lower push-button.


7-36

- Manual voltage Raise / Lower push-button.

- Excitation ON push-button.

- Excitation OFF push-button.

- Auto / Manual OFF push-button.

- Excitation ON / OFF Mode (Auto / Manual) Selector switch.

Excitation system will be fully automatic with a provision for automatic change over to the

manual control system. Both the automatic and manual operation circuit will be provided with

independent power supply.

The excitation transformer will be air natural (AN) cooled, dry insulated type using non-

flammable Class F insulating material. The rated power of this transformer shall be 10% above

the power necessary for the excitation of one unit.

7.9.13.3 Power Transformer

This plant shall evacuate the power through common transformer. Three units of single phase

transformer shall be used to make a three phase bank. Transformers will be installed at

powerhouse switchyard. The salient features of the power transformer will be as per the

following Error! Reference source not found.:

Table 7-5: Details of Power Transformer

Particular Specifications

Type 1-phase,oilimmersed

No. of units 3+1 as spare

Installation Outdoor

Rated capacity 6600 kVA

Rated HV (secondary) 132kV

Rated LV (primary) 11kV

Efficiency 99%

Cooling ONAN

Rated frequency 50Hz

Vector group YNd11


7-37

Following protections are proposed to be implemented in power transformers:

Transformer differential protection,

Restricted earth fault protection,

Neutral earth fault protection,

Overfluxing protection,

Thermal protection,

Pressure relief device,

Buchholtz (gas operated relays) protection,

Low oil level alarm,

Over current and earth fault, and

High winding and high oil temperature.

7.9.13.4 Station Supply Transformer

The station auxiliary transformer, used for station power supply, will be three phases, indoor,

dry type, AN type of 400kVA. Two numbers of auxiliary transformers shall be used, with one in

operation and second as stand-by as shown in Error! Reference source not found..

Table 7-6: Details of Station Auxiliary Transformer

Description Specifications

Number of Transformers 3 Phase × 2

Type Indoor

Cooling AN

Type of Tap changing Off Load on High Voltage side

Tap Changing Range ±5% in Steps of 2.5

Power Frequency Withstand

Voltage (kVrms)

HV-275, LV-28

Lightning Impulse withstand

voltage (kVpeak)

HV-650, LV-95


7-38

Rating 350kVA

Maximum Voltage Primary side – 12kV and Secondary Side

– 0.44kV

Rated Voltage (Line to Line) Primary side – 11kV and Secondary Side

-0.4kV

Power Frequency Withstand

Voltage (kVrms)

Primary side - 28kV and Secondary Side

-3kV

Type of Tap changing Off Load

7.9.13.5 11 kV Protection and Measuring Equipment

A. Vacuum Circuit Breaker

Metal enclosed draw out type, cubicle indoor, three phase vacuum circuit breakers are used in

the 11 kV side of the power house equipments. This includes generator circuit breaker (2 Nos.),

delta side of main power transformer (1 Nos.) and delta side of station auxiliary transformer (2

Nos.). Technical specification of the circuit breakers are given in Error! Reference source not

found.below:

Table 7-7: Details of VCB


Type Vacuum, Metal Enclosed,

Cubicle Indoor Type

Rated Voltage 12 kV

Rated normal current (In) 630 A.

Rated Short Circuit Breaking Current 25 kA

B. Instrument Transformers

Instrument transformers i.e., voltage transformers and current transformers continuously

measure the voltage and current of the electrical system and are responsible to give feedback

signals to the relays to enable them to detect the abnormal conditions. Preliminary ratings of

Current Transformers (CTs) and Potential Transformers (PTs) used in the power house are as

shown in the Single Line Diagram (SLD) of this report.

Current Transformer

The rating, burden and location of current transformer shall be as specified in Single Line Diagram

(SLD).

11 kV Potential Transformer


7-39

The technical details of potential transformer will be as follows in Error! Reference source not

found..

Table 7-8: Details of 11kV Potential Transformer


Type Indoor, oil-immersed

Rated primary voltage 11kV/√3

Rated secondary voltage 0.11kV/√3

Impulse withstand voltage (peak) 95kV

Frequency 50Hz

Burden As specified in SLD

Accuracy As specified in SLD

C. 11 kV Lightning Arrestor

The lightning arrester will be provided in switchgear room as well as in the first pole of 11kV line

(if required for headworks supply) for protection of substation equipment from the possible

lightning strike and other abnormal voltages. The technical details of lightning arrester will be as

follows in Error! Reference source not found.:

Table 7-9: Details of 11kV Lightning Arrestor


Type Indoor, gapless Znoarrestor

Frequency 50Hz

System voltage 11kV

Rated voltage 10kV

Impulse withstand voltage 95kV

Power frequency withstand 28kVrms

Nominal discharge current 10kA

7.9.13.6 Air Circuit Breaker

Cubicle Indoor type, three phase Air circuit breakers are used in the 0.4kV side of Power house

equipments. This includes two breakers for Low voltage side of Station Auxiliary Transformers

and one for Diesel Generator. Technical specifications of the circuit breakers are given in Error!

Reference source not found. below.

Table 7-10: Details of Air Circuit Breaker


7-40


Type ACB, Cubicle Indoor Type

Rated Normal Current (In) 800 A for Station Auxiliary

Transformer and 500A for Diesel

Generator.

Number of Circuit Breakers 3

7.9.13.7 Diesel Generator

One emergency diesel generator set is proposed to be installed outside of the power house

building to provide an emergency source of power during a system or power outage. The set will

be of adequate rating for supplying sufficient power to enable the black start of one unit,

operation of the drainage pumps, governor oil pump, bearing oil pump, air compressor for

governor system, and feed the battery chargers. The preliminary estimated capacity of the

standby generator is about 200kVA, 400V at 0.8 power factor, 3 phases, 50 Hz as shown in single

line diagram. The diesel generator will have heating class B, insulation class F and IP23 type of

protection of enclosure.

7.9.13.8 Motor Control Centre

Based on the number of components fed, Motor Control Centers (MCC) feed to most

components in power house. These include motor operators for valves, small to medium

motors, lighting panels, etc. The motor control panels are comprised of vertical sections of

cubicles. A cubicle contains a molded case circuit breaker, motor starter, protection and

metering transformers, control fuses and wiring.

7.9.13.9 DC Power Supply

Maintenance free valve regulated lead acid battery bank unit of specified capacity, 110V / 500

AH shall be used in the power house.

1 No. float and float cum boost charger (SCR controlled) operating on 3 Phase,415 V, 50 Hz, AC

supply of solid state design to charge the battery shall be used. The operation of the charger

shall be automatic. Normally, float charger will be feeding the load and charging battery. In case

battery requires boost charging the same shall be done automatically.

The following meters shall be provided in the charger

A.C Voltmeter 0 – 500 V

D.C. Ammeter


7-41

D.C Voltmeter 0-200 V, DC

Centre zero DC Ammeter 50 A- 0 – 50 A for battery.

AC Main supply failure relay

Rectifier fuse failure relay

Charger failure relay

Battery earth fault relay

Over current Relay.

Auxiliary Relay

110 V DC system will be used for switchgear operations, emergency lighting, generator field

flashing, relay panels, inverter supply, continuously energized coils, solenoids, annunciations,

control, emergency lighting and other purposes. In order to obtain 24V DC voltage requirement

of microprocessor based electronic control circuits like PLC and SCADA, a DC-DC converter shall

be used.

7.9.13.10 Grounding/Earthing System

Adequate earthing is necessary to be provided inside the powerhouse and the switchyard. The

grounding/earthling grid will be designed such that the touch and step potentials will be within

the safety margin. The overall grid earth resistance will not exceed 1 ohm.

The low grounding resistance will be achieved by increasing the grounding area i.e.,

interconnecting the powerhouse ground system with the tailrace pond and other areas. The

ground resistivity measurements will be required which will be performed during the detail

design of the grounding grid.

Power House roof shall be provided with Lightning spikes properly connected to ground mat.

7.9.13.11 Black Start/Island Mode Operation

The power plant shall have black start facilities and shall be able to operate in islanding mode

operation. The detail of islanding mode of the operation shall be as fixed in the connection

agreement or as per the NEA grid code.


7-42

7.9.13.12 Communication System

For communications between Upper Irkhuwa Khola Hydropower Plant, other power

houses/substations together with the Load Dispatch Center (LDC) of NEA, trunk dialing

telephone system (either CDMA, V-SAT communication or Landline phone will be used).

In the control room, one or more telephone service will also be installed with trunk dialing facility

to contact the LDC and other substations.

An automatic PABX telephone system is proposed for the communication between different

sections of the powerhouse, offices, residence of operational staffs, guard house and the

headworks area.

OPGW shall also be used to communicate between power plant and substation/LDC.

7.9.13.13 Control and SCADA System

The computer supervisory and control system at SAKP shall adopt the full distributed mode in

open environment in accordance with international open system concepts so that compatibility

of selection of various computers, transplant ability of system expanding and renewal of

equipment shall be assured.

The open environment shall include application development environment, user interface

environment and interlink of system environment, which shall comply with the specifications of

the open environment recommended by international open system organizations.

The computer supervisory and control system shall have station control level (main control level)

and local control unit level.

