MAWPHU-II HYDRO ELECTRIC PROJECTenvironmentclearance.nic.in/writereaddata/Online/TOR/20_May_2016... · maphu-ii hydro electric project (85mw) mawphu-ii hydro electric project (85mw)

MAWPHU-II HYDRO ELECTRIC PROJECT(85 MW)

APRIL. 2016

PRE FEASIBILITY REPORT

MAPHU-II HYDRO ELECTRIC PROJECT (85MW)

MAWPHU-II HYDRO ELECTRIC PROJECT (85MW)

PRE-FEASIBILITY REPORT

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TABLE OF CONTENTS

CHAPTER - I: EXECUTIVE SUMMARY

A. INTRODUCTION ……………………………………………………………………………..... 1

B. LOCATION OF THE PROJECT ………………………………….…………………………… 1

C. HYDROLOGY ……………….…………………………………………………………………..... 1

D. GEOLOGY ………………………………………………………………………………………. 3

E. POWER POTENTIAL STUDIES ……………………………….……………………………… 5

F. PROPOSED LAYOUT OF THE PROJECT ……………………………………………………. 5

G. CLIMATE ………………………………………………………………….……………………… 6

H. ELECTRO-MECHNICAL EQUIPMENTS ……………………………………………………. 6

I. POWER EVACUATION SYSTEM …………………………………………………………….. 7

J. CONSTRUCTION SCHEDULE ………………………………..……………………………… 7

K. ENVIRONMENTAL ASPECTS ……………………………………………………………… 7

L. ESTIMATE OF THE COST ……………………………………………………………………… 7

M. FINANCIAL ANALYSIS ……………………………………………………………………… 8

N. SALIENT FEATURES …………………………………………………………………………… 9

CHAPTER - II: BACKGROUND INFORMATION

2.1 GENERAL …………………………………………………………………………………… 16

2.2 POWER SCENARIO IN NORTH EASTERN REGION ………………………………….. 16

2.3 DEVELOPMENT OF HYDRO POWER DEMAND …………………………………………. 19

2.4 NECESSITY OF THE PROJECT ………………………..………………………………… 20

CHAPTER - III: THE PROJECT AREA

3.1 GENERAL …………………………………………………………………………………… 22

3.2 PROJECT BACKGROUND …………………………………………………………………… 23

3.3 ALTERNATIVE STUDIES …………………………………………………………………… 25

3.3.1 ALTERNATIVE LOCATIONS OF DAM …………………………………………………… 25

3.3.1.1 OLD PFR LOCATION …………….………………………………………………………….. 26

3.3.1.2 ALTERNATIVE - 1 ………………………………….…………………………………………….. 27

3.3.1.3 ALTERNATIVE - 2 …………………….………………………………………………………….. 28

3.3.1.4 ALTERNATIVE - 3 ...……………………………………………………………………………… 28

3.3.1.5 ALTERNATIVE - 3A ………………………………………………………………………… 30

3.4 UPDATED PFR WITH REVISED INSTALLED CAPACITY OF 85MW ………………… 30

3.5 BASIN CHARACTERISTICS ……………..…………………………………………………… 31

3.6 CLIMATE …………………………….………………………………………………………….. 32

3.7 SOCIO-ECONOMIC PROFILE ………………………..……………………………………….. 32

CHAPTER - IV: TOPOGRAPHIC AND GEOTECHNICAL ASPECTS

4.1 GENERAL ………………………………….…………………………………………………….. 37




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4.2 TOPOGRAPHY AND MAPPING .………………………………………………………….. 37

4.2.1 EXISTING TOPOGRAPHIC INFORMATION ……………………………………….……..... 37

4.2.2 TOPOGRAPHICAL FIELD SURVEYING ……………………………………..………………. 37

4.2.3 BATHYMETRIC SURVEY ………………………..…………………………………………… 40

4.3 SITE INVESTIGATION AND GEOLOGY ………………………………………………….. 41

4.3.1 INTRODUCTION …………………..………….……………………………………………….. 41

4.3.2 GEOLOGY OF THE PROJECT AREA ………………………………………..…………….. 41

4.3.3 FIELD INVESTIGATIONS ………………………………………………….……………….. 42

4.3.3.1 ALTERNATIVE DAM SITES …………………..…………………………………………….. 42

4.3.3.2 GEOLOGICAL MAPPING ………………………………………..……………………….. 45

4.3.3.3 DRILLING …………………………………………………………….………………………….. 46

4.3.3.4 WATER PRESSURE/ PERMEABILITY TESTS ………………………………………….. 48

4.3.3.5 SPT ……………………………………..…………..…………………………………………….. 48

4.3.3.6 GROUTABILITY TEST ………..……………………………..……………………….. 48

4.3.3.7 EXPLORATORY DRIFTING ……………………………………….………………………….. 48

4.3.3.8 ROCK MECHANIC TESTS …………………………..……………………………………….. 48

4.3.3.9 PETROGRAPHY ……………………..…………..…………………………………………….. 53

4.3.3.10 GEOPHYSICAL STUDIES …………..……………………………..……………………….. 53

4.3.3.11 SEISMOLOGICAL STUDIES ……………………………………….………………………….. 53

4.4 GEOTECHNICAL EVALUATION OF CIVIL STRUCTURES …………………………….. 53

4.4.1 DAM …………………………………..…………..…………………………………………….. 53

4.4.2 ENERGY DISSIPATOR ………….………..……………………………..……………………….. 55

4.4.3 COFFER DAM ……………………………………………………….………………………….. 55

4.4.3.1 UPSTREAM COFFER DAM ………………………………..………………………….. 55

4.4.3.2 DOWNSTREAM COFFER DAM …..…………..…………………………………………….. 56

4.4.4 DIVERSION TUNNEL ………….………..……………………………..……………………….. 56

4.4.4.1 DT INLET AREA ………………………………………………….………………………….. 56

4.4.4.2 DT INTERMEDIATE AREA ………………………………..………………………….. 57

4.4.4.3 DT OUTLET AREA ……………….…………..…………………………………………….. 57

4.4.5 POWER INTAKE ………….………..……………………………..……………………….. 57

4.4.6 HEAD RACE TUNNEL …………………………………………….………………………….. 58

4.4.6.1 REACH I (RD 0 – 700M) ………………….………………………..………………………….. 59

4.4.6.2 REACH II (RD 700– 1165M) …………………..…………………………………………….. 59

4.4.6.3 REACH III (RD 1165 -1640 M) ………………………………………..……………………….. 60

4.4.6.4 REACH IV (RD 1640 - 2240 M) …………..……………………….………………………….. 60

4.4.6.5 REACH V (RD 2240-2620 M) …………….………………………..………………………….. 61

4.4.6.6 CONCLUSION …………………..……………..…………………………………………….. 61

4.4.7 SURGE SHAFT ………………….…………………………………..……………………….. 62

4.4.8 PRESSURE SHAFT …………………….…..……………………….………………………….. 63

4.4.8.1 TOP HORIZONTAL PRESSURE SHAFT ………………………..………………………….. 64

4.4.8.2 VERTICAL PRESSURE SHAFT ……………..…………………………….. 64




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4.4.8.3 BOTTOM HORIZONTAL PRESSURE SHAFT …………………..……………………….. 64

4.4.9 POWER HOUSE ………….…………….…..……………………….………………………….. 65

4.4.10 TAIL RACE CHANNEL …………………………….……………..………………………….. 67

4.4.11 CONSTRUCTION MATERIAL ………………………….………..…………………………….. 68

4.4.11.1 INTRODUCTION ………………………….……………..……………………….. 68

4.4.11.2 VARIOUS SOURCES OF CONSTRUCTION MATERIAL ……….………………………….. 69

CHAPTER - V: HYDROLOGY

5.1 GENERAL ………………………………….……………………………………………………... 72

5.2 THE PROJECT ………………………….………………………………………………………. 72

5.3 THE RIVER SYSTEM AND BASIN CHARACTERISTICS …………………………………. 72

5.4 THE CATCHMENT …….…………….….…………………………………………………… 74

5.4.1 HYPSOMETRY OF THE CATCHMENT ……………………………………………………... 76

5.4.2 ESTIMATION OF MEAN CATCHMENT ELEVATION …………….……………………. 77

5.4.3 EQUIVALENT SLOPE ……………………..…..…………………………………………... 77

5.4.4 L – SECTION OF RIVER UMIEW ………….…………………………………………………. 80

5.5 PROJECTS IN UMIEW RIVER – A GLANCE ………………………………………………... 80

5.5.1 GREATER SHILLONG WATER SUPPLY SCHEME (GSWSS) ………………………………. 80

5.5.2 MAWPHU STAGE I HEP (90 MW) …………………………..………………………………. 81

5.6 METEOROLOGICAL CHARACTERISTICS …………………………………………………… 82

5.6.1 CLIMATE ………………………………………………………………………………………... 82

5.6.2 RAINFALL ……………………………………………………….……….……………………. 82

5.6.3 TEMPARATURE & RELATIVE HUMIDITY ……..…………………………………………... 82

5.7 DATA AVAILABILITY …………………….…………………………………………………. 83

5.7.1 RAINFALL DATA ……………………………………..………………………………………... 83

5.7.2 GAUGE AND DISCHARGE DATA ………………………………..………………………. 83

5.8 ANALYSIS OF DATA ……………..…………………………..………………………………. 95

5.8.1 FILLING DATA GAPS …………………………………………………… 95

5.9 WATER AVAILABILITY STUDIES ………………………………………………………... 107

5.9.1 EXTENSION OF RAINFALL DATA …………………………….……….……………………. 107

5.9.2 RAINFALL-RUNOFF CORELATION …………..…………………………………………... 110

5.9.3 EXTENSION OF FLOW SERIES AT MAWPLANG ………………………………………. 113

5.9.4 ESTIMATION OF YEILD CORRECTION FACTOR ……………………………………... 114

5.9.5 DEVELOPMENT OF FLOW SERIES AT DAM SITE ………………..………………………. 114

5.10 DEPENDABILITY STUDIES ………..…………………………..………………………………. 115

5.11 DESIGN FLOOD STUDIES …………..…………………………………………………… 125

5.12 CLASSIFICATION OF DAMS ………………………………………………………... 125

5.13 DESIGN FLOOD CRITERIA ……………….…………………….……….……………………. 125

5.14 ESTIMATION OF DESIGN FLOOD …………..…………………………………………... 126

5.14.1 DEVELOPMENT OF SYNTHETIC UNIT HYDROGRAPH (SUG) ………………………. 126

5.14.2 DESIGN STORM ……………………………………………..…………………………………... 128




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5.14.3 TEMPORAL DISTRIBUTION ………………………..……………..………………………. 129

5.14.4 DESIGN LOSS RATE ……………..…..…………………………..………………………………. 131

5.14.5 DETERMINATION OF RAINFALL EXCESS ………………………………………… 131

5.14.6 BASE FLOW ……………………………..……………………………………………………... 132

5.14.7 CONVOLUTION OF DESIGN STORM WITH UG ………….……….……………………. 132

5.14.8 CONCLUSIONS AND RECOMMENDATIONS ……………………………………………... 133

5.15 DIVERSION FLOOD STUDIES ………………………………………………………………. 133

5.16 DESIGN CRITERIA ………………………………………………………………. 133

5.17 DATA UTILIZED ……………………………………………..…………………………………... 134

5.18 METHODOLOGY ADOPTED ………………………..……………..………………………. 135

5.19 SEDIMENTATION STUDIES …..…………………………..………………………………. 136

5.20 ELEVATION AREA CAPACITY …………………………….……………………………… 137

5.21 DATA REQUIREMENT ……………..……………………………………………………... 138

5.22 LONG TERM ANNUAL AVERAGE SEDIMENTATION RATE …….……………………. 138

5.23 CLASSIFICATION OF SEDIMENT PROBLEM ……………………………………………... 138

5.24 SEDIMENT MANAGEMENT MEASURES ……………………………………………………. 139

CHAPTER - VI: POWER POTENTIAL & INSTALLED CAPACITY

6.1 GENERAL …………………..………………………………………………………………….. 140

6.2 PROJECT PARAMETERS ….……………………………………………………………….. 140

6.3 HEAD COMPUTATION …………………………………………………………..…………. 141

6.4 WATER AVAILABILITY …………..…………………………………………………………. 141

6.5 DEPENDABLE FLOWS ………………………………………………..………………….. 141

6.6 FIRM POWER ………………………………………………………………………………….. 143

6.7 INSTALLED CAPACITY …….……….………………………………………………………… 143

6.7.1 RANGE OF INSTALLED CAPACITIES ……..………………..………………………………. 143

6.7.2 OPTIMUM INSTALLED CAPACITY …………………..…….………………………………... 144

6.8 50% DEPENDABLE YEAR ENERGY GENERATION ………………………………………. 146

6.9 DESIGN ENERGY …………………………………………………………. 146

6.10 ANNUAL PLANT LOAD FACTOR …………………………………………………………. 147

6.11 LEAN PERIOD LOAD FACTOR …………………………………………………………. 147

6.12 PEAKING OPERATION …………………………………………………………. 147

6.13 NUMBER OF UNITS …………………………………………………………. 147

6.14 SUMMARY …………………………………………………………. 148

6.15 LIST OF ANNEXURE …………………………………………………………. 148

CHAPTER - VII: DESIGN OF CIVIL AND HYDRO-MECHANICAL STRUCTURES

7.1 GENERAL …………………………………………………………………………………….. 157

7.2 PROPOSED LAYOUT OF THE PROJECT …………………………………………………... 157

7.3 DIFFERENT STRUCTURES ………………………………………………………………….. 158

7.3.1 DIVERSION TUNNEL …………….….…………….………………………………………….. 158




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7.3.2 UPSTREAM COFFER DAM ……………….………………………………………………….. 158

7.3.3 DOWNSTREAM COFFER DAM …………….……..………………………………………….. 158

7.3.4 CONCRETE DIVERSION DAM ……………………………………………………………. 159

7.3.4.1 TYPE OF DAM ……………………..………………………………………………………... 159

7.3.4.2 DAM LAYOUT DETAILS ………………………………………………………… 160

7.3.4.3 SPILLWAY …………..……………………………………………………...…………………….. 161

7.3.5 POWER INTAKES ……………………………….………………………………………………. 162

7.3.6 HEAD RACE TUNNEL ………………………………………………………………. 164

7.3.7 REQUIREMENT OF SURGE SHAFT ………………………………………………………..…. 167

7.3.8 PRESSURE SHAFT ………………………………………………………………………….…… 170

7.3.9 POWER HOUSE ……………………………………………….…………. 173

7.4 HYDRO-MECHANICAL WORKS ……………………………………………….…………. 176

7.4.1 GATES AND PENSTOCKS ………………………………………………….……………… 176

7.4.1.1 SCOPE ………………………………………………….……………… 176

7.4.1.2 DIVERSION TUNNEL GATE: (8.0M X 8.0M -1 NO.) …………….……………… 176

7.4.1.3 STOPLOGS FOR SLUICE SPILLWAY RADIAL GATES …………….……………… 177

7.4.1.4 SLUICE SPILLWAY RADIAL GATES: (8.0M X 11.5M - 5NOS.) ……………….……. 179

7.4.1.5 INTAKE TRASH RACKS (5.0M X 2.0M -2SETS/20 PANELS) ………………….……. 180

7.4.1.6 TRASH RACK CLEANING MACHINE (TRCM) …………………………..…………. 181

7.4.1.7 INTAKE EMERGENCY GATE: (4.8M X 4.8M – 1NO.) ……………………………………... 182

7.4.1.8 INTAKE SERVICE GATE: (4.8M X 4.8M – 1NO.) ……………………………….………... 183

7.4.1.9 SURGE SHAFT GATES: (3.5M X 3.5M - 1NO.) ………………………….……………….… 184

7.4.1.10 STEEL LINED PRESSURE SHAFT ……………………………………..…………………. 185

7.4.1.11 DRAFT TUBE GATES: (3.75M X 2.35M - 2NOS.) …………………….……………………... 186

CHAPTER - VIII: DESIGN OF ELECTRO-MECHANICAL WORKS

8.1 GENERAL …………………………………………………………………………………….. 189

8.2 TURBINE ……………..……………………………………………………. 189

8.3 GENERATORS ………………………………………………………………… 191

8.4 AUXILIARY ELECTRICAL SERVICES ………….……………………………. 192

8.4.1 MAIN STEP UP TRANSFORMERS ……….……………………………………. 192

8.4.2 GENERATOR – TRANSFORMER CONNECTIONS ……………………………………….. 192

8.4.3 145KV GAS INSULATED SWITCHGEAR ………….…………………………………………. 193

8.4.4 145KV XLPE CABLES ………………………………………….………..…………………… 193

8.4.5 CONTROL AND MONITORING SYSTEM …..………..…………………………………. 194

8.4.6 PROTECTION SYSTEM ……………………………………………………………………… 195

8.4.7 AC AUXILIARY POWER SYSTEM ……………..………………………………………. 196

8.4.7.1 POWER TO DAM SITE AREA ………………………………... 196

8.4.7.2 POWER TO PENSTOCK PROTECTION VALVE HOUSE ………………………………. 197

8.4.7.3 POWER TO COLONY AND OFFICE AREA ………….…………………………………….. 197

8.4.8 DC AUXILIARY SERVICES ……………………………………………………………... 197




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8.4.9 EARTHING SYSTEM …………………..……………………………………………………... 197

8.4.10 POWER, CONTROL AND INSTRUMENTATION CABLES ……………………………….. 198

8.4.11 ILLUMINATION SYSTEM …………………………………………………………………. 198

8.4.12 TEST LABORATORY ………………………………….…………………………… 199

8.4.13 COMMUNICATION SYSTEM …………………………..………………………………. 199

8.5 AUXILIARY MECHANICAL SERVICES ……………………………………………….. 199

8.5.1 COOLING WATER SYSTEM ……………………………………………………………... 200

8.5.2 DRAINAGE AND DEWATERING SYSTEMS ………………………………………………... 200

8.5.3 FIRE PROTECTION …………………………………………….………………………….. 201

8.5.4 HEATING,VENTILATION AND AIR CONDITIONING(HVAC) ………………… 202

8.5.5 COMPRESSED AIR SYSTEM ………………………………….…………………………… 203

8.5.6 ELECTRICAL LIFTS AND ELEVATORS ……………..………………………………. 203

8.5.7 WORKSHOP EQUIPMENT ……………………………………………….. 203

8.6 POWER EVACUATION ARRANGEMENT ……………………………………………….. 204

CHAPTER - IX: INFRASTRUCTURE FACILITIES

9.1 GENERAL ………………………………………………………...…………………………….. 205

9.2 TRANSPORTATION ………………………….….……………..…………………………….. 205

9.3 CONSTRUCTION FACILITIES …………..……………………….………………………….. 205

9.3.1 PROJECT ROADS INCLUDING TEMPORARY/ PERMANENT BRIDGES ……………. 206

9.3.2 SITE OFFICES AND RESIDENTIAL/ NON-RESIDENTIAL COMPLEXES ……………….. 207

9.3.2.1 SITE OFFICES …………………………………………………………………………………….. 207

9.3.2.2 RESIDENTIAL ACCOMODATION AT PROJECT SITE ………..……………………….. 207

9.3.2.3 NON-RESIDENTIAL COMPLEXES AT PROJECT SITE …………………….…………….. 208

9.3.3 WORKSHOPS ………………………………………………………………..………………. 208

9.3.4 WAREHOUSES/ STORES COMPLEX …………………………….……………….. 208

9.3.5 MUCK DISPOSAL AREA …………………………………………….. 208

9.3.6 EXPLOSIVE MAGAZINE …………………………………………………………….. 209

9.3.7 CONSTRUCTION PLANT FACILITIES ……………………………….. 209

9.3.7.1 CRUSHING PLANT …………………………….……………..…………….. 209

9.3.7.2 BATCHING AND MIXING PLANT …………………………….……..…………………….. 209

9.3.8 LAND REQUIREMENT ………...…………………..………………..……………………….. 210

9.3.9 CONSTRUCTION POWER …………..……………………………………….………………….. 211

9.3.10 TELECOMMUNICATION ………………..…..……………….. 212

9.3.11 WATER SUPPLY SYSTEM ………………………..…..…………. 212

9.3.12 SECURITY AND SAFETY ARRANGEMENT ………………………..…..…………. 212

9.3.12.1 SECURITY STAFF OFFICES AND CHECK POST ………………………..…..……….. 212

9.3.12.2 FIRE STATION ………………………..…..………….. 212

CHAPTER - X: CONSTRUCTION PLANNING

10.1 PROJECT COMPONENTS ………………….…….………………………..……………….. 213




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10.2 CLIMATIC CONDITIONS …………………………..………….……………………….. 213

10.3 ASSUMPTIONS WHILE FRAMING THE SCHEDULE ………..……………………………… 214

10.4 SCHEDULE OF WORK …………………………..……………………………… 214

10.4.1 RIVER DIVERSION WORKS ………………………………………………..……………….. 214

10.4.2 DAM AND SPILLWAYS ……………….…………………………..……………….. 216

10.4.3 HEAD RACE TUNNELS AND ADITS ……………………………………..……………….. 219

10.4.4 POWER HOUSE ……………………………..……………………………..……………….. 221

CHAPTER - XI: ENVIRONMENT AND ECOLOGY

11.1 INTRODUCTION ……………………………………………………………………………….. 222

11.2 ENVIRONMENTAL BASELINE SETTING ………………………………………………….. 222

11.2.1 PHYSIO-CHEMICAL ASPECTS …………………………………………………….. 222

11.2.2 ECOLOGICAL ASPECTS …………………………………………………………………….. 223

11.2.3 SOCIO-ECONOMIC ASPECTS ………………………………………………………………….. 226

11.3 PREDICTION OF IMPACTS ………….……………………………………… 227

11.4 IMPACTS ON LAND ENVIRONMENT ……………………………………………….. 227

11.5 IMPACTS ON WATER RESOURCES …………………………………………. 230

11.6 IMPACTS ON WATER QUALITY …………………………………………………………… 230

11.7 IMPACT ON TERRESTRIAL FLORA …………………………………………………….. 231

11.8 IMPACTS ON TERRESTRIAL FAUNA …………………………………………………….. 233

11.9 IMPACTS ON AQUATIC ECOLOGY …………………………………………………….. 233

11.10 IMPACTS ON NOISE ENVIRONMENT ………………………………………………….. 234

11.11 AIR POLLUTION ……………………………………………….. 234

11.12 IMPACTS ON SOCIO-ECONOMIC ENVIRONMENT …………………………………….. 234

11.13 SUMMARY OF IMPACTS AND EMP ……………………………………………………….. 235

CHAPTER - XII: PRELIMINARY COST ESTIMATE

12.1 GENERAL ……………..………………………………………………………………………….. 239

12.2 BASIC ESTIMATE ………………………………………………………….……….………….. 239

12.2.1 GENERAL ……..…………………………………………………………………………….. 239

12.2.2 TAXES AND DUTIES …………….………………………………………………………… 239

12.2.3 I - WORKS ………………………..……………….……………………………………………. 239

12.2.4 A - PRELIMINARY ………..……….………………………………………………………….. 239

12.2.5 B - LAND ………………..………………………………………………………………………. 239

12.2.6 C - WORKS ……..…………………………………………………………………………….. 240

12.2.7 J - POWER PLANT CIVIL WORKS ……………………………………………………………… 240

12.2.8 K - BUILDINGS …………………………..……….……………………………………………. 240

12.2.9 M - PLANTATION ………..…………………………………………………………….. 240

12.2.10 O - MISCELLANEOUS …………………………………………………………………………. 240

12.2.11 P - MAINTENANCE DURING CONSTRUCTION & Y- LOSSES ON STOCK ……..…….. 241

12.2.12 Q - SPECIAL TOOLS AND PLANT ………………….…………………………………… 241




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12.2.13 R - COMMUNICATION ………………….……………………………………………. 241

12.2.14 X - ENVIRONMENT AND ECOLOGY ………..…………………………………………….. 241

12.2.15 Y - LOSSES ON STOCK ………………………………………………………………………. 241

12.2.16 ELECTRICAL WORKS AND GENERATING PLANT …….…………………………….. 241

12.2.17 II - ESTABLISHMENT …………………………………………………………………………… 241

12.2.18 III - TOOLS AND PLANTS ………………….……………………………………………. 242

12.2.19 IV - SUSPENSE ………..………………………………………………………………………. 242

12.2.20 V - RECEIPTS AND RECOVERIES ………………………………………………………. 242

CHAPTER - XIII: ECONOMIC AND FINANCIAL EVALUATION

13.1 GENERAL ………………………………………………………………………………………….. 244

13.2 PROJECT COST …..……………………………………………………………………………… 244

13.3 PHASING OF COST ……….……………………………………………………………………… 245

13.4 ESCALATION IN COST ……….…………………………………………………………………. 245

13.5 FINANCING …………………….…………………………………………………………………. 245

13.6 ENERGY BENEFITS ……………………………………………………………………………. 245

13.7 ENERGY SALE PRICE ……………………………………………………………………. 246

13.8 THE ASSUMPTIONS TAKEN FOR WORKING OUT THE TARIFF ……..………………... 246

13.8.1 PROJECT LIFE …………………………………………………………………………………... 246

13.8.2 INTEREST RATE …………………………………………………………………………………. 246

13.8.3 RETURN ON EQUITY …………………………………………………………………………... 246

13.8.4 DEPRECIATION ……………..………………………………………………………………… 246

13.8.5 OPERATION AND MAINTENANCE CHARGES ………….………………………………… 246

13.8.6 INTEREST ON WORKING CAPITAL …………………..…………………………………….. 246

13.8.7 AUXILIARY AND TRANSFORMATION LOSSES …….……………………………………… 247

13.8.8 OTHER MISCELLANEOUS ASSUMPTIONS ……….………………………………………… 247

13.8.9 TARIFF COMPUTATION …………………….………………………………………………….. 247

CHAPTER - I

EXECUTIVE SUMMARY




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CHAPTER I

EXECUTIVE SUMMARY

A. INTRODUCTION

Mawphu Hydro Electric Project, Stage - II is proposed as a run-of-river scheme on the

river Umiew in East Khasi Hills District of Meghalaya. The proposed dam site is located

at about 3.17km downstream of Umduna HEP (90 MW) Power House location and the

Power House site is located at about 2km downstream of Thieddieng village on the right

bank of the river. The project is being implemented by North Eastern Electric Power

Corporation Ltd, a Government of India enterprise. Environmental Clearance for pre-

construction activities along with approved TOR was accorded by MoEF&CC in May

2014. This clearance was obtained with project installed capacity of 75MW and other

associated parameters. EIA/EMP studies have been carried out and completed based on

above stated TOR. In the meantime, installed capacity of the project has undergone

upward revision to 85MW as per recommendation of CEA. Project parameters have

remained unaltered with the above change in installed capacity barring changes in

Power House dimensions, Design Energy & Turbine-Generators. Instant PFR has been

prepared based on revised installed capacity of 85MW.

B. LOCATION OF THE PROJECT

Mawphu HEP, Stage - II is located on the Umiew river in East Khasi Hills district

of Meghalaya. The proposed dam site is located at latitude 25°18’32”N and longitude

91°38’19”E. The project area can be accessed from Guwahati airport, which is at about 120

km from Shillong, the capital of Meghalaya. The nearest rail head is located at Guwahati.

State Highway is available from Shillong to reach Mawsynram, which is a small town at

about 60km from Shillong. Mawsynram is connected with Thieddieng village through

about 6km foot track. Road is also existing from Mawsynram towards Thieddieng for

about 4km and the same is under construction. The dam site can be accessed from

Thieddieng (at about 2km) through footpath. The power house site is also accessed from

Thieddieng village (at about 2km) through footpath.

C. HYDROLOGY

i) Water Availability studies




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Available rainfall data at Shillong and Mawphlang along with observed discharge data at

Mawphlang dam site from January 1979 to December 1987 was utilized for water

availability studies. Gaps in the available rainfall and discharge data at Mawphlang filled.

Consistency checks on the data were applied. Available discharges at Mawphlang for the

period 1979-80 to 1987-88 extended up to 2004-05 using rainfall-runoff relations. Based on

TRMM data for the period 1998-2009, catchment rainfall worked out to 4415 mm.

Adopting runoff factor of 0.8, runoff at Mawphu II dam site comes to 3538 mm. Mean

annual runoff at Mawphlang based on observed data is 3018 mm. Hence yield correction

factor for dam site comes to 1.17. The discharges at dam site were estimated by increasing

Mawphlang discharges in catchment proportion and by applying yield correction factor.

Considering the withdrawal by GSWSS, available 10-daily discharges at dam site

determined by subtracting 0.5 cumecs from the 10-daily estimated discharges at the dam

site, to obtain the available discharges for the period 1979-80 to 2004-05. From the 10-daily

discharges at dam site, annual flows for the period 1979-80 to 2004-05 worked out and

arranged in descending order. % Age dependability estimated using Weibull’s equation.

90 % & 50 % dependable flows worked out as 887 & 1020 MCM, which correspond to the

years 1996-97 & 2002-03 respectively. 10-Daily flows during 90 % dependable year (1996-

97) have been used for power potential studies. Water availability studies have been

examined and approved by CWC vide U. O. No. 4/161/2013-Hyd (NE)/104-05 dated

11/03/14.

ii) Design Flood Studies:

As per BIS guidelines dams with gross storage capacity greater than 60 MCM or

hydraulic height greater than 30 m are to be designed to safely pass Probable Maximum

Flood (PMF).Since height of the dam is more than 30 m, the project is designed to safely

pass the PMF. Synthetic UG at the dam site was estimated from the basin characteristics

viz. A, L, Lc, S, etc., using report for “Estimation of Design Flood for South Bank

Tributaries of the Brahmaputra, Sub-zone 2 (b)”. Since time to peak worked out as 10.1

hours which appeared to be on the higher side for a catchment area of 308 sq km and

having steep slope. Hence as advised by CWC, time of concentration has been estimated

using Kirpch formula, California formula etc., which worked out to about 5 hours.

Synthetic UG was therefore developed using Sub-Zone 2 (a) report of CWC and

convoluted with 1-day PMP given by IMD. From above, design flood of 9,970 cumecs has

been adopted.




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iii) Diversion Flood:

As per IS - 14815:2000 for planning river diversion works for concrete dams, 1 in 25 year

flood of non-monsoon months or maximum observed during these months; whichever is

higher, is to be considered. From the available daily discharges of River Umiew at

Mawphlang (C.A. = 115 sq km) for the period 1980-81 to 1996-97, non-monsoon peaks

were worked out. The annual peaks thus obtained were subjected to frequency analysis to

determine the floods for various return periods. It is seen that 25 yr return period flood at

Mawphlang works out to 154 cumecs which is less than the observed non-monsoon flood

of 174 cumecs. Hence, as per IS -14815:2000, diversion flood at Mawphlang comes to 174

cumecs. Transforming this flood using Dicken’s equation, the diversion flood at Mawphu

HEP, stage II works out to 375 cumecs.

iv) Sedimentation Studies:

Based on the topographical survey of the reservoir areas and capacities at various

elevations have been worked out. Since sedimentation observation of Umiew river at the

project site or at any other site in the vicinity are not available, sediment rate of 1mm/sq

km/yr has been adopted for the studies. From the capacity inflow ratio, trap efficiency

from Brune’s curve works out to 0.5%, which indicates that most of the sediment will not

be trapped in the reservoir and would flow downstream. Hence following measures for

sediment management have been provided in the design aspects.

i) Operating the reservoir at MDDL during the monsoon months to route the

incoming sediment downstream of the project site.

ii) Provision of low level sluice spillway crest for flushing the silt downstream

during flood season.

iii) Reservoir drawdown flushing two times every year, to ensure that live storage is

always available.

iv) Adequate vertical separation between the water conductor intake sill level and the

sluice spillway crest level for effective silt flushing.

D. GEOLOGY

i) Geological set up of the Project Area

The project area falls in the central part of Meghalaya, where the Gneissic Complex has

multiple deformational & metamorphic episodes. In general, the grade of metamorphism

varies from the green schist to amphibolites facies. The Meghalaya plateau and the Mikir




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hills occur in between the E-W aligned Eastern Himalaya to the north and the broadly

NNESSW Indo-Myanmar mobile belt to the east. The Northern and North-eastern

boundary with Bengal basin lies to its south. These geological domains are separated

from the main Himalayan belt by the Brahmaputra alluvium. The Mikir Hills are

separated from the Meghalaya Plateau by the alluvium tract of Kopili River and the NE-

SW Kopili fault.Dauki fault is located 12 km south of project area.

ii) Field Investigations

In last couple of years, the Project components have been studied in detail through

� Geological mapping

� Exploratory drilling

� Drifting

� In-Situ Test and Laboratory test

� Petrography

� Groutability test

� Geophysical Survey

Geological mapping has been done in Dam and appurtenant structure, reservoir, HRT

Adit portals, Suege Shaft, Pressure Shaft and Pressure Shaft Adit, Power House and Tail

Race Channel in 1: 1000 scale. The same has been done in HRT in 1: 2500 scale.

In addition to 3 bore holes with aggregating length of 90m for Groutability test, 20 bore

holes having cumulative lengths of 950m have been drilled so far. Out of these 20 drill

holes, 12holes with cumulative length of 475m have been drilled to explore Dam and its

appurtenant structures and 2 holes of 50m & 60 m length were drilled to explore surface

Power house whereas 4 bore holes were drilled to explore pressure shaft and Surge shaft

was explored by one hole of 110m. 2 Drifts each with length of 30m has been done on

both abutments of the dam.

Laboratory rock-mechanics tests, geo-physical investigation,etc. have also been

completed for the project.

iii) Seismological studies

The project is located in North Eastern region of India which falls in Zone V of the seismic

zoning map of India and is considered to be seismically active region. Analysis of the

earthquake data obtained from different sources reveals that 137 major earthquakes

shocked the area from 1845 to 1980. For a large number of events depths of hypocenters




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are not known which has limited the scope of the present study to some extent. For better

understanding of the Seismicity of project area, Dept of Earthquake Engineering IIT

Roorkee was entrusted the job to carry out the study for evaluating seismic design

parameters for the project components. Based on the studies, the maximum value

estimated for horizontal peak ground acceleration (PGA) is 0.42gfor MCE and 0.24 for

DBE condition respectively for both Horizontal and Vertical ground motion.

E. POWER POTENTIAL STUDIES

The power potential studies have been carried out based on 26 years (1979-80 to 2004-05)

generated flow series on 10-daily basis at dam site. The net storage capacity of the

reservoir between MDDL at EL.464.00 m and FRL at EL.470.00m is 0.52 Mcum. The net

head available for the turbine is 230.50m and the design discharge is 40.8 cumecs without

overload.

The environment releases as per the Terms of Reference (ToR) of October 2014 mentioned

by the Ministry of Environment and Forests and Climate Change (MoEF&CC) as given

below have been considered for computing the available discharges for power

generation.

Sl. No. Period Percentage discharge

considered

1. Monsoon Period (June to September) 30% of river discharge

2. Lean Period (December to March) 20% of average discharge

3. Non-Monsoon/Non-Lean Period (April, May

and October, November)

25% of average discharge

The proposed installed capacity is 85 MW (2 x 42.50 MW) with 10% continuous overload.

The annual energy generation in 90% dependable year (1996-97) with 95% plant

availability is 331MU. The plant load factor is 45.12%.

F. PROPOSED LAYOUT OF THE PROJECT

The proposed civil components of the project are as follows:

� A concrete gravity dam of 51m high from the deepest foundation level with low

level spillway comprising 6 bays each with radial gate of size 9.00m (W) x 12.00m

(H) to pass the design flood of 9970 cumecs.




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� Temporary river diversion works comprise a Horse Shoe shaped diversion tunnel of

7m diameter, about 384m long on the left bank and 18m (Maximum) high upstream

and 6m high downstream cofferdams.

� A Power Intake with inclined trash rack on the right bank.

� One number of Horse Shoe shaped Head Race Tunnel of 4.8m dia and 2622m long

up to Surge Shaft.

� One number of restricted orifice type Surge Shaft of 10m dia and 54m high.

� One number of circular Pressure Shaft of 3.5m dia and 869m long which bifurcates

into 2.5m dia and 32m long pressure shafts to feed two turbine units.

� A Surface Power House of 66.0m (L) x 18.0m (W) x 30.5m (H) housing two Vertical

Axis Francis Turbines and Generator units of 42.50 MW each.

� One tail race channel of 8m wide and 51m long (including recovery bay) to

discharge the water into the river.

G. CLIMATE

The proposed dam is near to the village Mawphu (L/B) and the power house is near to

Thieddieng village (R/B) in East Khasi Hills District of Meghalaya. The climate of the

sub-basin characterized by torrential rains caused by South West monsoon and 60% to

70% rainfall occurs between June to September. The river flows in deep channel and

swells into torrents during the rainy season while during the remaining months it has not

much significant flow. The river has floods during June to October with peaks mostly

occurring in July to September.

H. ELECTRO-MECHNICAL EQUIPMENTS

The surface power plant comprises two units of Vertical axis Francis Turbines each with

42.50MW capacity with 10% continuous overload. The rated speed of the turbines is

428.6rpm with the rated head of about 230.5m. Vertical shaft synchronous generators

with maximum rated capacity of 47.3MVA will be provided which will be directly

coupled to the respective turbines. The generation voltage selected is 11kV. The

generator step up transformers are housed upstream of the powerhouse, connected

through segregated phase bus ducts. The transformers will be further connected to the

132kV Gas insulated switchgear located on the floor above the generator transformers.




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I. POWER EVACUATION SYSTEM

The power generated from the Mawphu HEP, Stage - II is proposed to be pooled at

Mawlai Substation through a 132kV double circuit transmission line taking off from

Mawphu HEP. It is proposed to provide two outgoing bays for evacuating power at

132kV level from Mawphu HEP.

J. CONSTRUCTION SCHEDULE

The project has been planned to be constructed in a period of 60 months including 15

months for pre-construction activities. Main construction activity is planned to be

completed in about 45 months after accord of TEC by CEA and Environmental & Forest

clearance from MOEF. Excavation of dam below river bed level and concreting in dam

up to river bed level is the critical activity of the project. Apart from the dam, excavation

of Power House is also a critical component of the project, though it is not driving the

project schedule.

Excavation of 2.62 km long HRT can be carried out from 3 faces and hence is not

envisaged to be critical, as excavation is likely to be carried out in favorable geological

conditions.

K. ENVIRONMENTAL ASPECTS

The submergence area in the reservoir of the project at FRL is 13 Ha. Land will also be

required for the project components and the same has been arrived as 97 Ha based on

preliminary assessment. Approximately 22 Ha of forest land will be affected by the

project. A total provision of Rs.20 crores has been kept towards Environment & Ecology

of the project. No significant adverse impact is anticipated on the environment and

ecology due to the implementation of this project.

The environment releases as per the Terms of Reference (ToR) mentioned by the

Ministry of Environment and Forests (MoEF) in October 2014 shall be adopted in the

project.

L. ESTIMATE OF THE COST

The cost of construction of the project has been estimated at April 2016 price level with a

construction period of 60 months. The estimated Present Day Cost of the project is Rs.




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892.57 crore, including Rs. 770.96 crore of Hard Cost and Rs. 121.61crore as IDC &

financial charges at April 2016 price level. Total completed cost of the project stands at Rs.

940.20 crore with Rs. 127.39 crore as cost towards IDC and financial charges. The

completion cost is based on the tentative financial assessment and it may vary based on

firm financial package.

M. FINANCIAL ANALYSIS

Financial evaluation of the project has been carried out for the project life of 35 years.

The tariff has been worked out considering the financial aspects as mentioned below.

Debt-Equity Ratio 70:30

Return on Equity 15.50%

Annual Interest Rate on Loan 9.0%

O&M Charges Including Insurance 2.0%

Abstract of tariff is shown below:

Present day cost (PL April 2016)

1st year = Rs. 5.32/unit

Levellized tariff: - Rs. 5.46/unit

Completed cost






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N. SALIENT FEATURES

NAME OF THE PROJECT

Mawphu Hydroelectric Project , Stage-II

INSTALLED CAPACITY

2x42.5MW

TYPE OF SCHEME

Run-of-River

RIVER

Umiew

LOCATION

State

Meghalaya

District

East Khasi Hills

Dam site

Latitude 25o18’32”N ; Longitude 91o38’19”E

Power House Site

Latitude 25o16’45”N ; Longitude 91o37’45”E

ACCESS TO PROJECT SITE

a. Dam Site

Nearest Village

Thieddieng (Right Bank)/Mawphu (Left Bank)

Distance

Dam site to Thieddieng – about 2km through footpath

Thieddieng to Mawsynram – about 6km through foot track

Access road (under construction) is available from Mawsynram for about 4km towards Thieddieng

Mawsynram to Shillong – about 60km

Shillong to Guwahati – about 120km

b.Power House Site

Nearest Village

Thieddieng

Distance

Power House site to Thieddieng – about 2km through footpath

Nearest Airport Guwahati




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Nearest Rail Head (Broad Gauge)

Guwahati

HYDROLOGY

Catchment area at dam site

308 Sq km

90% Dependable Annual Runoff

887 MCM

50% Dependable Annual Runoff

1020 MCM

Minimum Environmental Release:

Lean Season

20% of Average Discharge

Monsoon

30% of inflow

Non-Monsoon/Non-Lean Season

25% of Average Discharge

RESERVOIR

Full Reservoir Level (FRL)

EL. 470.00 m

Maximum Water Level (MWL)

EL. 470.50 m

Minimum Drawdown level (MDDL)

EL. 464.00 m

Gross Storage at FRL

1.55 MCM

Live Storage

0.5 MCM

Submergence Area at FRL

13 ha

Length of Reservoir

1.2 km

DAM

Type

Concrete Gravity Dam

Top Elevation of dam

EL. 472.00 m

Top Width

5.00 m

Length of dam at top

140 m

Height of Dam from deepest foundation level

51.00 m

Average River Bed Level EL. 434.00 m




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SPILLWAY

PMF (Design flood)

9970 cumecs

Type of Spillway

Surface Ogee type with breast wall

Crest Elevation

EL. 443.00 m

Number of bays

6 Nos.

Size of Radial Gates

9 m x 12 m

Length of Spillway

79.00 m

Energy Dissipation Arrangement

Trajectory bucket

DIVERSION ARRANGEMENT

Type, Shape and Size

Tunnel, 1 No. Horse shoe shaped, 7m dia and 384m long

Location

Left Bank

Diversion Flood

375 cumecs

Inlet invert level

EL. 446.00 m

Outlet invert level

EL. 429.50 m

Top width of upstream Coffer Dam

5.00 m

Height of upstream coffer dam

18.00 m

Top width of downstream Coffer Dam

3.00 m

Height of downstream coffer dam

6.00 m

POWER INTAKE

Number

1 No.

Centre line of intake

EL. 454.40 m

Invert level

EL. 452.00 m

Size of Gate Opening

4.80 m x 4.80 m

Design discharge

40.80 cumecs




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HEAD RACE TUNNEL

Number

1

Size and Shape

4.80 m and Horse-shoe Shaped

Length

2.62 km

Design discharge

40.80 cumecs

ADITS TO HRT

Number of Adits

2 Nos.

Near Power Intake

Nil

Intermediate Adit (Adit-1)

One at RD.862.00 m, 6 m dia, D-shaped, 78m long

Near Surge Shaft (Adit-2) One, upstream of Surge Shaft, 6 m dia, D-shaped, 124 m long

SURGE SHAFT

Number

1

Type

Restricted Orifice type

Size

10.0 m φ

Top of Surge Shaft

EL.492.00 m

Bottom of Surge Shaft

EL.438.00 m

Height

54.00 m

PRESSURE SHAFT

Number

1

Main Pressure Shaft

3.5 m φ and 869 m long

Top Horizontal

69.00m

Vertical

127.00m




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Bottom Horizontal

673.00m

Branch Pressure Shaft

2.5 m φ and 32 m each (2 nos)

ADITS TO PRESSURE SHAFT

Number of Adits

3 Nos.

Adit-2A to top horizontal Pressure Shaft

6 m dia, D-Shaped and 108 m long branched from Adit-2 to HRT

Adit-2B to erection chamber

6 m dia, D-Shaped and 81 m long branched from Adit-2 to HRT

Adit-3 to bottom horizontal Pressure Shaft

6 m dia, D-Shaped and 455 m long

ERECTION CHAMBER FOR PRESSURE

SHAFT

Number of Chambers

1 No.

Size of Chamber

8 m x 8 m x 8 m

POWER HOUSE

Type

Surface

Installed capacity

85 MW (2 X 42.50 MW)

Number of units

2

Power House cavern size (main)

66 m x 18.00 m x 30.50 m

Type of turbine

Vertical Axis Francis Turbine

Generator

Vertical Shaft synchronous generators 46 MVA

Combine Efficiency of Turbine and Generators

92.12%

Rated Net Head

230.5 m

Design Discharge

40.80 cumecs

Plant Load Factor

45.12%

TAIL RACE CHANNEL




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Length of Recovery Bay

35 m

Width of Recovery Bay

27 m

Length of Tail Race Channel up to river bank including Recovery Bay

51 m

Width of Tail Race Channel

8 m

Minimum River bed level at tail race outfall

EL.230.20 m

Min. TWL

EL.231.00 m

Normal TWL

EL.232.00 m

Max TWL

EL.239.5 m

GAS INSULATED SWITCHGEAR

Type

132kV Gas Insulated Switchgear

Location

On the floor above Transformers

POWER EVACUATION

Nearby Sub-station

Mawlai sub-station

Evacuation System

132 kV D/C Line

ENERGY GENERATION

Annual Energy Generation in 90% dependable year

335.96 MU

Annual Energy Generation in 50% dependable year

267.42 MU

Design Energy in 90% dependable year (With 95% plant availability)

331.09 MU

COST

Civil and Hydro-Mechanical

Rs.643.46 crores

Electro-Mechanical

Rs.127.50 crores

IDC

Rs.120.85 crores




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IDC and FC

Rs.127.39 crores

Escalation

Rs.41.82 crores

Total Cost

Rs.940.17 crores

First Year Tariff

Rs. 5.32/kWh

Levellised Tariff

Rs. 5.46/kWh

Construction Period

60 Months (including preconstruction activities)

CHAPTER - II

BACKGROUND INFORMATION




Page: 16

CHAPTER II

BACKGROUND INFORMATION

2.1 GENERAL

The North-Eastern Region of India has vast potential for hydro power development. The

potential of two major river systems, namely the Brahmaputra and the Barak remains

largely untapped as on date. This may be the prime reason for poor electricity generation

in the region with cascading effect on industrialization and standard of living of people.

