Rangyong - Ministry of Power

CHAPTER 

I 

TABLE OF CONTENTS 

DESCRIPTION 

Executive Summary 

Preliminary Feasibility Report 

Rangyong HE Project (3 x 47 MW) 

PAGE NO. 

1-11 

II Background Information 12-19 

III Project Area 20-27 

IV Topographical & Geo-technical Aspects 28-33 

V Hydrology 34-58 

VI Conceptual Layout and Planning 59-71 

VII Power Potential Studies 72-102 

VIII Power Evacuation 103 

IX Environmental Aspects 104-124 

X Infrastructure 125-128 

XI Construction Planning & Schedule 129-134 

XII Cost Estimate 135-174 

XIII Economic Evaluation 175-182 

Plates 

Annexures

TITLE 

LIST OF PLATES 



PLATE 

No. 

Preliminary Ranking Study Layout 1 

Cascade Development of Teesta River Basin 2 

Layout Plan of Schemes in Upper Part of Teesta Basin 3 

Cascade Development of Tolung River Basin 4 

Geological Plan of The Project Area 4.1 

Vicinity Map 6.1 

Project Layout Plan 6.2 

Dam Area Layout Plan 6.3 

Power House Area Layout Plan 6.4 

Water Conductor System L-Section 6.5 

Upper Dam Upstream Elevation 6.6 

Lower Dam Upstream Elevation 6.7 

Dam: Spillway & Non-Overflow Cross Section 6.8 

Typical Cross Section Of Constituents Of Water 

Conductor System & Diversion Tunnel 

Single Line Diagram – Power Evacuation 8.1 

6.9

TITLE 

ANNEXURES 



No. 

Geology of the Area Around the Project- By G SI 4.1 

Technical Report on Seismic History and 

Seismicity- By IMD 

4.2 

Preliminary Ranking Study Report- By CEA 6.1 

Reply on CEA/CWC Comments on Draft PFR 6.2



CHAPTER – I 

EXECUTIVE SUMMARY

1.0 INTRODUCTION 

CHAPTER-I 

EXECUTIVE SUMMARY 

1 



The Rangyong Hydroelectric Project located in North Sikkim district of Sikkim 

envisages utilization of the waters of the river Rangyong Chu a tributary of river Teesta 

for power generation on a run of river type development, harnessing a head of about 

738m by constructing two dams, one at downstream of confluence of Passaram Chu and 

Umram Chu tributaries of Rangyong Chu (Upper Dam) and other at Rangyong Chu 

(Lower dam). 

The project with a proposed installation of 141 MW (3 x 47MW) would afford an annual 

energy generation of 639.52 GWh in a 90% dependable year. The tariff from the project 

at present day cost would be Rs2.49 per KWh(levellised). 

The diversion sites are located at Latitude 27º36’00” North, Longitude 88º22’26” East 

(Upper Dam) and Latitude 27º35’00” North, Longitude 88º26’00” East (Lower Dam). 

The upper dam site is located just downstream of the confluence of Passaram Chu and 

Umram Chu and lower dam site on Rangyong chu . Presently lower dam site is not 

approachable while the upper dam site is approachable by a difficult foot path via 

Phontong from road ending at Lingza. The nearest road end is at Lingdem/ Lingza, 

which is about 15km from Mangan, the head quarters of North Sikkim District of Sikkim. 

The nearest railhead is at New Jalpaiguri and airport at Bagdogra. 

1.1 GENERAL PROJECT FEATURES 

The Rangyong HE Project envisages construction of : 

1. Two concrete dams, both 65 m high, one across river Rangyong Chu (Lower 

dam) and other at downstream of the confluence of Passaram Chu and Umram

2 



Chu to provide a total live storage of 1.97mcum. with FRL at 1845m and MDDL 

at 1825m; 

2. one link tunnel of 2.0km length and 3.3m diameter connecting upper dam with 

lower dam 

3. two intakes and two desilting chambers of size 125m(L)x 6 m(W)x 9m(H) to 

remove silt particles of size 0.2mm and above; 

4. a 7.5km long , 3.3m diameter head race tunnel terminating in a surge shaft; 

5. a 75m high, 10m dia surge shaft; 

6. 1000m long, 2.5m dia one pressure shaft; 

7. an underground power house having an installation of 3 Pelton turbine generating 

units of 47 MW each operating under a net head of about 723m; and 

8. a 300m long, 3.3m diameter tailrace tunnel to carry the power house release back 

to the river; 

The power generated from the project would be evacuated through one number 220KV 

double circuit lines to a proposed pooling station near Teesta II HE Project to feed power 

to the national grid. 

The salient features of the project are as under. 

LOCATION 

SALIENT FEATURES 

State Sikkim 

District North Sikkim 

Location of Upper Dam Just D/S of confluence of Umram 

chu and Passaram chu 

Location of Lower Dam On Rangyong Chu 

Location of Power House Just u/s of Reservoir of Panan H.E. 

project 

Nearest Rail head New Jalpaiguri

Nearest Airport Bagdogra 

Latitude upper dam & Power house 27º36’00’’& 27º33’14’’ 

Latitude lower dam & Power house 27º35’00’’& 27º33’14’’ 

Longitude of upper dam & Power house 88º22’26’’& 88º26’00’’ 

Longitude of lower dam & Power house 88º21’48’’& 88º26’00’’ 

HYDROLOGY 

Catchment area upper dam 146 km 2 

Catchment area Lower dam 127 km 2 

Design Flood for upper dam 750 m 3 /sec 

Design Flood for lower dam 675 m 3 /sec 

DIVERSION TUNNEL (for both dams) 

Diameter & Shape 3.3 m, Horse-shoe shaped 

Length 300 m 

Diversion Discharge ± 100 m 3 /sec 

Diversion Tunnel Gate 1 No. Vertical lift gate 

Size of Gate 

COFFER DAMS (for both dams) 

3 

3.3 m × 4 m 



Type Rockfill with central clay core. 

Maximum height of upstream coffer dam ± 15.0 m 

Maximum height of downstream coffer dam ± 8.0 m 

UPPER DAM 

Type Concrete Gravity 

Dam Top EL. 1850 m 

Length at Dam top 300 m

River bed level at dam site EL.1795m 

Maximum Dam height (above deepest 

foundation level) 

Dam height (above River bed level) 

LOWER DAM 

4 

65 m 

55 m 

Type Concrete Gravity 

Dam Top EL. 1850 m 

Length at Dam top 250 m 

River bed level at dam site EL.1795m 

Maximum Dam height (above deepest 

foundation level) 

65 m 

Dam height (above River bed level) 55 m 

SPILLWAY (For both the dams) 

Type Orifice Type 

No. of bays 3 

Crest level of spillway EL. 1805 m 

Size of the opening 3m(w) X 6m(H) 

Design flood (PMF) 750 / 675 m 3 /sec 

RESERVOIR 

UPPER DAM 

Full Reservoir Level (FRL) EL.1845 m 

Minimum draw down level (MDDL) EL.1825 m 


Rangyong HE Project (3 x 47 MW)

Area under submergence at FRL 15.62 Ha 

Gross Storage 3.05 MCM 

Live Storage 1.67 MCM 

LOWER DAM 

Full Reservoir Level (FRL) EL.1845 m 

Minimum draw down level (MDDL) EL.1825 m 

Area under submergence at FRL 2.5 Ha 

Gross Storage 0.525 MCM 

Live Storage 0.30 MCM 

LINK TUNNEL 

Invert level EL.1815 m 

Size 3.3 m diameter 

Size of Gate 3.3 m × 3.3 m 

5 



Trash Rack Steel Trash Racks with Raking 

Machine 

Length 1 Km 

INTAKE 

Number Two 

Invert level EL.1815 m 

Size of each Gate 3 m × 3 m 

Trash Rack Steel Trash Racks with Raking 

2 

Machine 

Design discharge 13.38 m 3 /sec in each intake

DESILTING ARRANGEMENT 

6 



No., Type & size of desilting chamber 2 Nos.,Dufour type chambers each 

Total Design Discharge in each chamber 13.38 m 3 /sec 

125 m long, 6 m wide, ht.9 m 

Particle size to be removed ≥ 0.2 mm (90% efficiency) 

SILT FLUSHING TUNNEL 

Size & shape 1.5 m x 3.0 m, D-shaped 

HEADRACE TUNNEL 

Size & type 3.3 m Dia, Horse –shoe shaped, 

concrete lined 

Design discharge 22.30 m 3 /sec 

Length 7.5 Km 

Adits 3 No.; 3.3 m D-shaped 

SURGE SHAFT 

Size & type 10m diameter 

Vertical Shaft height ± 75 m 

PRESSURE SHAFT 

Type Steel Lined; one, Inclined 

Diameter 

Length 

Adits to Pressure Shaft 

2.5 m 

1000 m 

2 Nos., 3.3 m dia

POWER HOUSE COMPLEX 

Type Under ground 

Tail water level at outlet 1098 m 

Turbine Axis Elevation 1100.15 m 

Type of Turbine Vertical Pelton 

Generating Capacity 3X47 MW 

Gross head 738.18 m 

Rated Net head 723.18 m 

Design Discharge 22.30 m 3 /sec 

Power House Size 100m X 22.5m X 40m 

TRT 

Diameter and type 3.3m dia, Horse-shoe 

Tail Water level at outlet 1098m 

Length 300 m 

SWITCH YARD 

Size 155 M X 100M 

COST ESTIMATES & FIANANCIAL ASPECTS ( Rs. Crores) 

Civil Works 672.71 

Electro Mechanical Works 113.11 

Sub Total (Generation) 785.82 

Transmission Works 13.68 

7 



Total (Hard Cost) 799.50 at June,2003 Price Level 

Interest During Construction 91.32 

Grand Total 890.82 

Tariff for first year per KWh 

a. with 12% free power 

Rs. 3.07

. without 12% free power Rs. 2.70 

Levellised Tariff per KWh 

a. with 12% free power 

b. without free power 

8 

Rs. 2.49 

Rs. 2.19 

COSTRUCTION PERIOD 4 years 

1.2 STUDIES/INVESTIGATIONS UNDERTAKEN 

• Study of topographic maps and remote sensing imageries 



• Reconnaissance of area for identifying probable alternative sites of projects 

components. 

• Study of regional geotechnical features/ seimotectonic aspects. 

• Geological appraisal of proposed project components. 

• Water availability design flood studies based on available meteorological/ 

hydrological data. 

• Conceptual layout and project planning. 

• Power potential studies. 

• Study of biotic environment, socio-economic environment for prediction of 

environmental impacts of the projects. 

• Study of existing infrastructure. 

• Cost benefit and economic evaluation. 

1.3 RESULTS OF STUDIES AND INVESTIGATIONS 

1.3.1 Geology 

The preliminary geological survey of the locations of all the structures on the ground was 

carried out after site visits. The site-specific geological data were got collected and 

utilized in the design of various component of the project. The survey of the near by area 

was also carried out to co-relate the geology of the project area. The underground 

powerhouse has been fixed after observing the competency of rock and its cover.

1.3.2 Hydrology 

9 



The rivers Rangyong Chu, Umram Chu and Passaram Chu drain a total catchment area of 

about 273sq.km at the proposed dam sites. The water availability for the project has been 

considered on the basis of 10-daily discharge series at Lachen for the period from 1976- 

1997. The water availability at the upper/lower dam sites has been derived from the 

above data on the basis of catchment area proportion and applying an overall reduction 

factor of 16 % and 17.8% respectively. The computed inflow series works out has been 

utilized for Power Potential Studies. The design flood has been assessed as 750 and 675 

cumecs for upper and lower dam sites respectively. 

1.3.3 Power Potential Studies 

The computed inflow series for 22 years viz Jan 1976 to Dec 97 has been considered in 

the assessment of a power benefits from the project. As per GOI notification for tariff the 

year 1976-77 corresponds to 90% dependable year. An installation of 141MW 

comprising 3 generating units of 47MW has been proposed. The energy availability from 

the project in a 90%dependable and an average year has been summarized below: 

Annual Energy Generation 

Annual Energy Generation (GWh) 639.52 

Annual Load Factor (%) 51.78 

Generation during Lean Flow Season 

Energy Output (GWh) 343.76 

Load Factor (%) 37.21 

The design energy for tariff at 95% availability in a 90% dependable year has been 

worked out at 639.52 GWh. 

A pondage of 1.97 mcum has been provided in the diversion dams, which would enable 

the station to operate as peaking station. The pondage is equivalent to 3460 MWh which 

sufficient to operate the station for 4 hours.

1.3.4 Power Evacuation Aspects 

10 



The power generated from the project would be evacuated through 220KV, double circuit 

lines to a proposed pooling station near Teesta Stage-II project to feed into the Grid 

which in turn connected to National Grid. 

1.3.5 Environmental Aspects 

The project is located in north district of Sikkim. The total land requirement for the 

construction of various components is about 144ha. Most of the land falls under the 

category of private land. Based on assessment of environmental impacts, management 

plans have to be formulated for Catchment Area Treatment, compensatory afforestation 

and other environmental issues. These issues would be addressed during the investigation 

for DPR. 

1.3.6 Estimates Of The Cost 

The project is estimated to cost Rs. 890.82 crores including IDC at June,2003 price 

levels. The preliminary cost estimate of the project has been prepared as per guidelines of 

CEA/CWC. The break down of the cost estimate (Rs. Crores) is given below: 

Civil works : 672.71 

Electro Mechanical Works : 113.11 

Sub Total (Generation) : 785.82 

Transmission Works : 13.68 

Total (Hard Cost) : 799.50 

Interest During Construction : 91.32 

Grand Total : 890.82 

1.3.7 Financial Aspects 

As indicated above, the Rangyongl HE project with an estimated cost of Rs. 890.82 

crores (including IDC of Rs. 91.32 crores) and design energy of 639.52GWh in a 90% 

dependable year is proposed to be completed in a period of 4 years. The tariff has been

11 



worked out considering a debt-equity ratio of 70:30, 16% return on equity, annual interest 

rate on loan at 10% and 12% of energy as free power to Home State available after 

losses. The tariff for the first year and levellised tariff has been worked out Rs. 3.07/KWh 

& Rs. 2.49/KWh respectively. 

1.3.8 Conclusion 

The Rangyong HE project involves simple civil works and could be completed in 4 years. 

The project would afford a design energy of 639.52 GWh in a 90% dependable year. The 

cost per MW installed work out Rs.5.57 crores. The Preliminary Feasibility Report 

indicates that the scheme merit consideration for taking up for Survey & Investigation 

and preparation of DPR.



CHAPTER – II 

BACKGROUND INFORMATION

2.1 GENERAL Information 

2.1.1 Introduction 

CHAPTER –II 

BACKGROUND INFORMATION 

12 



Sikkim has become 22 nd state of India in 1975. It is one of the most picturesque regions 

of Asia. The bowl like, mountain –girdled state in the eastern Himalayas bordered on the 

west by Nepal, on the north by Tibet, on the east by Bhutan and the south by Darjeeling 

district of the West Bengal, lies between 27 0 to 28 0 north latitude and 88 0 to 89 0 east 

longitudes. The Sikkim is the youngest and small hill state of India having an area of 

7096 Sqkm. Sikkim is surrounded by important mountain ranges. The chola range of 

mountains on its east forms the watershed between it and Bhutan on one side and chumbi 

valley of Tibet on the other. The well-known singalila ridge is of the great Himalayas 

peaks. 

Sikkim is divided into four districts. The most populated area is the Eastern district, 

which contains the capital town Gangtok followed by Southern and Western districts. 

The northern district is sparsely populated because of its inhospitable climate and steep 

ridges. Lying along the slopes of Himalayas between Tibet and plain of India, cut off 

from the rest of the world by mighty mountains, Sikkim’s scenic beauty has no parallel in 

the East Sikkim’s historic past, mystic religion, sublime monasteries and age old rituals 

have an attraction hardly to be found anywhere else in the world. 

Sikkim is mountainous terrain with cliffs and valleys. Dominating both legend and 

landscape is the mighty massif of Kanchendzonga known to the outside world as 

Kanchenjunga, it is the third highest peak in the world, towering at 8550 meters. Sikkim 

is drained by number of Perennial Rivers. However, the two main river systems are 

Teesta and Rangit. The other entire stream eventually joins one or the other. Rangit also 

joins the Teesta just near the broader between Sikkim and West Bengal at Melli. Besides

13 



the river, there are number of lakes and hot springs which add to the beauty of the region. 

The important hot springs are Phut sachu, Raeong sachu, Yumthang and Momay. 

2.1.2 Topography 

Geographical area of Sikkim State is about 7300 sq. km. The maximum horizontal length 

from north to south is about 112 Km. whereas the maximum width from east to west is 90 

Km. The Tibetan Plateau on the north, Nathula and other passes on the north east, Bhutan 

on the south east, Darjeeling district of West Bengal on the south and Singalila range of 

Nepal from the boundaries of this picturesque Himalayan State. It is a hill state having no 

plain area. The altitude above mean sea level varies from 213m in the south to over 

8500m in the northwest. The Khangchedzonga, the third highest peak in the world at an 

elevation of about 8550m adorns the state with its beautiful range covered with shining 

snow. Gangtok, the capital is about 1677m above mean sea level. The northern part of the 

state is cut into deep escarpments. The northern part is not populated except in Lachung 

and Lachen valleys. Southern Sikkim is, however, more open and fairly well cultivated. 

2.1.3 Rivers 

The river Teesta is one of the main Himalayan Rivers, which originates in the glaciers of 

Sikkim at an elevation of over 8500m above mean sea level. River rises in mountainous 

terrain and is formed mainly by the union of two hill streams Lachen Chu and Lachung 

Chu at Chungthang in North Sikkim. After the confluence of Lachen Chu and Lachung 

chu at Chungthang, the river gradually increases in width and takes a wide flowing down 

to Singhik, dropping in elevation from 1550m to 750m. At Singhik, the river receives one 

of the its major tributaries, the Talung chu on its right. Tolung Chu originates from the 

Talung glaciers, which are the part of the Khangchendzonga range. From Singhik, the 

rivers flow towards Dikchu in a very deep valley and drops from 750mto 550m. From 

Dikchu the river flows in a big curve again down to the Singtam with a drop of about 

200m. The Rongnichu, which drains the Changu lake area joins Teesta from left at 

Singtam and the river receives Rangpo Chu at Rangpo. After Rangpo, Teesta start

14 



widening rapidly and is joined by the great Rangit at Melli bazar on Sikkim – West 

Bengal border. 

2.1.4 Communication 

By Air 

Bagdogra is the nearest airport of Sikkim. There are regular scheduled flights operated by 

the Indian airlines and other private airlines between Calcutta, the capital of West Bengal 

and Bagdogra and also between New Delhi and Bagdogra. Jeep taxis are available 

outsides Bagdogra airport for Gangtok. Gangtok is 124 kms from Bagdogra and the 

journey takes about 4 hours by jeep and 5 hours by bus. 

By Rail /Road 

The two closest railway stations to Gangtok are Siliguri junction, (Meter Gauge) which is 

114km away and New Jailpaiguri (Broad Gauge), which is 125km away. A number of 

trains are available for Calcutta, Delhi, Guwhati and other important cities of India. 

Besides jeep taxis, Sikkim National Transport and other private buses ply regularly 

between Sikkim and Siliguri. 

2.1.5 The Project 

2.1.5.1 Background 

In order to exploit vast hydro potential in the country and to achieve the ideal hydro 

thermal mix of 40:60, the Honourable Prime Minister of India had launched a hydro- 

electric initiative on 24th May 2003 to develop 50,000MW hydro power potential in the 

country. Accordingly, based on the results of the preliminary ranking studies of Central 

Electricity Authority, 162 hydroelectric power schemes with estimated installed capacity 

of 50,560MW were selected in 16 states for preparation of Pre Feasibility Reports. The 

work of preparation of PFR’s was entrusted by Ministry of Power under overall 

coordination of CEA to NHPC Ltd, SJVN Ltd, NEEPCO, WAPCOS, KPCL, HPSEB and 

UJVN Ltd as consultancy work. NHPC was entrusted a total number of 43 schemes of

15 



21345 MW comprising of 7 schemes in Indus-Jhelam Basin J&K, 25 schemes in Dihang- 

Dibang-Subansiri Basins Arunachal Pradesh, 1 scheme in Narmada Basin Madhya 

Pradesh and 10 schemes in Teesta Basin Sikkim. The Rangyong is one of the such 

scheme for PFR. 

2.1.5.2 About The Project 

The project is located on the river Rangyong chu in Dzongu area of North district of 

Sikkim. The headquarter of the district North Sikkim is at Mangan. The project involves 

construction of two 65m high concrete dams, a 2.0 Km link tunnel, a 7.5 Km long 

headrace tunnel and an underground powerhouse with an installed capacity of 141 MW. 

The project shall generate 639.52 MU of energy in a 90% dependable year. The 

upperdam is located just downstream of the confluence of Umram Chu and Passaram 

Chu. The lowerdam is located on the river Rangyong Chu near by the place called 

Singnok.The underground powerhouse is located just u/s of the confluence of Rangyong 

Chu and Ringyong Chu. The place Singnok nearest to Dam site, is connected from 

Mangan by 18 km long state PWD road upto Lavan and a footpath of about 12km via 

Phontong. The underground power house is located just u/s of confluence of Ringyong 

Chu and Rangyong Chu. 

2.2 POWER SCENARIO AND EXISTING INSTALLATION 

2.2.1 Power System In India 

The Power System in India has grown from small, isolated stations, serving limited 

consumers in and around large cities, into large regional Power Grids. The generating 

capacity installed in the country has already grown to 107903.53 MW by March 2003. 

For the purpose of system planning and operation the country has been divided into 

following five geopolitical regions: Northern, Western, Southern, Eastern and North- 

Eastern regional power grids and the transmission system are being progressively inter- 

connected for efficient operation of these five regional grids.

16 



The objective of the system development is to evolve self-sufficient regional grid catering 

to the individual regional power demands. It is also aimed at achieving the maximum 

benefits from integrated operation, through a proper mix of thermal and hydro generation 

and ultimately to tie the five regional grids together to form a strong National Power 

Gird, providing even greater reliability. 

2.2.2 Power Position in North Sikkim Region 

The total installed capacity in Eastern Region is 16696.68 MW. Out of this only 2459.51 

MW is hydel installation. Thus the Hydro-thermal mix is 15:85, which is well below the 

national average of 25:75 and desirable ratio of 40:60. 

The power supply position for Eastern region during 10th and 11th Five Year Plans is 

summarised in Table2.1. The power and energy availability and requirements during and 

after 10th Plan period in the Eastern Region is shown in Tables as projected in the 16th 

Electric Power Survey, published by CEA. 

Even considering the coordinated operation of existing hydro and thermal stations, as 

well as benefits from ongoing projects and also from the schemes cleared by CEA, the 

Eastern region is expected to face peak power and energy deficits during most of the 10th 

five Year Plan. The power situation in the region is dynamic and it is expected that the 

power generated from this project shall be cheap and helpful to the region as compared to 

thermal and other expensive power in the region. 

2.2.3 Existing Power Installations In Sikkim 

First time, a micro hydel station was established in Sikkim on the bank of Ranikhola at 

Lower Sichey Busty with an installed capacity of 10 KW on 27 th May 1927 for the needs 

of the members of the Royal family and Gangtok. Later, Lower Lagyap Hydel Project with 

an installed capacity of 12MW was constructed by Govt. of Sikkim and this was a big

17 



boom. Presently following hydel schemes totaling 95.70MW are under operation in the 

state. 

Sl. 

Hydel Schemes Year of 

Installed 

Firm 

No. 1 2 Completion 3 Capacities 4 Capacity 5 

1 Jali Power House 1966 2.10 1.20 

2 Rothak Micro Hydel 1971-72 0.20 0.10 

3 Rimbi Micro Hydel, Stage-I 1970-71 0.60 0.30 

4 Lower Lagyap HEP 1979-80 12.00 5.50 

5 Lachen Micro Hydel 1989-90 0.10 0.05 

6 Rimbi Stage-II 1989-90 1.00 0.50 

7 Rongnichu Micro Hydel-II 1988-89 2.50 1.20 

8 Lachung Micro Hydel 1991-92 0.20 0.10 

9 Mayongchu 1993-94 4.00 2.00 

10 Upper Rongnichu HEP 1994-95 8.00 4.00 

11 Kalej Khola 1995-96 2.00 1.00 

12 Rangit Hydel Project 1999-00 60.00 20.00 

13 Robom Micro Hydel 2003-04 3.0 1.00 

I - Total Hydel Power 95.70 36.95 

II - Total Diesel Power 2.70 2.70 

Total Generation Capacity 98.40 39.65 

2.2.4 Load Demand & Power Position of Eastern Grid 

Table-2.1 shows the power supply position of Eastern grid up to 2011-12.

18 



2.2.5 NECESSITY OF THE PROJECT AND RELATED ASPECTS 

The need for Rangyong H.E. Project has been considered in the context of increasing 

demand of power in the eastern region. It has been assumed that eastern region will have 

energy requirements at the rate 10% per annum rise of each year. This is a run of the 

river scheme with little pondage in Teesta basin in North Sikkim District, Sikkim. It will 

generate 639.52 MU in 90% dependable year (1976-77) with 95% machine availability. 

The power generated at Rangyong HEP (3 X 47MW) would be evacuated through one 

number 220KV double circuit lines to a proposed pooling station near Teesta II HE 

Project to feed power to the national grid.

Table 2.1 

POWER SUPPLY POSITION OF EASTERN REGION 

WITHOUT RANGYONG HE PROJECT, (141MW) 

10th Plan 11th Plan 

19 


Rangyong HE Project, (3 x 47 MW) 

Eastern Region 2002-03 2003-04 2004-05 2005-06 2006-07 2007-08 2008-09 2009-10 2010-11 2011-12 

1 2 3 4 5 6 7 8 9 10 

Installed Capacity MW 16697 17197 18327 20077 21237 22369 23269 24769 25429 26749 

Peak availability MW 7676 7906 8425 9230 9763 10284 10697 11387 11690 12297 

Peak requirement MW 8076 8527 9002 9505 10035 10586 11167 11780 12427 13109 

Peak Surplus(Deficit) MW -400 -621 -577 -275 -272 -302 -470 -393 -737 -812 

Peak Surplus(Deficit) % -4.95% -7.28% -6.41% -2.89% -2.71% -2.86% -4.21% -3.34% -5.93% -6.19% 

Energy availability MU 50260 51765 55167 60434 63926 67334 70043 74558 76545 80518 

Energy requirement MU 51653 54484 57469 60619 63941 67400 71046 74890 78941 83212 

Energy Surplus (Deficit) MU -1393 -2718 -2303 -184 -14 -66 -1003 -331 -2396 -2694 

Energy Surplus (Deficit) % -2.70% -4.99% -4.01% -0.30% -0.02% -0.10% -1.41% -0.44% -3.04% -3.24% 

1. All the data for the year 2002-2003 has been taken from the website www.cea.nic.in. 

2. Energy availability for the year 2002-2003 onwards have been estimated on the basis of ratio of Energy availability to Installed capacity for the year 2002- 

2003. 

3. Peak availability for the year 2002-2003 onwards have been estimated on the basis of ratio of Peak availability to installed capacity for the year 2002-2003. 

4. Energy requirement & peak requirement for the year 2002-2003 onwards is based on the annual increments given at page -117 & 118 of "Sixteenth Electric 

Power Survey Of India". 

5. Micro/mini projects have not been considered for the study. 

Note:- This is a statistical analysis based on various publications mentioned above and are meant for study and planning purposes.



CHAPTER – III 

PROJECT AREA

CHAPTER –III 

PROJECT AREA 

3.1 DESCRIPTION OF PROJECT INCLUDING RIVER SYSTEM 

20 



Rangyong H.E. Project is situated in the Dzongu area of north district of Sikkim .The 

project envisages construction of 65 m high two concrete gravity dams one just 

downstream of the confluence of Umram Chu and Passaram Chu and another on the river 

Rangyong Chu nearby the place called Singnok. The under ground powerhouse is just 

upstream of the Confluence of Rangyong Chu and Ringyong Chu . The rivers water shall 

be diverted through a diversion tunnels of 300 m long each and 3.3 m dia for construction 

of dams. A 2.0Km long link tunnel shall connect both the dams and a 7.5 km length 

headrace tunnel of 3.3m dia shall carry a discharge of 22.30 cumecs of water to the 

powerhouse. Two number of desilting chambers of 175m x 10m x 12 m size shall be 

constructed to separate the silt particles of 0.2mm size and above from the water. A surge 

shaft of 10 m dia and 75 m high along with one pressure shaft of 2.5m dia & 1000 m 

length shall be constructed. A tailrace tunnel of 300m length and 3.3 m dia shall 

discharge the water back into the river. A switchyard of 155m x 100m size shall also be 

constructed. The powerhouse shall have installed capacity of 141 MW to generate 639.52 

MU of energy in a 90% dependable year. 

The river Umram Chu and Pasaram Chu are the tributaries of the Rangyong Chu 

originating in the glaciers of North Sikkim at an elevation of about 5000 m above mean 

sea level and meets Rangyong Chu upstream of the confluence of Ravingrum Chu .The 

other tributaries of the Rangyong Chu /Tolung Chu are Rukel Chu, Pokhram Chu, Ringpi 

Chu, Ringyang Chu, Rangli Chu and Rahi Chu. Both the rivers Rahi Chu and Rangyong 

Chu meets Teesta river near village Singhik . After running about 14 Km from the 

confluence, the Dikchu River joins the Teesta River near the village Dikchu. In the 

downstream the Rongni Chu joins Teesta River at Singtam, Rangpo Chu at Rangpo and 

Rangit at Melli.

3.2 SOCIO-ECONOMIC AND OTHER ASPECTS 

3.2.1 Demographic Features 

21 



As per the 2001 census of India, the total population of the State is 540,493. The overall 

density of population in the State is 57 per sq. Km. East district is the most populated 

where as North's density is only 7 and is the least populated. Sex ratio (females per 

thousand male) in 1981 was 835, where as it had improved in 1991 to 878 and in 2001 

has shown a declining trend with a value of 875. There are only eight urban towns and 

constitutes only 9.10% of total population. Literacy rate was 56.94% (19th position) in 

1991 and has increased to 70.65% in 2001. The rural literacy rate in 2001 is 68.59% 

whereas the urban literacy rate is 85.80%. 

The economy of Sikkim is mainly based on agricultural and animal husbandry. 

Approximately 11% of the total geographical area is under agriculture. The work force 

participation rate as per 1991 census is 40.44%. The female participation rate in Sikkim is 

also much higher than the national average. This is an important aspect in the hill 

economy, as productivity is low and hence the people are engaged in agriculture and 

other activities. Cultivators account for the greater majority of the people in the State. 

Animal husbandry is an integral part of the house holds economy of the region. There are 

certain household industries also which substantially adds to household incomes. The 

past one and half decade has witnessed a tremendous upward swing in various 

development programme giving a new thrust to the Sikkim economy. This process has 

increased wage employment opportunities. There is very little human habitation in the 

vicinity of the proposed project site. Only a few small villages, comprised of few hamlets 

only, viz. Sakyong, Phontong, Singnak, Myong and Shabrung under Sakyong Pentong 

Revenue Block fall within 10km radius of the project area. The human population as per 

the 1991 census up to different aerial distances from the project are given below. 