The station control level, real time supervisor and control center of the plant shall be responsible

for automatic functions of the whole plant (AGC, AVC, generating optimization control etc.),

historical data process (various operation tables, operation archives of important equipments

and various operating parameters etc.) and man machine dialogue of whole plant (operation

monitor of plant equipment, accident and failure alarm, manual intervention of operating

equipment, modifying and setting of various parameters for the Computer Supervisory and

Control System). Station control level shall be made up of the relevant equipment located at

computer room and central control room. The main computer will adopt dual computers for

redundancy and hot standby. At normal condition a computer works and the other is backing-

up. When master computer receives failure, the main computer is changed-over by back-up.

The local Control unit (LCU) shall have turbine-generator local control unit. Each LCU shall

manipulate production procedures and accomplish the supervision and control functions under

controlling. LCUs will be connected with the production procedures by means of input and


7-43

output interface, with the network by communication interface and exchanging information with

main control level through network. The information shall be exchanged among LCUs. LCUs may

be independent from main control level relatively. They shall directly finish real time data

acquisition and pre-processing, supervision, adjustment and control etc. of unit equipment

conditions with station control level divorced.

The operator’s console in the central control room shall be equipped with CRT display that

displays operation conditions of the power station. When the power station is under normal

operation, the operator can monitor the conditions of each equipment in the power station. The

major monitoring items shall be as follow:

Operating conditions and output of generating units

Operating conditions of auxiliary equipments of the generating units

Operating conditions of the transformers

Status of circuit breakers, disconnectors and earthing switches.

Operating conditions and transmission power of power lines

Opening level of gates, main inlet valves, nozzle openings and deflector positions

Operation mode of station service power, and

Other important parameters

When the system receives any fault or the equipment has abnormality during operation, the

supervisory control system shall automatically give alarm in both sound and picture striking to

the eye to indicate nature, location, time and abnormal parameter values of the event.

7.9.14. Interconnection Point and Switchyard

7.9.14.1 High Voltage Switchyard

A 132 kV outdoor type switchyard shall be constructed near the powerhouse to evacuate the

generated power. The switchyard components shall be suitable for hot, humid and moderately

polluted environment. The switchgear system for this switchyard shall be equipped with Circuit

breakers, Current transformers, potential transformers, disconnecting switches with/without

earthing and Lightning Arrestors and synchronous check relay etc. for 132 kV incoming and

outgoing circuits. The switchgear system here will work in coordination with the associated

control panels accommodated in the control room and shall ensure the overall protection of the

switchyard.


7-44

7.9.14.2 132 kV Measuring and Protecting Equipments

A measuring and protection equipments shall be installed for 132kV side protection of the

outgoing line as well as the interconnection substation as shown in the SLD. The technical details

of measuring and protection equipment shall be as follows in Error! Reference source not

found..

Table 7-11: Details of 132kV SF6 Breaker


Type VCB, Indoor/outdoor type

Nominal system voltage 132kV

Rated maximum voltage 145kV

Rated continuous current 1600A

Rated short circuit breaking current 40kA

One minute power frequency withstand

voltage (rms)

275kV

Impulse withstand voltage (peak) 650kV

Frequency 50Hz

Re-closing duty cycle O-0.3sec-CO-3min-CO

132kV Current Transformer

The technical details of current transformer will be as follows in Error! Reference source not

found..

Table 7-12: Details of CT on 132kV side


Type Outdoor

Nominal system voltage 132kV

Rated maximum voltage 145kV

Frequency 50Hz

Current ratio As shown in SLD

Accuracy As shown in SLD

132kV Potential Transformer

The technical details of potential transformer will be as follows in Error! Reference source not

found..


7-45

Table 7-13: Details of PT on 132kV side


Type Indoor

Rated primary voltage 132kV/√3

Rated secondary voltage 0.11kV/√3

Frequency 50Hz

Accuracy As shown in SLD

7.9.14.3 Power Evacuation

The Delivery Point shall be 132kV bus bar of proposed Khadbari substation which is about 10km

from powerhouse. Upper Irkhuwa Khola Hydropower Project shall construct 132kV line up to the

switchyard of connecting substation. Main and Check meters of accuracy class 0.1 shall be

installed at Khadbari substation.

7.9.15. Construction Power

11 kV transmission line is the cheapest mode of power required for the construction of project.

The other source of construction power could be Diesel Generator installed at different work

fronts of the project. Tentative breakdown of power requirement at different work fronts is

presented herewith. 11kV transmission line is expected to feed the power for the project

construction purpose.

The construction power required will be approximately 1.5 MW at peak load. The number and

capacity of transformer are estimated, as mentioned in the Error! Reference source not

found.below.

Table 7-14: Power Requirement for Construction Purpose

Description Numbe

r

Unit Remarks

400kVA transformer 2 No Headworks site and adit

250kVA transformer 2 No Power house site

250kVA transformer 1 No Employers camp and contractor

camp at headworks

250kVA transformer 1 No Contractor camp & labor camps

at PH site.

7.9.16. Electro-Mechanical Works Cost

The cost of the electro-mechanical equipment is summarized in the attached detailed cost

estimate table. These costs were estimated by a combination of methods including:


7-46

Interpretation of budget prices supplied by potential suppliers, mainly for the

larger and more expensive equipment such as turbines, generators, power

transformers and main inlet valves.

Estimates using established international prices and / or relationships for more

routine items, the information being based on years of collection of price data,

and often eliminates the errors of variations of prices occurring due to abrupt

changes in supply and demand.

Percentage of lumpsum provisions on a ratio basis, based on experience for lesser

miscellaneous items.

In mechanical services, the empirical relation, developed for estimation

includes; heating, ventilation, aircondition, drainage, dewatering, oilstorage,

cooling water, compressed air, embedded/ exposed piping ducts, elevator,

diesel generator, maintenance equipment and waterlevel measurements; and

In electrical services, the empirical relation developed for estimation includes;

low voltage switching, control equipment, DC equipment, system transformers,

communication equipment and station service equipment.


8-1

8. POWER AND ENERGY

8.1. Introduction

This chapter includes power and energy scenario of the Project and the country as a whole.

Regarding the generated power and energy, the Nepal Electricity Authority (NEA) is solely

responsible for the planning and distribution of power & energy generated by its own as well as

private sector hydropower plants. All the private developers require Power Purchase Agreement

(PPA) with the NEA prior to the construction of hydropower plants. Hence, the NEA is the sole

buyer of the power generated from the Project. Once the power is generated, it will be

connected to the national grid and the private hydropower plants get paid as per the rate in

Power Purchase Agreement.

8.2. Integrated Nepal Power System

Despite of tremendous hydropower potential of the country, the current installed capacity of

Integrated Nepal Power System (INPS) including solar and thermal plants is 855.88 MW by

August 2016.Table 8-1 illustrates the national power scenario from different sources:

Table 8-1: National power scenario from different options

Sources Installed Capacity

(MW)

Total Major Hydro (NEA) - Grid

Connected

473.39

Total Small Hydro (NEA) -

Isolated

4.54

Total IPP Hydro 324.44

Thermal 53.41

Solar 0.10

Total 855.88

Here it will be worthwhile to mention that the existing hydropower plants have never been able

to meet the capacity mentioned in Table 10.1. Moreover, NEA imports about 150 MW from India.

At present, Kaligandaki “A” Hydropower Plant (144 MW), commissioned in 2003, is the largest

power plant in the country followed by Middle Marshyangdi Hydropower Plant (70 MW) being

operated since 2008. Kulekhani is the only storage project in the country having two power

plants, namely, Kulekhani-I (60 MW) and Kulekhani-II (32 MW) which are operated in tandem.

There are also a number of small and micro hydropower plants in the isolated parts of the


8-2

country. The total installed capacity of such plants is nearly 6 MW. Among the private

hydropower plants, Khimti Hydropower Plant (60 MW) owned by Himal Power Company Ltd. is

the largest one.

As far as thermal energy is concerned, Duhabi Multifuel generates 39 MW and Hetauda Diesel

Plant generates 14.4 MW after recent rehabilitation works. The smaller diesel units including

privately owned captive power contributes about 5 MW.

8.2.1. Load Forecast

The load forecast for the INPS is prepared by the System Planning Department of the NEA. The

NEA conducted Power System Master Plan (PSMP) in 1997 for load forecast and it is updated

annually. The load forecast and the required energy generation from 2012 to 2028 are given

below in Table 8-2andFigure 8-1. The load factor is assumed to stabilize at 50%.

Table 8-2: Load and energy forecast

Year Energy

(GWh)

Peak Load

(MW)

2012-13 5349.60 1163.20

2013-14 5859.90 1271.70

2014-15 6403.80 1387.20

2015-16 6984.10 1510.00

2016-17 7603.70 1640.80

2017-18 8218.80 1770.20

2018-19 8870.20 1906.90

2019-20 9562.90 2052.00

2020-21 10300.10 2206.00

2021-22 11053.60 2363.00

2022-23 11929.10 2545.40

2023-24 12870.20 2741.10

2024-25 13882.40 2951.10

2025-26 14971.20 3176.70

2026-27 16142.7 3418.90

2027-28 17403.6 3679.10


8-3

Figure 8-1: Load forecast for next 15 years

The regional load demand distribution pattern shows that the Central Region requires 68% of

total load demand followed by the Eastern Region 14%, Western Region 10%, Mid-Western

Region 6% and Far-Western Region with only 2%.