In recent times, major emphasis has been given to develop different power projects like

hydro, thermal, solar, wind etc. in the region. The gas based power projects have not been

able to fulfill the promises for uninterrupted less polluting electricity due to severe gap

between estimated gas to be developed and actual available at site. Most of the projects

based on alternative sources like wind, solar are in planning stage without much

presence on ground.

2.2 POWER SCENARIO IN NORTH EASTERN REGION

The North Eastern Region comprises of the States of Arunachal Pradesh, Assam,

Manipur, Meghalaya, Mizoram, Nagaland, Sikkim and Tripura. The whole region is

endowed with various perennial rivers and water bodies, hence, the region is blessed

with huge hydro electricity potential. As per Re-assessment Studies carried out by CEA,

hydro potential of the North Eastern Region in terms of installed capacity has been

estimated as 58971 MW (58356 MW above25 MW capacity) i.e. almost 40% of the

country's total hydro potential. Out of the above, 1242 MW (above 25 MW capacity) have

been harnessed, while projects amounting to 2954 MW are under construction as on May

2015.

The State-wise estimated hydroelectric potential of North Eastern Region and its status of

development is given below as on May 2015 (Source: CEA website):




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Table 2.1: The State-wise estimated Hydroelectric Potential of North Eastern Region and its Status

Additionally, the Region has been assessed to have huge resource of coal, oil and gas for

thermal power generation. Per capita energy consumption of the region is lowest in the

country albeit huge potential for power development. Poor development of power

projects and resultant poor per capita electricity consumption is largely due to

inhospitable tough climatic conditions, remote location and inaccessibility of

geographical locations. However with continual improvement of infrastructure and

communication facilities, the North East region is poised to become power generation

hub in coming decade. Hydro power shall obviously take the lion’s share in total future

generation.

Hydro power development is of vital importance for well being of the people of the

North East India and for its potential contribution to the national economy, and to the

strengthening of links and economic relations with neighboring countries. The

Government has taken a number of initiatives in recent years for accelerated

development of hydro power projects with special emphasis for North East India.

Environmental and social concerns against haphazard growth in the sector have shaped

some policy changes. The main emphasis has been to develop hydro power projects in a

sustainable manner with minimal damage to already fragile and vulnerable

(Figures in MW)

State Identified Potential as per Re-assessment Study (MW)

Capacity Developed (above 25 MW Capacity) (MW)

Capacity under construction (above 25 MW Capacity) (MW)

Arunachal Pradesh

50328 405 2854

Assam 680 375 0

Manipur 1784 105 0

Meghalaya 2394 282 40

Mizoram 2196 0 60

Nagaland 1574 75 0

Tripura 15 0 0

Total 58971 1242 2954




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environmentof the region. The main emphasis has been on integrated basin development

with detailed study on cumulative impact of environment.

This region of India has been consistently suffering from shortages in meeting the peak

energy demand during the last decade. The shortfall of energy has become more

aggravated since 1991. Overall power scenario of the North Eastern region is described

in the tables below:

Table 2.2: Installed capacity including allocated shares as on 31.07.2015

(Figures in MW)

State Hydro Thermal Nuclear RES Total

Coal Gas Diesel Total

Arunachal Pradesh

97.57 12.35 43.06 0.00 55.41 0.00 104.64 257.62

Assam 429.72 187.00 718.62 0.00 905.62 0.00 34.11 1369.45

Manipur 80.98 15.70 67.98 36.00 119.68 0.00 5.45 206.11

Meghalaya 356.58 17.70 105.14 0.00 122.84 0.00 31.03 510.45

Mizoram 34.31 10.35 38.29 0.00 48.64 0.00 36.47 119.42

Nagaland 53.32 10.70 46.35 0.00 57.05 0.00 29.67 140.04

Tripura 62.37 18.70 538.82 0.00 557.52 0.00 21.01 640.90

Central (unallocated)

127.15 37.50 104.44 0.00 141.94 0.00 0.00 269.09

Total 1242.00 310.00 1662.70 36.00 2008.70 0.00 262.38 3513.08

Source: CEA website

Table 2.3: Total Installed Capacity in North Eastern Region as on 31.07.2015

(Figures in MW)

State Hydro Thermal Nuclear RES Total


Central 860.00 250.00 1192.50 0.00 1442.50 0.00 0.00 2302.50

State 382.00 60.00 445.70 36.00 541.70 0.00 253.25 1176.95

Private 0.00 24.50 0.00 24.50 0.00 9.13 33.63

Total 1242.00 310.00 1662.70 36.00 2008.70 0.00 262.38 3513.08

Source: CEA website




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Table 2.4: Actual Power Supply Position in the country in July 2015

Region Energy Peak

Requirement

Availability

Surplus /Deficit(-)

Demand Met Surplus(+) /Deficit(-)

(MU) (MU) (MU) (%) (MW) (MW) (MW) (%)

Northern 32,099 30,474 -1,625 -5.1 51,072 48,166 -2,906 -5.7

Western 27,189 27,091 -98 -0.4 42,452 41,728 -724 -1.7

Southern 25,301 25,168 -133 -0.5 36,016 36,016 0 0

Eastern 10,508 10,445 -63 -0.6 17977 17851 -126 -0.7

North-Eastern

1,309 1,242 -67 -5.1 2,355 2,224 -131 -5.6

Table 2.5: Likely Capacity addition during the 12th Plan in North-Eastern Region

(Figures in MW)

State Hydro Thermal Nuclear Total


Arunachal Pradesh

2710 0 0 0 0 0 2710

Assam 0 250 100 0 350 0 350

Meghalaya 40 0 0 0 0 0 40

Mizoram 60 0 0 0 0 0 60

Tripura 0 826 0 826 0 826

Sikkim 1367 0 0 0 0 0 1367

Total 2810 250 926 0 1176 0 3986

2.3 DEVELOPMENT OF HYDRO POWER DEMAND

Under the provisions of Section 3(1) of the Electricity Act, 2003, the Central Government

has prepared the National Electricity Policy for development of the power sector based

on optimal utilization of resources. The Policy has been evolved after extensive

consultations with the States, other stake holders, the Central Electricity Authority and

after considering the advice of the Central Electricity Regulatory Commission.

The National Electricity Policy is one of the key instruments for providing policy

guidance to the Electricity Regulatory Commissions in discharging of their functions and

to the Central Electricity Authority for preparation of the National Electricity Plan. The




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Policy aims at accelerated development of the power sector, providing supply of

electricity to all areas and protecting interests of consumers and other stakeholders

keeping in view availability of energy resources, technology available to exploit these

resources, economics of generation using different resources, and energy security issues.

As per 18th Electric Power Survey (EPS) report, the projected all-India peak demand and

energy requirement at the end of 12th Plan (2016-17) is 199,540 MW and 1354.874 BU

respectively at power station bus-bar. To meet this projected demand, capacity addition

of 88,537 MW is required during 12th Five Year Plan from conventional sources including

thermal and hydro. In addition, the installed capacity of grid-interactive renewable

sources of power generation is expected to be about 54,000 MW at the end of 12th Plan

period.

2.4 NECESSITY OF THE PROJECT

The great Himalayan mountain range with its permanently snow covered mountain

peaks; the mighty Brahmaputra and its perennial tributaries, flowing in loops and bends

and passing through breath taking deep valleys and narrow gorges; the south-east

monsoon causing highest rainfall in Meghalaya, are the natural parameters responsible

for North-East India to emerge as a boon for hydroelectric power generation. Central

Electricity Authority (CEA), in this publication “Hydroelectric Power Potential of

India 1988” estimated the optimum installable capacity of Brahmaputra basin as about

66,065 MW, out of which only about 2% have been harnessed so far. Due to increase in

population, urbanization and industrialization, the power demand has increased

considerably. To meet the increased power demand, Central Government and various

State Governments of the region are making all out efforts to develop the hydropower

potential of the region.

During the year 2012-13, the total energy requirement of Meghalaya was 1,828 MU

whereas the energy availability was 1,607 MU. i.e the total energy deficit was 221 MU.

The total energy deficit in terms of percentage is 12.1%.

The total peak demand of Meghalaya, during the year 2012-13, was 334 MW and the total

peak supply was 330 MW. i.e the total peak deficit was 4 MW and the same in terms of

percentage was 1.2%.

(Source: Load Generation Balance Report 2013-14 of CEA)




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Therefore, in order to meet the increasing peak energy demand of the state as well as the

region, it is an essential requirement to utilize the hydro power potential of Meghalaya to

boost the industrial as well as overall growth in the state.

Though Mawphu HEP, Stage – II, has been planned as a Run-of-the River scheme, it

would however be possible to derive peaking benefits with the help of diurnal

storage being provided.

CHAPTER - III

PROJECT AREA




Page: 22

CHAPTER - III

THE PROJECT AREA

3.1 GENERAL

Mawphu Hydro Electric Project, Stage - II is proposed as a run-of-river scheme on

the river Umiew in East Khasi Hills District of Meghalaya. The proposed dam site

is located at about 3.17km downstream of Umduna HEP (90 MW) Power House

location and the Power House site is located at about 2km downstream of

Thieddieng village on the right bank of the river. The proposed dam site is located at

latitude 25°18’32”N and longitude 91°38’19”E.

The Umiew River (known as Umlam in initial reaches) originates as a small stream

between latitudes 25° 19’ N and 25° 33’ N and longitudes 91° 35‘ 30” E and 91° 56’ E at an

elevation of about 1940 m in East Khasi hills of Meghalaya. Initially the river flows in

southern direction for about 4 km with a slope of about 1 in 30. For the next 6 km, it flows

in south-eastern direction with relatively flat gradient of 1 in 225. Few small streams and

nallas join in this stretch enriching its discharge. It then turns westwards and continues

its path for further 12 km before it turns in south west direction. The 7 km journey in

south west direction upto Mawphlang is quite steep with a gradient of about 1 in

12. At Mawphlang the river is barricaded by a dam to form a reservoir for a scheme

project known as Greater Shillong Water Supply Scheme (GSWSS). Fulfilling the drinking

water need of Shillong is the primary objective of the scheme.

Main tributaries of Umiew up to GSWSS are Umjilling, Umtongsieum and Wah Umsaw.

After crossing this scheme project, river extends its journey for about 13 km in a gradient

of about 1 in 175. Nallas like Umjaut, Umduna join in its right bank and Umlong joins in

its left bank. The discharges of these nallas increase the potential of the river to develop

the proposed Mawphu HEP, Stage - I (90 MW) Hydro Power Project. Mawphu HEP,

Stage - II (85 MW) Project lies further 13 km downstream of Mawphu HEP, Stage - I

Project with additional contributions from Umjngut & Umkynrem nallas, which join in

the right bank. The total length of the river up to the project site is 54.54 km. The river

reach in between two projects comprises of many loops and bends which gives a

panoramic view to the observers. Further the river flows towards the south below the

confluence along the southern slopes of Khasi Hills and enters Bangladesh beyond Shella




Page: 23

in Indo-Bangladesh border and joins the River Surma. Finally the river joins

Brahmaputra and in turn flows to Bay of Bengal via Sundarbans Delta.

The basin is bounded by Mawsynram in west, Shillong in North and Cherrapunji in east

and in fact world’s highest annual rainfall occurs at Cherrapunji and Mawsynram. The

slopes of the basin are covered with dense rainforests of coniferous and deciduous

trees with a number of small tribal villages in between. The predominant land use

pattern in the catchment area is forest of the type “Tropical Moist Deciduous”. Very

small area is under agricultural use including wet rice cultivation in the intercept valleys.

3.2 PROJECT BACKGROUND

Under the 50000 MW hydro power initiatives, Pre-Feasibility Reports for the following

three projects on Umiew River Basin of Meghalaya were prepared by WAPCOS (Figure

3.1).

i. Umjaut HEP (69MW): FRL-1346m, TWL - 952m

ii. Umduna HEP (57MW): FRL-950m, TWL - 687m

iii. Mawphu HEP (120MW): FRL-684m, TWL - 210.5m

Figure 3.1: Umiew River Projects (WAPCOS)




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After receiving authorization from the Govt. of Meghalaya in May'2005, NEEPCO took

up detailed Survey & Investigation for preparation of DPR of Mawphu HEP (120MW).

However, as observed by GSI, NER, the dam site location as mentioned in the PFR was

found to be not suitable because of non availability of abutment and it was also advised

for an alternative location. At the same time, some of the project parameters as cited in its

PFR were found to have some discrepancy with respect to the relevant topo sheet as well

as the actual field values. Hence, NEEPCO went ahead for selection of alternate site. As a

consequence, the whole lay out underwent alteration. After carrying out overall study of

the basin, it was found that for the other projects also, the parameters were deviating

with respect to topo sheet.

Considering all the above factors and comments of CEA regarding the unviability of

Umjaut HEP (69MW), NEEPCO carried out an optimization study (Figure 3.2) of the

whole basin in the following location limits.

i. Umjaut HEP (50 MW) : FRL-1346m, TWL-1025m.

ii. Mawphu HEP (90 MW) : FRL-1018.6m, TWL-542.68 m.

(In place of Umduna HEP-57 MW)

iii. Mawphu HEP (Stage-II) - 85MW: FRL-540m, TWL-210m.

NEEPCO prepared the DPR for Mawphu HEP (90MW) and submitted to MOP/CEA in

Mar' 2007. But later on, Govt. of Meghalaya allotted this along with Umjaut HEP to a

private developer (M/s ETA Star Infrastructures Ltd.) and NEEPCO was given the

downstream Mawphu HEP (Stage-II).

In June 2012, NEEPCO invited bids from engineering consultants for detailed survey,

investigations and preparation of detailed project report of Mawphu HEP Stage-II

and awarded the work to M/s Energy Infratech Pvt. Ltd. (EIPL) in December 2012.

EIPL has studied the available PFR and found that there is very less free stretch of river

between the proposed FRL at EL 540.00 m and upstream project power house TWL at

542.68m. EIPL pointed out this issue as it is much less than that of 1 km required for

environmental considerations of MoEF.




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Figure 3.2: Umiew River Project 3.3 ALTERNATIVE STUDIES

3.3.1 ALTERNATIVE LOCATIONS OF DAM

The following aspects were considered in general for the selection of the dam site:

� Topographical features of the site

� Preliminary geological and geo-technical considerations

� Accommodation of spillway arrangement to pass the design flood

� Location of Energy Dissipation arrangement

� Availability of Construction Materials

� Location of proposed u/s and d/s projects

� Environmental Requirements

Various alternative locations were identified to select the most suitable location for dam.

As the river is flowing through number of sharp bends (Figure 3.3), the dam alternatives

were identified immediately downstream of such bends so that maximum straight reach

would remain downstream for energy dissipation point of view.

Following locations have been considered for Dam:




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A. Old PFR Location (about 1km downstream of proposed Power House

location of upstream project - Umduna HEP)

B. Alt-1 about 2km downstream of Umduna HEP Power House Location

C. Alt-2 about 2.5km downstream of Umduna HEP Power House Location

D. Alt-3 about 3.1km downstream of Umduna HEP Power House Location

E. Alt-3A about 70 m downstream of Alt-3

3.3.1.1 OLD PFR (2010) LOCATION

� This location is about 1.2 km downstream of upstream project power house location.

The upstream project TWL is EL 542.68 m and FRL of this project was at El 540.00

m. Considering the average slope of 1 in 22 m there will be a free stretch of river of

about 50-60 m between two projects. View of site is presented in following

photographs.

� The river is filled up with big boulders (average ~5 m dia). Width of river is about

100 m and more than 50 % bed is exposed with in-situ rock. The river starts flowing

in sharp bend after about 300-400 m downstream of the proposed dam location.

� Sound rock shall be available at shallow depth at both the abutments.




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Figure 3.3: Umiew River showing flow in sharp bends

3.3.1.2 ALTERNATIVE - 1

� This alternative is located at about 2 km downstream of PH location of

Umduna/Mawphu HEP and about 350 downstream of Umtong Nalla. This is

located immediate downstream of first bend where the river is about 110 to130m

wide. Left abutment is flatter and covered by slope wash material whereas slope of

the right bank is reasonably steep with most of the area exposing bed rock.

Consequently, the length of dam at this location would be more.

� The downstream reach is defined by a mild curvature and do not have sufficient

straight reach for accommodating energy dissipation arrangement. At this location,

considering the river slope of 1 in 25, a head of about 40 m is anticipated to get

reduced comparing the same with PFR location.

� Moderate to thinly foliated granite gneiss is seen to be exposed herewith foliation

striking perpendicular to the river. The upstream of dam location has a sharp bend

and manifest number of small to medium side scar indicating instability in close

proximity of the dam alignment.




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� This alternative is located at about 2.5 km downstream of PH location of

Umduna/ Mawphu HEP and about 200 m downstream of confluence of a small left

bank Nalla and immediate downstream of second bend.

� The river width at this location is about 100 to120m.

� Upstream location shows mild bend whereas downstream reach provides about 150

to 200 m straight course which may not be adequate for accommodating spillway

and energy dissipation arrangement.

� The left abutment falls in a ridge between two left bank nalla (Umtong Nalla and

Weisu Nalla) and HRT alignment will cross very deep Weisu Nalla in the

upstream reach. Locating an adit for HRT in this reach shall be difficult.

� At this stretch river slope seems to be 1 in 25 which would result a loss of head of

about 60 m when compared the same with PFR location.

� Both the banks at this location are subdued and are covered by deep slope wash

material of unknown thickness. However sporadic bed rock exposures constituted of

granite gneiss with mica rich bands exist.


� This alternative is located at about 3.1 km downstream of PH location of

Umduna/ Mawphu HEP and about 250m downstream of confluence of right bank

Weisu Nalla.

� River is about 70-80 m wide. Right bank is consistently very steep and exposes

bedrock upto about 70m

� Initial slope of left Bank is steep upto about 30m above the present River bed level

after which the slope becomes gentle. About 300m long straight course exist in the

downstream reach, which can be considered acceptable for accommodating energy

dissipation arrangement.

� The HRT alignment is found to be more favorable as the same is not intersecting any

major nala.

� At this location considering the river slope of 1 in 25, head of about 80 m is

anticipated to get reduced comparing the same with PFR location.

� The discharge from the two perennial nalla Umtong & Weisu shall contribute

towards the overall discharge.




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A comparison has been presented in following table considering various aspects.

Table 3.1 Comparative of Alternatives (Score out of 10)

Parameter of comparison PFR (2010)

Location

Alt-1 Alt-2 Alt-3

River Bed Geology 8 6 6 8

Left Abutment Geology 6 5 4 5

Right Abutment 6 8 5 8

River Width 7 6 5 8

Straight reach at upstream 8 5 5 5

Straight reach at downstream 7 5 5 6

HRT Alignment 7 7 6 9

Flow increments 0 0 1 3

Head unutilised 10 8 7 6

Total 59 50 44 58

Environmental aspects 0 2 10 10

Total with Environmental

Considerations

59 52 54 68

From the above table, the PFR location was the preferential location without

environmental aspects. Since MoEF instructed NEEPCO to maintain a free reach of a

minimum of 1 km between two consecutive projects i.e. TWL of Mawphu (Umduna) and

FRL of Mawphu HEP (Stage-II), the PFR location does not satisfy the condition. Out of

alternatives 1, 2 and 3, the alternative-3 was chosen on the basis of above summarized

points.

CHANGE OF DAM SITE

During the meeting of NEEPCO with MoEF for clearance of TOR for EIA/EMP studies, it

was the apprehension that MoEF may agree to leave a free stretch of about 250 between

FRL of Mawphu (Stage-II) and TWL of Mawphu HEP. In view of this apprehension,

further reconnaissance survey was made for changing the dam site to meet out the MoEF

requirement as well as utilization of maximum potential of Umiew river and a new dam

site, which is about 250-300 m downstream of PFR (2010) location was finalized for

further investigations. More details of the alternatives are note described in this report as




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it was cancelled after receipt of written instructions of MoEF to maintain a minimum of 1

km free stretch between FRL of Mawphu (Stage-II) and TWL of Mawphu HEP. Therefore

further investigations were made on the earlier chosen location as Alternative-3.

3.3.1.5 ALTERNATIVE - 3A

� During the sub-surface investigations at dam alternative-3 DH-07, drilled at axis Alt-

3 encountered deep overburden down to 30.5m on the left bank of dam axis. Such

depressed bed rock profile indicates possible scouring/erosion of bed rock close to

concave side of the curvature along the river beyond the rock ledge.

� In view of the above and to find a suitable location, 70m downstream of Alternate-3,

a drill hole DH-09 was drilled on the left bank. The drill hole revealed the availability

of bed rock at a shallow depth and accordingly this alignment was favored.

� In view of these observations, Alternative-3a, located 70m downstream of Alternate-

3 and 340m downstream of Weisu Nalla was finalized for taking up further detailed

investigation.

MINOR ADJUSTMENT IN THE DAM AXIS ALTERNATIVE-3A

Initially during the preparation of PFR (Jan 2014), the design flood was estimated as 6000

cumecs and accordingly spillway bays were arranged in the dam layout plan. During the

clearance of hydrological studies from CWC, CWC recommended their suggestions and

design flood (PMF) was increased to 9970 cumecs.

In order to pass the design flood through spillway with 10% gate inoperative, two more

bays were required in the earlier spillway arrangement. Therefore, to accommodate

additional number of spillway bays, the dam axis proposed in the new PFR was rotated

slightly by about 30 in the clockwise direction through centre of river to avoid hitting of

water jet on the left abutment.

3.4 UPDATED PFR WITH REVISED INSTALLED CAPACITY OF 85MW

Environmental Clearance for pre-construction activities along with approved TOR was

accorded by MoEF&CC in May 2014. This clearance was obtained with project installed

capacity of 75MW and other associated parameters. EIA/EMP studies have been carried

out and completed based on above stated TOR. In the meantime, installed capacity of the




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project has undergone upward revision to 85MW as per recommendation of CEA vide

letter No. 20/14/2016-HPA-II/381 Dated 16.3.2016 (copy enclosed as Annexure 3.1).

Project parameters have remained unaltered with the above change in installed capacity

barring changes in Power House dimensions, Design Energy & Turbine-Generators.

Instant PFR has been prepared based on revised installed capacity of 85MW.

3.5 BASIN CHARACTERISTICS

Mawphu Hydro Electric Power Project (Stage-II) is planned in East Khasi Hills District in

the state of Meghalaya on the River Umiew, a tributary of the River Surma, which itself is

one of the major left bank tributaries of Brahmaputra. Mawphu Hydro Electric Project

(Stage-II) envisages the construction of a concrete gravity dam of about 51 m height (from

deepest bed level) across river Umiew to utilize a net head of about 232 m for hydro

power generation. The proposed dam is located near Mawphu village, about 8 km away

from Mawsynram and 2 km away from Thieddieng village. The catchment area up to the

dam site is 308 sq. km and the entire catchment is rain – fed. The Umiew River (known as

Umlam in initial reaches) originates as a small stream between latitudes 25º 19’ N and 25º

33’ N and longitudes 91º 35‘30” E and 91º 56’E at an elevation of about 1940 m in East

Khasi hills of Meghalaya. Initially the River flows in southern direction for about 4 km

with a slope of about 1 in 30. For the next 6 km, it flows in south-eastern direction with

relatively flat gradient of 1 in 225. Few small streams and nallas join in this stretch

enriching its discharge. It then turns westwards and continues its path for further 12 km

before it turns in south west direction. The 7 km journey in south west direction up to

Mawphlang is quite steep with a gradient of about 1 in 12. At Mawphlang the river is

barricaded by a dam to form a reservoir for a scheme project known as Greater Shillong

Water Supply Scheme (GSWSS). Fulfilling the drinking water need of Shillong is the

primary objective of the scheme.

Main tributaries of Umiew up to GSWSS are Umjilling, Umtongsieum and Wah Umsaw.

After crossing this scheme project, river extends its journey for about 13 km in a gradient

of about 1 in 175. Nallas like Umjaut, Umduna join in its right bank and Umlong joins in

its left bank.

The discharges of these nallas increase the potential of the river to develop the proposed

Mawphu Stage I (90 MW) Hydro Power Project. Mawphu Stage II (85 MW) Project lies

further 13 km downstream of Mawphu Stage I Project with additional contributions from




Page: 32

Umjngut & Umkynrem nallas, which join in the right bank. The total length of the river

up to the project site is 54.54 km.

The basin is bounded by Mawsynram in west, Shillong in North and Cherrapunji in east

and in fact world’s highest annual rainfall occurs at Cherrapunji and Mawsynram. The

slopes of the basin are covered with dense rainforests of coniferous and deciduous trees

with a number of small tribal villages in between. The predominant land use pattern in

the catchment area is forest of the type “Tropical Moist Deciduous”. Very small area is

under agricultural use including wet rice cultivation in the intercept valleys.

3.6 CLIMATE


Thieddieng village (R/B) in East Khasi Hills District of Meghalaya. The climate of the

sub-basin characterized by torrential rains caused by South West monsoon and 60% to

70% rainfall occurs between June to September. The river flows in deep channel and

swells into torrents during the rainy season while during the remaining months it has not

much significant flow. The river has floods during June to October with peaks mostly

occurring in July to September.

3.7 SOCIO-ECONOMIC PROFILE

Meghalaya gained status of Union State on 21st Jan. 1972. The State is situated between

the Brahmaputra valley on the North and Bangladesh on the south. Meghalaya has been

bestowed with abundant rainfall, plenty of sun shine, forest wealth, high plateaus and

waterfalls with river system meandering out to Bangladesh. The undulating topography

predominates the state with the highest peak rising to El 1965 m. The rainfall is highly

variable. East Khasi Hills is one of the seven districts of Meghalaya covering an area of

2748 sq. km. Shillong is the district headquarters of East Khasi Hills which is also the

capital of Meghalaya. Shillong is well connected by road with other places in the district

as well as with the rest of the Meghalaya and Assam. Shillong is connected by road with

all major north eastern states. Two major National Highways pass through East Khasi

Hills District -National Highway 40 connects Shillong to Jorabat, Assam in the north and

extends southwards to Dauki, at Bangladesh border and National Highway 44 connects

Shillong to states of Tripura and Mizoram. As per 2011 census (provisional), the total

population of the district is about 824,059 with male population of 410,360 and female

population of 413,699 (a sex ratio of about 1008 females per thousand males), with rural




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population of 458,010 and urban population of 366,049. The main occupation of the

population in the district is agriculture. In census enumeration, data regarding child

under 0-6 age were also collected for all districts including East Khasi Hills. There were

total 139,055 children under age of 0-6 against 115,169 of 2001 census. Of total 139,055

male and female were 70,805 and 68,250 respectively. Child Sex Ratio as per census 2011

was 964 compared to 972 of census 2001. In 2011, Children under 0-6 formed 16.84

percent of East Khasi Hills District compared to 17.43 percent of 2001. There was net

change of -0.59 percent in this compared to previous census of India In census

enumeration, data regarding child under 0-6 age were also collected for all districts

including East Khasi Hills. There were total 139,055 children under age of 0-6 against

115,169 of 2001 census. Of total 139,055 male and female were 70,805 and 68,250

respectively. Child Sex Ratio as per census 2011 was 964 compared to 972 of census 2001.

In 2011, Children under 0-6 formed 16.84 percent of East Khasi Hills District compared to

17.43 percent of 2001. Therewas net change of -0.59 percent in this compared to previous

census of India Description 2011.

THE PEOPLE

The Khasis occupying the northern lowlands and foothills are generally called Bhois.

Those who live in the southern tracts are termed Wars. Again among the Wars, those

living in the Khasi Hills are called War-Khasis and those in the Jaintia Hills, War-Pnars or

War-Jaintias. In the Jaintia Hills we have Khyrwangs, Labangs, Nangphylluts, Nangtungs

in the north-eastern part and in the east. In the Khasi Hills the Lyngngams live in the

north-western part. But all of them claim to have descended from the 'Ki Hynniew Trep'

and are now known by the generic name of Khasi-Pnars or simply Khasis. They have the

same traditions, customs and usage with a little variation owing to geographical

divisions.

DRESS

The traditional Khasi male dress is "Jymphong" or a longish sleeveless coat without collar,

fastened by thongs in front. Now, the Khasis have adopted the western dress. On

ceremonial occasions, they appear in “Jymphong" and dhoti with an ornamental waist-

band. The Khasi traditional female dress is rather elaborate with several pieces of cloth,

giving the body a cylindrical shape. On ceremonial occasions, they wear a crown of silver

or gold on the head. A spike or peak is fixed to the back of the crown, corresponding to

the feathers worn by the menfolk.




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FOOD & DRINKS

The staple food of Khasis is rice. They also take fish and meat. Like the other tribes in the

North-East, the Khasis also ferment rice-beer, and make spirit out of rice or millets by

distillation. Use of rice-beer is a must for every ceremonial and religious occasion.

SOCIAL STRUCTURE

The Khasis, the Jaintias and the Garos have a matrilineal society. Descent is traced

through the mother, but the father plays an important role in the material and mental life

of the family. While, writing on the Khasi and the Jaintia people, David Roy observed, 'a

man is the defender of the woman, but the woman is the keeper of his trust'. No better

description of Meghalayan matrilineal society could perhaps be possible.

RELIGION

The Khasis are now mostly Christians. But before that, they believed in a Supreme Being,

The Creator - U Blei Nongthaw and under Him, there were several deities of water and of

mountains and also of other natural objects.

MUSIC, CRAFTS AND COSTUMES

The Garos generally sing folk songs relating to birth, marriage, festivals, love and heroic

deeds sung to the accompaniments of different types of drums and flutes. The Khasis and

Jaintias are particularly fond of songs praising the nature like lakes, waterfalls, hills etc.

and also expressing love for their land. They use different types of musical instruments

like drums, duitaras and instruments similar to guitars, flutes, pipes and cymbals.

CRAFTS

Weaving is an ancient craft of the tribals of Meghalaya - be it weaving of cane or cloth.

The Khasis are famous for weaving cane mat, stools and baskets. They make a special

kind of cane mat called 'Tlieng', which guarantees a good utility of around 20-30 years.

The Garos weave the material used for their costumes called the 'Dakmanda'. Khasis and

Jaintias also weave cloth. The Khasis have also been involved in extracting iron ore and

then manufacture domestic knives, utensils and even guns and other warfare weapons

using it.

COSTUMES AND JEWELLERY

The three major tribes of Meghalaya have distinct costumes and jewellery. However, with

the change of time as in the rest of the country, the males have adopted the western code




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of dress leaving the ladies to continue the tradition of ethnic sartorial elegance. The Khasi

lady wears a dress called 'Jainsem' which flows loose to the ankles. The jewellery of the

Khasis and the Jaintias are also alike and the pendant is called 'Kynjri Ksiar', being made

of 24 carat gold. The Khasis and the Jaintias also wear a string of thick red coral beads

round their neck called 'Paila during festive occasions. The Garo ladies wear Rigitok,

which are thin fluted stems of glass strung by fine thread.

FESTIVALS

Nongkrem Dance is a religious festival in thanksgiving to God Almighty for good

harvest, peace and prosperity of the community. It is held annually during October/

November, at Smit, the capital of the Khyrim Syiemship near Shillong.

One of the most important festivals of the Khasis is Ka Shad Suk Mynsiem or Dance of

the joyful heart. It is an annual thanksgiving dance held in Shillong in April. Men and

women, dressed in traditional fineries dance to the accompaniment of drums and the

flute. The festival lasts for three days.

CULTURE OF EAST KHASI HILLS DISTRICT

Culture of East Khasi Hills District is a reflection of the traditions, cultures and religious

beliefs of the tribal communities residing here. Khasi tribe mainly inhabits this district

and thus, it can be said that the culture is chiefly tribal in character. Other tribal groups

inhabiting the district are Garo Tribe and Jaintias. Art and craft, costumes, songs and

dance forms and festivals like Nongkrem Dance and Shad Suk Mynsiem constitute the

culture of East Khasi Hills District.

TOURISM IN EAST KHASI HILLS DISTRICT

Tourism in East Khasi Hills District offers visits to several sites that are worth visiting.

The tourist attractions of this district attract people from different parts of the world.

Some of the popular attractions of East Khasi Hills District are Ward`s Lake and Botanical

Garden, Butterfly Museum, Meghalaya State Museum, Lady Hydari Park, Shillong Peak,

Elephant Falls, Spread Eagle Falls, Cathedral Church, Mawsmai Cave, Mawsmai Falls,

Nohkalikai Falls, Kynrem Falls, Mawjymbuin Caves, Symper Peak, Crinoline Falls,

Laitshyngiar Cave, Thangkharang Park and more.




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Annexure 3.1

CHAPTER - IV

TOPOGRAPHIC AND GEOTECHNICAL ASPECTS




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CHAPTER - IV

TOPOGRAPHY AND GEOTECHNICAL ASPECTS

4.1 GENERAL

Topographical survey works carried out in the project area for the preparation of detailed

project report have been illustrated in the chapter. These include transfer of Bench Mark

from Survey of India Bench Mark to project sites and topographical survey.

4.2 TOPOGRAPHY AND MAPPING

4.2.1 EXISTING TOPOGRAPHIC INFORMATION

At the beginning of the Study, EIPL acquired existing Survey of India topo-sheet (78-

O/11) in a scale 1:50,000 with 20-meter contour intervals. For the purpose of catchment

area calculations, other upstream topo-sheets were procured. A pre-feasibility report was

prepared by NEEPCO, which was based on 1 in 50,000 scale topo-sheet and no specific

terrestrial survey was carried out earlier.

4.2.2 TOPOGRAPHICAL FIELD SURVEYING

The Consultant conducted detailed topographic field surveys at the Mawphu-

Stage-II project by total station. Initially the survey was conducted with the arbitrary

bench mark and then joined the survey with the Survey of India (SOI) Bench Mark.

Two bench mark locations were found in the area of power house and surge shaft of

upstream project, but could not be used due to unavailability of their co-ordinates. There

were no nearby SOI bench marks found in the project area. Two SOI bench marks are

available, one at Mawphlang and other one at Cherrapunji. Mawphlang bench mark is

about 40km and Cherrapunji is about 23.33 km from project area. Therefore the

benchmark was transferred from Cherrapunji by high accuracy auto level and was

checked by closing the level traverse. As the SOI bench mark has elevation only,

Northing and Easting coordinates were taken arbitrarily.

Control points in the project area were established by DGPS and then detailed survey

was carried out with using the control points.

Five nos. permanent bench marks and 30 cement concrete pillar with coordinates




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marks were established for future reference. Details of coordinates are presented in

the following table:

Table 4.1: Coordinate details of Survey Bench marks

Sl. No. Easting (m) Northing (m) Height (m) Code Location

1. 361838.117 2796772.840 269.004 PH-1 POWER HOUSE AREA (BENCH MARK)

2. 361881.590 2796699.445 265.377 PH-2 POWER HOUSE AREA (BENCH MARK)

3. 361549.824 2796867.059 296.926 PH-3 POWER HOUSE AREA

4. 361559.097 2796820.658 292.134 PH-4 POWER HOUSE AREA

5. 362000.983 2797147.272 288.178 PH-5 PRESSURE SHAFT AREA

6. 361974.229 2797129.060 289.968 PH-6 PRESSURE SHAFT AREA

7. 362366.172 2799219.803 533.371 HRT-1 HEAD RACE TUNNEL AREA







14. 361744.630 2797449.471 429.726 ADT-1 ADIT AREA

15. 361752.650 2797477.477 438.098 ADT-2 ADIT AREA

16. 361562.249 2797518.658 532.439 S-1 SURGE SHAFT AREA

17. 361624.093 2797493.165 503.888 S-2 SURGE SHAFT AREA

18. 362566.879 2799956.662 448.436 D-1 DAM AREA (BENCH MARK)

19. 362511.669 2800065.435 446.023 D-2 DAM AREA (BENCH MARK)

20. 362424.609 2800079.713 461.610 Pillar-3 RESERVOIR AREA





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32. 361647.538 2798735.761 795.217 G-1 THIEDDIENG VILLAGE FOOTBALL GROUND AREA

33. 361674.116 2798683.335 796.826 G-2 THIEDDIENG VILLAGE (BENCHMARK NEAR BURIAL GROUND AREA)

34. 362365.974 2800109.565 473.458 P-4A DAM AREA

35. 362159.123 2800143.014 470.883 P-4B DAM AREA

Figure 4.1: Project Layout showing 5 Bench Marks established in the Project Area




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Having in mind the steep topography of the area, for the purpose of the hydro power

plant DPR stage design, the Consultant developed topographical maps with respect to

contour intervals as follows:

� Map of the reservoir area with tentative scale of 1:2,500 with contour interval of 2 m,

� Map of the project site area with tentative scale of 1:500 with contour interval of 2 m.

� Map of colony, access road etc. with tentative scale of 1:1000 with contour interval of

2 m.

It is to be noted that herein produced accuracies are better than in the project’s terms of

references.

4.2.3 BATHYMETRIC SURVEY

In order to provide the input for the hydraulic study, a topographic sectioning of

41 river profiles at dam area and 41 profiles at power house area were done. These

profiles were taken at every 100 m, which cover 2 km upstream and 2 km downstream of

the river at both the locations. The river has covered with scattered big boulder and

water flows along a small creek in between the boulders in lean season and over the

boulders in monsoon. The river profiles were taken in lean season, when the flow in the

river was in the range of 5-10 cumecs. Depth of water in the river was less and

therefore the profiles could possible without special bathymetric survey equipment.

These data were primarily used for the hydraulic analysis of the tail water levels.

The location of the surveyed cross sections is given in Figure 4.2.

Fig 4.2 Locations of the River Cross Sections surveyed u/s and d/s of Dam Axis




Page: 41

Geological and geo-technical survey and investigations including sub-surface

investigations namely exploratory drilling, drifting, in-situ and lab tests, geo-physical

survey in the project area have been presented in detail below.

4.3 SITE INVESTIGATION AND GEOLOGY

4.3.1 INTRODUCTION

The Mawphu HE Project Stage-II is located on river Umiew in the Himalayas of East

Khasi Hill district of Meghalaya. The project area falls within Archean gneiss of

Meghalaya plateau, which is characterized by wide structural and geological diversity.

The Mawphu HE Project Stage-II is a part of a cascade development scheme on

Umiew River which is the main drainage in East Khasi Hill district. It is formed at

elevation of about 1850 m. After running a considerable stretch in Meghalaya, India, it

enters into Bangladesh to reach Brahmaputra via Surma, a major tributary of River

Brahmaputra. River Umiew is joined by number of right bank tributary namely

Umkynrem, Umtong and Waisu. Approximately 232m head is available between the

dam near Mawphu village and Tail Race Tunnel outlet near Thieddieng village. The river

course is circuitous, flowing with moderately steep gradient which has been utilized for

hydropower scheme. All along its course, Umiew River flows through a narrow valley,

thus providing number of prospective sites for dam construction. River Umiew and its

tributaries are mainly rain fed. Medium to heavy rainfall in catchment area ensures

significant water availability in the river.

4.3.2 GEOLOGY OF THE PROJECT AREA

The project area falls in the central part of Meghalaya, where the Gneissic Complex has

multiple deformational & metamorphic episodes. In general, the grade of

metamorphism varies from the green schist to amphibolites facies. The Meghalaya

plateau and the Mikir hills occur in between the E-W aligned Eastern Himalaya to the

north and the broadly NNE- SSW Indo-Myanmar mobile belt to the east. The Northern

and North-eastern boundary with Bengal basin lies to its south. These geological

domains are separated from the main Himalayan belt by the Brahmaputra alluvium. The

Mikir Hills are separated from the Meghalaya Plateau by the alluvium tract of Kopili

River and the NE-SW Kopili fault.




Page: 42

Rocks comprising the Meghalaya plateau and Mikir hills represent the re-

emergence of shield elements on the east of the gap. The highland generated by

these shield rocks occupies a crucial position between the Himalaya and the Indo –

Myanmar arc. The plateau is dominated by high grade Archean Gneissic complex,

overlain by Proterozoic intracratonic sediments of Shillong group with metavolcanic

Khasi greenstone, both intruded by Upper Proterozoic–early Palaeozoic granites.

Jurassic-cretaceous volcanism represented by the Sylhet trap occurs along the southern

margin of the plateau and is intimately associated with the E-W Dauk i fault system.

Cretaceous to Eocene stable shelf sediments cover the southern and eastern

periphery of the plateau and southern fringe of the mikir hills which towards east are

juxtaposed with sediments of the trench facies of the Indo Myanmar mobile belt. Almost

uninterrupted intra-continental sedimentation continued along the southern margin of

the plateau till quaternary period. The occurrence of Upper cretaceous carbonatite–

ultramafic complex along a NE fracture zone in the east central part of the plateau and

in Mikir hills is noteworthy. N-S to NW-SE trending active faults /fractures predominate

in this domain.

Table 4.2 Stratigraphic Succession of Meghalaya

Age Group Name Formation Lithology Holocene

Newer Alluvium (Thickness not known)

Unclassified

Sand, silt and clay

Pleistocene Older Alluvium (Thickness not known)

Unclassified

Sand, clay, pebble, gravel and

boulder deposit

----------------------------------------------- Unconformity ---------------------------------

Mio-Pliocene

Dupi Tila

Formation (1050m)

Mottled clay, feldspathic Sandstone

and conglomerate




Page: 43

----------------------------------- Unconformity/Disconformity ------------------------ Oligo-

Miocene

Garo Group

Chengapara

Formation (700m) Coarse sandstone, siltstone, clay

and marl

Baghmara

Formation (530m)

Coarse, feldspathic sandstone,

pebble, conglomerate, clay, silty

clay with a fossiliferous

limestone horizon at the top

Simsang

Formation (1150m)

Siltstone & fine sandstone and

alternations of siltstone-mudstone

Eocene -

Oligocene

Barail Group

……………………

Coarse sandstone, shale,

carbonaceous shale with streaks

and minor lenses of coal

Paleocene-

Eocene Jaintia Group

Kopili Formation

(50m)

Shale, sandstone, marl and coal

Shella Formation

(600m) Alternation of sandstone, limestone

Langer Formation

(100m.)

Calcareous shale, sandstone,

limestone

Upper

Cretaceous

Khasi Group

Mahadek

Formation (150 m)

Arkosic sandstone (often

Glauconitic & Uraniferous)

Age Group Name Formation Lithology

Conglomerate

(25m)

Conglomerate

Jadukata

Formation (140m)

Conglomerate/sandstone

------------------------------------------- Unconformity ------------------------------------ Cretaceous

Alkaline-

Ultramafic-

Carbonatite

Complex of

Sung

…………………….

Pyroxenite - Serpentinite with

abundant development of melilite

pyroxene rock, oolite, syenite and

carbonatite

---------------------------------------------------- Unconformity ---------------------------------------------

Cretaceous

Sylhet Trap

(600m)

Basalt, alkali basalt, rhyolite and

acid tuff




Page: 44

------------------------------------------ Unconformity ------------------------------------- Carboniferou

s to Permian

Lower

Gondwana

Karharbari

Formation

Very coarse to coarse grained

sandstone with conglomerate

lense, siltstone, shale,

carbonaceous

shale and coal

Talchir Formation

Basal tillite, with sandstone bands,

siltstone and shale

--------------------------------------------- Unconformity -----------------------------------

Neo

Proterozoic-

Early

Paleozoic

Granite Plutons

:Kyrdem Granite

pluton (479 ± 26

Ma) Nongpoh

Granite (550 ± 15

Ma)Mylliem

Granite(607 ±

13

Ma)South

Khasi Granite

Porphyritic coarse granite,

pegmatite, aplite/quartz vein

traversed by epidiorite, dolerite

and basalt dykes.

------------------------------------------- Intrusive contact -------------------------------

Proterozoic

Khasi Basic-

Ultrabasic

intrusives

.............................

Epidiorite, dolerite amphibolites

and pyroxenite dykes and sills

Paleo - Meso

Proterozoic

Shillong

Group

.............................

Quartzite,phyllite, quartz-sericite

schist, Conglomerate Age Group Name Formation Lithology

--------------------------------------------- Unconformity -----------------------------------

Archean (?) -

Proterozoic

Meghalaya

Gneissic

Complex

Biotite gneiss, biotite hornblende

gneiss, granite gneiss, mica

schist, sillimanite-quartz schist,

biotite- granulite- amphibolites,

pyroxene granulite, gabbro and

diorite

4.3.3 FIELD INVESTIGATIONS

4.3.3.1 ALTERNATIVE DAM SITES

Earlier during PFR stage, several alternative sites were identified to select the most

suitable one for dam in downstream of Umiew River and Umkynrem River. As Old




Page: 45

PFR Dam location proposed by NEEPCO does not fulfill the environmental

requirement formulated by Expert Appraisal Committee (EAC) of MoEF, Alt-1, Alt. 2 &

Alt.3 were chosen for review during site visit. It was found that Alt-3 was a suitable

location which is at about 3.1km downstream of proposed Umduna HEP Power House

location and accordingly an exploration plan was drawn at the axis for investigation for

DPR preparation.

The identification of the Dam alternatives was done from the existing right bank

footrack and left bank foot rack based on general topography, presence of suitable

abutments and availability of sufficient head. As the river is flowing through number

of sharp bends, the dam alternative sites were identified immediately downstream of

such bends so that a reasonable straight reach would remain available in downstream

so as to accommodate the energy dissipation arrangement.