Up to 2 km Up to 2-5 km Up to 5-10 km 

Population Nil 199 694 

Households Nil 49 145

3.2.2 Ethnographic details (Details of the tribals in the area) 

22 



In Sikkim various communities with their own customs, religion and culture intermingle 

freely to constitute a homogeneous blend. The predominant communities are the 

Lepchas, Bhutias and Sherpas. Lepchas, Bhutias, Sherpas are categorized as Scheduled 

Tribes. The Lepchas are the original inhabitants of the State. Compared to other ethnic 

groups, the Lepchas still maintain many of their traditional ways. The Bhutias comprise, 

the Sikkimese Bhutia and Bhutia from Bhutan and Tibet. The Sherpas are a marginal 

ethnic group in the State. Over 80% population consists of Nepalese. Many people from 

the plains have also settled, especially in the urban areas and they are almost always 

engaged in business or Government services. A small part of the population consists of 

migrant labourers from Bihar, West Bengal, Eastern UP and Nepal. The population near 

the dam site is quite thin dominated by yak and sheep grazers. Some marginal 

agricultural farmers also live nearby. Crops like cardamom, ginger, potato, millet, wheat 

and maize are grown in the area. 

3.2.3 Health & Education 

There are 4 district hospitals, Gyalshing, Namchi, Singtam & Mangan and one Central 

Referral Hospital at Gangtok, besides 25 Primary health centers 150 Primary health sub- 

centre, 9 Veterinary hospitals and 25 Veterinary dispensaries. There is a blood bank at 

Gangtok. There are 1234 doctors. Small pox and Kalzor have been eliminated from the 

state and many schemes for the provision of safe drinking water to the villages and 

bazars have been implemented. Sikkim has 700 Pre-nursery schools, 531Primary schools, 

122 Middle schools, 64 Secondary schools, and 28 Higher secondary schools 2 Public 

schools. There is a Training Institute for primary teachers, a Law college, a B.Ed. college, 

2 Degree colleges, one Industrial Training Institution, a Medical and an Engineering 

college.

3.2.4 Religion 

23 



Hinduism and Buddhism are the two main religions prevalent in Sikkim. Hindus and 

Buddhists constitute 99 percent of the population; Christians, Muslims, Jains and Sikhs 

together are less than one per cent. 

3.2.5 Trade & Industry 

Sikkim has a State Industrial Development Investment Corporation, which is encouraging 

establishment of industrial units in Sikkim. The Industrial Training Institute located at 

Rangpo is providing necessary expertise to the younger people for self-independence in 

the trade and the know-how. Sikkim has two distilleries , one tannery, and other ancillary 

units. Rangpo area has been declared as an industrial Zone. A Brewery is located at 

Melli, South Sikkim. and another at Rangpo, East Sikkim. There is also a fruit 

preservation factory at Singtam. The Sikkim Mining Corporation mines copper, zinc, lead 

etc in the state. The Sikkim Time Corporation a watch-manufacturing factory is located at 

Gangtok, which is producing one of the latest watches in India. There is a jewel factory 

located at Gangtok. Besides the above a good number of entrepreneurs have recently 

proposed to set up new factories. Some of the units are manufacturing leather goods, 

safety matches, local crafts, carpet weaving, handmade paper, woodcarving and similar 

works. The Sikkim State Tea Board has also been established for quality tea production. 

3.2.6 Natural Resources 

Sikkim is gifted with abundant natural resources. The resources can be grouped into a 

biotic & biotic both of which can be renewable and non-renewable. Biotic resources 

include agricultural crops, forests etc. The entire Himalayan region is endowed with 

natural flora and fauna and is a natural paradise for nature lovers, conservationists, 

botanists, zoo lists and environmentalists. There are 4500 species of flowering plants, 300 

species of primulas, 20 species of bamboos etc., 45 species of rhododendrons and around 

450 species of orchids.

24 



The State is very rich in fauna also. There are 144 species of mammals, 500-600 species 

of birds, over 400 species of butterflies and moths and many species of reptiles are 

available. Sikkim is rich in medicinal plants/herbs and also important shrubs are found in 

low and high altitude areas. The State is endowed with water resources, tourism, 

hydroelectric potential etc. Under economic geology minerals like copper, iron, lime, 

dolomite, limestone, coal, quartzite, silicate & graphite are available in the state. As per 

the available data around 60% of cardamom production in India is from Sikkim. There is 

a vast potential for hydroelectric power generation. Tourism development deserves 

considerable attention to add to the economy of the region. 

3.2.7 Hydropower Potential 

The Teesta and Rangit are the two main rivers of Sikkim where considerable hydro 

potential is available. Sikkim have developed 95.7 MW of hydropower potential so far by 

constructing mini & micro hydel projects and about 600 MW hydel potential is under 

development in different stages. The details of hydropower potential identified is as 

under: 

Teesta Basin : 

According to the preliminary reconnaissance survey, the river could be harnessed under a 

cascade development for hydropower generation is six stages as under : 

i) Teesta Stage-I 

It is possible to diver the water of Teesta river d/s of confluence Chento chu near 

Shacham and d/s of confluence Lhonak chu and Poke chu by constructing diversion 

structures at EL ± 3330 and interconnecting tunnels discharging the Tail water at an EL ± 

2623 near the place Zema. The scheme will have installed capacity of about 320 MW. 

ii) Teesta Stage-II 

Under this scheme, a diversion dam of 83 m high is proposed near Bonsoi to divert the 

tail water of Teesta Stage-I and the power house at Chungthang. The scheme shall 

generate 330 MW.

iii) Teesta Stage-III 

25 



The schemes involve construction of Teesta River and Lachung chu near Chungthang and 

a Power house near Singhik. The scheme shall have the installed capacity of 1200 MW . 

iv) Teesta Stage-IV 

A diversion dam is proposed just d/s of confluence of Teesta and Tolung chu near the 

place called Sanklan and power house near the village Dikchu. The scheme shall have 

installed capacity of 495 MW. 

v) Teesta Stage-V 

A diversion dam has been proposed d/s of confluence of Dikchu chu and Teesta river and 

a power house near the village Sherwani. The scheme shall have installed capacity of 510 

MW. 

vi)Teesta Stage-VI 

Power Potential of Rangit Basin It envisages construction of a 76 m high concrete dam 

near Khanitar d/s of the confluence of the Teesta and Rongni chu in East Sikkim and the 

power house near the village Namthang/Tarkhola in South Sikkim with installed capacity 

of 360 MW. 

Rangit Basin 

The hydropower development of Rangit river was identified in four stages as under : 

i) Rangit HE Project Stage –I 

The Rathong chu, a major perennial tributary of Rangit river has a very steep bad slop. 

The river takes a big loop near Yoksum. It is proposed to divert the water of Rathong chu 

at an elevation of about 2300 m U/S of Yoksum to elevation of 100 m near village 

Thingtom. The scheme shall generate 47 MW of power at 60 % load factor. 

ii) Rangit HE Project Stage-II 

It is proposed to divert the water of Rimbhi chu near Sigglitem and allow the water to 

drop through 425 m near Lingchum on Kalet chu to generate 10 MW of power at 60% 

load factor.

iii) Rangit HE Project Stage –III 

26 



A dam has been constructed just d/s of confluence of Rathong chu and Rangit river and a 

power house near the village Mongbru. The installed capacity of the scheme is 60 MW. 

The project has been commissioned by NHPC in the year 1999 and is in operation. 

iv) Rangit HE Project Stage-IV 

The scheme shall utilize a drop of 110 m from an elevation of 440 m to 355 m in Reshi 

loop. The scheme shall generate 18 MW of power at 60 % load factor. 

Schemes For PFR in Teesta Basin 

The Cenrtral Elecrtricity authority entrusted 10 schemes with total installed capacity of 

1569 MW for preparation of prefeasibility reports as per details given below: 

Sl. Name of Scheme Installed Name of 

District 

No. 

Capacity (MW) River 

1. Dikchu 105 Bakchachu/Dikchu chu East 

2. Rongni 195 Rongni chu East 

3. Namlum 160 Rangit South 

4. Panan 200 Tolung chu North 

5. Lingza 160 Ringpi North 

6. Rangyong 141 Rangyong/ Umramchu North 

7. Ringpi 70 Ringpi North 

8. Rukel 33 Rukel/Rangyong North 

9. Jedang 185 Jhonak chu North 

10. Teesta Stage-I 320 Teesta & Zemu chu North 

OTHER SCHEMES IDENTIFIED BY CEA AND SIKKIM 

The CEA in the preliminary ranking studies and Sikkim in the preliminary studies 

identified the fallowing schemes: 

Sl. Name of Scheme Installed Capacity Name of River 

No. 

(MW) 

1. KalepHE Project 40 Teesta 

2. Talem HE Scheme 65 Teesta 

3. Serum HE Scheme 50 Lachung Chu 

4. Lachung HE Scheme 30 Lachung 

5. Chhota Pathing/Rolep 55 Chu/Sebokong Rangpo Chu 

Chu

27 



6. Chuzachen 13 Rangpo Chu 

7. Suntalitar HE Scheme 25 Rangpo Chu 

8. Mana 37 Rangit 

9. Gompa 46 Rangit 

10. Rammam Stage-I 70 Rammam 

11. Rammam Stage-II 85 Rammam 

12. Rammam Stage-III 100 Rammam 

13 Chakhung Chu hydel 30 Chakhung Chu 

In addition to above schemes, the Govt. of Sikkim have identified about 40 mini/micro/ 

small schemes for hydropower development in the region.



CHAPTER – IV 

TOPOGRAPHICAL & 

GEO-TECHNICAL ASPECTS

CHAPTER-IV 

28 



TOPOGRAPHIC AND GEOTECHNICAL ASPECTS 


The Rangyong Scheme envisages construction of a diversion scheme on Rangyong Chhu 

about 1.2Km upstream of its confluence with Umram Chhu, a water conductor system in 

the right bank and a Power House downstream of confluence of Rangyong Chhu and 

Ringpi Chhu. The scheme has been proposed by Central Electricity Authority in order to 

tap the water potential of Rangyong Chhu. Another scheme namely Rukel scheme has 

been proposed with the tail water discharging upstream of the diversion structure of 

Rangyong Chhu. However, in order to augment the water potential of Rangyong Chhu 

the water from Umram Chhu, a left bank tributary of Rangyong Chhu shall be discharged 

into the reservoir of the proposed scheme through a 2km long link tunnel. The scheme is 

expected to generate approximately 141MW of power. The present appraisal is based on 

study of topographic sheet 78 A/6 and a report of GSI titled “Geology of the Area 

Around the Proposed Rangyong Hydroelectric Project” which is enclosed a Annexure – 

4.1. 

As a part of MOU between NHPC and CEA preparation of pre-feasibility report has been 

assigned to NHPC. Attempts were made to visit the area however, the same could not be 

matured since the footpath from Lingza to Sakkyong was damaged. As a result the 

present appraisal is based on regional geological data and geological assessment of the 

area made during the visits to Pannan, Lingza and Ringpi schemes. 

4.2 REGIONAL TOPOGRAPHIC AND GEOTECHNICAL FEATURES 

River Teesta in Sikkim is a major river originating from Zemeu glaciers and generally 

flows in north-south direction, at a steeper gradient. The river is joined by several 

tributaries major amongst them being Yumthang Chu, Zemu Chu, Talung Chu, Dik Chu, 

Rangpo Chu and Rangit Chu, apart from others join the river. The river valleys in this

29 



region are U-shaped while, as the tributaries had developed deep gorges, which are bound 

by steep slopes. A thick vegetal cover occupies the hill slopes. These hill slopes are 

generally used for cultivation of cardamom. 

A brief of regional geological aspect of this area has been provided. The Eastern 

Himalaya covers the Sikkim-Darjeeling-Bhutan and Arunachal Pradesh sectors, 

extending from the Eastern Nepal to Western Burma. The higher Himalaya is a zone of 

crystalline rocks dividing two distinct lithofacies association in the South and North. It is 

designed as the Axial belt. The Northern zone comprising the Tethyan Palaeo-Mesozoic 

sedimentary sequence forms the Trans-Axial belt. To the South of the Axial belt occurs 

the Inner belt, comprising thrust sheets of Proterozoic-Upper Palaeozoic formations, 

while the foothill belt is represented by para-autochthonous Siwaliks. This scheme is 

valid for the entire Eastern Himalaya, upto the Lohit District of Arunachal Pradesh, 

where the geological picture does not conform to this general scheme. The stratigraphic 

sequence provided by GSI report on Rangyong Hydroelectric Scheme has been brought 

out hereunder for the purpose of regional geological set-up of the area. According to this 

report the region from South to North is occupied by Gondwana, Daling, Chungthang and 

Central Crystalline Geneissic group of rocks. 

Group Lithology 

Gondwana Grits, pebble cum boulder beds and carbonaccous shale with 

occasional coal seams, pegmatite, quartzite(Tourmaline 

bearing) 

Daling • Interbedded quartzite and chlorite sericite 

phyllite/schist. 

• Lingza Granite. 

• Quartzite/Biotite schist. 

Chungthang • Interbedded quartzite and garnetiferous quart biotite 

schist.

Central Crystalline 

Geneissic Complex 

• Cale-silicate rock/marble. 

30 



• Garnet-Kyanite-sillimanite-biotite-quartz-schist. 

Banded gneiss with augen gneiss and quart-biotite gneiss. 

Augen gneiss. 

Rock types belonging to Central Crystallines of Higher Himalaya occupy the area. The 

rock types are represented mainly by high-grade gneiss with interbands of 

metasedimentaries represented by cale-silicate/quartzite and high-grade schist. As 

reported by GSI, the metasedimentaries occur as enclaves in the high-grade gneiss. All 

the rock types have discordant intrusions tourmaline bearing quartz veins and pegmatite. 

4.3 TOPOGRAPHIC AND GEOTECHNICAL ASPECTS OF COMPONENT 

STRUCTURES 

The region is moderately to thickly vegetated and falls within Sakkyong (upstream) and 

Tolung Reserve Forest (left bank area). The right bank area falls within Sakkyong reserve 

forest. Rukel Chhu, which originates from a glacier flows SE and takes an easterly swing 

and meets Umram Chhu near Lam. Umram Chhu also originates from a glacier and meets 

SW flowing nala Pasram Chhu before these confluence with Rukel/Rangyong Chhu near 

Lam Rangyong swings SE and then takes an easterly bend till it meets Ravingam Chhu. 

Further downstream Rangyong Chhu flows SE upto its confluence with Ringyong Chhu. 

In the right bank Rangyong Chhu is joined by few nalas major being Pokram Chhu. The 

area is bound by ridges, which trend N-S and NE-SW. The river flows in moderate to 

steep gradient Rangyong Chhu from the proposed diversion location upto Sakkyong 

flows across the strike of formations, however beyond, it flows almost parallel to the 

strike of formations. Entire area has a highly rugged terrain with elevation in vicinity 

varying from 2000M to 6000M.

31 



The area is approachable by a fair weather road upto Lingza beyond which a foot track 

reaches Sakkyong. In general the valley slopes are occupied by slope wash material with 

few rock exposures. Rock formations are also exposed as steep ridges. 

4.3.1 Diversion Structure 

Near the proposed diversion structure Rangyong Chhu flows easterly till its confluence 

with Umram Chhu at Lam. The other diversion proposed on Umram Chhu shall be 

located below the confluence of Umram Chhu and Pasram Chhu. Water from Umram 

Chhu shall be diverted into the reservoir of Rangyong Chhu. In vicinity of the proposed 

structure on Umram Chhu the nala flows SE. The area is bound by steep ridges, which 

trend N-S and NE-SW. The hill ridge separating Umram Chhu and Rangyong Chhu 

trends NW-SE. Both the nalas flow in moderate to steep gradient. The proposed diversion 

structures are expected to be located within gneisses and augen gneisses. Quartzites and 

quartz biotite schists/biotite gneisses are also reported in the area. These rock types 

belong to Central Crystallines of higher Himalaya. The rocks are foliated and jointed. 

The gneisses of the area as studied at other locations namely Lingza, Ishana and Tolung 

are strong to very strong and are expected to provide good abutment conditions. 

Nevertheless, abutment conditions are required to be studied during the future course of 

investigations. Also, depth of overburden at the proposed diversion locations shall be 

ascertained. Prima facie it appears that overburden depths may not be of higher order as 

has been found during the course of studies in this region. 

4.3.2 Water Conductor System 

A7.5km long water conductor system has been proposed in the right hill. This area is 

bound by steep ridges, which trend N-S and NE-SW. In the stretch between the proposed 

diversion structure and confluence of Rangyong Chhu with Ringyong Chhu the proposed 

water conductor system area is dissected by several drainages. A major drainage namely 

Pokram Chhu is located above the tunnel alignment, however the other drainages do not 

appear to have deeply incised the area. Accordingly, availability of rock cover above

32 



water conductor system, here, shall be ascertained during future investigations. Prima 

facie sufficient superincumbent cover is available above the alignment. The water 

conductor system is expected to negotiate high grade gneisses with few intermittent 

stretches of quartz biotite schist. Few patches of Ligtse gneiss have been reported in the 

area. Fair to good tunneling media is expected however, few stretches especially contact 

zones and shear zones may provide poor rock media. Generally the area is thickly 

vegetated. A detailed assessment of the area shall however, be made during the further 

course of investigations. 

4.3.3. Power House 

The proposed Power House is located upstream of the confluence of Rangyong Chhu and 

Ringyong Chhu in the right bank of Rangyong Chhu. At present an underground Power 

House has been contemplated on the basis of topographic conditions. The area is bound 

by steep ridges and occupied by a thick vegetal cover. The proposed Power House cavern 

is expected to lie within quartzite and quartz biotite schists and/or gneisses. The rock 

types are expected to offer fair to good tunneling media. At the proposed Power House 

location the formation are exposed as steep rocky escarpments. Sufficient 

superincumbent cover is available above the proposed Power House cavern. The 

orientation of Power House shall be suitably aligned with respect to principal 

discontinuity. Towards the tailrace portion the area appears to be occupied by a veneer of 

slope wash material as was observed during the investigation of Lingza scheme. 

4.4 SEISMICITY 

The site lies within Zone-IV of seismic zoning map of India IS 1893 (Part-I) 2002. IMD 

data of the region covering longitude 86-90 0 and 25-29 0 has been places at Annexure 4.2 

, which gives a list of earthquake events also that have occurred within the region. The 

probable intensity of earthquake within seismic zone–IV corresponds to intensity VIII on 

Modified Mercali Scale. Notable earthquakes that have occurred close to this area are 

Cachar 1869 (M 7.5), Great Assam Earthquake 1897(M 8.7), Dhubri 1930 (M 7.1) Bihar-

33 



Nepal Earthquake 1934 (M 8.3), Assam Earthquake 1950 (M 8.5) and Nepal-India border 

earthquake 1988 (M 6.4). The maximum intensity experienced in Sikkim region during 

Great Assam Earthquake 1897 was VIII(MMI) and during Bihar-Nepal border 

earthquake 1934 was VII(MMI). 

Two major tectonic features occurs in the area namely MBT (Main Boundary Thrust) and 

MCT (Main Central Thrust) besides other minor features. Many past occurrences of 

earthquake have been associated with these major lineaments. 

4.5 GEO-PHYSICAL SURVEY 

The dam sites are located in remote area, where proper approaches are not available due 

which Geo-Physical survey was not feasible. However the powerhouse site is having rock 

exposures, hence the Geophysical survey is not required. 

4.6 CONSTRUCTION MATERIAL SURVEY 

Although, the riverbed is full of boulders, which may not be sufficient for requirement of 

construction materials. However, the area is bounded by steep rocky ridges, therefore 

quarries for construction material can be developed. 

4.7 RECOMMENDATIONS 

• The foundation for structures are required to be investigated by subsurface 

explorations to assess overburden thickness and its amenability for construction of 

various structures. 

• Detailed geological mapping of the project components need to be carried out. 

• Suitability of construction material may be assessed after conducting required 

tests.



CHAPTER – V 

HYDROLOGY

5.1 GENERAL 

CHAPTER –V 

HYDROLOGY 

34 



Rangyong H.E project is a run of the river scheme, in which two dams have been 

proposed to utilize the discharge of Rangyong Chu, a major right bank tributary of river 

Teesta. One dam is proposed on Rangyong Chu and another downstream of the 

confluence of Umram Chu and Passaram Chu, both tributaries of Rangyong Chu. The 

project envisages construction of two diversion structures, a 65 m high dam on Rangyong 

Chu with a gross storage capacity of about 0.525 Mcum and area of submergence as 2.5 

Ha at EL 1845 m and another 65m high dam, d/s of confluence of Umram Chu and 

Passaram Chu with a gross storage capacity of about 3.05 Mcum and area of 

submergence as 15.62 Ha at EL 1845 m. 

The hydrological investigations and analysis have been carried out for Rangyong Project 

with a view to: 

• Assess the availability of water for power generation by establishing a series of 

average 10-daily discharges for the project site. 

• Establish the spillway design flood 

• Determine the capacity of the reservoir and the area of submergence at different 

levels including FRL and MDDL. 

• Reservoir sedimentation. 

5.2 RIVER SYSTEM AND BASIN CHARACTERISTICS 

Rangyong Chu is one of the major tributary of river Teesta which meets river Teesta at 

Singhik on its right bank. Rangyong Chu originates from the Talung glacier, which is a 

part of the Kanchanjunga range. The river is known by different names in different 

reaches. In the upper reach it is known as Rukel Chu, further downstream it is called 

Rangyong Chu and in the lower reaches it is known as Tolung Chu. Rangyong Chu is fed

35 



by a number of tributaries having large drainage areas at their confluence. Umram Chu 

and Passaram Chu are also major tributaries of Rangyong Chu and intercept large 

drainage areas. 

The river Teesta is one of the main Himalayan Rivers, which originates in the glaciers of 

Sikkim at an elevation of over 8500m above mean sea level. It is being snow fed by the 

glaciers Zemu, Changame Khanpu, Talung etc. It is an international river, which flows 

through the states of Sikkim and West Bengal in Indian Territory and then to Bangladesh. 

The river rises in mountainous terrain and is formed mainly by the union of two hill 

streams Lachen Chu and Lachung Chu at Chunthang in North Sikkim. The river upto this 

reach generally flows in a very steep gradient and the slope of the Teesta river upto the 

confluence of Lachen chu and Lachung chu is about 1 in 20. After the confluence of 

Lachen chu and Lachung chu at Chungthang the river gradually increases in width and 

takes a wide loop flowing down to Singhik dropping in elevation from EL 1550 m to EL 

750 m. It is here after traversing about 20 Km that the river confluences with Tolung 

Chu. 

The area has a rugged terrain with the surrounding peaks reaching a maximum elevation 

of approximately 4000m. The minimum river bed elevation at both the proposed dam 

sites is about 1795m. Tolung Chu joins Teesta river almost perpendicularly. The terrain 

hosts a rich growth of vegetation. In general the river flows in southeasterly direction. 

Numerous valleys are seen in the area, which are occupied by cultivated terraces. Few 

high level terraces have been observed in this area especially in vicinity of Lingza and 

Kayem village. 

5.2.1 CASCADE DEVELOPMENT IN TEESTA BASIN 

The river Teesta has tremendous potential for development of hydro power, as the river 

descends from an elevation of about 3600m to about 300m over a distance of about 175 

Km. According to the preliminary reconnaissance survey by Central water and power

36 



Commission in 1974, the river could be harnessed under a cascade development for 

hydro power generation. The cascade development proposed at that stage consisted of 

power generation in six stages on river Teesta. Out of these schemes, NHPC had 

submitted a DPR for Teesta H.E project, Stage-III in 1990. The diversion structure for 

Teesta-III was proposed to be constructed at Chungthang, which lies downstream of the 

confluence of Lachen Chu and Lachung Chu. Another project under Teesta Basin 

development, which is under execution by NHPC, is Teesta Stage-V having an installed 

capacity of 510 MW, where a diversion structure is being built at Dikchu, about 2 Km 

downstream of confluence of Dikchu with Teesta. About 70km downstream of Teesta-V, 

NHPC has been entrusted two projects namely, Teesta Low Dam H.E projects, Stage-III 

& IV, having an installed capacity of 132 MW and 160 MW respectively. 

The proposed Rangyong H.E project on Rangyong Chu, lies downstream of Chungthang 

on Teesta river, which was the proposed damsite of Teesta-III H.E project. 

5.2.2 CATCHMENT AREA 

The catchment area of the proposed scheme lies between Longitude 88 o 11′00” E to 

88 o 25′00” E and Latitude 27 o 30′00” N to 27 o 45’00” N. The catchment area upto the 

proposed dam site on Rangyong Chu is about 127 Sq.km and upto the proposed dam site 

d/s of Umram Chu and Passaram Chu is about 146 Sq.km. Both the catchments are 

snowfed as well as rainfed. The proposed diversion structure on Rangyong Chu lies at 

Longitude 88 o 21′48” E and latitude 27 o 35′00” N and that d/s of Umram Chu and 

Passaram Chu lies at Longitude 88 o 22′26” E and latitude 27 o 36′00” N. The catchment 

Plan showing both the proposed dam sites is shown in Plate-5.1. 

The catchment plan has been prepared from 1:50000, Survey of India toposheets. The 

entire catchment is covered in toposheets no. 78A/6, and 78A/2. The area above 

EL4600m for dam on Rangyong Chu is about 25 Sq.km and for dam d/s of Umram Chu 

and Passaram Chu is about 54 Sq.km and the same has been assumed to be the snowfed

37 



area in the catchment. Thus the rainfed and snowfed area in the catchments of both dams 

are 102 Sq.km and 25 Sq.km respectively and 92 Sq.km and 54 Sq.km respectively. 

5.2.3 Temperature And Humidity 

The climate in the region is fairly humid and moist. The abrupt variation in altitude is 

chiefly responsible for abrupt changes in the climatic conditions and aided by the 

complex orography, the area experiences frequent rainfall of varying intensity and 

duration. The maximum and minimum temperature varies from 39 0 C in summer to 6 0 C 

in winter and the relative humidity varies from 80% to 100%. Temperature and relative 

humidity observations are being made in the basin at Dikchu site where Teesta-V H.E 

project is being constructed by NHPC and at TLDP-III and TLDP-IV sites, as a part of 

cascade development on Teesta river. The monthly maximum, minimum temperatutre 

and relative humidity at Dikchu from Jan 1998 to Dec 2001 is enclosed as Annexure-5.1 

and annual maximum and minimum temperature from 1998 to 2001 is given in Table 5- 

1. 

Year 

TABLE 5-1 

Temperature And Humidity Data At Dikchu 

Maximum 

Temp o C 

Minimum Temp 

o C 

Max. Relative 

Humidity % 

Min. 

Relative 

Humidity 

1998 38.0 7.0 99.0 89.0 

1999 39.0 6.0 99.0 90.0 

2000 39.0 7.0 97.0 85.0 

2001 31.0 11.0 97.0 90.0 

Overall 39.0 6.0 99.0 85.0 

%

5.2.4 Precipitation Characterstics 

38 



In the Teesta basin the southwest monsoon normally sets in the third week of May and 

withdraws in the second week of October. The major portion of the catchment being hilly 

and the river flowing in steep gradient, heavy rains in the upper and middle catchments 

has an immediate effect of rendering the plains to flash floods. 

Sh. B.Biswas and C.V.V Bhadram in their paper titled “A study of major rainstorms of 

Teesta Basin” and published in Mausam (1984), have studied the rainfall distribution, 

major rainstorms and their associated synoptic situations over the catchment based on 22 

years data (1960-81). The entire Teesta catchment extending from its origin in north upto 

the Indo Bangladesh border has been considered. On the basis of the rainfall distribution, 

the Teesta catchment has been divided into three parts viz. upper, middle & lower. The 

average annual rainfall is 1328 mm, 2619 mm & 3289 mm for the upper, middle and 

lower parts respectively. The monthly breakup of the annual rainfall of the basin is given 

in Table 5-2 . 

Table 5-2 

Average Monthly Rainfall (mm) of Teesta Basin 

Month 

Catchment 

Upper Middle Lower 

Jan 21 23 6 

Feb 41 32 16 

Mar 73 66 30 

Apr 72 147 144 

May 142 274 315 

Jun 245 463 547 

Jul 236 621 866 

Aug 222 512 645 

Sep 171 338 495

Oct 77 112 191 

Nov 15 19 21 

Dec 13 12 13 

Annual 1328 2619 3289 

39 



From the table it is clear that July is the wettest month followed by August and June. The 

upper, middle and lower catchments receive 71.6%, 78.1% and 83.4% of the annual 

rainfall respectively due to southwest monsoon. The catchment area upto the present 

proposed scheme comprises the upper and middle portions only. 

The authors have considered 53 rainstorms of duration ranging from one to three days in 

the study. The selection of storms is based on isohyetal analysis of daily rainfall values. 

Out of the 53 rain storms 40 were of 1 day, 11 were of 2 day and only 2 were of 3-day 

duration. It was concluded that 1-day duration storm are more frequent, a fact which is 

also supported by the narrow width of the catchment for which the effect of any system 

lasts for a shorter duration. No storm of longer duration than 3 day is reported. Majority 

of the storms have been reported in July & August. It has also been concluded that rain 

storms over this catchment occur in association with any of the following synoptic 

situations: 

(i) Break monsoon conditions i.e. shifting of the axis of trough close to the 

foothills of the Himalayas. 

(ii) Eastern end of monsoon trough lying north of Latitude 24 0 N. 

(iii) Movement of trough in west lies across the eastern Himalayas ; and 

(iv) Low pressure system lying over or to the west of the catchment. 

Many of the rainstorms studied by the authors were seen to occur due to either of the first 

two synoptic situations in July & August. A combination of first three synoptic situations 

is also a common feature over the area, giving rise to heavy precipitation.

5.2.4.1 Rain Gauge Network 

40 



As per the paper of Sh. B.Biswas and C.V.V Bhadram, the network density of rain 

gauges in the basin works out to be one raingauge per 300 Sq.km of the basin area. The 

data used by them is of 42 raingauge stations working under Indian Meteorology 

Department (IMD) and Central Water Commision (CWC), 24 of which are equipped with 

self recording raingauges. The rainfall data availability status of the raingauge stations in 

the catchment upto Teesta-V H.E project, with NHPC, is shown in Table 5-3. 

Table 5-3 

Data Availability Status Of Raingauge Stations Upto Teesta-V 

S.No Name of station Period of data availability 

1. Lachung Jul 57 to Dec 58, 1960 to 1964,1970 to 1981, 

Feb 91 to Dec 97 

2. Chunthang Apr 57 to Dec 58, 1960 to 1964,1970 to Jul 85, 

1991 to 1997 

3. Lachen Jan 57 to Dec 58, Jan 60 to Apr64, 1971, Sep 

77 to Jan 78, Jun 92 to Dec 97 

4. Yumthang Jul 57 to Oct 57, 1958, 1960 to 1964, Jan 70 to 

Sep 82, Jan 83 to Apr 85 

5. Singhik Sep 75 to Sep 85, 1991 to 1993 

6. Thangu Jan 57 to Dec 58, 1960 to 1964, 1970 to 1974, 

7. Dikchu (near Teesta- 

V dam site) 

Jan to Apr 83 

8. Gayzing 1978 to 1988 

9. Yoksam 1978 to 1988 

10 Rangit dam site 1991 to 1997 

1992 to 1997, 2001 to Oct 03 

11. Pelling May 93 to Dec 96

41 



At all the above raingauge sites, data for few months is missing in between. Raingauge 

sites have also been established near Teesta Low dam projects, Stage-III & IV and are 

operational since August 2000. Lot of efforts has been made to collect all available 

rainfall data in the basin but only rainfall data of 11 stations mentioned above is available 

at present. None of the above rainfall stations lie in the catchment of the proposed project 

so this data has not been used in the hydrological analysis. 