8.2.2. Committed Generation for INPS

The projects under construction are supposed to generate and contribute committed power to

the national grid system. The private sector projects which have already signed PPA or obtained

construction license are also considered as the committed projects for power generation and

contribution to INPS.

After the NEA's most awaited project, Middle Marshyangdi (70 MW) completion, other projects

such as Chameliya (30 MW), Rahughat (32 MW) and Upper Tamakoshi (456 MW) are in the

middle and final phase of construction and expected to complete in few years. In addition, the

NEA has entered into PPA with a number of private developers. Apart from that, the NEA has

planned a number of candidate projects to fulfill increasing power demand but the

implementation is being very slow.

8.3. Energy Definitions

In general, the definition of energy depends upon the way how the energy estimates are carried

out. Here, the energy has been defined based on the standards that are used in Power Purchase

Agreement (PPA) in Nepal, according to which the available energy is classified as dry energy and

wet energy. Dry energy is defined as the energy generated in Poush, Magh, Falgun and Chaitra

(mid December to mid April) of Nepali calendar and wet energy is defined as the energy

generated during the remaining eight months of a year at a particular exceedance of flow.


8-4

8.4. Power and Energy Generation

The power generated from this project at a particular exceedance of flow has been calculated

with a custom spreadsheet program. A number of simulations were carried out for different

installed capacities. The input data and assumptions used for the calculation and the results

obtained are summarized below inTable 8-3.

Table 8-3: Input parameters and assumptions

Surge Tank normal water

level

923 m

Turbine Axis Level 701.5 m

Gross Head 221.5 m

Net Head 217.85 m

Design Discharge 7.8 m3/s

Number of Turbine Units 2

Installed Capacity 14.5 MW

Overall Efficiency 87.44%

The monthly power generated has been converted to energy by multiplying the power by the

time period for which it is generated. The wet and dry energy are calculated separately

considering 5% outage in wet and dry season respectively. The results of calculation are shown

below inTable 8-4.

Table 8-4: Monthly power and energy generation

Installed Capacity 14.5 MW

Rated Efficiency

Design Discharge 7.8 m3/s

Downstream Release 0.26 m3/s

Outage + Losses (Dry

Season)

5% Generator 96.0%

Outage + Losses (Wet

Season)

5% Turbine 92.00%

Gross Head 221.5 m Transforme

r

99.0%

Plant Factor 70.94% Overall 87.44%


8-5

Mo

nth

Op

erat

ion

Riv

er F

low

Usa

ble

Mo

nth

ly

Flo

w

Des

ign

Flo

w

Net

Hea

d

Gen

erat

ion

Cap

acit

y

Ou

tage

, %

Dry

Se

aso

n

Ene

rgy

Wet

Se

aso

n

Ene

rgy

Tota

l En

erg

y

Da

ys

m3/s m3/s m3/s M kW Dry Wet GWh/ Month

Baisakh 30

4.07 3.74 3.74 220.42 7070 0 5 0.00

4.84 4.84

Jestha 31

12.14 11.81 7.8 217.85 14500 0 5 0.00

10.63 10.3

Asadh 32

34.86 34.53 7.8 217.85 14500 0 5 0.00

10.63 10.63

Shrawan 31

50.68 50.35 7.8 217.85 14500 0 5 0.00

10.30 10.30

Bhadra 32

41.20 40.87 7.8 217.85 14500 0 5 0.00

10.63 10.63

Aswin 30

22.81 22.48 7.8 217.85 14500 0 5 0.00

9.97 9.97

Kartik 30

10.68 10.35 7.8 217.85 14500 0 5 0.00

9.97 9.97

Mangsir 30

5.89 7.49 7.49 218.90 10429 0 5 0.00

7.14 7.14

Poush 29

4.03 4.83 4.83 220.19 6987 5

4.62 4.62

Magh 30

3.55 3.47 3.47 220.64 6093 5

4.17 4.17

Falgun 30

3.54 2.95 2.95 220.78 6078 5

4.16 4.16

Chaitra 30

3.33 3.00 3.00 220.77 5633 5

3.85 3.85

Total 16.80 73.78 90.58

The monthly energy generation pattern is presented graphically below in Figure 8-2.

Figure 8-2: Mean monthly energy generation

0.00

2.00

4.00

6.00

8.00

10.00

12.00

En

erg

y G

wH

Month

Energy Generation


8-6

8.5. Power and Energy Benefits

Power and Energy benefits are evaluated either as tariff values applicable to the project or as

replacement cost which is difference between the project cost and the cost of alternative. For

hydropower projects, it is customary to use the second method comparing the cost with that of

thermal power plant. For the hydropower projects with capacity less than 25 MW, the usual tariff

structure promised by the NEA either for dry and wet season is about 5.25 NRs/ kWh with 3%

escalation up to 6 years. As the installed capacity of Upper Irkhuwa Khola Hydropower Project is

less than 25 MW (i.e. 14.5 MW), this tariff structure of about Nrs. 5.25 per unit cost has been

used for the economic and financial evaluation of the Project.

The energy rates of some of the medium size projects that have been fixed in the past are given

below in Table 8-5.

Table 8-5: Energy rate for the projects bigger than 25 MW

Projects Capacity

(MW)

Year PPA rate in Cents per

kWh

Khimti – I 60 1994 5.94

Bhote Koshi 36 1995 6.00

Likhu –4 120 2010 5.99

Sanjen –2 44 2010 Equivalent 7.5 cents

Upper Marshyangdi – A 50 2008 5.9

8.6. Power Evacuation

The power generated from proposed Upper rkhuwa Khola Hydropower Project is proposed to

be evacuated at the proposed Shitalpati substation of Integrated Nepal Power System (INPS).

The proposed Shitalpati substation will have a substation of 132/33/11 kV system. Also a

220/132/33 kV substation will be constructed at Tumlingtar and Baneshwor substation in the

same district. Shitalpati Hub will be connected by a 33 kV double circuit 5 km Transmission line.

Following are the proposed projects of IPPs at Sitalpati Hub.

Sankhuwa Khola Hydropower Project - 30 MW

Upper Sankhuwa Khola Hydropower Project - 32 MW

Kasuwa Khola Hydropower Project - 45 MW

Irkhuwa Khola B Hydropower Project – 15.5 MW

Chirkhuwa Khola Hydropower Project - 5 MW


8-7

And following are the proposed projects of IPPs at Tumlingtar Hub.

Sabha Khola Hydropower Project - 22 MW

Hewa Khola Hydropower Project - 5 MW

8.7. Conclusions and Recommendations

The power and energy calculated above may change with the revision of

hydrology prior to the detail design.

The net head changes with the flow variation and it affects in power and energy

generation. The calculation of power and energy shall be carried out more

precisely prior to PPA.

The usual practice for the tariff structure introduced by NEA for the projects for

less 25 MW has been considered to calculate revenue from the Project.


9-1

9. CONSTRUCTION PLANNING AND SCHEDULING

9.1. General

The Upper Irkhuwa Khola Small Hydropower Project is situated in Dobhane, Khatama and

Kudakaule Village Development Committees (VDCs) of Bhojpur district in eastern Nepal.

Tumlingtar Bazaar, in the Sankhuwasabha district, is 185 km north along Koshi Highway from

Itahari Bazaar on the East-West Highway. From Tumlingtar, the proposed Project is accessible by

approximate 25 km fair-weather road up to Gothe bazaar via Nepaldanda. The development of

this Project requires timely improvement of this road as well as timely completion of under

construction bridge in Tumlingtar.

The feasibility study shows that implementation of this project is technically and financially

viable and worth for implementation. Financial study has been carried out to check the feasibility

of this project. Accordingly, the implementation schedule of Upper Irkhuwa Khola Hydropower

Project has been prepared for the construction of the Project and is presented in Figure 9-1.

The major work item with estimated quantity of civil works of the Upper Irkhuwa Khola

Hydropower Project are summarized below:

Earthwork excavation 50,750 m3

Rock excavation 61,950 m3

Concrete work 23,150 m3

Stone Masonry 2,750 m3

Formwork 45,750 m2

Reinforcing steel bar 1260 Mtn

Penstock Pipe 291 Mtn

The critical sequences of major project activities following the takeover of the Project

implementation are as follows:

Detail engineering and tender documents preparation

Infrastructure development (Access roads and construction camps)

Tendering of main civil works, electromechanical and hydro-mechanical works

Mobilization of construction equipment and construction materials

Excavation of headworks, headrace alignment, powerhouse and tailrace canal


9-2

Concreting in headworks, waterway alignment and powerhouse

Construction of headwork, headrace alignment, powerhouse structures and

tailrace

Construction of surge tank, penstock and installation of penstock pipe

Installation of hydro-mechanical/ electro-mechanical equipments

Dry and wet test

Commissioning

Project construction schedule and cost estimate of the project are prepared on the basis of the

present study. It will be refined during the detailed engineering of the Project.

