Post on 27-Mar-2020
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)
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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
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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
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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
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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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
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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
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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
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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
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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
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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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
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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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
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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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
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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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
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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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
Figure 4-12: Stereographic Projection of the Rockmass of the waterways alignment (ch 0+980 to
1+200) ........................................................................................................................... 4-35
Figure 4-13: Stereographic Projection of the Rockmass of the waterways alignment (ch 1+200 to
1+600) ........................................................................................................................... 4-36
Figure 4-14: Stereographic Projection of the Rockmass of the waterways alignment (ch 1+600 to
2+930) ........................................................................................................................... 4-37
Figure 4-15: Stereographic Projection of the Rockmass of the waterways alignment (ch 2+930 to
3+300) ........................................................................................................................... 4-38
Figure 4-16: Stereographic Projection of the Rockmass of the waterways alignment (ch 3+300 to
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
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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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.
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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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.
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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’.
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
1. Progress Report 1-5
Figure 1-1: Map of Nepal showing the Irkhuwa Khola B Hydropower Project site
Project Area
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
Feasibility Study Report 1-6
Figure 1-2: Location of the Project area in Bhojpur district Map
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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’
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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
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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
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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.
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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.
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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.
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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
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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
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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
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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
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Avg.
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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
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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
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Avg.
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
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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
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Avg.
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.
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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
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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.
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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
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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.
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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
Gumbel's Method (Below 3000 m)
Log Pearson Type III (Below 3000 m)
Log Normal (Below 3000 m)
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
Gumbel's Method (Below 3000 m)
Log Pearson Type III (Below 3000 m)
Log Normal (Below 3000 m)
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
:
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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
Gumbel's Method (Below 3000 m)
Log Pearson Type III (Below 3000 m)
Log Normal (Below 3000 m)
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
Gumbel's Method (Below 3000 m)
Log Pearson Type III (Below 3000 m)
Log Normal (Below 3000 m)
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,
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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
Return Period (Years)
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
Return Period (Years)
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.
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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
Return Period (Years)
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
Return Period (Years)
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
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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)
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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.
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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
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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.
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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
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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.
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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)
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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.
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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
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(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.
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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.
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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
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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
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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.
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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
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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
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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).
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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
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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.
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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.
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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.
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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
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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
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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
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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
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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
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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
Weathering and Strength
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.
Slope Stability Condition
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.
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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
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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
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
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. .
Weathering and Strength
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.
Slope Stability Condition
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.
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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
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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
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 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.
Weathering and Strength
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
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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.
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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
spacing of 2.0 m x 2.0 m and 10 cm thick steel fiber shotcrete
Fair to good rock
mass
RS III 25 mm diameter 1.5 m long systematic grouted rock bolts at a
spacing of 1.5 m x 1.5 m and 15 cm thick steel fiber shotcrete
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.
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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
spacing of 1.3 m x 1.3 m and 20 cm thick steel fiber shotcrete.
Extremely poor
rock mass
RS VI 25mm diameter 1.5 m long systematic grouted rock bolts at a
spacing of 1.2 m x 1.2 m and 20 cm thick steel fiber shotcrete.
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
spacing of 1.1 m x 1.1 m and 20 cm thick steel fiber shotcrete.
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
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. Advance pre-injection
grouting to control water inflow into the tunnel.
Ch.1+200-Ch.1+600
Class III RS III
25 mm diameter 1.5 m long systematic grouted
rock bolts at a spacing of 1.5 m x 1.5 m and 15 cm
thick steel fiber shotcrete
Ch.1+600- Ch.2+930 Class IV 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. Advance pre-injection
grouting to control water inflow into the tunnel.
Ch. 2+930- Ch.3+300
Class III RS III
25 mm diameter 1.5 m long systematic grouted
rock bolts at a spacing of 1.5 m x 1.5 m and 15 cm
thick steel fiber shotcrete
Ch.3+300-Ch.3+800 Class IV RS IV
25 mm diameter 3 m long systematic grouted
rock bolts at a spacing of 1.3 m x 1.5 m and 20 cm
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thick steel fiber shotcrete. Advance pre-injection
grouting to control water inflow into the tunnel.
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.
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Slope Stability Condition
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)
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Figure 4-12: Stereographic Projection of the Rockmass of the waterways alignment (ch 0+980 to 1+200)
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Figure 4-13: Stereographic Projection of the Rockmass of the waterways alignment (ch 1+200 to 1+600)
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Figure 4-14: Stereographic Projection of the Rockmass of the waterways alignment (ch 1+600 to 2+930)
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Figure 4-15: Stereographic Projection of the Rockmass of the waterways alignment (ch 2+930 to 3+300)
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Figure 4-16: Stereographic Projection of the Rockmass of the waterways alignment (ch 3+300 to 3+800)
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
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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
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 51 and it indicates that the rock mass of
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.