5.3 WATER AVAILABILITY STUDY 

5.3.1 Stream flow and River gauges 

Since Teesta River offers ideal conditions for cascade development of hydroelectric 

schemes, the discharge passing through the river is measured at various sites by CWC. 

Recently NHPC has also established its various G&D sites on Teesta river since a 

number of projects have been entrusted to NHPC as a part of cascade development on the 

river. These include Teesta-V, and Teesta Low Dam projects, Stage-III & IV. However, 

no G&D data is available in the catchment of Rangyong H.E project. The various G&D 

sites and period of data availability in Teesta Basin is shown in Table 5-4. 

Table 5-4 

Data Availability Status Of G&D Sites In Teesta Basin 

S.No Name of site River Period of availabilty Catchment 

1. Chunthang (before 

confluence of Lachung 

& Lachung Chu) 

2. Chungthang (after 

3. 

confluence of Lachung 

& Lachung Chu) 

Lachen 

Chu 

Third Mile Tolung 

Area 

(Sq.km) 

Jan 75 to Aug 85 1919.25 

Teesta Jan 75 to Jun 86 2786.8 

Chu 

Jan 75 to Aug 85, Apr 

90 to Apr 98 

731.25

4. Lachung Lachung 

5. Chuba 

Chu 

Yumtha 

6. Zema 

ng Chu 

Zema 

Chu 

42 



May 76 to Aug 85 634.50 

Jan 78 to Aug 85 355.5 

Jan 79 to Aug 85 900.0 

7. Sankalang Teesta Dec 89 to May 98 

8. Dikchu (near Teesta-V 

damsite) 

9. Sirwani (Power house 

site-TeestaV) 

10. Legship (near Rangit 

damsite) 

Teesta Jan 84 to Oct 96, Jan 

97 to Oct 03 

Teesta May 84 to Mar 97, 

2000 

Rangit Jan 77 to Dec 79, Apr 

87 to Dec 87, Jan 90 

to Dec 91 

11. Teesta Bazar Teesta 1972 to 1994 

4307 

12. Samco Ropeway Teesta Aug 2000 till date 7755 

13. Coronation Bridge Teesta 1972 to 1994, Aug 

2000 till date 

14. Domohoni Teesta 1972 to 2000 

. 

5.3.2 Present Study 

8065 

No daily G&D data was available on Umram Chu and Passaram Chu, on which one of 

the dam sites for the present project is proposed. For the pre feasibility study, water 

availability for the proposed project has been computed based on the following 

methodologies:

43 



(i) Based on observed discharges at Tolung Chu (Jan 75 to Aug 85, Apr 90 to Apr 

98) 

The two proposed diversion structures for Rangyong project are located on Rangyong 

Chu and another d/s of confluence of Umram chu and Passaram Chu, both of which are 

tributaries of Rangyong Chu/Tolung Chu. Daily G&D data is available on Tolung Chu 

from Jan 75 to Aug 85 and Apr 90 to Apr 98. The G&D site lies downstream of the 

proposed project on Tolung Chu, having a catchment area of 731 Sq.km. Average 10- 

daily series has been prepared based on this observed data and reduced to the proposed 

dam sites using catchment area proportion, using a reduction factor of 0.175 and 0.158. 

(ii) Based on discharge series of Teesta-III H.E project (1976-1984) 

Average10-daily series recommended for Teesta-III H.E project by CWC at Chungthang 

has been converted at both the proposed sites using catchment area reduction (catchment 

reduction factor – 0.12 and 0.11). Thus a series for the period 1976 to 1984 has been 

obtained. 

(iii) Based on observed G&D data at Lachen (1976-1997) 

G&D data observed at Lachen has been converted at both the proposed sites using 

catchment area reduction (catchment reduction factor – 0.178 and 0.16). Thus a series for 

the period 1976 to 1997 has been obtained. Data at Lachen is missing for the years 1986- 

1988, i.e for 3 years. This missing data has been filled from the observed data at Dikchu 

G&D site (Teesta-V) using catchment area reduction. 

(iv) Based on discharge series of Teesta-V H.E project (1976-Feb 2003) 

The 10-daily series at Teesta-V H.E project for the period 1976- Feb 2003 has been 

converted at both the proposed dam sites using catchment area reduction (catchment 

reduction factor – 0.05 and 0.045). The series from 1976-1996 is the approved series by

44 



CWC for Teesa-V and from 1997 to Feb 2003 is the observed data at Dikchu G&D site, 

where observations are being taken by NHPC. 

Average 10-daily discharge for all the above four series developed is worked out and 

compared at both the proposed dam sites. The plots showing this comparison of average 

10-daily discharge is enclosed at Figure-5.1 and Figure-5.2. From the plots it is obvious 

that the average 10-daily of the series obtained on the basis of G&D data observed on 

Tolung Chu is on a much higher side as compared to other three series. Rainfall-runoff 

relationship for consistency check could not be established for the observed data on 

Tolung Chu as no rainfall data in the catchment of the proposed project was available. 

Hence, for pre-feasibility study, the series so obtained on the basis of Tolung Chu data 

cannot be adopted as such, it comparatively being on a higher side. Average 10-daily 

obtained from other three approaches are almost comparable so need for further statistical 

checks is not felt necessary. For pre-feasibility stage, the average 10-daily obtained from 

G&D data at Lachen is recommended for both the dams proposed for Rangyong H.E 

project. Though the catchment area reduction factor is very low for all three series, this 

series has been adopted as Lachen G&D site has a smaller catchment area as compared to 

Chungthang and Teesta-V. After estabilishing G&D site near proposed dam axis and 

obtaining more rainfall data in the catchment, detailed water availability study need be 

done during feasibility/DPR stage. The final 10-daily series at both the proposed dam 

sites is enclosed as Annexure-5.2 and 5.3. 

5.4 RESERVOIR ELEVATION AREA CAPACITY CURVE 

The reservoir elevation-area-capacity curve for both the proposed dam sites of Rangyong 

H.E project has been prepared from 1:50000 Survey of India toposheets. The contours are 

available at an interval of 40m the minimum contour being of 1840m. The area enclosed 

within the contours has been found using Autocad. Area has been found from elevation 

1840m to 1960m at an interval of 40m. The volume between any two elevations is 

calculated using the conical formula :

V = H/3 * (A1+A2+√A1A2) 

Where 

V = Volume between two contours 

H = Contour interval 

A1 = Area at level of first contour 

A2 = Area at level of second contour 

45 



The incremental volumes thus computed are added up to obtain cumulative volume. The 

resultant area capacity curve for both the dams is enclosed as Figure-5.3 and Figure-5.4. 

The curve may be improved after receiving toposheets in scale of 1:25000. The gross 

storage capacity for dam on Rangyong Chu at FRL 1845m is 0.525 Mcum and 

submergence area is 2.5 Ha and for dam d/s of confluence of Umram Chu and Passaram 

Chu, the gross storage capacity at FRL 1845m is 3.05 Mcum and submergence area is 

15.62 Ha. 

5.5 DESIGN FLOOD 

Design Flood for a project can be estimated by following approaches: 

(i) Deterministic approach using Unit Hydrograph technique. 

(ii) Statistical approach using Flood frequency analysis 

(iii) Empirical methods 

• Unit Hydrograph technique 

Due to non-availability of G&D data and hourly gauges, design storm values in the 

proposed catchment, rating curves and observed flood hydrographs could not be 

developed for computing the Unit Hydrograph and Design Flood hydrograph. 

• Flood Frequency analysis 

Due to non-availability of long term, consistent G&D data near the proposed scheme, 

frequency analysis could not be done to estimate the design flood.

• Empirical Methods 

46 



The following empirical relationships have been used to estimate the design flood peak: 

(i) Dicken’s formula 

Q = CA 3/4 

Where C = Dickens constant with value between 11-14 for North- Indian Hilly 

catchment. A value of 14 has been adopted in present study. 

A = Catchment area in sq.km 

Therefore, Q 1 = 14 x 127 3/4 

= 530 cumec 

Q 2 = 14 x 146 3/4 

= 588 cumec 

where subscript 1 and 2 stand for the two proposed dams, first on Rangyong Chu and 

second d/s of confluence of Umram Chu and Passaram Chu respectively. 

(ii) Ali Nawab Jung formula 

Q = C(0.386A) (0.925-1/14logA) 

Where C = 49 to 60 (55 used) 

Q1 = 55* (0.386*127) (0.925-1/14log(127)) 

= 1259 cumec 

Q2 = 55* (0.386*146) (0.925-1/14log(146)) 

= 1384 cumec 

where subscript 1 and 2 stand for the two proposed dams as explained above. 

(iii) Computation of Design Flood from Design Flood at Teetsa-III using Dicken’s 

formula 

The design flood recommended for Teesta H.E project, Stage-III was 4572 cumec. The 

total catchment area upto Stage-III dam site is 2786 Sq.km. Rangyong H.E project is 

located on Rangyong Chu, which is a major tributary of Teesta river and both the 

catchments can be assumed to be hydrologically and hydro-meteorologically similar. 

Therefore, it seems logical to transpose the design flood value of Teesta-III to proposed

47 



dam sites on Rangyong Chu and d/s of confluence of Umram Chu and Passaram Chu. 

This transposition has been done by Dicken’s formula using a conversion factor of 0.099 

and 0.11 respectively. 

Q 1 = CA 1 n 

Q 2 = CA 2 n 

Where, A 1 = Catchment area of Rangyong project 

A 2 = Catchment area of Teesta-III project 

Q 1 = Design Flood for Rangyong project 

Q 2 = Design Flood for Teesta-III project 

C = Dicken’s constant 

n= 0.75 

Q Rangyong I = Q Teesta-III * (A Rangyong I/A Teesta-III) 0.75 

= 451 cumec 

Q Rangyong II = Q Teesta-III * (A Rangyong II/A Teesta-III) 0.75 

= 501 cumec 

(iv) Computation of Design Flood from Design Flood at Teetsa-V using Dicken’s 

formula 

The design flood for Rangyong project has also been estimated by transposing the design 

flood at Teesta-V H.E project using Dicken’s formula. The design flood recommended 

for Teesta-V H.E project, having a catchment area of 4307 Sq.km is 9500 cumec. The 

conversion factor for converting it at proposed dam sites for Rangyong project, having a 

catchment area of 127 Sq.km and 146 Sq.km, comes out to be 0.071 and 0.079 

respectively. 

Q Rangyong I = Q Teesta-V * (A Rangyong I/A Teesta-V) 0.75 

= 676 cumec 

Q Rangyong II = Q Teesta-V * (A Rangyong II/A Teesta-V) 0.75 

= 751 cumec 

A comparative study of flood peak computed from various methods at both the proposed 

dam sites is placed as Table 5-5.

Sl.No 

TABLE 5- 5 

Comparison Of Various Flood Values 

Method Used 

Design Flood- 

48 

Dam on 

Rangyong Chu 

(cumec) 

1. Dickens Formula 530 588 

2. Ali Nawaz Jung 

Formula 

3. Transposition of Teesta- 

III Flood peak on the 

basis of Dickens 

formula. 

4. Transposition of Teesta- 

V Flood peak on the 

basis of Dickens 

formula. 



Design Flood-Dam d/s of 

confluence of Umram Chu 

& Passaram Chu (cumec) 

1259 1384 

451 501 

676 751 

For pre-feasibility stage study, a design flood of 675 cumec and 750 cumec has been 

recommended for the proposed dam sites, one on Rangyong Chu and second d/s of 

confluence of Umram Chu and Passaram Chu respectively. It is worth to mention here 

that one of the methods of working out the design flood is on the basis of design flood at 

Teesta-III and Teesta-V, which has been computed using both unit hydrograph technique 

and flood frequency analysis 

On availability of more data/information, design flood will have to be estimated by 

deterministic approach using unit hydrograph technique and probabilistic approach using 

flood frequency analysis in feasibility stage.

5.6 SEDIMENTATION 

49 



A rate of sedimentation of 0.1385 Ham/Sq.km/Year has been worked out for Teesta-V 

H.E project based on suspended sediment observations at Dikchu. In the absence of 

sediment data at or near the proposed dam site, the same silt rate of Dikchu may be 

adopted for Rangyong H.E project too. 

The necessity of Detailed sedimentation study is not felt during PFR stage and the same 

need be done during feasibility/DPR stage with more observed data at the proposed site 

using a suitable method.

50 


Rangyongl HE Project, (3x 47 MW) 

TEESTA BASIN PROJECTS Annexure 5.1 

Maximum, Minimum monthly temperature and Relative humidity at Dikchu (Teesta-V dam site) 

Month 1998 1999 2000 2001 

TEMPERATURE RELATIVE 

RELATIVE 

RELATIVE TEMPERATURE 

HUMIDITY TEMPERATURE HUMIDITY TEMPERATURE HUMIDITY 

(%) 

(%) 

(%) 

Max O C Min O C 




RELATIVE 

HUMIDITY 

(%) 

Jan 25 7 92 23 6 90 22 9 90 20 11 96 

Feb 27 8 90 24 7 92 24 7 92 22 14 93 

Mar 30 10 92 28 9 91 N.A N.A N.A 24 15 91 

Apr 36 12 89 34 16 94 32 22 90 29 20 92 

May 38 14 91 35 18 93 36 17 87 29 19 91 

Jun 36 20 98 37 20 99 38 20 89 31 22 93 

Jul 35 20 99 39 21 96 39 22 90 31 20 90 

Aug 36 21 93 38 20 96 36 21 89 30 22 97 

Sep 35 20 93 34 16 97 35 20 89 28 22 95 

Oct 31 16 93 30 15 96 35 16 85 27 19 96 

Nov 29 14 92 28 13 91 31 14 90 25 16 95 

Dec 24 9 92 23 9 91 25 10 97 N.A N.A N.A

AVERAGE 10-DAILY DISCHARGE FOR DAM ON RANGYONG CHU 

51 



Annexure-5.2 

YEAR/MONTH JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC AVG 

I 3.99 3.71 4.34 5.88 6.96 11.06 20.02 16.92 17.97 6.41 5.08 3.06 

1976 II 3.82 3.64 4.65 6.44 5.51 21.58 19.07 18.45 10.36 5.06 4.21 2.62 8.54 

III 3.63 3.80 5.04 7.53 7.73 15.66 14.52 19.72 7.56 5.11 3.76 2.42 

I 2.16 3.61 2.00 3.83 4.18 11.89 17.53 20.18 13.84 11.52 6.02 3.75 

1977 II 2.05 3.52 2.85 3.60 5.16 21.10 20.63 16.98 11.32 7.26 5.49 3.96 8.50 

III 1.96 2.11 2.64 3.82 7.36 15.34 24.71 19.82 9.44 5.80 4.14 4.48 

I 3.08 2.85 2.60 3.70 6.40 17.57 20.46 25.05 13.18 12.41 6.61 4.68 

1978 II 2.76 2.79 2.78 4.74 13.11 18.43 21.93 21.17 17.17 9.68 4.93 3.96 10.04 

III 2.82 2.57 3.08 5.62 15.31 23.30 21.17 15.89 12.90 8.25 4.85 3.56 

I 3.29 2.71 3.02 5.75 10.77 12.51 22.30 22.08 18.19 19.40 9.90 7.23 

1979 II 3.03 2.71 3.17 5.72 13.73 14.97 21.33 17.43 15.87 13.24 8.06 5.95 10.79 

III 2.98 2.94 3.90 7.18 10.50 21.47 23.89 18.49 11.64 9.93 7.59 5.73 

I 5.40 4.95 5.68 8.84 12.32 17.23 27.15 29.43 25.71 12.76 8.63 6.72 

1980 II 5.20 5.18 5.83 11.34 10.54 22.93 27.80 32.31 20.15 10.97 7.86 6.11 13.74 

III 5.15 5.53 7.87 12.92 11.23 25.66 29.12 26.91 16.31 10.22 7.23 5.55 

I 5.35 4.60 5.66 7.08 12.97 14.96 31.03 24.41 23.96 15.01 10.35 6.28 

1981 II 5.01 4.73 5.99 8.97 14.01 17.89 26.61 25.75 20.54 13.89 8.26 5.65 13.19 

III 4.95 5.72 7.07 10.56 13.59 24.29 25.03 25.04 16.37 12.14 6.84 4.42 

I 4.06 4.42 4.65 7.80 10.82 20.85 22.29 19.79 16.91 11.36 7.20 5.37 

1982 II 4.52 4.59 5.21 7.78 12.15 22.96 24.97 18.73 24.46 9.54 6.28 4.95 11.95 

III 4.46 4.47 6.20 8.63 11.81 25.38 29.45 21.99 16.05 9.19 6.08 4.69 

I 4.65 2.64 3.92 6.67 10.99 22.04 34.18 23.61 23.51 21.44 11.78 7.44 

1983 II 4.14 2.62 5.03 5.46 13.17 21.39 29.08 25.04 26.44 21.14 10.82 6.97 14.66 

III 2.90 3.65 4.53 6.83 17.53 29.85 28.85 29.25 30.50 14.41 8.91 6.25

52 




I 5.58 4.71 10.36 11.96 14.48 31.23 38.82 37.13 40.14 25.60 18.64 9.18 

1984 II 5.49 4.89 11.58 12.75 21.16 37.56 38.95 37.23 38.31 32.47 16.11 9.03 21.38 

III 4.88 4.69 11.38 12.76 30.05 33.73 41.17 38.98 30.39 25.01 14.32 9.07 

I 9.14 8.22 11.55 14.02 14.38 14.92 41.60 36.89 19.43 13.37 7.84 5.14 

1985 II 8.69 7.51 12.51 16.92 16.69 18.62 54.29 38.91 18.56 11.72 6.81 4.65 18.49 

III 7.52 9.09 11.65 19.98 23.25 52.77 45.65 47.64 15.55 9.66 6.03 4.28 

I 4.05 3.86 4.84 5.32 7.24 9.86 21.46 21.40 17.88 14.58 7.83 5.38 

1986 II 4.03 3.97 5.27 6.88 7.70 16.72 26.81 18.40 22.21 10.90 6.96 4.96 10.93 

III 3.82 4.54 5.41 7.72 8.11 24.77 24.11 20.36 18.08 8.51 6.01 3.66 

I 3.19 2.67 2.71 7.37 7.69 16.65 23.29 23.57 30.92 14.09 7.28 3.68 

1987 II 3.00 2.65 3.22 5.15 8.55 24.19 22.26 25.72 16.54 10.49 4.44 3.37 11.12 

III 2.82 2.90 4.04 6.80 10.04 20.30 24.89 17.19 22.69 8.97 3.90 3.08 

I 3.00 2.91 3.51 6.12 8.22 13.16 32.42 27.86 18.52 11.80 5.19 4.15 

1988 II 3.00 3.05 5.21 6.91 12.32 19.05 25.47 25.57 12.49 7.83 4.69 3.93 11.63 

III 2.97 3.39 5.35 8.04 16.32 20.86 28.07 38.80 13.97 6.30 4.37 3.72 

I 2.28 2.44 2.70 2.94 7.42 16.58 29.58 23.50 17.53 12.46 5.37 3.45 

1989 II 2.22 2.23 2.75 3.52 7.66 27.47 29.09 18.44 15.88 10.61 4.35 3.00 10.81 

III 2.20 2.38 2.83 4.23 18.68 29.05 27.08 18.09 15.78 8.63 3.96 2.62 

I 2.39 1.98 1.64 1.41 4.25 18.17 22.88 21.26 18.40 10.28 5.27 3.01 

1990 II 2.22 1.86 1.34 2.32 7.48 17.75 29.17 21.60 17.62 10.47 3.94 2.49 9.36 

III 2.01 1.79 1.36 2.88 8.61 20.76 24.96 19.17 12.27 8.61 3.29 2.14 

I 2.17 2.04 2.09 6.60 6.69 9.65 16.00 19.48 18.69 12.21 6.58 3.73 

1991 II 2.13 1.94 2.39 3.76 8.15 15.23 15.59 22.45 19.74 9.68 5.82 2.86 8.75 

III 2.11 1.96 2.52 3.98 9.01 14.01 16.99 18.55 15.29 7.94 4.44 2.52 

I 2.29 2.05 2.03 2.49 3.13 4.05 9.61 12.09 11.58 7.12 3.21 2.57 

1992 II 1.90 1.98 2.05 3.50 3.65 5.77 9.73 12.14 11.40 5.11 2.85 2.23 5.31 

III 1.94 1.90 2.11 3.20 3.67 11.19 11.05 13.20 9.43 4.35 2.60 2.06 

I 2.09 1.92 3.21 3.41 5.66 6.63 22.82 30.01 28.67 20.29 10.71 8.44 

1993 II 2.11 2.04 3.21 3.73 5.10 8.47 22.82 28.45 24.15 15.06 9.44 7.76 11.36 

III 1.98 1.97 3.36 4.46 5.17 10.90 26.76 27.25 22.83 12.90 8.65 6.37

53 




I 6.00 5.57 5.26 5.83 7.50 13.73 18.05 17.92 15.97 10.81 7.24 4.81 

1994 II 5.59 5.33 4.75 7.30 7.73 18.18 19.14 17.51 15.99 9.61 5.97 4.40 10.14 

III 5.65 5.71 6.01 6.70 9.51 21.11 19.50 18.83 13.82 8.80 4.99 4.16 

I 3.95 3.91 3.56 4.55 11.99 20.77 28.56 20.12 16.27 10.35 5.12 4.40 

1995 II 3.99 3.89 3.37 5.63 18.51 22.22 23.96 20.30 14.57 10.08 5.85 3.92 11.08 

III 3.94 3.92 4.65 8.22 17.89 22.51 18.42 18.03 14.02 7.87 5.88 3.64 

I 3.14 3.41 3.38 3.83 10.10 11.49 19.31 17.69 16.60 12.11 9.03 5.14 

1996 II 3.12 3.04 3.91 3.72 8.85 9.73 20.79 16.50 15.84 11.10 8.39 4.65 9.56 

III 3.30 3.33 4.17 8.28 12.25 17.38 18.51 16.63 13.78 9.92 7.46 4.28 

I 4.84 4.67 4.71 5.17 6.17 8.10 17.78 14.73 12.63 9.11 4.32 3.26 

1997 II 4.60 4.65 4.94 5.14 7.10 11.55 15.39 17.97 14.30 5.97 3.99 3.18 7.87 

III 4.68 4.60 5.39 5.29 7.33 14.22 12.85 11.81 11.58 4.71 3.61 3.00 

I 3.99 3.71 4.34 5.88 8.80 14.92 24.21 22.75 19.43 13.37 7.84 5.14 

AVG II 3.82 3.64 4.65 6.44 10.50 18.62 24.75 22.49 18.56 11.72 6.81 4.65 11.34 

III 3.63 3.80 5.04 7.53 12.66 22.56 24.19 22.38 15.55 9.66 6.03 4.28 

Note : 1) All discharge data is in cumec. 

2) Total no. of years -22

AVERAGE 10-DAILY DISCHARGE FOR THE DAM D/S OF CONFLUENCE OF UMRAM CHU & PASSARAM CHU 

54 



Annexure-5.3 


I 3.53 3.27 3.83 5.36 6.28 9.97 18.05 15.26 16.21 5.78 4.58 2.76 

1976 II 3.38 3.23 4.18 5.79 4.97 19.46 17.20 16.64 9.35 4.57 3.80 2.36 7.69 

III 3.22 3.40 4.53 6.79 6.97 14.12 13.09 17.79 6.82 4.61 3.39 2.18 

I 1.94 3.26 1.80 3.46 3.77 10.73 15.81 18.20 12.49 10.39 5.43 3.38 

1977 II 1.85 3.18 2.57 3.25 4.66 19.03 18.61 15.31 10.21 6.55 4.95 3.57 7.67 

III 1.77 1.90 2.38 3.45 6.64 13.84 22.29 17.88 8.51 5.23 3.74 4.04 

I 2.78 2.57 2.34 3.34 5.77 15.84 18.45 22.60 11.89 11.20 5.96 4.22 

1978 II 2.49 2.52 2.51 4.27 11.83 16.62 19.78 19.09 15.48 8.73 4.45 3.58 9.05 

III 2.54 2.31 2.78 5.06 13.81 21.02 19.09 14.34 11.64 7.44 4.38 3.21 

I 2.96 2.45 2.73 5.19 9.71 11.29 20.11 19.91 16.40 17.50 8.93 6.52 

1979 II 2.73 2.44 2.86 5.16 12.38 13.51 19.24 15.72 14.31 11.94 7.27 5.37 9.74 

III 2.69 2.66 3.51 6.47 9.47 19.36 21.55 16.68 10.50 8.96 6.84 5.17 

I 4.87 4.46 5.13 7.97 11.11 15.54 24.49 26.54 23.19 11.51 7.78 6.06 

1980 II 4.69 4.68 5.26 10.23 9.50 20.68 25.07 29.15 18.18 9.89 7.09 5.51 12.40 

III 4.65 4.98 7.10 11.65 10.13 23.14 26.27 24.27 14.71 9.21 6.52 5.00 

I 4.82 4.15 5.10 6.39 11.70 13.49 27.99 22.01 21.62 13.54 9.33 5.66 

1981 II 4.52 4.27 5.40 8.09 12.64 16.14 24.00 23.23 18.53 12.53 7.45 5.09 11.90 

III 4.46 5.16 6.38 9.53 12.26 21.91 22.57 22.58 14.76 10.95 6.17 3.99 

I 3.67 3.99 4.20 7.03 9.76 18.80 20.10 17.85 15.26 10.25 6.49 4.85 

1982 II 4.08 4.14 4.70 7.02 10.96 20.71 22.52 16.90 22.06 8.61 5.66 4.47 10.78 

III 4.02 4.03 5.60 7.79 10.65 22.89 26.56 19.83 14.48 8.29 5.48 4.23 

I 4.19 2.38 3.54 6.02 9.91 19.88 30.83 21.30 21.21 19.34 10.62 6.71 

1983 II 3.73 2.37 4.54 4.92 11.88 19.29 26.23 22.58 23.84 19.07 9.76 6.29 13.22 

III 2.62 3.29 4.09 6.16 15.81 26.92 26.02 26.39 27.51 13.00 8.04 5.64

55 




I 5.03 4.24 9.35 10.79 13.06 28.17 35.01 33.49 36.21 23.09 16.81 8.28 

1984 II 4.95 4.41 10.45 11.50 19.08 33.87 35.13 33.58 34.55 29.28 14.53 8.15 19.29 

III 4.40 4.23 10.26 11.50 27.11 30.42 37.14 35.15 27.41 22.56 12.91 8.18 

I 8.25 7.41 10.42 12.65 12.97 13.24 37.52 33.27 17.91 12.07 6.93 4.54 

1985 II 7.83 6.77 11.28 15.26 15.05 16.97 48.97 35.10 16.55 10.31 5.96 4.12 16.65 

III 6.78 8.20 10.51 18.02 20.97 47.59 41.17 42.97 14.38 8.49 5.28 3.75 

I 3.66 3.48 4.37 4.80 6.53 8.89 19.35 19.30 16.13 13.15 7.06 4.86 

1986 II 3.64 3.58 4.75 6.21 6.94 15.08 24.18 16.59 20.03 9.83 6.28 4.47 9.86 

III 3.44 4.10 4.88 6.96 7.31 22.34 21.75 18.37 16.30 7.68 5.42 3.30 

I 2.88 2.41 2.45 6.64 6.94 15.02 21.01 21.26 27.89 12.71 6.57 3.32 

1987 II 2.71 2.39 2.90 4.64 7.72 21.82 20.08 23.20 14.92 9.46 4.01 3.04 10.03 

III 2.54 2.62 3.64 6.13 9.05 18.31 22.45 15.50 20.46 8.09 3.52 2.78 

I 2.71 2.63 3.17 5.52 7.41 11.87 29.24 25.13 16.71 10.64 4.68 3.74 

1988 II 2.71 2.75 4.70 6.24 11.11 17.18 22.97 23.06 11.27 7.06 4.23 3.55 10.49 

III 2.68 3.06 4.83 7.25 14.72 18.82 25.32 34.99 12.60 5.68 3.94 3.36 

I 2.05 2.20 2.44 2.65 6.69 14.96 26.68 21.20 15.81 11.24 4.84 3.12 

1989 II 2.00 2.01 2.48 3.18 6.91 24.78 26.24 16.63 14.32 9.57 3.93 2.70 9.75 

III 1.98 2.14 2.55 3.81 16.84 26.20 24.43 16.32 14.23 7.78 3.57 2.37 

I 2.16 1.78 1.48 1.27 3.83 16.39 20.64 19.18 16.59 9.27 4.76 2.72 

1990 II 2.00 1.67 1.21 2.09 6.75 16.01 26.31 19.48 15.89 9.45 3.55 2.24 8.44 

III 1.81 1.62 1.23 2.60 7.76 18.72 22.52 17.29 11.07 7.77 2.97 1.93 

I 1.96 1.84 1.89 5.96 6.03 8.70 14.43 17.57 16.85 11.01 5.94 3.37 

1991 II 1.92 1.75 2.15 3.40 7.35 13.74 14.06 20.25 17.81 8.73 5.25 2.58 7.89 

III 1.90 1.77 2.27 3.59 8.13 12.64 15.33 16.73 13.79 7.17 4.01 2.27 

I 2.07 1.85 1.84 2.24 2.83 3.65 8.67 10.91 10.44 6.43 2.90 2.32 

1992 II 1.72 1.79 1.85 3.15 3.29 5.21 8.77 10.95 10.28 4.61 2.57 2.01 4.79 

III 1.75 1.71 1.90 2.88 3.31 10.09 9.97 11.91 8.51 3.92 2.35 1.85 

I 1.88 1.73 2.90 3.08 5.11 5.98 20.58 27.07 25.86 18.30 9.66 7.61 

1993 II 1.90 1.84 2.89 3.36 4.60 7.64 20.58 25.66 21.78 13.58 8.51 7.00 10.24 

III 1.79 1.77 3.03 4.03 4.66 9.83 24.14 24.58 20.59 11.64 7.80 5.75

56 




I 5.42 5.02 4.74 5.26 6.77 12.39 16.28 16.17 14.40 9.75 6.53 4.34 

1994 II 5.04 4.80 4.28 6.58 6.98 16.40 17.26 15.79 14.43 8.67 5.38 3.97 9.14 

III 5.09 5.15 5.42 6.04 8.58 19.04 17.59 16.98 12.46 7.94 4.50 3.75 

I 3.56 3.52 3.21 4.10 10.82 18.74 25.76 18.15 14.68 9.34 4.62 3.97 

1995 II 3.60 3.51 3.04 5.08 16.70 20.04 21.61 18.31 13.14 9.09 5.28 3.53 9.99 

III 3.55 3.53 4.19 7.42 16.14 20.30 16.61 16.27 12.64 7.10 5.30 3.28 

I 2.83 3.08 3.05 3.46 9.11 10.36 17.42 15.96 14.97 10.92 8.14 4.54 

1996 II 2.81 2.74 3.53 3.36 7.98 8.78 18.75 14.88 14.29 10.01 7.57 4.12 8.61 

III 2.97 3.00 3.76 7.47 11.05 15.67 16.69 15.00 12.43 8.95 6.73 3.75 

I 4.36 4.21 4.25 4.66 5.56 7.31 16.04 13.29 11.39 8.21 3.89 2.94 

1997 II 4.15 4.20 4.46 4.64 6.40 10.42 13.88 16.21 12.90 5.38 3.60 2.87 7.10 

III 4.22 4.15 4.86 4.77 6.61 12.83 11.59 10.65 10.44 4.25 3.26 2.71 

I 3.53 3.27 3.83 5.36 7.80 13.24 22.02 20.71 17.91 12.07 6.93 4.54 

AVG II 3.38 3.23 4.18 5.79 9.35 16.97 22.34 20.38 16.55 10.31 5.96 4.12 10.21 

III 3.22 3.40 4.53 6.79 11.27 20.27 22.01 20.57 14.38 8.49 5.28 3.75 

Note: 1. All discharge data in cumec. 