9.2. Preparatory Works

9.2.1. Access and Project Road

Both headworks and powerhouse sites of the project lie on the right bank of Irkhuwa Khola. Total

of about 4 km of access road from the Gothe Bazaar needs to be constructed to reach the whole

alignment of project components. Other improvement is necessary for 25 km road from

Tumlingtar as well as Bridge in Arun river at Tumlingtar.

9.2.2. Construction Power

It is assumed that central grid will reach to Nepaledanda/Gahate during the project

commencement work. From Nepaledanda / Gahate, approximately 10 km of 11 kV transmission

line has to be constructed by the Project for supplying the construction power required at

different components of the Project.

The headworks, penstock alignment and powerhouse / tailrace will be fed from separate

distribution transformers from the planned 11 kV line going to the constructed by the Project.

Approximately the construction power required will be 0.75 MW at peak load.

Alternatives for supply of construction power during construction of Upper Irkhuwa Khola Small

Hydropower Project are:

Diesel generators on site

Depending on the load requirements in different load centers, it will be necessary to install

several diesel generator units and LV distribution boards for power distribution to the different

load centers around the construction site.


9-3

Contractors must arranged alternative supply of power facility

Use of available power supply from the NEA is the optimum solution with contractual provision

for all the contractors to provide and arrange their own backup diesel generator supply for short

interruptions of up to 8 hours (one day).

An approximate of 300 hours per year interruption with max single interruption of 1 day can be

assumed as the standard outage rate for this line. For the outage, contractors should arrange

their own back-up supply for the essential loads of construction site. The standby diesel-set

would be provided by the individual contractor.

For employer’s camp in headworks and powerhouse, diesel generator needs to be installed for

urgent works only. The diesel generator for headwork for operation should be supplied earlier

and used for powerhouse camps and office.

9.2.3. Construction Camps

Construction camps at three different construction sites will be needed during the

implementation of the Project. Three separate labor camps will be as follows.

For the headworks, Dobhane bazaar in the middle of the confluence of irkhuwa

Khola and Phedi Khola is selected for construction of a contractor’s camp. The

same area located closer from the headworks site is proposed for the labor camp.

For employer’s permanent camps and office, left bank of the Irkhuwa upstream

of the confluence with Benkhuwa khola in the cultivated land opposite of the

powerhouse site seems appropriate. For the construction of headrace tunnel,

temporary construction camp will be needed and it will be arranged in different

locations of the alignment.

9.2.4. Water Supply System

Water supply system is planned to off take water for the camps at two locations. For all two

locations intake structures with filtration plant will be installed. In the headworks area, nearby

available source will be used for the contractor camp and labor camp. For the employer’s

permanent camp and office near powerhouse site, nearby water source can be used for the

purpose.


9-4

9.3. Construction Scheduling of Individual Structures

9.3.1. River Diversion and Construction of Weir and Intake Structures

The headwork structures are planned to be constructed in two consecutive dry seasons.

Estimated 1 in 20 year dry season flood of 46.84 m3/s has been considered for the river diversion.

Sequence of construction of headwork structures in various stages of river diversion are as

follows.

First year dry season

First year monsoon

Second year dry season

Second year monsoon

Third year dry season

Activities to be executed in each dry and wet season are as follows:

First Year Dry Season

In the first dry season, construction of headworks will be carried out with the following

construction sequences.

Cofferdam around 150m upstream of the proposed weir axis up to the

downstream will be constructed to divert the river flow through the left side of

the river.

Excavation and construction of main weir, undersluice, intake structure

River flow will be channelized through the left side excavated in the left bank. After the flow

diversion, excavation for main weir, undersluice and intake foundation will be carried out. After

completion of proper curtain grouting and PCC work, concrete work for undersluice, main weir

portion and intake structure will be carried out. In this season, concrete work for undersluice

part and intake part will be completed up to sill level.

First Year Monsoon

In the first year monsoon period, construction of water ways like desander, headrace tunnel,

powerhouse etc. will be carried out with the following construction sequences.


9-5

Flow towards the right side will be continued unless any unexpected flow occurs

and breaches the cofferdam

Construction of the Intake, Undersluice, desander, headrace tunnel, surge tank,

powerhouse etc. is carried out continuously

Second Year Dry Season

In the second year dry season, the construction sequences will be as follows.

Construction of cofferdam if breached in first monsoon season and river flow

diverted from the undersluice structure.

Works continues for remaining protion of weir, wing walls in the right bank etc up

to the superstructure level

Second Year Monsoon

Remaining excavation work and concreting work in all fronts will be continued.

Third Year Dry Season

Gates, stop logs and trashracks in diversion weir, undersluice, intake etc. will be installed.

9.3.2. Desanding Basin and Tunnel Inlet Portal

For the construction of desanding basin, two construction sides can be used from upstream and

downstream faces. Altogether 12 months is allocated for the construction works.

9.3.3. Headrace Tunnel

For the construction of 3720m long headrace alignment, two sites will be managed from

upstream and downstream faces. Total of 20 months time is allocated for this work.

9.3.4. Surge Tank

The construction face of downstream will be used to approach the bottom of surge tank. A pilot

shaft will be made at the center of surge tank with series of drill holes from top level of surge

tank down it its full depth of 25m. Around 3m diameter pilot shaft will be made with charging

drill holes from bottom and blasting the segment of 2-3 m at a time. Once the pilot shaft is made,

second stage of excavation will be executed by enlarging to the full size of 5m diameter of the

surge tank from top. Enlargement will be done by conventional drilling and blasting with

lowering 2m in each cycle of blast and followed by shotcrete and rock bolting. Muck will be

disposed from the pilot shaft down to the surge tank bottom and will be removed through the

construction face downstream.


9-6

Total time required for the excavation of surge tank including excavation, rock bolting and

shotcrete lining is estimated about 16 months. Concrete lining will be executed after completion

of excavation works.

9.3.5. Penstock Installation

The first 25 m of the penstock just after the surge shaft lies in horizontal tunnel followed by

surface penstock having 375m length. The manufacture and transportation of steel penstock is

scheduled in 12 months time. Installation of the penstock pipe and second stage concreting will

be completed in the next 6 months time. The total time required for the civil and hydro-

mechanical works will be about 24 months.

9.3.6. Powerhouse& Tailrace

Surface powerhouse will be constructed about 250m upstream of the confluence between

Benkhuwa Khola and Irkhuwa Khola. The excavation for the powerhouse will be started in

parallel to the construction of the other structures as headworks and headrace tunnel. Total time

allocated for the powerhouse excavation is 16 months. Foundation concreting and frame

structures in the powerhouse will be commenced after the completion of excavation work.

Foundation concreting, frame structures and all other activities in the powerhouse are scheduled

to complete in 12 months time.

Construction of tailrace structure will be carried out simultaneously with the construction of

powerhouse. Total construction time for the completion of tailrace has been estimated same as

powerhouse of 16 months.

9.3.7. Turbine and Generator Installation

The design, fabrication and shipment of the turbines, generators and other accessories are

scheduled in 18 months. Additional 6 months are scheduled for erection and commissioning of

all three units.

9.3.8. Transmission Line and Sub-Station

21 months time is allocated for the design, fabrication, delivery and erection including stringing

of transmission line, construction of sub-station equipment, erection including towers and

conductors. The work will be executed immediately after the contract award of civil and

electromechanical works.


9-7

9.4. Materials Handling

9.4.1. Handling of Construction Materials

The major local and other construction materials required for the Project consists of the

followings:

Cement

Coarse aggregates

Fine aggregates

Reinforcement bars

Explosives

Diesel

9.4.2. Local Construction Materials

9.4.2.1 Sand

Total quantity of sand required for civil construction works will be about 7500 m3. Total quantity

of sand available within 10 km range from the construction site is morethan sufficient for this

Project. Other borrow areas along the Arun River in the downstream are the potential sources

of sand and aggregates from where the deficit quantity of sand can be extracted.

9.4.2.2 Gravel

Total quantity of aggregates required for civil construction works is estimated about 15,000m3.

Total quantity of aggregate available from the potential borrow areas within 5 km range from

the construction site is more than sufficient for this Project. Other borrow areas along the Arun

River in the downstream are the potential sources of aggregates from where deficit quantity can

be fulfilled.

The rest of aggregates required shall be obtained from the quarry site and by processing of the

excavated materials.

9.4.2.3 Rubble Stone

Rubble stones required for cofferdam, diversion weir intake structure and gabion works will be

collected from the river banks on the right and left banks of Irkhuwa Khola within the Project

area and from the excavated materials of surface works.


9-8

9.4.3. Other Construction Materials

9.4.3.1 Cement

Required quantity of cement can be purchased within Nepal or may be required to import from

India and other countries. The total distance for haulage from Nepal/ India border at Rani to

Project site will be around 250 km.

9.4.3.2 Reinforcement Steel

Reinforcement steels available in the local market from the steel factories of Nepal will be

managed to the extent possible. Only the deficit quantity of reinforcement steel should be

imported from India and other countries.

9.4.3.3 Explosives

For the surface excavation in rock and boulder blasting, explosive products of Nepal Army will

be utilized. All types of detonators need to be imported from Indian market.

9.4.4. Spoil Materials Handling

Spoil materials derived from the excavation of diversion weir, intake, desander and headrace

alignment will be managed in allocated dumping areas as explained in Chapter IV of this report.