Following locations have been considered for Dam

1. Old PFR Location (about 1km downstream of proposed

Power House location of upstream project - Umduna HEP)

2. Alt-1 about 2km downstream of Umduna HEP Power House

Location

3. Alt-2 about 2.5km downstream of Umduna HEP Power House

Location

4. Alt-3 about 3.1km downstream of Umduna HEP Power House

Location

5. Alt-3A about 70m downstream of Alt-3 location

During drilling at Alt-3 location, drill hole DH-07 encountered deep overburden on

the left bank of dam axis. So, it was proposed that the dam axis needs to be shifted

slightly downstream by about 70m to avoid deep overburden on the left abutment.

Accordingly, Alt- 3A has been chosen as a possible location for further investigation

works.

4.3.3.2 GEOLOGICAL MAPPING

The Proposed project component have been geologically mapped and studied by EIPL




Page: 46

geologists to collect site specific geological/geotechnical data. Some of the area is

rugged and difficult to access generally along the HRT alignment. However all

efforts have been made to delineate rock/overburden boundaries and to understand the

physical characteristics of the rock mass by collecting geotechnical parameters from the

available outcrops. Detailed geological mapping was carried out for various

components of the projects in scales as given below:

Component Scale

Dam and its appurtenant Structure

1:1000

Reservoir 1:1000

HRT

1:2500

HRT Adit portals

1:1000

Power House Complex

Surge Shaft

1:1000

Pressure shaft and Pressure shaft Adits

1:1000

Power House and Tail race channel

1:1000 4.3.3.3 DRILLING

In addition to 3 bore holes with aggregating length of 90m for Groutability test, 18

bore holes having cumulative lengths of 875m have been drilled so far. Out of these 18

drill holes, 11 holes with cumulative length of 445m have been drilled to explore Dam

and its appurtenant structures and 2 holes of 50m & 60 m length were drilled to

explore surface Power house whereas 4 bore holes were drilled to explore pressure

shaft and Surge shaft was explored by one hole of 110m .One 40m deep hole planned

to explore HRT and is under progress. Summarized details of the bore holes drilled at

the Dam site, Power House, Pressure shaft, Surge Shaft and HRT given below.

Sl. No. Drill Hole No.

Structure Location Co-ordinates Ground Elevation

(m)

Bed Rock Elevation/depth

(m)

Total Depth (m)

1. DH-01

Dam, Alt-3

River bed, Dam axis

E362385.79 429.37 421.97/7.4 40

N2799993.69

2. DH-02

Dam, Alt-3

River bed, Dam Axis

E362388.47 429.257 423.56/6 40

N2800009.81




Page: 47

3. DH-03

Dam,Alt- 3a

Center of river bed, Dam Axis

E362452.10 432.19 426.19 40

N2800026.54

4. DH-04

Power Intake, Alt-3a

Right bank, Dam Axis

E362438.89 433.02 424.62/8.4 40

N2800000.13

5. DH-05

Dam, Alt- 3a

Left Bank, River Bed

E362456.67 433.4 429.40/4 40

N2800049.00

6. DH-06

Stilling Basin, Alt- 3a

Center of River bed

E362479.97 431.54 426.14/5.40 40

N2800009.34

7. DH-07

Dam, Alt-3

Left Bank E36239.616 488.41 457.91/30.5 45

N2800114.38

8. DH-08

Dam, Alt-3

Left Bank E3624.14.729 501.613 482.113/19.5 40

N2800134.91

9. DH-09

Dam, Alt- 3a

Left bank E362462.889 503.407 492.907/10.5 40

N2800122.57

10. DH-10

Stilling Basin, Alt- 3a

Center of River bed

E362517.453 431.161 424.461/6.70 40.5

N2800032.78

11. DH-11

Diversion Tunnel

Left Bank E362325.943 502.89 496.89/6 40

N2800178.01

12. DH-101

Power House

Power House

E361559.16 276 268.6/7.4 50

N2796776.06

13. DH-102

Power House

Power House

E361500.24 287.37 278.37/9 60

N2796793.95

14. DH-103

Pressure shaft

Pressure shaft Alignment

E361559.18 292.54 258.04/34.5 60

N2796833.28

E361585.79

15. DH-104

Pressure shaft


N2796879.08 297.9 263.4/34.5 50

E361550.206

16. DH-105

Surge Shaft

Center Line of Surge Shaft

N2797534.082 534.16 507.16/27 110

E362385.79

17. DH-106

Pressure Shaft

Pressure Shaft Alignment

Abandoned due to local hindrance

18. DH-106a

Pressure shaft


E361571.84 514 487/27 50

N2797448.54

19. DH-107

Pressure shaft


E361596.06 438.26 396.26/42 50

N2797168.92

20. DH-108

HRT HRT Under Progress

40




Page: 48

4.3.3.4 WATER PRESSURE/ PERMEABILITY TESTS

In total 402 numbers of water pressure tests were conducted for assessing

permeability in all the exploratory drill holes .Water Pressure Tests in bedrock were

conducted using double packer in 3m stages in ascending order as per IS 5529(Part -

II).Reporting Lugeon values were determined by Houlsby A.C(1974) method. Water was

pumped at steady rate and constant pressure for periods of 5 minutes. A cycle of water

pressure tests have been conducted on the same stage at varying pressures. Reporting

Lugeon values have been incorporated in the drill hole logs. Permeability tests in

overburden were conducted by constant head method as per IS: 5529(Part – I) and has

incorporated in the drill hole logs.

4.3.3.5 SPT

In total 106 numbers of Standard penetration test were conducted for assessing bearing

capacity of overburden, SPT were conducted in accordance with IS 2131 and results

were incorporated in the respective drill logs.

4.3.3.6 GROUTABILITY TEST

Groutability test has been carried out on the river bed (Dam foundation) to

ascertain the extent of amenability of foundation rock to systematic grouting. The

pattern and depth of hole is governed primarily by the design requirement and the

nature of rock. Giving due cognizance to variation of strike of foliation and other

intersecting joints Triangular pattern was adopted for conducting Groutability test.

4.3.3.7 EXPLORATORY DRIFTING

The dam abutments of Alternative-3a have been planned to be investigated by

excavating two drifts.viz LBD-1 having 30m length at left bank and RBD-1 having

30m length at left bank. A total length of 60m of drifting at the Dam location been

proposed to be carried out.

4.3.3.8 ROCK MECHANIC TESTS

In order to determine both physio mechanical and engineering properties such as specific

gravity, UCS, tensile strength, cohesion, friction angle, deformation modulus of the

various rock types occurring in the project area, laboratory tests on rock cores

collected from drill holes were carried out at the ATES laboratory.




Page: 49

Summarized results of Rock mechanics test (Dam area)

Sam

ple N

o.

Dep

th

Rock

Type

Ten

sile stren

gth

(dry)

Ten

sile stren

gth

(Saturated)

UCS (dry)

UCS (Saturated)

Unconfined

compressive strength

Triaxial

Test

Shear

Modulus of

Elasticity

Poisson’s ratio

Slake durability index

C Φ

(m)

(MPa)

(MP a)

Degree

(GPa) %

DH-

01/59 14.58

Granitic gneiss/Gn

eiss

76.17

40.17

0.26

DH-

02/25 8.5

Granitic gneiss/Gn

eiss

133.3 95.3

114.1

52.05 0.2

DH-

02/198 39.6

Granitic gneiss/Gn

eiss

6.18

50.66

DH-

01/34 10

Granitic gneiss/Gn

eiss

68.97 59.5

DH-

01/167 36.54

Granitic gneiss/Gn

eiss

56.62 37

DH-

01/61 15.1

Granitic gneiss/Gn

eiss

3.63

45.09

DH-

03/20 8.6

Granitic gneiss/Gn

eiss

36.64

DH-

03/13 7.37

Granitic gneiss/Gn

eiss

108.6 80.8

DH-

03/29

10.4

Granitic gneiss/Gn

eiss

83.65

DH-

8

Granitic gneiss/Gneiss

6.85

52.82




Page: 50

DH-

03/17

8


99.24

DH-

06/45

10.6


26.84

DH-

06/95

19.7


3.78

45.74

DH-

06/24

8


99.39

DH-

06/46

10.77


44.37 29.2

DH-

10/14

4

26.5


41.37

HRT

rock

sampl

e

99.54

Summarized results of Rock mechanics test (Surge shaft, Pressure shaft &Power house)

Sam

ple N

o.

Dep

th

Rock

Type

Tensile stren

gth

(dry)

Tensile stren

gth

(Saturated)

UCS (dry)

UCS (Saturated)

Unconfined

compressive

strength

Triaxial Test

Shear

Parameter Modulus of

Elasticity

Poisson’s ratio

Slake durability

index

(m)

(Mpa)

C (MPa)

Degree

(GPa)

%

DH-

102/267 58.25

Granitic gneiss/Gnei

ss

48.14

0.2

2

DH-

102/247

53.7


ss

137

106

DH-

102/116

34.5


ss

79.57




Page: 51

DH-

102/125

36.55


ss

76.57

DH-

102/249

55.22


ss

103.05

DH-

103/74

39.85


ss

75.18

DH-101/

277,279,2

81

47,46.62,46.30


ss

4.87

48.98

DH-

102/102

37.3


ss

4.79

45.1

DH-102/

125,130

36.55,

37.50


ss

2.12

37.18

DH-

102/257

56.7

Granitic

gneiss/Gnei

ss

3.75

36.75

DH-

103/47,42

34.64,

36.25

Granitic

gneiss/Gnei

ss

4.21

39.99

DH-

101/209

34.55

Granitic

gneiss/Gnei

ss

7.1

6.1

DH-

102/67

28.15

Granitic

gneiss/Gnei

ss

6.2

5.5

DH-

103/39

35

Granitic

gneiss/Gnei

ss

6.3

5.5

DH-

102/249

55.5

Granitic

gneiss/Gnei

ss

99.5

DH- 105/236,2

37

90.3, 94.5

Granitic

gneiss/Gnei

ss

11.2

8.5

DH-

105/52

44.83

Granitic

gneiss/Gnei

ss

31.5




Page: 52

DH-

105/50

44.5

Granitic

gneiss/Gnei

ss

99.44

DH-

105/53

45

Granitic

gneiss/Gnei

ss

44. 59

42.

8

DH- 105/133

63.66

Granitic

gneiss/Gnei

ss

7.13

51.9

DH- 104/109

47.2

Granitic

gneiss/Gnei

ss

44. 5

23. 4

DH- 104/104

46.3

Granitic

gneiss/Gn

eiss

28.8 4

DH- 104/107

46.96

Granitic

gneiss/Gn

eiss

85.73

DH- 104/92

44.5

Granitic

gneiss/Gn

eiss

3.43

45.21

DH- 104/76

42.5

Granitic

gneiss/Gn

eiss

99.08

DH- 107/92

46.13

Granitic

gneiss/Gn

eiss

7.8

52.62

DH- 107/103

49.86

Granitic

gneiss/Gn

eiss

99.59

DH- 107/85

45

Granitic

gneiss/Gn

eiss

42.42

DH- 107/90

45.68

Granitic

gneiss/Gn

eiss

156 .6

139




Page: 53

DH- 107/92

46.13

Granitic

gneiss/Gn

eiss

112.6

4.3.3.9 PETROGRAPHY

Specimens of rocks obtained from various rock exposures and rock cores from various

drill holes of Dam site, Surge Shaft and surface Power House were utilized by the GSI

Petrology Laboratory located at Faridabad for Petrographical studies. Furthermore, 2 silt

samples were also tested and 2 tests are under progress in same laboratory for estimating

of mineral distribution in silt samples.

4.3.3.10 GEOPHYSICAL STUDIES

Geophysical explorations involving seismic refraction profiling were carried out in the

project area with a view to decipher the interface between the overburden and bedrock

as well as to determine the overburden/bedrock characteristics. In total 7 profiles

aggregating length of 860m covering Dam, Power house and adit has been carried out.

4.3.3.11 SEISMOLOGICAL STUDIES

The project is located in North Eastern region of India which falls in Zone V of the

seismic zoning map of India and is considered to be seismically active region. Analysis of

the earthquake data obtained from different sources reveals that 137 major

earthquakes shocked the area from 1845 to 1980. For a large number of events depths

of hypocenters are not known which has limited the scope of the present study to

some extent. For better understanding of the Seismicity of project area, Dept of

Earthquake Engineering IIT Roorkee was entrusted the job to carry out the study for

evaluating seismic design parameters for the project components. Based on the above,

the maximum value estimated for horizontal peak ground acceleration(PGA) is 0.42gfor

MCE and 0.24 for DBE condition respectively for both Horizontal and Vertical ground

motion.

4.4 GEOTECHNICAL EVALUATION OF CIVIL STRUCTURES

4.4.1 DAM

The 51m high concrete dam, from deepest foundation level, shall have a length of




Page: 54

139.85m at the top. The top of the dam has been kept at El. 472m. The FRL is expected to

be at El. 470m with a submergence area at FRL of 13 hectares. The river channel flows at

the center while right bank and left flank hugging water way are occupied by River

borne deposits. The river bed is occupied by large pell mell boulders of size varying from

0.5 to 6-7m, some of these large boulders could be colluvial blocks. The river bed was

explored by six drill holes i.e. DH-01, DH-02, DH-03, DH-05, DH-06 and DH-10.

Based on the above drill hole data it is inferred that in the river bed area, overburden

which is mainly RBM, thickness of which varies from 4m to 7.4m. Permeability values

range from 1-6 Lugeon and suggests reasonably tight foundation condition in the

riverbed. In any of the drill hole no major fracture zone or crushed/shear zone was

encountered, making it suitable for laying concrete dam.

On the right bank, the abutment between river bed level (El. 434 m) and El. 530 m is

approximately 55°. Along the right bank, rock outcrops of fine to medium grained

granite gneiss are occurring near the river water line were delineated in the

upstream and downstream of the dam axis. At right bank few thick veins of

pegmatite were encountered during the surface mapping. In the course of the abutment

excavation, no major problem is foreseen as right bank exposes strong granite gneiss

upto EL.510m and beyond the top of dam(EL.472m).No adverse zone was observed

during surface mapping of right bank.

The left bank abutment slopes at 52° to 55° between river level (El. 436 m) and El. 480

m, and subsequently flattens to 40° till El. 520 m. Upto elevation of 460m from river

bed level (El. 434m), rock is exposed on the left bank then above that, it is covered

by overburden material constituted of slope wash comprising top soil and rounded to

sub-rounded pebble to boulder grade detritus of granite gneiss, pink granite, grey granite

and quartzite in a sandy to silty matrix. Granitic gneiss belonging to Archean gneissic

complex are exposed here. Bedrock exposures are visible till El 460m after which the

slope is covered by hill wash deposits comprising rounded to sub-rounded cobble,

pebble and boulder of granite gneiss, pink granite, grey granite in a sandy to silty

matrix. The thickness of the overburden has been seen to ranges between 10.5m to

30.5m as has been observed from drill hole DH-07, DH-08 and DH-09. In DH-07,

overburden thickness of 30.5m comprising unsorted assemblage of rounded to

sub-rounded pebble to boulder grade detritus of granite gneiss, pink granite, grey




Page: 55

granite and quartzite in a sandy to silty matrix was encountered. In DH-07 water table

was encountered at 30.10m depth having corresponding El. 458.31m. Such depressed bed

rock profile indicates possible scouring/erosion of bed rock close to concave side of the

curvature along the river beyond the rock ledge. In view of such thick overburden and

to know the lateral extent of depressed rock profile, DH-08 was drilled 40 m towards

hillside from the DH-07 on dam axis Alt-3. Here also overburden of 19.5m was

intersected with corresponding (El 482.11m). In view of such thick overburden, it was

decided to shift to dam to downstream. To know the possible extent of the depression

in downstream side of the left bank a drill hole DH-09 was proposed at 70m downstream

from earlier Dam axis. In DH-09, overburden thickness of 10.5m EL.492m was

encountered which is above the level of the top of the dam. An assemblage of

rounded to sub rounded pebble to boulder of pink granite, gneiss and quartzite was

intersected. Here in overburden, a thick patch of sand was encountered at 3m to 6m

depth. Water table was not encountered in this drill hole. Accordingly, dam axis was

shifted to new location Alt-3a located 70m downstream of previously proposed dam

axis, Alt-3.

4.4.2 ENERGY DISSIPATOR

The energy dissipater area has been explored by a drill hole DH-06 and DH-10

located at the center of the river channel. Based on the drill hole data it is assessed

that at the flip bucket the overburden depth, comprising riverine would be between

5.4m to 6.70m.The underlying bedrock shall be of dominantly fine to coarse grained

granitic gneiss. After removing the bedrock a stripping depth of approx. 2-3m is

envisaged. The Insitu permeability values of 1.86 to 3.25 Lugeon suggest fairly tight

foundation conditions and the same gets corroborate through the results of Groutability

test.

4.4.3 COFFER DAM 4.4.3.1 UPSTREAM COFFER DAM

An Eighteen m high coffer dam has been proposed about 205 upstream of dam axis for

diversion of water through diversion tunnel. Surface geological mapping reveals the

presence of isolated patches of bedrock represented by quartz biotite gneiss and

gneiss on the surface on the left flank of the coffer dam whereas on the right flank

continuous outcrop of gneiss are well exposed. In the river bed portion, as revealed




Page: 56

from the seismic survey the overburden thickness shall range from 7 m to 17m. On the

basis of various boreholes drilled in the dam area particularly DH-01 and DH-02,

overburden permeability is expected to range between 1.02 to 1.2 X 10-2 cm/sec. Wheres

that of bedrock would vary between 3 to 6 Lugeon. In view of this as seepage

control measure jet grouting provisions has been kept below the coffer dam to minimize

seepage into the dam pit during construction.

4.4.3.2 DOWNSTREAM COFFER DAM

Downstream Coffer dam has been proposed to be located at 160m D/S of dam axis, right

abutment of the structure has been positioned utilizing the exposed rock ledge. DH-10

drilled for subsurface investigation of the stilling basin, it is opined that thickness of

overburdened, constituted of large boulder pebbles, cobbles, gravels of granite/granitic

gneiss mixed with sand shall be of the order of 5 to 7m and shall be followed by strong to

very strong bed rock quartz biotite gneiss. Overburden permeability is anticipated to

range between 3.8 to 4.8X10-3 cm/sec and therefore suitable pumping arrangement

shall be required during construction.

4.4.4 DIVERSION TUNNEL

During the construction, the river water is proposed to be diverted through a 384.6m

long, 7m dia. horse shoe shaped diversion tunnel on the left bank that would cater to a

maximum discharge of 375cumecs. The entire Diversion Tunnel area has been divided

into three parts giving due cognizance to Geological condition, nature and extent of

overburden/rock cover (both lateral and top), condition of conspicuous joint sets,

tunneling direction and proximity to river.

1) DT Inlet Area: RD 0 – RD 65m

2) Intermediate Area: RD 65 – RD 328m 3.) Outlet Area: RD 328m – RD 384.6m

4.4.4.1 DT INLET AREA

DT Inlet Area extends from RD 0- RD 65m.The DT inlet portal with invert at EL

446mm is located in granite gneiss. An appreciable length of the portal structure is

expected to lie in a low cover zone where rock cover could range from 7 to 10m

providing rock cover of less than 2D. The initial reach of the portal where overburden




Page: 57

is estimated to be 15 – 20m shall be in class IV i.e. poor rock mass necessitating

pregrouting. Hence a sufficiently thick cover of SFRS has been proposed in the support

provisions for attaining sufficient stand up time to allow timely installation of rock

support before rock distress steps in. However overall tunneling media for this reach

estimated to be Predominantly Class IV with patches of Class III and minor class V.

4.4.4.2 DT INTERMEDIATE AREA

DT Inlet Area extends from RD 65 - RD 328m. This reach of the tunnel will generally

negotiate moderately strong to strong, moderately jointed Granite gneiss. Tunneling

media between RD 65 – RD 205m is estimated to be in predominantly of Class III with

intermittent Class II band and few Class V patches. However, RD 205 - RD 308m is

estimated to be in predominantly Class II with intermittent class III band and a few

class IV patches.

4.4.4.3 DT OUTLET AREA

DT Outlet area extends from RD 328 - RD 384.6m.The DT outlet portal is located in

partially weathered Granite gneiss. The portal structure is expected to lie in a low cover

zone of the order of 6 to 14 m which is less/equal to 2D.Such conditions could continue

for a length of almost 15m .However overall tunneling media for this reach estimated

to be predominantly of Class III with patches of Class IV and Class V.

4.4.5 POWER INTAKE

Water from Dam shall be diverted to head race tunnel through a power intake structure

proposed to be located on the right bank of Umiew River at about 15.0m u/s of the dam

axis. A geological section has been developed along the intake structure s h o w i n g

orientation of various discontinuities expected to be encountered in the excavation. The

slope defining S3 joint sets shown in the drawing has been recorded during surface

mapping and it is apprehended that this set will control the slope geometry and hence

stability of excavation. Necessary support provision for avoiding formation of wedge by

installation of suitable length of bolts with moderate spacing and SFRS so that the

stability of excavation is maintained till the construction of Intake is completed.




Page: 58

Table 4.3 Discontinuity Characteristics for Power Intake area

Discontinuity Characteristics for Power Intake

Set

No.

Range of

Orientation

Average

Orientation Aperture (mm)

Spacing(cm)

Persistence

(m)

Condition

S1

8°-26°/095°-

147°

17°/120°

Tight to Partially

Open(<5m

10-60 & 60-

200

10-20

Rough

Planar

S2

72°-88°/019°-

048°

82°/028°

2 & 10-50

20-200

3-10 & 10-

20 S3

80°-88°/275°-

291°

85°/283°

Tight

10-50 & >200

1-5

S4

87°-78°/178°-

187°

84°/182°

2

100-200

1-5

S5

78°-86°/108°-

122°

83°/113°

2-10

100-200

3-10

4.4.6 HEAD RACE TUNNEL

A 4.8m dia, 2.622km long, horse shoe shaped, concrete lined Head Race Tunnel has been

proposed on the right bank of the Umiew River to convey 40.80 cumecs design discharge

to Power house . The surface data collected is depicted in the geological plan of HRT

and projected at tunnel grade in the geological section. On the basis of geological

study of varying rock condition & giving due cognizance to similar geological,

geotechnical conditions, ground water levels, thickness of overburden and vertical cover,

tunnel length has been divided into following reaches.

Sl. no.

Reach

RD(m) % of total

length

1 Reach I 0 - 700 27

2 Reach II 700 – 1165 18

3 Reach III 1165 – 1640 18

4 Reach IV 1640 – 2240 23

5 Reach V 4 - 2622 14




Page: 59

4.4.6.1 REACH I (RD 0 – 700m)

In this segment, the tunnel is aligned in N180˚ direction, and then it swings towards N

188˚, has a superincumbent cover ranging from 20m to 170m and lateral cover varying

from 175 to 485m. The overburden at NSL is expected to vary from 8 to 10m. This

approx. 700m length of the HRT is expected to be negotiated in slightly weathered,

moderately strong to strong, moderately jointed Granite Gneiss. The rock mass ratings

computed from surface outcrops along the tunnel reach and giving due cognizance to

vertical cover, anticipated seepage condition, its obliquity with principle joint set a

tentative rock class percentage has been computed for estimation purpose of this reach

and is tabulated below

Table 4.4 Rock Class Percentage in Reach I

Class II Class III Class IV Class V

60 30 8 2

4.4.6.2 REACH II (RD 700– 1165m)

In this reach, the tunnel is aligned in N188˚ direction, and then swings towards N 207˚,

has a superincumbent cover ranging from 48m to 150m and lateral cover varying

from 180 to 490m. The overburden at NSL is estimated to vary from to 10-12m. Bedrock

exposures are disposed along the banks of most nallah while the intervening areas are

covered with overburden. The bedrock exposures generally consist of light gray medium

grained, moderately jointed to massive, strong granite gneiss. The rock mass ratings

computed from surface outcrops along the tunnel reach and giving due cognizance to

attitude of foliation, vertical cover, anticipated seepage condition, its obliquity with

principle joint set a tentative rock class percentage has computed for this reach and is

tabulated below

Table 4.5 Rock Class Percentage in Reach II


20 65 10 5

The fracture zones and shears with clay infillings below the nallah bed are also indicative

of probable water charged horizons in the area associated with less competent rock mass.

Furthermore except these seasonal nallah no indications of a any weak feature are




Page: 60

present on the surface which is under overburden cover. Hence provision for advance

probing at tunnel grade is being kept for probing this reach.

4.4.6.3 REACH III (RD 1165 -1640 m)

In this stretch, the tunnel is aligned in N207˚ direction, has a superincumbent

cover estimated to be ranging from 145m to 215m and lateral cover varying from 290

to 545m. Surface exposures are generally absent or limited and comprising of Granite. A

drill hole DH-108(40m) has been planned and is under progress, geological log will

be appended in final DPR. During geological mapping it was seen that this reach

mainly covered by slope wash material of the order of 15-17m thick consisting of

pebbles of medium grained grey granite in a greenish grey sandy and clayey matrix.

Huge Granite boulders of size 5-7m are also noted in this reach. In order to confirm the

material property, depth to bed rock, water level, effect of weathering and nature of bed

rock in this stretch a drill hole DH-108 has been planned, which has been progressed so

far down to 12m. The rock mass ratings computed from surface outcrops along the

tunnel reach and giving due cognizance to attitude of foliation vertical cover,

anticipated seepage condition, its obliquity with principle joint set a tentative rock

class percentage has been computed for this reach and is tabulated below

Table 4.6 Rock Class Percentage in Reach III


20 65 10 5

4.4.6.4 REACH IV (RD 1640 - 2240 m)

In this stretch, the tunnel is aligned in N207˚ direction, and having an estimated

superincumbent cover to be ranging from 225m to 268m and lateral cover varying from

934 to 1065m. During geological mapping it was seen that this reach is mainly covered

by slope wash material of the order of 20-25m, consisting of pebbles of medium grained

grey granite in a greenish grey sandy and clayey matrix. Huge boulders of 5-7m dia of

Granite are also observed pointing to the fact that bedrock in this reach is Granite. Due to

lack of surface exposure in this reach discontinuity survey could not be done Tunneling

in this reach is expected to be in Granite. However, deep selective weathering could be

deciphered. Tunneling in this reach is expected to be in Granite. Rock mass ratings




Page: 61

evolved from surface out crops for this reach and giving due cognizance to vertical

cover, anticipated seepage condition in the tunnel, irregular nature and extent of

weathering due to decay of feldspars suggest that the tunnel would dominantly (60%)

be excavated in class II (Good rock) with zones (25%) of class III (Fair) rock and 10 % in

class IV (poor) & 5% in class V (very poor) rock. Refer table below.

Table 4.7 Rock Class Percentage in Reach IV


60 25 10 5

4.4.6.5 REACH V (RD 2240-2620 m)

From RD 2240 to RD 2620m the HRT is aligned in N207°Direction. Superincumbent cover

is estimated to be ranging from 100 m to 205m and lateral cover from 650m to 790m. The

overburden at NSL is observed to vary from to 25-28m mainly consisting of pebbles

of medium to fine grained greenish grey granite in a greenish grey sandy and clayey

matrix. At RD 2362m there is possibility of encountering contact zone between Granite

and granite gneiss and as such possibility of fractured rock mass with considerable

outflow of seepage in the vicinity of the contact cannot be ruled out. Rock mass ratings

computed from surface out crops for this reach giving due cognizance to attitude

of foliation, vertical cover, anticipated seepage condition, drill hole data from surge

shaft in the tunnel suggest that the tunnel would dominantly (70%) be excavated in

class III (Fair rock) with a few zones (20%)of class II (Good) rock and 10% in class IV

(poor) rock .refer Table below

Table 4.8 Rock Class Percentage in reach V

Class II Class III Class IV

20 70 10

4.4.6.6 CONCLUSION

The approximately 2.6 km long tunnel has been proposed on the Right bank of Umiew

River in the Archean Gneissic complex forming a major constituent of the East Khasi

hills in the South Meghalaya plateau. The bed rock consists of variants of granite

gneiss with Quartzo feldspathic bands and intrusions of granite. Summary of




Page: 62

anticipated tunneling conditions

Summary of anticipated tunneling conditions

� Rock classes in various stretches of HRT have been predicted on the

basis of surface exposures details.

� Based on geomechanical classification of rock mass percentage of rock class

to be encountered in HRT shall be as under

Table4.9 Rock Class Percentage Head race tunnel

Rock Class Percentage in HRT


40 45 10 5

� Low cover and weak zones apart from areas where copious seepage is

anticipated are proposed to be evaluated further by advance probing.

� Adequate preparedness shall be made in respect of sufficient dewatering

arrangements. Installation of concurrent support shall be required while

negotiating weak rock conditions as envisaged.

4.4.7 SURGE SHAFT

The 54m deep, 10m dia, restricted orifice type surge shaft with top at El 492m is

proposed to be accommodated in moderately jointed to massive, strong, quartz biotite

gneiss/granite gneiss conditions expected to be encountered along the shaft have been

assessed from data generated from the drill hole DH-105 as no rock exposure were

found even after the aggressive searching and traversing in Surge shaft and nearby area.

Exploratory data collected from the drill hole DH-106a, were also perused to have a fair

idea about disposition of various joint sets and rock overburden interface.

For open excavation, initially about 10m of overburden excavation shall be in silty soil

and would be followed by slope was material characterized by medium sized angular to

sub- angular rock blocks/ fragments with silty matrix till El 507m.The

overburden slopes mentioned above would contain rock blocks of partially

disintegrated rock confined within a clayey matrix. While excavating these zones




Page: 63

instability is anticipated to get initiated, especially when the material will be

saturated. As such the dressed slopes need to be provided with suitable drainage and

soil anchors for stability.

From El 507m to El 492m i.e. top of the surge shaft, the excavation shall be in moderately

strong, moderately to highly weathered granite gneiss with biotite schist banding.

As no major shear zone was encountered during drilling as such no serious difficulty

during the excavation of shaft is anticipated. In general there is an improvement in rock

strength, weathering and opening of the joints with the depth barring few exceptions at

EL.491m, EL.482m, EL472m, EL.451m and EL.436m where RQD has been found to be

low though the recovery remains constantly high. In such area provision of

consolidation grouting shall be required for ground improvement. Considering the

nature of rock encountered in drill holes and observed rock mechanic parameters, it is

anticipated that the major part of Surge shaft shall negotiate fair to good rock with

occasional patches of poor rock. The suitable rock support consisting of rock bolts, SFRS

and pressure relief holes shall be installed concurrent to excavation. It is assessed that in

the initial and terminal part of the surge shaft excavation would require circular steel

set tied firmly to each other along periphery with back fill concrete in view of the

observed weakness especially in these two areas.

4.4.8 PRESSURE SHAFT

One 3.5m dia, 869 m long, circular pressure shaft which includes a 69m long top

horizontal pressure shaft, , followed by a 171m deep vertical shaft and a 673m long

horizontal pressure shaft bifurcating into two 2.5m dia, 32m long tunnels has been

envisaged for feeding two turbines. The area encompassing the above mentioned

structure has been geologically investigated by surface geological mapping on 1:1000

scale. However no rock exposure could be found in the vicinity of pressure shaft area.

In order to collect vital subsurface information along the pressure shaft four, boreholes

namely DH103, DH-104, DH-106a and DH-107, 50m long each, were drilled along the

alignment of the pressure shaft. The detailed geological account though can be referred

from individual drill hole log in Appendix- 14, 15, 16, 17, 18.It is opined that the entire

length of pressure shaft shall be in the reasonably competent Gneiss/Quartz biotite

gneiss.




Page: 64

4.4.8.1 TOP HORIZONTAL PRESSURE SHAFT

69m long, 3.5 m dia top horizontal pressure shaft shall pass through rock with

superincumbent cover including overburden varying from 84m near top bend to 110m

near surge shaft. However, rock cover above horizontal pressure shaft varies from

57m (El 490.5m) near bend to 74m (El 507.36m) near surge shaft. Giving due

consideration to subsurface information from exploration and results of rock

mechanic test, sufficient suitable rock cover over the structure exists in this part of

pressure shaft and is anticipated to negotiate generally fair to good rock with patches

of very good and poor to very poor rock class. For estimation purpose the following

percentage of rock class can be considered for top horizontal pressure

Table 4.10 Percentage wise rock class in Top Horizontal Pressure Shaft

STRUCTURE

ROCK

CLASS

PERCENTAGE

Top Horizontal

Class- II 20%

Class- III 70%

Class- IV 5%

Class- V 5%

4.4.8.2 VERTICAL PRESSURE SHAFT

Vertical part of pressure shaft structure shall pass through rock with superincumbent

cover including overburden is 84m top bend of pressure shaft El 490.5m

Giving due consideration to subsurface information from exploration and results of rock

mechanic tests sufficient and suitable vertical as well as lateral rock cover exist around

this part of pressure shaft and is anticipated to negotiate generally fair to good rock

with occasional weak features manifested by thick clay filled joints encountered in one of

the boreholes.

4.4.8.3 BOTTOM HORIZONTAL PRESSURE SHAFT

Bottom horizontal pressure shaft shall pass through rock with superincumbent cover

including overburden varying from 230m near vertical pressure shaft side to 72m near

power house side. Giving due consideration to subsurface information from




Page: 65

exploration and results of rock mechanics test and rock cover over the structure, this

part of structure i.e. from 0 – 540 m is anticipated to negotiate generally very good

rock with intermediate length of fair and patches of poor to very poor rock class.

For estimation purpose the following percentage of rock class can be considered for

bottom horizontal pressure shaft from 0-540m

Table 4.11 Percentage wise rock class in Bottom Pressure Shaft (0-540m)

STRUCTURE

ROCK

CLASS

PERCENTAGE

Bottom

Horizontal

pressure shaft

Class- II 68%

Class- III 25%

Class- IV 5%

Class- V 2%

For estimation purpose the following percentage of rock class can be considered for

bottom horizontal pressure shaft from 540-673m

Table 4.12 Percentage wise rock class in Bottom Pressure Shaft (540m to 673m)

STRUCTURE ROCK CLASS PERCENTAGE

Bottom horizontal pressure

shaft

Class- II 20%

Class- III 65%

Class- IV 10%

Class- V 5%

4.4.9 POWER HOUSE

A surface power house having size 66.0m x 18.0 m x 30.5 m shall be accommodated in

greyish, medium to coarse grained, strong, moderately jointed to massive granite gneiss.

The structure has been explored by two drill holes, aggregating length of 110m m.

Assessment of subsurface conditions and its geotechnical evaluation has been carried out

based on surface exposures near the river bed and the drill hole DH 101and DH-102. The




Page: 66

long axis of surface power has been oriented in N119°direction i.e. Perpendicular to

prominent strike of foliation (N028°-N208).

Table 4.13 Discontinuity characteristics Power House Area

Discontinuity Characteristics for Power house (Right bank)

Set

No. Range of

Orientation Average

Orientation

Aperture

(mm)

Spacing (cm)

Persistence

(m)

Condition

S1 14° - 36°/090°

- 143° 24°/118° Tight 10-60 & 60-200 10-20 & 8-10

Rough

Planar

S2 64° - 81°/014°

- 045° 71°/030° 1-5 20-50 10-20

S3 66° - 86°/248°

- 280° 78°/261° 10-30 20-60 & 60-200 3-10 & 10-15

S4

68° - 87°/159° - 186°

80°/172°

Tight to

Partially

open 20-60 & 60-200 3-10 & 10-15

S6 71° - 80°/312°

- 322° 79°/317° 1-2 100-200 1-5

In PIA, height of cut in the rock will be around 38m whereas in overburden it

will be of the order of 45- 50m.Coefficeint of permeability in overburden ranges

from 0.29X10-3cm/sec to 2X10-3cm/sec which indicate highly pervious nature of

overburden. Since overburden is of river borne material indicative of a pre-existing river

terrace, presence of water table at a depth of 12- 14m will make this material more

susceptible to instability. Accordingly necessary measure to avoid surcharging of the

overburden slope shall be adopted during excavation of this material. Surface power

house appears to have been placed suitably with respect to strike of foliation.

Generally Core recovery in rock vary from 80-95% and RQD vary from 30-80%.In view of

above ,during excavation in selected weak media consolidation grouting shall be

resorted. However Rock mechanics test conducted on the cores samples from power

house area reveals the UCS value of 106 to 137 MPa. It is therefore concluded that

foundation of the surface power house shall be in sound rock.

The entire excavation for Power house pit shall be in bedrock having indicative

RMR (without rating adjustment) ranges from 50 to 59 computed on the basis of

geotechnical parameter collected from the outcrops and collating the finding from




Page: 67

boreholes DH-101 and DH-102 in which bedrock was encountered at El 268.6m and

262.2m respectively.

4.4.10 TAIL RACE CHANNEL

In order to release of downstream discharge from Power House back to the river, a 23m

X 26m recovery bay and 35m long tail race channel aligned along N 230° having

width of about 8m with El 230m at river bed level has been provided.

The initial part at NSL exhibits consistent presence of overburden material characterized

by the presence of recent fluvial material constituted of sand gravel silt etc whereas

terminal stretch of TRC is seem to be occupied by outcrops of gneiss. Minimum

excavation level from a draft tube is El ± 219 m from where channel approaches

further through recovery bay with reverse gradient to meet the river at EL ± 230m. The

entire excavation for recovery bay and TRC shall be in bedrock having indicative RMR

(without rating adjustment) ranges from 50 To 59 computed on the basis of geotechnical

parameter collected from the outcrops and collating the finding from boreholes DH-101

and DH-102 in which bedrock was encountered at El 268.6m and 262.2m respectively.

In view of this it opined that tail race system including the recovery bay shall be on bed

rock constituted of slightly weathered strong to very strong, moderately jointed, grey

gneiss.

To minimize the effect of some of these adversely oriented joints on excavation

particularly on the western wall, systematic rock support with rock bolts of 25mm Ø

4 to 6m long with spacing of 2m center to center, adequate thickness of SFRS,

and pressure relief arrangement shall be required to installed concurrent to the

excavation. Furthermore, provision of consolidation grouting shall be made as ground

improvement measure.




Page: 68

4.4.11 CONSTRUCTION MATERIAL

4.4.11.1 INTRODUCTION

During DPR stage investigation of Mawphu stage – II availability of construction

material was studied giving due consideration to the requirement, lead distance and

the impact of the same on environment.

The estimated quantity of concrete & shotcrete required for the construction of

Concrete Dam, Diversion Tunnel, Pressure Shaft, Power House and other appurtenant

structures of the project is 2.2 Lac m3. The requirement of construction material (coarse

and fine aggregate) for various structures of the project has been worked out and is as

under

Table 4.14 Requirement of Construction Material for Various Structures

Sl. No.

Source

Total

Estimated

Qty from

Excavation

(solid

volumes)

in

Lac m3

Usable

material

which can

be extracted

(Assuming

60%

wastage) in

Lac m3

Mater

ial

Req.

in Lac

m3

Assumed

shortage

of

material

in Lac m3

Action Required

1

Dam ,

Power

intake,

Diversion

Tunnel,

with inlet

and outlet

1.6

1.0

*CA(W)-0.1

*CA-1.5

*FA-0.8

Total-2.4

1.4

Rock Quarry

MWR/DS-II and

MWR/DS-I and

needs to be

acquired for

Dam works.

Blending with

crushed fine

aggregate MWG-I

shall be used, if

required

2

Coffer

Dam

nil

nil

Rock

fill

0.65

0.65

Material from MWR-

DS-III and MWG-

III needs to be

utilized




Page: 69

3

HRT and

Adits

0.86

0.5

*CA-0.23

*FA-0.12

Total-0.35

0.15 in

excess

Additionally, if required

MWR/HRT-I or

MWR/PS-I quarry

shall be utilizes.

Alternatively, Power

House excavation

material can also be

used

4

Surge

Shaft,

Pressure

Shaft with

Adits, Power

House and

Tail Race

Channel

1.87

1.1

*CA-0.4

*FA-0.2

Total-0.6

0.5 in

excess

To be utilized

from Power

House

excavation i.e.

MWR/PH-3

* CA- Coarse aggregate, CA (W)- Coarse aggregate (wearing surface), FA- Fine aggregate

4.4.11.2 VARIOUS SOURCES OF CONSTRUCTION MATERIAL

To meet the requirement, various quarries and shoals are identified in the vicinity

project area.(Ref DWG NO. 0933-GDC-07C-001) The identified rock quarries and

shoals are as beloe

Table 4.15 Details of Construction Material Locations

S.No.

Structure

Quarry area

Nomenclature

Distance

from

Dam site

Distance

from

Power

house

Availability

(m3)

1

Dam

Rock Quarry

near Waisu nala

MWR/DS-I 0.3km

3 Km

1.0

2

Rock Quarry

in Reservoir

Area

MWR/DS-II

0.7km

3 Km

.60

3

Rock Quarry

Left bank,

Dam/DT

Excavation

MWR/DS-III

0.1km

3km




Page: 70

4

Rock Quarry

right bank,

Dam/PI

Excavation

MWR/DS-IV

0.1km

3km

1.0

5

River bed

material, Dam Site

MWG-III 0.1km

3km

.70

6

HRT

Granite boulders

near HRT Adit-1

MWR/HRT-I

2 km

1.5km

.19

7

Rock quarry

near Umblai

bridge

MWR/HRT-II

3km

2km

.92

8

Pressure

shaft

Rock Quarry

near Pressure shaft

adit

MWR/PS-I

3 km

1km

1.0

9

Power

house

Rock Quarry on

Mawsynram road

MWR/PH-I

4km

4km

6.0

10 Rock Quarry on

Mawsynram road MWR/PH-II 4km 4km 3.2

11 Rock Quarry near

Power House MWR/PH-III 3km 0.1km 1.1

12

Balat

All in aggregates

deposit near Balat MWG-I 45km 45km 1.1

13 Fine aggregates

deposit in Balat MWG-II 45km 45km 57

Coarse and fine aggregate samples collected from different river terraces and rock

quarries were tested for complete range of physical parameters as well as alkali

aggregate reactive test. On the basis of test result of the various sample and estimated

quantity of available coarse and fine aggregate, it can be concluded that sufficient

quantity of various construction material of suitable quantity is available within a

reasonable distance from both power house and Dam site. As narrow gorge and steep

gradient of the river negates the possibility of locating good number of prospective shoal

deposits, it will be imperative to bank upon the crushed sand to cater the requirement of




Page: 71

major part of fine aggregate. However, if need be, to maintain the proper grading of

fine aggregate blending of river sand of appropriate selected grain size range from

Balat Shoal deposit can be made. To enlarge the data base beyond BOQ for

construction material survey few more samples from the dam area have also been

collected and shall be perused once the report is received. The samples except

MWR/HRT-II, collected and tested from the entire project area in this campaign, confirm

its suitability as both wearing and non-wearing surfaces and also in regards to their alkali

aggregate reactivity status being tested innocuous. However, MWR/ HRT-II collected

from granitic area are observed to be marginally deficient with respect to impart

value, Loa Angeles abrasion value, crushing value i.e. 27.61, 38.6 and 29.4 respectively.

In view of this, to take care of in homogeneity of the granitic material, it is proposed to

collect more samples during construction or in pre-construction stage from the granitic

area to decipher its possible utility as wearing surface, through segregation once the

report becomes available

A serious effort was made to assess the suitability of the excavated material anticipated

to be generated during construction of the project. This would not only have a positive

impact in the project cost but also shall ensure minimum adverse impact on

environment.

CHAPTER - V

HYDROLOGY




Page: 72

CHAPTER - V

HYDROLOGY

5.1. GENERAL

The great Himalayan mountain range with its permanently snow covered mountain

peaks; the mighty Brahmaputra and its perennial tributaries, flowing in loops and

bends and the south-east monsoon causing highest rainfall in Meghalaya, are the

natural parameters responsible for North-East India to emerge as a boon for

hydro-electric power generation. Central Electricity Authority (CEA), in their

publication “Hydro-Electric Power Potential of India-1988” estimated the optimum

installable capacity of Brahmaputra basin as about 66,065 MW, out of which only

about 2% have been harnessed so far. Due to increase in population,

urbanization and industrialization, the power demand has increased considerably.

To meet the increased power demand, Central Government and various State

Governments of the region are making all out efforts to develop the hydro-power

potential of the region.

5.2. THE PROJECT

Mawphu-II Hydroelectric Project is planned in East Khasi Hills District in the State of

Meghalaya on the River Umiew, a tributary of the River Surma, which itself is

one of the major left bank tributaries of Brahmaputra. The project envisages the

construction of a concrete gravity dam of 51 m high (from the deepest foundation

level) across river Umiew to utilize a gross head of 238 m for hydro power generation.

The proposed dam is located near Mawphu village (located on the left bank), about

8 km away from Mawsynram and 2 km away from Thieddieng village (located

on the right bank). The project is located at latitude 25° 18’ 32’’N and longitude 91°

38’19”E. The catchment area up to the dam site is 308 sq. km and the entire catchment

is rain –fed.

5.3. THE RIVER SYSTEM AND BASIN CHARACTERISTICS

The Umiew River (known as Umlam in initial reaches) originates as a small




Page: 73

stream at an elevation of about 1940 m in East Khasi hills of Meghalaya. Initially the

River flows in southern direction for about 4 km with a slope of about 1 in 30. For

the next 6 km, it flows in south- eastern direction with relatively flat gradient of 1

in 225. Few small Streams and Nallas join in this stretch enriching its discharge. It

then turns westwards and continues its path for further 12 km before it turns in south

west direction. The 7 km journey in south west direction up to Mawphlang is

quite steep with a gradient of about 1 in 12. At Mawphlang the river is barricaded by

a dam to form a reservoir for a scheme project known as Greater Shillong Water

Supply Scheme (GSWSS). Fulfilling the drinking water need of Shillong is the

primary objective of the scheme.

Main tributaries of Umiew up to GSWSS are Umjilling, Umtongsieum and Wah

Umsaw. After crossing this scheme project, river extends its journey for about 13 km

in a gradient of about 1 in 175. Nallas like Umjaut, Umduna join in its right bank and

Umlong joins in its left bank. The discharges of these nallas increase the potential of

the river to develop the proposed Mawphu Stage I (90 MW) Hydro Power Project.