2. Total no. of years -22



CHAPTER – VI 

CONCEPTUAL LAYOUT & 

PLANNING


CHPAPER-VI 

CONCEPTUAL PLANNING AND LAYOUT 

59 



The Rangyong H.E. project is located in the North district of Sikkim state. It is a run of 

the river scheme proposed to harness hydel potential of the Rangyong Chu, a Sub- 

tributary of river Teesta. The available gross head of 737 m is proposed to be utilised for 

generating 141 MW of Power. Two small reservoirs of adequate capacity have been 

provided as operating pools to meet diurnal peaking load demands. 

6.2 PROJECT COMPONENTS 

• Two 3.3 m diameter, 300 m long Diversion Tunnel with u/s & d/s coffer dams. 

• Upper concrete Dam 65 m high above deepest level & 300m long with a central 

spillway. 

• Lower concrete Dam 65 m high high above deepest level & 250m long with a 

central spillway. 

• One 3.3m diameter horseshoe shaped concrete lined and 2 kms long link tunnel. 

• Power Intake Structure leading to 2 Nos. 3 m dia D-shaped intake tunnels. 

• Two Nos. Underground Desilting Chambers of size 125m (L) X 6 m (W) X 9 m 

(H). 

• One 3.3m diameter horseshoe shaped concrete lined and 7.5 kms long Head Race 

Tunnel with three adits. 

• One 10 m diameter & approx. 75 m high semi-Underground Surge Shaft. 

• One circular inclined Pressure Shaft of 2.5m diameters, 1000 m long with 

mainfold to feed three Pelton wheel turbines. 

• Underground Power House of size 100m x 22.5m x 40m consisting of 3 Pelton 

units of 47 MW each. 

• One no.3.3m diameter Horseshoe shaped tailrace tunnel of about 300 m length.

60 



The conceptual planning and lay-out of project components have been worked out based 

on S.O.I topo sheets no.78A/6 of 1:50000 scale with contour intervals 40 m. 

6.2.1 Conceptual Layout 

The choice of location of the dams has been made keeping in view the topography, 

geology and maximum water availability at the prospective sites. Two reservoirs have 

been created in two basins and connected with a link tunnel to fulfill peaking 

requirement. The location of power house has been fixed keeping the tailrace outlet at 

El.1098.00m taking into consideration the FRL of upcoming Panan H E project. 

The location of major components of the project, riverbed levels at dam sites, TRT outlet 

site and generation capacity of the project as identified in the ranking study undertaken 

by CEA in 1990 have been considered during the preparation of this report.The upcoming 

hydroelectric projects on Rangyong/Tolung Chu have been taken into consideration in 

the conceptual planning of the project. 

The layout plan of the project and brief write up as envisaged by CEA have been 

enclosed as plate-1 and annexure 6.1 respectively. The cascade development schemes 

on the Teesta River as prepared by CEA is enclosed as plate-2 and of Tolung River basin 

as plate 3 and 4. 

Based on the hydrological and topographical study, reconnaissance survey of the site and 

input data of ranking study, a conceptual layout plan of the project was prepared and 

discussed in CEA for vetting during Nov’03. 

6.2.2 Dam and River Diversion Works 

Construction of two 65m high concrete Dams have been proposed keeping in view the 

topography, geology and availability of construction material.The availability of

61 



construction material for the dam, cofferdam and its suitability has been discussed 

elsewhere in the report. 

Upper Dam 

Upper Dam is proposed on d/s of confluence of Umram Chu and Passaram Chu. Width 

of the valley at this Dam site varies from 50 m at riverbed level to 300 m at EL 1850 m, 

which is suitable for a concrete dam. Average bed level at Dam site is EL 1795 m. The 

overflow section of this dam is 27 m long and Non –overflow section is 273 m consisting 

166 m on right abutment and 107 m on left abutment. 

Lower dam 

Lower Dam is proposed across the river rangyong Chu. Width of the valley at this Dam 

site varies from 50 m at riverbed level to 250 m at EL 1850 m., which is suitable for a 

concrete dam. FRL is proposed to be fixed at EL 1845 and MDDL at El.1825 m. keeping 

in view the pondage requirement and inflow of water in Rangyong Chu and Umram chu 

and Passaram chu during lean period The overflow section of lower dam is 27 m long and 

Non overflow section is 223 m consisting 105 m on right abutment and 118 m on left 

abutment. 

The top of both the dams has been proposed to be kept at EL 1850 m and foundation of 

the dam at EL 1785 m after removal of approx. 10.0 m thick overburden.Both the 

spillways have three bays each of size 3 m X 6 m with 3.0 m wide piers for both the 

dams. The spillway is designed to pass a probable maximum flood of 750 cumecs and 

675 cumecs for upper and lower dams respectively with one gate inoperative. The crest 

of spillways has been kept at EL1805 m. The low-level orifice type spillway has been 

provided to flush out the sediment accumulated in the reservoir to maintain the live 

storage capacity of the reservoir. The top width of non-overflow has been fixed as 8 m. 

The d/s slope of the Non-overflow section has been proposed as 0.8H: 1V and u/s slope 

as 0.1H: 1V. The project area falls within Zone-IV of seismic zoning map.

62 



The reservoir capacity formed by construction of both the dams has a gross storage pre- 

sedimentation capacity of 3.57 M.cum and live storage capacity of 1.97 M cum out of 

which the upper reservoir has the gross storage pre-sedimentation capacity of 3.05 

M.cum and live storage capacity of 1.67 M while lower reservoir has the gross storage 

pre-sedimentation capacity of 0.525 M.cum and live storage capacity of 0.3 M 

respectively. After sedimentation, the reservoir is likely to have an adequate live storage 

capacity of more than what is adequate for running the power station at full capacity for 

3-4 hours in a day during the period of lean flows. Both the reservoirs have been 

connected by one 3.3m diameter horseshoe shaped concrete lined and 2 kms long link 

tunnel. The invert level of the link tunnel has been kept at EL1815 taking into 

consideration the water seal requirement to prevent the vortex formation and air 

entrainment. The intake structure shall be provided with the trash racks to prevent the 

entry of trash in the link tunnel. 

Two no. Concrete lined 3.3 m dia 300 m long diversion tunnels have been proposed for 

both the dams on the left banks of the river to divert a flood of approx. 100 cumecs The 

design diversion discharge has been decided based on the experience of various ongoing 

NHPC projects in Teesta valley. This data shall however needs to be firmed up during the 

preparation of detailed project report with the availability of more hydrological data & 

experience gained in the basin e.g.: during the construction of Teesta-V project. In order 

to divert the river during construction of the dams, an u/s cofferdam of approx. height 

15m and d/s cofferdam of 8 m height is proposed for both the dams. 

6.2.3 Power Intake & Desilting Chambers 

The proposed power intake is on the right bank of the Rangyong Chu and consists of two 

no. intake and two no. D-shaped intake tunnels of dia 3 m each. Two no intakes are 

proposed to keep the desilting chambers dimension within the manageable limits and to 

put either of the desilting chambers to inspection and maintenance while the other is in 

operation. The intake structures are designed to pass 26.76 cumecs, which includes

63 



flushing discharge i.e. about 20% of turbine discharge (22.30 cumecs). The invert level of 

the intake structure has been kept at 10m higher than the spillway crest to check the 

sediments entry in the water conductor system. The intake structure shall be provided 

with the trash racks to prevent the entry of trash into the water conductor system. The 

gross area of the trash racks shall be determined to give a velocity of not more than 

1.5m/s. A mechanical raking machine operated from El.1850m shall clean the racks. 

For the efficient, trouble free and continuous operation of turbines with least possible 

wearing and erosion damages due to silt, it is necessary to remove 90% of the sediments 

larger than 0.2 mm-particle size. Two nos. 6 m wide Dufour type Desilting chambers 

with height 9 m shall be provided to remove 90% of particles having size greater than or 

equal to 0.2 mm. Two separate intakes lead the water to two independent desilting 

chambers 125 m long spaced at 30 m c/c, through 25 m long upstream transition which 

will gradually reduce the velocity of water in the chamber to less than 0.25m /sec. The 

chambers have been provided with central gutter with holes to facilitate the flushing of 

settled silt particles through the flushing tunnel. A silt flushing conduit at the bottom of 

each chamber runs along the length and two flushing tunnels join to form a single silt 

flushing tunnel of size 1.5 m x 3.0 m d-shaped and 500 m length which will discharge the 

sediment back into the river d/s of the dam. Thus practically silt free water will be led 

into the headrace tunnel. The requirement of desilting chambers is being foreseen, on the 

lines of Teesta-V project, which is located d/s of this project. 

6.2.4 Head Race Tunnel, Surge Shaft, and Pressure Shaft 

The proposed 3.3 m diameter concrete lined horseshoe shaped headrace tunnel of 7.5 

km length, and having a slope of 1 in 250 is designed to carry a design discharge of 26.76 

cumec. The diameter of the headrace tunnel has been fixed from the minimum working 

area requirements. The Invert level of headrace tunnel is fixed at EL. 1815 m near intake. 

The rock cover above headrace tunnel generally varies from +25 m to +600 m. The low 

cover reaches are confined to prominent nalla crossings. Three nos. construction Adits of

64 



3.3m dia are proposed to facilitate excavation of headrace tunnel within the scheduled 

completion time. The length of tunnel between 250 m long adit-1 & 500 m long adit-2 is 

3 Km and the length of tunnel between 500 m long adit-2 & 600 m long adit-3 is 3 Km. 

The location of the adits and portals are indicative and the actual lengths may vary. The 

tunnel is proposed to be concrete lined with 250 mm thick plain M-20 concrete. The rock 

support treatment shall consist of grouted rock bolts/anchors and shotcrete with or 

without wire mesh. In rock class of IV & V steel ribs supports is envisaged. 

A vertical, restricted orifice type semi-underground surge shaft of 10 m finished dia and 

about 75 m height has been proposed with its top opening into a platform at elevation EL 

+1860 m. Surge shaft is proposed to be concrete lined with 0.75 m thick R.C.C. Its 

bottom is kept at EL 1785 m at the HRT and surge shaft junction. The transient studies 

shall be required to be done to work out the maximum and minimum levels for the worst 

operation conditions. 

One no. Steel lined inclined circular Pressure Shaft of 2.5m diameter and 1000 m length 

takes off from the surge shaft, which further bifurcates at two points to feed water to 

three units of Pelton turbines each of 47 MW. 

6.2.5 Power House Complex & Tail Race Channel 

The underground Power House is located on the Right bank of rangyong Chu u/s of 

Panan dam. It will have an installed capacity of 141 MW (3 generating units of 47 MW 

each). The support system shall comprise of rock bolts and shotcrete. The centerline of 

the turbines is proposed at EL 1100.15 m. One number electrically operated overhead 

traveling crane (E.O.T) shall be provided for handling the electrical and mechanical 

equipment. A lift shall be provided near the service bay for approaching the lower parts 

of powerhouse. The overall dimensions of the Power House are 100m x 22.5m x 40m. A

65 



Control block area shall be located on one end of machine hall. The transformer cavern 

cum gate shaft is proposed 30m d/s of powerhouse cavern. 

A cable tunnel of size 2.0 m x 3.0 m will take off from transformer area and shall carry 

cables to a surface switchyard. The Switchyard measuring approx. 155 m x 100 m shall 

be formed in cutting/filling. 

Water from the turbines is discharged through three lined tailrace tunnels, which merge 

into a single tailrace tunnel of diameter 3.3 m near Tolung Chu. This tunnel is 3.3 m 

diameter horseshoe and about 300m long with invert at EL.1097 at tailrace outlet. The 

tailrace outlet level has been kept at El. 1098 m in conformity with the FRL of proposed 

Panan H E Project to maintain an open channel flow in the TRT. 

6.3 Further Studies 

6.3.1 Topographical Studies 

1. Topographical contour Survey of the dam area and Power House area in 1:5000 

scales with 5m contour intervals. 

2. Survey in 1:1000 scale for locating the adits of the HRT. 

3. The riverbed survey including the cross sections at Dam axis and tailrace outlet shall 

be undertaken to firm up the power potential of the project. 

6.3.2 Geological and Geo-technical investigations 

1. Geological/ geotechnical investigations including surface mapping and subsurface 

explorations like exploratory drilling and seismic profiling at the dam and 

powerhouse area. 

2. Rock mechanic lab tests shall be required for finding out the properties of the rock 

material. 

3. Construction material survey shall be required to be undertaken involving drifts, pits, 

and topographical surveys of the borrow/quarry areas.

66 



4. Site-specific studies for earthquake design parameters shall also be required to be 

undertaken. 

6.3.3 Design Studies 

1. Hydraulic design of various structures like spillway, power intake, desilting 

chambers, transient studies of surge shaft shall be required for firming up the 

dimensions. 

2. Stability analysis of non-overflow and overflow sections shall have to be done taking 

into account the approved seismic parameters. 

3. Hydraulic model studies for reservoir and Dam spillway shall be required for the 

confirmation of design parameters. 

4. Structural design of various components of the project. 

5. Sedimentation analysis for working out the post sedimentation storage capacity of the 

reservoir. 

6. Alternative studies for location, type and layout of main components based on 

detailed topographical and geological studies. 

6.4 HYDRO- MECHENICAL EQUIPMENT 

6.4.1 Diversion Tunnel Gates And Hoists-Upper Reservoir 

For the diversion of water during construction stage, one number horseshoe shaped 

diversion tunnel of 3.3m diameter has been proposed.After the construction of the dam, 

for the purpose of plugging the diversion tunnels, one number fixed wheel type gate will 

be provided at the inlet of the tunnel. The gate shall be operated by means of electrically 

operated rope drum hoist located on the hoist platform installed over the trestle above 

deck level. The gate is meant for one time closure, just before plugging of the tunnel. 

Height of the cofferdam is 15m and gate is to be designed for operation against water 

height corresponding to 19.0m.

67 



6.4.2 Spillway Radial Gates, Hoists, Spillway Bulkhead Gate And Gantry Crane- 

Upper Reservoir 

Three submerged type radial gates shall be provided to control the discharge through the 

gated portion of the spillway. Each gate shall be operated by means of suitable capacity 

hydraulic hoist from a power pack and two double acting cylinders having a provision of 

25% pushing force (one on each end of the gate). 

One trolley mounted mobile gasoline engines operated power pack capable of operating 

two gates at 25% of the normal rated speed are envisaged for emergency operation of 

spillway radial gates. 

One portable oil filter unit for filtration, dehydration and degasification of hydraulic oil is 

also being provided. 

One set of spillway bulkhead gate has been envisaged to cater to the maintenance 

requirement of three nos. spillway radial gates. The spillway bulkhead gate shall be 

lowered / raised under balanced head condition by means of a suitable capacity of Gantry 

Crane. 

6.4.2.1 Instrument And Remote Control 

Gates shall be provided with PLC based remote control system for Control and operation 

of gates and automatic control of the reservoir level. 

6.4.2.2 Diesel Generating Set 

One diesel generating set complete with all accessories, equipment, instrument and 

wiring for making the equipment complete and for warranting a trouble free safe 

operation including its design, manufacturing, testing and commissioning will be 

provided for emergency operation of gates and hoists.

68 



6.4.3 Trash Rack And Trash Rack Cleaning Machine At Link Tunnel- Upper 

Reservoir 

Upstream face of the link tunnel shall be provided with the trash rack screen, which will 

be cleaned by means of a trash rack-cleaning machine. 

6.4.4 Link Tunnel Gate, Bulkhead Gate And Hoists-Upper Reservoir 

One number fixed wheel type gate shall be provided just downstream of the bell mouth of 

the link tunnel. The link tunnel gate is to be designed for self-lowering against upstream 

water level corresponding to FRL. The gate shall be operated by means of electrically 

operated rope drum hoist of suitable capacity. 

For maintenance and inspection of link tunnel gate and embedded parts, one number 

vertical slide type bulkhead gate has been proposed on the upstream of the link tunnel 

gate. The bulkhead gate shall be operated by means of a electrically operated rope drum 

hoist under balance head condition. 

6.4.5 Diversion Tunnel Gate And Hoist- Lower Reservoir 

For the diversion of water during construction stage, one number horseshoe shaped 

diversion tunnel of 3.3m diameter has been proposed. After the construction of the dam, 

for the purpose of plugging the diversion tunnels, one number fixed wheel type gate will 

be provided at the inlet of the tunnel. The gate shall be operated by means of electrically 

operated rope drum hoist located on the hoist platform installed over the trestle above 

deck level. The gate is meant for one time closure, just before plugging of the tunnel. 

Height of the cofferdam is 15m and gate is to be designed for operation against water 

height corresponding to 19.0m.

69 



6.4.6 Spillway Radial Gates, Hoists, Spillway Bulkhead Gate And Gantry Crane- 

Lower Reservoir 

Three submerged type radial gates shall be provided to control the discharge through the 

gated portion of the spillway. Each gate shall be operated by means of suitable capacity 

hydraulic hoist from a power pack and two double acting cylinders having a provision of 

25% pushing force (one on each end of the gate). 

One trolley mounted mobile gasoline engines operated power pack capable of operating 

two gates at 25% of the normal rated speed are envisaged for emergency operation of 

spillway radial gates. 

One set of spillway bulkhead gate has been envisaged to cater to the maintenance 

requirement of three nos. spillway radial gates. The spillway bulkhead gate shall be 

lowered / raised under balanced head condition by means of a suitable capacity of Gantry 

Crane. 

6.4.6.1 Instruments And Remote Control 

Gates shall be provided with PLC based remote control system for Control and operation 

of gates and automatic control of the reservoir level. 

Remote control system of both the reservoirs shall be interconnected together with the 

help of optical fibre cable, which will be routed through the link tunnel. 

6.4.6.2 Diesel Generating Set 

One diesel generating set complete with all accessories, equipment, instrument and 

wiring for making the equipment complete and for warranting a trouble free safe 

operation including its design, manufacturing, testing and commissioning will be 

provided for emergency operation of gates and hoists.

6.4.7 Link Tunnel Bulkhead Gate And Hoist-Lower Reservoir 

70 



For maintenance and inspection of link tunnel, one number vertical slide gate has been 

proposed. The slide gate shall be operated by means of an electrically operated rope drum 

hoist under balance head condition. 

6.4.8 Intake Trash Rack And Trash Rack Cleaning Machine-Lower Reservoir 

Upstream face of the link tunnel shall be provided with the trash rack screen, which will 

be cleaned by means of a trash rack-cleaning machine. 

6.4.9 Intake Gates, Bulkhead Gates And Hoists 

Two number fixed wheel type gates shall be provided just downstream of the bell mouth 

of the intake. The intake gates are to be designed for self-lowering against upstream 

water level corresponding to FRL. The gates shall be operated by means of electrically 

operated rope drum hoist of suitable capacity. 

For maintenance and inspection of intake gates and embedded parts, two numbers 

vertical slide gates have been proposed on the upstream of the intake gates. The slide 

gates shall be operated by means of a electrically operated rope drum hoist under balance 

head condition. 

6.4.10 Desilting Chamber Gate 

One set of slide type gate has been envisaged to cater to the maintenance requirement of 

two nos. desilting chambers. The gate shall be lowered / raised under balanced head 

condition by means of a suitable Capacity EOT Crane. 

6.4.11 Silt Flushing Tunnel Gates And Hoists 

In two silt-flushing tunnels, each tunnel is provided with a set of two slide (emergency & 

service) gates for regulating the discharge through flushing tunnels. Both the (emergency 

& service) gates shall be operated by means of hydraulic hoists. The gate grooves are

71 



provided with bonnet structures embedded in the concrete & a watertight bonnet cover at 

the top of the groove. 

6.4.12 Surge Shaft Gate And Hoist 

The intake of pressure shaft is provided with a slide type gate. The gate shall be operated 

under balanced head condition by means of an electrically operated rope drum hoist. 

6.4.13 Tailrace Gate And Hoist 

To isolate powerhouse from the river during flood, one number of fixed wheel type gate 

has been envisaged. The fixed wheel gate shall be operated under unbalanced head 

condition by a suitable capacity electrically operated monorail hoist placed in the 

transformer cavern. 

6.4.14 Adit Inspection Gates 

Three nos. adits shall be provided with manually operated hinged type gates in the 

concrete plug at the HRT construction to give access to the head race tunnel in the event 

of any inspection, repair and maintenance. 

6.4.15 Pressure Shaft Steel Liner 

One no. Pressure Shaft of dia. 2500 mm fully steel lined will take off from d/s of steel 

transition of Surge Shaft to feed the turbine placed in the power house. It comprises 

horizontal & inclined ferrules, 2 nos. vertical bends, 2 nos. plan bends, 2 nos. 

bifurcations and branch pipes for feeding three turbines. 

The material of Pressure Shaft liner shall conform to ASTM A537 Class 1. However 

bifurcation material shall conform to ASTM A517 Gr. F.



CHAPTER – VII 

POWER POTENTIAL STUDIES

7.1 GENERAL 

CHAPTER-VII 

POWER POTENTIAL STUDIES 

68 



The Power potential studies of Rangyong HE Project has been made for 90% dependable 

year based on 21 hydrological years, from 1976-77 (June) to 1996-97 (May) as given in 

table 7.1. The salient features of the project are as follows: 

FRL (EL) =1845 m 

MDDL (EL) =1825 m 

TWL = EL 1098 m 

Centre line of M/C = EL 1100.15 m 

Rated net head = 723.18 m 

Type of turbine = Vertical Pelton 

Rated Discharge of Plant =22.30 cumecs 

Proposed Plant Capacity =141 MW (3 x 47MW) 

Generation voltage = 11KV 

Design Energy = 639.52 MU in the 90% dependable year with 95% 

machine availability 

Minimum Peaking (Hrs) = 4.01hrs (approx.) 

7.2 Available Flow 

The discharge data for the 90% dependable hydrological year is given in Table 7.3. For 

carrying out the power potential and optimisation studies, the following statistics have 

been computed. 

Year: 

Each 10-daily period of the year represents the average of the flow recorded for the 

corresponding period of each year.

90% Dependable Year: 

69 



This is the lower decile of the series of the corresponding 10-daily period of the record 

i.e. (N+1) x 0.9th year where N is the years for which continuous hydrological data are 

available. The 90% dependable year comes out to be 1976-77 whose calculations are 

shown in table 7.2. 

7.3 DEFINITION OF TERMS 

Annual Energy 

This is the yearly energy provided during the 90% dependable hydrological year with 

95% machine availability. 

Firm Power 

This is the power capacity, which can be guaranteed continuously during the lean period 

in 90% dependable year. During lean inflow period the firm power comes out to be 23.58 

MW. 

7.4 FULL RESERVOIR LEVEL (FRL) AND MINIMUM DRAW DOWN 

LEVEL (MDDL) 

FRL and MDDL have been fixed at EL 1845 m & EL 1825 m respectively based on civil 

consideration. This project is envisaged as a run of the river scheme with small pondage. 

7.5 OPERATING HEAD AND HEAD LOSSES 

The net operating head for turbines has been derived from the following formula where 

head losses are taken as 15 m. 

Net operating head =MDDL+2/3 (FRL-MDDL)-TCL-Head losses 

The net operating head comes out to 723.18 m. 

7.6 INSTALLED CAPACITY 

The studies for power output and annual energy generation for the 90% dependable year 

has been given in Table 7.4 (A). Considering water availability the total installed capacity 

has been selected as 141 MW.

7.7 SIZE OF GENERATING UNITS 

70 



The power load demand in India is increasing at a very rapid rate and both hydroelectric 

and thermal (including nuclear) Power potential in the country are being developed not 

only to meet the overall requirements, but stimulatingly also to provide a proper mix of 

hydro and thermal power for optimum operation of the system. Keeping this in view 

current practice is to opt for largest size hydro units permissible within the parameters of 

economy, operating efficiency, maintenance, optimum utilization of available water, 

transport limitation etc. It is therefore proposed to install 3 units each of 47 MW capacity 

with Pelton turbine as prime mover. 

7.8 ENERGY GENERATION 

The energy generation in the 90% dependable year (1976-77) indicating lean inflow 

period and high inflow period is shown in Table 7.4 (B). It may be seen from Table 7.4 

(A) that the total unrestricted energy generation is 826.686 MU. Annual energy 

generation at 141 MW comes out to be 639.52 MU. Annual load factor for lean and 

monsoon periods of all years have been shown in Table 7.4 (C). Incremental benefits 

have been shown in Table 7.6 which comes out to be 2.63 for this year. Also annual 

energy generation unrestricted has been indicated in table 7.7(A) to 7.7(U) for 21 

hydrological years. Energy available at bus bar shall be 631.87 MU after allowing 

auxiliary consumption of 0.7% and transformer losses of 0.5% respectively.

Table-7.1 

DISCHARGE DATA 

75 



1976- 1977- 1978- 1979- 1980- 1981- 1982- 1983- 1984- 1985- 1986- 1987- 1988- 1989- 1990- 1991- 1992- 1993- 1994- 1995- 1996- 

PERIOD 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 

I 21.03 22.62 33.41 23.80 32.76 28.45 39.65 41.91 59.40 28.15 18.75 31.67 25.04 31.54 34.57 18.35 7.70 12.61 26.12 39.51 21.85 

JUN II 41.04 40.12 35.06 28.48 43.60 34.03 43.67 40.68 71.43 35.59 31.80 46.00 36.23 52.24 33.77 28.98 10.98 16.11 34.58 42.26 18.51 

III 29.78 29.18 44.32 40.83 48.80 46.20 48.27 56.77 64.15 100.36 47.12 38.61 39.68 55.25 39.48 26.65 21.28 20.73 40.14 42.80 33.05 

I 38.07 33.35 38.91 42.41 51.64 59.02 42.39 65.01 73.83 79.13 40.81 44.29 61.67 56.26 43.52 30.43 18.28 43.40 34.33 54.32 36.73 

JUL II 36.28 39.24 41.71 40.56 52.87 50.61 47.49 55.31 74.07 103.26 50.99 42.34 48.44 55.34 55.48 29.65 18.50 43.40 36.40 45.57 39.54 

III 27.61 46.99 40.26 45.44 55.39 47.60 56.02 54.87 78.31 86.82 45.86 47.35 53.39 51.51 47.48 32.32 21.01 50.90 37.09 35.03 35.20 

I 32.19 38.37 47.65 41.99 55.97 46.42 37.64 44.91 70.62 70.16 40.70 44.83 52.99 44.70 40.44 37.06 23.00 57.09 34.09 38.27 33.65 

AUG II 35.09 32.29 40.26 33.16 61.46 48.98 35.63 47.62 70.81 74.01 34.99 48.91 48.63 35.07 41.09 42.69 23.09 54.12 33.30 38.61 31.38 

III 37.51 37.70 30.23 35.17 51.19 47.62 41.82 55.64 74.13 90.61 38.73 32.69 73.79 34.40 36.46 35.28 25.11 51.83 35.81 34.30 31.63 

I 34.17 26.33 25.07 34.59 48.90 45.58 32.17 44.72 76.35 37.35 34.01 58.81 35.23 33.35 34.99 35.54 22.02 54.53 30.37 30.95 31.57 

SEP II 19.71 21.53 32.65 30.18 38.33 39.06 46.52 50.28 72.86 35.11 42.24 31.46 23.76 30.21 33.51 37.55 21.67 45.93 30.42 27.71 30.13 

III 14.39 17.95 24.54 22.14 31.03 31.13 30.53 58.00 57.80 29.93 34.38 43.15 26.57 30.01 23.34 29.08 17.94 43.43 26.28 26.66 26.20 

I 12.19 21.91 23.61 36.90 24.27 28.55 21.61 40.78 48.68 25.44 27.73 26.80 22.43 23.70 19.55 23.22 13.55 38.59 20.56 19.69 23.04 

OCT II 9.63 13.82 18.41 25.18 20.86 26.42 18.15 40.20 61.75 22.03 20.73 19.96 14.89 20.17 19.92 18.41 9.72 28.63 18.28 19.17 21.11 

III 9.72 11.04 15.69 18.89 19.43 23.09 17.48 27.40 47.57 18.14 16.19 17.07 11.98 16.41 16.38 15.11 8.27 24.54 16.73 14.98 18.87 

I 9.67 11.44 12.57 18.83 16.42 19.68 13.69 22.40 35.45 14.77 14.89 13.85 9.87 10.21 10.03 12.52 6.11 20.36 13.77 9.74 17.17 

NOV II 8.00 10.44 9.38 15.33 14.95 15.70 11.94 20.58 30.64 12.77 13.24 8.45 8.91 8.28 7.50 11.07 5.43 17.95 11.35 11.12 15.96 

III 7.16 7.88 9.23 14.43 13.76 13.01 11.56 16.95 27.23 11.31 11.44 7.42 8.31 7.53 6.26 8.45 4.95 16.45 9.49 11.19 14.20 

I 5.82 7.12 8.90 13.75 12.78 11.94 10.22 14.14 17.46 9.68 10.24 7.00 7.88 6.57 5.73 7.10 4.89 16.06 9.15 8.37 9.68 

DEC II 4.98 7.53 7.54 11.32 11.62 10.74 9.42 13.26 17.18 8.77 9.43 6.41 7.48 5.70 4.73 5.45 4.23 14.75 8.37 7.45 8.77 

III 4.60 8.52 6.77 10.90 10.55 8.42 8.92 11.88 17.24 8.02 6.95 5.86 7.08 4.99 4.08 4.79 3.91 12.12 7.92 6.92 8.02 

I 4.10 5.86 6.25 10.27 10.17 7.73 8.84 10.61 17.39 7.71 6.07 5.71 4.33 4.55 4.13 4.36 3.97 11.42 7.50 5.96 9.20 

JAN II 3.90 5.25 5.77 9.89 9.53 8.60 7.87 10.44 16.52 7.67 5.71 5.71 4.22 4.22 4.05 3.62 4.01 10.63 7.59 5.93 8.75 

III 3.73 5.36 5.67 9.80 9.41 8.48 5.52 9.29 14.30 7.26 5.36 5.65 4.18 3.82 4.01 3.70 3.77 10.74 7.49 6.27 8.90 

I 6.87 5.42 5.16 9.41 8.75 8.41 5.02 8.95 15.63 7.34 5.08 5.54 4.65 3.76 3.88 3.91 3.65 10.59 7.43 6.49 8.88 

FEB II 6.70 5.31 5.15 9.86 9.00 8.74 4.99 9.29 14.29 7.55 5.03 5.80 4.25 3.53 3.69 3.77 3.87 10.13 7.41 5.78 8.85 

III 4.01 4.88 5.60 10.51 10.88 8.49 6.94 8.93 17.29 8.64 5.52 6.44 4.52 3.41 3.73 3.61 3.74 10.86 7.45 6.33 8.75 

I 3.80 4.94 5.75 10.81 10.76 8.85 7.46 19.71 21.97 9.21 5.16 6.68 5.14 3.11 3.98 3.87 6.11 10.01 6.77 6.42 8.95 

MAR II 5.42 5.28 6.02 11.09 11.39 9.91 9.56 22.03 23.79 10.03 6.12 9.90 5.24 2.54 4.54 3.90 6.10 9.03 6.42 7.44 9.40 

III 5.03 5.86 7.41 14.97 13.45 11.80 8.63 21.64 22.16 10.30 7.68 10.18 5.38 2.59 4.79 4.01 6.39 11.42 8.84 7.93 10.25 

I 7.29 7.04 10.94 16.81 13.47 14.83 12.69 22.75 26.67 10.12 14.01 11.64 5.60 2.68 12.56 4.73 6.49 11.09 8.65 7.29 9.83 

APR II 6.84 9.01 10.88 21.57 17.05 14.80 10.38 24.25 32.19 13.09 9.79 13.15 6.70 4.42 7.16 6.65 7.09 13.88 10.71 7.08 9.78 

III 7.27 10.68 13.65 24.57 20.09 16.42 12.99 24.26 38.01 14.68 12.94 15.29 8.04 5.47 7.58 6.08 8.49 12.73 15.64 15.75 10.06 

I 7.95 12.17 20.48 23.43 24.68 20.58 20.90 27.53 27.35 13.76 14.63 15.64 14.11 8.08 12.72 5.96 10.77 14.27 22.81 19.20 11.73 

MAY II 9.82 24.94 26.11 20.04 26.65 23.12 25.05 40.24 31.75 14.64 16.27 23.42 14.58 14.23 15.50 6.94 9.70 14.71 35.21 16.84 13.50 

III 14.00 29.12 19.97 21.36 25.85 22.46 33.33 57.16 44.22 15.42 19.09 31.04 35.52 16.37 17.15 6.97 9.82 18.09 34.03 23.30 13.94

YEAR 

Table-7.2 

UNRESTRICTED ENERGY GENERATION 

UNRESTRICTED 

ENERGY ARRANGED IN 

DESCENDING ORDER 

76 



RANK OF THE YEAR 

1984-1985 2332.049 1 

1983-1984 1765.222 2 

1985-1986 1639.993 3 

1980-1981 1447.736 4 

1981-1982 1351.618 5 

1993-1994 1333.717 6 

1979-1980 1249.271 7 

1982-1983 1245.435 8 

1987-1988 1227.705 9 

1988-1989 1166.822 10 

1986-1987 1126.798 11 

1995-1996 1099.951 12 

1994-1995 1095.294 13 

1978-1979 1081.120 14 

1989-1990 1075.182 15 

1990-1991 1031.968 16 

1996-1997 1013.595 17 

1977-1978 971.124 18 

1991-1992 867.428 19 

1976-1977 826.686 20 

1992-1993 595.886 21 

90% dependable year 

=(N+1) x 0.9th year (where N=no. of years) 

=(21+1)*0.9th year 

=20 

1976-77 is 90% dependable year 

1986-87 is 50% dependable year 

Unrestricted energy of 90% dependable year is 826.686 MU 

90% dependable energy when power restricted to 141 MW is 639.52 MU

Table-7.3 

90% DEPENDABLE FLOWS FOR POWER GENERATION 

77 



MONTH/PERIOD 90% dependable year 1976-77 inflow (cumecs) 

10- daily series for the dam 

d/s of confluence of Umram 

Chu & Passaram Chu. 