The part of the excavated materials will be utilized for producing sand, aggregates and boulders.

9.5. Contract Packages

Construction of the Project is broadly separated into five different lots and work packages in

each lot are as follows.

9.5.1. Lot 1 - Infrastructure Works

Package 1.1: Access Road & Truss Bridge

Package 1.2: Construction Power

Package 1.3: Construction Camps

9.5.2. Lot 2 - Civil Works

Package 2.1: Surface Works: headworks structures, temporary bridges, river

training works, powerhouse & tailrace etc.

Package 2.2: Underground works: Headrace tunnel, Surge tank, civil works for

penstock etc.


9-9

9.5.3. Lot 3 - Hydro-Mechanical Works

Package 3.1: Design, manufacture, supply and installation of gates, trash racks,

stop logs, valves, hoists and cranes, etc.

Package 3.2: Fabrication and erection of penstock pipe

9.5.4. Lot 4 - Electro-mechanical Works

Design, manufacture, supply and installation of electrical and mechanical

equipment (turbine, generators with accessories, transformers and electrical

auxiliaries)

9.5.5. Lot 5 - Transmission Line

Design, supply and installation of transmission towers and stringling as well as

construction of sub-station facilities

9.6. Overall Duration of Project Construction

All preparatory works including tender documents preparation, land acquisition, construction of

camp and infrastructure development will be carried out in the detail engineering phase. The

main construction work of the project is scheduled in 3 years duration from the award of contract

to commissioning. The detailed schedule for the implementation of Upper Irkhuwa Khola

Hydropower Project has been presented in Figure 9-1.


9-10

Figure 9-1: Implementation schedule of Irkhuwa Khola Hydropower Project


10-1

10. PROJECT COST AND REVENUE

10.1. Project Cost

The Project is calculated in Nepali Rupees with reference to district rate published by the District

Development Committee (DDC) of Bhojpur district for the year 2016. All relevant taxes and

duties are included in the cost. The cost of electromechanical equipment, metal work and

materials are obtained from the respective manufacturers and suppliers where possible. Past

experiences in the hydropower construction is also taken into consideration where cost for

specific work is not available.

The cost estimation has been carried out in parallel with construction planning approach as

discussed in the construction planning section of this report. The Bill of Quantities (BOQ) of

various items is estimated for each work and then the total estimated project cost is calculated.

Utilizing the basic norms of GoN (Government of Nepal), the rate analysis for civil construction

work has been carried out.

The rates are based on 2016 price level and fixed exchange rate of Nepali rupee with Indian

Rupee at Rs. 1.60 and US Dollar at Rs. 110 are assumed. The fluctuations in the market price and

exchange rate of Nepali rupee with foreign currencies may change the price estimates. Also the

variation in design and drawings during construction due to the site condition may change this

estimate. Therefore, a provision of price escalation has been included in the estimates.

10.2. Assumed Conditions & Sequential Execution.

The cost estimate of the Project is made under the following conditions:

The cost estimation has been carried out in parallel with construction planning approach

as discussed in the construction planning section of this report.

Breakdown of the Project into a number of distinct structures like diversion weir and

undersluice, intake, gravel trap, headrace tunnel, desanding basin, balancing reservoir,

powerhouse and tailrace canal.

Identification of distinct construction tasks & measurable pay items such as excavation,

formwork, concrete works etc.

It is assumed that the contractor shall bring all the plants and equipments.


10-2

To obtain the labour cost, the quantity of different categorical labours, i.e. skilled, semi-

skilled and unskilled required for each unit of work has been estimated in accordance

with the norms and the experiences gained in the construction of hydropower projects

in Nepal.

To obtain the cost of construction materials for a particular work, the quantity has been

estimated as per the standard norms. The cost of material includes procurement cost,

freight, transportation, sales tax and insurance charges where applicable.

The estimated rates for locally available materials such as sand, stones, aggregate,

timber, etc. are based on local price.

Each unit cost for civil work includes the contractor’s overhead and profit. It is assumed

to be 15% of the direct cost. The overhead includes office rent, depreciation of

equipments, salaries etc. Small tools, ladder, ropes etc that the contractor provides to

workmen are also included in the overhead charge. This overhead charge is taken at the

rate of 5 % of the cost. A profit of 10% is considered reasonable for such contracts. Hence

a provision of 15% of unit cost has been adopted for overhead and profit.

Price of electromechanical equipments is taken from the suppliers’ quotation.

The quoted price by suppliers for hydro-mechanical equipments including price of metal,

fabrication & installation and transportation cost has been used.

10.3. Total Project Cost

The total cost of Upper Irkhuwa Khola Hydropower Project is estimated at Rs. 2,602,270

thousands. The cost per kilowatt of the Project is US$ 1,631 (1 US$= Rs. 110). The construction

period of the Project is estimated to be 36 months. The total investment cost of the Project is

shown in Table 10-1. Further detail breakdown of each heading is presented in Volume III.

Table 10-1: Detail Breakdown of the Project Cost

No. Headings Amount

(000') US Dollar %

1 Preliminary Expenses 22,300 202,700 0.9%

2 Land Procurement 21,400 194,500 0.8%

3 Infrastructure Development 9,100 82,700 0.3%


10-3

4 Site Office & Camping Facilities Construction 44,750 406,800 1.7%

5 Construction Design & BOQ Preparation 22,000 200,000 0.8%

6 Civil Construction Works 1,500,473 13,640,700 57.7%

7 Metal Works 129,838 1,180,300 5.0%

8 Electro-Mechanical Plant & Machinery 518,375 4,712,500 19.9%

9 Transmission Line & Switchyard 85,000 772,700 3.3%

10 Project Management & Supervision 35,500 322,700 1.4%

11 Office Equipment & Vehicle 30,230 274,800 1.2%

12 Miscelleneous 3,600 32,700 0.1%

Total Cost without IDC 2,428,664 21,415,011 93.5%

13 Interest During Construction 170,006 1,545,500 6.5%

Total Cost 2,602,270 23,657,000 100.00%

Figure 10-1: Classification of Total Cost

10.3.1. Preliminary Expenses

To convert rational ideas into a real life project needs a substantial amount of investment. This

heading includes cost related to feasibility study, establishment of the company, salaries,

Preliminary Expenses , 0.9%

Civil Construction Works, 57.7%

Site Office & Camping Facilities Construction , 1.7%Land Procurement , 0.8%

Infrastructure Development, 0.3%

Metal Works , 5.0%

Interest Capitalization Cost (during construction), 6.5%

Bank charges, 0.1%

Office Equipment & Vehicle, 1.2%

Electro-Mechanical Plant & Machinery , 19.9%

Transmission Line & Switchyard , 3.3%

Project Management & Supervision , 1.4%

Construction Design & BOQ Preparation , 0.8%

Environmental Mitigation, 0.4%


10-4

allowances, consultant fees,statutory fees, travelling expenses, etc. Rs. 22,300 thousands (0.8

percent) has been allocated for this purpose.

10.3.2. Land Procurement

The Project has to purchase a total of 225 Ropanis land for the construction of project structures

such as headworks, canal, access road, power house, switchyard, office complex and camping

facilities. Under this heading, Rs. 21,400 thousands has been allocated

10.3.3. Infrastructures Development

Development of access road, water supply system, construction power, telephone line and

community development activities falls under this heading. A total of Rs. 9,100 is estimated for

this purpose.

10.3.4. Site Office & Camping Facilities Construction

The Project requires development of camping facilities to the large number of manpower.

Different types of buildings as office complex, staff quarter, helper quarter, godown, workshop

etc are required during construction and afterwards. A total of Rs. 406,800 is estimated for this

purpose.

10.3.5. Construction Design & BOQ Preparation

A provision of Rs. 22,000 thousand has been made for detail design & BOQ preparation. This

amount is about 0.80% of the total cost of the project.

10.3.6. Civil Construction Works

Civil construction work is the largest component in the Project. A total of Rs. 1,500,473 thousands

(57.7 percent) has been estimated for all the civil construction works ie Headworks, Waterway,

Powerhouse etc.

10.3.7. Metal Works

The cost of hydro-mechanical work includes steel sheet procurement, transportation, pipe

fabrication & erection, bell mouth, y-furcations, man hole, linings, powerhouse roof truss & gate,

trashrack, gates, stoplogs & expansion joints. A total of Rs. 129,838 thousands (5 percent) has

been allocated for this heading.

10.3.8. Electro-Mechanical Plants & Machinery

The Project shall import plants and equipments. The cost of Electro-Mechanical Equipment

includes the cost of design, manufacturing, erection, commissioning & testing of all powerhouse


10-5

electrical and mechanical equipments. A total of Rs. 518,375 thousands (19.9 percent) is required

for this headings. The cost for electro-mechanical equipments has been taken from the

suppliers' quotations.

10.3.9. Transmission Line & Switchyard

The cost of transmission & electrical work includes a complete cost of high voltage transmission

line connections for power evacuation and interconnection facilities. A total of 10 km 132kV

transmission line has to be constructed from powerhouse to purposed Khandbari substation.

The total amount of Rs. 85,000 thousands (3.3 percent) is allocated under this heading.