Mawphu-II (85 MW) Project lies further 13 km downstream of Mawphu Stage

I Project with additional contributions from Umjngut & Umkynrem nallas,

which join in the right bank. The total length of the river up to the project site is 54.54

km. Further the river flows towards the south below the confluence along the southern

slopes of Khasi Hills and enters Bangladesh beyond Shella in Indo-Bangladesh

border and joins the River Surma. Finally the River joins Brahmaputra and in turn

flows to Bay of Bengal via Sundarbans Delta.

The basin is bounded by Mawsynram in west, Shillong in North and Cherrapunji in

east and in fact world’s highest annual rainfall occurs at Cherrapunji and

Mawsynram. The slopes of the basin are covered with dense rainforests of

coniferous and deciduous trees with a number of small tribal villages in between.

The predominant land use pattern in the catchment area is forest of the type “Tropical

Moist Deciduous”. Very small area is under agricultural use including wet rice

cultivation in the intercept valleys.




Page: 74

5.4. THE CATCHMENT The catchment up to the dam site could be covered by Survey of India Topo Sheet

nos. 78 O/10, 78 O/11, 78 O/14, 78 O/15. With the help of remote sensed satellite

images and also with the help of Arc GIS software, the catchment boundary has

been marked. The names of the nallas / tributaries of the Umiew River have been

extracted from the Topo sheets as well as from Google Earth to prepare the final

catchment area plan. The catchment area up to dam site has been worked out as 308

sq. km. The catchment lies between latitude 25°18’08”N to 25°32’50”N and Longitude

91° 35‘15”E and 91°55’30”E. Catchment area plan showing the location of gauge,

discharge and rain gauge station is given in Figure 5.1.




Page: 75

308




Page: 76

5.4.1. HYPSOMETRY OF THE CATCHMENT

The hypsometry of the catchment has been determined using Digital Elevation Model

(DEM) by Arc GIS software. Information derived from DEM includes: catchment area, mean

catchment elevation, maximum river length (maximum flow path), equivalent stream

slope, and the latitude/ longitude of the catchment’s centroid. The hypsometry of the

catchment has been determined and is as given in Table 5.1 and plotted in Figure 5.2.

Table 5.1: Hypsometry of the Catchment Area

SL.

No

Elevation

(m)

Area

Cumulative

(sq km)

Area

above EL

(sq km)

% Area

Above EL

1 434 0.00 308 99.8

2 564 1.01 304 99.5

3 754 5.41 302 98.1

4 928 12.19 300 96.0

5 1095 21.65 298.5 93.1

6 1256 31.88 288.3 89.9

7 1412 41.90 278.3 86.8

8 1554 54.61 265.6 82.8

9 1668 109.72 210.5 65.6

10 1764 197.02 123.2 38.4

11 308 308 0.00 0.00

Figure 5.2: Hypsometry of the Catchment

It is seen that the maximum elevation of the catchment is Shillong Peak, at an




Page: 77

elevation of about 1963 m, which indicates that the entire catchment is rain – fed.

Catchment area above 1500 m elevation is about 84 %.

5.4.2. ESTIMATION OF MEAN CATCHMENT ELEVATION

From the hypsometric data of the catchment, mean elevation of the catchment

has been worked out and the computations are given below in Table 5.2.

Table 5.2: Mean Catchment Elevation

Mean elevation of the catchment thus works out to 1354.4 m.

5.4.3. EQUIVALENT SLOPE

For determining the equivalent slope of River Umiew up to the dam site, the river

has been divided in to a number of segments. The computations for the equivalent

slope of the river are given in Table 5.3.

S.

No

Elevation

Range (m)

Mean

Elevation

(m)

Cumulative

Area (sq km)

Incremental

Area (sq km)

Mean Elevation

X Incremental

Area

1 434 – 564 499 1.0125 1.0125 505.2

2 564 – 754 659 5.4108 4.3983 2898.5

3 754 – 928 841 12.1905 6.7797 5701.7

4 928 – 1095 1011.5 21.6513 9.4608 9569.6

5 1095 - 1256 1175.5 31.8816 10.2303 12025.7

6 1256 - 1412 1334 41.9013 10.0197 13366.3

7 1412 - 1554 1483 54.6102 12.7089 18847.3

8 1554 - 1668 1611 109.7226 55.1124 88786.1

9 1668 - 1764 1716 197.0163 87.2937 149796.0

10 1764 - 1963 1042.1 308 110.9837 115656.1 Sum 308.0 417152.5 Mean Elevation 1354.4




Page: 78

Table 5.3: Equivalent Slope of Umiew River

Cumulative Length

Di Di+(Di-1) Li{Di+(Di-1)} To Elevation

0 0 0 0 451

0.071 17 17 1.2 496

0.169 62 79 7.78 508

0.221 74 136 7.07 520

0.56 86 160 54.2 540

1.59 106 192 197.82 560

2.184 126 232 137.67 580

2.602 146 272 113.84 600

3.168 166 312 176.6 620

3.926 186 352 266.91 640

4.476 206 392 215.26 660

5.054 226 432 250.02 680

5.551 246 472 234.39 700

5.965 266 512 212.08 703

6.033 269 535 36.39 720

6.508 286 555 263.43 740

6.7 306 592 113.83 760

7.246 326 632 344.98 780

7.531 346 672 191.28 800

7.861 366 712 235.11 820

8.018 386 752 118.3 840

8.348 406 792 261.16 860

8.517 426 832 140.52 880

8.971 446 872 396.2 900

9.128 466 912 142.9 920

9.712 486 952 556.19 940

10.105 506 992 389.51 960

10.302 526 1032 204.14 980

10.579 546 1072 296.58 1000

10.845 566 1112 295.52 1004

10.909 570 1136 72.38 1020

11.062 586 1156 177.24 1040

11.189 606 1192 151.93 1060

11.715 626 1232 647.7 1080

12.182 646 1272 594.02 1100

12.535 666 1312 462.57 1120

12.978 686 1352 599.85 1140

13.107 706 1392 179 1160

13.33 726 1432 319.13 1180

13.611 746 1472 413.8 1200




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13.721 766 1512 166.53 1220

13.817 786 1552 148.4 1240

14.01 806 1592 308.27 1260

14.229 826 1632 357.69 1280

14.523 846 1672 490.8 1300

14.662 866 1712 237.61 1320

14.774 886 1752 196.64 1340

14.995 906 1792 395.47 1360

15.088 926 1832 171.75 1380

15.269 946 1872 338.46 1400

15.469 966 1912 382.65 1420

16.339 986 1952 1697.27 1440

16.542 1006 1992 405.23 1460

16.665 1026 2032 249.35 1480

16.727 1046 2072 128.08 1500

17.828 1066 2112 2325.71 1520

19.355 1086 2152 3285.81 1540

21.401 1106 2192 4484.69 1560

25.479 1126 2232 9101.7 1580

28.224 1146 2272 6236.78 1600

29.804 1166 2312 3654.38 1620

30.04 1186 2352 553.67 1640

30.502 1206 2392 1106.54 1660

31.183 1226 2432 1655.91 1680

32.786 1246 2472 3962.21 1700

33.271 1266 2512 1218.91 1720

33.544 1286 2552 695.45 1740

38.428 1306 2592 12658.93 1760

45.818 1326 2632 19450.15 1780

50.307 1346 2672 11994.62 1800

52.272 1366 2712 5330.1 1820

52.795 1386 2752 1440.55 1840

53.464 1406 2792 1866.07 1860

54.106 1426 2832 1819.04 1880

54.194 1446 2872 253.05 1900

54.38 1466 2912 542.13 1920

54.467 1486 2952 255.17 1925

54.537 1491 2977 210.34

Sum 109254.6

L2 2974.33

Equivalent

Slope 36.73




Page: 80

It is thus seen that the total length of River Umiew from the source to the dam site is

54.54 km. The equivalent slope (S) of the river has been worked out as 36.73 m/ km.

5.4.4. L – SECTION OF RIVER UMIEW

From the elevations of the river at various segments, from the proposed dam site to

the source of the river, longitudinal section of the river has been plotted in Figure 5.3.

Figure 5.3: Longitudinal Section of River Umiew up to Dam Site

From the longitudinal section, it is seen that the river slope for about 4 km from its

source is about 1 in 25, and then it becomes relatively flat with a slope of about 1 in

120 for about 34 km. Near the project site for a length of about 17 km the river has a

steep slope of about of about 1 in 16.

5.5. PROJECTS IN UMIEW RIVER – A GLANCE

5.5.1. GREATER SHILLONG WATER SUPPLY SCHEME (GSWSS)

A dam across River Umiew built by Public Health Engineering Department,

Meghalaya is the main source of water supply for Shillong. The dam is about 50 m

high and 130 m long (at top- level) with reservoir area at FRL of about 0.59 sq. km &

gross storage is about 0.35 TMC. As per the report of City Development Plan




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prepared by Jawaharlal Nehru National Urban Renewal Mission (JNNURM) by

Feb 2007, the quantity of water generated from GSWSS is 11.3 mld (0.5 cumecs).

5.5.2. MAWPHU STAGE I HEP (90 MW)

As stated in the old PFR of Mawphu II, Under the 50000 MW hydro Power

Initiative, Pre- Feasibility Reports for the following projects on Umiew River basin of

Meghalaya were prepared by WAPCOS:

Umjaut HEP (69 MW) : FRL- 1346 m & TWL – 952 m

Umduna HEP (57 MW) : FRL – 950 m & TWL – 687 m

Mawphu HEP(120 MW) : FRL – 684 m & TWL – 210.5 m

In May 2005, Govt. Of Meghalaya authorized NEEPCO to prepare DPR of Mawphu HEP

(120 MW). During survey and investigation process of the project, NEEPCO observed

some of the project parameters as cited in its PFR were found to have some

discrepancy with actual site parameters. Hence, NEEPCO went ahead for the selection of

alternate site and consequently the whole layout underwent alteration since the actual

parameters were deviating with respect to Topo sheets. Considering all the above

factors and comments of CEA regarding the non- viability of Umjaut HEP (69 MW),

NEEPCO carried out an optimization study of the whole basin in the following location

limits.

Umjaut HEP (50MW): FRL – 1346 m & TWL – 1025 m

Mawphu HEP Stage I (90 MW) : FRL – 1018.6 m & TWL – 543 m

Mawphu HEP Stage II (85 MW): FRL – 540 m & TWL – 210 m

The Mawhu H. E. Project Stage I envisages the construction of 48 m high concrete

gravity dam across river Umiew near Laitlyndop village to utilize a gross head

of 480 m for power generation. The proposed dam site is located at about 10

km downstream of the existing Greater Shillong Water Supply Scheme. The FRL is

kept at EI 1018.60 m and MDDL at EI 1006.00 m with diurnal storage of 0.61 MCM.




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5.6. METEOROLOGICAL CHARACTERISTICS

5.6.1. CLIMATE

The Umiew basin falls in climatic zone I, which comprises of North & North Eastern

part of India including Myanmar, Nepal, Bhutan, Bangladesh & part of Pakistan. The

climate of the basin is tropical monsoon. The rainfall in the basin is mainly

influenced by the mountain system and occurs due to South West Monsoon in the

months of May to October. Winter prevails from late November to early March and

from middle of March to early May is the pre monsoon season. The annual rainfall in

the basin varies from 2000 mm to 6500 mm and about 70 % of this occurs between June

to September.

5.6.2. RAINFALL

Catchment area of the Umiew River is situated in windward slope of Khasi hills

in between Mawsynram and Cherrapunji, where the annual rainfall is the highest in

the world. Cherrapunji receives rains from the Bay of Bengal arm of the Indian summer

monsoon. Based on the data of a recent few decades, Mawsynram, located about 15

km north-west of Cherrapunji in the State of Meghalaya (India) appears to be the

wettest place in the world, or the place with the highest average annual rainfall.

Mawsynram receives nearly 12 m of rain in an average year, and a vast majority of it

falls during the monsoon months.

5.6.3. TEMPARATURE & RELATIVE HUMIDITY

Primarily due to the high altitude, it seldom gets truly hot in Mawsynram, which is

located near the catchment boundary. Average monthly temperatures range from

around 10° C in January to just above 20° C in August. In general the temperature in

the foothill region of the basin is hot during summer. However during the winter

months it is relatively cold in the upper portion of the catchment with temperatures

dipping as low as 5°C. The mean relative humidity of the project area is about 60%.




Page: 83

5.7. DATA AVAILABILITY

Observation of hydro meteorological data for the basin is essential for proper

planning of the project features and later on for operation of the project for

deriving optimal benefits. The catchment plan showing the location of gauge,

discharge and rain gauge stations is given in Figure 5.1.

5.7.1. RAINFALL DATA

The rainfall data of the following rain gauge stations within and around the

catchment maintained by various departments are given in Table 5 .4. The observed

monthly rainfall data available at various stations are given in Table 5.5 to Table 5.10.

Table 5.4: Availability of Rainfall Data

S.

No

Station

Observed

by

Approx. Coordinates Altitude

(m)

Data

Availability

Remarks

Latitude Longitude 1

Mawphlang

PHED,

Meghala

ya

25 27' N

91 45' N

1815

Jan 1889 -

Dec 1963,

Jan 1978 -

Dec 1986

With Gaps

2 Mawphlang

NEEPCO

25 27' N

91 45' N

1815

Aug 2005 -

Apr 2009

3 Shillong

IMD

25 35' N

91 53' N

1485

Jan 1979 -

Dec 2005

1986 NA

4 Tyrsad

NEEPCO

25 24' N

91 39' N

1635

Aug 2005 -

Apr 2009

5 Pomlakrai

NEEPCO

25 31' N

91 52' N

1830

Jul 2006 -

Apr 2009

6 Laitlyndop

NEEPCO

--

--

--

Aug 2005 -

Apr 2009

5.7.2. GAUGE AND DISCHARGE DATA

The status of availability of G – D data at various stations within and around the

basin is given in Table 5.11. 10-Daily discharge data of the above mentioned stations

are enclosed in Table 5.12 and Table 5.14.




Page: 84

Table 5.11: Status of Availability of Gauge & Discharge Data

Sl.

No

Station

River

CA

(sq km)

Observed

by

Data

Availability

Remarks

1

287 m U/S of

Mawphlang

Umiew

115

PHED,

Meghalaya

May 1980 -

Dec 1997

With Gaps

2

Mawphlang

Dam Site

Umiew

115

ASEB

Jan 1979 to

Dec 1987

With Gaps

3

Mawphu I

Dam Site

Umiew

232

NEEPCO

Nov III 2005

- Mar 2009

Mawphu-II H.E. Project (85 MW)

Pre-Feasibility Report

Table 5.12: 10 Daily Discharges at Mawphlang observed by PHED (Cumecs)

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Table 5.13: 10 Daily Discharges at Mawphlang observed by ASEB (Cumecs)

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Table 5.19: Monthly Discharges at Mawphlang after filling Data Gaps (cumecs)

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Table 5.30 : Monthly & Annual Runoff at Mawphlang after Extension (mm)

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Table 5.31 :10-Daily discharges at Mawphlang, observed and computed (cumecs)

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5.33 : 10-Daily Discharges at Mawphu II Dam Site without Considering GSWSS Withdrawals (cumecs)

Page: 90



5.34: 10-Daily Discharges at Mawphu-II Dam Site after Considering GSWSS Withdrawals (cumecs)

Page: 91



Table 5.48: Convolution of UG with Rainfall

Page: 92



Fig 5.26: Synthetic Unit Hydrograph

Page: 93



Fig 5.28: Design Flood Hydrograph

Page: 94




Page: 95

5.8. ANALYSIS OF DATA

Detailed calculations on water availability and flood magnitude will lead to selecting

the design features of the project (installed capacity, turbine flow, spillway capacity, etc.).

Those features will directly reflect on the project cost and on the quantity and value of

energy produced. Before utilizing the hydro – meteorological data for the studies, consistency

checks on the data were made to check its accuracy and consistency. Since there were

gaps in the available rainfall and discharge data, the same were filled before subjecting

the data to consistency checks.

5.8.1. FILLING DATA GAPS

a) Shillong Rainfall

On examination of the daily rainfall data at Shillong observed by IMD, it was found

that the daily data for the periods 22nd to 31st October 1979, 27th to 30th June

1980 & 22nd to 23rd November 1982 were not available. These data were filled by

adopting the average value of all other available rainfall data for the concerned days.

The rainfall data for the year 1986 was not available and this year’s data has not

been considered for the studies. From the daily rainfall data, monthly rainfall values

have been computed. It is seen that during the monsoon months (May to October),

there was only one data gap for the month of October 2005. This gap has been

filled by developing relationship between the average monthly rainfalls for the

observed period and the available monthly rainfall during the year 2005. The plot is

given in Figure 5.4. The monthly rainfall data of Shillong after filling the data gap is

given in Table 5.15.




Page: 96

Figure 5.4: Relationship between Observed Average Monthly Rainfall & Monthly

Rainfall during 2005 at Shillong

b) Mawphlang Rainfall

On examining the monthly rainfall data, it is seen that data for the years 1926, 1947,

and 1964– 1977 are not available and the same were not considered for the study.

For the available period of records, it was found that gaps during 3 monsoon months

viz. October 1907 & 1942, July 1982 exist. Gaps in monsoon data were filled by

developing relationship between average monthly data of all years and monthly rainfall

data of the concerned year for which the data is missing. The correlations thus

obtained were utilized to get the missing values. The plots for various years are given

in Figure 5.5 to Figure 5.7.

Figure 5.5: Relationship between Observed Average Monthly Rainfall & Monthly Rainfall

during 1907 at Mawphlang




Page: 97





Using the above correlations, the monthly gaps in the rainfall data for the

monsoon months were filled. For filling the gaps in the data during non-monsoon

months, the following procedure was adopted:

Ratio of average rainfall of each non-monsoon month (November to April) to the

sum of average rainfall of monsoon months (May to October) have been determined

and given in Table 5.16.




Page: 98

Table 5.16: Ratio of Rainfall during Non- Monsoon Months to Monsoon Rainfall at Mawphlang

Jan

Feb

Mar

Apr

Nov

Dec

0.011 0.012 0.022 0.049 0.028 0.006 The missing data was obtained by multiplying the average monsoon rainfall

of the concerned year with the ratio for the concerned month. Monthly rainfall data at

Mawphlang, after filling the data gaps is given in Table 5.17.

c) Mawphlang Discharges (Observed by PHED, Meghalaya)

Daily discharge data for the period May 1980 - Dec 1997 is available with some gaps.

From the daily discharges, average monthly discharges have been computed. Gaps in

the data during monsoon months have been filled by correlating average

monthly runoff of all the years with available monthly runoff for the concerned

year in which the data for few months is missing. The equations obtained are


Table 5.18: Correlation Obtained at Mawphlang (PHED) for Filling Data Gaps in

Discharge

Year Equation R2

1980 & 1981 y = 0.785x – 2.135 0.736

1983 y = 1.262x – 8.303 0.668

1984 y = 1.779x – 17.03 0.681

1985 y = 1.060x – 12.18 0.887

1987 y = 1.930x – 12.40 0.819

1990 y = 0.589x + 3.729 0.874

1992 y = 0.884x + 3.478 0.894

To fill gaps of non-monsoon months, ratios were derived for every non-monsoon

month by dividing the average observed discharge of concerned month, with

average discharge of monsoon months. The ratio of the concerned month for

which the data is missing is multiplied by the average monsoon discharge of that

year to fill the data gap. The monthly flow series after filling the data gaps is given in

Table 5.19.




Page: 99

d) Mawphlang Discharges (Observed by ASEB)

10 –Daily observed discharge data for the period Jan 1979 to Dec 1987 is available

with some gaps. The gap in the data for the 10-daily period of monsoon month

(October 1986), have been filled by correlating average 10-daily runoff of all the years

with available 10-daily runoff for the year 1986 in which the data is missing. The

correlation graph is plotted in Figure 3.8 and the following correlation has been

obtained.

Figure 5.8: Relationship between Average Observed Monthly Discharge & MonthlyDischarge during 1986 at Mawphlang (ASEB)

Using the correlation, missing discharges during three 10-daily periods of October

1986 have been filled. To fill gaps during non-monsoon periods, the following

procedure was adopted:

From the available observed data, average discharge for each 10-daily period was

worked out.

Ratio of average 10-daily discharge during each non-monsoon period to average 10-

daily discharge during the monsoon period (May to October) was worked out. The

ratios thus obtained are given in Table 5.20.

Table 5.20: Ratio of Runoff during Non- Monsoon Period to Monsoon Rainfall at Mawphlang

November December January February March Apri

I II II I II II I II II I II II I II II I II II0.24 0.17 0.14 0.12 0.14 0.10 0.10 0.12 0.09 0.08 0.08 0.07 0.08 0.10 0.11 0.11 0.11 0.20

The ratio of the concerned period for which the data is missing is multiplied by the

average 10-daily monsoon discharge of that year to fill the data gap. The 10-daily flow




Page: 100

series after filling the data gaps is given in Table 5.21.

5.8.2. CONSISTENCY CHECKS

All the available rainfall and discharge data was catalogued and organized into

consistent data format and then analyzed for consistency and reliability in order to:

Ensure that the records actually reflect the catchment’s behavior;

Eliminate or reduce the effect of extraneous influences;

Eliminate doubtful data.

The following consistency checks were applied:

a) Consistency Checks on Rainfall Data

Consistency of the available rainfall data at 2 stations was checked by following

methods:

I) Single Mass Curve

Single Mass curve and double mass curve techniques have been used to verify the

presence of any systematic error in rainfall values for any rain gauge station.

Since continuous annual rainfall data is not available at Mawphlang and Shillong

stations, cumulative annual rainfalls values have been worked out for the continuous

periods of records at these stations. From the annual rainfall values cumulative

annual rainfall values at Mawphlang and Shillong have been worked out and given

in Table 5.22 & Table 5.23. The mass curves for cumulative rainfall at Mawphlang and

Shillong have been plotted in Figure 5.9 & Figure 5.10 respectively.




Page: 101

Figure 5.9: Single Mass Curves for Various Rainfall Data Lengths at Mawphlang

Since the mass curves of cumulative rainfall at Mawphlang are nearly straight line, the

rainfall data at Mawphlang, can be concluded to be consistent.

Table 5.22: Annual & Cumulative Rainfall at Mawphlang (mm)

Year

Rainfall (mm)

Year Rainfall (mm)

Annual Annual Cumulative 1937 3693 1899 3,916 3916 1938 4219 1900 2,694 6610 1939 4104 1901 3,314 9924 1940 3995 1902 3,622 13545 1941 4445 1903 3,561 17106 1942 3194 1904 2,748 19854 1943 3586 1905 4,249 24103 1944 6173 1906 4,129 28232 1945 6624 1907 2,603 30835 1946 5553 1908 2,168 33003 1947 NA 1909 2,919 35923 1948 3644 1910 4,875 40798 1949 3875 1911 3,716 44514 1950 2728 1912 3,334 47848 1951 4610 1913 3,596 51445 1952 4498 1914 3,048 54492 1953 3558 1915 3,650 58142 1954 3279 1916 3,828 61970 1955 4167 1917 2,516 64486 1956 5043 1918 4,566 69051 1957 2540 1919 3,011 72062 1958 2284 1920 2,753 74815




Page: 102

1959 3124 1921 3,748 78563 1960 4246 1922 3,191 81754 1961 2260 1923 2,165 83919 1962 2354 1924 4,078 87997 1963 3568 1925 2,092 90090

1964-78 NA 1926 NA NA

1978 2231 1927 3100 3100 1979 3713 1928 2827 5927 1980 3022 1929 3024 8950 1981 3417 1930 2433 11383 1982 3144 1931 4102 15485 1983 3845 1932 3132 18616 1984 5234 1933 2213 20829 1985 2883 1934 4798 25627 1986 2866 1935 3243 28870

1936 3721 32591

Table 5.23: Annual & Cumulative Rainfall at Various Sites (mm)

Year

Shillong

Annual Cumulative

1979 1879 1879

1980 1948 3827

1981 2169 5996

1982 2266 8263

1983 2459 10722

1984 2375 13096

1985 1848 14944

1986 NA NA

1987 2875 2875

1988 3807 6682

1989 2793 9474

1990 1893 11367

1991 2540 13907

Year Shillong

Annual Cumulative

1992 1871 15778

1993 2085 17863

1994 1574 19437

1995 2304 21741

1996 1814 23555

1997 2138 25692

1998 2009 27701

1999 2314 30015

2000 2187 32202

2001 2126 34328

2002 2479 36807

2003 2082 38888

2004 3069 41957

2005 1830 43787




Page: 103

Figure 5.10: Single Mass Curves for Various Data Lengths at Shillong

Since the mass curves of cumulative rainfall at Shillong are nearly straight line, the

rainfall data at Shillong can be concluded to be consistent.

II) Double Mass Curves

Consistency of the rainfall data at Mawphlang & Shillong have also been checked

by double Mass Curve technique. Double mass curves have been developed using the available

rainfall data for the concurrent period at various sites.

Double Mass Curve (Mawphlang & Shillong Rainfall)

The annual & cumulative annual rainfall for the concurrent period for the above

stations have been worked out and given in Table 5.24 and the double mass curve is

plotted in Figure 5.11.

Table 5.24: Annual & Cumulative Rainfall (mm)

Mawphlang Shillong

Year Annual Cumulative Annual Cumulative

1979 3713 3713 1879 1879

1980 3022 6735 1948 3827

1981 3417 10151 2169 5996

1982 3144 13296 2266 8263

1983 3845 17141 2459 10722

1984 5234 22375 2375 13096

1985 2883 25258 1848 14944




Page: 104

Figure 5.11: Double Mass Curves for Shillong & Mawphlang Rainfall

The double mass curve is nearly a straight line with some deviation during the year

1984, when very heavy rainfall occurred at Mawphlang. But after 1984, the double

mass curve nearly follows the slope of the mass curve prior to 1984. In view of this,

the rainfall data at the two stations are consistent.

b) Consistency Checks on Discharge Data

The following consistency checks on the observed discharge data at various sites

have been made.

i) Single Mass Curve

From the observed discharges of River Umiew at GSWSS Dam site at Mawphlang

observed by ASEB and 287 m Upstream of GSWSS dam site, observed by PHED,

Meghalaya, annual and cumulative runoff have been computed and given in Table

5.25. Cumulative annual flows at these sites have been plotted in Figure 5.12 & Figure

5.13.




Page: 105

Table 5.25: Annual and Cumulative Annual Runoff at Mawphlang (MCM)

Year

Mawphlang (ASEB) Mawphlang (PHED)

Yield (MCM)

Annual Cumulative

Annual

Cumulative

1979 287.6 287.6 -- --

1980 287.9 575.5 440 440 1981 301.6 877.1 574 1014

1982 308.5 1185.5 543 1557 1983 331.2 1516.7 713 2271 1984 473.6 1990.3 739 3010 1985 287.6 2277.9 480 3489 1986 334.2 2612.1 577 4066 1987 657.0 3269.1 1041 5107 1988 1049 6156 1989 819 6975 1990 546 7521

1991 697 8219 1992 728 8947 1993 778 9725 1994 707 10431 1995 912 11343 1996 828 12171 1997 836 13007

Figure 5.12: Single Mass Curve Mawphlang (ASEB)




Page: 106

Figure 5.13: Single Mass Curve Mawphlang (PHED, Meghalaya)

Since the mass curve of cumulative Discharges at Mawphlang (Observed by ASEB &

PHED) is nearly straight line; the discharge data at these stations can be concluded to be

consistent.

II) Comparison of Rainfall & Runoff

From observed discharges at Mawphlang observed by ASEB and also by PHED,

annual runoff in mm has been computed and compared with the corresponding annual

rainfall at Mawphlang. The comparison is given below in Table 5.26.

Table 5.26: Rainfall – Runoff Comparison at Mawphlang

Year

Mawphlang

Rainfall

(mm)

Mawphlang

(ASEB)

Mawphlang

(PHED) Runoff

(mm)

Runoff /

Rainfall

Runoff

(mm)

Runoff /

Rainfall 1979 3714 2500 0.67 -- --

1980 3012 2504 0.83 3828 1.27

1981 3422 2622 0.77 4993 1.46

1982 3179 2682 0.84 4721 1.50

1983 3854 2880 0.75 6203 1.61

1984 5254 4118 0.78 6427 1.23

1985 2890 2501 0.87 4170 1.45

1986 2873 2906 1.01 5015 1.75 Average 3381 2839 0.82 5051 1.47

It is seen that for the observed discharges at Mawphlang observed by PHED,




Page: 107

Meghalaya the runoff is considerably high during all the years as compared to the

rainfall. In view of this the discharge data at Mawphlang observed by PHED is

considered to be unreliable and has not been considered for the studies.

On comparing the observed discharges at Mawphlang observed by ASEB, it is seen

that the runoff is less than the rainfall except for the year 1986. Average runoff factor

for the Mawphlang discharges works out to 0.82. Hence the discharge data at

Mawphlang observed by ASEB is considered to be reliable and has been utilized for

the studies.

5.9. WATER AVAILABILITY STUDIES

Since Mawphu II HEP is a run of river scheme having a provision of daily storage

in order to meet the diurnal variation, therefore 10 daily flow series for a minimum

period of about 10 years may be desirable for project planning as per the guidelines

issued by MOWR. Since observed discharge data at Mawphlang is available for a

short period, an effort has been made to extend the available discharge series using

rainfall – runoff relations.

5.9.1. EXTENSION OF RAINFALL DATA

For extending the rainfall data at Mawphlang, from 1987 to 2005, monthly

correlations for the monsoon months (May to October) between the concurrent

rainfall at Mawphlang and Shillong for the period 1979 to 1986 have been

developed. The relations have been developed by ignoring one or two outliers, if

any. Plots of monthly correlations thus developed are given in Figure 5.14 to Figure 5.19.




Page: 108

Figure 5.14: Correlation of Shillong and Mawphlang Rainfall (May)

Figure 5.15: Correlation of Shillong and Mawphlang Rainfall (June)

Figure 5.16: Correlation of Shillong and Mawphlang Rainfall (July)




Page: 109

Figure 5.17: Correlation of Shillong and Mawphlang Rainfall (August)

Figure 5.18: Correlation of Shillong and Mawphlang Rainfall (September)

Figure 5.19: Correlation of Shillong and Mawphlang Rainfall (October)

Using these monsoon monthly correlations and available monthly rainfall at




Page: 110

Shillong, monthly rainfall at Mawphlang during monsoon months for the period

1986-87 to 2005-06 has been generated.

For estimating the rainfall during the non-monsoon months, ratios of monthly

rainfall during non-monsoon months to the monsoon rainfall have been worked

out from the available observed rainfall data at Mawphlang for the period

1898-99 to 1985-86. The ratios thus obtained are given in Table 5.27.

Table 5.27: Ratio of Monthly Rainfall to Monsoon Rainfall

Nov Dec Jan Feb Mar Apr

0.029 0.006 0.011 0.012 0.022 0.049

The monthly rainfall during the non-monsoon months have been determined by

multiplying the above ratio with the monsoon rainfall for the concerned year. Monthly and

annual rainfall at Mawphlang thus obtained is given in Table 5.28.

5.9.2. RAINFALL-RUNOFF CORELATION

Concurrent rainfall and runoff data at Mawphlang (ASEB) is available for the period

1979-80 to 1987-88. Observed flows series at Mawphlang (ASEB) for the period 1979-

80 to 1987-88 has been converted into mm and given in Table 5.29. Using the

available rainfall & runoff data for the concurrent period, monthly rainfall - runoff

correlation have been developed for the monsoon months of May to October. Plot of

monthly rainfall and runoff for May to October is given in Figure 5.20 to Figure 5.25.




Page: 111

Figure 5.20: Rainfall – Runoff Correlation (May)

Figure 5.21: Rainfall – Runoff Correlation (June)

Figure 5.22: Rainfall – Runoff Correlation (July)




Page: 112

Figure 5.23: Rainfall – Runoff Correlation (August)

Figure 5.24: Rainfall – Runoff Correlation (September) f

Figure 5.25: Rainfall – Runoff Correlation (October)




Page: 113

5.9.3. EXTENSION OF FLOW SERIES AT MAWPLANG For the formulation of a long term monthly discharge series at Mawphlang, the

following methodology has been adopted:

Using the monthly monsoon rainfall - runoff correlations and the available monthly

rainfall at Mawphlang for the period 1988 to 2005 (Table 5.29), monthly flow series

for the monsoon period from 1988 to 2005 has been generated.

To estimate the runoff for non-monsoon months, average ratios of monthly non

monsoon runoff to average monsoon runoff were developed using the observed runoff

for the period 1979 – 80 to 1987 – 88. The following ratios were obtained:

Nov Dec Jan Feb Mar Apr

0.196 0.131 0.100 0.071 0.098 0.138

The runoff for the non-monsoon months of November to April have been

estimated by multiplying the monthly ratios as obtained above, with the monsoon

runoff for the concerned year. Monthly flow series at Mawphlang, for the period

May 1988 to Dec. 2005 has thus been generated. The combined flow series at

Mawphlang (observed & generated) for the period 1979-80 to 2004-05 in mm is given

in Table 5.30.

To generate 10 – daily flow series form the monthly series developed above, average

10 – daily flows have been worked out from the observed 10 – daily discharge data

for the period May 1979 to April 1988. The ratio of each 10 – daily runoff with

respect to corresponding total runoff of the month has been estimated and

computations are given in Table 5.30.

Monthly flows generated for the period 1988 - 2005 in Table 5.30 have been

multiplied with the corresponding monthly 10 – daily ratio to obtain the 10 – daily flow series.

This series has been converted to cumecs. The combined 10 – daily flow series




Page: 114

at Mawphlang; observed for the period 1979-80 to 1987-88 & generated for the

period 1988-89 to 2004-05 is given in Table 5.31.

5.9.4. ESTIMATION OF YEILD CORRECTION FACTOR Based on 12 year annual TRMM data for the period 1998 to 2009, the average rainfall

values in various parts of the catchment up to the project site were determined as given

in Table 5.32

Table 5.32: Determination of Catchment Rainfall

Sub –

Area

Average

Rainfall ‘R’

(mm)

Catchment

Area ‘A’ (sq m)

A x R

1 2500 29 72500

2 3000 33 99000

3 4150 129 535350

4 5300 76 402800

5 6100 41 250100 308 1359750

Catchment Representative Rainfall = 1359750 / 308

=

4415 mm

As suggested by CWC, considering a runoff factor of 0.8, mean annual runoff at

Mawphu-II dam site works out to 3532 mm (4415 X 0.8).

Mean annual runoff at Mawphlang (Table 5.31) = 3018 mm

Yield correction factor = 3532 / 3018

= 1.170

5.9.5. DEVELOPMENT OF FLOW SERIES AT DAM SITE

The 10-daily flow series at Mawphlang, for the period1979-80 to 2004-05 (Table

5.31) has been transferred to Mawphu-II dam site in catchment area proportion.

Yield correction factor determined in Para 7.5 is then applied to the transformed

series. The 10-daily flow series for the period 1979 – 80 to 2004-05, thus obtained at Table

5.31




Page: 115

Mawphu-II dam site is given in Table 5.33. The Public Health Engineering

Department (PHED), Meghalaya proposes to withdraw 11.3 Million Gallon / day

(mld), which works out to 0.495 cumecs (say 0.5 cumecs). Hence the available 10-

daily discharges at Mawphu-II Dam Si te af ter considering the withdrawal by

GSWSS have been determined by subtracting 0.5 cumces from the 10-daily

discharge series obtained in Table 5.33. Available 10-daily discharges at Mawphu-II

Dam site, thus obtained are given in Table 5.34.

5.10. DEPENDABILITY STUDIES

Annual flows for the River Umiew at Mawphu II Dam Site for the period 1979 – 80

to 2004 – 05 have been computed from the 10 – daily flows given in Table 5.34.

The annual flows thus derived have been arranged in descending order and the

percentage dependability estimated using Weibull’s equation, viz.:

D = m / (n+1) * 100

Where, m = ranking, when the flows are arranged in descending order n = number of years of data available D = Percentage dependability The computations for estimating the percentage dependability are given in Table 5.35.

Table 5.35: Estimation of 50 % & 90 % Dependable Year

S. No

Year

Annual

Yield

(MCM)

%

Dependabilit

y

Corresponding

Yield (MCM)

Corresponding

Year

1 1979-80 921 3.7 2134 1987-88

2 1980-81 917 7.4 1688 1988-89

3 1981-82 1049 11.1 1522 1984-85

4 1982-83 994 14.8 1515 2004-05

5 1983-84 1060 18.5 1417 1989-90

6 1984-85 1522 22.2 1289 1991-92

7 1985-86 922 25.9 1178 1999-00

8 1986-87 1069 29.6 1107 1995-96

9 1987-88 2134 33.3 1069 1986-87




Page: 116

10 1988-89 1688 37.0 1061 2001-02

11 1989-90 1417 40.7 1060 1983-84

12 1990-91 816 44.4 1049 1981-82

13 1991-92 1289 48.1 1020 2002-03

14 1992-93 963 51.9 994 1982-83

15 1993-94 950 55.6 970 2000-01

16 1994-95 691 59.3 963 1997-98

17 1995-96 1107 63.0 963 1992-93

18 1996-97 887 66.7 950 1993-94

19 1997-98 963 70.4 946 2003-04

20 1998-99 918 74.1 922 1985-86

21 1999-00 1178 77.8 921 1979-80

22 2000-01 970 81.5 918 1998-99

23 2001-02 1061 85.2 917 1980-81

24 2002-03 1020 88.9 887 1996-97

25 2003-04 946 92.6 816 1990-91

26 2004-05 1515 96.3 691 1994-95

From Table 5.35, it is seen that 90 % and 50 % dependable annual flows work out as

853 MCM & 982 MCM, which correspond to the years 1996-97 & 2002-03

respectively. 10-Daily flows during 90 % dependable year (1996-97) have been

considered for power potential studies.




Page: 117

Table 5.5: Observed Monthly & Annual Rainfall at Mawphlang (PHED)




Page: 118

Table 5.6: Observed Monthly & Annual Rainfall at Mawphlang (NEEPCO)

Months 2005 2006 2007 2008 2009 Average

Jan NA 0.00 0.00 46.25 0.00

Feb NA 7.75 111.25 22.50 0.00

Mar NA 14.75 9.25 82.75 61.75

Apr NA 165.50 242.75 28.50 109.50

May NA 723.00 348.25 228.75

Jun NA 420.75 1116.75 506.75

Jul NA 420.25 1372.25 759.00

Aug 530.75 175.00 263.25 581.75

Sep 185.00 371.25 638.75 224.00

Oct 351.50 114.75 290.75 382.50

Nov 0.00 18.25 189.25 0.00

Dec 16.00 30.25 46.25 3.75

Annual -- 2461.50 4628.75 2866.50 -- 3318.92

Table 5.7: Observed Monthly & Annual Rainfall at Shillong (IMD)




Page: 119

Table 5.8: Monthly & Annual Rainfall at Tyrsad (mm)

Table 5.9: Monthly & Annual Rainfall at Pomlakrai (mm)

Table 5.10: Monthly & Annual Rainfall at Laitlyndop (mm)




Page: 120

Table 5.14: Observed 10-Daily Discharges at Mawphu-I Dam Site (cumecs)




Page: 121

Table 5.15: Monthly & Annual Rainfall at Shillong after filling Data Gaps (mm)




Page: 122

Table 5.17: Monthly & Annual Rainfall at Mawphlang after filling Data Gaps




Page: 123

Table 5.21: 10-Daily Discharges at Mawphlang (ASEB) after filling Data Gaps (cumecs)




Page: 124

Table 5.28: Monthly & Annual Rainfall at Mawphlang after Extension (mm)

Table 5.29: Monthly flows at Mawphlang (ASEB) (mm)




Page: 125

5.11. DESIGN FLOOD STUDIES

Design flood studies are essential for proper planning & functioning of water resource

projects. If the selected design flood is too high, it results in unnecessary costly

structure; while adoption of a low design flood may result in the loss of the structure

itself, causing untold misery to the people downstream, in addition to the damage to

the structure and valuable properties. Hence the selection of design flood involves

the prescription of appropriate value of characteristics feature / features of flood

events for dimensioning of the hydraulic structure to ensure the desired level of

safety commensurate with the economic and social objectives and limitations of the data

and technology available.

5.12. CLASSIFICATION OF DAMS

For design of spillways, the dams have been classified as small, intermediate,

large & very large, depending on the catchment area, gross storage & hydraulic

head. The classification of dams is given in Table 5.36.

Table 5.36: Classification of Dams

Class

Catchment

Area (Sq. km)

Gross

Storage

(MCM)

Hydraulic

Head (m)

Probability of

Design Flood

(Years) Small < 100 0.5 to 10 7.5 to 12 1 in 100

Intermediate 100 to 1,000 10 to 60 12 to 30 1 in 1,000

Large 1,000 to 10,000 60 to 100 30 to 100 1 in 10,000

Very Large > 10,000 > 100 > 100 1 in 1,00,000 5.13. DESIGN FLOOD CRITERIA




Page: 126

As per “Manual on Estimation of Design Flood (CWC 2001) as well as BIS: 11223

– 1985,“Guidelines for Fixing Spillway Capacity”, the inflow design flood for the

safety of the dam is decided based on the gross storage as well as hydraulic head.

The standards and guidelines for the prescription of the appropriate design flood given

by CWC & Bureau of Indian Standards (BIS) are summarized in Table 5.37.

Table 5.37: Design Flood Prescription Criteria

Type of

Structure

Flood Prescription

CWC: criteria

for pick up weir

According to the importance and level conditions, a flood of 50

to 100 years return period should be adopted

IS: 6966 (1989):

Criteria for

hydraulic

design of

barrages &

weirs

For purpose of design of items other than free board, a design

of 50 years may normally suffice. In such cases, where

risks and hazards are involved, a review of this criteria

is based on site conditions may be necessary. For

designing the free board, a minimum of 500 years

return period flood or the Standard Project Flood (SPF)

may be desirable. IS 11223 (1985):

Guidelines for

determining

spillway

capacity

Spillways of small dams with gross storage between 0.5 and

10 MCM and hydraulic head between 7.5 and 12 m are to

be designed to safely pass the 100 year flood.

Intermediate dams with gross storage capacity

between 10 and 60 MCM and hydraulic head between

12 and 30 m are to be designed for safely pass the

Standard Project Flood (SPF).

Since the hydraulic head in case of Mawphu-II HEP is more than 30 m, it has to be

designed to safely pass the probable maximum flood.

5.14. ESTIMATION OF DESIGN FLOOD

5.14.1. DEVELOPMENT OF SYNTHETIC UNIT HYDROGRAPH (SUG)

The project area falls in Sub – zone 2 (c), for which Design Flood Estimation Report




Page: 127

has not been prepared by CWC. Hence the Report for Estimation of Design Flood for the

South Bank Tributaries of the Brahmaputra (Sub-zone 2(b)), prepared by CWC was

utilized for developing the synthetic unit hydrograph.

The values of basin characteristics viz. catchment area (A), length of the longest river

from the dam site (L) and length of the river from the dam site to the centroid of the

catchment (Lc) were determined from the catchment area plan obtained using GIS

software ERDAS imagine 9.1 and Arc GIS 9.2. The catchment area up to the dam site works

out as 320 sq. km and the whole catchment is rain – fed (below an elevation of 4500 m).

The values of L and Lc were found out as 54.4 km and 21.45 km respectively. Considering

the length of the river between various elevations, the equivalent slope of the river (S) has

been worked out as 36.73 m / km in Table 5.3. The computations of synthetic UG

parameters are given in Table 5.38.

Table 5.38: Derivation of Synthetic UG from Basin Characteristics

Catchment Area (A) = 320 Sq.km

Longest River length (L) = 54.54 km

Lc = 21.45 km

S = 36.73 m / km

tr = 1 hr

tP 2.870/(qp)0.839 = 10.1 hrs

QP 0.905*(A)0.758 = 71.7 cumec

W50 2.304 /(qp)1.035 = 10.8 hrs

W75 1.339/(qp)0.978 = 5.8 hrs

WR50 0.814/(qp)1.018 = 3.7 hrs

WR75 0.494/(qp)0.966 = 2.1 hrs

T

tp + (tr)/2 = 10.6 hrs

TB 2.447 * (Tp)1.157 = 35.4 hrs

qp Qp/ A = 0.22 cumec/sq km

It is seen that the time to peak (tp) works out as 10.1 hours, which appears to be on the

higher side for a catchment area of 320.2 sq km and having steep river bed slope. In view

of this, as suggested by CWC, tp has been estimated using Kirpich formula, California

formula etc.

The following basin parameters of the catchment were used for estimation of the Time of

Concentration using various formulae / methodologies.




Page: 128

Time of Concentration by Various Methods

As suggested by CWC, time to peak has been estimated by the following methods and

the computations are given below:

Kirpich

California Kerby's

Equation

Subzone

2(a)

Subzone

2(b)

Time of

Concentration

(Hrs)

5.77

5.77

7.42

4.29

10.6

Since, time to peak estimated using Subzone 2 (b) report appears to be very high.

Considering the time of concentration estimated using Kirpich Formula, California

Formula, Kerby’s equation and Sub-zone 2(a) Report, time to peak of 5.0 hours has been

adopted and synthetic unit hydrograph developed using Subzone 2(a) report of CWC.

The unit hydrograph parameters thus obtained are given

Knowing the peak & time to peak of the unit hydrograph (UH), width of UH at 50

% & 75 %peak and base width, unit hydrograph was plotted and its volume adjusted

to give 1 cm runoff. The ordinates of unit Hydrograph are given in Table 5.39 and the

unit hydrograph is plotted in Figure 5.26.