10- daily series for the dam 

on Rangyong Chu. 

I 11.06 9.97 

JUN II 21.58 19.46 

III 15.66 14.12 

I 20.02 18.05 

JUL II 19.07 17.20 

III 14.52 13.09 

I 16.92 15.26 

AUG II 18.45 16.64 

III 19.72 17.79 

I 17.97 16.21 

SEP II 10.36 9.35 

III 7.56 6.82 

I 6.41 5.78 

OCT II 5.06 4.57 

III 5.11 4.61 

I 5.08 4.58 

NOV II 4.21 3.80 

III 3.76 3.39 

I 3.06 2.76 

DEC II 2.62 2.36 

III 2.42 2.18 

I 2.16 1.94 

JAN II 2.05 1.85 

III 1.96 1.77 

I 3.61 3.26 

FEB II 3.52 3.18 

III 2.11 1.90 

I 2.00 1.80 

MAR II 2.85 2.57 

III 2.64 2.38 

I 3.83 3.46 

APR II 3.60 3.25 

III 3.82 3.45 

I 4.18 3.77 

MAY II 5.16 4.66 

III 7.36 6.64

PERIOD INFLO 

W 

HEAD POWE 

R 

UNRES 

ENERGY 

Table-7.4 (A) 

POWER POTENTIAL STUDY OF 90% DEPENDABLE YEAR 1976-1977 

78 

ENERGY AT DIFFERENT RESTRICTED CAPACITIES 



CUME 

(M) IN MW (MU) 114 MW 117 MW 120 MW 123 MW 126 MW 129 MW 132 MW 135 MW 138 MW 141 MW 144 MW 147 MW 150 MW 153 MW 156 MW 159 MW 162 MW 

C 

JUNE I 21.03 723.18 132.966 31.912 25.992 26.676 27.360 28.044 28.728 29.412 30.096 30.316 30.316 31.912 31.912 31.912 31.912 31.912 31.912 31.912 31.912 

II 41.04 723.18 259.483 62.276 25.992 26.676 27.360 28.044 28.728 29.412 30.096 30.780 31.464 32.148 32.832 33.516 34.200 34.884 35.568 36.252 36.936 

III 29.78 723.18 188.290 45.190 25.992 26.676 27.360 28.044 28.728 29.412 30.096 30.780 31.464 32.148 32.832 33.516 34.200 34.884 35.568 36.252 36.936 

JULY I 38.07 723.18 240.705 57.769 25.992 26.676 27.360 28.044 28.728 29.412 30.096 30.780 31.464 32.148 32.832 33.516 34.200 34.884 35.568 36.252 36.936 

II 36.28 723.18 229.387 55.053 25.992 26.676 27.360 28.044 28.728 29.412 30.096 30.780 31.464 32.148 32.832 33.516 34.200 34.884 35.568 36.252 36.936 

5 III 27.61 723.18 174.570 46.086 28.591 29.344 30.096 30.848 31.601 32.353 33.106 33.858 34.610 35.363 36.115 36.868 37.620 38.372 39.125 39.877 40.630 

AUG I 32.19 723.18 203.527 48.847 25.992 26.676 27.360 28.044 28.728 29.412 30.096 30.780 31.464 32.148 32.832 33.516 34.200 34.884 35.568 36.252 36.936 

II 35.09 723.18 221.863 53.247 25.992 26.676 27.360 28.044 28.728 29.412 30.096 30.780 31.464 32.148 32.832 33.516 34.200 34.884 35.568 36.252 36.936 

III 37.51 723.18 237.164 62.611 28.591 29.344 30.096 30.848 31.601 32.353 33.106 33.858 34.610 35.363 36.115 36.868 37.620 38.372 39.125 39.877 40.630 

SEPT I 34.17 723.18 216.046 51.851 25.992 26.676 27.360 28.044 28.728 29.412 30.096 30.780 31.464 32.148 32.832 33.516 34.200 34.884 35.568 36.252 36.936 

II 19.71 723.18 124.620 29.909 25.992 26.676 27.360 28.044 28.413 28.413 29.909 29.909 29.909 29.909 29.909 29.909 29.909 29.909 29.909 29.909 29.909 

III 14.39 723.18 90.984 21.836 21.836 21.836 21.836 21.836 21.836 21.836 21.836 21.836 21.836 21.836 21.836 21.836 21.836 21.836 21.836 21.836 21.836 

OCT I 12.19 723.18 77.074 18.498 18.498 18.498 18.498 18.498 18.498 18.498 18.498 18.498 18.498 18.498 18.498 18.498 18.498 18.498 18.498 18.498 18.498 

II 9.63 723.18 60.888 14.613 14.613 14.613 14.613 14.613 14.613 14.613 14.613 14.613 14.613 14.613 14.613 14.613 14.613 14.613 14.613 14.613 14.613 

III 9.72 723.18 61.457 16.225 16.225 16.225 16.225 16.225 16.225 16.225 16.225 16.225 16.225 16.225 16.225 16.225 16.225 16.225 16.225 16.225 16.225 

NOV I 9.67 723.18 61.140 14.674 14.674 14.674 14.674 14.674 14.674 14.674 14.674 14.674 14.674 14.674 14.674 14.674 14.674 14.674 14.674 14.674 14.674 

II 8.00 723.18 50.582 12.140 12.140 12.140 12.140 12.140 12.140 12.140 12.140 12.140 12.140 12.140 12.140 12.140 12.140 12.140 12.140 12.140 12.140 

III 7.16 723.18 45.270 10.865 10.865 10.865 10.865 10.865 10.865 10.865 10.865 10.865 10.865 10.865 10.865 10.865 10.865 10.865 10.865 10.865 10.865 

DEC I 5.82 723.18 36.798 8.832 8.832 8.832 8.832 8.832 8.832 8.832 8.832 8.832 8.832 8.832 8.832 8.832 8.832 8.832 8.832 8.832 8.832 

II 4.98 723.18 31.487 7.557 7.557 7.557 7.557 7.557 7.557 7.557 7.557 7.557 7.557 7.557 7.557 7.557 7.557 7.557 7.557 7.557 7.557 

III 4.60 723.18 29.084 7.678 7.678 7.678 7.678 7.678 7.678 7.678 7.678 7.678 7.678 7.678 7.678 7.678 7.678 7.678 7.678 7.678 7.678 

JAN I 4.10 723.18 25.923 6.222 6.222 6.222 6.222 6.222 6.222 6.222 6.222 6.222 6.222 6.222 6.222 6.222 6.222 6.222 6.222 6.222 6.222 

II 3.90 723.18 24.658 5.918 5.918 5.918 5.918 5.918 5.918 5.918 5.918 5.918 5.918 5.918 5.918 5.918 5.918 5.918 5.918 5.918 5.918 

III 3.73 723.18 23.584 6.226 6.226 6.226 6.226 6.226 6.226 6.226 6.226 6.226 6.226 6.226 6.226 6.226 6.226 6.226 6.226 6.226 6.226 

FEB I 6.87 723.18 43.437 10.425 10.425 10.425 10.425 10.425 10.425 10.425 10.425 10.425 10.425 10.425 10.425 10.425 10.425 10.425 10.425 10.425 10.425 

II 6.70 723.18 42.362 10.167 10.167 10.167 10.167 10.167 10.167 10.167 10.167 10.167 10.167 10.167 10.167 10.167 10.167 10.167 10.167 10.167 10.167 

III 4.01 723.18 25.354 4.868 4.868 4.868 4.868 4.868 4.868 4.868 4.868 4.868 4.868 4.868 4.868 4.868 4.868 4.868 4.868 4.868 4.868 

MAR I 3.80 723.18 24.026 5.766 5.766 5.766 5.766 5.766 5.766 5.766 5.766 5.766 5.766 5.766 5.766 5.766 5.766 5.766 5.766 5.766 5.766 

II 5.42 723.18 34.269 8.225 8.225 8.225 8.225 8.225 8.225 8.225 8.225 8.225 8.225 8.225 8.225 8.225 8.225 8.225 8.225 8.225 8.225 

III 5.03 723.18 31.803 8.396 8.396 8.396 8.396 8.396 8.396 8.396 8.396 8.396 8.396 8.396 8.396 8.396 8.396 8.396 8.396 8.396 8.396 

APR I 7.29 723.18 46.092 11.062 11.062 11.062 11.062 11.062 11.062 11.062 11.062 11.062 11.062 11.062 11.062 11.062 11.062 11.062 11.062 11.062 11.062 

II 6.84 723.18 43.247 10.379 10.379 10.379 10.379 10.379 10.379 10.379 10.379 10.379 10.379 10.379 10.379 10.379 10.379 10.379 10.379 10.379 10.379 

III 7.27 723.18 45.966 11.032 11.032 11.032 11.032 11.032 11.032 11.032 11.032 11.032 11.032 11.032 11.032 11.032 11.032 11.032 11.032 11.032 11.032 

MAY I 7.95 723.18 50.265 12.064 12.064 12.064 12.064 12.064 12.064 12.064 12.064 12.064 12.064 12.064 12.064 12.064 12.064 12.064 12.064 12.064 12.064 

II 9.82 723.18 62.089 14.901 14.901 14.901 14.901 14.901 14.901 14.901 14.901 14.901 14.901 14.901 14.901 14.901 14.901 14.901 14.901 14.901 14.901 

III 14.00 723.18 88.518 23.369 23.369 23.369 23.369 23.369 23.369 23.369 23.369 23.369 23.369 23.369 23.369 23.369 23.369 23.369 23.369 23.369 23.369 

ENERGY OBTAINED ON 95% M/C AVAILABILITY 826.686 573.05 580.71 588.37 596.03 603.37 610.35 618.82 625.34 631.63 639.52 645.81 652.10 658.40 664.69 670.98 677.27 683.57 

FRL= EL 1845 

MDDL= EL 1825 

TWL= 1098 

LOSSES= 15 

OVERALL EFFICIENCY= 89.30%

Table-7.4 (B) 

79 


RangyongHE Project (3 x 47 MW) 

POWER POTENTIAL STUDY OF 90% DEPENDABLE YEAR 1976-1977 WITH 

95% MACHINE AVAILABILITY 

Net Head 723.18 m Design Discharge 22.30 Overall efficiency 89.30% 

Period 

Inflow Head Unrestri Unrestrict Power Energy (Mu) Energy Energy 

(Cumecs) (M) cted ed Restrict At 141 Mw During During 

Power In Energy ed To With 95% High Lean 

Mw (Mu) 141 Mw Machine Inflow Inflow 

Availability Period Period 

JUNE 

JULY 

AUG 

SEPT 

OCT 

NOV 

DEC 

JAN 

FEB 

MAR 

APR 

MAY 

10 1-10 21.03 723.18 132.97 31.912 132.97 31.912 0.000 31.912 

10 11-20 41.04 723.18 259.48 62.276 141.00 32.148 32.148 0.000 

10 21-30 29.78 723.18 188.29 45.190 141.00 32.148 32.148 0.000 

10 1-10 38.07 723.18 240.70 57.769 141.00 32.148 32.148 0.000 

10 11-20 36.28 723.18 229.39 55.053 141.00 32.148 32.148 0.000 

11 21-31 27.61 723.18 174.57 46.086 141.00 35.363 35.363 0.000 

10 1-10 32.19 723.18 203.53 48.847 141.00 32.148 32.148 0.000 

10 11-20 35.09 723.18 221.86 53.247 141.00 32.148 32.148 0.000 

11 21-31 37.51 723.18 237.16 62.611 141.00 35.363 35.363 0.000 

10 1-10 34.17 723.18 216.05 51.851 141.00 32.148 32.148 0.000 

10 11-20 19.71 723.18 124.62 29.909 124.62 29.909 0.000 29.909 

10 21-30 14.39 723.18 90.98 21.836 90.98 21.836 0.000 21.836 

10 1-10 12.19 723.18 77.07 18.498 77.07 18.498 0.000 18.498 

10 11-20 9.63 723.18 60.89 14.613 60.89 14.613 0.000 14.613 

11 21-31 9.72 723.18 61.46 16.225 61.46 16.225 0.000 16.225 

10 1-10 9.67 723.18 61.14 14.674 61.14 14.674 0.000 14.674 

10 11-20 8.00 723.18 50.58 12.140 50.58 12.140 0.000 12.140 

10 21-30 7.16 723.18 45.27 10.865 45.27 10.865 0.000 10.865 

10 1-10 5.82 723.18 36.80 8.832 36.80 8.832 0.000 8.832 

10 11-20 4.98 723.18 31.49 7.557 31.49 7.557 0.000 7.557 

11 21-31 4.60 723.18 29.08 7.678 29.08 7.678 0.000 7.678 

10 1-10 4.10 723.18 25.92 6.222 25.92 6.222 0.000 6.222 

10 11-20 3.90 723.18 24.66 5.918 24.66 5.918 0.000 5.918 

11 21-31 3.73 723.18 23.58 6.226 23.58 6.226 0.000 6.226 

10 1-10 6.87 723.18 43.44 10.425 43.44 10.425 0.000 10.425 

10 11-20 6.70 723.18 42.36 10.167 42.36 10.167 0.000 10.167 

8 21-28 4.01 723.18 25.35 4.868 25.35 4.868 0.000 4.868 

10 1-10 3.80 723.18 24.03 5.766 24.03 5.766 0.000 5.766 

10 11-20 5.42 723.18 34.27 8.225 34.27 8.225 0.000 8.225 

11 21-31 5.03 723.18 31.80 8.396 31.80 8.396 0.000 8.396 

10 1-10 7.29 723.18 46.09 11.062 46.09 11.062 0.000 11.062 

10 11-20 6.84 723.18 43.25 10.379 43.25 10.379 0.000 10.379 

10 21-30 7.27 723.18 45.97 11.032 45.97 11.032 0.000 11.032 

10 1-10 7.95 723.18 50.27 12.064 50.27 12.064 0.000 12.064 

10 11-20 9.82 723.18 62.09 14.901 62.09 14.901 0.000 14.901 

11 21-31 14.00 723.18 88.52 23.369 88.52 23.369 0.000 23.369 

Energy obtained on 95% machine availability 639.52 295.76 343.76 

LOAD FACTOR 51.78 95.00 37.21

Period 

Yearly 

inflow 

(M Cum) 

Annual Energy 

Generation 

(MU) 

Table 7.4 (C) 

80 

Annual 

Load 

Factor 

(%) 

Load Factor 

during high in 

flow period 

(%) 



Load Factor 

during lean 

inflow period 

(%) 

1976-1977 535.37 639.52 51.78% 95.00% 37.21% 

1977-1978 626.49 738.62 59.80% 95.00% 47.94% 

1978-1979 700.98 792.80 64.19% 95.00% 53.80% 

1979-1980 808.67 951.71 77.05% 95.00% 71.00% 

1980-1981 937.71 929.82 75.28% 95.00% 68.63% 

1981-1982 875.47 905.81 73.34% 95.00% 66.03% 

1982-1983 804.96 833.56 67.49% 95.00% 58.21% 

1983-1984 1140.39 1021.78 82.72% 95.00% 78.59% 

1984-1985 1510.49 1106.43 89.58% 95.00% 87.75% 

1985-1986 1058.83 827.99 67.03% 95.00% 57.61% 

1986-1987 729.68 793.94 64.28% 95.00% 53.93% 

1987-1988 794.72 805.34 65.20% 95.00% 55.16% 

1988-1989 750.71 716.62 58.02% 95.00% 45.56% 

1989-1990 696.22 676.82 54.80% 95.00% 41.25% 

1990-1991 667.78 707.14 57.25% 95.00% 44.53% 

1991-1992 561.78 659.92 53.43% 95.00% 39.42% 

1992-1993 385.61 578.76 46.86% 86.60% 33.46% 

1993-1994 863.13 895.88 72.53% 92.30% 65.87% 

1994-1995 708.50 825.90 66.87% 95.00% 57.38% 

1995-1996 712.63 786.17 63.65% 95.00% 53.08% 

1996-1997 657.03 827.53 67.00% 93.70% 58.00%

Period 

Table-7.5 

POWER GENERATION IN 90% DEPENDABLE YEAR 1976-77 

90% 

Dependable 

Flow 

(Cumecs) 

81 



Power In Mw Energy In Gwh Monthly 

Energy 

In Gwh 

Un Restricted 

Restricted To Installed 

Capacity Of 

141 Mw 

Un Restricted Restricted To 

Installed 

Capacity Of 

141 Mw 

1 2 3 4 5 6 7 

JUN 

1-10 

11-20 

21.03 

41.04 

132.966 

259.483 

132.97 

141.00 

31.912 

62.276 

31.912 

32.148 96.21 

21-30 29.78 188.290 141.00 45.190 32.148 

1-10 38.07 240.705 141.00 57.769 32.148 

JULY 11-20 36.28 229.387 141.00 55.053 32.148 99.66 

21-31 27.61 174.570 141.00 46.086 35.363 

1-10 32.19 203.527 141.00 48.847 32.148 

AUG 11-20 35.09 221.863 141.00 53.247 32.148 99.66 

21-31 37.51 237.164 141.00 62.611 35.363 

1-10 34.17 216.046 141.00 51.851 32.148 

SEPT 11-20 19.71 124.620 124.62 29.909 29.909 83.89 

21-30 14.39 90.984 90.98 21.836 21.836 

1-10 12.19 77.074 77.07 18.498 18.498 

OCT 11-20 9.63 60.888 60.89 14.613 14.613 49.34 

21-31 9.72 61.457 61.46 16.225 16.225 

1-10 9.67 61.140 61.14 14.674 14.674 

NOV 11-20 8.00 50.582 50.58 12.140 12.140 37.68 

21-30 7.16 45.270 45.27 10.865 10.865 

1-10 5.82 36.798 36.80 8.832 8.832 

DEC 11-20 4.98 31.487 31.49 7.557 7.557 24.07 

21-31 4.60 29.084 29.08 7.678 7.678 

1-10 4.10 25.923 25.92 6.222 6.222 

JAN 11-20 3.90 24.658 24.66 5.918 5.918 18.37 

21-31 3.73 23.584 23.58 6.226 6.226 

1-10 6.87 43.437 43.44 10.425 10.425 

FEB 11-20 6.70 42.362 42.36 10.167 10.167 25.46 

21-28 4.01 25.354 25.35 4.868 4.868 

1-10 3.80 24.026 24.03 5.766 5.766 

MAR 11-20 5.42 34.269 34.27 8.225 8.225 22.39 

21-31 5.03 31.803 31.80 8.396 8.396 

1-10 7.29 46.092 46.09 11.062 11.062 

APR 11-20 6.84 43.247 43.25 10.379 10.379 32.47 

21-30 7.27 45.966 45.97 11.032 11.032 

1-10 7.95 50.265 50.27 12.064 12.064 

MAY 11-20 9.82 62.089 62.09 14.901 14.901 50.33 

21-31 14.00 88.518 88.52 23.369 23.369 

ENERGY OBTAINED ON 95% M/C AVAILABILITY 639.52

Table-7.6 

82 



INCREMENTAL BENEFIT IN 90% DEPENDABLE YEAR 1976-77 

MW MU ? MU/? MW 

Load Factor 

(%) 

Annual Load Factor 

for additional capacity 

(%) 

120 588.37 55.97% 29.15% 

2.55 

123 596.03 55.32% 29.15% 

2.45 

126 603.37 54.67% 27.95% 

2.33 

129 610.35 54.01% 26.55% 

2.82 

132 618.82 53.52% 32.24% 

2.17 

135 625.34 52.88% 24.78% 

2.10 

138 631.63 52.25% 23.95% 

2.63 

141 639.52 51.78% 30.02% 

2.10 

144 645.81 51.20% 23.95% 

2.10 

147 652.10 50.64% 23.95% 

2.10 

150 658.40 50.11% 23.95% 

2.10 

153 664.69 49.59% 23.95% 

2.10 

156 670.98 49.10% 23.95% 

2.10 

159 677.27 48.63% 23.95% 

2.10 

162 683.567 48.17% 23.95%

Table-7.7 (A) 

83 



UNRESTRICTED ENERGY GENERATION IN YEAR 1976-77 

PERIOD INFLOW HEAD POWER UNRESTRICTED 

ENERGY 

CUMEC (M) (MW) (MU) 

JUNE I 21.03 723.18 132.966 31.912 

II 41.04 723.18 259.483 62.276 

III 29.78 723.18 188.290 45.190 

JULY I 38.07 723.18 240.705 57.769 

II 36.28 723.18 229.387 55.053 

III 27.61 723.18 174.570 46.086 

AUG I 32.19 723.18 203.527 48.847 

II 35.09 723.18 221.863 53.247 

III 37.51 723.18 237.164 62.611 

SEPT I 34.17 723.18 216.046 51.851 

II 19.71 723.18 124.620 29.909 

III 14.39 723.18 90.984 21.836 

OCT I 12.19 723.18 77.074 18.498 

II 9.63 723.18 60.888 14.613 

III 9.72 723.18 61.457 16.225 

NOV I 9.67 723.18 61.140 14.674 

II 8.00 723.18 50.582 12.140 

III 7.16 723.18 45.270 10.865 

DEC I 5.82 723.18 36.798 8.832 

II 4.98 723.18 31.487 7.557 

III 4.60 723.18 29.084 7.678 

JAN I 4.10 723.18 25.923 6.222 

II 3.90 723.18 24.658 5.918 

III 3.73 723.18 23.584 6.226 

FEB I 6.87 723.18 43.437 10.425 

II 6.70 723.18 42.362 10.167 

III 4.01 723.18 25.354 4.868 

MAR I 3.80 723.18 24.026 5.766 

II 5.42 723.18 34.269 8.225 

III 5.03 723.18 31.803 8.396 

APR I 7.29 723.18 46.092 11.062 

II 6.84 723.18 43.247 10.379 

III 7.27 723.18 45.966 11.032 

MAY I 7.95 723.18 50.265 12.064 

II 9.82 723.18 62.089 14.901 

III 14.00 723.18 88.518 23.369 

ENERGY OBTAINED 826.686

84 



Table-7.7 (B) 



ENERGY 


JUNE I 22.62 723.18 143.019 34.325 

II 40.12 723.18 253.666 60.880 

III 29.18 723.18 184.496 44.279 

JULY I 33.35 723.18 210.862 50.607 

II 39.24 723.18 248.102 59.545 

III 46.99 723.18 297.103 78.435 

AUG I 38.37 723.18 242.602 58.224 

II 32.29 723.18 204.160 48.998 

III 37.70 723.18 238.365 62.928 

SEPT I 26.33 723.18 166.476 39.954 

II 21.53 723.18 136.128 32.671 

III 17.95 723.18 113.492 27.238 

OCT I 21.91 723.18 138.530 33.247 

II 13.82 723.18 87.380 20.971 

III 11.04 723.18 69.803 18.428 

NOV I 11.44 723.18 72.332 17.360 

II 10.44 723.18 66.009 15.842 

III 7.88 723.18 49.823 11.957 

DEC I 7.12 723.18 45.018 10.804 

II 7.53 723.18 47.610 11.426 

III 8.52 723.18 53.869 14.222 

JAN I 5.86 723.18 37.051 8.892 

II 5.25 723.18 33.194 7.967 

III 5.36 723.18 33.890 8.947 

FEB I 5.42 723.18 34.269 8.225 

II 5.31 723.18 33.573 8.058 

III 4.88 723.18 30.855 5.924 

MAR I 4.94 723.18 31.234 7.496 

II 5.28 723.18 33.384 8.012 

III 5.86 723.18 37.051 9.781 

APR I 7.04 723.18 44.512 10.683 

II 9.01 723.18 56.967 13.672 

III 10.68 723.18 67.526 16.206 

MAY I 12.17 723.18 76.947 18.467 

II 24.94 723.18 157.688 37.845 

III 29.12 723.18 184.117 48.607 


85 



Table-7.7 (C) 



ENERGY 


JUNE I 33.41 723.18 211.241 50.698 

II 35.06 723.18 221.674 53.202 

III 44.32 723.18 280.222 67.253 

JULY I 38.91 723.18 246.016 59.044 

II 41.71 723.18 263.719 63.293 

III 40.26 723.18 254.552 67.202 

AUG I 47.65 723.18 301.276 72.306 

II 40.26 723.18 254.552 61.092 

III 30.23 723.18 191.135 50.460 

SEPT I 25.07 723.18 158.510 38.042 

II 32.65 723.18 206.436 49.545 

III 24.54 723.18 155.159 37.238 

OCT I 23.61 723.18 149.279 35.827 

II 18.41 723.18 116.401 27.936 

III 15.69 723.18 99.203 26.190 

NOV I 12.57 723.18 79.476 19.074 

II 9.38 723.18 59.307 14.234 

III 9.23 723.18 58.358 14.006 

DEC I 8.90 723.18 56.272 13.505 

II 7.54 723.18 47.673 11.442 

III 6.77 723.18 42.805 11.300 

JAN I 6.25 723.18 39.517 9.484 

II 5.77 723.18 36.482 8.756 

III 5.67 723.18 35.850 9.464 

FEB I 5.16 723.18 32.625 7.830 

II 5.15 723.18 32.562 7.815 

III 5.60 723.18 35.407 6.798 

MAR I 5.75 723.18 36.355 8.725 

II 6.02 723.18 38.063 9.135 

III 7.41 723.18 46.851 12.369 

APR I 10.94 723.18 69.170 16.601 

II 10.88 723.18 68.791 16.510 

III 13.65 723.18 86.305 20.713 

MAY I 20.48 723.18 129.489 31.077 

II 26.11 723.18 165.085 39.621 

III 19.97 723.18 126.264 33.334 


86 



Table-7.7 (D) 



ENERGY 


JUNE I 23.80 723.18 150.480 36.115 

II 28.48 723.18 180.070 43.217 

III 40.83 723.18 258.155 61.957 

JULY I 42.41 723.18 268.145 64.355 

II 40.56 723.18 256.448 61.548 

III 45.44 723.18 287.303 75.848 

AUG I 41.99 723.18 265.490 63.718 

II 33.16 723.18 209.660 50.319 

III 35.17 723.18 222.369 58.705 

SEPT I 34.59 723.18 218.702 52.488 

II 30.18 723.18 190.819 45.797 

III 22.14 723.18 139.984 33.596 

OCT I 36.90 723.18 233.307 55.994 

II 25.18 723.18 159.205 38.209 

III 18.89 723.18 119.436 31.531 

NOV I 18.83 723.18 119.056 28.574 

II 15.33 723.18 96.927 23.262 

III 14.43 723.18 91.236 21.897 

DEC I 13.75 723.18 86.937 20.865 

II 11.32 723.18 71.573 17.177 

III 10.90 723.18 68.917 18.194 

JAN I 10.27 723.18 64.934 15.584 

II 9.89 723.18 62.531 15.008 

III 9.80 723.18 61.962 16.358 

FEB I 9.41 723.18 59.497 14.279 

II 9.86 723.18 62.342 14.962 

III 10.51 723.18 66.451 14.354 

MAR I 10.81 723.18 68.348 16.404 

II 11.09 723.18 70.119 16.828 

III 14.97 723.18 94.651 24.988 

APR I 16.81 723.18 106.284 25.508 

II 21.57 723.18 136.380 32.731 

III 24.57 723.18 155.349 37.284 

MAY I 23.43 723.18 148.141 35.554 

II 20.04 723.18 126.707 30.410 

III 21.36 723.18 135.053 35.654 


87 



Table-7.7 (E) 



ENERGY 


JUNE I 32.76 723.18 207.131 49.712 

II 43.60 723.18 275.669 66.161 

III 48.80 723.18 308.547 74.051 

JULY I 51.64 723.18 326.504 78.361 

II 52.87 723.18 334.281 80.227 

III 55.39 723.18 350.214 92.456 

AUG I 55.97 723.18 353.881 84.931 

II 61.46 723.18 388.593 93.262 

III 51.19 723.18 323.659 85.446 

SEPT I 48.90 723.18 309.180 74.203 

II 38.33 723.18 242.349 58.164 

III 31.03 723.18 196.193 47.086 

OCT I 24.27 723.18 153.452 36.828 

II 20.86 723.18 131.891 31.654 

III 19.43 723.18 122.850 32.432 

NOV I 16.42 723.18 103.819 24.916 

II 14.95 723.18 94.524 22.686 

III 13.76 723.18 87.000 20.880 

DEC I 12.78 723.18 80.804 19.393 

II 11.62 723.18 73.470 17.633 

III 10.55 723.18 66.704 17.610 

JAN I 10.17 723.18 64.302 15.432 

II 9.53 723.18 60.255 14.461 

III 9.41 723.18 59.497 15.707 

FEB I 8.75 723.18 55.324 13.278 

II 9.00 723.18 56.904 13.657 

III 10.88 723.18 68.791 13.208 

MAR I 10.76 723.18 68.032 16.328 

II 11.39 723.18 72.015 17.284 

III 13.45 723.18 85.040 22.451 

APR I 13.47 723.18 85.167 20.440 

II 17.05 723.18 107.802 25.872 

III 20.09 723.18 127.023 30.485 

MAY I 24.68 723.18 156.044 37.451 

II 26.65 723.18 168.500 40.440 

III 25.85 723.18 163.442 43.149 


88 



Table-7.7 (F) 