10.3.10. Project Management & Supervision

This heading occupies 1.4 percentage of the total project cost. It includes the cost of office

operation at the head office and site office, salaries and allowance, office rent,expert fees,

travelling & meeting expenses and expenses related in the operation of the office during the

construction of the project.The total amount of Rs. 35,500 thousands is allocated under this

heading.

10.3.11. Office Equipment & Vehicle

The Project needs to invest Rs. 30,230 thousands (1.2 percent) for vehicles and office

equipments. Jeep, pick-up and motorbikes are the vehicles that need to be purchased. Likewise

computers, furniture, survey equipments and office equipments are some of the important items

to be purchased for the Project.

10.3.12. Miscellaneous

A total of Rs. 3,600 thousands 0.1 percent) has been allocated for this heading. This cost is related

to the bank charges needed for the debt service required for the project financing.

10.3.13. Interest During Construction

The interest rate on bank loan is assumed to be 10 percent. The total construction period of the

Project shall be 36 months. The interest on borrowed capital cannot be paid during the

construction period. Hence, the total project cost includes a total of Rs. 170,006 thousands (6.5

percent) that has been capitalized.

10.4. Energy Generation

The objective of the Project is to generate power and supply energy to the national grid. The

Project has an installed capacity of 14.5 MW. The net energy after deducting 5 percent loss is

90,577,956 kWh per year. The details of the energy generation is shown in Table 10-2 below.


10-6

Table 10-2: Energy Generation

Nepali

Months Days

Discharge

for Power

Generation

(m3/sec)

Net

Head

Monthly

Efficiency

Monthly

Power

(kW)

Monthly

Generation

Before

Outage &

Losses

(kWh)

Outage

Including

Losses

(kWh)

Net

Available

Contract

Energy

(kWh)

Baisakh 30 3.74 220.42 87.44% 7070 5090498 254525 4835973

Jestha 31 7.8 217.85 87.44% 14575 10843971 516879 10301773

Ashad 32 7.8 217.85 87.44% 14575 11193777 559689 10634088

Shrawan 31 7.8 217.85 87.44% 14575 10843971 542199 10301773

Bhadra 32 7.8 217.85 87.44% 14575 11193777 559689 10634088

Ashwin 30 7.8 217.85 87.44% 14575 10494166 524708 9969458

Kartik 30 7.8 217.85 87.44% 14575 10494166 524708 9969458

Marg 30 5.55 218.90 87.44% 10429 7509076 375454 7133622

Poush 29 3.7 220.19 87.44% 6987 4863099 243155 4619944

Magh 30 3.22 220.64 87.44% 6093 4387008 219350 4167658

Falgun 30 3.21 220.78 87.44% 6078 4376157 218808 4157349

Chaitra 30 2.97 220.77 87.44% 5633 4055550 202778 3852773

Total 365 95,345,217 4,767,261 90,577,956

10.4.1. Revenue Potential

NEA, the only power purchaser in country, buys energy at Rs. 4.80 per kWh during wet season

and Rs. 8.40 per kWh during dry season. The details of the revenues are shown in Table 10-3

below.

Table 10-3: Revenue Generation

Nepali Months Net Available Contract Energy

(kWh) Rate per kWh Amount in Rs. (000')

Baisakh 4835973 8.4 40,622

Jestha 1 4984729 8.4 41872

Jestha 2 5317044 4.8 25522

Ashad 10634088 4.80 51,044

Shrawan 10301773 4.80 49,449


10-7

Bhadra 10634088 4.80 51,044

Ashwin 9969458 4.80 47,853

Kartik 9969458 4.80 47,853

Marg 1 3566811 4.80 17121

Marg 2 3566811 8.4 29961

Poush 4619944 8.40 38,807

Magh 4167658 8.40 35,008

Falgun 4157349 8.40 34,921

Chaitra 3852773 8.40 32,363

Total 87,131,176 5.34 543,441

The Project will generate revenue of Rs. 543,441 thousands in the first year of operation. The

month of Chaitra will have the lowest revenue generation while the revenue will be higher in the

month of Jestha.

10.4.2. Yearly Revenue

The latest announcement by the National Energy Crisis Reduction and Electricity Development

Decade declares 3 percent escalation for 8 years for project up to 100 MW. In the first year of

operation, the yearly revenue of the project is estimated at Rs. 543,441. From 9th year, the yearly

revenue will be Rs. 709,067 thousands.


11-1

11. PROJECT FINANCING & PROJECTIONS

11.1. Investment Structure

The total investment of the Project is Rs. 2,602,271 thousands. Hydropower projects are capital

intensive and long-term investment in nature. The promoters alone cannot finance the total

investment demand. Hence, it requires a proper financial arrangement between equity and loan.

The Project will be financed from promoter's capital and borrowings from banks and financial

institutions. Rs. 780,681 thousands (30 percent) shall be financed from equity and the remaining

Rs. 1,821,590 thousands (70 percent) shall be financed from bank (Table 11-1).

Table 11-1: Investment structure

Particulars Amount (000) Percent

Equity 780,681 30.0%

Debt 1,821,590 70.0%

Total 2,602,271 100.00%

11.2. Projected Financial Statements

Projected income statement, cash flow statement and balance sheet of the Project for 30 years

are shown in Volume III.

11.2.1. Sales

The only income of the Project is through sale of energy at the rate fixed by NEA. The energy

produced shall be sold to NEA at the rate Rs. 4.80 for the wet months and Rs. 8.40 for the dry

months. There is an escalation of three percent from the commercial operation date for the first

eight years. The income from energy sale in the first year is Rs.543,441 thousands. It reaches to

Rs 709,067 thousands in the ninth year and remains constant throughout the project life

afterwards.

11.2.2. Government Subsidy

The Government of Nepal has declared Rs. 5 million per every MW to encourage hydropower

construction. This subsidy is included in the calculation.


11-2

11.2.3. Operation and Maintenance Cost

The annual operation and maintenance (O&M) cost includes staff salaries & allowances, house

rent, office expenses, repair and maintenance of the Project, insurance against flood, natural

calamities and fire, contribution to the local development etc. In the first year of operation, a

total of Rs. 38,253 thousands is estimated as O&M cost. Staff salary and allowances shall increase

by five percent every year. The other remaining O&M cost is assumed to increase by two percent

annually.

11.2.4. Royalty

The Government of Nepal imposes Rs. 150 per year for each installed kW as capacity royalty and

1.85 percent of energy revenue as revenue royalty. From the 16th year onwards, the capacity

royalty increases to Rs. 1,200 and the revenue royalty increases to 10 percent.

11.2.5. Employees’ Bonus

The staff bonus shall be two percent of the Profit before tax (PBT). In the first year of operation,

the staff bonus shall be Rs. 1,000 thousands.

11.2.6. Depreciation

Depreciation is calculated under straight line method. The total cost of the Project of Rs.

2,602,271 thousands includes Pre-operating Expenses and Land Procurement. These are

excluded while calculating depreciation. The Project life shall be PPA duration, which is 30 years.

The salvage value at the end of the Project life shall be 5 percent of the total depreciable assets.

As such; depreciation is calculated by taking these things into considerations.

11.2.7. Amortization

The total project cost includes pre-operating expenses of Rs. 22,300 thousands. This component

is not a depreciable asset. Hence, it is amortized for the first five years of operation.

11.2.8. Tax

As stipulated in Income tax act 2058, the applicable corporate tax rate for enterprises

undertaking electricity generation is 20 percent. The tax rate is assumed to remain 20 percent

throughout the project life. However, there is a tax exempt for hydropower companies for the

first ten years of operation. Also there is a tax exempt of 50 percent for the next five years. Thus,

these things are taken into consideration while calculating tax.

11.2.9. E&M Replacement

The E&M replacement cost is estimated at 20 percent of the original value which will be replaced

once in every 15 years.


11-3

11.2.10. Bank Loans and Interest Repayment

The bank loan shall be repaid within twelve years from the date of commercial operation. The

details of the bank loan and repayment is shown in Table 11-2 below.

Table 11-2: Bank loan repayment plan

Year Principal(000) Interest(000) Total(000) Outstanding(000)

0 0 0 1,821,590

1 82,801 178,432 261,233 1,738,789

2 91,471 169,762 261,233 1,647,317

3 101,049 160,184 261,233 1,546,268

4 111,631 149,602 261,233 1,434,637

5 123,320 137,913 261,233 1,311,317

6 136,233 125,000 261,233 1,175,084

7 150,498 110,735 261,233 1,024,586

8 166,258 94,975 261,233 858,328

9 183,667 77,566 261,233 674,661

10 202,899 58,334 261,233 471,762

11 224,146 37,088 261,233 247,616

12 247,616 13,617 261,233 0

1,821,590 1,313,207 3,134,797

11.2.11. Agency Fee

Domestic banks and financial institutions charges 0.25 percent on the total loan outstanding as

an agency fee. This is taken into consideration.


12-1

12. PROJECT EVALUATION

Apart from technical, environmental and socio-economical aspects of a hydropower project,

financial analysis provides the most important indicators for the acceptability of a project for

investment. The financial evaluation is aimed at giving potential investors an overview of the

risks and benefits associated with financing the project.

12.1. Parameters and Assumptions

The relevant specific parameters and assumptions applied for the financial analysis in this study

are as follows in the Table 12-1 below.