Table 5.39: Synthetic UG Ordinates

Time U H

Ordinates

Time U H

Ordinates

(hours) (cumec) (hours) (cumec)

0 0 9 47

1 10 10 37

2 33 11 28

3 82 12 20

4 150 13 14

5 177 14 10

6 129 15 6

7 83 16 3

8 60 17 0

5.14.2. DESIGN STORM




Page: 129

India Meteorological Department (IMD) was requested to supply the design storm

value for the project. The values of 1 – day and 2 – day Standard Project

Storm (SPS) and Probable Maximum Precipitation (PMP) supplied by IMD are


Table 5.40: Design Storm Values Given by IMD

Duration SPS (cm) PMP (cm)

1 – Day 99.8 130.7

2 – Day 195.6

5.14.3. TEMPORAL DISTRIBUTION

Temporal distribution of 1 – day and 2 – day design storm values given by IMD

are given in Table 5.41.

Table 5.41: Temporal Distribution Given by IMD

Time

(Hrs)

3 6

9

12

15

18

21

24

27

30

33

36

39

42

45

48

% of 24

Hrs

Storm

36

55

66

74

82

89

95

100

% of 48

Hrs

Storm

24

38

50

59

66

71

75

79

83

86

89

92

95

97

99

100

Time distribution of 1 – day and 2 – day storms given by IMD is plotted in Figure

3.27 and hourly percent temporal values read from the plot. The 1 – day and 2 –

day PMP values for Mawphu II HEP given by IMD are 130.7 cm and 248.9 cm

respectively. From the 48 hour temporal distribution given by IMD, it is seen the 24

hour storm value is 79% of the 48 hour storm. Applying this distribution, to the 2-

day storm of 248.9cm, 24 hour storm works out to 196.6 cm. Applying a clock hour

correction of 15% to the 1-day PMP value of 130.7 cm given by IMD, the 24-hour PMP

value comes to 150.3 cm, which is less than the value estimated from the 2-day storm.

Since 24 hour PMP value cannot be less than the 24 hour PMP value estimated

248.9




Page: 130

from the 2 – day storm, it is concluded that the temporal distribution of 2-day storm is

not appropriate. Hence the temporal distribution of 1-day storm given by IMD

has been considered. From the plot of 24 hour temporal distribution (Figure

5.27), hourly percent temporal distribution values for 24 - hour storm have been read.

The temporal distribution of 12– hour storm has been obtained by dividing the

temporal distribution of 24 hour by 0.74. The hourly values of temporal distribution

of 24 and 12 hour storm thus obtained are given in Table 5.35.

Figure 5.27: Temporal Distribution Given by IMD

Table 5.42: Temporal Distribution of 24 hr and 12 hr Storm

Since the PMP is assumed to occur in two bells of 12 – hour each, the PMP occurring

during the first 12 hours and later 12 hours of each day storm are 74 % and 26 %

respectively. Hence the PMP values during the 1st & 2nd bells work out as 88.37 cm &

31.05 cm respectively




Page: 131

5.14.4. DESIGN LOSS RATE It is assumed that at the time of occurrence of design storm, the soil is nearly

saturated. Design loss rate of 0.36 cm / hour as suggested in Subzone 2(b) Report

has been adopted and hourly rainfall excess values computed.

5.14.5. DETERMINATION OF RAINFALL EXCESS

Using the temporal distribution of 12 hour storm obtained in Table 5.35, cumulative

and hourly incremental values of PMP for the two bells each of first and second

day PMP have been determined. Subtracting the design loss rate from the hourly

rainfall values for all the four 12 - hour bells, hourly rainfall excess values have been found

out. Hourly rainfall values for all the four 12 - hour bells have been arranged in critical

and reverse critical order. The computations are given in Table 5.44 to Table 5.47.

Table 5.44: Computation of Effective Rainfall, First Day - First Bell

1st

bell Time

Percentage

of 12 hr

Rainfall

Cumulative

Rainfall

Incremental

Rainfall

Effective

Rainfall

Critical

Reverse

Critical

0 0.00 0.00 0.00

1 0.19 16.72 16.72 16.37 3.23 2.04

2 0.35 31.05 14.33 13.98 6.81 3.23

3 0.49 42.99 11.94 11.59 13.98 3.23

4 0.59 52.54 9.55 9.20 16.37 4.43

5 0.68 59.71 7.16 6.81 11.59 4.43

6 0.74 65.68 5.97 5.62 9.2 5.62

7 0.80 70.46 4.78 4.43 5.62 9.20

8 0.85 75.23 4.78 4.43 4.43 11.59

9 0.89 78.81 3.58 3.23 4.43 16.37

10 0.93 82.40 3.58 3.23 3.23 13.98

11 0.97 85.98 3.58 3.23 3.23 6.81

12 1.00 88.37 2.39 2.04 2.04 3.23

Table 5.45: Computation of Effective Rainfall, First Day - Second Bell

2nd

bell Time

co.Eff

Cumulative

Rainfall

Incremental

Rainfall

Effective

Rainfall

Critical

Reverse

Critical




Page: 132

0 0 0.00 0.00

1 0.19 5.87 5.87 5.52 0.91 0.49

2 0.35 10.91 5.03 4.68 2.17 0.91

3 0.49 15.10 4.20 3.85 4.68 0.91

4 0.59 18.46 3.36 3.01 5.52 1.33

5 0.68 20.98 2.52 2.17 3.85 1.33

6 0.74 23.08 2.10 1.75 3.01 1.75

7 0.80 24.75 1.68 1.33 1.75 3.01

8 0.85 26.43 1.68 1.33 1.33 3.85

9 0.89 27.69 1.26 0.91 1.33 5.52

10 0.93 28.95 1.26 0.91 0.91 4.68

11 0.97 30.21 1.26 0.91 0.91 2.17

12 1.00 31.05 0.84 0.49 0.49 0.91

5.14.6. BASE FLOW

The design base flow of 0.05 cumecs per sq km of the catchment area has been

recommended in the report of subzone 2 (b) for the catchments of South Bank

Tributaries of Brahmaputra. Adopting a flow rate of 0.05 cumecs / sq. km, base flow

works out as 16 cumecs.

5.14.7. CONVOLUTION OF DESIGN STORM WITH UG

The effective rainfall values obtained above are applied to 1 hour unit hydrograph

ordinates. The effective rainfall ordinates are arranged against the ordinates of the UH in

such a way that the maximum value of rainfall is placed against the peak value of the UH,

the next lower rainfall values are arranged against the next lower values of the UH in

appropriate order. The order of the effective rainfall values thus obtained is

reversed to get the critical sequence.

To obtain the critical value of the design flood, the arrangement of the rainfall values has

been arranged such that second bell rainfall values precede the first bell rainfall values.

The first rainfall excess value is multiplied with each of the UH ordinate to obtain the

corresponding direct runoff ordinates. The computation is repeated with the

remaining rainfall excess values & the direct surface runoff derived from each

successive rainfall excess is lagged by 1 hour. The total direct surface runoff for various




Page: 133

time periods is added to get the direct surface runoff hydrograph. The base flow is then

added to each of the direct surface runoff hydrograph ordinate, to get the values of

design flood hydrograph (Probable Maximum Flood) ordinates. The detailed

computations are given in Table 5-48 it is seen that the peak value of the Design Flood is

estimated at 8889 cumecs.

However a PMF of 9970 cumecs has been adopted as per CWC recommendation in

Figure 5.28.

5.14.8. CONCLUSIONS AND RECOMMENDATIONS

A PMF of 9970 cumecs has been adopted as per CWC’s recommendation.

5.15. DIVERSION FLOOD STUDIES

For the design of any diversion work, it is not economically feasible to plan the

diversion for the largest flood that has ever occurred or may be expected to occur.

The diversion flood depends upon the risks involved in case failure of the diversion

structure. For an earth fill dam where, considerable areas of the foundation and the

structure are exposed while under construction, may result in serious damage or loss

of the partially completed work, the importance eliminating the risk of flooding is

relatively great. In case of concrete dam, overtopping / damage to the diversion

structure during the construction of the dam will not have significance adverse

effect.

In view of this, the following design criteria have been considered while planning the

diversion structure for the project.

5.16. DESIGN CRITERIA

The value of diversion flood should be such that the river flow can be

diverted safely by construction of the diversion tunnel or channel and cofferdam, so

that construction of the main dam should go without any hindrance. The following

should be considered while deciding the diversion flood capacity of different structures as

per IS - 14815:2000.




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Proposed working period during the year.

The period of stoppage of works during flood seasons & the number of flood

seasons, which are to be managed during the work.

The cost of possible damage to the completed work or work still under construction, if

it is flooded.

The cost of delay in completion of work in case of failure of diversion works.

The safety of workmen and downstream inhabitants in case of sudden failure of

diversion works.

The diversion flood is generally dependent on the construction schedule of the head

works. If the construction work is proposed to be continued throughout the year, the

diversion structure to divert the monsoon flood will be high and costlier. Since it is

proposed to carry out construction activities for the dam during the non – monsoon

period, it is proposed to plan the river diversion works for the project for 1 in 25 year

flood utilizing the instant annual flood peak series for the non – monsoon period (Oct

– Apr) or maximum observed flood; whichever is higher.

5.17. DATA UTILIZED

Daily discharge data of River Umiew at Mawphlang (C.A = 115 sq km) observed

by Public Health Engineering Department, Meghalaya (PHED) is available for the

period 1980-81 to 1996- 97. The peak non-monsoon flows for the following periods

have been worked out and given in Table 5.49.

Table 5.49: Observed Non-monsoon Peaks at Mawphlang (cumecs)

1st Oct to

30th Apr

16th Oct to

30th Apr

1st Nov to

30th Apr

1st Nov to

30th Mar 1980-81 55.3 55.3 53.9 10.1

1981-82 42.3 42.3 42.3 35.1

1982-83 19.3 19.3 19.3 19.3

1983-84 84.0 50.9 7.1 7.1

1984-85 41.3 13.9 7.7 7.7

1985-86 28.8 28.8 28.8 5.0

1986-87 438.1 42.2 42.2 34.8

1987-88 111.0 111.0 111.0 6.2

1988-89 174.4 174.4 174.4 174.4

1989-90 425.3 425.3 17.7 17.7




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1990-91 425.3 12.7 12.7 12.7

1991-92 337.7 44.1 15.2 15.2

1992-93 62.5 61.5 61.5 20.8

1993-94 94.4 28.0 28.0 28.0

1994-95 213.3 20.1 16.0 16.0

1995-96 76.7 47.2 45.7 45.7

1996-97 259.2 259.2 57.7 30.3 5.18. METHODOLOGY ADOPTED

From Table 5.49 it is seen that considerably high flows have been observed in October.

In view of this annual peaks from 1st November to 30th April have been considered

for estimating the diversion flood. After considering the observed flood peaks for

the non-monsoon period (1st November to 30th April), mean and standard deviation

have been worked out as given in Table 5.50.

Table 5.50: Mean & Standard Deviation of the Flood Peaks (November to April)

S. No

Period

Peak

Discharge

(cumecs)

1 1980-81 53.9

2 1981-82 42.3

3 1982-83 19.3

4 1983-84 7.1

5 1984-85 7.7

6 1985-86 28.8

7 1986-87 42.2

8 1987-88 111.0

9 1988-89 174.4

10 1989-90 17.7

11 1990-91 12.7

12 1991-92 15.2

13 1992-93 61.5

14 1993-94 28.0

15 1994-95 16.0

16 1995-96 45.7

17 1996-97 57.7 Mean 43.6 Standard

Deviation

42.69




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The peak flood values obtained for the period 1980-81 to 1996-97 have been subjected

to flood frequency analysis using Gumbel’s distribution. The values of floods for various

return periods from 5 years to 100 years have been worked out. The flood values have

been transformed to Mawphu-II HEP dam site using Dicken’s formula and the values

are given below in Table 5.51.

Table 5.51: Return Period Floods

Return

Period

5Yr

10Yr

15Yr

20Yr

25Yr

50Yr

100Yr

Yt 1.500 2.250 2.674 2.970 3.199 3.902 4.600

K 0.943 1.664 2.071 2.355 2.575 3.250 3.921

Q(Mawphlang 84 115 132 144 154 182 211

Q (Dam site) 181 247 284 311 331 393 455

It is seen that 25 – year return period flood at Mawphlang works out to 154 cumecs,

which is less than the observed non monsoon flood of 174 cumecs. As per IS

14815:2000, the higher of the 25 years return period flow or the maximum observed

non-monsoon flow has to be adopted.

In view of this the diversion flood at Mawphlang comes to 174 cumecs. Transforming

this flood using Dicken’s equation, the diversion flood at Mawphu-II HEP dam

site works out to 376 cumecs. Hence diversion flood of 375 cumecs has been adopted.

5.19. SEDIMENTATION STUDIES

Reservoir sedimentation studies are essential to assess the feasible /economic

life of a reservoir. When a river flows along a steep gradient, it carries a lot of

suspended sediment load. When a hydraulic structure/dam is built across the river,

it creates a reservoir, which tends to accumulate the sediment, as the suspended

silt load settles down due to the decrease in velocity. This process of encroachment

of reservoir storage is a continuous phenomenon, which has negative impact on the intended

purpose of the project. The sediment load does not only settle down in the dead storage

area, as used to be believed earlier, it also encroach the live storage area, thus

depleting the design capacity of the reservoir. Hence it is very much essential to

determine the volume of sediment accumulating in the reservoir so as to assess/predict the

damage to the economic life of the reservoir.




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5.20. ELEVATION AREA CAPACITY

Based on the topographical survey of the reservoir, reservoir areas at various

elevations have been found out. Capacities of the reservoir at various elevations have

been worked out by trapezoidal formula viz. (An + An+1) / 2 * H. Cumulative

capacities at various elevations have then been determined. Elevation-area –capacity

for Mawphu II HEP is given in Table 5.52 & plotted in Figure 5.29. It is seen that at

FRL of 470m, the reservoir area and capacity are 10 ha and 155 ha-m respectively.

Figure 5.29: Elevation – Area – Capacity Curve

Table 5.52: Elevation – Area – Capacity

Elevation (m)

Area (ha)

Capacity

(ha m)

Cumulative Capacity

ha m MCM

434 0.010 0.000 0.000 0.00

436 0.270 0.280 0.280 0.00

438 0.743 1.013 1.293 0.01

440 1.145 1.888 3.180 0.03

442 1.696 2.841 6.021 0.06

444 2.084 3.780 9.801 0.10




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446 2.794 4.878 14.679 0.15

448 3.048 5.842 20.521 0.21

450 3.330 6.378 26.899 0.27

452 3.886 7.215 34.114 0.34

454 4.469 8.355 42.470 0.42

456 5.180 9.650 52.119 0.52

458 5.846 11.026 63.146 0.63

460 6.438 12.285 75.430 0.75

462 6.938 13.376 88.807 0.89

464 7.514 14.452 103.258 1.03

466 8.006 15.519 118.777 1.19

468 9.137 17.142 135.920 1.36

470 9.990 19.127 155.047 1.55 5.21. DATA REQUIREMENT

The required data for sedimentation studies is deepest river bed level at the dam

site, Full Reservoir Level (FRL), average annual flow, annual rate of sedimentation,

catchment area and the elevation – area – capacity curve / Table for the reservoir.

5.22. LONG TERM ANNUAL AVERAGE SEDIMENTATION RATE

Presently sediment observations of Umiew River at the project site or any other site

are not available. Sediment observations for Kynshi HEP in the adjacent basin have

been made for the period 2001 – 2008. Based on this observed data, sediment rate for

Kynshi HEP has been estimated as 0.3 mm / year. This sediment rate appears to be

low, as the sediment rate of Himalayan Rivers, as recommended by Central Water

Commission (CWC) is 1 mm /sq km/year. Hence sediment rate of 1 mm / sq km /

year has been adopted for the studies.

5.23. CLASSIFICATION OF SEDIMENT PROBLEM

For determination of severity of the sedimentation problem, the capacity inflow

ratio (C/I) is worked out.

Gross capacity (C) at FRL = 1.55 MCM




Page: 139

Long term average = 1114.13

As per Brune’s curve, trap efficiency = 0.5 %, which indicates that most of the sediment

will not be trapped in the reservoir and would flow downstream.

The above capacity-inflow ratio clearly indicates that the storage capacity of the

project is very small as compared to the average annual inflow. Therefore Mawphu-II

HEP is virtually a diversion scheme and not a storage scheme. Hence detailed sediment

studies to determine the New Zero Elevation and revised areas and capacities after

70-year sedimentation are not necessary. For effective management of the reservoir,

proper sediment management measures have to be taken.

5.24. SEDIMENT MANAGEMENT MEASURES

Since Mawphu-II HEP is virtually a diversion scheme and not a storage scheme, the

following design aspects have been provided for the purpose of silt management:

operating the reservoir at MDDL during the monsoon months to route the

incoming sediment downstream of the project site.

Provision of low level sluice spillway crest for flushing the silt downstream

during flood season.

Reservoir drawdown flushing two times every year, to ensure that live storage is

always available.

Adequate vertical separation between the water conductor intake sill level and the

sluice spillway crest level for effective silt flushing.

CHAPTER - VI

POWER POTENTIAL & INSTALLED CAPACITY




Page: 140

CHAPTER - VI

POWER POTENTIAL STUDIES

6.1. GENERAL

Mawphu-II Hydroelectric Pro ject is located in East Khasi Hi l ls distr ic t of

Meghalaya. The diversion dam is located at lat itude 25o18’32”N and Longitude

91o38’19”E. The project is envisaged as Run-of- River scheme with diurnal pondage

for peaking benefits.

The Project is proposed to be constructed utilizing the discharges of the river

Umiew by constructing a diversion structure, intake arrangement, water conductor

system comprising of head race tunnel, surge shaft and pressure shaft. The power is

proposed to be generated in a surface powerhouse with tail race channel to evacuate

the water from the turbines which will flow back to the river.

The power potential studies have been carried out for working out the Installed

Capacity and other project features.

6.2. PROJECT PARAMETERS Following parameters have been considered for carrying out the power potential

studies.

1.

Full reservoir level, FRL

EL 470.00m

2.

Minimum draw down level, MDDL

EL 464.00m

3.

Normal tail water level, TWL

EL 232.00m

4.

Head loss in water conductor system

5.5m

5.

Combined efficiency of Turbine and Generators,

92.12%

6.

Rated Head

230.5 m

7.

Live storage

0.5 Million Cubic meter (MCM)




Page: 141

The minimum draw down level of the Project has been raised from EL 460m to EL 464m,

for better silt management in consultation with the Central Water Commission.

6.3. HEAD COMPUTATION

For energy generation the head computations have been done as below:

Gross head = FRL – TWL = 470 – 232 = 238m,

Rated net head = (MDDL + (2/3) (FRL – MDDL) – TWL) – Losses in water conductor

system,

= (464 + (2/3) (470 – 464) – 232) - 5.5 = 230.5m

6.4. WATER AVAILABILITY

The data on water availability is available for 26 years i.e. from year 1979-80 to 2004-

05 and is indicated in (Annexure-1). The environment releases as per guidelines of Ministry of

Environment and Forests (MoEF) are as below:

During monsoon months i.e. from June to September, the water to be released from the

Dam has to be 30% of the river discharge. During transition months i.e. post-monsoon

of October and November, and pre-monsoon of April and May, the water to be

released has to be 25% of the river discharge and during lean season i.e. from

December to March, the water to be released will be 20% of the river discharge.

For computing the available discharges for power generation, environment

releases as mentioned above have been deducted from the available discharges.

6.5. DEPENDABLE FLOWS

The dependable flows for analysis of installed capacity etc. are based on 90%

dependable year as per guidelines of CEA. For obtaining the dependable flows, unrestricted energy

generation has been computed for all the 26 years and arranged in descending order of

the energy values. (Annexure-2).




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The 90% and 50% dependable year have been obtained from the following relations:

90% dependable year = 0.9 (N + 1)th year.

50% dependable year = 0.5 (N + 1)th year. Where n is the number of years for which discharge data is available, which is 26.

The year 1990-91 and 1982-83 works out to be the 90% and 50% dependable

years respectively. The discharges of 90% and 50% dependable years are shown

in (Annexure 3). 90%dependable year discharges after deducting the environment

releases are indicated in Table 6.1 below.

Table 6.1: 90% dependable year discharges after deducting the environment releases

Month TD Days 90%

Dependable Year (m3/s)

Environment Release

Environment Release (m3/s)

Discharge for Energy Generation (m3/s)

May

I 10 29.91 25% 7.48 22.43

II 10 36.97 25% 9.24 27.72

III 11 61.51 25% 15.38 46.13

Jun

I 10 34.48 30% 10.35 24.14

II 10 58.95 30% 17.68 41.26

III 10 64.63 30% 19.39 45.24

Jul

I 10 49.87 30% 14.96 34.91

II 10 29.44 30% 8.83 20.61

III 11 44.98 30% 13.49 31.48

Aug

I 10 42.85 30% 12.86 30

II 10 53.39 30% 16.02 37.37

III 11 42 30% 12.6 29.4

Sep

I 10 44.84 30% 13.45 31.39

II 10 49.4 30% 14.82 34.58

III 10 40.56 30% 12.17 28.4

Oct

I 10 54 25% 13.5 40.5

II 10 53.94 25% 13.48 40.45

III 11 38.39 25% 9.6 28.79

Nov

I 10 11.8 25% 2.95 8.85

II 10 8.13 25% 2.03 6.1

III 10 6.53 25% 1.63 4.9




Page: 143

Dec

I 10 5.72 20% 1.14 4.58

II 10 6.44 20% 1.29 5.15

III 11 4.53 20% 0.91 3.62

Jan

I 10 4.25 20% 0.85 3.4

II 10 4.9 20% 0.98 3.92

III 10 3.71 20% 0.74 2.97

Feb

I 10 3.42 20% 0.68 2.74

II 10 3.23 20% 0.65 2.59

III 8 2.55 20% 0.51 2.04

Mar

I 10 3.23 20% 0.65 2.59

II 10 4.01 20% 0.8 3.21

III 11 4.73 20% 0.95 3.78

Apr

I 10 4.69 25% 1.17 3.52

II 10 4.42 25% 1.1 3.31

III 10 9.06 25% 2.27 6.8

6.6. FIRM POWER

Firm power has been computed from the average discharge after deducting mandatory

releases during the lean period months from December to March i.e. 3.38 cumecs.

The firm power, thus computed is:

Firm Power = (9.81 x 230.5 x 0.9212 x 3.38)/ 1000 MW

= 7.04 MW

The lean period load factor for Peaking Plant is normally between 12% and 25%.

Installed capacity with 12% LPLF = (7.04 x 100)/ 12 = 58.6 MW, and

Installed capacity with 25% LPLF = (7.04 x 100)/ 25 = 28.1 MW

6.7 INSTALLED CAPACITY

6.7.1. RANGE OF INSTALLED CAPACITIES

The energy generations for various installed capacities ranging from 60MW to 100MW

have been computed for 90% dependable year to analyze the energy generation and

arrive at the optimum installed capacity. For this purpose an increment of 5MW has been

selected. The computations of the energy generations for various installed capacities




Page: 144

are indicated in Annexure 4. The extracts are also shown in table below:

Table 6.2: Energy Generation with various Installed Capacities

Installed Capacity Annual Energy Annual Energy

(in MW) Generation (in MU) per MW MU/ MW

60 291.78 4.86

65 304.94 4.69

70 314.91 4.5

75 323.37 4.31

80 330.17 4.13

85 335.96 3.95

90 338.71 3.76

95 341.05 3.59

100 341.33 3.41

110 341.33 3.10

6.7.2. OPTIMUM INSTALLED CAPACITY

To work out the optimum installed capacity, ratio of incremental energy per MW

increment in installed capacity has been computed and shown in the table below and

also indicated in the sketch below:

Table 6.3: Ratio of incremental energy (∆AE) and increment in installed capacity (∆IC)

Range of Installed

Incremental Energy Incremental Energy/

Capacity (MW) (MU) Increment in Installed

(MU/MW)

60-65 13.16 2.63

65-70 9.96 1.99

70-75 8.46 1.69

75-80 6.8 1.36

80-85 5.79 1.16

85-90 2.75 0.55

90-95 2.34 0.47

95-100 0.29 0.06

100-105 0 0

105-110 0 0




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Figure 6.1: Graph between incremental energy (MU/MW) and Installed capacity

From the Figure 6.1, above, it is seen that the optimum installed capacity lies between

80MW and 90MW as beyond 85MW there is sharp fall in incremental energy.

Basic parameters with installed capacity of 80, 85 and 90MW are mentioned hereunder:

Table 6.4: Basic parameters with installed capacity of 80, 85 and 90 MW

Installed capacity 80 85 90

Annual energy generation (MU) 330.17 335.96 338.71

MU/MW 4.13 3.95 3.76

∆MU/∆IC 1.36 1.16 0.55




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The potential exploited with various installed capacities is indicated in the Table

6.5 given below:

Table 6.5: Water utilization for various installed capacities

Installed Capacity

(in MW)

Water utilization

(in %)

60 85.48

65 89.34

70 92.26

75 94.74

80 96.73

85 98.43

90 99.23

95 99.92

100 100.00

105 100.00

110 100.00

Keeping in view the techno-economic viability as well as optimum exploitation of

the site, 85 MW i.e. selected as the optimum installed capacity.

6.8. 50% DEPENDABLE YEAR ENERGY GENERATION

With the installed capacity of 85 MW, the energy generation in 50% dependable year has

been worked out as 267.42 MU as indicated in Annexure 5. It is also observed that the

mandatory release in the first two ten dailies in the month of May, the environmental

release in 90% dependable year is greater than the inflows in the 50% dependable year,

therefore no generation in these two ten dailies is envisaged.

6.9. DESIGN ENERGY

Based on the CERC guidelines, the design energy has been computed in 90% dependable

year with plant availability of 95%. The design energy thus works out as 331.09 MU as




Page: 147

X

indicated in Annexure 6.

6.10. ANNUAL PLANT LOAD FACTOR

The annual plant load factor for the Project is worked out as below:

PLF = (335.96 x 10, 00,000(kWh)/ {85000(kW) X 365(days) X 24(hrs)} X 100

i.e. 45.12%.

6.11. LEAN PERIOD LOAD FACTOR

Lean period load factor = x 100 = 7.04/ 85 x 100 = 8.28%

Firm power is the power considering the average inflows in the lean period from

December to March after deducting the mandatory releases.

6.12 PEAKING OPERATION

For peaking operation for three hours during lean months, the storage required

will be: Design discharge x Peaking time x 3600

Design Discharge = (85x1000)/ (0.9212x230.5) x 9.81=40.80 Cumec

Thus, the storage required = 40.80 x 3 x 3600 ~ 0.4407 Million cubic meters (MCM)

The available live storage between the full reservoir level and the minimum draw

down level is about 0.5 Million cubic meters. The additional storage available would

be utilized to meet contingencies.

6.13 NUMBER OF UNITS

The number of units for any plant are chosen based on reliability

consideration and transportation constraints, it is proposed to install 2 (two) units

of 42.5MW each keeping in view the reliability of operation of the plant. No difficulty

100




Page: 148

is anticipated in transporting the generating equipment.

6.14. SUMMARY The summary of the data for the optimum installed capacity is as below:

SL NO. PARAMETER VALUE

1 Installed Capacity 85 MW

2 Annual Energy generation at 90% dependable year 335.96 MU

3 Annual Energy generation at 50% dependable year 267.42 MU

4 Design Energy in 90% dependable year(with 95% plant availability)

331.09 MU

5 Storage required for peaking 0.44 MCUM

6 Storage available 0.5 MCUM

7 Annual plant load factor 45.12 %

8 Lean period load factor 8.28 %

6.15. LIST OF ANNEXURE

Annexure 1: Discharge series (Approved).

Annexure 2: Dependable year computation.

Annexure 3: Discharges in 90% and 50% dependable years. Annexure 4: Energy generation in various installed capacities.

Annexure 5: Energy generation in 50% dependable year.

Annexure 6: Design energy in 90% dependable year




Page: 149




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CHAPTER - VII

DESIGN OF CIVIL AND HYDRO-MECHANICAL

STRUCTURES




Page: 157

CHAPTER - VII

DESIGN OF CIVIL AND HYDRO-MECHANICAL STRUCTURES

7.1 GENERAL

Mawphu Hydro Electric Project (Stage-II) is a run of the river scheme proposed on

Umiew River in East Khasi Hills district of Meghalaya. The project is proposed to utilize

a net head of about 230.5m and design discharge of 40.8 cumecs for generation of 85 MW

(2x42.5MW). The project is being implemented by North Eastern Electric Power

Corporation Ltd, a Government of India enterprise.

This chapter deals with design of various civil engineering structures of the project.

7.2 PROPOSED LAYOUT OF THE PROJECT

The selected project layout comprises a concrete gravity dam on Umiew River and an

intake structure on the right bank for diversion of 40.8 cumecs of water for power

generation. The reservoir is proposed to have 0.5 MCM of live storage and 1.2km long at

FRL. Water is diverted from the river and is conveyed through right bank head race

tunnel to the surge shaft. Surge shaft is proposed at the junction of HRT and pressure

shaft to take care of the transient conditions in the water conductor system. A pressure

shaft, which will be bifurcated near the power house, will feed water to two vertical axis

Francis turbines each of 42.5 MW installed capacity housed in surface power house.

The proposed civil components of the project are as follows:

(i) A concrete gravity dam of 51m high from the deepest foundation level with low

level spillway comprising 6 bays each with radial gate of size 9.00m (W) x 12.00m

(H) to pass the design flood of 9970 cumecs.

(ii) Temporary river diversion works comprise a Horse Shoe shaped diversion tunnel

of 7m diameter, about 384m long on the left bank and 18m (Maximum) high

upstream and 6m high downstream cofferdams.

(iii) A Power Intake with inclined trash rack on the right bank.

(iv) One number of Horse Shoe shaped Head Race Tunnel of 4.8m dia and 2622m long

up to Surge Shaft.

(v) One number of restricted orifice type Surge Shaft of 10m dia and 54m high.




Page: 158

(vi) One number of circular Pressure Shaft of 3.5m dia and 869m long which bifurcates

into 2.5m dia and 32m long pressure shafts to feed two turbine units.

(vii) A Surface Power House of 66.0m (L) x 18.0m (W) x 30.5m (H) housing two Vertical

Axis Francis Turbines and Generator units of 42.50 MW each.

(viii) One tail race channel of 8m wide and 51m long (including recovery bay) to

discharge the water into the river.

7.3 DIFFERENT STRUCTURES

7.3.1 DIVERSION TUNNEL

One diversion tunnel of 7.0 m dia, horse shoe shaped is proposed on the left bank. The

length of the tunnel is about 384m. The inlet is kept at EL. 446.00 and outlet is at EL.

429.50. The invert levels are about 1.0 m above the average river bed level at the

proposed location.

One gate of size 8.00 m x 8.00 m for the opening at inlet shall be provided to facilitate the

closure of the tunnel and plugging of the tunnel before reservoir filling. The gate shall be

operated with hoist at EL. 457.50 m.

7.3.2 UPSTREAM COFFERDAM

Surface geological mapping reveals the presence of isolated patches of bedrock

represented by quartz biotite gneiss and gneiss on the surface on the left flank of the

coffer dam whereas on the right flank continuous outcrop of gneiss are well exposed. In

the river bed portion, as revealed from the seismic survey the overburden thickness shall

range from 7 m to 17m.

On the basis of various boreholes drilled in the dam area particularly DH-01 and DH-02,

overburden permeability is expected to range between 1.02 to 1.2 X 10-2 cm/sec whereas

that of bedrock would vary between 3 to 6 Lugeon. In view of this as seepage

control measure jet grouting provisions has been kept below the coffer dam to minimize

seepage into the dam pit during construction.

7.3.3 DOWNSTREAM COFFERDAM

On the basis of bore hole data, DH-10 drilled for subsurface investigation in the energy

dissipator area, it is opined that thickness of overburdened, constituted of large boulder

pebbles, cobbles, gravels of granite/granitic gneiss mixed with sand shall be of the order




Page: 159

of 5 to 7m and shall be followed by strong to very strong bed rock quartz biotite gneiss.

Overburden permeability is anticipated to range between 3.8 to 4.8 X10-3 and therefore

suitable pumping arrangement shall be required during construction.

7.3.4 CONCRETE DIVERSION DAM

7.3.4.1 TYPE OF DAM

Following aspects have been considered for the selection of type of dam:

� Topographical and Geological Aspects:

The type of dam to be adopted is governed by the topographical, geotechnical,

availability of construction materials and spillway arrangement. Rock exposures are

available on both the banks of the river and rock is anticipated at shallow depth in the

river bed.

� Spillway Arrangement:

The width of the river is about 73m. Dam height and basic parameters have been decided

based on techno-economical considerations as described in Section-2.3 in Chapter-2. The

height of the dam is 38m from the average river bed level and spillway crest is proposed

at about 9m above the average river bed level. The design flood (PMF) is 9970 cumecs.

Spillway of 79m long including piers and abutments are required to pass the design flood

with one gate inoperative condition. Therefore, the whole river width shall

be accommodated with spillway blocks or overflow (OF) block and the length of NOF

(non overflow) is less.

� Foundation Condition:

The foundation rock of dam area comprises Quartz Biotite Gneiss/Gneiss. The bed rock

is hard, moderate to closely jointed rock mass. The foundation rock is strong and is

suitable for adoption of a concrete gravity dam. Investigation data also indicates the

suitability of foundation condition for concrete gravity dam.

� Availability of Construction Material

Quarries and shoals are available/identified at various places near the dam axis. Rock

quarry near the Weisu nallah which is about 400m u/s of dam axis and rock quarry in the




Page: 160

reservoir area which is at about 1000m u/s of dam axis are some of the quarries identified

in addition to other quarries. From the preliminary assessment, it is expected that apart

from excavated quantity in the dam area, these available quarries and shoals near the

dam axis will satisfy the maximum requirement of coarse and fine aggregates for the

concrete dam. Therefore, availability of construction material will not be a constraint for

concrete gravity dam.

A concrete gravity dam has been finalized considering the following aspects:

� Foundation conditions are favourable for seating a concrete gravity dam.

� The most of the part of diversion is spillway structure.

� The dam height of 38m (from average river bed level) is required to meet out live

storage for peaking requirements and rock is available at shallow depth therefore

barrage is not considered as a suitable diversion structure.

7.3.4.2 DAM LAYOUT DETAILS

As per layout arrangement, the power intake is placed at right bank. The spillway has

been proposed close to the intake to avoid the silt deposition in front of intake. However,

due to high PMF of 9970 cumecs, the spillway arrangement is provided utilizing the

whole width of the river.

The dam layout comprises the following arrangement:

� Concrete gravity dam of 140m long (at top) and 51m high (from the deepest

foundation level) with its top at EL.472.00m.

� Non-Overflow (NOF) blocks have been proposed on the left bank side. The length

of first NOF block has been kept as 17.75m and of second block as 15.0m. The

height of the blocks varies from 6.25 to 36.5m.

� NOF blocks have been proposed on the right bank side. The lengths of blocks are

15.0m and 13.25m. The height of the blocks varies from 7m to 43m.

� A downstream slope of 0.8 (H):1 (V) is proposed for the NOF section based

on the preliminary design.




Page: 161

� Overflow (OF) blocks have been proposed with 6 bays (controlled by radial gates)

utilizing the available width of the river. The pier width has been kept as 3.0m.

7.3.4.3 SPILLWAY

Following aspects have been considered for the selection of type of dam:

Sluice type Ogee spillway has been proposed to pass the design flood. The crest level of

the spillway has been provided at lower elevation in view of effective silt management in

the reservoir. The design flood for the spillway, its flood discharge capacity and the ogee

profile are described below.

DESIGN FLOOD FOR SPILLWAY

On the basis of hydraulic head and gross storage capacity, cl: 3.1.2 of IS 11223-1985

classifies the dams in three categories viz. large, intermediate and small as shown below.

Considering the minimum dam height requirement arrived, the hydraulic head of

Mawphu HEP (Stage-II) dam is greater than 30m and hence as per the above

classification, the dam falls under the category of large dam. Also, Cl: 3.1.3 of IS 11223

specifies the inflow flood to be adopted to design the spillway based on the classification

of dam as given below.

Accordingly, Mawphu HEP (Stage-II) dam being large, PMF has been considered as the

inflow flood to design the spillway and the same has been arrived as 9970 cumecs.

SPILLWAY CAPACITY

A parametric study has been carried out for fixing the optimal size of the spillway

arrangement. As a result, 6 bays, each of size 9.00m (W) x 12.00m (H) with crest level at

EL.443.00m have been arrived. The provision of 10% of the total number of gates with a

minimum of one gate being inoperative has also been considered for handling emergency

situation during mechanical and human failure as per IS: 11223-1985. Maximum Water

Level (MWL) has been fixed at 470.50m to pass the design flood during

emergency situation.

OGEE PROFILE

The ogee profile consists of two quadrants, the upstream quadrant and the downstream

quadrant. Upstream quadrant of the ogee spillway conforms to the elliptical equation




Page: 162

and downstream profile conforms to the parabolic equation as per Cl: 4.1.3.1 IS 6934:1998

and joins with the bucket profile tangentially.

UPSTREAM QUADRANT OF THE OGEE SPILLWAY

Elliptical equation used for the upstream quadrant of the ogee spillway.

7.3.5 POWER INTAKES

The power intake is located close to the dam (15.0m u/s of the dam axis) and invert of

intake sill is proposed at about 9 m above the spillway sluice to avoid bed load entry into

the power intake. The power intake will be proposed on the right bank of Umiew River.

Two bays each of 5 m wide and 8m high protected by trash screens will receive water

from the reservoir and will deliver into a concrete section of 4.8 m square shaped. Two

gates, one is service gate and another one is maintenance gate (stoplogs) are provided in

the concrete square section, which will be operated from top of intake at El. 472.00 m. The

concrete section will transit into horse shoe shaped tunnel at the portal of intake. Power

Intake has been designed for the design discharge of 44.88 cumecs with 10% overload.

Average river bed level in front of the intake structure is at El.434.00m. The centre line

level of the Power Intake has been arrived at El.454.40m considering the minimum

submergence requirement as per BIS (Bureau of Indian Standard) provisions with respect

to reservoir at MDDL. The waterway entrances are bell mouth shaped to minimize

hydraulic losses. An inclined trash rack is proposed for efficient cleaning by trash rack

cleaning machine from the top of intake structure. The maximum velocity through the

trash racks for 50% clogging condition is well within permissible value.

Operational platform of 18m wide has been provided at the top of intake structure and

shall be used for the operation of trash cleaning machine and gates.

The entrance of the intake structure should be sufficiently submerged so as to avoid

vortex formations in front of the inlet section. Vortices intruding into the pressure shaft

adversely affect the turbines and the operation of the plant. Therefore, in order to have

intake structure free of vortex, the centre line of the intake inlet should be located

in such a way that minimum submergence requirements are met as per IS 9761:1995.




Page: 163

SILT MANAGEMENT

The river umiew carries silt during high flows in monsoon. The discharge in the river

varies from 5-10 cumecs in lean season and 100-150 cumecs in monsoon season. As the

spillway gates are proposed at 9 m below the power intake sill level, and reservoir has

enough area to reduce the flow through velocity for settling of sediments, a preliminary

study of desilting through reservoir has been carried out. In many projects in India,

desilting arrangement is being carried out through The reservoir length is about 1.2 km,

however only 300 m length has been considered in the analysis of reservoir as a desilting

basin.

Average cross sectional area of river from crest elevation to MDDL for initial 300 m reach

of reservoir is about 1600 sqm. This area will be increased to about 3000 sqm for reservoir

upto FRL.

Limiting discharges have been worked out by trial and error for flow through velocity of

25 cm/s and 35 cm/s corresponding to settling of particles of coarser than 0.2 mm and 0.3

mm respectively.

Velocities are worked out for various discharges are shown in Table 7.1.

Table 7.1:Velocities for various discharges

Sl.

No.

For settling of

particles

coarser

Limiting

flow

through

velocity

Cross

sectional

area upto

MDDL

Limiting

Discharge

cumec

Cross

sectional

area upto

FRL

Limiting

Discharge

cumec

1. 0.2 mm 0.25 m/s 1600 sqm 400 3000 sqm 750

2. 0.3 mm 0.35 m/s 1600 sqm 550 3000 sqm 1050

Required length of reservoir for settlement of particles coarser than 0.2 mm has

been worked out as about 220 m for MDDL operating conditions and 340 m for FRL

conditions. The length of reservoir is about 1.2 km and a reservoir of 300-400 m length

may be considered as desilting chamber.

From the above table, it may be seen that the reservoir will work as a desilting chamber

for removal of >= 0.2 mm and >=0.3 mm particle for maximum discharge of 400 cumecs

and 550 cumecs respectively for MDDL operations.




Page: 164

It is expected that during high flows, the silt concentration will be high and will require

shut off the plant. Therefore even provision of desilting chamber along the diverted water

conductor system, the plant needs to be shut-off.

Continuous silt flushing shall be made through closest spillway gate by releasing

minimum environmental flow of 30% of inflow. Also, reservoir flushing will be carried

out prior and after the monsoon with drawdown of reservoir. However, detailed studies

will be carried out at detailed design stage and to be verified by physical model test.

In view of the above, desilting arrangement has been proposed through reservoir itself in

lieu of separate desilting chamber.

7.3.6 HEAD RACE TUNNEL

A 4.8m dia, 2.62km long, horse shoe shaped, concrete lined Head Race Tunnel has been

proposed on the right bank of the Umiew River to convey 40.80 cumecs design discharge

to Surge Shaft.

SIZE OF THE TUNNEL

The size of the tunnel has been arrived based on the detailed analysis carried out for the

economic diameter giving due focus on constructability. The velocity in the tunnel will be

2.14m/s. Economical diameter has been arrived as 4.8m.

SHAPE OF THE TUNNEL

Shape of the tunnel is decided based on geological conditions, hydraulic requirements,

structural considerations and functional requirements. Common shapes of tunnel used in

practice are circular, horse-shoe, modified horse-shoe and D-shaped. Each shape has got

advantages and disadvantages compared to other shapes.

In Mawphu HEP (Stage-II), the size of the tunnel is 4.8m. The size of the tunnel also

influences the shape of the tunnel. Circular shaped tunnel is hydraulically and

structurally suitable but it does not satisfy the functional requirements. D-shaped tunnel

is appropriate from hydraulic and functional point of the view whereas it is not suitable

from structural point of view. Therefore, horse-shoe shape which provides sufficient base

for construction facility and is hydraulically as well as structurally suitable, has been

adopted for HRT.




Page: 165

ALIGNMENT OF THE TUNNEL

The alignment of tunnel is tried to keep as much as straight from power intake to surge

shaft to minimize the tunnel length as well as head losses. However a small bend is given

to push the HRT towards the river to reduce the length of an intermediate adit.

In view of the surface works of power intake, the intake portal may not be available for

construction of HRT throughout the time and therefore the HRT may fall on critical path.

Being underground excavation, any unforeseen adverse geological conditions may push

put this activity on further criticality. In view of this, an intermediate adit of D-Shaped,

6m dia and 78m long has been provided at RD. 862m. The junction of adit divides the

HRT as 873 m upstream up to intake and 1749 m downstream upto surge shaft. The HRT

follows along the right hill slope and maximum rock cover available along the alignment

is around 250m.

GEOLOGICAL AND GEO-TECHNICAL ASPECTS

As indicated in the geological report, rock classes in various stretches of HRT as

predicted on the basis of surface exposures details are 40% for class-II, 45% for class-III,

10% for class-IV and 5% for class-V. Low cover and weak zones apart from zones where

seepage is anticipated are proposed to be evaluated further by advance probing.

Wedge analysis results indicate the formation of gravity wedges at certain reaches of the

tunnel crown, for which appropriate support measures shall be provided.

ROCK SUPPORT SYSTEM FOR THE TUNNEL

The HRT will negotiate different rock types of variable strength with different tunneling

conditions along its length ranging from good rock to very poor rock. The tunnel

excavation will be done by drill and blast method with full face excavation.

In order to design the initial support system for the tunnel, the rock mass along the

tunnel was categorized into five groups based on RMR values/Q values, and the

following support system for each group was designed.

The supporting system comprises of rock bolts, SFRS and steel ribs as mentioned in Table

7.2. In the class-IV and V zones, pre-grouting with microfine cement may be required.

Forepoling, will be resorted as per requirement while boring in class V type of rock.

Probe drilling shall be resorted for identifying the problem areas and suitable prior

remedial measure shall be kept ready before hand.




Page: 166

Table 7.2: Rock Support Systems for Head Race Tunnel

Rock Mass

Rating

Length

(%)

SFRS

(mm)

Rock bolt (25Ø)/ Anchors Steel Ribs/ Lattice Girder

Remarks

Length (m)

Longitudinal Spacing (m)

I - Very Good rock RMR: 100-81 Q: 100 to 40

0

II - Good rock RMR: 80-61 Q: 40 to 10

40 50mm in

crown

4m long rock bolt, 5 Nos.

2.0 m Nil

III - Fair rock RMR: 60-41 Q: 10 to 4

45 100 mm in crown and sides

4m long rock bolt, 7 Nos.

1.75 m Nil

IV - Poor rock RMR: 40-21 Q: 4 to 1


4m long rock hollow core SDA, 9 Nos.

1.5 m Lattice Girder @ 1000 mm c/c

Pre-grouting with

micro fine cement

V - Very Poor rock RMR: <20 Q: 1 to 0.1


4m long rock hollow core SDA, 9 Nos.

1.5 m ISHB 150 @ 500 mm c/c

Pre-grouting & Fore- poling 32 dia, 6m long, 3m c/c

PCC concrete lining of 250 thick has been provided. Reinforcement will be required in the

concrete lining in low cover areas, adit junctions, vicinity of surge shaft and geologically

weak reaches. A provision of reinforced lining in 130m (about 5%) of tunnel length has

been kept.

Consolidation grouting is provided in class-IV and V and contact grouting is provided for

the entire length of the tunnel.

CONSTRUCTION ADITS TO HRT

One adit (Adit-1) of D-Shaped, 6m dia and 78m long has been provided at RD.873m and

another adit (Adit-2) of 124m long at RD.2597m just upstream of surge shaft to facilitate

the construction in HRT. The maximum face length available for the HRT is 875m.