ENERGY 


JUNE I 28.45 723.18 179.881 43.171 

II 34.03 723.18 215.161 51.639 

III 46.20 723.18 292.108 70.106 

JULY I 59.02 723.18 373.165 89.560 

II 50.61 723.18 319.991 76.798 

III 47.60 723.18 300.960 79.453 

AUG I 46.42 723.18 293.499 70.440 

II 48.98 723.18 309.685 74.325 

III 47.62 723.18 301.087 79.487 

SEPT I 45.58 723.18 288.188 69.165 

II 39.06 723.18 246.964 59.271 

III 31.13 723.18 196.825 47.238 

OCT I 28.55 723.18 180.513 43.323 

II 26.42 723.18 167.046 40.091 

III 23.09 723.18 145.991 38.542 

NOV I 19.68 723.18 124.431 29.863 

II 15.70 723.18 99.266 23.824 

III 13.01 723.18 82.258 19.742 

DEC I 11.94 723.18 75.493 18.118 

II 10.74 723.18 67.906 16.297 

III 8.42 723.18 53.237 14.055 

JAN I 7.73 723.18 48.874 11.730 

II 8.60 723.18 54.375 13.050 

III 8.48 723.18 53.616 14.155 

FEB I 8.41 723.18 53.174 12.762 

II 8.74 723.18 55.260 13.262 

III 8.49 723.18 53.680 10.306 

MAR I 8.85 723.18 55.956 13.429 

II 9.91 723.18 62.658 15.038 

III 11.80 723.18 74.608 19.696 

APR I 14.83 723.18 93.766 22.504 

II 14.80 723.18 93.576 22.458 

III 16.42 723.18 103.819 24.916 

MAY I 20.58 723.18 130.121 31.229 

II 23.12 723.18 146.181 35.083 

III 22.46 723.18 142.008 37.490 


89 



Table-7.7 (G) 



ENERGY 


JUNE I 39.65 723.18 250.695 60.167 

II 43.67 723.18 276.112 66.267 

III 48.27 723.18 305.196 73.247 

JULY I 42.39 723.18 268.019 64.325 

II 47.49 723.18 300.265 72.064 

III 56.02 723.18 354.197 93.508 

AUG I 37.64 723.18 237.986 57.117 

II 35.63 723.18 225.277 54.067 

III 41.82 723.18 264.415 69.806 

SEPT I 32.17 723.18 203.401 48.816 

II 46.52 723.18 294.132 70.592 

III 30.53 723.18 193.032 46.328 

OCT I 21.61 723.18 136.633 32.792 

II 18.15 723.18 114.757 27.542 

III 17.48 723.18 110.521 29.177 

NOV I 13.69 723.18 86.558 20.774 

II 11.94 723.18 75.493 18.118 

III 11.56 723.18 73.090 17.542 

DEC I 10.22 723.18 64.618 15.508 

II 9.42 723.18 59.560 14.294 

III 8.92 723.18 56.398 14.889 

JAN I 8.84 723.18 55.893 13.414 

II 7.87 723.18 49.760 11.942 

III 5.52 723.18 34.901 9.214 

FEB I 5.02 723.18 31.740 7.618 

II 4.99 723.18 31.550 7.572 

III 6.94 723.18 43.879 8.425 

MAR I 7.46 723.18 47.167 11.320 

II 9.56 723.18 60.445 14.507 

III 8.63 723.18 54.565 14.405 

APR I 12.69 723.18 80.235 19.256 

II 10.38 723.18 65.630 15.751 

III 12.99 723.18 82.132 19.712 

MAY I 20.90 723.18 132.144 31.715 

II 25.05 723.18 158.383 38.012 

III 33.33 723.18 210.735 55.634 


90 



Table-7.7 (H) 



ENERGY 


JUNE I 41.91 723.18 264.984 63.596 

II 40.68 723.18 257.207 61.730 

III 56.77 723.18 358.939 86.145 

JULY I 65.01 723.18 411.038 98.649 

II 55.31 723.18 349.708 83.930 

III 54.87 723.18 346.926 91.588 

AUG I 44.91 723.18 283.952 68.148 

II 47.62 723.18 301.087 72.261 

III 55.64 723.18 351.795 92.874 

SEPT I 44.72 723.18 282.751 67.860 

II 50.28 723.18 317.905 76.297 

III 58.00 723.18 366.716 88.012 

OCT I 40.78 723.18 257.839 61.881 

II 40.20 723.18 254.172 61.001 

III 27.40 723.18 173.242 45.736 

NOV I 22.40 723.18 141.628 33.991 

II 20.58 723.18 130.121 31.229 

III 16.95 723.18 107.170 25.721 

DEC I 14.14 723.18 89.403 21.457 

II 13.26 723.18 83.839 20.121 

III 11.88 723.18 75.114 19.830 

JAN I 10.61 723.18 67.084 16.100 

II 10.44 723.18 66.009 15.842 

III 9.29 723.18 58.738 15.507 

FEB I 8.95 723.18 56.588 13.581 

II 9.29 723.18 58.738 14.097 

III 8.93 723.18 56.462 12.196 

MAR I 19.71 723.18 124.620 29.909 

II 22.03 723.18 139.289 33.429 

III 21.64 723.18 136.823 36.121 

APR I 22.75 723.18 143.841 34.522 

II 24.25 723.18 153.325 36.798 

III 24.26 723.18 153.388 36.813 

MAY I 27.53 723.18 174.064 41.775 

II 40.24 723.18 254.425 61.062 

III 57.16 723.18 361.405 95.411 


91 



Table-7.7 (I) 



ENERGY 


JUNE I 59.40 723.18 375.568 90.136 

II 71.43 723.18 451.630 108.391 

III 64.15 723.18 405.601 97.344 

JULY I 73.83 723.18 466.804 112.033 

II 74.07 723.18 468.322 112.397 

III 78.31 723.18 495.130 130.714 

AUG I 70.62 723.18 446.508 107.162 

II 70.81 723.18 447.710 107.450 

III 74.13 723.18 468.701 123.737 

SEPT I 76.35 723.18 482.737 115.857 

II 72.86 723.18 460.671 110.561 

III 57.80 723.18 365.452 87.708 

OCT I 48.68 723.18 307.789 73.869 

II 61.75 723.18 390.426 93.702 

III 47.57 723.18 300.770 79.403 

NOV I 35.45 723.18 224.139 53.793 

II 30.64 723.18 193.727 46.495 

III 27.23 723.18 172.167 41.320 

DEC I 17.46 723.18 110.394 26.495 

II 17.18 723.18 108.624 26.070 

III 17.24 723.18 109.003 28.777 

JAN I 17.39 723.18 109.952 26.388 

II 16.52 723.18 104.451 25.068 

III 14.30 723.18 90.414 23.869 

FEB I 15.63 723.18 98.824 23.718 

II 14.29 723.18 90.351 21.684 

III 17.29 723.18 109.319 20.989 

MAR I 21.97 723.18 138.910 33.338 

II 23.79 723.18 150.417 36.100 

III 22.16 723.18 140.111 36.989 

APR I 26.67 723.18 168.626 40.470 

II 32.19 723.18 203.527 48.847 

III 38.01 723.18 240.326 57.678 

MAY I 27.35 723.18 172.926 41.502 

II 31.75 723.18 200.745 48.179 

III 44.22 723.18 279.589 73.812 


92 



Table-7.7 (J) 



ENERGY 


JUNE I 28.15 723.18 177.984 42.716 

II 35.59 723.18 225.025 54.006 

III 100.36 723.18 634.545 152.291 

JULY I 79.13 723.18 500.315 120.075 

II 103.26 723.18 652.881 156.691 

III 86.82 723.18 548.936 144.919 

AUG I 70.16 723.18 443.600 106.464 

II 74.01 723.18 467.942 112.306 

III 90.61 723.18 572.899 151.245 

SEPT I 37.35 723.18 236.153 56.677 

II 35.11 723.18 221.990 53.278 

III 29.93 723.18 189.238 45.417 

OCT I 25.44 723.18 160.849 38.604 

II 22.03 723.18 139.289 33.429 

III 18.14 723.18 114.694 30.279 

NOV I 14.77 723.18 93.386 22.413 

II 12.77 723.18 80.741 19.378 

III 11.31 723.18 71.510 17.162 

DEC I 9.68 723.18 61.204 14.689 

II 8.77 723.18 55.450 13.308 

III 8.02 723.18 50.708 13.387 

JAN I 7.71 723.18 48.748 11.700 

II 7.67 723.18 48.495 11.639 

III 7.26 723.18 45.903 12.118 

FEB I 7.34 723.18 46.409 11.138 

II 7.55 723.18 47.736 11.457 

III 8.64 723.18 54.628 10.489 

MAR I 9.21 723.18 58.232 13.976 

II 10.03 723.18 63.417 15.220 

III 10.30 723.18 65.124 17.193 

APR I 10.12 723.18 63.986 15.357 

II 13.09 723.18 82.764 19.863 

III 14.68 723.18 92.817 22.276 

MAY I 13.76 723.18 87.000 20.880 

II 14.64 723.18 92.564 22.215 

III 15.42 723.18 97.496 25.739 


93 



Table-7.7 (K) 



ENERGY 


JUNE I 18.75 723.18 118.550 28.452 

II 31.80 723.18 201.062 48.255 

III 47.12 723.18 297.925 71.502 

JULY I 40.81 723.18 258.029 61.927 

II 50.99 723.18 322.394 77.375 

III 45.86 723.18 289.959 76.549 

AUG I 40.70 723.18 257.334 61.760 

II 34.99 723.18 221.231 53.095 

III 38.73 723.18 244.878 64.648 

SEPT I 34.01 723.18 215.035 51.608 

II 42.24 723.18 267.070 64.097 

III 34.38 723.18 217.374 52.170 

OCT I 27.73 723.18 175.328 42.079 

II 20.73 723.18 131.069 31.457 

III 16.19 723.18 102.364 27.024 

NOV I 14.89 723.18 94.145 22.595 

II 13.24 723.18 83.712 20.091 

III 11.44 723.18 72.332 17.360 

DEC I 10.24 723.18 64.744 15.539 

II 9.43 723.18 59.623 14.310 

III 6.95 723.18 43.943 11.601 

JAN I 6.07 723.18 38.379 9.211 

II 5.71 723.18 36.103 8.665 

III 5.36 723.18 33.890 8.947 

FEB I 5.08 723.18 32.119 7.709 

II 5.03 723.18 31.803 7.633 

III 5.52 723.18 34.901 6.701 

MAR I 5.16 723.18 32.625 7.830 

II 6.12 723.18 38.695 9.287 

III 7.68 723.18 48.558 12.819 

APR I 14.01 723.18 88.581 21.259 

II 9.79 723.18 61.899 14.856 

III 12.94 723.18 81.816 19.636 

MAY I 14.63 723.18 92.501 22.200 

II 16.27 723.18 102.870 24.689 

III 19.09 723.18 120.700 31.865 


94 



Table-7.7 (L) 



ENERGY 


JUNE I 31.67 723.18 200.240 48.058 

II 46.00 723.18 290.844 69.803 

III 38.61 723.18 244.119 58.589 

JULY I 44.29 723.18 280.032 67.208 

II 42.34 723.18 267.703 64.249 

III 47.35 723.18 299.379 79.036 

AUG I 44.83 723.18 283.446 68.027 

II 48.91 723.18 309.243 74.218 

III 32.69 723.18 206.689 54.566 

SEPT I 58.81 723.18 371.837 89.241 

II 31.46 723.18 198.912 47.739 

III 43.15 723.18 272.824 65.478 

OCT I 26.80 723.18 169.448 40.668 

II 19.96 723.18 126.201 30.288 

III 17.07 723.18 107.928 28.493 

NOV I 13.85 723.18 87.569 21.017 

II 8.45 723.18 53.427 12.822 

III 7.42 723.18 46.914 11.259 

DEC I 7.00 723.18 44.259 10.622 

II 6.41 723.18 40.528 9.727 

III 5.86 723.18 37.051 9.781 

JAN I 5.71 723.18 36.103 8.665 

II 5.71 723.18 36.103 8.665 

III 5.65 723.18 35.723 9.431 

FEB I 5.54 723.18 35.028 8.407 

II 5.80 723.18 36.672 8.801 

III 6.44 723.18 40.718 8.795 

MAR I 6.68 723.18 42.236 10.137 

II 9.90 723.18 62.595 15.023 

III 10.18 723.18 64.365 16.992 

APR I 11.64 723.18 73.596 17.663 

II 13.15 723.18 83.143 19.954 

III 15.29 723.18 96.674 23.202 

MAY I 15.64 723.18 98.887 23.733 

II 23.42 723.18 148.077 35.539 

III 31.04 723.18 196.256 51.812 


95 



Table-7.7 (M) 



ENERGY 


JUNE I 25.04 723.18 158.320 37.997 

II 36.23 723.18 229.071 54.977 

III 39.68 723.18 250.884 60.212 

JULY I 61.67 723.18 389.920 93.581 

II 48.44 723.18 306.271 73.505 

III 53.39 723.18 337.568 89.118 

AUG I 52.99 723.18 335.039 80.409 

II 48.63 723.18 307.472 73.793 

III 73.79 723.18 466.551 123.170 

SEPT I 35.23 723.18 222.748 53.460 

II 23.76 723.18 150.227 36.055 

III 26.57 723.18 167.994 40.319 

OCT I 22.43 723.18 141.818 34.036 

II 14.89 723.18 94.145 22.595 

III 11.98 723.18 75.746 19.997 

NOV I 9.87 723.18 62.405 14.977 

II 8.91 723.18 56.335 13.520 

III 8.31 723.18 52.542 12.610 

DEC I 7.88 723.18 49.823 11.957 

II 7.48 723.18 47.294 11.350 

III 7.08 723.18 44.765 11.818 

JAN I 4.33 723.18 27.377 6.571 

II 4.22 723.18 26.682 6.404 

III 4.18 723.18 26.429 6.977 

FEB I 4.65 723.18 29.401 7.056 

II 4.25 723.18 26.871 6.449 

III 4.52 723.18 28.579 5.487 

MAR I 5.14 723.18 32.499 7.800 

II 5.24 723.18 33.131 7.951 

III 5.38 723.18 34.016 8.980 

APR I 5.60 723.18 35.407 8.498 

II 6.70 723.18 42.362 10.167 

III 8.04 723.18 50.834 12.200 

MAY I 14.11 723.18 89.213 21.411 

II 14.58 723.18 92.185 22.124 

III 35.52 723.18 224.582 59.290 


96 



Table-7.7 (N) 



ENERGY 


JUNE I 31.54 723.18 199.418 47.860 

II 52.24 723.18 330.297 79.271 

III 55.25 723.18 349.329 83.839 

JULY I 56.26 723.18 355.715 85.372 

II 55.34 723.18 349.898 83.975 

III 51.51 723.18 325.682 85.980 

AUG I 44.70 723.18 282.624 67.830 

II 35.07 723.18 221.737 53.217 

III 34.40 723.18 217.501 57.420 

SEPT I 33.35 723.18 210.862 50.607 

II 30.21 723.18 191.009 45.842 

III 30.01 723.18 189.744 45.539 

OCT I 23.70 723.18 149.848 35.963 

II 20.17 723.18 127.529 30.607 

III 16.41 723.18 103.755 27.391 

NOV I 10.21 723.18 64.555 15.493 

II 8.28 723.18 52.352 12.564 

III 7.53 723.18 47.610 11.426 

DEC I 6.57 723.18 41.540 9.970 

II 5.70 723.18 36.039 8.649 

III 4.99 723.18 31.550 8.329 

JAN I 4.55 723.18 28.768 6.904 

II 4.22 723.18 26.682 6.404 

III 3.82 723.18 24.153 6.376 

FEB I 3.76 723.18 23.773 5.706 

II 3.53 723.18 22.319 5.357 

III 3.41 723.18 21.560 4.140 

MAR I 3.11 723.18 19.664 4.719 

II 2.54 723.18 16.060 3.854 

III 2.59 723.18 16.376 4.323 

APR I 2.68 723.18 16.945 4.067 

II 4.42 723.18 27.946 6.707 

III 5.47 723.18 34.585 8.300 

MAY I 8.08 723.18 51.087 12.261 

II 14.23 723.18 89.972 21.593 

III 16.37 723.18 103.502 27.325 


Table-7.7 (O) 

97 





ENERGY 


JUNE I 34.57 723.18 218.575 52.458 

II 33.77 723.18 213.517 51.244 

III 39.48 723.18 249.620 59.909 

JULY I 43.52 723.18 275.164 66.039 

II 55.48 723.18 350.783 84.188 

III 47.48 723.18 300.201 79.253 

AUG I 40.44 723.18 255.690 61.366 

II 41.09 723.18 259.799 62.352 

III 36.46 723.18 230.525 60.859 

SEPT I 34.99 723.18 221.231 53.095 

II 33.51 723.18 211.873 50.850 

III 23.34 723.18 147.572 35.417 

OCT I 19.55 723.18 123.609 29.666 

II 19.92 723.18 125.948 30.228 

III 16.38 723.18 103.566 27.341 

NOV I 10.03 723.18 63.417 15.220 

II 7.50 723.18 47.420 11.381 

III 6.26 723.18 39.580 9.499 

DEC I 5.73 723.18 36.229 8.695 

II 4.73 723.18 29.906 7.178 

III 4.08 723.18 25.797 6.810 

JAN I 4.13 723.18 26.113 6.267 

II 4.05 723.18 25.607 6.146 

III 4.01 723.18 25.354 6.693 

FEB I 3.88 723.18 24.532 5.888 

II 3.69 723.18 23.331 5.599 

III 3.73 723.18 23.584 4.528 

MAR I 3.98 723.18 25.164 6.039 

II 4.54 723.18 28.705 6.889 

III 4.79 723.18 30.286 7.995 

APR I 12.56 723.18 79.413 19.059 

II 7.16 723.18 45.270 10.865 

III 7.58 723.18 47.926 11.502 

MAY I 12.72 723.18 80.425 19.302 

II 15.50 723.18 98.002 23.520 

III 17.15 723.18 108.434 28.627 


98 



Table-7.7 (P) 



ENERGY 


JUNE I 18.35 723.18 116.021 27.845 

II 28.98 723.18 183.232 43.976 

III 26.65 723.18 168.500 40.440 

JULY I 30.43 723.18 192.400 46.176 

II 29.65 723.18 187.468 44.992 

III 32.32 723.18 204.349 53.948 

AUG I 37.06 723.18 234.319 56.237 

II 42.69 723.18 269.916 64.780 

III 35.28 723.18 223.065 58.889 

SEPT I 35.54 723.18 224.708 53.930 

II 37.55 723.18 237.417 56.980 

III 29.08 723.18 183.864 44.127 

OCT I 23.22 723.18 146.813 35.235 

II 18.41 723.18 116.401 27.936 

III 15.11 723.18 95.536 25.221 

NOV I 12.52 723.18 79.160 18.998 

II 11.07 723.18 69.992 16.798 

III 8.45 723.18 53.427 12.822 

DEC I 7.10 723.18 44.891 10.774 

II 5.45 723.18 34.459 8.270 

III 4.79 723.18 30.286 7.995 

JAN I 4.36 723.18 27.567 6.616 

II 3.62 723.18 22.888 5.493 

III 3.70 723.18 23.394 6.176 

FEB I 3.91 723.18 24.722 5.933 

II 3.77 723.18 23.837 5.721 

III 3.61 723.18 22.825 4.930 

MAR I 3.87 723.18 24.469 5.873 

II 3.90 723.18 24.658 5.918 

III 4.01 723.18 25.354 6.693 

APR I 4.73 723.18 29.906 7.178 

II 6.65 723.18 42.046 10.091 

III 6.08 723.18 38.442 9.226 

MAY I 5.96 723.18 37.683 9.044 

II 6.94 723.18 43.879 10.531 

III 6.97 723.18 44.069 11.634 


99 



Table-7.7 (Q) 



ENERGY 


JUNE I 7.70 723.18 48.685 11.684 

II 10.98 723.18 69.423 16.662 

III 21.28 723.18 134.547 32.291 

JULY I 18.28 723.18 115.579 27.739 

II 18.50 723.18 116.970 28.073 

III 21.01 723.18 132.840 35.070 

AUG I 23.00 723.18 145.422 34.901 

II 23.09 723.18 145.991 35.038 

III 25.11 723.18 158.763 41.913 

SEPT I 22.02 723.18 139.226 33.414 

II 21.67 723.18 137.013 32.883 

III 17.94 723.18 113.429 27.223 

OCT I 13.55 723.18 85.672 20.561 

II 9.72 723.18 61.457 14.750 

III 8.27 723.18 52.289 13.804 

NOV I 6.11 723.18 38.632 9.272 

II 5.43 723.18 34.332 8.240 

III 4.95 723.18 31.297 7.511 

DEC I 4.89 723.18 30.918 7.420 

II 4.23 723.18 26.745 6.419 

III 3.91 723.18 24.722 6.527 

JAN I 3.97 723.18 25.101 6.024 

II 4.01 723.18 25.354 6.085 

III 3.77 723.18 23.837 6.293 

FEB I 3.65 723.18 23.078 5.539 

II 3.87 723.18 24.469 5.873 

III 3.74 723.18 23.647 4.540 

MAR I 6.11 723.18 38.632 9.272 

II 6.10 723.18 38.568 9.256 

III 6.39 723.18 40.402 10.666 

APR I 6.49 723.18 41.034 9.848 

II 7.09 723.18 44.828 10.759 

III 8.49 723.18 53.680 12.883 

MAY I 10.77 723.18 68.095 16.343 

II 9.70 723.18 61.330 14.719 

III 9.82 723.18 62.089 16.391 


100 



Table-7.7 (R) 



ENERGY 


JUNE I 12.61 723.18 79.729 19.135 

II 16.11 723.18 101.859 24.446 

III 20.73 723.18 131.069 31.457 

JULY I 43.40 723.18 274.405 65.857 

II 43.40 723.18 274.405 65.857 

III 50.90 723.18 321.825 84.962 

AUG I 57.09 723.18 360.962 86.631 

II 54.12 723.18 342.184 82.124 

III 51.83 723.18 327.705 86.514 

SEPT I 54.53 723.18 344.776 82.746 

II 45.93 723.18 290.401 69.696 

III 43.43 723.18 274.594 65.903 

OCT I 38.59 723.18 243.993 58.558 

II 28.63 723.18 181.019 43.444 

III 24.54 723.18 155.159 40.962 

NOV I 20.36 723.18 128.730 30.895 

II 17.95 723.18 113.492 27.238 

III 16.45 723.18 104.008 24.962 

DEC I 16.06 723.18 101.542 24.370 

II 14.75 723.18 93.260 22.382 

III 12.12 723.18 76.631 20.231 

JAN I 11.42 723.18 72.205 17.329 

II 10.63 723.18 67.210 16.130 

III 10.74 723.18 67.906 17.927 

FEB I 10.59 723.18 66.957 16.070 

II 10.13 723.18 64.049 15.372 

III 10.86 723.18 68.664 13.184 

MAR I 10.01 723.18 63.290 15.190 

II 9.03 723.18 57.094 13.703 

III 11.42 723.18 72.205 19.062 

APR I 11.09 723.18 70.119 16.828 

II 13.88 723.18 87.759 21.062 

III 12.73 723.18 80.488 19.317 

MAY I 14.27 723.18 90.225 21.654 

II 14.71 723.18 93.007 22.322 

III 18.09 723.18 114.377 30.196 


101 



Table-7.7 (S) 



ENERGY 


JUNE I 26.12 723.18 165.149 39.636 

II 34.58 723.18 218.639 52.473 

III 40.14 723.18 253.793 60.910 

JULY I 34.33 723.18 217.058 52.094 

II 36.40 723.18 230.146 55.235 

III 37.09 723.18 234.509 61.910 

AUG I 34.09 723.18 215.541 51.730 

II 33.30 723.18 210.546 50.531 

III 35.81 723.18 226.416 59.774 

SEPT I 30.37 723.18 192.020 46.085 

II 30.42 723.18 192.336 46.161 

III 26.28 723.18 166.160 39.878 

OCT I 20.56 723.18 129.995 31.199 

II 18.28 723.18 115.579 27.739 

III 16.73 723.18 105.779 27.926 

NOV I 13.77 723.18 87.063 20.895 

II 11.35 723.18 71.763 17.223 

III 9.49 723.18 60.002 14.401 

DEC I 9.15 723.18 57.853 13.885 

II 8.37 723.18 52.921 12.701 

III 7.92 723.18 50.076 13.220 

JAN I 7.50 723.18 47.420 11.381 

II 7.59 723.18 47.989 11.517 

III 7.49 723.18 47.357 12.502 

FEB I 7.43 723.18 46.978 11.275 

II 7.41 723.18 46.851 11.244 

III 7.45 723.18 47.104 9.044 

MAR I 6.77 723.18 42.805 10.273 

II 6.42 723.18 40.592 9.742 

III 8.84 723.18 55.893 14.756 

APR I 8.65 723.18 54.691 13.126 

II 10.71 723.18 67.716 16.252 

III 15.64 723.18 98.887 23.733 

MAY I 22.81 723.18 144.221 34.613 

II 35.21 723.18 222.622 53.429 

III 34.03 723.18 215.161 56.803 


102 



Table-7.7 (T) 



ENERGY 


JUNE I 39.51 723.18 249.810 59.954 

II 42.26 723.18 267.197 64.127 

III 42.80 723.18 270.611 64.947 

JULY I 54.32 723.18 343.449 82.428 

II 45.57 723.18 288.125 69.150 

III 35.03 723.18 221.484 58.472 

AUG I 38.27 723.18 241.969 58.073 

II 38.61 723.18 244.119 58.589 

III 34.30 723.18 216.868 57.253 

SEPT I 30.95 723.18 195.687 46.965 

II 27.71 723.18 175.202 42.048 

III 26.66 723.18 168.563 40.455 

OCT I 19.69 723.18 124.494 29.879 

II 19.17 723.18 121.206 29.089 

III 14.98 723.18 94.714 25.004 

NOV I 9.74 723.18 61.583 14.780 

II 11.12 723.18 70.308 16.874 

III 11.19 723.18 70.751 16.980 

DEC I 8.37 723.18 52.921 12.701 

II 7.45 723.18 47.104 11.305 

III 6.92 723.18 43.753 11.551 

JAN I 5.96 723.18 37.683 9.044 

II 5.93 723.18 37.494 8.998 

III 6.27 723.18 39.643 10.466 

FEB I 6.49 723.18 41.034 9.848 

II 5.78 723.18 36.545 8.771 

III 6.33 723.18 40.023 8.645 

MAR I 6.42 723.18 40.592 9.742 

II 7.44 723.18 47.041 11.290 

III 7.93 723.18 50.139 13.237 

APR I 7.29 723.18 46.092 11.062 

II 7.08 723.18 44.765 10.744 

III 15.75 723.18 99.582 23.900 

MAY I 19.20 723.18 121.396 29.135 

II 16.84 723.18 106.474 25.554 

III 23.30 723.18 147.319 38.892 


103 



Table-7.7 (U) 



ENERGY 


JUNE I 21.85 723.18 138.151 33.156 

II 18.51 723.18 117.033 28.088 

III 33.05 723.18 208.965 50.152 

JULY I 36.73 723.18 232.232 55.736 

II 39.54 723.18 249.999 60.000 

III 35.20 723.18 222.559 58.756 

AUG I 33.65 723.18 212.759 51.062 

II 31.38 723.18 198.406 47.617 

III 31.63 723.18 199.987 52.796 

SEPT I 31.57 723.18 199.607 47.906 

II 30.13 723.18 190.503 45.721 

III 26.20 723.18 165.655 39.757 

OCT I 23.04 723.18 145.675 34.962 

II 21.11 723.18 133.472 32.033 

III 18.87 723.18 119.309 31.498 

NOV I 17.17 723.18 108.561 26.055 

II 15.96 723.18 100.910 24.218 

III 14.20 723.18 89.782 21.548 

DEC I 9.68 723.18 61.204 14.689 

II 8.77 723.18 55.450 13.308 

III 8.02 723.18 50.708 13.387 

JAN I 9.20 723.18 58.169 13.961 

II 8.75 723.18 55.324 13.278 

III 8.90 723.18 56.272 14.856 

FEB I 8.88 723.18 56.146 13.475 

II 8.85 723.18 55.956 13.429 

III 8.75 723.18 55.324 10.622 

MAR I 8.95 723.18 56.588 13.581 

II 9.40 723.18 59.433 14.264 

III 10.25 723.18 64.808 17.109 

APR I 9.83 723.18 62.152 14.916 

II 9.78 723.18 61.836 14.841 

III 10.06 723.18 63.606 15.266 

MAY I 11.73 723.18 74.165 17.800 

II 13.50 723.18 85.356 20.486 

III 13.94 723.18 88.138 23.269 




CHAPTER – VIII 

POWER EVACUATION

8.1 GENERAL 

CHAPTER-VIII 

POWER EVACUATION 

103 



This chapter contains data regarding existing Power network of the Eastern region and 

the power evacuation arrangement required, consequent upon power generation at the 

proposed Rangyong Hydro Electric Project. 

8.2 APPRAISAL OF EXISTING POWER EVACUATION FACILITIES 

The nearest pooling point being proposed is a new 400/220 KV substation at Siliguri 

(New Jalpaiguri) where power from Tala H.E.P and Teesta stages is expected to be 

pooled. Adjoining to this is also a new substation of 220/132 KV level being created by 

WBSEB. Hence power evacuation with respect to development of national grid and 

consumption by the state can be considered as assured for the present project. Underlying 

220/132 KV 200 MVA PGCIL and 132 KV network in the entire area is available to 

cater for local loads. 

8.3 PROPOSED EVACUATION ARRANGEMENT TO THE NEAREST 

FACILITY 

After study of existing power evacuation facilities, it emerges that evacuation of power 

generated at Rangyong Hydro Electric Project can be done through one no. 220 kV 

double circuit line to be connected at the pooling point which can be assumed to come up 

near Teesta II H.E.P (2 km from Teesta –II H E Project). The length of this 220 kV 

double circuit line would be approximately 30 km.