Table 12-1: Parameters and Assumptions

Installed Capacity in MW 14.5

Wet Energy (Gwh per Year) 60.39

Dry Energy (Gwh per Year) 30.18

Total Sellable Energy (Gwh per Year) 90.57

Equity in 000' (30%) 780,681

Debt in 000' (70%) 1,821,590

Total Financial Cost in 000' 2,602,271

Annual Depreciation St. Line Method

Salvage Value 5%

Discount Rate 10%

Wet Energy Price per kWh 4.80

Dry Energy Price per kWh 8.40

Average Energy Price per kWh 5.34

Increment in Energy Price for the first 8 years of Operation 3%

Interest Capitalization During Construction 3 months

Interest on Long Term Debt 10%

Loan Repayment Duration 12

Agency Fee 0.50%

Financial Analysis 30


12-2

Corporate Tax 20%

Bonus and Welfare Fund 2%

Tax Holiday

First 10 years 100% tax holiday

Next 5 years 50% off

Revenue Royalty

First 15 years 1.85%

After 15 years 10%

Capacity Royalty (Rs/kW)

First 15 Years 150

After 15 Years 1,200

Project Insurance 0.50%

Repair & Maintenance 0.50%

Maintenance Reserve (% of Annual Revenue till NPR 100 million) 2%

Percentage of O&M as of Total Project Cost 2%

Salary Increment 5%

Other O&M increment 2%

Government Subsidy

NRs. Per MW (000') 5,000

E&M Replacement

In every 15 years @ 20% of the total E&M Cost 20%

Construction Period 3 years

Exchange Rate 110

12.2. Financial Analysis

The financial analysis is carried out by the usual discounted cash flow technique. Different

financial indicators are used to examine the feasibility of Upper Irkhuwa Khola Hydropower

Project. Analysis has been done by calculating the payback period, net present value, internal

rate of return, benefit cost ratio, plant factor, cost per kilowatt etc. The analysis is carried out in

Nepalese Rupees (Rs.).


12-3

12.2.1. Annuity

Annuity is a stream of equal cash flows for a specified number of periods. Annuity method is

widely used in the analysis of hydropower projects because they yield a fixed income over the

life. The general equation of the present value of an annuity is as follows:

n

niii

1

1PMT..............

1

1PMT

1

1PMTPVA

21

………………….... (1)

=

n

t

t

iT

1 1

1PM ……………….………………………….……….… (2)

= PMT (PVIFAi,n) …...………………..………………………….………(3)

Where,

PVAn = Present value if an annuity for period is n.

PMT = Series of payment of an equal amount of money for period n.

n = Specified number of period (Years).

i = Discount rate.

PVIFA = Present value of interest factor of an annuity.

ni

n

,PVIFA

PVAPMT ………………………………………………….(4)

= 11

)1(PVA

n

nn

i

ii………………………………………… (5)

The total investment cost (PV) of the Project is Rs. 2,602,271 thousands. The amount required

for repayment of capital over the lifetime of the project (PMT) is calculated as follows:


12-4

1-10.01

10.0110.02,602,271PMT

30

30

= Rs. 276,046 thousands.

The Project will generate revenue of Rs. 543,441 thousands in the first year of operation and out

of which Rs. 229,425 thousand (42.22 percent) needs to be allocated for the payment of interest

and principal in annuity method. On the basis of this analysis, the income of the Project has

adequate fund to service the debt in annuity method; hence, the Project is desirable to invest.

12.2.2. Time Value of Money

A rational individual would not value the opportunity to receive a specific amount of money in

future if he/she can have same amount of money today. Most individuals value the opportunity

to receive money now rather than waiting for some period of time to receive the same amount.

This phenomenon is referred as an individual's time preference for money. Thus, an individual's

preference for possessions of a given amount of cash today, rather than in future is called 'time

preference for money' or 'Time Value of Money'. The time value of money is generally expressed

by an interest rate or discount rate.

Capital has an alternative use. So the opportunity cost of capital should also be considered while

evaluating the investment proposals. The opportunity cost may be defined as the rate or return

on the best available alternative investment of equal risk. Commercial banks in Nepal charge 11

to 13 percent interest on project loan. The interest rate on bank loan for this project is assumed

to be 10 percent.

i) Net Present Value

Net Present Value (NPV) method is the classic economic method of evaluating investment

proposals. It is one of the discounted cash flow (DCF) techniques explicitly recognizing 'time value

of money'. NPV may be defined as the excess of present value of cash inflows over present value

of cash out flows. To calculate Net Present Value, first an appropriate rate of interest is selected

to discount the cash flows. Then, present value of investment (i.e. cash inflows) and present

value of investment outlay (i.e. cash outflows) is computed using interest rate as the discounting

rate. Finally, the net present value is computed by subtracting the present value of cash outflows

from the present value of cash inflows. Net Present Value can be calculated by using the

following equation:


12-5

nn

iii

1

CF...............

1

CF

1

CFCFNPV

2

2

1

10 …………………………… (6)

=

n

tti0 1

CF ……………………………………………………… (7)

Where,

Interest rate (i) = 10%

Project Life (n) = 30 Years

Or,

NPV = Total PV – PV of Investment

Where,

Total PV = PV of CIF – PIV of COF

By adding present value of net cash flow for 30 years and then deducting initial investment, NPV

of the Project has been computed.

NPV10% Discount Rate = 1,179,307 thousands

A project is said to be financially viable if it provides positive Net Present Value (NPV).

ii) Internal Rate of Return

The internal rate of return (IRR) method is another discounted cash flow technique which takes

account of the magnitude and timing of cash flows. This technique is also known as yield on

investment, marginal efficiency of capital, marginal productivity of capital, rate of return, time

adjusted rate of return and so on. It is a method of evaluating investment proposals using the

rate of return on an asset investment, which is calculated by finding the discount rate that

equates the present value of future cash flows to the investment's cost. Thus, IRR is that discount

rate which equates the present value of cash inflows with the present value of cash outflows.

We can use the following equation to calculate the project's IRR:


12-6

0

1.............

112

2

1

10

n

n

IRR

Cf

IRR

Cf

IRR

CfCf ……………………(8)

010

n

tt

t

IRR

Cf…………………………………………………... (9)

NPV = 0

In other words, internal rate of return (IRR) is that discount rate at which the Project NPV is zero.

Since the present value of cash inflows is equal to the present value of cash outflows at the

discount rate of 14.98%, IRR of the Project is 14.98% percent. A project is feasible if its IRR is

greater than the cost of capital (here the discount rate is 10%). Therefore, the Project is

profitable and investment worthy.

iii) Benefit/Cost ratio or Profitability Index (PI)

Another time-adjusted method for evaluating the investment proposals is Benefit/Cost ratio or

profitability index (PI). It is the ratio of present value of future values (NPV + the Initial

Investment), divided by the Initial Investment.

Rules of Profitability Index

If PI > 1, Good Investment

If PI < 1, Bad Investment

The formula to calculate benefit-cost ratio or profitability index is as follows:

Investment Initial

Investment Initial NPV Ratio B/Cor PI

………………………………………….(10)

271,602,2

578,781,3 Ratio B/Cor PI

= 1.45

B/C ratio of this Project at 10 percent discount rate is found to be 1.45 times. This means, for

every Re 1 invested in this Project, the total value created is Rs 1.45 which indicates that the


12-7

Project is profitable. The benefit cost ratios of the Project at different discount rates are shown

in Table 12-2 below.

Table 12-2: Benefit cost ratio at different discount rates

Discount Rate NPV (000) B/C Ratio

0% 9,324,767 4.58

5% 3,585,225 2.38

10% 1,173,907 1.45

12% 614,434 1.24

14.98% 0 1

iv) Payback Period

The payback period is one of the most popular and widely recognized methods for evaluating

investment proposals. This method identifies required number of years to pay the original cost

of investment, normally disregarding salvage value. Cash flow here represents CFAT. Thus, the

payback method measures the number of years required for the cash flow to pay back the initial

outlay required. Payback period can be calculated in two different ways:

a) Simple Payback Period

Simple payback period may be defined as the number of years required to recover the initial

cash invested in a project. The payback period can be calculated by using the formula given

below.

InflowCash sYear'Next

Amount dUnrecovererecovery full beforeYear PeriodPayback Simple ……(11)

The simple payback period of the Project is calculated as follows:

512,454

363,0736 PeriodPayback Simple

= 6.78 years

b) Discounted Payback Period

The discounted payback period is the length of time required for a project to recover its initial

capital outlay from the cash inflows discounted at the firm's cost of capital, i. We can calculate

the discounted payback period by using the following formula:


12-8

InflowCash Disounted sYear'Next

Amount dUnrecovere recovery full beforeYear PBP Discounted …(12)

The discounted payback period of the Project is calculated as follows:

159,152

26,285 11 PeriodBack Pay Discounted Rate)Discount (10%

= 11.17 Years

The analysis suggests that the earnings from energy sale can repay the investment cost in 6.78

years under the simple payback period technique whereas the investment cost is recovered in

11.17 years under the discounted payback method. This means, the Project is able to get its

money back within the Projects' life in both methods (Simple Payback and Discounted Payback).