Rock support systems proposed for Adits are given below.

PLUGS AND NITCHES




Page: 167

After completion of all works in HRT, it is proposed to plug all adits with concrete M20.

Plug in Adit-2 which is just upstream of surge shaft is proposed with gate for vehicle

access. Dewatering arrangement has also been provided in the plugs with 300mm pipes.

Contact and consolidation grouting shall be carried out in all the plugs after concreting.

Niches are proposed in the HRT for the convenience of the vehicle crossing and

temporary storage of the materials and these niches will be backfilled with lean concrete.

7.3.7 REQUIREMENT OF SURGE SHAFT

The requirement of the surge shaft is verified based on codal provisions and the

acceleration time of the hydraulic system. The following criteria are usually adopted to

determine whether a surge tank is required for a given hydraulic system.

a) According to codal provision, surge tank is usually necessary if L/H is equal to or

more than 5 to 7, ‘L’ being length of HRT and ‘H’ the net head.

In the case of Mawphu HEP (Stage-II), L=2622m and H = 232m, giving L/H of 11.30.

Consequently, a surge tank is clearly required.

b) Another criterion is based on the acceleration time of the hydraulic system. The

acceleration time (Ta) of a hydraulic system is given by the equation

��

��

Where L = Length of water conductor

V = velocity of flow in water conductor

H = Net head

g = Acceleration due to gravity

If the acceleration time of a hydraulic system is less than 2 seconds, no surge shaft is

required in the hydraulic system. For acceleration time between 2 and 5 seconds, surge

tank may be provided for a stable operation of the system. For acceleration time greater

than 5 sec, a surge tank is almost always required.

In the present case, L = 2622 m, H = 232 m and V = 2.14 m/s which gives an acceleration

time, Ta of 2.47 seconds and hence there is a requirement for a surge tank.

The surge shaft would also help in supplying water to turbines in case of sudden start up

of a machine.




Page: 168

In view of above, it is proposed to provide a surge shaft.

SELECTION OF THE TYPE OF SURGE SHAFT

Many different types of surge shaft have been developed and the most common among

them are

� Simple Surge Tank

� Orifice type Surge Tank

SIMPLE SURGE TANKS

These tanks are simpler to construct but have large oscillations compared to other type of

tanks. Therefore, the required height will be large. Besides, the oscillations take a long

time in dying out due to slow damping and therefore may remain relatively unstable.

ORIFICE TYPE SURGE TANKS

In this type, tank is connected to HRT through an orifice. When there is sudden injection

of load, the water flows into the tank through the orifice creating an instant high pressure

under the orifice slab. The rise in pressure helps in damping of the oscillations. The

oscillations have shorter amplitude as compared with simple surge tank. The orifice

type tanks are lesser in height for the same size of simple tank. The oscillations die out

rather quickly. This is the main advantage of having orifice type tanks.

Therefore, in Mawphu HEP (Stage-II), out of above two types of surge tanks, orifice type

tank, being advantageous compared to simple tank, is provided.

HYDRAULIC DESIGN OF SURGE SHAFT

Hydraulic design of the surge shaft has been carried out as per IS 7396 (Part-1)-1985. To

ensure the hydraulic stability of surge tank, its minimum area has been calculated

according to Thoma criteria as mentioned below.

Asth��

� ��

A factor of safety of 1.60 has been considered as per IS: 7396 (Part-1) 1985, which yields

an area of 16.12 m2 equivalent to 4.53m dia. Accordingly, a 10.0m dia surge shaft has been

provided.

Transient conditions have been analyzed using the computer program 'WHAMO' (Water

Hammer and Mass Oscillation) developed by US Army Corps of Engineers.




Page: 169

WHAMO provides dynamic simulation application of fluid distribution systems in hydro

power plants.

The transient analysis has been carried out to determine the maximum upsurge and

down surge levels in the surge tank with respect to different loading/unloading of

generating units corresponding to load acceptance and load rejection conditions when

reservoir is at FRL (EL. 470 m) and at MDDL (EL. 460 m).

The surge levels have been computed with respect to the 100% load rejection and

acceptance and various other combinations of specified load acceptance and rejection to

arrive at the maximum and minimum water levels anticipated in the surge shaft, under

worst conditions as per IS: 7396.

Considering a free board of 3.0 m, top of the surge shaft is kept at EL. 492.00 m MSL and

adequate water cushion below the minimum down surge level, bottom of the surge shaft

at EL. 438.00 m MSL. The diameter of orifice is adopted as 2.80 m.

GEOLOGICAL AND GEO-TECHNICAL ASPECTS FOR SURGE SHAFT

10 m dia surge shaft has been proposed to be excavated after removing the overburden of

27m and 15.16m of rock, the top of the surge shaft from where sinking will start is at El

492m where as rock is encountered at El 507.16. For open excavation, initially about 10m

of overburden excavation shall be in silty soil and would be followed by slope was

material characterized by medium sized angular to sub-angular rock blocks/ fragments

with silty matrix till El 507m.

The overburden slopes mentioned above would contain rock blocks of partially

disintegrated rock confined within a clayey matrix. While excavating these zones

instability is anticipated to get initiated, especially when the material will be saturated.

As such the dressed slopes need to be provided with suitable drainage and soil anchors

for stability.

From El 507m to El 492m i.e. top of the surge shaft, the excavation shall be in moderately

strong, moderately to highly weathered granite gneiss with biotite schist banding. As no

major shear zone was encountered during drilling as such no serious difficulty during the

excavation of shaft is anticipated. In general there is an improvement in rock strength,

weathering and opening of the joints with the depth barring few exceptions at El.491m,




Page: 170

El.482m, El.472m, El.451m and El.436m where RQD has been found to be low though the

recovery remains constantly high. In such area provision of consolidation grouting shall

be required for ground improvement.

Considering the nature of rock encountered in drill holes and observed rock mechanic

parameters, it is anticipated that the major part of Surge shaft shall negotiate fair to good

rock with occasional patches of poor rock. The suitable rock support consists of rock

bolts, SFRS and pressure relief holes shall be installed concurrent to excavation.

It is assessed that in the initial and terminal part of the surge shaft excavation would

require circular steel set tied firmly to each other along periphery with back fill concrete

in view of the observed weakness especially in these two areas.

SUPPORT SYSTEM

The support system consists of rock bolts and SFRS. In the class-IV and V regions, steel

ribs and pre-grouting with micro-fine cement may be required.

7.3.8 PRESSURE SHAFT

A pressure shaft of size 3.5 m dia and 869m long (main shaft) is proposed downstream of

surge shaft. Pressure shaft drops vertically from El. 433.40m to El. 291.50m. The bottom

horizontal pressure shaft is provided with a slope of 1 in 12 from El.291.50m up to

El.227m in line with the center line of unit.

Main pressure shaft bifurcates into 2.50m dia and 32m long branch pressure shafts to feed

two turbine units in the power house. The size of the pressure shaft has been arrived

based on the detailed economic studies.

The diameter of the branch pressure shafts have been fixed in such a way that the

velocity is in line with the main pressure shaft. Velocity through pressure shaft works

out to around 4.42m/sec.

Considering thick overburden and vertical bends throughout the surface alignment,

underground pressure shaft is proposed. Two alternatives, one, connecting the top and

bottom horizontal pressure shaft with an inclined shaft and another, connecting the two

with a vertical shaft were examined. It was found that the length of the bottom horizontal

pressure shaft is relatively less with an inclined shaft and is suitable from economic




Page: 171

considerations. However, from construction point of view, as vertical pressure shaft

is preferable, the same is proposed.


For top horizontal pressure shaft, the alignment pass through rock with superincumbent

cover including overburden varying from 84m near top bend to 110m near surge shaft.

However, rock cover above horizontal pressure shaft varies from 57m (El. 490.5m) near

bend to 74m (El. 507.36m) near surge shaft. The subsurface information from exploration

and results of rock mechanic test indicate sufficient suitable rock cover over the

structure exists in this part of pressure shaft and is anticipated to negotiate

generally fair to good rock with patches of very good and poor to very poor rock class as

20% in class-II, 70% in class-III, 5% in class-IV and 5% in class-V.

The vertical pressure shaft shall pass through rock with superincumbent cover including

overburden of 84m near top bend of pressure shaft EL. 490.5m. The subsurface

information from exploration and results of rock mechanic tests indicate that

sufficient and suitable vertical as well as lateral rock cover exist around vertical pressure

shaft and is anticipated to negotiate generally fair to good rock with occasional weak

features.

The bottom horizontal pressure shaft shall pass through rock with superincumbent cover

including overburden varying from 230m near vertical pressure shaft side to 72m near

power house side. For the first 540m of bottom pressure shaft, rock cover above structure

can be varying between 37m (El. 272.5 m) near power house and 205.9 m (El. 480.7m)

near vertical pressure shaft. The subsurface information from exploration and results of

rock mechanics test indicate that sufficient rock cover exists over the structure and

bottom horizontal pressure shaft is anticipated to negotiate generally very good

rock with intermediate length of fair and patches of poor to very poor rock class as 68%

in class-II, 25% in class-III, 5% in class-IV and 2% in class-V for the first 540m length and

20% in class- II, 65% in class-III, 10% in class-IV and 5% in class-V.

ROCK SUPPORT SYSTEM FOR PRESSURE SHAFT

The Pressure Shaft will negotiate different rock types of variable strength with different

tunneling conditions along its length ranging from good rock to very poor rock. The

tunnel excavation will be done by drill and blast method with full face excavation.




Page: 172

In order to design the initial support system for the tunnel, the rock mass along the

tunnel was categorized into five groups based on RMR values/Q values, and the support

system for each group as mentioned in the below table was designed for both main

pressure shaft and branch pressure shaft.

The supporting system comprises of rock bolts, SFRS and steel ribs as mentioned in the

below Table 7.3. In the class-IV and V zones, pre-grouting with microfine cement may be

required. Forepoling, will be resorted as per requirement while boring in class V type of

rock. Probe drilling shall be resorted for identifying the problem areas and suitable prior

remedial measure shall be kept ready before hand.

Table 7.3 Rock Support Systems

Main Pressure Shaft

Rock Mass

Rating

Length

(%)

SFRS

(mm)

Rock bolt (25Ø)/ Anchors Steel Ribs/ Lattice Girder

Remarks

Length (m)

Longitudinal Spacing (m)

I - Very Good rock RMR: 100-81 Q: 100 to 40

0 Generally no support required except spot

bolting and SFRS at local region.


60 50mm in

crown

2.5m long rock bolt, 5 Nos.

2.0 m Nil




1.75 m Nil



2.5m long rock hollow core SDA, 9 Nos.


Pre-grouting with

micro fine cement




1.5 m ISMB 200 @ 500 mm c/c


Branch Pressure Shaft

I - Very Good rock RMR: 100-81

0 Generally no support required except spot

bolting and SFRS at local region.




Page: 173

Q: 100 to 40


20 50mm in

crown


2.0 m Nil




1.75 m Nil





Pre-grouting with

micro fine cement




1.5 m ISMB 150 @ 500 mm c/c


7.3.9 POWER HOUSE

Mawphu H.E.P.(Stage-II) envisages installation of 2 units, each of 42.5MW in a surface

Power House with Machine Hall of size 31.0 m (L) x 18.0 m (B) x 30.50 m (H) on the right

bank of the Umiew River. 23.0m long Service Bay is provided at the right side of the

Machine Hall. Control Block of size 12.0 m (L) x 18.0 m (B) x 23.50 m (H) is provided on

the left side of the Power House. Transformer/GIS Hall of size 66.0 m (L) x 12.0 m (B) x

18.0 m (H) is proposed upstream of the Machine Hall. 51m long tailrace channel

including Recovery Bay is proposed to discharge Power house water back into the

Umiew River.


A surface power house shall be accommodated in greyish, medium to coarse

grained, strong, moderately jointed to massive granite gneiss. The Surface power house is

located on the subdued topography of right bank hill with a lateral distance of 45-60m

towards the hill side. The structure has been explored by two drill holes, aggregating

length of 110m. Assessment of subsurface conditions and its geotechnical evaluation has

been carried out based on surface exposures near the river bed and the drill hole DH 101




Page: 174

and DH-102. The long axis of surface power has been oriented in N119°direction i.e.

perpendicular to prominent strike of foliation (N028°-N208).

Two geological sections have been developed w.r.t the power house for better appraisal

of geological and geotechnical conditions. It is evident from these section that height of

cutting in the rock will around 38m whereas in overburden it will be of the order

of 45- 50m.Coefficeint of permeability in overburden ranges from 0.29X10-3cm/sec to

2X10-3cm/sec which indicate highly pervious nature of overburden. Since overburden is

of river borne material indicative of a pre-existing river terrace, presence of water table at

a depth of 12 - 14m will make this material more susceptible to instability. Accordingly in

view of very high rainfall, the project area receives, elaborate and effective slope

stabilization measure to avoid surcharging of the overburden and erosion of slope

due to storm water shall be adopted to maintain long term stability of the cut slope.

Surface power house has been placed suitably with respect to strike of foliation. However

in view of sub parallelism of width wise excavation line of service bay viz-a –viz. the

strike of foliation and dip of foliation being towards excavation, plane failure is

anticipated. In view of the same notwithstanding the limited cutting at service bay

section appropriate support measures needs to be kept in provision which would include

6m long rock bolts with spacing of 2 to 3m.

Apart from this foliation, S2(030/71) joint set striking almost parallel to the power house

alignment ,dipping steeply from upstream wall of power house towards the power house

pit and has the potential to create unstable wedge due to toppling effect in the upstream

wall. The set combining with other limiting planes would generate plane failure on the

downstream wall of Power house. Accordingly necessary support measure should be

kept in provision of suitable length of rock bolt, SFRS and pressure relieve

arrangement. In view of predominance of adversely oriented joints enhancement of

support in the form of longer rock bolts exceeding 6m may have to be installed in the top

one third portion of rock slope. However the same shall be decided during the

progressive excavation of the pit.

As can be seen from slope stability analysis for back slope, set S2 (030/71) is seem to

contribute in formation of unstable wedges by topple failure which have a tendency to

fail toward the valley side or into the excavation. Apart from this toppling failure sliding




Page: 175

wedge failure also expected to be occur for the given cut slope by intersection of the joint

set S4(172/80) and joint set S3 (261/78) in which sliding direction of wedge is 222/75.

Permeability in rock ranges from 2-5 Lugeon indicating its fairly tight nature

of discontinuities. However, higher Lugeon reported only from the overburden bedrock

interface or from the fractured zones. Accordingly pressure relieve arrangement in each

wall of the power house shall be made.

Generally Core recovery in rock vary from 80-95% and RQD vary from 30-80%.In view of

above during excavation in selected weak media consolidation grouting shall be resorted.

However Rock mechanics test conducted on the cores samples from Power House area

reveals the UCS value of 106 to 137 MPa. It is therefore concluded that foundation of the

surface power house shall be in sound rock.

The entire excavation for Power house pit shall be in bedrock having indicative

RMR (without rating adjustment) ranges from 50 To 59 computed on the basis of

geotechnical parameter collected from the outcrops and collating the finding from

boreholes DH-101 and DH-102 in which bedrock was encountered at El 268.6m and

262.2m respectively.

POWER HOUSE CUT SLOPE SUPPORT SYSTEM

Keeping in view of the geology and topography existing there, a flatter slope of 1.5 (H):

1(V) has been proposed for the overburden with slope support measures in the form of

Geo- Textile, Grouted Anchors, low pressure consolidation grouting and Drainage holes

with filters for relieving the hydrostatic pressure. Berms with a height of 10m have also

been proposed which will not only serve the purpose of stabilizing the Power House cut

slope but also facilitate the excavation activities during construction. Berms width is kept

as 5m including drain. Toe drains of 500mmx500m with 1 in 500 slopes have also been

planned to collect and discharge the rain water to a suitable location. Cut slope of 1 (H):

6(V) has been planned for the rocky starta with adequate slope support in the form of

SFRS, Anchor bolts and Drainage holes with filters.




Page: 176

7.4 HYDRO-MECHANICAL WORKS

7.4.1 GATES AND PENSTOCKS

7.4.1.1 SCOPE

Following hydro-mechanical equipments consisting of various types of gates,

stoplogs, hoists, gantry cranes, and penstocks have been envisaged to divert and

control Umiew river waters during construction, to regulate reservoir levels and

facilitate the maintenance of the Turbine Generator units and various other

components of project during operation.

The general scope of supply and requirements are given in Annexure 7.1.

7.4.1.2 DIVERSION TUNNEL GATE: (8.0M X 8.0M -1 NO.)

For the diversion of water during construction stage, one numbers of 7.0 m horseshoe

shaped diversion tunnel has been proposed on the Left bank of the river.

Table 7.4: Technical data for Diversion Tunnel Gate as per IS: 4622:2003

Item Particulars

No. of Tunnel 1no

No. of Gate 1no

Clear Width of Opening 8.0 m

Clear Height Of Opening 8.0 m

Crest Level El. 446.00 m

Top of Coffer Dam El. 457.50 m

Design Head 12.0m

Operating Condition Lowering : Flowing water condition, and

Lifting : Under unbalanced head condition

Gate Lifting Speed 0.5 m/min

Gate Lowering Speed 0.5 m/min

Type of Hoist

Fixed Rope Drum provided on regulating

platform and Trestles.

Type of Sealing arrangement and seals.

Downstream Sealing: Music Note Type

Teflon Cladded Rubber Seal IS: 11855

Lifting Height 12.0m




Page: 177

For 7.0 m horseshoe shaped diversion tunnel one gate of size 8.0m x 8.0m is proposed at

the inlet portals to facilitate regulation during diversion and plugging before

commissioning of the project. This gate is provided with individual rope drum hoist and

designed as fixed wheel type gate having downstream skin plate and downstream

sealing. The sill level of gate is kept at EL.446.00m and the gate is to be designed for a

head of 12.0m corresponding to Top of coffer dam level El. 457.50m plus projected

overflow depth.

On the other hand hoist capacity of the gates is determined for their operation during

diversion and shall be calculated for water head corresponding to Cofferdam top level of

El. 457.50m.

The gate shall be operated by means of electrically operated rope drum hoist of adequate

capacity, located on the hoist platform installed over trestles above deck level, EL.

457.50m.

7.4.1.3 STOPLOGS FOR SLUICE SPILLWAY RADIAL GATES: (8.0M X 16.2M – 1SET)

For the passing of the water downstream for maintaining reservoir level 5 Nos.

Sluice Spillway Radial gates of 8.0m x 11.5m have been envisaged.

Stoplog units shall be required to be lowered in the stoplog groove of a particular bay, the

radial gate of which is under inspection/maintenance. The stoplogs shall be lowered

under flowing water conditions and lifted under balanced head condition. Inspection,

maintenance and repairs of radial gate shall be planned to be started and completed

preferably in lean period. Each stop log unit shall be self closing i.e. by gravity under its

own weight. The stoplog units shall be handled by a gantry crane of adequate capacity.

For the maintenance of 5 numbers of Sluice Spillway Radial gates, one sets of stoplogs,

each set consisting of 7 units of size 8.0m x 2.32m shall be provided.

Table 7.5: Technical data for Sluice Spillway Radial Gates as per IS: 4622:2003

Item Particulars

No of Opening 4.0

No of Sets 1(Each set consists of 5 interchangeable units,

1 top unit and 1 bottom unit each of size 7.0

m x 2.32m)




Page: 178

Clear Width of Opening 8.0 m

Clear Height Of Opening 16.2m

Sill Level of stoplogs El. 442.81m

F.R.L El. 470.00m

Design Head 27.19m

Top of Dam El. 472.00m


Lifting : Top unit shall be crack opened to

achieve balanced head condition

Type of Hoist Gantry Crane

Lifting Speed 0.75 m/min

Lowering Speed 0.75 m/min





Automatic engaging and disengaging

Lifting Beam

1 No.

When not in use the stop logs shall be stored on latches in the grooves above

FRL and one stoplog storage bay provided on Dam Block No.3. One number

automatically engaging and disengaging lifting beam shall be provided to facilitate

operation of the stoplogs with the help of gantry crane.

The stop log units for Sluice Spillway Radial gates shall be of fabricated steel construction

with upstream skin plate and downstream sealing. The units shall be capable of use in

any of the 5 openings. The stop log units shall normally be lowered in flowing water

condition and lifted in balanced head conditions when water level is at Full Reservoir

Level El. 470.00m or below it. All the stop log units except the top unit having top seal

shall be inter-changeable.

On the other hand hoist capacity of the stoplogs is determined for their operation during

maintenance of radial gates and shall be calculated for water head corresponding to FRL

El.470.00m.




Page: 179

7.4.1.4 SLUICE SPILLWAY RADIAL GATES: (8.0M X 11.5M - 5NOS.)

All the gates shall be operated with hydraulic hoists of adequate capacity and shall be

designed to regulate discharge under design heads and flow conditions mentioned herein

after:

The Sluice spillway radial gates shall normally remain in closed position during power

generation. When the water level in the reservoir starts rising above the Full Reservoir

Level i.e. EL 470.00m the FRL will be maintained by operating these gates.

The Sluice spillway radial gates shall also be operated to flush out the deposited silt

during the periods of heavy discharges. Since there would be lot of abrasion due to high

velocity water flow carrying silt load, it is proposed to provide skin plate of

stainless steel conforming to AISI 420 grade steel. Also, the spillway profile

downstream of radial gates shall be steel lined upto height of 1m higher than max.

discharge nape.

Table 7.6: Technical data for Sluice Spillway Radial Gates as per IS: 4623:2000

Item Particulars

No of Opening 5 Nos.

No of Gates 5 Nos.

Clear Width of Opening 8.0m


Radius of Gate 14.0m

C/C of Trunion Level EL. 455.80m

Sill level EL. 443.90m

Top of Dam EL. 472.00m

F.R.L El. 470.00m

Design Head 26.1m


Lifting : Under unbalanced head condition

Gate Lifting Speed 0.50 m/min




Page: 180

Gate Lowering Speed 0.50 m/min; 0.15m/min for last 30 cm

travels.


Type of Hoist Hydraulic Hoists

The crest of gate has been kept at El. 443.90m. The radial gates will be operated by an

individual hydraulic hoists of adequate capacity; consisting of power pack and shall have

twin hydraulic cylinders one on each side of the gate. The gates shall be operated locally

with a power pack from the control room, which would be located on top of the dam in a

room. The hydraulic cylinder hanging bracket elevation is kept at EL. 461.01m. The

cylinder shall be connects on downstream of the skin plate. The power pack shall have

provision to operate gate of adjacent bays. The trunnion shall be located at EL. 455.80m

such that it is at least 1.5 m higher than the nape.

The minimum speeds of travel of ate shall be: for opening 0.50 m/min., for lowering

0.50m/min., for last 30 cm travels in lowering 0.15 m/min.

To limit the sway of the gate during operation, guide rollers shall be provided on each

side of the gate. Each radial gate trunnion support beam shall be suitably anchored to the

pier. The gate shall be provided with dogging devices to hold the gate in fully raised

position when the hoist is disconnected from the gate during maintenance. These radial

gates shall be designed in accordance with IS: 4623: 2000 recommendations.

The gates shall have Teflon cladded side and top seals and wedge type rubber bottom

seal. The seals shall be designed and constructed as per IS: 11855: 2004 and IS 15466: 2004.

7.4.1.5 INTAKE TRASH RACKS (5.0M X 2.0M -2SETS/20 PANELS)

The trash racks shall be required to be installed in the trash rack grooves of Intake

structure U/S of Emergency gate groove to prevent entry of extraneous material into the

water conductor system. These shall be of fabricated steel construction consisting of trash

bars supported on horizontal girders, which in turn shall be supported on end

channels/members to bear against the downstream face of slots. Trash racks for one

opening shall be split into two vents each and each vent consists of 10 panels of 5.0m

width and 2.0m height. The trash rack sill is kept at El.452.00m and shall be provided up

to the top of intake for cleaning with trash cleaning machine.




Page: 181

For easy handling trash rack shall be divided into no of panels of equal height. The size of

panel shall be 5.0m x 2.0m (W x H) and as such there shall be 20panels for the intake

opening. The panels shall be interchangeable and each unit shall have two lifting points.

The trash racks panels shall be handled by any winch/ crane available at the project

using an automatic lifting beam capable of grappling/un-grappling automatically under

water. The lifting beam shall also travel in the same groove as the trash racks. The trash

rack shall be designed for differential head of 6.0 to 7.0m in accordance with the

provision made in IS: 11388:1995. The velocity through the racks shall be restricted1.5

m/second Cleaning of trash racks shall be done by trash rack cleaning machine. Each of

the ten trash rack sets corresponding to each opening would be aligned along to the right

bank of dam and shall be inclined at 10 degrees with the vertical to facilitate cleaning of

the T-racks mechanically. All the trash rack panels will be kept in a straight line so that

one single unit of trash rack cleaning machine could be used for all the units.

Table 7.7: Technical data for Trash Rack as per IS: 11388:1995

Item Particulars

No. of Intake Tunnels/Bays 1 Nos.

No of Opening in each bay 2 Nos.

No of Trash Rack panels per Opening 10 Nos.

Total no. of Trash rack panels 20 Nos.

Trash Rack Panel Size 5.0m x 2.0m

Crest Level El. 452.00m

Top of Dam El. 472.00m

Design Head 6.0m and 7.0m Differential Head for bars and

supporting members respectively.


Trash racks panel shall be cleaned with the help of a trash cleaning machine (TRCM)

which shall also have log grappling attachment for removing the trees. The machine shall

be hydraulically operated.

7.4.1.6 TRASH RACK CLEANING MACHINE (TRCM)




Page: 182

This Automatic Trash Rack Cleaning Machine shall be provided at the top of intake

structure at EL 472.00m and will travel on rails of length 16.0m. This machine shall be

provided with wheel type bucket for proper travelling on the Trash Rack support

channel. Side Guide rollers shall be provided on this bucket for its proper alignment on

the Trash Rack support channels. The bucket shall be raised/ lowered by an electric hoist.

This machine shall also be provided with the hydraulic system for the purpose of tilting

during it’s unloading. The TRCM shall be provided with wheel and rail for its movement

on the intake structure so as to cover all the Trash rack bays for cleaning of the trash

accumulated in front of Trash Racks and for removing debris/logs along the intake

structure. Longitudinal motion shall be performed with the help of an electric motor

provided on this machine. The TRCM shall be out door travelling type machine. The

hoist and longitudinal motors shall be of suitable capacity totally enclosed fan cooled,

squirrel cage type design to suit 3 phases 415/440V AC, 50 HZ conforming to IS-325:1996.

The TRCM shall also be provided with a 2 T capacity log grappling mounted on a

hydraulic log boom.

7.4.1.7 INTAKE EMERGENCY GATE: (4.8M X 4.8M – 1NO.)

At the inlet of water conductor system, one no. fixed wheel type service gates and one

number emergency gates is proposed. The emergency gate would be at upstream of the

service gate after the Bell mouth entry of tunnel. The size of the opening, where gate is to

be installed shall be 4.8m x 4.8m.

The gate shall be lifted in balanced head conditions. However gate shall be designed to

close under water flowing condition. This gate is provided with individual rope drum

hoist and designed as fixed wheel type gate having upstream skin plate and upstream

sealing. The sill level of gate is kept at EL. 452.00m and the gate is to be designed for a

head of 18.0m corresponding to FRL El. 470.0m

The gate shall be operating with the help of a electrically operated rope drum hoist of

adequate capacity. The Gate shall be designed as per IS: 4622:2003.

Table 7.8: Technical data for Intake Emergency Gate as per IS: 4622:2003

Item Particulars

No of Intake Tunnel 1 No.




Page: 183

No of Emergency gate 1 No.




F.R.L El. 470.00m

Design Head 18.0m


Upstream Sealing: Music Note Type Teflon

Cladded Rubber Seal IS: 11855


Lifting : Under balanced head condition.



Type of Hoist




7.4.1.8 INTAKE SERVICE GATE: (4.8M X 4.8M – 1NO.)

For the inspection and maintenance of water conductor system, one number fixed wheel

type service gate of size 4.8m x 4.8m with upstream skin plate and sealing, shall be

provided downstream of the emergency gate. This gate shall be designed to withstand

full static head corresponding to FRL El. 470.00m water level. The lifting of gates shall be

under unbalanced head conditions with the help of individual Electrically Operated Rope

Drum Hoists of adequate capacity. The gate shall be self closing under its own weight

under water flowing conditions.

This gate is provided with individual rope drum hoist and designed as fixed wheel type

gate. The sill level of gate is kept at EL. 452.00m and the gate is to be designed for a head

of 18.0m corresponding to FRL El. 470.0m.

Table 7.9: Technical data for Intake Service Gate as per IS: 4622:2003

Item Particulars

No of Intake Tunnel 1 No.




Page: 184

No of Service gate 1 No.




F.R.L El. 470.00m

Design Head 18.0m





Lifting : Under unbalanced head condition.



Type of Hoist




7.4.1.9 SURGE SHAFT GATES: (3.5M X 3.5M - 1NO.)

1 No. pressure shaft of 3.5m diameters take off from the surge shaft. The pressure shaft

shall have 1 no. of 3.50m x 3.50m size Vertical Lift fixed wheel type gate provided at their

entrance. The Pressure shaft shall carry water to feed 2 turbines. The role of surge shaft

gates is of prime importance and shall facilitate isolating the Pressure shaft for their

repair /maintenance.

This gate is provided with individual rope drum hoist and designed as fixed wheel type

gate having downstream skin plate and downstream sealing. The sill level of gate is kept

at EL.431.65m and the gate is to be designed for a head of 35.35m corresponding to FRL

El. 470.00m. The gate shall be operated by means of electrically operated rope drum hoist

of adequate capacity, located on the hoist platform installed over trestles at top of surge

shaft, EL. 492.00m.

Table 7.10: Technical data for Surge Shaft Gate as per IS: 4622:2003

Item Particulars

Number of gate 1 No.




Page: 185

Clear width of opening 3.5m

Clear height of opening 3.5m

Sill level of gate El. 431.65m

Maximum Surge level El. 488.72m

Static Level/ FRL El. 470.00m

Top of the Surge Shaft El. 492.00m

Design Head 35.35m

Type of Gate Fixed Wheel Gate


Downstream Sealing: Double stem Type


Operating Condition Lowering: Flowing water condition, and

Lifting: Under unbalanced head condition.

Lifting Speed 0.75m/min

Lowering Speed 0.75m/min

Type of Hoist



Lifting height 61.0m

7.4.1.10 STEEL LINED PRESSURE SHAFT

The water conductor system from the Dam Intake to the Power House consists of one no.

steel lined pressure shaft of diameter 3.5 m originate from surge shaft. Elevation of the

centre line of the pressure shaft at surge shaft is 433.40m. This pressure shaft branch in to

the two penstocks of dia. 2.5m each to feed two number generating units. The pressure

shafts shall be designed for the following parameters.

Diameter of steel liner 3.5m

Material of steel liner IS: 2002 Gr. 3 or Equivalent.

SUMITEN 610F/DILLIMAX 500 ML or Equivalent

Design Discharge Pressure Shaft 44.88 cumecs. Designed Velocity 4.66 m/sec.




Page: 186

Pressure shaft steel liner with transition, bends, branch pipes, manholes, Thrust collar etc.

having the following data:

A. Main liner 3.5m dia.

a) Length of Top horizontal Portion 45.00 m

b) Length of Top Vertical Bend 23.56 m

c) Length of Vertical Portion 124.91 m

d). Length of Bottom Vertical Bend 22.32 m

e) Length of Inclined Portion 589.87 m

f) Length of Bottom Horizontal Portion 57.05 m

Total length of Pressure Shaft 863.95 m

B. Branch pipes 2.5m dia.

Length of branch penstock Each 32 m

C. Centre line of the unit EL. 229.5 m

FRL EL 470 m

The Steel Liner shall be designed for the internal as well for external water pressures. The

dynamic loads have also been considered while designing.

The grades of boiler quality steel for the fabrication have been selected as per codal and

design requirements.

7.4.1.11 DRAFT TUBE GATES: (3.75M X 2.35M - 2NOS.)

In order to isolate any of the units from the tailrace side, without affecting installation

and operation of the remaining units, 2 nos. of draft tube gates of size 3.75m x 2.35m are

provided for all both the units. These gates shall be provided with downstream skin plate

and downstream sealing in accordance with IS: 11855 & 15466 considering flow from the

TRT side.

The sill level of gate is kept at EL. 223.98m and the gate is to be designed for a head of

12.02m corresponding to Maximum tail water level El. 236.00m.

The gate shall be operated by means of electrically operated rope drum hoist of adequate

capacity, located on the hoist platform installed over trestles above deck level, EL.

241.60m.




Page: 187

Table 7.11: Technical data for Draft Tube Gate as per IS: 4622:2003

Item Particulars

Number of Draft Tubes 2 Nos.

Number of gates 2 Nos.

Clear width of opening 3.75m

Clear height of opening 2.35m

Sill level of gate El. 223.98m

Maximum Tail Water level El. 236.00m

Top of Piers El. 241.60m

Design Head 12.02m

Type of Gate Fixed Wheel Gate




Operating Condition Lowering: Flowing water condition, and

Lifting: Under balanced head condition.

Lifting Speed 0. 5m/min

Lowering Speed 0.5m/min

Type of Hoist



Lifting height 18.0m

Annexure 7.1

Sl.No.

Description

No. of sets

Size of gate

Type of gate

Hoist

A-01

Diversion Tunnel

Gate

1 No. 8.0m x 8.0m Fixed Wheel Rope drum Hoist

A-02

Stop logs for

Sluice Spillway

Radial gates

1 set 8.0m x 16.2m

Stop logs Gantry Crane




Page: 188

A-03

Sluice Spillway

Radial gates

5 Nos. 8.0m x 11.5m Radial Hydraulic Hoist

A-04

Intake Trash

racks

2 sets / 20 pannels

5.0m x 2.0m inclined(10º) TRCM

A-05

Intake

Emergency gate


A-06

Intake service

gate


A-07 Surge shaft gate 1 No. 3.5m x 3.5m

Fixed Wheel Rope drum

Hoist A-08

Main Pressure

Shaft

1 No. Dia=3.5m, Length – 864 m

Branch Penstock 2 Nos. Dia=2.5m, Length – 32 m each

A-09 Draft Tube Gates 2 Nos. 3.75m x 2.35m Fixed Wheel Rope Drum Hoist

CHAPTER - VIII

DESIGN OF ELECTRO-MECHANICAL WORKS




Page: 189

CHAPTER - VIII

DESIGN OF ELECTRO-MECHANICAL WORKS

8.1 GENERAL

The surface powerhouse shall have two generating units of 42.5MW each with all the

auxiliary facilities such as cooling water system, heating, ventilation and air conditioning

system, fire protection system, oil pressure system, overhead crane system, compressed

air supply system etc. The total generating capacity of power house shall be 85MW.The

entire two units would be identical and comprise of vertical axis Francis turbine directly

coupled with synchronous generator. Power will be generated at 11kv voltage level and

stepped up to 132kv level by generator step up transformer. Both the generating units

will be provided with 10% continuous overload capacity as per CEA grid connectivity

regulations. The Generator step up transformer with 10% overload capacity shall be

provided.

The powerhouse will comprise of the Service Bay, Machine Hall, Generator Floor,

Turbine Floor, Transformer Deck (located at the upstream of the powerhouse).145kV Gas

Insulated Switchgear will be installed in the GIS hall, at the floor above the transformer

deck and the Control Block will be located on one side of the powerhouse.

The terminal equipment for 132kV double circuit transmission line would be placed in

the pothead yard located near the powerhouse. The connection between pothead yard

and 145kV Gas Insulated Switchgear would be made through 145kV XLPE cables to be

laid in a cable duct. 132kV equipment located at the pothead yard will consist of

capacitive voltage transformers, wave traps, lightening arrestors, gantry structure etc.

8.2 TURBINE

The turbine selected is vertical Francis with rated speed of 428.6 rpm working under a

rated head of about 230.5m. The turbine shall be hydraulically and mechanically

designed for trouble free operation at all heads, between the maximum and minimum

normal head. The rated output of the turbine would be matching with a rated output of

the 42.5MW generators. The turbines will have a weighted average efficiency of about

93% and the peak efficiency of about 94%.

The runner and other critical under water components of the turbine will be of 13:4 Cr/

Ni Stainless steel with high resistance to silt abrasion. Suitable protection like HVOF




Page: 190

coating for the underwater turbine parts like guide vanes and runners will be provided to

mitigate silt erosion which will be finalized in consultation with the turbine designer.

The turbines will have provision of runner removal to facilitate repairs as and when

required. The runner removal will be done from the bottom, by dismantling the draft

tube cone assembly and after installation of temporary rails and supports to lower the

runner.

GOVERNORS

Each turbine shall be provided with an Electro hydraulic; Digital Microprocessor based

Governor for speed and output control, load sharing between units under any condition

of load and speed etc.The governor system shall be connected to and should be fully

compatible with the power station control and monitoring equipment.

The following functions will be included in the governor:

� Speed control at no load operation

� Automatic start and stop sequences, including automatic synchronisation

� Power output control; operation at output limitation with power feed back

� Frequency regulation

� Water level regulation (if required)

� Load sharing between the units in "joint control" mode

� Emergency shutdown in two different sequences

� Emergency shutdown on electrical failures.

� Quick shutdown in case of mechanical failures.

MAIN INLET VALVE

Each turbine will be provided with spherical inlet valve operated by hydraulic pressure

and proposed to install on upstream side of each turbine inlet to isolate the machines in

case of emergency and to afford flexibility of operation of the power plant. The valve will

be automatically closed/ opened after electrical signal from various electrical and

mechanical devices provided. The MIV shall be of 1700mm nominal. The valve body and

valve rotor would be made of cast steel. The material for valve seals will be stainless steel

(13% Cr & 4% Ni).

The valve shall be of dual seal type i.e. one main or service seal and one repair or

maintenance seal for repairing the service seal without the need for dewatering the

penstock header/pressure shaft. The valve will be designed to withstand the maximum

pressure inclusive of water hammer.




Page: 191

It will be operated by the same grade of oil as of the governor oil to open and the closing

shall be by counter weight mechanism. The valve shall be provided with emergency

closure function also i.e. capable of closing against full flows.

The opening and closing of butterfly valves shall normally be done under balanced water

condition. Suitable number of air release valves shall be provided at the appropriate

location on the downstream side to allow the air trapped in the penstock to escape when

it is filled with water through the bypass valve and for supplying / admitting the air

when the valve is suddenly closed.

PENSTOCK PROTECTION VALVE

1 (One) number of 3500mm diameter butterfly type valve will be provided between the

surge shaft and the vertical pressure for maintenance of the MIV seals and pressure shaft

without dewatering of the head race tunnel. The valve shall be provided with control

panel, oil pressure unit and associated auxiliary equipment.

8.3 GENERATORS

Synchronous generators shall be vertical axis, salient pole. Rating of generator shall be

47.3MVA, 0.9 power factor lagging, 428.6 rpm and 50Hz conforming to IEC 60034.

Generation voltage selected is 11KV. The choice of generation voltage shall be further

reviewed during detailed engineering stage in consultation with the manufacturers.

Generators shall be suspended type with air cooled stator, rotor, turbine shaft, thrust and

guide bearing, upper bracket, lower bracket and other component. The efficiency of

generator shall be 98%.

Excitation system for generator shall be digital static excitation system. Necessary power

for excitation system shall be obtained directly from 11KV bus duct through excitation

transformer. This excitation system shall consist of AVR and Thyristor Bridge with 100%

redundancy.

The generator shall be air cooled where air after cooling shall be cooled by stator cooler

and circulated inside generator by rotor. Water for stator cooler shall be circulated by

closed loop cooling water system.

Each generator shall be provided with pneumatically operated brakes of sufficient

capacity to stop the rotating parts of the generator and turbine from a predetermined

speed. The generator will be grounded through Neutral grounding transformer.




Page: 192

The generator stator and rotor windings will be provided with Class F insulation but

temperature rise with maximum output will be limited to that corresponding to Class B

insulation.

The generator phase terminals will be brought out of the barrel for connection to Isolated

Phase Bus Ducts.

Online monitoring equipment will also be provided for the following:

� Vibration monitoring,

� Shaft current monitoring,

� Stator winding partial discharge monitoring, and

� Rotor air gap monitoring.

8.4 AUXILIARY ELECTRICAL SERVICES

8.4.1 MAIN STEP UP TRANSFORMERS

Two (2) numbers of 52MVA three phase generator step up transformer will be provided

which will step up 11KV generation voltage to 132KV transmission voltage. The

transformer will meet 10% continuous overload capability of generator. The transformer

will be located at the upstream of power house at service bay elevation. Transformer will

be provided with rails for movement in case of maintenance, replacement and installation

purpose. The type of cooling for transformer will be ODWF with oil directed water forced

coolers. A mulsifire protection system including fire detection, fire alarm and sprinkling

will be installed around transformer for adequate fire protection. The transformer will be

compliant to IS 2026.

The transformers will be provided with necessary protective and monitoring devices

including Buchholz relay, oil temperature and winding temperature indicators, pressure

relief device etc.

Transformers will be provided with off circuit tap changer at the HV side, with range of

+2.5% to -7.5% in four steps, each of 2.5%.

8.4.2 GENERATOR – TRANSFORMER CONNECTIONS

11kV isolated phase bus ducts conforming to IS 8084 will be provided for connection

between the generator and generator step up transformers.

Tentative current rating of the main run bus ducts would be 3000A.




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The bus ducts will be naturally air cooled and the temperature rise limits shall be as per

IS 8084 and as below:

� Bus duct conductor – Aluminium – 40 deg C above ambient temperature

� Bus duct enclosure – Aluminium – 30 deg C above ambient temperature

The bus ducts will be complete with continuous type Aluminium enclosure, conductor

supported on support insulators with self aligning arrangement, wall frame assembly,

seal off bushing, flexible connections at the termination points, the tap off bus ducts for

connection with LAVT cubicle, Excitation Transformer, Unit Auxiliary Transformer etc.

On the neutral side, the bus ducts, after forming star will be connected with the neutral

grounding cubicle which will house the grounding transformer and the grounding

resistor.

8.4.3 145KV GAS INSULATED SWITCHGEAR

As sufficient space for accommodating 132kV outdoor switchyard is not available near

the powerhouse, it is proposed to provide a 145kV gas insulated switchgear with 7

(Seven) bays comprising of 2 (Two) generator incomers, 2 (Two) feeder bays, 2 (Two)

Station Auxiliary Transformer bays and 1 (One) bus coupler bay. The bus bar scheme

adopted is double bus scheme with a bus coupler.

The GIS equipment will be located on the floor above the step up transformers in the

transformer deck. The connection between the transformers and the GIS bays would be

done through 145kV SF6 gas insulated bus ducts (GIBD).

The feeder bay will be connected with 145kV XLPE cables through SF6 – Cable bushing.

8.4.4 145KV XLPE CABLES

The connection between the GIS feeder bay and the pothead yard will be made through

145kV XLPE cables. The cables will be 400sqmm with Copper conductors with

Corrugated Aluminium sheath.

The cables will be laid along a cable duct originating from the powerhouse. The duct will

be provided with drain to evacuate any drainage water entering the duct. The cables will

be clamped and routed along the duct with support structures designed to bear the cable

load and also withstand the short circuit forces.

The cables will be provided with the necessary, sheath voltage limiters and earth boxes,

which will be detailed during the detailed engineering stage.




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8.4.5 CONTROL AND MONITORING SYSTEM

Supervisory control and data acquisition system (SCADA) for control and monitoring of

power plant will be provided using man machine interface and data acquisition system

(DAS) computer. The system is intended to meet all the operating functions of power

plant which are normally performed by power plant operators. The control system will

be configured in mainly three control levels.

The first level will be station control level which would comprise of a number of

functional systems for supervisory control and human machine communication. This

level will cover overall control and supervision of the station.

The second level will be local level at unit control board which would comprise of a

number of functional groups such as generating units, bay controllers, generator

transformers, gas insulated switchgear etc.

The third level will be equipment control level which can directly and manually control

equipment and will be mainly used for testing and adjustment.

Overall control will be executed from the control room. The highest control level will be

the operator console. This will consist of a reliable process computer, video display units,

printer units and operating keyboards with trackballs. Operation from the central control

room where operator will get information and will have the necessary controls to

perform a simple and reliable operation of the generating units, step-up transformers,

132KV switchyard, and common station auxiliaries/services will be provided. The

system will have provision for generation of customized trend reports. There will be a

provision for event logging with time stamping at a least count of 1ms.

The data transmission between the station control level and the local control level will be

accomplished by means of LAN with high speed large capacity data bus of optical fibre

cables.

A mimic bus diagram board will be provided to depict the status and operational

information of the transmission lines, the EHV bus, the generating units and the station

service circuits in real time and to operate the equipment with functional switches. Dam

water level indicators will also be provided on this board.

The whole system will have a total redundancy in the main CPUs, programmable

controllers of the local control units, LAN system and power supply units. Even if one

group has a failure, the backup group will instantly succeed the operation seamlessly.




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8.4.6 PROTECTION SYSTEM

Hydro turbo- generator should be protected against mechanical, electrical, hydraulic and

thermal damage that may occur as a result of abnormal condition in the plant or in the

utility system to which plant is electrically connected. Fully graded protection system

with requisite speed, sensitivity, selectivity and reliability will be provided for the entire

station. The electrical protection system for generators, step up transformers, switchgear,

station auxiliary transformer, 132KV, 11KV lines etc will be provided with numeric type

integrated protection relays with 100% redundancy. Back up electromagnetic relay with

instrument transformer may be provided. Mechanical protection for temperature

detection of stator winding, stator core, bearing, governor oil pressure low/high, fire

protection may be provided as part of integrated numerical relay.

8.4.7 AC AUXILIARY POWER SYSTEM

The station auxiliary power will be supplied through 2 (Two) Nos., 5MVA, 132/ 11kV,

Oil filled, ONAN Station Auxiliary Transformers (SAT) located in the transformer deck.