CHAPTER – IX 

ENVIRONMENTAL ASPECTS

CHAPTER - IX 

ENVIRONMENTAL ASPECTS 

104 




9.1.1 General 

The proposed Rangyong H. E. Scheme is one of the various projects proposed in Teesta 

river basin in Sikkim (Fig 9.1). The project envisages construction of two dams, i.e. upper 

dam to be located immediately downstream to the confluence of Umram chu and Passaram 

chu in North district of Sikkim and lower dam on Rangyong chu, upstream to the confluence 

of Umram chu with Rangyong chu (Fig. 9.2). The upper dam is located between longitude 

88 o 22’26’’ & 88 o 26’00’’E and latitude 27 o 36’00’’ & 27 o 33’14’’N while the lower dam is 

located between longitude 88 o 21’48’’ & 88 o 26’00’’E and latitude 27 o 35’00’’ & 

27 o 33’14’’N. The project involves construction of 55m high upper dam and diversion of 

water to the lower dam reservoir through a 2 km long link tunnel. The water from the 55m 

high lower dam is proposed to be diverted through a 7.5 km long headrace tunnel (Fig. 9.2). 

An underground powerhouse is proposed immediately upstream to the reservoir of Panan 

H.E. Scheme. The proposed project envisages power generation of 141 (3 x 47) MW. 

9.1.2 Location 

Town : Singnok 

Revenue Block : Sakyong Pentong 

Sub-division : Mangan 

District : North Sikkim 

State : Sikkim 

New Jalpaiguri is the nearest railhead and Bagdogra is the nearest airport.

9.2 PHYSICAL ENVIRONMENT 

9.2.1 Climate/Meteorology 

105 



For most of the period in the year, the climate is cold and humid. The region experiences 

a cold winter from November to February and monsoons from May to mid- October. The 

rainfall in the project area varies from 300-360 cm in most parts of valley. Snowfall is 

seen at higher altitudes of the catchment area from November to April. The area enjoys 

sub tropical to alpine conditions. Temperature varies with altitude and slope. Fog is a 

common feature in the area especially from September to February. 

9.2.2 Topography 

Sikkim encompasses the Lesser Himalaya, Central Himalaya, and the Tethys Himalaya. 

It is essentially a mountainous State without flat piece of land of any extent anywhere. 

The mountains rise in elevation northward. The northern portion of the State is deeply cut 

into steep escarpments. South Sikkim is lower, more open, and fairly well cultivated. 

This configuration of the State is partly due to the direction of the main drainage, which 

is towards the south. The trend of the mountain system is generally in east-west direction. 

The Rangit and the Teesta, which form the main channels of drainage, run nearly north 

south. The valleys cut by these rivers and their feeders are very deep and are rather open 

towards the top, but usually attain a steep gorge like structure as they approach the bed of 

the rivers. 

9.2.3 Soils 

The soil depth varies from 100- 150 cm deep in most areas. There are also certain rock 

outcrops in the soil. The soil is mainly coarse to fine loam in texture. Some soils have a 

gray tint of color and rich in humus in most places. The State of Sikkim enjoys a wide 

range of climate, physiography, geology and vegetation which have further influenced 

formation of different kinds of soils that are classified under 5 broad physiographic units. 

Table 9.1 gives area wise details of these soils. The light textured soil and rocky areas are 

prone to sliding. Topsoil in most area is rich in humus and organic matter. The water

106 



holding capacity in most area is low and has low cohesiveness. The soil in general is 

loamy sand to silty clay loam with a depth of 30 cm to 100 cm and in some cases even 

more than 120 cm. Based on the soil survey conducted by the National Bureau of Soil 

Survey of India & Landuse Planning; the State has been classified into 3 main soil 

groups: 

Udalf: High base status soil of humid region. 

Orthants: Recently formed soil. 

Odhepts: Shallow blocks, brown and alluvial soil. 

No 

. 

Table 9.1: Major physiographic units of soil in Sikkim 

Physiographic units Area (ha) % of total geographic 

area 

1 Summit & Ridge (>30%) 31459.45 4.43 

2 

2.1 

2.2 

2.3 

2.4 

Slide slope of hills 

Very steep slope (>50%) 

Escarpments (>50%) 

Steeply sloping (30-50%) 

Moderately sloping (15-30%) 

213100.01 

30480.73 

214641.28 

16024.82 

30.03 

4.3 

30.24 

2.26 

3 Valleys (

9.2.4 Geomorphology and Geology 

The stratigraphic sequence of the proposed project site is given below: 

GROUP LITHOLOGY 

107 



Gondwana Grits, pebble cum boulder beds and carbonaceous 

shales with occasional coal seam, pegmatite and 

quartzite (tourmaline bearing) 

Daling Inter-bedded quartzite and chlorite sericite 

phyllite/schist 

Lingza granite. 

Quartzite/Biotite schist. 

Chungthang Interbedded quartzite and garnetiferous quartz biotite 

Central Crystalline 

Gneissic complex 

(CCGC) 

schist. 

Calc-silicate rock/marble. 

Garnet-kyanite-silimanite-biotite-quartz-schist 

Banded gneiss with augen gneiss and quartz-biotite 

gneiss. 

Augen gneiss 

The area falls within axial belt of Central Crystalline Zone of the North Sikkim 

Himalayas where the rock types are mainly high grade gneisses (CCGC) having inter- 

bands of meta-sedimentaries represented by calc-silicate/quartzite, high-grade schist and 

their fine inter laminations. The meta-sedimentaies occur as enclaves in the high-grade 

gneisses in the area around the proposed project. Discordant tourmaline bearing quartz 

veins and pegmatite often intrudes all these rock types. 

9.2.5 Seismicity 

Sikkim is a part of active Himalayan belt, which is tectonically young. The area has 

experienced mild tremors in the recent past. One earthquake of magnitude 6.0 on Richter

108 



scale was recorded on November 20 th , 1980. The project area falls in Zone IV of Seismic 

Zoning Map of India as per IS 1893 - 1984. 

9.2.6 Catchment Area 

The catchment area of the upper dam is 146 sq km while that of the lower dam is 127 sq 

km. The catchment is mountainous with rugged terrain. The tributaries are angular and 

have dendritic drainage patterns. Streams have moderate to steep slopes in upper reaches. 

The natural vegetation consists of shrubby to alpine in many places at upper reaches and 

mixed forest at lower elevations. 

9.2.7 River System 

Rangyong chu originates from Tingchen glacier and drains the slopes of Narsingh peak. It 

is joined by Rukel Chu on its left bank. Rukel Chu originates from Tongshiong and Talung 

glaciers at the base of South Kanchendzonga peak (8,476 m). Along its course Rukel Chu 

also receives drainage from South Simvo glacier on its left bank (Fig 9.3). Most of the 

Rukel Chu catchment is predominantly glaciated with a number of high peaks like South 

Kachendzonga peak, Talung (7,349m), Kabru Dome (6,545m) and a number of peaks 

above 7,000m marking the western boundary, Simvo (6,811m) lies on the northern 

boundary, while Gocha peak (6,115m), Pandim (6,691m) and Narsingh (5,825m) form the 

southern boundary. The catchment area up to upper dam site is 146 sq km and of lower 

dam is 127 sq km. Total length of Umram Chu from its origin up to the upper dam site is 

about 11 km and total length of Rangyong Chu from its origin up to the lower dam site is 

about 12 km. 

9.2.8 Submergence 

The project envisages construction of two dams each 55m high from the river bed level. 

The reservoir of upper dam would result in inundation of 15.62 ha of land whereas the 

lower dam reservoir is likely to submerge only 2.5 ha of land. Therefore, Rangyong H.E. 

project would inundate 18.12 ha of land. The spread of the two reservoirs is indicated in

109 



Figure 9.8. The predominant landuse in the submergence area of upper dam is alpine 

open scrub forest (63%) and dense mixed forest (34%) and the rest of the area is 

characterized by rockyland. The area likely to be submerged by the lower dam reservoir 

is comprised only of dense mixed forests (89%) and alpine scrub (11%). The proposed 

project, however, does not involve inundation of any village or human habitation. 

9.2.9 Landuse pattern 

The landuse/landcover pattern within the 7 km radius of the proposed Rangyong H.E. 

project was interpreted and generated from LISS-III scene of Path/Row 107/051 of 19th 

January, 2000 and PAN D scene of Path/Row 107/051 of 13th January, 2002. LISS and 

Pan scenes of area covering 7 km radius of the project site are given in Figures 9.4 & 

9.5. The first level classified landuse/landcover map generated from these two scenes 

coupled with ground truthing is given in Figure 9.6. Area covered by various 

landuse/lancover categories is given in Table 9.1 and the percent representation of each 

of the landuse/landcover type is shown in Figure 9.7. From the studies it is clear that the 

vegetation of the area concerned is typically that of high altitude Himalayan region. The 

predominant landuse of the area is a mixture of forests, alpine scrub, rockfalls, rockyland, 

snow and ice cover. The dense mixed forests, which occupy the lower altitudes of the 

catchment along river slopes constitute about 47% of the land area while alpine open 

scrubs constitute 29% of the total land area. Rockylands and rockfall areas in the 

catchment constitute the important landuse/landcover of the area covering about 1890 ha 

(10%) of the land. Similarly, large areas in the catchment are either under permanent ice 

cover/glaciers (5%) or snow cover (8%). In addition a small part of the catchment is 

under settlements/ agriculture which constitutes about 1% of the land area. These sparse 

human habitation sites and managed ecosystems like agricultural fields, etc. are restricted 

to areas downstream of the proposed power house site. These areas are around Lingza, 

Nung, Namprik and Lingdem on the two banks of the Rangyong Chhu. Majority of the 

area is covered by natural ecosystems and the landscape conditions in the area are also 

quite natural without any human disturbance. The dense forests are present along the

110 



Passaram Chhu and Umram Chhu in the north and northwest, respectively. The western 

forests are represented by Sakkyong Reserve Forest mostly along right bank of Rangyong 

Chhu. The forests in the north and northeast and northwest are represented by Tolung 

Reserve Forest. In the southern part these forests are represented by Lingdem Reserve 

Forest. These forests are mostly broad-leaf forests with occasional representation of 

bamboo in them, particularly in the warmer areas. The areas above these dense mixed 

forests are represented by alpine/open scrub type of vegetation. 

Table 9.2. Area (ha) under different landuse/landcover categories in 7 km radius of 

Rangyong H.E. Project 

Landuse/landcover Area (ha) 

Dense Mixed Forest 9443.86 

Open Scrub 5768.01 

Rockyland 1541.61 

Rockfalls 348.48 

Cultivation/settlements 43.32 

Ice/Glacier 917.51 

Snow 1627.89

8% 

1% 

2% 

29% 

5% 

8% 

Dense Mixed Forest Open Scrub Rockyland Rockfalls 

Cultivation/Settlements Ice/Glacier Snow 

111 



Figure 9.7: Percent area under various landuse/landcover categories in 7 km radius 

of the proposed Rangyong H.E. Project 

9.3. BIOTIC ENVIRONMENT 

Sikkim stretches from the low lands in the south with tropical climate to the mountainous 

regions in the north. The altitude varies right from sea level to mountain peaks covering a 

wide spectrum of flora and fauna. Nowhere in the world in such a small area can one find 

flora and fauna of all varieties - Tropical to the Alpines. Sikkim's botanical and 

zoological richness is awe- inspiring, boasting of more than 4500 species of flowering 

plants. 30% of all the birds in the country are found in Sikkim. 

9.3.1 Flora 

The two dam sites are located in temperate and alpine montane terrain and the area of in 

the vicinity of the project is comprised of dense mixed forests along the river course and 

alpine and open scrub higher up on the slopes. This area experiences cool and humid 

47%

112 



summers and severe cold winters. Owing to good moisture conditions and cool 

temperatures throughout the year at these altitudes the vegetation is constituted mostly by 

the cold temperate evergreen plant species. The forests are mostly confined to lower 

slopes in the river valley and are represented by all the physiognomic forms – trees, 

shrubs and herbs. The woody elements in these mixed forests are represented by Alnus 

nepalensis, Engelhardtia spicata, Litsea doshia, Neolitsea sp., Prunus cerasoides and 

Quercus lineata. In addition Euonymous pendulus, Lyonia ovalifolia, Macaranga 

denticulata and Rhamnus virgatus are commonly met with in these riverine dense forests. 

A few patches of bamboo were also seen interspersed within these forests. In the higher 

slopes where scrub vegetation dominates species of Rhododendron, Salix, Viburnum and 

several members of Rosaceae and Ericaceae are seen growing predominantly in the 

region. The alpine meadows harbour several species of Primulaceae, Gentianaceae, 

Papavaraceae, Brassicaceae, Poaceae and Juncaceae. The catchment area harbour some 

of the important endemic and endangered medicinal plant species of Himalaya. Among 

these species Artemisia vulgaris, Podophyllum hexandrum, Aconitum spp., Saussurea 

spp., Nardostachys jatamansi, Picrorrhiza kurroa and Meconopsis spp. are noteworthy. 

9.3.2 Fauna and Wildlife 

As the area represents a rich diversity of wildlife it forms a part of Kanchendzonga 

National Park. The upper parts of catchments of Ringpi Chhu and Tolung (Rangyong) 

Chhu harbour several faunal species like Himalayan brown bear (Selenarctos thibetanus), 

Great Tibetan sheep, Snow leopard (Panthera uncia), Bharal, Himalayan tahr 

(Hemitragus jemlahicus), Hoary-bellied squirrel (Callossciurus pygerithrus), Orange- 

bellied squirrel (Dremomys lokhriah), Assamese macaque (Macaca assamensis), 

Himalayan palm civet (Paguma larvata), Stone marten (Martes foina) and jackals (Canis 

aureus). Some of these animals are generally found in the vicinity of agricultural crops 

particularly in southern parts of the catchment. In addition there are also species like 

Civets (Viverra zibetha), porcupines (Hystrix brachyura), Grey musk shrew (Suncus

113 



murinus), the house mouse (Mus musculus) and Bandicoot rat (Bandicota bengalensis). 

The upper reaches, i.e. the alpine areas of the catchment harbour mammalian species, 

which include Nayan, Bharal, Snow leopard, bear, Himalayan tahr, Barking Deer, 

Himalayan marmot and pikas. These animals however are not known to come down to 

lower altitudes i.e. 2,200 m or below. The avifauna of the catchments is represented by 

bird species like bulbuls, thrushes, eagles, partridges, pigeons, doves, koels, owls, 

kingfishers, nightjars, woodpeckers, orioles, drongos, mynas, flycatchers, babblers, 

robins, etc. The invertebrates are represented by many species of butterflies and 

dragonflies in the surrounding area. 

Among the various faunal species present in the catchment Panthera uncia, P. pardus, 

Neofelis nebulosa, Felis bengalensis, Macaca assemensis and Cervus duvaucelli are 

Scheduled as threatened animals of India while Panthera tigris, Selenarctos thibetanus 

and Cervus duvaucelli are considered as globally threatened species. 

9.3.3 Aquatic life 

The rivers in Sikkim harbour a variety of fish species. Ichthyofauna in the river 

comprised mainly of Balm, Asala, Chepti, Gadela, etc. Snow trouts and other minor 

trouts are found at higher elevations. Some of the identified fish species found in the area 

are Schizothorax richardsonii, Salmo trutta fario, Labeo pangusia, Noemacheilus 

kanjupkhulens, Bagarius bagarius, etc. 

9.4. EXISTENCE OF ANY PROTECTED AREA/ARCHAEOLOGICAL SITES 

The proposed project area lies entirely within the boundary of Kachendzonga National 

Park. However, except the National Park there are no sites or monuments of 

archaeological or national importance, which would be affected by the project activities 

directly or indirectly.

9.5 PREDICTION OF ENVIRONMENTAL IMPACTS 

9.5.1. Impacts on Land Environment 

114 



Sufficient amount of land will be required for construction of the proposed dam, 

powerhouse, colonies & approach roads etc. The reservoir of upper dam would result in 

inundation of 15.62 ha of land whereas the lower dam reservoir is likely to submerge 

only 2.5 ha of land. Therefore, Rangyong H.E. project would inundate 18.12 ha of land. 

All these activities would mean some disturbance and change in the landscape. There 

will be changes in the Landuse of the area and in its physical composition. 

9.5.2 Impacts on Water Environment 

The construction of a reservoir replaces the river eco-system by a lacustrine ecosystem. 

The vector of various diseases breeds in shallow areas not very far from reservoir 

margins. The breeding site for mosquitoes and other vectors in impounded water is in 

direct proportion to the length of the shoreline. The construction of the reservoir would 

increase the shoreline many times as compared to the pre-project shoreline of various 

rivers and tributaries under submergence. Thus the construction of the proposed 

reservoir may enhance the potential breeding sites for various disease vectors. 

9.5.3 Impacts on Air Environment 

The construction of the proposed dam would increase dust generation in the area and 

some vehicular pollution. However, these would only be limited to the construction 

period. 

9.5.4 Impacts on Flora/Fauna 

9.5.4.1 Impacts on terrestrial flora 

About 18.12 ha of land will be inundated due to construction of the proposed dam. The 

direct impact of construction activity of a water resources project in a hilly terrain is 

generally limited to the vicinity of the construction sites. A large number of labourers 

and technical staff and other groups of people are likely to aggregate in the area during

115 



construction phase. In this area majority of forest dwelling rural community depends on 

forest for food, fodder and timber. Submergence of forest area in primary impact zone 

may reduce the availability of resources for the local people. This would also result in 

significant changes at the structural resource level in forest. The acquisition of land for 

various project activities would also lead to cutting of vegetation on these lands. 

9.5.4.2 Impacts on terrestrial fauna 

During the construction phase, a large number of machinery and construction labour will 

have to be mobilized. This activity may cause some disturbance to the wildlife 

population. The operation of various construction equipments is likely to generate 

significant noise. Likewise blasting too is likely to generate noise level and vibration 

intermittently. The noise may scare the fauna in the region and force them to migrate to 

other areas. There might be some impacts due to increased human interference. 

9.5.4.3 Impacts on avi-fauna 

The construction of the proposed dam will lead to formation of a reservoir, which will 

have a fluctuation in the water level, which precisely means the reservoir bank will 

remain wet throughout the year. Due to such reasons grasses may grow along the 

reservoir banks. Such conditions are generally ideal for various kinds of birds, especially 

water birds. However, because of the presence of a good habitat, it is quite likely that 

water birds will flock in this area in a large number. The birds from cold climatic areas 

could also use this area during the winter season. 

9.5.4.4 Impacts on aquatic ecology 

The major physical change upstream of the proposed dam will be formation of a 

lacustrine habitat from a riverine habitat. Whereas below the damsite, there will be 

regulated water or very little water in river course. As such there will be some changes in 

the aquatic environment in this stretch. For this the water quality analysis shall be 

conducted regularly. Moreover, some migratory fish species may get affected due to

116 



construction of the dam. Also some fish species, which are riverine and are not 

accustomed to deep lake environment, may also get replaced. 

9.5.5 Impacts on Socio-Economic Environment 

Since the submergence area is small and is confined to the river valley, no village will be 

submerged. Thus displacement is not anticipated. At present, there are small business 

and little employment facilities in the project area. However, with the construction of the 

project new business and employment opportunities will open up for the local people 

which are likely to improve the economic conditions of the local people. Further, there 

will be development of infrastructure facilities as housing, water supply, medical 

facilities, schools, transportation and communications. These factors are expected to 

bring about positive impact on the socio-economic status of the people living in the 

project area. There is possibility of changes in lifestyle and cultural values of local 

people due to migrant worker population. However, the impact is expected to be low as 

the number of immigrant people will be small for the small project and most of the 

labourers employed in the project will be local people. 

As a part of the Environmental Impact Assessment Study, a detailed socio-economic 

survey would be carried out to determine the following: 

Information on various aspects of the affected population viz; 

demographic details, socio-economic and cultural characteristics, 

enumeration of personal properties of the affected population, education 

level and occupational profile etc. 

Enumeration of social infrastructure and community property resources in 

the submergence area. 

Ethnographic assessment of PAFs.

9.6 ENVIRONMENTAL MANAGEMENT PLANS 

117 



The objective of the Environmental Management Plan (EMP) is to ameliorate the 

negative impacts of a developmental project. The most reliable way to ensure proper 

implementation of these management plans is to integrate the same with various 

processes involved during project planning, designing, construction and operation phases. 

Based on the assessment of environmental impacts, following management plans will be 

formulated: 

Catchment Area Treatment 

Compensatory Afforestation 

Wildlife Conservation 

Resettlement and Rehabilitation 

Public Health Management System 

Muck Disposal 

Fishery Management 

Restoration of Construction Area 

Green Belt Development 

Free Fuel Provision 

Disaster Management



CHAPTER – X 

INFRASTRUCTURE

CHAPTER – X 

INFRASTRUCTURE 

10.1 EXISTING ACCESS AND INFRASTRUCTURE FACILITIES 

10.1.1 Road Communication 

125 



The upper dam site is located just downstream of the confluence of Passaram Chu and 

Umram Chu and lower dam site is on river Rangyong Chu nearby the place Singnok. The 

lower dam site is presently not approachable, while the upper dam site is approachable by 

a diffcult path via Phontang from road head at Lingza. The Power house is located on the 

right bank of Rangyong Chu just upstream of confluence of Ringyong Chu and 

Rangyong Chu. The nearest road end is at Lingza/Lingdem which is 15Km from 

Mangan, the head quater of North Sikkim District of Sikkim, about 60 Km from Singtam 

(NH31A), about 160 Km from NJP railway station and about 161 Km from Bagdogra 

airport. The Lingza/Lingdem village is connected form Mangan by a PWD road. The 

Siliguri-Gangtok (NH-31A) and Singtam-Mangan-Sanklan state highways are being 

maintained by BRO. 

10.1.2 Housing And Community Facilities 

Singnok is the name of the place near the Dam sites where even basic facilities of health 

care, schooling, market, postal and telephone etc. are not available. It is therefore 

necessary to plan housing, office, recreation, store etc. for meeting the requirement of the 

project. 

10.1.3 Power Availability 

Sikkim, at present, is dependent mainly its mini and micro hydel power stations for 

meeting its power demand. The total installed capacity of state at present is about 95 

MW. The state gets some share of power from Chukha Hydel Electric Project in Bhutan, 

Farakka Thermal Power Station, West Bengal and Rangit Hydel Power Project of NHPC 

Ltd. Teesta (V) HE Project, 510 MW being executed by NHPC in central sector is also

126 



under advance stage of construction. The existing transmission system of this state 

comprises of mainly 66 KV and 11 KV transmission lines. A 132 KV S/C transmission 

line is being constructed from Melli border town of Sikkim-West Bengal to Ranipool. A 

132 KV sub station is being constructed at Melli. A substation of 2.5MVA, 66/11KV is 

located at Phodong near Mangan. Therefore , the necessary construction power shall be 

available for the execution of Rangyong H.E. Project from some where nearby Mangan 

but the exact location may be decided at the time of FR/DPR. 

10.2 PROPOSED ACCESS AND INFRASTRUCTURE FACILITIES 

Keeping in view the available infrastructure facilities of communication,, housing and 

power, the requirement of the same for Rangyong H.E. Project has been worked out. 

10.2.1 Improvement Of Existing Road And Bridges 

The Powerhouse is located on just u/s of confluence of Rangyong Chu and Ringyong 

Chu. The approach roads from Mangan are available upto Lingza/ Lingdem. Further the 

power house and upper dam site are approachable by a difficult footpath. While there is 

no approach is available to lower dam site. Since the Rangyong H.E. Project is on u/s of 

the Panan project, therefore it has been presumed that all the roads and bridges shall be 

ready upto dam site of Panan H.E. Project. 

10.2.2 Construction Of Roads & Bridges 

The power house shall be approached from Mangan – Lingza road from right bank for 

which a new project roads shall be constructed from the dam site of Panan H.E. Project. 

The Dam sites shall be approached from powerhouse on right bank and bridges across the 

rivers Pokharam Chu and Rangyong Chu are proposed. 

10.2.3 Accommodation For Residential Purpose 

To accommodate the project employees and contractors, land would be required for 

construction of suitable residential complexes. The residential colony has been proposed

127 



at Sakkyong. The project colony would have accommodation for all categories of 

officials deployed for the construction. The strength of the officials and staff of various 

categories required for the project has been worked out. Each personal would be provided 

with the accommodation as per the entitlement. Keeping in view the construction period 

and subsequent operation and maintenance of the project, it is proposed to construct 

about 50% of the buildings as the permanent and the remaining as temporary. This 

conclusion has been drawn on the basis that 50% of the staff strength would be required 

for maintenance and operation after the completion of the project. 

Requirement of built up accommodation has been worked out to 4138Sq.m of permanent 

built up area and 4514 Sq.m of temporary builtup area would be required. Total plinth 

area for residential accommodation worked out to be 8648Sq.m, 

10.2.4 Accommodation For Non-Residential Purposes 

The office complexes are proposed to be located at Sakkyong. Workshops, laboratories, 

stores, water supply, fire stations, electrical substations etc would be accommodated in 

the project area. One stockyard is proposed at railhead near new Jalpaiguri Railway 

station where construction materials like cement, steel and machinery and equipments 

would be store for further transportation to the project site, Batching and mixing plants 

are to be commissioned, one near dam site and the other near power house site. 

Accommodation required for non residential purposes have been worked out to be 

9630Sq.m of which about 50% would be permanent and rest will be temporary. 

10.3 TELECOMMUNICATION FACILITIES 

The different work sites of the project, offices, stores, laboratories, workshop and 

residences would be connected through a telecommunication network. The 

telecommunication facilities would also be provided between the projects and outside. 

Therefore, an internal telephone exchange would be provided at the project for

128 



communication within and outside the project. Most parts of Sikkim are presently 

connected with different parts of the world through satellite telecommunication network 

for which an earth satellite station with electronic exchange exists. The same network 

would be extended to the project area for telecommunication with outstation agencies. 

10.4 CONSTRUCTION POWER 

The construction power for the project shall be available at the time of construction of the 

project and it is presumed that till that time some mega projects in the d/s i.e. Teesta 

(V), Teesta(III) and Teesta(IV) would have been commissioned and a transmission line 

of about 10Km may be required for arranging construction power.



CHAPTER – XI 

CONSRUCTION PLANNING & 

SCHEDULE


CHAPTER –XI 

CONSTRUCTION PLANNING & SCHEDULE 

129 



The Equipment Planning & Construction Methodology of Rangyong H.E. Project (3x47 

MW) in Teesta Basin Sikkim has been developed on following consideration. 

1. The project construction period has been considered as four years after 

completion of Stage I & II activities. 

2. Available Geological Data at PFR stage. 

3. Requirement of Construction Equipment has been planned to handle the quantities 

worked out on the basis of preliminary layout. 

4. Five months (May to September) rainy season has been considered while 

planning surface works. 

11.2 CONSTRUCTION METHODOLOGY: 

11.2.1 Infrastructure Works: 

The main infrastructure development is proposed to be carried out in period of 12 

months. During infrastructure period Land Acquisition, construction of approach roads, 

bridges& culverts, arrangement of construction power will be undertaken. Critical 

component of project would be started from 5 th month after construction of approach 

roads. Platform to accommodate batching plant, stores for construction material, site 

workshop, offices and other buildings (residential/ non residential) colonies will also be 

developed in infrastructure period. Crawler Dozer, Loader cum Excavator, Air 

compressor, Road Roller etc. are proposed for deployment during infrastructure stage. 

11.2.2 Diversion of River 

The construction of two diversion tunnels 3.3 m finished dia., Horse shoe shaped 300 m 

long each, for both Dams would be carried out by full face method. Excavation of

130 



Diversion Tunnel will be carried out by deploying separate set of equipment i.e single 

Boom drill jumbo, Jack hammers, 1.0 cum Conway mucker & 10 T Tippers.. Excavation 

& concreting of both diversion tunnel would be completed in 9 months. The concreting 

equipment proposed are two set of 38 cum Concrete pump, Transit mixer, shotcrete 

machine, Grout pump, shutters etc. Concreting requirement would be catered by the same 

batching & mixing Plant and Aggregate processing Plant, being proposed for each Dam . 

U/s & D/s Coffer dam would be constructed immediately after construction of diversion 

tunnel in 3 months to divert the river. River bed excavation would be taken up after 

completion of coffer dam. 

11.2.3 Upper Concrete Dam 

Dam abutment stripping is proposed to be carried out in 13 months. The excavation of 

river bed & foundation treatment would be carried out in 3 months. Excavated material 

will be handled by 1.0 cum Hyd. Excavator and 10T Tippers/20 T Dumpers. Concreting 

of Dam & HM work would be carried out in further 23 months. Concreting would be 

done by deploying 2 nos. Travelling Tower cranes (4.5 T at 60 m radius), 1 No. 120 

cum/hr Batching& Mixing plant and 250TPH Aggregate Processing plant. 

11.2.4 Lower Concrete Dam 

Dam abutment stripping of lower Dam is proposed to be carried out in 13 months. 

Thereafter excavation of river bed & foundation treatment would be carried out in 4 

months. Excavated material will be handled by 1.0 cum Hyd. Excavator and 10T 

Tippers/20 T Dumpers. Concreting of Dam & HM work would be carried out in further 

22 months. Concreting would be done by deploying 2 nos. Travelling Tower crane (4.5 

T at 60 m radius), 1 No. 120 cum/hr Batching& Mixing plant and 250TPH Aggregate 

Processing plant.

11.2.5 Link Tunnel 

131 



Initially construction of approaches for link tunnel would be carried out in four months. 

Thereafter excavation of 3.3m dia 2.0 km long link tunnel would be carried out in the 

same way as diversion tunnels in 20 months. Concreting & HM works of tunnel would be 

carried in further 15 months. Concreting would be carried out by deploying concrete 

pump, Transit Mixer etc. 

11.2.6 Intake Structure, Desilting Chamber , Silt Flushing tunnel & HRT 

Initially excavation of adits & approaches would be carried out in 4 months. 

Thereafter,2 Nos. Intake structure having gate size of 3 m x3m, 2 Nos. Dufour type 

Desilting chambers of size 175m X10mX12m each and HRT of 3.3 m dia. would be 

excavated in 24 months . After excavation of intake structure, 2 nos. intake tunnel 3m 

dia. each would be excavated by full face method. Excavation of Desilting Chamber 

would be taken up from intake tunnel. Intake tunnel would be extended upto full length 

of Desilting Chamber. Thereafter it will be expanded side wise to the full width of 

desilting chamber resulting in desilting chamber dome. Mucking of excavated material 

would be done through the tunnel. After the excavation of desilting chamber, concreting 

will be carried out. Excavation of silt flushing tunnel & gate operation chamber would be 

a parallel activity. The equipment to be deployed are Jack hammers, wagon drills, air 

compressors, skid steer loader, tippers, concrete pump, transit mixers etc. 

Excavation of 7.5 km long, 3.3 m finished diameter horse shoe shaped Head Race Tunnel 

is proposed by full face drilling & blasting method. It will be excavated through 3 nos 

adits. Excavation would be carried out by deploying three set of equipment i.e single 

boom drill jumbo, 1.0 cum Conway mucker and 10 T tipper. Concreting will be carried 

out by deploying concreting equipment i.e. Concrete pump, Transit Mixer etc. Concreting 

requirement would be catered by Batching & Mixing Plant & aggregate processing plant 

installed at dam site.

11.2.7 Surge Shaft : 

132 



For Construction of 10m diameter, 75 m high Surge Shaft, an approach to surge shaft top 

would be constructed in four months. After the completion of approach, Excavation of 

surge shaft would be carried out manually in 15 months. Excavation would be carried out 

with the help of Jack hammers, motorized winch 10 T capacity etc.. Mucking will be 

done from the top. Concreting would be completed employing 2 m shutter, concrete 

pump, Transit Mixer & 30 cum/hr batching &mixing plant . Construction of surge shaft 

would be completed in 27 months. 