Even for a large and capital intensive project like this, the recoupment period is relatively short.

Hence, this is an attractive project.

12.3. Plant Factor

The ratio of average loaded output to the installed capacity of the plant is called plant factor.

The plant factor is calculated as follows:

Capacity Installed x Hours

Output LoadedNet Factor Plant ……………(13)

100% 14,500 8,760

90,577,956 Factor Plant

Plant Factor = 70.94%

The type of project is a run of the river. The analysis suggests that the plant shall be running at

70.94 percent of the full capacity every year. Since the plant factor is above 60 percent, the

Project is attractive for construction.


12-9

12.4. Unit Energy Cost

One of the important indicators for privately built hydropower project is unit cost per kilowatt.

If unit cost per kilowatt hour is lower than the price fixed by NEA, then the project is said to be

feasible and vice versa.

The energy shall be sold to NEA at the rate of Rs. 4.80 for the wet months and Rs. 8.40 for the

dry months. The latest trend adopted by the NEA is an increment of 8 percent in energy price for

the first eight years after operation. This makes an average price per kilowatt-hour of Rs. 6.95.

The average unit price varies from one project to another depending on their plant factor. The

unit energy cost of the Project has been calculated by using the following formula:

PF 8,760 P

M O C Cost Energy Unit

ins

anan …………………………(14)

Where,

Can = Annuity Cost (Interest and Principal Repayment) = Rs. 276,047,000

O+M = Annual Operation and Maintenance Cost + Annual Royalty = Rs. 127,413,000

Pins = Installed Capacity = 14,500 Kilowatt

PF = Plant Factor = 70.94%

Unit Energy Cost = Rs. 4.45

The power generated from this Project can be sold at Rs. 5.99 in the first year of operation which

shall increase over the period of time. Unit Energy Cost of the Project is lower than the price

fixed by NEA. Thus, this Project is profitable.

12.5. Debt Service Coverage Ratio

This Project will be financed by equity and bank loans. The capital will be required at different

stages of the project development cycle. The capital structure of the Project consists of 30.0

percent equity and 70.0 percent bank loan. The shareholders are the real owner of the Project.

0.7094 8,760 14,500

0127,413,00 0276,047,00 Cost Energy Unit


12-10

They get profit if the Project earns it. On the contrary, the bank loan has to be paid back with

interest. The debt service coverage ratio (DSCR) is the ratio of net operating income to debt

payment. It is a popular benchmark used in the measurement of an income-producing project’s

ability to produce enough revenue to cover its debt payments. The rule of thumb says, "A project

is acceptable if the ratio is greater than one". Mathematically, it is calculated as:-

Interest) (Principal

onAmortization Depreciati EBIT Ratio Coverage ServiceDebt

…………. (15)

Where,

EBIT = Earnings before Interest and Tax.

Since the loan repayment duration for this Project is 12 years, DSCR is calculated for the first

twelve years, which is 2.08.

Typically, most commercial banks require DSCR ratio of 1.15 to 1.30 times to ensure cash flow

sufficient to cover loan payment is available on an ongoing basis. The result shows that there will

be surplus money left even after paying interest and loan. Hence, this Project can easily meet

the debt liability.

12.6. Sensitivity Analysis

Sensitivity analysis is done to examine the robustness of the Project during various extreme

unfavorable conditions. The sensitivity analysis of the proposed Irkhuwa Khola B Hydropower

Project has been carried out by varying one of the analysis parameter while keeping the rest

unchanged. Sensitivity analyses for following conditions have been carried out:

Increase in interest rate

Increase in project cost

Decrease in revenue

The results of the sensitivity analysis for different scenarios of possible loss in revenue, increased

capital investment cost, and for the increase in interest rate are shown in Table 12-3 below.

Table 12-3: Results for Sensitivity Analysis

Results IRR B/C Ratio

NPV

(000000) DSCR

Base Case 14.98% 1.45 1174 2.08


12-11

Case I: Project Cost Increased by

10% 13.22% 1.29 835 1.90

Case II: Project Cost Increased by

20% 11.74% 1.16 490 1.74

Case III: Decline in Power

Generation by 10% 12.84% 1.26 665 1.86

Case IV: Decline in Power

Generation by 20% 10.65% 1.06 151 1.63

From the results of, it is clearly seen that the proposed Upper Irkhuwa Khola Hydropower Project

has still positive NPV, IRR greater than the adopted interest rate, and B/C ratio greater than unity

even during all the possible unfavorable conditions. This indicates the robustness of the Project

under existing conditions; hence the Project is quite worthy investing.


13-1

13. CONCLUSIONS AND RECOMMENDATIONS

13.1. Conclusions

There is acute power shortage in all regions of Nepal. The construction of power plants in any

region shall reduce the transmission losses and provide reliable energy in the region. In this

context the construction of Upper Irkhuwa Khola Hydropower Project will add power in the

central region of Nepal. Khandbari and Tumlingtar are the growing market in the hilly region of

Sankhuwasabha district as well as main connecting towns for the proposed project. So, there will

be increased demand of energy in coming years.

With the construction of this project it will help to supply reliable power to the system in that

area of eastern region, which will help for industrial development in the region.

13.2. Recommendations

From the feasibility study report the Project is found to be feasible and profitable for the

construction. The water discharge from the Irkhuwa Khola has not been used for drinking water

and irrigation purpose. There is little negative environmental impact by constructing this project.

The study has suggested for the tunnel option while the canal option or pipe option will be

avoided due to geological, topographical, safety and the costing reasons.

A upgrading of the existing motorable road as infrastructure of this project is suggested. Though

it will increase the construction cost of the project it will benefit the project in the immediate

run and local people in the future.

Rural electrification in the surrounding villages have to be done and electrify the villages will help

to upgrade the living standard. A permanent drinking water scheme has to be built to facilitate

the project construction work and the local villages as well.

In order to increase the local people participation it is suggested to have maximum local people

participation in the equity shareholding of the company. It will increase the feeling of ownership

among the local people.


d

References

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Estimating Hydrologic Characteristics of Ungauged Locations in Nepal.

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Hydraulic Design of Stilling Basins and Energy Dissipaters: a Water Resources

Technical Publication.

K. Subramanya, Tata McGraw-Hill Publishing Company Limited, New Delhi;

Engineering Hydrology.

M. M. Dandekar, K. N. Sharma (1994); Water Power Engineering.

Helmut Lauterjung Gangolf Schmidt, Friedr. Vieweg & Sohn Braunschweig

Wiesbaden; Planning of Intake Structures.

P.C. Helwig, CIWEC, Nepal Electricity Authority; Report on Desander Design.

A Geneva Group, USA, Centre for Integrated Education (1990); How to Run a Small

Development Project.

Chakraworty M., Published by the Author, 21B, Bhabanda Road Calcutta India (1992);

Estimating Costing Specifications and Valuation in Civil Engineering.

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Development Group, ITDG (1993); Micro Hydro Design Manual.

D. Johnson Victor, Oxford & IBH Publishing Co. Pvt. Ltd., New Delhi, India (2001);

Essentials of Bridge Engineering.

ICIMOD (1997); A manual for Private and Community Based Mini and Micro

Hydropower Development in the Hindukush Himalayas.

Junejo A. A., ICIMOD, Kathmandu, Nepal (1995); The Orientation cum Training

Programme on Mini and Micro Hydropower Development in the HKH Region.

M. X. Khan, P. K. Jain, Tata McGraw Hill, New Delhi, India (1985); Financial

Management.

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Netherlands (1997); Sustainable Development of Hydropower in the Arun Valley,

Nepal: Master Degree Dissertation.

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Rural Business.


c

WECS, Kathmandu, Nepal (1988); Report of the Task Force on Rural Electrification

Impacts in Nepal: Report No. 4/4/220688/1/1, seq. 308.

J. Stöcklin & K. D. Bhattarai (1977); Geology of the Kathmandu Area and Central

Mahabharata Range, Nepal Himalayas: Report of Department of Mines &

Geology/UNDP.

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Society of the London, Vol. 137, pp. 1-34.

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Thesis submitted and accepted by Central Department of Geology, TU.

D. Driscoll (1979); Retaining Wall Design Guide: USDA Forest Service Region 6,

Foundation Sciences, Inc.

J. Krahenbuhl & A. Wagner (1983); Survey, Design, and Construction of Trail

Suspension Bridges for Remote Areas: Swiss Centre for Appropriate Technology,

Switzerland, Vol. B, pp. 325.

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Submitted to the International Institute of Seismology and Earthquake Engineering,

Japan.


I

Annex I – Photographs

Photo P-1: Headworks Site for Upper Irkhuwa Khola Hydropower Project

Photo P-2:Powerhouse location for Upper Irkhuwa Khola Hydropower Project


II

Photo P-3: Survey work in the headworks area before disturbance by local community

Photo P-4: Discharge Measurement at Irkhuwa Khola


III

Photo P-5: Gauge Station fixed at Irkhuwa Khola

Photo P-6: Map study by the experts during site visit


IV

Documents

aaratipower.com...Upper Irkhuwa Khola Hydropower Project Feasibility Study Report i Salient Features of Upper Irkhuwa Khola Hydropower Project 1. Project name : Upper Irkhuwa Khola