The HV side of the transformers will be connected with the 145kV GIS bay and the 11kV

side of the transformer will be connected with 11kV switchgear through 11kV XLPE

cables.

The feeders emanating from the 11kV switchgear are as below;

� 2 Nos. Station Service Feeders,

� 1 No. Dam site feeder,

� 1 No. Colony feeder,

� 1 No. Valve house feeder and,

� 2 Nos. Spare feeders.

The station service feeders from the 11kV switchgear will be connected to 2 (two) nos. of

Station Service Transformers (SST), 1MVA, 11/ 0.433kV, Dry type. The LV side of the

SSTs will be connected with the Station Service Board (SSB) through 1.1kV, PVC cables.

The SSB will cater to all the station auxiliary loads and will also be interconnected with

the Unit Auxiliary Board (UAB) which will dedicatedly feed the unit auxiliaries. Some of

the major loads to be connected with the SSB are;

� Unit Auxiliary Boards 1 and 2,

� Drainage and dewatering pumps,

� EOT crane,




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� Elevator,

� Illumination system,

� Ventilation and air conditioning,

� DC battery chargers,

� Air Compressor system,

� Workshop and Lab, etc.

The incomings to the SSB will be interlocked and the SSB bus will be provided with bus

coupler to avoid charging of the bus with two different sources. The SSB will be located

in the Control block at the Service bay floor level.

The UABs will be supplied auxiliary power from the UAT (500kVA, 11/ 0.433kV, dry

type transformer) and also be connected with SSB.

Unit auxiliary board will be provided for each unit and will be installed on the generator

floor, below the machine hall. The major loads of the UAB will be;

� Cooling water pumps,

� Oil Pressure Unit/s (Governor and MIV),

� Governor,

� Excitation System,

� Hydrostatic pressure lube oil system,

� Generator transformer oil pump,

� Brake dust fan and carbon dust collector system feeders, etc.

Emergency power will be catered by 1 (One) no. of 750kVA, 415V diesel generating sets

(1 main and 1 standby) which will be located near the powerhouse at service bay

elevation.

8.4.7.1 POWER TO DAM SITE AREA

The distance between the powerhouse and dam site is about 5kms, a 11kV line is

proposed to be constructed for power transmission to the dam site. Electric power will be

required at the dam site for operations of the gates, illumination, dewatering pumps and

for powering other communication devices. For this purpose a distribution transformer

of 750kVA, 11/ 0.433kV, oil filled type will be provided along with an LT panel with

feeders for connectivity with the loads through 1.1kV, PVC cables.

1 No. of 750kVA DG set will be provided for emergency power supply to the dam site.




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8.4.7.2 POWER TO PENSTOCK PROTECTION VALVE HOUSE

The distance between the powerhouse and penstock protection valve house is about

3kms, a 11kV transmission line is proposed to be constructed to cater to the power

requirements at the valve house. The auxiliary power requirement at the penstock

protection valve is mainly governed by the oil pressure unit for valve operation. For

catering to the loads of this area, a 100kVA, 11/ 0.433kV, oil filled type distribution

transformer along with LT panel with feeders for oil pressure unit, illumination

equipment, dewatering pump etc. will be provided.

8.4.7.3 POWER TO COLONY AND OFFICE AREA

The distance from powerhouse to the colony and office area is about 200m. A 11kV line

will be constructed for feeding power to the Colony and Office area. A distribution

transformer with capacity of 500kVA, 11/ 0.433kV, oil filled type is proposed to be

installed for this purpose along with associated LT panel and cables to connect the loads.

8.4.8 DC AUXILIARY SERVICES

DC system in power house will be required for the stabilised power supply requirement

of electronic panel of control boards, supply to trip coils and closing coils of switchgear,

SCADA system, semaphores, field flashing requirement of generator and for emergency

lighting. Batteries for protection, control and emergency lighting will be 220V DC and

those for communication system will be 48V DC. Two set of 220V, 400AH battery bank

and battery charger with facility of boost charging and trickle charging with float mode

will be provided for the power house. 48V/24V DC system required for the

communication system, including PLC (power line carrier) system, programmable logic

control type control system will be provided using DC-DC converter fed by the 220V DC

system. The DC distribution board will be provided with adequate number of feeders to

supply DC power at desired locations. Uninterrupted power supply (UPS) will be

supplied to SCADA system for their power requirement. The batteries will be lead acid

type for long life and high capacity.

8.4.9 EARTHING SYSTEM

The purpose of grounding system is as follows-

� To keep dangerous potential arising out due to fault condition within safe limit.




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� To provide least resistance path for grounded neutral circuit.

� To facilitate to clear ground fault, to provide a means for discharging current from a

electrical equipment to be handled safely by operator.

Grounding system will be provided for power house, pothead yard, transformer/GIS hall

and other civil/ hydraulic structure. The power house will be provided with earthing

grid. All the current carrying equipment of power house will be connected with the

earthing grid for the safety of working personnel and equipment. Grounding platforms

will be installed at all switch operators inside the switchyard.

The earthing system will be designed in compliance with IEEE80. Necessary risers and

lighting spikes at the powerhouse roofs and structures will be provided to avoid

damages due to lightening strikes.

8.4.10 POWER, CONTROL AND INSTRUMENTATION CABLES

11kV XLPE cables will be used for connection between stations auxiliary transformers

and the 11kV switchgear, and 11kV switchgear to the station service transformers.

1.1kV grade PVC insulated Al power cables will be used inside the powerhouse for

supplying power to various auxiliaries, while for control cables 1.1kV grade PVC

insulated Cu cables conforming to IS 1554 will be used. The cables will be Fire Resistant

Low smoke type.

The instrumentation cables including fibre optic cables used will be immune to

electromagnetic interference. The number of pairs/ cores required will be as per the

requirement of the system.

All the accessories like cable glands, ferrules, cable trays, conduits of adequate sizes as

required for the installation of cables will be provided.

8.4.11 ILLUMINATION SYSTEM

A complete illumination system for power house will be provided. Illumination system

will consist of indoor lighting system, outdoor lighting system and emergency lighting

system. Illumination level will be decided as per requirement. Lighting system for power

house will be supplied from illumination board which will be connected to SSB board.

The indoor illumination scheme will have mainly twin tube light fitting and high

pressure metal halide/mercury vapour lamps. Outdoor illumination for switchyard,

dam, intake, tunnel area, valve house, parking area etc will be provided through sodium




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vapour lamps and fluorescent tubes. Emergency lighting for power house will be

provided from 220V DC board. DC lamp for emergency lighting will be provided in the

machine hall, control room, stairways, valve gallery etc. Incandescent lamp will be used

for emergency lighting. The lux level of the illumination system will be designed in

compliance with IS 6665.

8.4.12 TEST LABORATORY

There should be testing and measuring equipment in power house for measurement,

monitoring and detection of abnormalities in electrical equipment. High voltage testing

kit, Meggers, relay testing kit, vibration meter, BDV measuring equipment, oil testing kit,

calibrating devices and other general electrical, mechanical tools and equipment etc. will

be provided in power house.

8.4.13 COMMUNICATION SYSTEM

The powerhouse, Dams and all other vital installations e.g. valve house, intake etc. will

be provided and interconnected with a reliable communication system. Telephone system

will consist of connection through telephone exchange, power line carrier communication

(PLCC) system and VSAT system. The power house will consist of internal telephone

communication system and public address system. One private automatic branch

exchange (PABX) telephone system for power house internal communication with dam,

intake, valve house and other offices will be provided. Public address system will consist

of loudspeaker, microphone, and power amplifier. Public address system will be used for

fire/emergency warning and it will be linked with PABX system of power house for

remote calling of operating personnel in case of emergency situation. Control room,

turbine pit, security gate, pump house, valve house, offices, and conference room,

canteen etc. may be provided with internal telephone system. Power line carrier

communication (PLCC) will be provided for communication with load dispatch centre

and other substation. Internet connection will be provided through VSAT or will be

provided through internet service provider.

8.5 AUXILIARY MECHANICAL SERVICES

EOT CRANE

One (1) number of EOT crane of 150/30T is proposed to be installed in power house for

handling turbine, MIV, Generator component, during erection, commissioning and




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maintenance work. The crane will be provided with auxiliary hook to handle equipment

like runner, rotor shaft, turbine shaft, panel, pumps etc. The crane will be

cabin/pendant/radio controlled.

A 5T EOT crane will also be provided for GIS to facilitate erection and subsequent

maintenance of GIS.

EOT crane will consist of operator cabin, trolley, bridge, main hoist, auxiliary hoist,

electrical controls, safety devices, fittings and connections. EOT crane will have all the

necessary accessories to handle equipment, including wire ropes for handling main hoist

and auxiliary hoist.

8.5.1 COOLING WATER SYSTEM

Cooling water system is required for the following purposes in power house:

� Generator air cooler.

� Generator thrust and upper guide bearing cooler.

� Turbine guide bearing cooler.

� Shaft seal cooler.

� Generator step up transformer cooler.

A closed loop cooling water system with sump will be provided in power house with

required pumping arrangement to circulate the water. This water will be again cooled by

circulating the water through the heat exchanger to be located in tail pool. The cooling

system will consist of three identical cooling water pump, automatic backwash strainers,

strainer, flow sensors, water pressure measuring devices, monitoring and control devices,

piping and valves etc. Cooling water system of the entire unit will be interconnected

through isolating valve for redundancy. three nos. of cooling water pump will be

provided, two of these pumps will be main pump and other pump will be standby pump.

Each cooling water pump will be capable of supplying the total required cooling water

discharge for full load operation of the generating unit. In case of failure of main pump,

standby pump will be started automatically. Cooling water from discharge line will be

released back into the tailrace of respective unit.

8.5.2 DRAINAGE AND DEWATERING SYSTEMS

The dewatering system provides means for dewatering of main unit turbine and their

associated water passage for inspection and maintenance purpose. Water trapped

between main inlet valve and draft tube will be drained out to dewatering sump. Two




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nos. of dewatering pumps will be provided to pump out the water from dewatering

sump to above maximum level of tail pool. Dewatering sump will have two number of

continuous rated submersible pump of adequate capacity to dewater the entire water

passage of penstock, turbine and draft tube in a single shift operation without raising the

level. Level switches will be provided to monitor the level of dewatering sump and to

automatically start/stop the pump. Dewatering system will consist of necessary pipes,

non return valve, level switches, sensors, pressure transmitter, pressure gauge etc.

All the drainage water within the power house will be collected inside the drainage

sump. Two nos. of drainage sump on the either side of power house will be provided.

The seepage of the entire power house and leakage water from all the units of power

house will be routed to nearby drainage sump. Generator fire fighting water after

operation of fire fighting system will be also routed to drainage sump. The drainage

water will be discharged to the tailrace above the maximum tail water level through two

nos. of submersible pump. Float /level switches will be provided in the drainage sump to

monitor the level of sump and to start/stop the drainage pump automatically. The

drainage system will consist of isolating valve, non return valve, float/level switches,

pressure transmitter, pressure gauge and other necessary instrument. During detail

project report provision for interconnection of drainage sump and dewatering sump will

be considered. Provisions in the layout will be made for protection in main station

building against flooding. This provision will be in line with clause 39 of the CEA

regulations 2010, Technical Standards for construction of electric plants and electric lines.

The provision will be deliberated in the detailed project report.

8.5.3 FIRE PROTECTION

The fire fighting system will consist of fire detection, alarm and protection system. Fire

protection system as well as hydrant will be provided, complying with the guidelines of

Tariff Advisory Committee/National Fire Protection Association.

Generators are normally provided with automatic CO2 extinguishing system. Fire

hydrants will be provided for powerhouse. Water based fire protection system will be

supplemented by chemical fire extinguishers.

Outdoor generator transformer will be provided with automatic high velocity water

spray (Emulsifier) system. This system automatically detects, control and extinguish the

outbreak of fire. This system consists of a pipe ring around the transformer with nozzle




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spray at selected points. Water supply to pipe ring will be through deluge valve

assemblies.

Portable fire extinguishers will be provided inside the electrical and mechanical utilities

area of power house.

Medium velocity water spray system will be provided for the 132KV XLPE cable trench

which will be further deliberated during the preparation of detailed project report.

Water for common fire fighting system will be provided through overhead tank of

sufficient capacity located at suitable area. Water in tank will be supplied by fire fighting

pump from common cooling water header. Automatic operation of these pumps will be

controlled by level switches/sensors mounted on overhead tank.

8.5.4 HEATING,VENTILATION AND AIR CONDITIONING(HVAC)

The main purpose of the HVAC system is:

� To provide clean and tempered air.

� To furnish outside fresh and clean air for human comfort.

� To provide for cooling and heating of power house area as per requirement.

� To remove waste and heated air from generator.

� To prevent variation of temperature at different locations of power house area.

HVAC system will consist of fresh air supply blower, air conditioning plant, air handling

unit and exhaust fans located at various power house floor, and control room. Air

circulation will be through duct routed in power house. The HVAC system will function

as an integral part of overall fire protection and evacuation plan for the complex. The

ventilation system will minimize the circulation of combustion product should a fire

occur. In power house area where moisture condensation is anticipated, dehumidified air

will be supplied as condensation causes corrosion of metal and breakdown of insulation

of electrical equipment. The air before entering the power house will be cleaned as the air

laden with dust particle may have abrasive effect on electrical machinery and may

interfere with the operation of electrical and electronic devices and also give a dirty

appearance to power house. Air cleaner upstream of air fan will be provided for cleaning

of air before entering the power house. The size of the air filter will be decided by velocity

of air entering the power house.

When desired temperature and humidity inside the power house is not achieved by

natural or forced ventilation, air conditioning will be provided by cooling and heating of




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entering air at desired location for comfort of working personnel. The control block with

control room, protection relays area, conference room, office room area, machine shop

will be provided with air conditioning.

Ventilation and air conditioning system should be designed in accordance with IS: 4720-

1982.

8.5.5 COMPRESSED AIR SYSTEM

Compressed air system is required in power house for operation and to facilitate

maintenance and repair of electrical utilities. Service air, brake air and governor air are

needed in power house. High pressure compressed (HP) air will be provided for turbine

governing system and oil pressure system for operation of main inlet valve (MIV).

However, Nitrogen bottle arrangement will also be looked into during detailed project

report stage for in place of HP compressed air system.

Low compressed (LP) air system will be provided to cater to requirement of braking air

and servicing air. Each air pressure system will consist of one main and one standby

electrical pump, starter, two air pressure accumulator, two air dryer, control, safety and

isolating valves, moisture trap, air filter, pressure switch and piping arrangement etc.

Compressor should be heavy duty. Each air receiver should confirm to design

construction and testing requirement of the ASME,”Boiler and pressure vessel code”.

8.5.6 ELECTRICAL LIFTS AND ELEVATORS

1 (one) elevator will be provided in the control block of the powerhouse to enable vertical

movements of personnel in the powerhouse. The elevator will connect all the floors of

power house. The elevator will be suitable for carrying tools and small equipment. The

elevator will be provided with all the safety devices, alarm, fire fighting equipment etc.

There should be provision in the elevator for landing to nearest floor in the case of power

supply failure.

8.5.7 WORKSHOP EQUIPMENT

There will be provision for one mechanical workshop for all essential maintenance work

and onsite repairs. The standard workshop equipment like centre lathe, pedestal grinding

machine, hacksaw machine, fitters, benches/ racks, mobile welding set, miscellaneous

and cutting tools, welding sets etc will be provided.




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8.6 POWER EVACUATION ARRANGEMENT

It is proposed to provide two outgoing bays for evacuating power at 132kV level from

Mawphu HEP. This power would be pooled at Mawlai Substation of Meghalaya State

Electricity Board (MeSEB)/ Meghalaya Energy Corporation Limited (MeCL) and carried

through one number 132kV double circuit transmission line taking off from Mawphu

HEP.

CHAPTER - IX

INFRASTRUCTURE FACILITIES




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CHAPTER - IX

INFRASTRUCTURE FACILITIES

9.1 GENERAL

Mawphu Hydroelectric Project, Stage - II is proposed as a run-of-river scheme on the




bank of the river. Development of adequate infrastructure is a pre-requisite for timely

implementation of the project. Establishment of proper infrastructure considering the

existing facilities in the nearby area and the requirement of different work sites for

various activities goes a long way in speedy execution of the works minimizing delays in

project completion.

9.2 TRANSPORTATION

RAIL HEAD FACILITIES

The nearest broad gauge railway station is at Guwahati which is about 180 km from

project site.

ROAD TRANSPORT FACILITIES

State Highway is available from Shillong to reach Mawsynram, which is a small town at

about 60km from Shillong. Mawsynram is connected with Thieddieng village through

about 6km long foot track. Road construction is in progress from Mawsynram towards

Thieddieng village and about 4km long formation cutting from Mawsynram has been

completed. The dam site can be accessed from Thieddieng (at about 2km) through

footpath. The power house site is also accessed from Thieddieng village (at about 2km)

through footpath. There is no direct connectivity between dam site and power house site.

BY AIR The project area can be accessed from Guwahati airport, which is at about 120 km from

Shillong, the capital of Meghalaya.

9.3 CONSTRUCTION FACILITIES

Construction Facilities for Mawphu HEP (Stage-II) have been divided into the following




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Components:-

a) Project Roads including Temporary/Permanent Bridges

b) Site Offices and Residential/Non-residential Complexes

c) Workshops

d) Warehouses/Stores Complex

e) Muck Disposal Area

f) Explosive Magazines

g) Construction Plant Facilities

h) Land Requirement

i) Construction Power

j) Telecommunication

k) Water Supply System

l) Security & Safety Arrangements

9.3.1 PROJECT ROADS INCLUDING TEMPORARY/ PERMANENT BRIDGES

Motorable road is available up to Mawsynram. Access road from Mawsynram to

Thieddieng village is under construction by PWD, Meghalaya. So far, formation cutting

for a distance of about 4km has been completed in this stretch. At present, Thieddieng

Village is accessed by foot track. Proposed dam site and Power House site can be

accessed from Thieddieng Village only by foot paths. Therefore, new approach roads to

dam site and Power House are required to be built. Similarly, new approach roads are to

be built to other components as well as to various construction facilities of the project.

The proposed roads to various components/construction facilities of the project include

approach roads to

� Dam Site & Power Intake

� Diversion Tunnel Inlet and Outlet

� Various Adit Portals

� Surge Shaft top

� Power House

� Muck Dumping/Disposal Area

� Various construction facilities

� Magazine

� Workshops




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� Store room/Ware house

About 19 km long approach roads (to all the project components and construction

facilities) have been proposed. Five bridges, two permanent bridges of about 100m long

and three temporary bridges of about 50m long each have been proposed. In addition, 20

nos. of culverts at nallah crossings have also been proposed.

Details of the proposed project roads are as follows:

SL No. DESCRIPTION LENGTH

1 Access Road From Adit-1 Portal To Dam Site 1200

2 Access Road from Adit-3 portal to Adit-1 portal 2500

3 Access Road to Adit-3 Portal 500

4 Access Road to Adit-2 Portal 250

5 Access Road to Surge Shaft 3800

6 Access Road from Thieddieng Village to Surge Shaft Road

4000

7 Quarry Roads 6000

TOTAL LENGTH OF ALL ROADS 18250(approx.)

9.3.2 SITE OFFICES AND RESIDENTIAL/ NON-RESIDENTIAL COMPLEXES

9.3.2.1 SITE OFFICES

The site offices are proposed near Power House site, which is at about 2km from

Thieddieng Village. The accommodations are broadly classified into two categories:

residential and nonresidential. Most of the residential and non-residential buildings are

proposed to be constructed in double/triple stories keeping in view the limited

availability of land.

9.3.2.2 RESIDENTIAL ACCOMODATION AT PROJECT SITE

Residential accommodation for staffs during construction and subsequently during

operation is necessary. Thus, the Residential Complexes are proposed near Dam site and

Power House site, which will accommodate dwelling units of different types for officers

and staff. Guest House would also be located in the Power house area. Contractor’s

colony and Labor colony would be at Dam, Adit-1 portal as well as power house complex

with all amenities.




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9.3.2.3 NON-RESIDENTIAL COMPLEXES AT PROJECT SITE

Non-residential complexes at Project Site will include Hospital/Dispensary, School,

Officers Club & Auditorium, Staff Club/ Union Office, Shopping Centre, Bank,

Telephone Exchange, Canteen, Stores, Sub-station, Fire Station, Filtration Plant, DG

Building, Quality Control Laboratory, CISF store/office, LPG Godown etc. and all these

structures will be needed during O & M stage as well. Most of the residential and non-

residential buildings are proposed to be constructed in double/triple stories at the project

site keeping in view the availability of land. The entire infrastructure will be utilized

during Operation & Maintenance (O&M) stage of the project also.

9.3.3 WORKSHOPS

Central workshop for heavy earth moving equipment and transport vehicles shall be set

up at the project site. The area shall be developed considering open space and parking

area. The workshop shall comprise of covered/semi-covered repair sheds. The workshop

shall comprise facilities for the engine repairs and overhauling, transmission, torque

converter repair shops, auto-electrical shops, machine shop, tyre repair shop, welding

and fabrication shops, chassis repairs, body and seat repairs, denting/painting,

maintenance yard etc.

9.3.4 WAREHOUSES/ STORES COMPLEX

Space for construction of stores for Cement, Steel and other materials including chemicals

will be identified in a relatively flatter area on the right bank of River. The steel and other

store items like bitumen etc. which do not require covered area would be kept outside in

open. For the purpose of cement storage, covered sheds shall be developed enabling

storage of adequate quantity of cement.

9.3.5 MUCK DISPOSAL AREA

The construction of various hydraulic structures like concrete dam, intake, power house

etc. will involve large excavation that would be disposed of in designated muck disposal

areas shown in the drawing no. 0933-CDC-01A-005-00, appended in Volume-IA of this

report. Muck arising from the cutting for roads would be utilized for filling wherever

required and the remaining would be disposed of in the nearby identified areas. The total

area identified for muck disposal for the whole project components is about 15.25 Ha.




Page: 209

9.3.6 EXPLOSIVE MAGAZINE

In order to cater for blasting requirements of various work sites, it is planned to provide

one permanent explosive magazine along with proportionate quantity of detonators. Two

portable site magazines of 500 kg capacity will also be provided to cater for the day to

day requirement of explosives. All safety codes and regulations prescribed by the Govt.

in this respect will be followed and magazines will be suitably guarded round the clock.

Necessary approvals will be taken from the concerned authorities for these magazines.

Magazine areas have been proposed one on right bank at Dam site, one between Adit 1

and 2.

9.3.7 CONSTRUCTION PLANT FACILITIES

Various installations like crushing plant, batching and mixing plant etc. are to be put up

by the contractor near the working sites.

9.3.7.1 CRUSHING PLANT

Aggregate Crushing plant will be provided for aggregate preparation from excavated

material from surface and underground works. The details are given below:

� Crushing plant of 1 no.170 TPH and 1 no.110 TPH Capacity will be located at dam

site.

� Crushing Plant of 1 no. 170TPH and 1 no. 40 TPH will be placed near Power house

site.

9.3.7.2 BATCHING AND MIXING PLANT

As per requirement of concreting at various work sites, batching and mixing plants are

planned as under

� B & M plant of 2 nos. 60 cum/hr capacity at Dam site to meet the peak production of

concrete.

� B & M plant of 30 cum/hr capacity each near Power house site

PRESSURE SHAFT FERRULE FABRICATION YARD

Site for fabrication of pressure shaft ferrules will be provided by the erection contractor of

pressure shaft on the right bank, u/s of Power House complex.




Page: 210

9.3.8 LAND REQUIREMENT

Land required for residential and non-residential buildings for the construction of the

approach roads, project components, workshops, stores, muck disposal, magazines,

construction plant facilities etc. will be acquired.

DETAILS OF LAND REQUIREMENT ARE AS FOLLOWS

Component Area(Ha)

Residential/Non Residential Area at Dam Site 1.5

Residential/Non Residential Area at PH Site 1.5

Total Area Required For Proposed Roads 17.70

Area proposed for Quarry area 6.5

Area Required for Power House 3.5

Area Required For Adit/Access Tunnels 2.25

Area Required at Surge Shaft Top 2.0

Area Required at Dam complex 9.0

Area required for HRT 6.2

Submergence area 13.0

Contractor facility/Labour Colony – Adit-1 1.0

Contractor facilities Area at Dam site 1.0

Fabrication Yard 1.5

Aggregate Crushing Plant near Dam site 1.0

Aggregate Crushing Plant near adit-1 1.0

Aggregate Crushing Plant near PH site 1.0

Area covering pressure shaft, road to power house, dumping, Area for SS, temporary colony for PH and adit-3 alignment (partly)

25.0




Page: 211

Muck Dumping

Near Dam Complex 5.25

Near Adit-1 2.5

Adit-2 2.0

Adit-3 2.0

Power House (Right Bank) 2.0

Power House (Left Bank) 1.5

Magazine

Dam complex 0.1

Between Adit 1 & 2 0.1

Total 110.0

9.3.9 CONSTRUCTION POWER

Power will be required at various project locations during construction to power the

construction equipment. The area to be catered for construction power will consist of the

Dam site, HRT adits, Surge shaft and Pressure Shaft, Power House and the tail pool and

colony and office area. Diesel generating sets will be used to power these areas and

associated LT boards and cables will be provided to distribute power at various

equipment.

In addition to the loads of construction equipment, construction power will also cater to

the power demands of the dewatering system, ventilation system, illumination system

etc. It will be ensured that the diesel generating sets are located close to the load centers

at the dam site, Power House, colony and office and the diesel generating sets for HRT

adits, surge shaft and pressure shaft will located at their adit portals. The possibility of

tapping the local grid power will also be studied during the tendering stage, wherein the

capability of the local grid to supply construction power can be assessed based on the

loads and distribution system of nearby areas.




Page: 212

9.3.10 TELECOMMUNICATION

The different work sites of the project offices, stores, laboratories, workshops and

residences etc. will be connected by a telecommunication network including telephones

for all offices and residences of senior officers etc. The telecommunication facilities will

also be provided between the project & various major cities of India.

9.3.11 WATER SUPPLY SYSTEM

Permanent residential area is planned at Power House area. A small one is also proposed

at Dam Site. In addition to this, labour camps are planned to be established at various

locations of activities. Arrangement of clean /portable water in the residential areas and

various construction sites are to be made for all these places.

9.3.12 SECURITY AND SAFETY ARRANGEMENT

9.3.12.1 SECURITY STAFF OFFICES AND CHECK POST

Two Nos. of Security staff Offices of suitable size each, one located at Dam site & the

other at Power House site are proposed to be provided. Along with these security staff

offices, check Posts are also to be provided. Sufficient Nos. of Security Personnel is

proposed to be provided including Day & Night shift duties. Those Security Personnel

will be looking after the entire project area.

9.3.12.2 FIRE STATION

Two Fire stations of suitable size each are proposed; one at dam site and other at power

house site. These Fire stations will be fully equipped with modern firefighting

equipment. Skilled Security Personnel will be used for firefighting Process.

CHAPTER - X

CONSTRUCTION PLANNING




Page: 213

CHAPTER - X

CONSTRUCTION PROGRAM AND PROJECT SCHEDULE

10.1. PROJECT COMPONENTS

The project comprises construction of following components:

a) 384m long, 7m φ Horse Shoe Shape Diversion Tunnel

b) b. 51m high Concrete Gravity Dam along with other appurtenant structures

c) c. Km long, 4.80m φ Horse Shoe Shaped Head Race Tunnel, with 2 intermediate

Adits

i) Adit – 1: 6m D - Shaped at RD 862 78m long

ii) Adit – 2: 6m D - Shaped near surge shaft 124m Long

d) 10m dia, 54 m high Surge Shaft

e) Pressure Shaft

i) 3.5m φ 864m long, bifurcating into 2 limb of 2.5 m φ each 32m long

ii) Adit-2A to top horizontal Pressure Shaft, 6m dia D shaped 95m long

iii) Adit-2B to erection chamber, 6m dia, 121 m long

iv) Adit 3 to bottom horizontal pressure shaft, 6m dia D-shaped, 455 m long

f) Erection Chamber of Pressure shaft 8m x 8mx 8m

g) Surface Power House (66.0 m x 18.00 m x 30.50 m), housing 2 no Vertical Axis

Francis Turbine ( 2 x 42.50MW)

h) 51m long Tail Race Channel including recovery bay

10.2 CLIMATIC CONDITIONS


Thieddieng village (R/B) in East Khasi Hills District of Meghalaya. The climate of the sub

basin is characterized by torrential rains caused by South West monsoon and 60% to 70%

rainfall occurs between June to September. The river flows in deep channel and swells

into torrents during the rainy season while during the remaining months it has not much

significant flow. The river has floods during June to October with peaks mostly occurring

in July to September.




Page: 214

10.3 ASSUMPTIONS WHILE FRAMING THE SCHEDULE

� Non monsoon Season from November to May.

� Monsoon Season – June to October. Due to heavy rainfall in the region, construction

activities for surface works like Dam & Power house would be significantly

impacted during the monsoon season. The underground works would also be

impacted, though relatively less as compared to surface construction works.

However, as the construction agency would remain mobilized at site during the

monsoon season, the construction activity shall be continued with less progress. For

preparing the schedule, it is assumed that:

� Surface works - Production in wet season (Monsoon period) shall be 30% of

production achieved in dry season for surface works.

� Underground Works - Production in wet season (Monsoon period) shall be

50% of production achieved in dry season for underground works.

� Work shall be carried out in 3 shifts of 8 hrs each, with 80% job efficiency factor

i.e. 50 min / hr.

10.4 SCHEDULE OF WORK 10.4.1 RIVER DIVERSION WORKS

A) DT INLET WORKS

Quantity in open excavation = 8162 m3

Quantity in Concreting = 1600 m3

The works shall commence in the Non monsoon season. The open excavation in rock and

overburden will be carried out according to the principle of “excavating from top to

down and by layers and benches”. The drilling pattern shall be such that per blast 250 m3

of rock is blasted and there shall be two such cycles/day ( i.e. one blast in 12 Hrs) .

Concreting in the DT inlet shall be taken up along with the lining works in the Diversion

tunnel after excavation of DT is completed. The procedure for concreting would be:

Foundation clearance -- surveying and setting out -- formwork erection --

reinforcement and water stop installation -- inspection- transportation of concrete --

concrete pouring -- formwork removal -- curing. The lift height would be around 1.5m.

The average cycle time for pouring concrete in one lift of height 1.5 meter shall be 2 days

and average quantity of concrete per poured shall be 110 cum.




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B) DIVERSION TUNNEL

Excavation will be carried out from Inlet and outlet end simultaneously. Full face

excavation will be implemented using drilling and blasting method. Average cycle time

for excavation in class 1,2 and 3 is worked out as 16.2 hrs and average cycle for

excavation in class 4 & 5 rock has been worked out as 19 hrs.

Total length of Tunnel : 384m

Length of Tunnel in Class 1, 2 and 3 : 308m

Length of Tunnel in Class 4 & 5 : 76m

Pull Planned / Blast : 03 m

Class of Rock Average rate of Progress

Total no of days

required to complete

Average rate of progress/day / face in Class 1,2,3 4.4m/day 70 days

Average rate of progress/day / face in Class 4 & 5 3.8m/day 20days

Total no of days for excavating DT from one face 90

Average rate of progress/day / for 4,2m / day

It is planned to carry out the lining in diversion tunnel using a 12 m long gantry. The

shutter shall move from Inlet toward the outlet, and concrete shall be feed from outlet

end of the tunnel. This arrangement will facilitate in carrying out concreting & HM work

at Inlet, simultaneously with the tunnel concreting. The average cycle time for concrete

lining shall be 26.7 hrs. And average rate of progress per day shall be 10.78 m/ day.

C) RIVER DIVERSION & CONSTRUCTION OF COFFER DAM

It is planned to divert the river in 6th month after the start of construction during lean

season flow. The river diversion shall be achieved by constructing a closure dyke. There

after the construction of Cofferdam shall be undertaken. U/s Cofferdam is proposed to

be founded on overburden. The maximum height of the coffer dam is 18m from the river

bed level. . The central core of the coffer dam is filled with clay. Materials from

excavation of Diversion Tunnel, DT inlet and outlet will be used for coffer dams. . Filling

of the cofferdam will be carried out in layers of no more than 100cm each. Compaction

roller will be used to compact in layers. Total quantity of rock fill in the coffer dam is

equal to 71,690 cum and targeted average rate of placing rock fill shall be 4320 cum.




Page: 216

10.4.2 DAM AND SPILLWAYS

Total excavation involved in dam

� Excavation in Overburden/Soil = 58,300 cum

� Excavation in Rock = 93.300 cum

Total = 1,51,600 cum

Further Break up of Excavation Qty :

i) In Abutment - From top to HFL = 34,000 cum

ii) Abutments – from HFL to River bed level = 15,000 cum

iii) From river bed level to deepest foundation level = 1,03,000 cum

Abutment above HFL involving quantity of 34,000 cum shall be taken up prior to river

diversion works. The excavation of abutments below the HFL shall be taken up after the

river diversion is achieved. Excavation in river bed shall also be taken up after the river

diversion has been achieved. The excavation in riverbed shall be undertaken only in non-

monsoon season. The works have been planned accordingly. The open excavation will be

carried out according to the principle of “excavating from top to down and by layers and

benches. The drilling pattern shall be such that per blast 500 m3 of rock is blasted and

there shall be two such cycles/day (i.e. one blast in 12 Hrs).

CONCRETING IN DAM

The procedure for concreting in dam is as following: Foundation clearance -- surveying

and setting out -- formwork erection -- reinforcement and water-stop installation –

inspection -- concrete pouring -- formwork removal -- curing.

Total quantity of concrete to be placed in dam =

From Deepest foundation level to river bed = 52,125 cum

From river bed level to Dam top = 86,875 cum

Total =1,39,000 cum

Peak placement of concrete in the dam would be when the concrete in poured in the

overflow blocks 3,4 and 5 below the river bed level. Following is planned for pouring the

concrete :

� Concrete shall be placed in lift heights of 1.5m. In each lift concrete shall be poured

in layers of 0.5m height.




Page: 217

� Subsequent lift in same block will be placed every 5 days (96 hrs) after the previous

pour is completed – 1 day for green cutting, curing, 3 days for preparing the lift

including moving forms and installing all materials as per design ( water stops,

contact grouting installations, reinforcement steel if any, cleaning of surface).

Quantity of concrete in each lift of from foundation up to River bed level is

worked out in below table.

Longitudinal length = 67.45 m & height of each lift = 1.5 m

Lift

No.

Block 3 Block 4 Block 5

From

To

Average

width in X-

section

( Autocad)

Total

Qty. of

Concrete

Average

width in

X- section

( Autocad)

Total

Qty. of

Concrete

Average

width in

X- section

(Autocad)

Total Qty.

of

Concrete

1 421.0 422.5 0.00 0.00 15.5 1568.21 16.9605 1715.98

2 422.5 424.0 0.00 0.00 23 2327.03 18.934 1915.65

3 424.0 425.5 3.5415 358.31 26 2630.55 20.908 2115.37

4 425.5 427.0 11.158 1128.91 26 2630.55 22.876 2314.48

5 427.0 428.5 16.302 1649.35 26 2630.55 24.8495 2514.15

6 428.5 430.0 18.3585 1857.42 26 2630.55 25.921 2622.56

7 430.0 431.5 20.333 2057.19 26 2630.55 26 2630.55

8 431.5 433.0 20.333 2057.19 26 2630.55 26 2630.55

9 433.0 434.0 20.333 1371.46 26 1753.70 26 1753.70

10479.841 21432.238 20212.978




Page: 218

Schedule for placing concrete in each lift from foundation upto river bed level is

shown in the table:

Month -1 Month -2

Day Block -3 Block -4 Block -5 Day Block -3 Block -4 Block -5

1 1568.00 1 2 2630.00 4

2 1 2 3 1 5

3 2 1716.00 3 4 2 2622.00

4 3 1 4 5 3 1

5 0.00 4 2 5 1857.00 4 2

6 1 5 3 6 1 5 3

7 2 2327.00 4 7 2 2630.00 4

8 3 1 5 8 3 1 5

9 4 2 1915.00 9 4 2 2630.00

10 5 3 1 10 5 3 1

11 0.00 4 2 11 2057.00 4 2

12 1 5 3 12 1 5 3

13 2 2630.00 4 13 2 2630.00 4

14 3 1 5 14 3 1 5

15 4 2 2115.00 15 4 2 2630.00

16 5 3 1 16 5 3 1

17 358.00 4 2 17 2057.00 4 2

18 1 5 3 18 1 5 3

19 2 2630.00 4 19 2 1753 4

20 3 1 5 20 3 5

21 4 2 2314.00 21 4 1753.00




Page: 219

Month -1 Month -2

Day Block -3 Block -4 Block -5 Day Block -3 Block -4 Block -5

22 5 3 1 22 5

23 1128.00 4 2 23 1371

24 1 5 3 24

25 2 2630.00 4 25

26 3 1 5 26

27 4 2 2514.00 27

28 5 3 1 28

29 1649.00 4 2 29

30 1 5 3 30

25494.0 26620.0

For concreting above the river bed level, as there would be heavy reinforcement, it is

expected that average rate of concreting / month shall be around 10,000 cum / month.

10.4.3 HEAD RACE TUNNELS AND ADITS

The water conductor system includes a horse shoe shaped Head Race Tunnel (HRT) of

finished diameter 4.80 m. The length of HRT is 2.62 Km. Tunneling is proposed to be

carried out by drilling & blasting method (DBM) .Rock support, comprising of shotcrete,

rock bolting and steel sets would be proposed as per site conditions.

Before taking up actual tunnel excavation, portal construction and slope stabilization

at the adits would be required. This shall involve open excavation, rock bolting,

shotcreting etc. 2 Construction Adits are proposed along the alignment of HRT to

facilitate the excavation of HRT. The RD of each Adit and distance between them is

given as under:

a) Adit – 1: 6m D - Shaped at RD 862, 78m long

b) Adit – 2: 6m D - Shaped near surge shaft, 124m Long

Full face excavation will be implemented using drilling and blasting method. Average

cycle time for excavation in class 1,2 and 3 is worked out as 16. hrs and average cycle for




Page: 220

excavation in class 4 & 5 rock has been worked out as 19 hrs.

Total length of Tunnel : 2622m

Length of Tunnel in Class 1,2 and 3 : 2229m

Length of Tunnel in Class 4 & 5 : 393m

Pull Planned per Blast : 2.3 m

As 2 Adits have been provided, excavation shall be carried out from 3 faces and each face

shall have independent set of construction equipments. It is also assumed that the in each

face, 85% of the rock shall be in class 1, 2 and 3. Length of Excavation of each face shall

be as:

Face 1 ( u/s of Adit -1) 86

Face -2 ( D/s of Adit -1) 92

Face -3 ( U/s of Adit- 2) 83

Average rate of progress/day / face in Class 1,2,3 = 4.0 m/ day

Average rate of progress/day / face in Class 4 & 5 = 3.5 m/day

It is planned to carry out the lining in tunnel using a 1 no 12 m long gantry from, as the

construction of HRT is not on the critical path and hence deployment of shutter at two

additional faces will only increase the cost of the equipment. Lining can be carried out

from Intake towards Surge shaft. Adit 1 shall be plugged after the crossover of junction to

prevent accumulation of diesel fumes in the Tunnel. The average cycle time for concrete

lining shall be 25.5 hrs. and average rate of progress per day shall be 11.30 m / day.

Class of Rock Face 1 Face-2 Face 3

Length (m) 862 928 832

No. days for excavation in 1,2, and 3 183 197 177

No. days for excavation in 4 & 4 37 40 36

No of days required to extend utilities ( 1

day / 20m of tunnel length )

43

46

42

Total no of days required for excavation 263 283 254

Average rate of progress (m / day ) 3.3 3.3 3.3

Total no of days required for Concrete

lining

232 days




Page: 221

10.4.4 POWER HOUSE

Quantity in open excavation = 5, 05,000 m3

Quantity in Concreting

� Sub structure = 3000 m3

� Superstructure = 6000 m3

The excavation works shall commence immediately after completing the mobilization.

The open excavation in rock and overburden will be carried out according to the

principle of “excavating from top to down and by layers and benches”. The drilling

pattern shall be such that per blast 500 m3 of rock is blasted and there shall be two such

cycles/day (i.e. one blast in 12 Hrs).

After completing the excavation & sub structure concreting, the erection of turbines &

generators shall be taken up, which will take about 12 months for each machine?

Superstructure Concreting shall continue with the erection of E&M equipment as and

when required.

CHAPTER - XI

ENVIRONMENT AND ECOLOGY




Page: 222

CHAPTER - XI

ENVIRONMENT AND ECOLOGY

11.1 INTRODUCTION

The environmental Examination of the proposed Mawhu H. E. Project has following

objectives which are proposed to be covered during various phases of development.

� Provide information on baseline environmental setting.

� Assessment of impacts likely to accrue during construction and operation phases;

� Identify key issues which need to be studied in detail during environmental studies

It is essential to ascertain the baseline status of relevant environmental parameters that

could undergo significant changes as a result of construction and operation of the project.

Baseline status has been ascertained through review of secondary data, reconnaissance

survey and interaction with the locals.

The environmental study has been conducted as a part of EIA study to forecast the future

environmental scenario of the project area that might be expected to occur as a result of

construction and operation of the proposed project. The key environmental impacts

which are likely to accrue as a result of the proposed developmental activity are

identified. Various impacts, which can endanger the environmental sustainability of a

project, are highlighted for comprehensive assessment as a part of next level of

environmental study.

11.2 ENVIRONMENTAL BASELINE SETTING

The study area includes the area within 7 km radius of various project appurtenances.

The data was collected through review of existing documents and various engineering

reports and reconnaissance surveys. The various parameters for which baseline setting

has been described have been classified into physio-chemical, ecological and socio-

ecological aspects.

11.2.1 PHYSIO-CHEMICAL ASPECTS

a) WATER QUALITY

The proposed hydroelectric project is located on Umiew river. The catchment area

intercepted at the project site has a low population density. The low cropping intensity




Page: 223

coupled with low agro-chemicals dosing ensures that the pollution loading due to agro-

chemicals is quite low. The absence of industries implies that there is no pollution

loading from this source as well. Thus, it can be concluded that there are no major

sources of pollution in the project area.

It has been observed that, water quality in such settings is quite good, characterized by

high DO and low BOD levels. The TDS levels too are low, i.e. well within the permissible

limits, which could be used for drinking purposes. The major sources of water are

various streams and nallahs flowing adjacent to various settlements. The water is

transported to the point of consumption under gravity. The sewage so generated too is

disposed without any treatment in natural streams and channels. Due to low population

density and presence of sufficient water for dilution, no adverse impact on water quality

is observed. Thus, water of Umiew river can be classified as class-A as per IS 2296, which

means that water can be used for meeting domestic requirements after disinfection, and

without conventional treatment. It is pertinent to mention that the Greater Shillong Water

Supply Scheme is located about 10 Km upstream of the proposed Dam site on the same

river.

b) LANDUSE

The submergence area is 13.0 ha at FRL, which comprises mainly of mixed forest and

water bodies. Additional land will be required for siting of various project appurtenances

as well.

11.2.2 ECOLOGICAL ASPECTS

a) VEGETATION

The proposed project site lies in the eastern Himalayas. The nature and type of vegetation

occurring in an area depends upon a combination of various factors including prevailing

climatic conditions altitude, topography, slope, biotic factors, etc.

As per the altitude the major vegetation type observed in the project area and the study

area is mixed forests. The characteristic feature of these forests is that top canopy is

predominated by deciduous species whose leafless period is short. In quality the forests

contain much poorer type of timber than the evergreen forests and are composed of a

number of species that are of little commercial value.

The major floral species observed in the study area are given in Table 11.1.




Page: 224

Table 11.1: Major floral species observed in the study area

FLORA

Sl. No. Botanical Name Local Name (Khasi)

1. Albizzia procera Kreit lieh

2. Artocarpus integrifolia Dieng Sohphan

3. Betula alnoides Dieng lieng lieh

4. Bauhinia purpuria Jalong

5. Baccurea sapida Sohramdieng

6. Bombax ceiba Kya

7. Cinamomum tamala Latypad

8. Castonopsis spp Soh ot, Soh stap

9. Chikrasia tabularis Bti lieh

10. Dysoxylum hamiltonii Dieng Kyrbei

11. Derris robusta Phyllut

12. Duabana grandiflora Dieng Bai

13. Erythrina indica Dieng Song

14. Engelhertia spicata Lba.

15. Euginea jambolana Soh Um

16. Ficus elastica Dieng Jri

17. Gynocardia odorata Bylliat

18. Mesua ferrea Dieng Ngai

19. Myrica esculanta Soh phie

20. Michelia champaca Dieng rai

21. Quercus spp Dieng sning

22. Rhododendron arboretum Dieng Sohthiang

23. Schima wallichii Dieng ngan

24. Toona cialata Bti ramsong

25. Terminalia myriocarpa Dieng tal

BAMBOO


1. Bambusa pallida Shken

2. Bambusa tulda Riniai

3. Bambusa hamiltoni Siejkhlaw

4. Dendrocalamus spp Siejktang




Page: 225

b) FAUNA

The forests in and around the project area varies from medium to dense as far as crown

cover density is concerned. Based on the review of secondary data and interaction with

the Forest Department, major faunal species reported in the forests of the study area

include leopard cat, Rhesus macaque, etc. Amongst the avi-fauna, the commonly

observed species included Galius gallus, Alcedo attis etc. Likewise Cobra, Viper etc. are

the major snake species observed in the study area. The other reptilian species observed

in the study area include Lizard calotes versicular, Rhabdophis etc.

The list of faunal species observed in the study area is outlined in Table 11.2.