Weathering and Strength
Rock mass is fresh to slightly weathered, with some fresh to slightly weathered rock exposed.
Slope Stability Condition
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).
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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.
Slope Stability Condition
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.
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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.
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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
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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)
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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.
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Figure 4-19: Epicenter of the Earthquke in Nepal Himalaya
Figure 4-20: Probabilistic Seismic Hazard Assessment Map of the Nepal Himalaya
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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
9 Dharchula, Far Central Nepal 1966 6.3
10 Dharchula, Far Central Nepal 1916 7.3
11 Gorkha, Central Nepal 2015 7.9
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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
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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
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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%.
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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
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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)
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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.
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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
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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
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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
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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
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(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.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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)
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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
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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
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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
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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
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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.
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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.
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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.
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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
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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.
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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.
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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.
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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��)∗����
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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.
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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.
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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:
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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
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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
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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.
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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:
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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
Sill Elevation = 920.75 masl
Inclination = 70 Degree
Quantity = 2 Sets
Clear Bar Spacing = 50 mm
(ii) Assumptions for Design
Material: = IS 2062:1999 Grade ‘B’
Bending stress ≤ 0.66 x (Yield Stress) x (1.23 -0.015L/t)
L/t ≤ 70
d/t ≤ 12
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L : Laterally unsupported length of bar
t : Thickness of bar
d : Depth of bar
(iii) Trashrack Body
Plate thickness ≥ 10 mm
Deflection Ratio (L / ymax) ≥ 500
7.8.3.2 Fine Trashrack
(i) Design Data
Trashrack Width (w) = 3.5 m
Trashrack Height (h) = 1.87m
Sill Elevation = 921.2 masl
Inclination = 70 Degree
Quantity = 1 Set
Clear Bar Spacing = 25 mm
(ii) Assumptions for Design
Material: = IS 2062:1999 Grade ‘B’
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
allowance to the calculated thickness of all steel plates for all exposed surfaces in water.
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(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 = Rope Drum Operated
Water Seal = Upstream, Four-way
(ii) Assumptions for Design
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 ≥ 60 mm
Roller Material = Cast Steel
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
allowance to the calculated thickness of all steel plates for all exposed surfaces in water.
(i) Design Data
Gate Width (w) = 2.0 m
Gate Height (h) = 1.65 m
Sill Elevation = 921.67 masl
Quantity = 2 Sets
Hoisting Type = Electric Chain Pulley Operated
Water Seal = Upstream, Three-way
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(ii) Assumptions for Design
Material: = IS 2062:1999 Grade ‘B’
Allowable Bending stress ≤ 120 N/ mm2
Allowable Shear Stress ≤ 70 N/ mm2
Deflection Ratio (L / ymax) ≥ 800
Roller Effective Width ≥ 60 mm
Roller Material = Cast Steel
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
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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
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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
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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.
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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
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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,
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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
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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.
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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 switch- gear
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
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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
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Description Parameters
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.
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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.
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- 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
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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
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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
Description Parameters
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
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The technical details of potential transformer will be as follows in Error! Reference source not
found..
Table 7-8: Details of 11kV Potential Transformer
Particular Specifications
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
Particular Specifications
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
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Description Parameters
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
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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.
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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
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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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.
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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
Particular Specifications
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
Particular Specifications
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..
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Table 7-13: Details of PT on 132kV side
Particular Specifications
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:
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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.
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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
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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
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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.
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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%
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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
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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
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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9-10
Figure 9-1: Implementation schedule of Irkhuwa Khola Hydropower Project
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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.
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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%
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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%
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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
Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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.
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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
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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.
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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.
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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.
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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.
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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
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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.).
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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:
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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:
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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:
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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
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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:
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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.
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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
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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
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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.
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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.
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References
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WECS, Kathmandu, Nepal (1988); Report of the Task Force on Rural Electrification
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Upper Irkhuwa Khola Hydropower Project Feasibility Study Report
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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
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Photo P-3: Survey work in the headworks area before disturbance by local community
Photo P-4: Discharge Measurement at Irkhuwa Khola
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Photo P-5: Gauge Station fixed at Irkhuwa Khola
Photo P-6: Map study by the experts during site visit
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