Table 11.2: List of faunal species observed in the study area

MAMMAL


1. Aretictis Bshad iong

2. Capricornis sumatraensis Khiat

3. Cervus Skei Shynrang

4. Felis bengalensis Khla thapsim

5. Felis chaus Miawkhlaw

6. Hoolock gibbon Tngaw

7. Hystrix indica Brai

8. Lutra lutra Ksih

9. Muntiacus muntyak Skei kynthei

10. Panthara pardos (Leopard) Khla rit

11. Petaurista Risang dieng

12. Rhesus macaque Shrieh saw

13. Selenarctos Dngiem lalu / Dngiemiong

14. Herpestes auropun Bsong

15. Vulpes bengalensis Myrsiang

16. Viverricula Bshad

Not encountered in the last few years

AVI-FAUNA


1. Apus affinis Sim Khar

2. Alcedo attis Simpuh dohkha




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3. Anthracoceros Koh –Karang

4. Galius gallus Syiar Khlaw

5. Cracula religiosa Moina iong

6. Chalcophaps indica Paro Blei

7. Lothura laupomelanos Syiar tung

8. Polyplectron bicalcaratum Klew rit

9. Psittacula eupatria Langlit

10. Treron pheonicotera Langwar-ku

11. Otus bakkamelna Dkhoh

12. Pyenonotus cafer Paitpuraw

REPTILES

Sl. No. Name Local Name (Khasi)

1. Cobra Bsein iong

2. Laphe prasiana Bsein her

3. Lizard calotes versicular Niang bshiah

4. Manis crassicaudata Kyrbei

5. Rhabdophis Bsein saw ryndang

c) FISHERIES

The proposed project lies on Umiew River. During interaction with the local Fisheries

Department, it was confirmed that no major data is available on the occurrence of various

fish species in this river. However, based on the studies conducted for other rivers in the

region, which also traverse through similar climatic and topographical settings, it is likely

that fish species of migratory nature could be present in the river. A detailed fisheries

survey is being conducted in river Umiew and its tributaries coming under submergence

to ascertain the presence of various species and distribution in various seasons of the

year.

11.2.3 SOCIO-ECONOMIC ASPECTS

It is imperative to study socio-economic characteristics including demographic profile of

the project area and the study area. No homestead is coming within reservoir

submergence. The ownership status of land to be acquired for other project




Page: 227

appurtenances is being ascertained. The ST population is the dominant caste group. The

SC population is virtually negligible in the project area. The literacy rate in the study area

is quite high, i.e. of the order of 60%. The male and female literacy rates are more or less

equal, which is a typical feature of many areas in the north-eastern part of the country.

The ST population in and around the project area is a matrilineal society and both male as

well as female population actively take part in various socio-economic activities.

11.3 PREDICTION OF IMPACTS

Based on the project details and the baseline environmental status, potential impacts as a

result of the construction and operation of the proposed project have been identified.

Impacts on various aspects listed as below have been assessed:

� Land environment

� Water resources

� Water quality

� Terrestrial flora

� Terrestrial fauna

� Aquatic ecology

� Noise environment

� Ambient air quality

� Socio-economic environment

11.4 IMPACTS ON LAND ENVIRONMENT

a) CONSTRUCTION PHASE

Sufficient quantity of coarse and fine aggregate is required for construction of a

hydroelectric project. The fine aggregates are generally available as river shoal deposits.

During excavation in the river shoals, clay particles are likely to get entrained, which can

increase the turbidity of the water body. This may marginally affect the primary

productivity of the river. However, this scenario is likely to last only during the time for

which material is being excavated. The water quality is likely to return to its original

turbidity levels, few days after the cessation of excavation operations. The depressions so

created after excavation of the construction material is likely to be filled up by the

sediments/silts brought down by the river from which the material is being excavated.




Page: 228

Thus, no specific management measures are required for extraction of construction

materials from shoal deposits.

The coarse aggregates will be extracted from various quarry sites in and around the

project area. The quarries have been located over non-forest land so as to minimize

adverse impacts on flora and fauna to the extent possible. The quarry sites are located

away from human settlements so as to avoid adverse impacts on them. Quarrying will be

done along the hill face, using semi-mechanized methods. Rock quality of the identified

quarries have been found to be very good. Proper care will be taken to provide required

slope during quarrying operation so that the quarrying faces remain stable. Since the

quality of rock encountered in the quarries is very good, weathering effect on the

quarried faces will not be significant and as such no additional treatment will be

required.

OPERATION OF CONSTRUCTION EQUIPMENT

During construction phase, various types of equipment will be brought to the site. These

include crushers, batching plant drillers, earthmover, rock bolters, etc. The sitting of

construction equipment would require significant amount of space. Similarly, space will

be required for storing various construction materials as well. The storage site will be

selected which is away from human habitations and faunal population.

There are no major habitation sites near the dam site and other project appurtenances.

Thus, sitting of construction equipment and storage of construction material are not

likely to have any adverse impacts.

SOIL EROSION

The runoff from the construction sites will have a natural tendency to flow towards

Umiew River or its tributaries. For some distance downstream of major construction

sites, such as dam, power house, etc. there is a possibility of increased sediment levels

which will lead to reduction in light penetration, which in turn could reduce the

photosynthetic activity to some extent of the aquatic plants as it depends directly on

sunlight. This change is likely to have an adverse impact on the primary biological

productivity of the affected stretch of the water body. Based on experience in other

projects, impacts on this account are not expected to be significant.




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PROBLEMS OF MUCK DISPOSAL

A large quantity of muck is expected to be generated as a result of tunneling operations,

excavation for Dam, construction of roads, etc. Normally, muck disposal sites are cleared

of vegetation before disposing the material. Trees are cut before muck disposal, however,

shrubs, grass or other types of undergrowth on which muck is disposed perishes.

In many projects, it has been observed that the muck generated by various sources is

disposed along the river valleys. The boulders are stacked along the river bank, and

during the next monsoons, the boulders can flow along with runoff, and ultimately find

their way into the river and finally into the plains. Hence, in this project adequate

measures wherever required, such as retaining walls, etc. will be constructed to

ameliorate the likely adverse impacts.

Construction of roads

The project construction would entail significant vehicular movement for transportation

of large construction material and heavy construction equipment. Most of the roads in

the project area would require widening. New roads would have to be constructed. The

construction of roads can lead to the following impacts:

� Removal of trees on slopes and re-working of the slopes in the immediate vicinity of

roads can encourage landslides, erosion gullies, etc. with the removal of vegetal

cover, erosive action of water gets pronounced and accelerates the process of soil

erosion and formation of deep gullies. Consequently, the hill faces are bared of soil

and vegetal cover and enormous quantities of soil and rock can move down the

rivers, and in some cases, the road itself may get washed out.

� Construction of new roads increases the accessibility of a hitherto undisturbed area

resulting in greater human interference and subsequent adverse impacts on the

ecosystem.

About 7 Km of the existing roads would require widening which are mostly passing over

plateau, as such, quantity involved in excavation & filling will be comparatively less. The

project would also require construction of new roads of about 19 Km length. Adequate

measures like stabilization of slopes, drainage, retaining wall, plantation of trees, grass

cover etc. will be taken for mitigating adverse impact of widening as well as construction

of new roads.




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b) OPERATION PHASE

The area coming under reservoir submergence is only 13.0 ha, comprising mainly of

mixed forest and water bodies. Additional area will be required for sitting of project

appurtenances, infrastructure, etc. The ownership category of such land needs to be

ascertained, once project layout is finalized as a part of DPR preparation. Based on the

type of land being acquired appropriate management measures shall be formulated.

Project appurtenances such as colonies, labour camps and other appurtenances, which

are not site-specific, will be located suitably so as to involve minimum cutting of trees etc.

11.5 IMPACTS ON WATER RESOURCES

The construction of dam as a part of the proposed project, diversion of discharge for

hydropower generation would lead to reduction in flow for a river stretch, downstream

of the dam site up to the confluence point of tail race discharge. Since there are no users

in the intervening stretch, hence, reduction in flow during lean season is unlikely to lead

to any significant impact. However, reduction in flow from the dam site up to the

confluence of these rivers is likely to have a minor impact on riverine ecology as the

discharge during lean flow is significantly less. Requirement for release of minimum

flow for sustenance of riverine fisheries is being assessed.

11.6 IMPACTS ON WATER QUALITY


EFFLUENT FROM LABOUR CAMPS

The project construction is likely to last for a period of 4-5 years apart from investigation

stage. About 1000 workers and 250 technical staff are likely to work during project

construction phase. The construction phase also leads to mushrooming of various allied

activities to meet the demands of the immigrant labour population in the project area.

Thus, the total increase in labour population during construction phase is expected to be

around 2500-3000. The total quantum of swage generated is expected to be of the order of

0.2 mld. The BOD load contributed by domestic sources will be about 135 kg/day. Since

disposal of untreated sewage could have adverse impacts on river water quality,

especially during lean season flow, care shall be taken not to dispose any untreated

sewage into Umiew river. It is a common practice during construction phase to

commission low cost sanitation treatment units and such units are required only during

the project construction phase. The sewage generated from the Labour Camps shall be




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treated through septic tanks.

EFFLUENT FROM CRUSHERS

The effluent from the crusher would contain high suspended solids. The effluent, if

disposed without treatment can lead led to marginal increase in the turbidity levels in the

receiving water bodies. However, no major adverse impacts are anticipated due to small

quantity of effluent and availability of sufficient water for dilution. The severity of

impacts would vary from season to season with variations in water availability for

dilution. A settling tank is proposed for arresting heavier solids from the effluent before

the effluent is disposed off.

b) OPERATION PHASE

EFFLUENT FROM PROJECT COLONY

In the operation phase, about 100 families will be residing in the area which would

generate about 0.08 mld of sewage. The quantum of sewage generated is not expected to

cause any significant adverse impact on riverine water quality. Adequate number of

septic tanks would be constructed for treatment of sewage to ameliorate the marginal

impacts.

IMPACTS ON RESERVOIR WATER QUALITY

The flooding of land with vegetation cover in the submergence area increases the

availability of nutrients resulting from decomposition of vegetative matter. Enrichment of

impounded water with organic and inorganic nutrients at times become a major water

quality problem immediately on commencement of the operation and is likely to

continue in the initial years of operation. In due course, the reservoir would support and

enhance the aquatic life including development of fisheries.

EUTROPHICATION RISKS

The fertilizer use in the project area is nil, hence, runoff at present does not contain

significant amount of nutrients. During post-project phase too, use of fertilizers in the

project catchment area is not expected to rise significantly. Eutrophication problems,

which are primarily caused by enrichment of nutrients in water are not anticipated in the

proposed project.

11.7 IMPACT ON TERRESTRIAL FLORA





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INCREASED HUMAN INTERFERENCES

As mentioned earlier, about 1250 technical staff, workers and other group of people are

likely to congregate in the area during the project construction phase. The total increase

in population is expected to be about 2500-3000. Workers and other population groups

residing in the area may use fuel wood, if no alternate fuel is provided. On an average,

the fuel wood requirements will be of the order of 1250-1350 m3 annually. Thus, every

year, fuel wood equivalent to about 400-450 trees will be cut, which implies that every

year on an average about 0.5 ha of dense forest area will be cleared for meeting fuel

wood requirements, if no alternate sources of fuel are provided. Dense forests are not

observed in the project and its surroundings. However, within the study area, some

pockets of dense forest are observed, which would be under threat if alternate fuel

sources are not provided to workers involved in project construction. The contractor

involved in construction activities will be asked to provide alternate source of fuel to the

labour population and their families involved in construction activities. Alternatively,

community kitchens using Kerosene or LPG as fuel can be run for the benefit of labour

population and their families.

b) OPERATION PHASE

The area coming under reservoir submergence comprises of mixed forest.

Compensatory afforestation will be required in this project as there is diversion of Forest

land involved. Adequate number of trees will be planted along the Reservoir fringe as

well as along the roads and other project areas. Species for plantation of trees will be

chosen in consultation with the State Forest Department officials for best results.

The construction of dam as a part of the proposed project, diversion of discharge for

hydropower generation would lead to reduction in flow for a river stretch, downstream

of the dam site up to the confluence point of tail race discharge. Since there are no users

in the intervening stretch, hence, reduction in flow during lean season is unlikely to lead

to any significant impact. However, reduction in flow from the dam site up to the

confluence of these rivers is likely to have a minor impact on riverine ecology as the

discharge during lean flow is significantly less. Requirement for release of minimum

flow for sustenance of riverine fisheries is being assessed.




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11.8 IMPACTS ON TERRESTRIAL FAUNA


As mentioned earlier, faunal population is not significant in the project area. Thus, no

major impact is anticipated on terrestrial fauna as a result of acquisition of land under

reservoir submergence. However, few faunal species are reported in the study area,

which could be indirectly affected due to increased interferences in project construction

phase.

b) OPERATION PHASE

IMPACTS DUE TO INCREASED ACCESSIBILITY

During project operation phase, accessibility to the area will improve due to

construction of roads, which in turn may increase human interference leading to

marginal adverse impacts on the terrestrial ecosystem. Since significant increase in

human population is not anticipated during project operation phase, adverse impacts

due to such interferences is likely to be very marginal.

11.9 IMPACTS ON AQUATIC ECOLOGY


During construction of a river valley project, huge quantity of muck is generated at

various construction sites, which if not properly disposed, invariably would flow down

the river during heavy precipitation. Such condition can lead to adverse impacts on the

development of aquatic life, which needs to be avoided.

The increased labour population during construction phase, could lead to increased

pressure on fish fauna, as a result of indiscriminate fishing by them. Adequate

protection measures at sensitive locations, identified on the basis of fisheries survey will

be implemented.

b) OPERATION PHASE

Data on fish species observed in Umiew river is not available. However, based on

studies conducted on other rivers in the region traversing in similar settings, some of the

migratory species may be present in the river. Detailed fisheries survey is being

conducted to ascertain the presence and distribution of various migratory fish species,

and also to assess the impacts due to disruption of hydrologic regime in the river stretch

downstream of diversion structure site to power house tail race site.




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11.10 IMPACTS ON NOISE ENVIRONMENT

Increased noise levels are anticipated only during construction phase due to operation of

various equipment, increased vehicular traffic and blasting etc. Increased noise level,

especially blasting could scare away wildlife from the area. Since, no major wildlife is

reported in the area, hence, significant impacts are not anticipated on this account.

Likewise, absence of large scale human population close to the project site, discounts the

probability of occurrence of adverse impacts on human population.

11.11 AIR POLLUTION

POLLUTION DUE TO FUEL COMBUSTION IN VARIOUS EQUIPMENT

The operation of various construction equipment requires combustion of fuel. Normally,

diesel is used in construction equipment. The major pollutant which gets emitted as a

result of diesel combustion is SO2. The SPM emissions are minimal due to low ash

content in diesel. Model studies conducted for various projects with similar level of fuel

consumption indicate that the short-term increase in SO2, even assuming that all the

equipment are operating at a common point, is quite low, i.e. of the order of less than 1

µg/m3. Hence no major impact is anticipated on this account.

EMISSIONS FROM VARIOUS CRUSHERS

The operation of the crusher during the construction phase is likely to generate fugitive

emissions, which can move even up to 1 km along the predominant wind direction.

During crushing operations, fugitive emissions comprising of the suspended particulate

will be generated. Since, there are no major settlements close to the project site; no major

adverse impacts on this account are anticipated. However, labour camp will be located

away from the construction sites and on the leeward side of the pre-dominant wind

direction in the area.

11.12 IMPACTS ON SOCIO-ECONOMIC ENVIRONMENT

a) PROJECT CONSTRUCTION PHASE

The construction phase will last for about 4-5 years. Those who would migrate to this

area are likely to come from various parts of the country mainly having different cultural,

ethnic and social backgrounds. During the construction period, the local inhabitants will

be exposed to various cultures, religious practices etc. which are followed by the




Page: 235

immigrants. However, since the socio-cultural entity of the local ST population is very

rich and vibrant, no major adverse impact is anticipated due to temporary migration of

labour force with different socio-cultural background.

Job opportunities will improve significantly in this area. At present most of the

population sustains by cultivation and allied activities. The project will open a large

number of jobs to the local population and open up avenues for economic activities.

Works which are not highly technical in nature will be got done through local contractors

which will help them in improving their socio-economic condition to a great extent.

Basic infrastructure facilities like post office, bank, school, dispensary if constructed for

the project, these facilities will also be extended to the local population.

b) PROJECT OPERATION PHASE

ACQUISITION OF PRIVATE LAND

The entire area required for the project falls under private land/community land.

Ownership of land and other details will be obtained during acquisition process.

However, no homesteads are likely to be submerged or acquired for the project.

INDUSTRIALIZATION AND URBANIZATION

The commissioning of a hydro-electric project provides significant impetus to economic

development in the area being supplied with power. Likewise, in the project area,

commissioning of a hydro-electric project would lead to mushrooming of various allied

activities, providing employment to locals in the area.

11.13 SUMMARY OF IMPACTS AND EMP

A summary of impacts and recommended management measures are summarized in

Table 11.3. A total provision of Rs.2000.00 Lakhs has been kept towards Environment &

Ecology of the project.




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Table 11.3: Summary of Impacts and suggested management measures

Sl. No. Parameters Impact Management Measures

1. Land Environment

Construction

Phase

� Soil erosion due to the

extraction of construction

material from various

quarry sites.

� Proper treatment of

quarry site.

� Temporary acquisition of

land for sitting of

construction equipment &

material, waste material.

� No specific

management

measures are required.

� Generation of muck due to

tunneling operations and

construction of roads,

excavation for Dam.

� Disposal at designated

sites and provision of

suitable management

measures including

bio-engineering

treatment measures

Operation

Phase

� There is no Forest land

involved and acquisition of

private land will be made.

� Suitable compensation

will be given to the

affected land owners

after assessment made

by the appropriate

authority

2. Water Resources

Operation

phase

� River stretch from

diversion structure site to

tail race outfall will have

reduced flow during lean

season.

� In case downstream

nallahs do not

contribute lean flows,

minimum flow will be

released to maintain

the riverine ecology.

3. Water Quality

Construction

Phase

� Water pollution due to

disposal of sewage from

labour colonies.

� Provision of

community toilets and

septic tanks.

Operation

Phase

� Deterioration of water

quality in the dry stretch of

river due to reduced flow

during the lean season.

� No significant impact

is anticipated.

� Disposal of sewage from

project colony.

� Provision of adequate

sewage treatment

facilities like Septic

tanks will be made.




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� Eutrophication problems. � Management

measures are not

required, as no

impacts are

anticipated on this

account.

4. Terrestrial Flora

Construction

Phase

� Cutting of trees for meeting

fuel wood requirements by

labour.

� Provision of

community kitchen by

the contractors

engaged in the project

construction.

Operation

Phase

� There is no Forest land

involved and acquisition of

private land will be made.

� Suitable compensation

will be given to the

affected land owners

after assessment made

by the appropriate

authority.

5. Terrestrial Fauna

Construction

Phase

� Significant impact on

wildlife due to operation of

various-construction-

equipment is not

anticipated.

� Specific management

measures are not

required.

Operation

Phase

� Disturbance to wildlife due

to increased accessibility in

the area.

� Specific management

measures are not

required.

6. Aquatic Ecology

Construction

Phase

� Marginal decrease in

aquatic productivity due to

increased turbidity and

lesser light penetration.

� Marginal impact,

hence no specific

management

measures are

suggested.

Operation

Phase

� Reduction in river flow in

stretch downstream of dam

site up to tail race outfall.

� Provision of release of

minimum flow in case

downstream nallahs

do not contribute to

lean flows and

adverse impacts on

water quality and

aquatic ecology are

anticipated.




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7. Noise Environment

Construction

phase

� Increase in noise levels

due to operation of various

construction equipment.

� Marginal impact,

hence no management

measures are

suggested.

8. Air Environment

Construction

phase

� Increase in air pollution

due to use of machinery

and other civil activities.

� Arrangement will be

provided to minimize

air pollution from

crushers.

9. Socio-Economic Environment

Construction

Phase

� Increase in employment

potential.

---

Operation

Phase

� Increased power

generation.

---

� Greater employment

opportunities.

---

CHAPTER - XII

COST ESTIMATE




Page: 239

CHAPTER - XII

PRELIMINARY COST ESTIMATE

12.1 GENERAL

The cost of the project has been worked out on the basis of preliminary designs and

drawings as referred and annexed in the present report. The unit rates for various are

taken based on available rates from similar Hydro Power Projects in the region of

Meghalaya.

12.2 BASIC ESTIMATE

12.2.1 GENERAL

The estimate has been prepared to arrive at the capital cost of Mawphu H.E. Project,

Stage - II. The base date of the estimate is April 2016. The Cost Estimate is divided into

Civil and Electrical Works. The cost estimate for Transmission works has not been

considered in this study.

12.2.2 TAXES AND DUTIES

In estimation of the cost of Civil works, E&M works, the Taxes and Duties (e.g. Excise

duty, Sales Tax, Custom Duty etc.) has been considered in the rate analysis. The cost

estimate is divided into Civil, Electrical works. For Civil Works, the sub heads are as

under:

12.2.3 I - WORKS

Under this heading, provision has been made for various components of the Project.

12.2.4 A - PRELIMINARY

The Under this heading, "provision has been made for surveys and investigations to be

conducted to arrive at the optimum of the project components.

12.2.5 B - LAND

This covers the provision for acquisition of land for construction of the project, structures,

colonies, offices etc. The provision has been kept in the estimate as per actual.




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12.2.6 C - WORKS

This covers the cost of Concrete Gravity Dam, Spillway, Coffer Dams, Diversion

Tunnel, Inlet & Outlet Portal and Plug along with associated Hydro-Mechanical

equipments.

12.2.7 J - POWER PLANT CIVIL WORKS

This covers the cost of Civil Works of Project components viz: Power Intake, Head Race

tunnel with its construction adits, Surge Shaft, Pressure Shaft, Power House, Tail race

channel & associated Hydro Mechanical equipments.

The quantities indicated in the estimates for C - Works & J-Power Plant Civil Works (Civil

& HM) are calculated from the Engineering drawings.

12.2.8 K - BUILDINGS

Buildings, both residential and non-residential have been provided under this head.

Under the permanent category only those structures have been included, which will be

subsequently utilized for the running and maintenance of the project utilities. The costs

are worked out on plinth area basis for the type of construction involved as per

prevailing rates in project area.

12.2.9 M - PLANTATION

The provision under this head covers the plantation programme including Gardens etc.

required for beautification as considered necessary downstream of Dam and

appurtenances around Power House and other important structure. The provision is

made on the lump sum basis.

12.2.10 O - MISCELLANEOUS

The provision under this head covers the capital cost & maintenance of Electrification,

Water supply, Sewage disposal and drainage works, Recreation, Medical, Fire fighting

equipments, Inspection vehicles, School bus, Pay van, Visit of dignitaries, welfare

works etc.




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12.2.11 P - MAINTENANCE DURING CONSTRUCTION & Y- LOSSES ON STOCK

The provision under this head covers the cost of maintenance of all works during the

construction period. A provision of 1% of the total cost under the heads of C-Works, J-

Power House Civil Works and K-Buildings is considered.

12.2.12 Q - SPECIAL TOOLS AND PLANT

It is assumed that the work will be carried through Contracts and accordingly provision

for general purpose equipment and inspection vehicle only has been made as per CWC

guidelines.

12.2.13 R - COMMUNICATION

Provision under this head covers the cost of construction of roads and bridges for project

works. The road widths have been planned to cater to the anticipated traffic including

carriage of equipment for the Project. The cost of roads is based on the present rate

structure prevalent in the area of the Project, for the type of construction involved.

12.2.14 X - ENVIRONMENT AND ECOLOGY

A provision has been made under this head towards Bio-diversity Conservation, Creation

of Green belt, Restoration of Construction Area, Catchment Area Treatment,

Compensatory, Afforestation etc. The provision is made on the lump sum basis.

12.2.15 Y - LOSSES ON STOCK

The provision is made at 0.25% of the total cost of C-Works, J-Power Plant Civil Works

and K-Buildings only as per the CEA Guidelines.

12.2.16 ELECTRICAL WORKS AND GENERATING PLANT

The cost of generating plant and equipment is based on sources from India. The prices of

auxiliary equipment and services are based on prevailing market prices/costs at other

ongoing or commissioned projects in India.

12.2.17 II - ESTABLISHMENT

Provision for establishment has been made @ 8% of civil works.




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12.2.18 III - TOOLS AND PLANTS

This provision is distinct from that under Q-Special T&P and is meant to cover cost of

survey instruments, camp equipment and other small tools and plants. A nominal

provision of Rs.1.0 crore has been kept in the cost estimate.

12.2.19 IV - SUSPENSE

No provision has been made under this head as all the outstanding suspense are expected

to be cleared by adjustment to appropriate heads at completion of the project.

12.2.20 V - RECEIPTS AND RECOVERIES

Under this head, provision has been made for estimated recoveries by way of resale or

transfer temporary buildings and special tools & plants.

Table 12.1: Abstract of cost

S. No. Item Code

ITEM Amount (Lacs Rs)

Total Amount (Lacs Rs)

1 I WORKS

1-(I) A Preliminary 3445.00

1-(II) B Cost of Land including R &R Plan

2010.64

1-(III) C Works 21565.35

C.1 Cofferdam 940.50

C.2 Diversion Tunnel 1501.93

C.3 Dam 19122.92

J Power Plant - Civil Works

21164.54

J.1 Intake 1180.23

J.2 Head Race Tunnel 4299.70

J.3 All adits of HRT 428.40

J.4 Surge Shaft 1352.24

J.5 Pressure Shaft 8777.90

J.6 Power House 5126.07

1-(V) Others 10670.78

K Buildings 2032.00

M Plantation 25.00

O Miscellaneous 1105.00

P Maintenance @ 1% of C,J & K 447.62

Q Special T&P 149.26

R Communication 4800.00




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X Environment and Ecology (*excluding establishment)

2000.00

Y Losses to Stock @ 0.25% of (C+J+K) 111.90

1 I Works (Total) 58856.31

2 II Establishment Charges @

5147.68

3 III Tools & Plants @ 100.00

4 III Receipts and Recoveries

-152.75

5 IV Indirect Charges- 394.81

(a) Audit & Accounts etc.

0.50% of I Works 294.28

(b) capitalisation of abatement of cost of land revenue (either 5% of the culturable land cost or 20 times of the annual revenue loss)

100.53

TOTAL I TO IV 64346.06

S Power Plant Electro Mechanical Works

12750.00

Power Plant, Sub-station and Transmission 12750.00

Total Cost (Civil + E&M Works) 77096.06

Interest during construction (IDC)

12085.61

Financing Charges 653.55

Escalation 4182.42

TOTAL CAPITALIZED COST OF THE PROJECT (LACS RS)

94017.64

Say 94020.00

CHAPTER - XIII

ECONOMIC AND FINANCIAL EVALUATION




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CHAPTER - XIII

ECONOMIC AND FINANCIAL EVALUATION

13.1 GENERAL

Mawphu Hydroelectric Project, Stage - II is proposed as a run-of-river scheme on the




bank of the river.

The Project is estimated to cost Rs. 898.38 Crore at April 2016 Price Level including Rs.

215.65 Crore on C-Civil works, Rs. 211.65 Crore on J-Works, Rs. 127.50 Crore on Electrical

Works. Completed cost of the project is Rs. 940.20 Crore with Rs. 41.82 crore as escalation

cost. Interest During Construction (IDC) on completion is Rs. 120.86 crore. Levellized

tariff of energy generated at powerhouse at bus bar has been worked out as Rs. 5.46/unit

at April 2016 P.L. (Excluding transmission cost). Corresponding tariff for first year is Rs.

5.32/unit. With completed cost, 1st year and levellised tariff stand at Rs. 5.61/unit and Rs.

5.75/unit respectively.

The benefits and financial evaluation of the project have been considered as per the

standard guidelines issued by the Government of India. The norms laid down by the

Central Electricity Regulatory Commission (CERC) for Hydro projects have also been

kept in view in this regard.

13.2 PROJECT COST

The cost of construction of the project has been estimated at April 2016 price level with a

construction period of 60 months. The estimated Present Day Cost of the project is Rs.

892.57 crore, including Rs. 770.96 crore of Hard Cost and Rs. 121.61crore as IDC &

financial charges at April 2016 price level. Total completed cost of the project stands at Rs.

940.20 crore with Rs. 127.39 crore as cost towards IDC and financial charges. The

completion cost is based on the tentative financial assessment and it may vary based on

firm financial package.




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13.3 PHASING OF COST

The phasing of expenditure has been worked out on the basis of anticipated construction

schedule. Half yearly wise phasing of funds and calculation of Interest during

Construction (IDC) is as per the following Table 13.1

Table 13.1-Project Cost including IDC

(All figures are in Rs. Lacs) Half

Year Phasing of Hard Cost

Equity (30%)

Loan Due

IDC Equity share of IDC

Loan share of IDC

Amount Equity

Loan Amount

HY-1 784 235 549 25 7 17 243 566

HY-2 2368 710 1657 63 19 44 729 1701

HY-3 5563 1669 3894 190 57 133 1726 4027

HY-4 9603 2881 6722 434 130 304 3011 7027

HY-5 12087 3626 8461 790 237 553 3863 9014

HY-6 15416 4625 10791 1248 374 874 4999 11665

HY-7 13887 4166 9721 1749 525 1224 4691 10945

HY-8 12336 3701 8636 2217 665 1552 4366 10187

HY-9 5796 1739 4057 2572 772 1801 2510 5858

HY-10 3438 1031 2407 2799 840 1959 1871 4366

81278 24384 56895 12086 3626 8460 28009 65355

Hard Cost 81278 Equity 28009 30%

IDC 12086 Loan 65355 70%

Total Cost 93364 Total Cost 93364

13.4 ESCALATION IN COST

Total escalation amount considering 60 months as construction period is Rs. 41.82 crore.

13.5 FINANCING

The project shall be financed at the rate of interest of 9% p.a. For analysis purpose 70% of

capital cost is considered as debt and balance is equity.

13.6 ENERGY BENEFITS




Page: 246

The financial analysis is based on the energy output on 90% dependable year at 95% plant

availability. 1.0% auxiliary consumption has been considered in preliminary financial

evaluation of the project. For the purpose of calculation of tariff the free power has been

considered as per provisions of CERC norms.

13.7 ENERGY SALE PRICE

The energy tariff has been worked out as per practice with 15.50% return on equity. The

same has been used for sale of the energy.

13.8 THE ASSUMPTIONS TAKEN FOR WORKING OUT THE TARIFF ARE AS

FOLLOWS:

13.8.1 PROJECT LIFE

The project life has been taken as 35 years for all the above cases as per prevailing Indian

Hydropower policy.

13.8.2 INTEREST RATE

The interest rate of 9.00% has been reckoned for working out the financial return. The

interest during construction has also been capitalized as 70% loan and 30% equity.

13.8.3 RETURN ON EQUITY

For working out the unit cost of energy, the return on equity has been taken at 15.5% as

per prevailing practice of Govt. of India.

13.8.4 DEPRECIATION

Uniform depreciation @ 2.56% per annum has been considered for initial 28 years. For

remaining 7 years, the balance depreciation i.e.90% of total project cost minus land cost

has been equally spread out.

13.8.5 OPERATION AND MAINTENANCE CHARGES

2.0% of capital cost has been taken for operation and maintenance charges with an annual

escalation of 6.64%.

13.8.6 INTEREST ON WORKING CAPITAL




Page: 247

Interest on Working Capital has been calculated as given below:

(i) Receivables equivalent to two months of fixed cost;

(ii) Maintenance spares @ 15% of operation and maintenance expenses and

(iii) Operation and maintenance expenses for one month.

13.8.7 AUXILIARY AND TRANSFORMATION LOSSES

The auxiliary and transformation losses have been taken as 1.0% of the design energy in

90% dependable year. (Design Energy= 331MU, Unit Sold = 283.34*(1-1.0%) =327.69MU)

13.8.8 OTHER MISCELLANEOUS ASSUMPTIONS

• Interest rate on Working Capital = 12.80%

• Discounting Rate = 12.07%

• Tenure for Loan Repayment = 28 Years

• Corporate tax is taken as 34.61% and Minimum alternate Tax is taken as

21.34% as per Govt. of India Hydropower Policy.

13.8.9 TARIFF COMPUTATION

With above assumptions the tariff for the project for 90% dependable year comes out to

be:

Present day cost (PL April 2016)



Completed cost



Refer Annexure 13.1 & 13.2 for tariff computations.




Page: i

Calculation of Tariff (Price Level April’2016) Annexure-13.1 Annual Design Energy

(MU)

= 331.00 Cost incl IDC (Rs Cr)

= 892.57 FI Loan and bond (Rs. Cr.)

= 624.80

Auxilary Loss (%) = 1.00% Equity (Rs Cr)

= 267.77 Loan and Bond Interest

= 9.00%

Free Power (%)

= 13.00% Interest on W.C.

= 12.80% Subordinate Loan (Rs. Cr.)

= 0.00

Net Saleable Energy (MU) = 285.09 Grant (Rs. Cr.) = 0.00 Subordinate Loan Interest

= 1.00%

Land Cost (Rs.

Crores)

= 20.41 O&M Charges

= 2.00%

Cost of R&R (Rs.crore)

= 10.15 Avg. Depriciation

Rate

= 2.56% Return on Equity (RoE)

= 15.50%

Discounting Factor = 12.07% Min Alternate Tax(MAT) = 21.34%

FI Loan Repayment

Period (Year)

= 28.00 Corporate Tax = 34.61%

SB Repayment Period

(Year)

= 15.00 Return on Equity (RoE) with MAT = 19.705%

Return on Equity (RoE) with Corporate

Tax

= 23.703%




Page: ii

Year

FI Loan

& Bond

Loan

Rep

aymen

t (R

s

Cr)

FI Loan

Rep

aymen

t (R

s

Cr)

SB Loan

Rep

aymen

t (R

s

Cr)

Interest on

Loan

(Rs

Cr)

Dep

reciation

(Rs Cr)

RoE (Rs Cr)

O &

M Charges

(Rs Cr)

Interest on Working Capital (Rs Cr)

Annual Fixed

Charges (Rs Cr)

Tariff (R

s /

unit)

O&M for

one

month

Two

month's

receivab

le

Maint.

spares

Interest

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 624.80 22.31 55.23 22.31 52.75 17.65 1.47 25.28 2.65 3.76 151.70 5.32

2 602.48 22.31 53.22 22.31 52.75 18.82 1.57 25.15 2.82 3.78 150.88 5.29

3 580.17 22.31 51.21 22.31 52.75 20.07 1.67 25.02 3.01 3.80 150.14 5.27

4 557.85 22.31 49.20 22.31 52.75 21.40 1.78 24.92 3.21 3.83 149.49 5.24

5 535.54 22.31 47.19 22.31 52.75 22.82 1.90 24.82 3.42 3.86 148.94 5.22

6 513.23 22.31 45.19 22.31 52.75 24.34 2.03 24.75 3.65 3.89 148.48 5.21

7 490.91 22.31 43.18 22.31 52.75 25.96 2.16 24.69 3.89 3.94 148.13 5.20

8 468.60 22.31 41.17 22.31 52.75 27.68 2.31 24.65 4.15 3.98 147.89 5.19

9 446.28 22.31 39.16 22.31 52.75 29.52 2.46 24.63 4.43 4.03 147.77 5.18

10 423.97 22.31 37.15 22.31 52.75 31.48 2.62 24.63 4.72 4.09 147.78 5.18

11 401.66 22.31 35.14 22.31 63.46 33.57 2.80 26.48 5.03 4.39 158.87 5.57

12 379.34 22.31 33.14 22.31 63.46 35.80 2.98 26.53 5.37 4.46 159.17 5.58

13 357.03 22.31 31.13 22.31 63.46 38.17 3.18 26.60 5.73 4.55 159.62 5.60

14 334.71 22.31 29.12 22.31 63.46 40.71 3.39 26.71 6.11 4.63 160.23 5.62

15 312.40 22.31 27.11 22.31 63.46 43.41 3.62 26.84 6.51 4.73 161.02 5.65

16 290.08 0.00 22.31 0.00 25.10 22.31 63.46 46.29 3.86 27.00 6.94 4.84 162.01 5.68

17 267.77 0.00 22.31 23.10 22.31 63.46 49.37 4.11 27.20 7.40 4.96 163.19 5.72

18 245.46 0.00 22.31 21.09 22.31 63.46 52.64 4.39 27.43 7.90 5.08 164.59 5.77

19 223.14 0.00 22.31 19.08 22.31 63.46 56.14 4.68 27.70 8.42 5.22 166.21 5.83

20 200.83 0.00 22.31 17.07 22.31 63.46 59.87 4.99 28.01 8.98 5.37 168.08 5.90

21 178.51 0.00 22.31 15.06 22.31 63.46 63.84 5.32 28.37 9.58 5.54 170.21 5.97




Page: iii

Year

FI Loan

& Bond

Loan

Rep

aymen

t (R

s

Cr)

FI Loan

Rep

aymen

t (R

s

Cr)

SB Loan

Rep

aymen

t (R

s

Cr)

Interest on

Loan

(Rs

Cr)

Dep

reciation

(Rs Cr)

RoE (Rs Cr)

O &

M Charges

(Rs Cr)


Annual Fixed

Charges (Rs Cr)

Tariff (R

s /

unit)

O&M for

one

month

Two

month's

receivab

le

Maint.

spares

Interest

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

22 156.20 0.00 22.31 13.05 22.31 63.46 68.08 5.67 28.77 10.21 5.72 172.62 6.06

23 133.89 0.00 22.31 11.05 22.31 63.46 72.60 6.05 29.22 10.89 5.91 175.33 6.15

24 111.57 0.00 22.31 9.04 22.31 63.46 77.42 6.45 29.72 11.61 6.12 178.35 6.26

25 89.26 0.00 22.31 7.03 22.31 63.46 82.56 6.88 30.28 12.38 6.34 181.71 6.37

26 66.94 0.00 22.31 5.02 22.31 63.46 88.05 7.34 30.90 13.21 6.59 185.42 6.50

27 44.63 0.00 22.31 3.01 22.31 63.46 93.89 7.82 31.59 14.08 6.85 189.52 6.65

28 22.31 0.00 22.31 1.00 22.31 63.46 100.13 8.34 32.34 15.02 7.13 194.03 6.81

29 0.00 0.00 0.00 0.00 22.31 63.46 106.77 8.90 33.33 16.02 7.46 200.00 7.02

30 0.00 0.00 0.00 0.00 22.31 63.46 113.86 9.49 34.58 17.08 7.83 207.46 7.28

31 0.00 0.00 0.00 0.00 23.13 63.46 121.43 10.12 36.04 18.21 8.24 216.26 7.59

32 0.00 0.00 0.00 0.00 23.13 63.46 129.49 10.79 37.46 19.42 8.66 224.74 7.88

33 0.00 0.00 0.00 0.00 23.13 63.46 138.09 11.51 38.96 20.71 9.11 233.79 8.20

34 0.00 0.00 0.00 0.00 23.13 63.46 147.25 12.27 40.57 22.09 9.59 243.44 8.54

35 0.00 0.00 0.00 0.00 23.13 63.46 157.03 13.09 42.29 23.55 10.10 253.73 8.90

624.80

0.00 784.94

NPV of Annual Fixed Charges (Rs Cr) = 1265.80 NPV energy MU)= 2318.21 Levellised Tariff = 5.46




Page: i

Calculation of Tariff (Price Level April’2016) Annexure-13.2 Annual Design Energy

(MU)

= 331.00 Cost incl IDC (Rs Cr)

= 940.20 FI Loan and bond (Rs. Cr.)

= 658.14

Auxilary Loss (%) = 1.00% Equity (Rs Cr)

= 282.06 Loan and Bond Interest

= 9.00%

Free Power (%)

= 13.00% Interest on W.C.

= 12.80% Subordinate Loan (Rs. Cr.)

= 0.00

Net Saleable Energy (MU) = 285.09 Grant (Rs. Cr.) = 0.00 Subordinate Loan Interest

= 1.00%

Land Cost (Rs.

Crores)

= 20.41 O&M Charges

= 2.00%

Cost of R&R (Rs.crore)

= 10.15 Avg. Depriciation

Rate

= 2.56% Return on Equity (RoE)

= 15.50%

Discounting Factor = 12.07% Min Alternate Tax(MAT) = 21.34%

FI Loan Repayment

Period (Year)

= 28.00 Corporate Tax = 34.61%

SB Repayment Period

(Year)

= 15.00 Return on Equity (RoE) with MAT = 19.705%

Return on Equity (RoE) with Corporate

Tax

= 23.703%




Page: ii

Year

FI Loan

& Bond

Loan

Rep

aymen

t (R

s

Cr)

FI Loan

Rep

aymen

t (R

s

Cr)

SB Loan

Rep

aymen

t (R

s

Cr)

Interest on

Loan

(Rs

Cr)

Dep

reciation

(Rs Cr)

RoE (Rs Cr)

O &

M Charges

(Rs Cr)


Annual Fixed

Charges (Rs Cr)

Tariff (R

s /

unit)

O&M for

one

month

Two

month's

receivab

le

Maint.

spares

Interest

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 658.14 23.51 58.17 23.50 55.57 18.60 1.55 26.63 2.79 3.96 159.81 5.61

2 634.64 23.51 56.06 23.50 55.57 19.84 1.65 26.49 2.98 3.98 158.95 5.58

3 611.13 23.51 53.94 23.50 55.57 21.15 1.76 26.36 3.17 4.01 158.17 5.55

4 587.63 23.51 51.83 23.50 55.57 22.56 1.88 26.25 3.38 4.03 157.49 5.52

5 564.12 23.51 49.71 23.50 55.57 24.06 2.00 26.15 3.61 4.07 156.90 5.50

6 540.62 23.51 47.60 23.50 55.57 25.65 2.14 26.07 3.85 4.10 156.42 5.49

7 517.11 23.51 45.48 23.50 55.57 27.36 2.28 26.01 4.10 4.15 156.05 5.47

8 493.61 23.51 43.37 23.50 55.57 29.17 2.43 25.97 4.38 4.20 155.80 5.46

9 470.10 23.51 41.25 23.50 55.57 31.11 2.59 25.95 4.67 4.25 155.68 5.46

10 446.60 23.51 39.14 23.50 55.57 33.18 2.76 25.95 4.98 4.31 155.69 5.46

11 423.09 23.51 37.02 23.50 66.85 35.38 2.95 27.90 5.31 4.63 167.37 5.87

12 399.59 23.51 34.90 23.50 66.85 37.73 3.14 27.95 5.66 4.70 167.69 5.88

13 376.08 23.51 32.79 23.50 66.85 40.23 3.35 28.03 6.03 4.79 168.16 5.90

14 352.58 23.51 30.67 23.50 66.85 42.90 3.58 28.13 6.44 4.88 168.81 5.92

15 329.07 23.51 28.56 23.50 66.85 45.75 3.81 28.27 6.86 4.99 169.65 5.95

16 305.57 0.00 23.51 0.00 26.44 23.50 66.85 48.79 4.07 28.45 7.32 5.10 170.68 5.99

17 282.06 0.00 23.51 24.33 23.50 66.85 52.03 4.34 28.65 7.80 5.22 171.93 6.03

18 258.56 0.00 23.51 22.21 23.50 66.85 55.49 4.62 28.90 8.32 5.36 173.40 6.08

19 235.05 0.00 23.51 20.10 23.50 66.85 59.17 4.93 29.19 8.88 5.50 175.12 6.14

20 211.55 0.00 23.51 17.98 23.50 66.85 63.10 5.26 29.52 9.46 5.66 177.09 6.21

21 188.04 0.00 23.51 15.87 23.50 66.85 67.29 5.61 29.89 10.09 5.84 179.34 6.29




Page: iii

Year

FI Loan

& Bond

Loan

Rep

aymen

t (R

s

Cr)

FI Loan

Rep

aymen

t (R

s

Cr)

SB Loan

Rep

aymen

t (R

s

Cr)

Interest on

Loan

(Rs

Cr)

Dep

reciation

(Rs Cr)

RoE (Rs Cr)

O &

M Charges

(Rs Cr)


Annual Fixed

Charges (Rs Cr)

Tariff (R

s /

unit)

O&M for

one

month

Two

month's

receivab

le

Maint.

spares

Interest

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

22 164.54 0.00 23.51 13.75 23.50 66.85 71.76 5.98 30.31 10.76 6.02 181.88 6.38

23 141.03 0.00 23.51 11.63 23.50 66.85 76.52 6.38 30.79 11.48 6.23 184.73 6.48

24 117.53 0.00 23.51 9.52 23.50 66.85 81.60 6.80 31.32 12.24 6.45 187.92 6.59

25 94.02 0.00 23.51 7.40 23.50 66.85 87.02 7.25 31.91 13.05 6.68 191.46 6.72

26 70.52 0.00 23.51 5.29 23.50 66.85 92.80 7.73 32.56 13.92 6.94 195.38 6.85

27 47.01 0.00 23.51 3.17 23.50 66.85 98.96 8.25 33.28 14.84 7.22 199.70 7.00

28 23.51 0.00 23.51 1.06 23.50 66.85 105.53 8.79 34.08 15.83 7.51 204.45 7.17

29 0.00 0.00 0.00 0.00 23.50 66.85 112.54 9.38 35.12 16.88 7.86 210.74 7.39

30 0.00 0.00 0.00 0.00 23.50 66.85 120.01 10.00 36.43 18.00 8.25 218.61 7.67

31 0.00 0.00 0.00 0.00 24.56 66.85 127.98 10.66 38.01 19.20 8.69 228.07 8.00

32 0.00 0.00 0.00 0.00 24.56 66.85 136.48 11.37 39.50 20.47 9.13 237.02 8.31

33 0.00 0.00 0.00 0.00 24.56 66.85 145.54 12.13 41.09 21.83 9.61 246.55 8.65

34 0.00 0.00 0.00 0.00 24.56 66.85 155.20 12.93 42.79 23.28 10.11 256.72 9.00

35 0.00 0.00 0.00 0.00 24.56 66.85 165.51 13.79 44.59 24.83 10.65 267.57 9.39

658.14

0.00 827.81

NPV of Annual Fixed Charges (Rs Cr) = 1333.55 NPV energy MU)= 2318.21 Levellised Tariff = 5.75

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