11.2.8 Pressure Shaft: 

Initially construction of approaches & adit would be done in 4 months. One no. 1000 m 

long 2.5 m dia. inclined pressure shaft, will be excavated in the same way as surge shaft 

by deploying Jack hammer, Motorized winch etc. However two nos. intermediate adit 

can be used to handle the muck. Steel liner erection & concreting will be carried out by 

deploying 10/20 t winches, Slipform liner etc. Construction of Pressure shaft would take 

around 30 months. 

11.2.9 Power House 

3 X 47 MW (141MW) underground power house (110 m X 22 m X 40 m size), 

Transformer Cavern & MIV would be excavated in 16 months. For excavation of Power 

House a construction adit would be excavated up to the crown of power house. Main 

access tunnel would also be excavated simultaneously. Construction adit would be 

extended up to full length of power House. Thereafter it will be expanded side wise to 

the full width of power house resulting in Power House Cavern. Mucking of excavated 

material would be done through the Construction adit. From Power House Cavern 3 

shafts of 2.0 m diameter would be excavated up to the bottom level of draft tube followed 

by benching of Power House cavern up to the bottom of Power House. Mucking will be 

carried out through Main access Tunnel/TRT. The equipment to be deployed for 

excavation are jack hammers, wagon drills, air compressors, loader, excavators, tippers,

133 



winches etc. Concreting of Powerhouse would be carried out in 20 months with the help 

of concrete pump, transit mixer etc. Concreting requirement would be catered by 

deploying 60 cum/hr batching & mixing plant and 100 TPH aggregate processing plant. 

Power house Installation & Testing of Machine would be undertaken in such a manner 

that Project get commissioned in 48 th month from the start of Project construction. 

11.2.10 Tail Race Tunnel: 

1 Nos. 300m long horse shoe shaped Tail Race Tunnel having 3.3 m finished diameter 

will be excavated by full face method. Excavation of Tail Race Tunnel would be carried 

out with single boom Drill Jumbo, Wagon drill, Conway mucker , 10 t tipper etc. The 

TRT will be excavated from 5th month & will be completed in further 6 month. After the 

excavation of power house the TRT will be concreted with the help of concrete pump, 

Transit mixer, Batching & mixing plant & aggregate processing plant ( installed at Power 

house). 

11.3 CONSTRUCTION SCHEDULE 

The schedule for stage I & II activities upto CCEA clearance and construction schedule 

has been prepared in the form of bar chart and placed as annexure –11.1 & 11.2 

respectively.

S. No. 

Details of works 

1 Preparation of stage-I activity estimates 1 

2 Data collec./ application for clearance from MOEF 

3 MOEF clearance 1 

4 Essent. Temp. infra./access 6 

5 Estab. of G&D sites, Metrological 

obser. And Hydrological measurement 

6 Essential Geological & Geo-physical 

exploration, Topographical surveys 

7 Formulation of Feasibility Report, 

preparation of estimate for st-II activities 

8 EIA / EMP studies 15 

9 Commercial viability from CEA 1 

10 Vetting & sanction of st-II activity estimates 1 

11 Detailed Topogr./Geological/Hydro 

metero. & Construction material survey 

12 MOEF clearance 3 

13 Const. of resid./non resid. buildings,roads 

bridges and arrangement of const. Power 

14 Preparation of Detailed Project Report 

and its submission 

Duration 

15 Techno Economic Clearance 3 

16 Pre PIB delibrations 1 

17 PIB Clearance 1 

18 CCEA Clearance (Investment Sanction) 1 

2 

24 

11 

14 

14 

19 

14 

SCHEDULE FOR STAGE-I&II ACTIVITIES (UP TO CCEA CLEARANCE) 

MONTHS 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 

*This schedule is in accordances with three stage clearance policy of Ministry of Power ,Govt. of India vide no. 16/31/2000-DO(NHPC) dated 8/6/2001 

133 

Annexure-11.1 

Contd. 

Contd. 

Zero date for 

Construction

Sl. 

No. 

CCEA Clearance 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 

1 INFRASTRUCTURE DEVELOPMENT 

a Acquisition of private & forest land Ha 8 

b Construction of roads & buildings LS 12 

2 AWARD OF CONTRACTS 

a Tendering , award and mobilization LS 4 

3 DIVERSION TUNNELS ( 2nos., 300 m 

long 3.3 m dia horse shoe) 

a 

Excavation m 3 40,000 5 

b Erection of shutters & Conc. Lining m 3 6,500 4 

c HM Works Job LS 4 

d Plugging of tunnels Job LS 2 

4 COFFER DAMS (U/s & D/s) 

Name of Work Unit Quantity Duration 

(months) 

a Const.of Coffer Dams & River Diversion m 3 75,000 3 

5 UPPER CONCRETE DAM 

(65 m High & 300 m Long at top ) 

a 

b 

Dam abutments stripping 

Excavation and foundation treatment 

m 2,10,000 

13 

3 

3 

c Mass Concreting m 3 3,76,000 19 

d Hyromechanical Works Job LS 12 

e Reservoir filling Job 2 

6 LOWER CONCRETE DAM 

( 65 m high & 250m long at top) 

a 

b 

Dam abutments stripping 

Excavation and foundation treatment 

m 1,55,000 

13 

4 

3 

c Mass Concreting m 3 3,24,000 18 

d Hyromechanical Works Job LS 12 

e Reservoir filling Job 2 

7 LINK TUNNEL (3.3m dia. 2000m long) 

a Construction of approaches Job LS 4 

b Excavation m 3 35,000 20 

c Concreting & HM Works m 3 12,000 15 

7 INTAKE, DESILTING CHAMBERS & 

HRT ( 7.5 Km of dia 3.3m horse shoe) 

a Excavation of adits(3 Nos. 3.3m of D-Shaped) & 

approches 

Job LS 4 

b Excavation m 3 1,94,100 24 

c Concrete Lining m 3 59,400 18 

d Grouting Job LS 12 

e HM Works Job LS 14 

f Cleanning, Adit pluggings etc. Job LS 2 

g Water conductor charging Job LS 1 

8 POWER HOUSE COMPLEX 

(3 Caverns i.e MIV, PH & TG) 

a Const. of Adits Job LS 4 

b Excavation of PH, MIV & TG m 3 2,30,000 16 

c Concreting in sub & super structures m 3 104,500 20 

d Erection of EOT crane Job LS 2 

9 SURGE SHAFT 

( 10 m dia.of 75 m height) 

a Const. of approches Job LS 4 

b Excavation m 3 

70,200 15 

c Concreting & HM Works m 3 

6,000 12 

10 STEEL LINED PRESSURE SHAFT 

( approx.2.5m dia ,1000 m long ) and 

penstocks 

a Const.of approaches & adit Job LS 4 

b Excavation m 3 

17,500 18 

c Erection of steel liners & Concreting m 3 

12,000 12 

11 TAILRACE TUNNEL 

( 3.3 m dia ,300 m length ) 

a Excavation m 3 

5,200 6 

b Concreting & HM Works m 3 

1,800 4 

12 POT HEAD YARD Job 

Exc 79000, 

Conc 3000 

12 

13 ELECTRO-MECHANICAL WORKS 

a Erection, Testing & Commisioning of all three Units 

Job 26 

Note: Since the date of CCEA clearance cannot be anticipated at this stage, the time assumed for various activities is inclusive of the effect of monsoon. 

CONSTRUCTION SCHEDULE OF RANGYONG HE PROJECT (3X47=141 MW), SIKKIM 

Ist year IInd year 

Schedule of Constructiom 

IIIrd year IVth year 

134 

Annexure 11.2



CHAPTER – XII 

COST ESTIMATE

CHAPTER -XII 

COST ESTIMATES 

135 



PRELIMINARY COST ESTIMATES FOR CIVIL, HYDRO-MECHANICAL, 

ELECTRO-MECHANICAL AND TRANSMISSION WORKS 

The estimate has been prepared to arrive at the capital cost of Rangyong H.E. Project and 

is of Pre-feasibility level of accuracy. The base date of the estimate is June 2003 Price 

Level and the cost is expressed in Indian Rupees. The Cost Estimate is divided into 

Civil, Electrical and Transmission Works. For Civil Works, the sub heads are as under: - 

12.1 I-WORKS 

Under this head, provision has been made for various components of the Project as 

detailed hereunder. 

A-Preliminary 

Under this head, provision has been made for all surveys and investigations to be 

conducted to arrive at the optimum of the project components. 

B-Land 

This covers the provision for acquisition of land for construction of the project colonies, 

offices and stores and compensation for trees and standing crops etc. 

C-Works 

This covers the cost of Diversion Tunnel and Coffer and Concrete Dam and Spillway 

along with associated hydro-mechanical equipment.

J-Power Plant Civil Works 

136 



This covers the cost of project components viz. Intake Structure, Headrace Tunnel, Power 

House and Transformer Cavern, Pressure Shaft, Surge Shaft, Tail Race Tunnel and other 

appurtenant works. 

The quantities indicated in the estimates for C - Works & J-Power Plant Civil Works 

(Civil & HM) are calculated from the Preliminary Engineering Drawings and as per 

experience of other on-going or commissioned projects. A provision has been made for 

contingencies. 

The unit rates for various items are taken as per the Guidelines issued by CEA for 

preparation of PFRs. It has been assumed that the quarry is available at a distance of 10 

Kms from the work site. 

K-Buildings 

Under this head provision for both residential and non-residential have been provided. 

Under the permanent category only those structures are included which will be 

subsequently utilized during the operation and maintenance of the project utilities. The 

costs are worked out on plinth area basis prevalent in the area for the type of construction 

involved. 

O-Miscellaneous 

Provision under this head has been made for C & J works for the Capital & running cost 

of Electrification, Water Supply, Sewage disposal, Fire fighting equipments, Medical 

assistance, Recreation, Post Office, Telephone and Telegraph Office, etc. also the 

Provisions are made for the Security arrangements, inspection vehicles, schools, transport 

of labour, Laboratory testing, R&M of Guest House and transit camps, Community 

center, Retrenchment compensation, photographic instruments as well as their R&M 

charges etc.

P-Maintenance During Construction And Y-Losses On Stock 

137 



A provision of 1% and 0.25% of C-Civil works, J-Power Plants, K-Buildings & R- 

Communications has been made for maintenance of works during construction period 

and losses on stock respectively. 

Q-Special Tools And Plant 

It is assumed that the work will be carried out through contracts and not through 

departmental construction. Accordingly, provision for general purpose equipment and 

inspection vehicles only has been made as per CWC Guidelines. 

R-Communication 

Provision under this head covers the cost of new roads, Widening/Improvement of roads 

and strengthening of bridges. The cost of roads and bridges are based on the prevalent 

rate structure prevalent in the area of the Project, for the type of construction involved. 

X-Environment And Ecology 

Provision under this head has been taken as 2% of I Works towards Bio-diversity 

Conservation, Creation of Green belt, Restoration of Construction Area, Catchment Area 

Treatment, Compensatory Afforestation etc 

12.2 II-ESTABLISHMENT 

Provision for establishment has been made at 8% of I-works minus B-Land for civil 

works. 

12.3 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. The outlay is 

provided at 1% of cost of I-works.

12.4 IV-SUSPENSE 

138 



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. 

12.5 V-RECEIPTS AND RECOVERIES 

Under this provision, estimated recoveries by way of resale or transfer of equipment used 

in infrastructure works are provided for @ 75% of value booked under head Q-Special 

Tools and Plants. Also, the provision for recoveries on account of resale of DG Set and 

temporary buildings has been considered 

12.6 ELECTRICAL WORKS AND GENERATING PLANT 

The cost of generating plant and equipment is based on indigenous sources. The prices of 

auxiliary equipment and services are based on prevailing market prices/costs incurred at 

other ongoing or commissioned projects.

ABSTRACT OF COST OF WORKS 

139 



S.No Description Amount 

(Rs. in Crores) 

( June 2003 P.L.) 

A CIVIL WORKS 

1. DIRECT CHARGES 

I - Works 

A - Preliminary 5.78 

B - Land 13.47 

C - Works 299.44 

J - Power Plant Civil Works 217.77 

K - Buildings 15.07 

O - Miscellaneous 8.78 

P - Maintenance 5.64 

Q-Special Tools & Plants 4.07 

R - Communication 31.62 

X - Environment & Ecology 12.31 

Y - Losses on Stock 1.41 

Total of I-Works 615.36 

II - Establishment @ 8% of cost of I-Works less B-Land 48.15 

III - Tools and Plants @ 1% of cost of I-Works 6.15 

IV - Suspense 0.00 

V - Receipt & Recoveries (-) -3.27 

TOTAL DIRECT CHARGES 666.40 

2. INDIRECT CHARGES 

a) Capitalised Value of Abatement of Land Revenue 0.17 

b) Audit and Account Charges @1% of cost of I-Works 6.15 

TOTAL INDIRECT CHARGES 6.32 

TOTAL OF DIRECT & INDIRECT CHARGES 672.71 

ABSTRACT : 

A Civil Works 672.71 

B Electrical Works 113.11 

C Transmission Works 13.68 

TOTAL COST 799.50 

C IDC 91.32 

D Total Cost With IDC 890.82

Sl 

No. 

A- Preliminary 

140 



Description of Work Unit Qty Rate 

Rs. In lakhs 

Amount 

1 Prefeasibility 

1.1 Preparation of Prefeasibility Report LS 14.00 

2.0 Preparation of Detailed Project Report 

2.1 Detail survey for final location of project 

componenets 

2.2 Aerial survey, contour survey for reservoir 

basin including establishment of permanent 

benchmarks. 

2.3 Geological and geophyical surveys and 

investigation 

LS 25.00 

LS 10.00 

I) Drifting m 800 0.10 80.00 

ii) Geophysical LS 30.00 

iii) Core drilling m 450 0.10 45.00 

2.4 Hydrological and Metrological surveys 

including establishment of rain gauges/ 

river gauges and discharge, sedimentation 

stations and their running charge for 1 year 

LS 16.00 

2.5 Investigations for foundation and rock 

testing 

2.6 Investigation for availability of construction 

materials. 

2.7 Construction of access roads to facilitate 

investigations 

LS 6.00 

LS 3.50 

LS 7.00 

2.8 Model experiment. LS 12.00 

2.9 Computer and telecommunication facilities. LS 3.00 

2.10 Vehicles for inspecting officers for site 

investigations 

LS 25.00 

2.11 Camping equipment LS 2.00 

2.12 Preliminary soil test, establishing soil 

testing laboratory. 

LS 6.00 

2.13 Consultant’s fees including charges for 

preliminary design work or device 

2.14 Training of engineers during investigation 

and preparation of project reports 

LS 15.00 

LS 6.00 

2.15 Ground water studies. LS 6.00 

2.16 Environment and ecological studies. LS 10.00

141 



2.17 Preparation and printing of DPR LS 10.00 

Total( I+II) 331.50 

3.0 Pre-Construction Stage Investigations 

3.1 Topographical Surveys LS 

3.2 Geological Investigation 

15.00 

I) Diamond Core Drilling m 200.00 0.1 20.00 

ii) Exploratory Drift m 200.00 0.1 20.00 

iii) Excavation in trenches & pits 

LS 

iv) Testing of Samples 

LS 

3.3 Hydrological and Silt data collection - 3 

sites for 4 years 

3.4 Meteorological Data Collection 3 sites for 4 

years Year 

3.5 Construction material survey 

I) Topographical Survey 

LS 

ii) Collection and Transportation of samples 

iii) Laboratory Testing of Samples including 

LS 

charges for all T&P and Machineries LS 

3.6 Model studies 

LS 

3.7 Seismological data collection for 4 years 

Year 

3.8 Survey for layout of colonies and roads 

0.75 

4.00 

12.00 2.00 24.00 

12.00 0.40 4.80 

5.00 0.05 0.25 

3.00 

6.00 

15.00 

4.00 1 4 

I) Residential-cum-Office accomodation 

Sqm. 

2.00 0.5 1.00 

ii) Batching Mixing Plant and Workshop Sqm. 1.00 0.5 0.50 

iii) Project and quarry site road Sqm. 0.50 0.5 0.25 

3.9 Workcharged establishment for unforseen 

works Year 

4.0 Design & Consultancy 

4.1 Cost of Design Establishement including 

procurement of printing stationery and 

preparation of completion report, History of 

Project etc. LS 

4.2 Cost of Special Studies and Designs 

LS 

4.3 Fees for Consultant and specialists 

LS 

4.4 Training of Engineers 

LS 

4.00 2 8.00 

25.00 

15.00 

15.00 

5.00

142 



5.0 Equipment LS 

5.1 Drawing and Mathematical Instruments LS 10.00 

5.3 Survey Instruments LS 30.00 

5.4 Office instruments 

LS 

20.00 

Grand Total :( I+II+III) 578.05

Sl. 

No. 

1.0 Private land Requirement 

B-LAND 

143 



Rs. In lakhs 

Description Qty. Rate Unit Amount 

Permanent residential and non residential 

buildings 

3.00 5.50 Ha 16.50 

Diversion tunnel 2.00 5.50 Ha 11.00 

Submerged in the reservoir area 27.00 5.50 Ha 148.50 

Construction of dam/ weir 8.00 5.50 Ha 44.00 

Construction material 2.00 5.50 Ha 11.00 

Construction of approach Roads 70.00 5.50 Ha 385.00 

Power house 2.00 5.50 Ha 11.00 

Construction of adits 3.00 5.50 Ha 16.50 

Switch Yard 1.00 5.50 Ha 5.50 

Surge Shaft 1.00 5.50 Ha 5.50 

Land for Misc Purpose 1.00 5.50 Ha 5.50 

Sub Total (1) 120.00 660.00 

2.0 Forest land 

River bed 10.00 0.00 Ha 0.00 

Underground 4.00 0.00 Ha 0.00 

Sub total (2) 14.00 0.00 0.00 

3.0 Other Compensation 

Cost of crops standing on cultivated land 

required @30% of cultivated land 

80 1.65 Ha 132.00 

Compensation for trees LS 10.00 

Compensation for relocating electric and 

telephone poles 

2.00 

Crop Compensation for submergence LS 200.00 

Total 344.00 

4 Land on lease/ hire for 4 Years 

Dumping area 0.50 2.40 Ha 1.20 

Dumping area for batching and mixing 0.50 2.40 Ha 1.20 

plant 

Temporary Residential and Non- 

Residential buildings 

2.00 2.40 Ha 4.80 

Contractors Colony 2.00 2.40 Ha 4.80 

Contractors Construction facilities 2.00 2.40 Ha 4.80 

Railway Siding Facilities 1.00 2.40 Ha 2.40

144 



Electro - Mechanical Works 1.00 2.40 Ha 2.40 

Hydro -Mechanical Works 1.00 2.40 Ha 2.40 

Total 24.00 

Total (1+2+3+4) 1028.00 

Interest charges on account of award for 

the period taking over possession of land 

and date of award @ 12% per year of 

25% cost of land acquisition for two years 

39.60 

Solatium charges for compulsory 

acquisition of land @ 30% of the cost of 

private land 

Provision for legal charges @1% on total 

compensation 

Labour and material required for 

measurement and demarcation of land and 

properties @ 1% of land acquisition 

Establishment charges @ 6.25% of cost 

of total compensation 

198.00 

10.28 

6.60 

64.25 

Total 1346.73

ABSTRACT OF COST OF C - WORKS 

145 



S. N. Description Amount (Rs. In Lakhs) 

Civil HM Total 

1. River Diversion Works 635.60 72.66 708.26 

2. Coffer Dam 1289.40 1289.40 

3. Upper Concrete Dam 10301.94 10301.94 

3. Lower Concrete Dam 8513.11 8513.11 

4. Spillway & Plunge Pool 7677.89 866.36 8544.25 

Total 28417.95 939.02 29356.96 

Add works tax @ 2% 568.36 18.78 587.14 

GRAND TOTAL 28986.30 957.80 29944.10

S. 

No. 

HYDRO MECHANICAL EQUIPMENT 

Detail of Items Unit Qnty. Rate in 

Rs. 

UPPER DAM 

1 Diversion tunnel gate 

Gate(Fixed wheel type)including ballast 

(3.3m x 4m)- 1 No. 

146 



Amount 

in Lakh 

Ton 16 60000 9.60 

Embedded Parts - 1 Set Ton 5 50000 2.50 

Ropedrum hoist 55 T Capacity Ton 17 100000 17.00 

Hoist Supporting structure and trestle Ton 11 50000 5.50 

2 Spillway structure 

a) Radial Gates (3m x 6.0m) - 3 Nos. Ton 114 100000 114.00 

Embedded Parts (including anchorages, 

hoist structure) including breast wall 

liners - 3 Set 

Ton 69 50000 34.50 

Hydraulic Hoist 50.0T capacity (One 

power pack + Two 50T cap. hydraulic 

cylinders with provision of 25% 

pushing force) 

Set 3 3500000 105.00 

Portable oil filter unit along with 

Contamination checking kit & Low 

vacuum dehydration and degassification 

unit 

Set 1 500000 5.00 

Portable trolley mounted gasoline 

engine operated power pack 

Set 1 750000 7.50 

b) Bulkhead Gate ( Slide type) 3.0m x 

7.5m - 1 Set 

Ton 18 60000 10.80 


Gantry crane 40 T capacity Set 1 4000000 40.00 

3 Instruments and Remote Control Set 1 7000000 70.00 

4 D G Set 250 KVA Set 1 1250000 12.50 

5 Link Tunnel structure 

a) TrashRacks and Embedded parts (5m 

x14m) - 1 No. 

Ton 25 50000 12.50 

Trash rack cleaning machine Set 1 10000000 100.00 

b) Fixed wheel Gate including ballast 

(3.3m x 3.3m) - 1 No. 

Ton 27 60000 16.20

147 




Rope drum hoist 50T Capacity Ton 17 100000 17.00 

Hoist platform and trestle Ton 11 50000 5.50 

C) Bulkhead Gate (Slide Type) 3.3m Ton 10 60000 6.00 

x3.3m - 1 No. 




LOWER DAM 

6 Diversion tunnel gate 

Gate(Fixed wheel type)including ballast 

(3.3m x 4m)- 1 No. 

Ton 16 60000 9.60 


Ropedrum hoist 55 T Capacity Ton 17 100000 17.00 

Hoist Supporting structure and trestle Ton 11 50000 5.50 

7 Spillway structure 

a) Radial Gates (3m x 6.0m) - 3 Nos. Ton 114 100000 114.00 

Embedded Parts (including anchorages, 

hoist structure) including breast wall 

liners - 3 Set 

Ton 66 50000 33.00 

Hydraulic Hoist 50.0T capacity (One 

power pack + Two 50T cap. hydraulic 

cylinders with provision of 25% 

pushing force) 

Set 3 3500000 105.00 

Portable oil filter unit along with 

Contamination checking kit & Low 

vacuum dehydration and degassification 

unit 

Set 1 500000 5.00 

Portable trolley mounted gasoline 

engine operated power pack 

Set 1 750000 7.50 

b) Bulkhead Gate ( Slide type) 3.0m x 

7.5m - 1 Set 

Ton 18 60000 10.80 


Gantry crane 40 T capacity Set 1 4000000 40.00 

8 Instruments and Remote Control Set 1 7000000 70.00 

9 Optical Fibre cables 3.0km 

(approx.)long for connecting upper 

dam & lower dam control systems. 

Set 1 1000000 10.00 

10 D G Set 250 KVA Set 1 1250000 12.50

11 Link Tunnel structure 

a) Bulkhead Gate (Slide Type) 3.3m 

x3.3m - 1 No. 

148 



Ton 10 60000 6.00 




12 Intake structure 

a) TrashRacks and Embedded parts (5m x 

14m) - 2 No. 

Ton 60 50000 30.00 

Trash rack cleaning machine Set 1 10000000 100.00 

b) Intake gate(fixed wheel type) including 

ballast (3m x 3m) - 2Nos. 

Ton 48 60000 28.80 


Rope drum hoist 50T Cap.-2set Ton 27 100000 27.00 

Hoist platform and trestle-2set Ton 18 50000 9.00 

C) Bulkhead Gate (Slide Type) 3m x3m - 2 Ton 16 60000 9.60 

No. 


Rope drum hoist 15T Cap.-2set Ton 9 100000 9.00 

Hoist platform and trestle-2set Ton 6 50000 3.00 

13 Desilting Chamber Gates 0.00 

Desilting Chamber Gate (Slide Type) 

3.3m x3.3m - 1 No. 

Ton 10 60000 6.00 

Embedded parts - 2 Set Ton 8 50000 4.00 

EOT crane with 20T Cap. Set 1 1500000 15.00 

14 Silt Flushing Gates (Slide Type) 

Gates (Service & Emergency) 1.5m 

x1.5m - 4 Nos. 

Embedded parts (including bonnet, 

bonnet cover,gate body liner etc.)-4Set 

Hydraulic Hoist 130T Cap. (Two 

Double acting cylinder and one power 

pack) 

Ton 10 100000 10.00 

Ton 70 50000 35.00 

Set 2 4800000 96.00 

15 Surge shaft gate 

Gate(Slide Type) 2.5m x4.5m - 1 No. Ton 14 60000 8.40 

Embedded parts - 1 Set Ton 15 50000 7.50 

Rope drum hoist 25T Cap. Ton 8 100000 8.00 

Hoist platform and trestle Ton 5 50000 2.50

16 Tailrace channel gate 

Gate (Fixed Wheel type) 3.3m x 3.3m - 

1 No. 

149 



Ton 4 60000 2.40 


Monorail hoist 10T Cap. Set 1 1000000 10.00 

17 Pressure shaft steel Liner 

Steel Liner - 1 No. (ASTM A 537 Cl. 1 

) 

Bifurcation (ASTM A 517 Gr. F ) - 2 

Nos. 

Ton 2750 70000 1925.00 

Ton 200 77000 154.00 

18 Adit Gates 

Adit gates (2.5m x2.5m) - 3 Nos. Ton 21 60000 12.60 


19 contingency @ 5% for spares air 

vent by pass etc 

Sub Total 3608.30 

5% 180.42 

Total 3788.72

S. 

No. 

DIVERSION TUNNEL 

Description Unit Quantity Rate 

(in 

Rs.) 

150 



Amount 

( Rs. in 

Lakhs) 

1.0 Surface Excavation 

1.1 Common excavation Cum 25,000 125 31.25 

1.2 Rock excavation Cum 5,000 300 15.00 

2.0 Underground excavation Cum 10,000 1000 100.00 

3.0 Rock Support System 

3.1 Rock bolts M 7,000 400 28.00 

3.2 Steel Supports T 50 42000 21.00 

3.3 Shotcreting Cum 700 4000 28.00 

3.4 Concrete lagging (if required) Cum 150 7000 10.50 

4.0 Concrete 

4.1 Cement concrete lining M-20 Cum 2,000 4000 80.00 

4.2 M15 Cum 1,400 2930 41.02 

4.3 M20 Cum 100 3390 3.39 

4.4 M25 Cum 3,000 3610 108.30 

5.0 Reinforcement Steel T 300 27000 81.00 

Sub Total (A) 547.46 

6.0 Miscellaneous and Ancillary 

Works 

6.1 Various Miscellaneous works like 

wire mesh/steel fibre 

reinforcement, drilling & grouting, 

PVC pipes for drainage, slope 

protection works etc.(7% - 8% of 

Sub Total (A) depending upon the 

site conditions & type of structure) 

7.50% 41.06 

Sub Total (B) 588.52 

7.0 Instrumentation (1% of Sub -Total 

(B) 

1% 5.89 

8.0 Dewatering (2% of Sub -Total (B) 2% 11.77 

9.0 Contingencies (3% of Sub -Total 3% 17.66 

(B) 

10.0 Work Charged Establishment(2% 

of Sub -Total (B) 

2% 11.77 

Total 635.60

S. 

No. 

COFFER DAMS 

DESCRIPTION UNIT QTY. RATE(in 

Rs.) 

151 



Amount 

(Rs. in 

Lakhs) 


1.1 Common Excavation Cum 70,000 125 87.50 

2.0 Embankment Construction 

2.1 Earth/rock fill Cum 50000 518 259.00 

2.2 Impervious core Cum 20000 354 70.80 

2.3 Filter Cum 5000 901 45.05 

3.0 Concrete 

3.1 M10 Cum 1,000 2560 25.60 

3.2 Concrete cut-off wall Sqm 3,500 20000 700.00 


4.0 Miscellaneous 

4.1 Various Miscellaneous works 

like, drilling & grouting 

etc.(0.0% - 0.5% of Sub Total 

(A) depending upon the site 

conditions & type of 

structure) 

0.50% 5.94 


5.0 Dewatering 3% of Sub -Total 

(B) 

6.0 Contingencies 3% of Sub - 

Total (B) 

7.0 Work Charged Establishment 

2% of Sub -Total (B) 

3% 35.82 

3% 35.82 

2% 23.88 

Total of 1 to 7 1289.40

S. 

No. 

UPPER CONCRETE DAM 


Rs.) 

152 



Amount 

(Rs. in 

Lakhs) 



1.2 Rock Excavation Cum 30,000 300 90.00 


2.1 Rock bolts M 1,500 400 6.00 

2.2 Shot Crete Cum 500 4000 20.00 

3.0 Concrete 

3.1 M10 Cum 500 2560 12.80 

3.2 M15 Cum 270,000 2930 7911.00 

3.3 M20 Cum 20,000 3390 678.00 

3.4 M25 Cum 5,000 3610 180.50 

4.0 Reinforcement Steel MT 500 27000 135.00 



Works 


like wire mesh/steel fibre 

reinforcement, drilling & 

grouting, PVC pipes, water 

stops, other steel works, slope 

protection works, road works, 

architectural works for dam 

etc.(2% - 3% of Sub Total (A) 

depending upon the site 


structure) 

2.50% 230.52 

Sub Total (B) of 1 to 5 9451.32 

6.0 Instrumentation 1% of Sub - 

Total (B) 

1% 94.51 


(B) 

3% 283.54 

8.0 Contingencies 3% of Sub - 3% 283.54 

Total (B) 



2% 189.03 

Total 10301.94

S. 

No. 

LOWER CONCRETE DAM 


Rs.) 

153 



Amount 

(Rs. in 

Lakhs) 





2.1 Rock bolts M 1,500 400 6.00 

2.2 Shot Crete Cum 500 4000 20.00 

3.0 Concrete 

3.1 M10 Cum 500 2560 12.80 

3.2 M15 Cum 218,000 2930 6387.40 

3.3 M20 Cum 20,000 3390 678.00 

3.4 M25 Cum 5,000 3610 180.50 

4.0 Reinforcement Steel MT 500 27000 135.00 



Works 


like wire mesh/steel fibre 


grouting, PVC pipes, water 

stops, other steel works, slope 

protection works, road works, 

architectural works for dam 




structure) 

2.50% 190.49 



Total (B) 

1% 78.10 


(B) 

3% 234.31 

8.0 Contingencies 3% of Sub - 3% 234.31 

Total (B) 



2% 156.20 

Total 8513.11

S. 

No. 

SPILLWAY (Upper & Lower Dam) 


Rs.) 

154 



Amount 

(Rs. in 

Lakhs) 




2.0 Concrete 

2.1 M10 Cum 2,000 2560 51.20 

2.2 M15 Cum 96,000 2930 2812.80 

2.3 M20 Cum 4,000 3390 135.60 

2.4 M25 Cum 60,000 3610 2166.00 

3.0 Reinforcement Steel T 6,000 27000 1620.00 

4.0 Structural Steel T 300 42000 126.00 

Sub Total (A) of 1 to 4 7004.10 


Works 


like drilling & grouting, PVC 

pipes, water stops, other steel 

works, slope protection works, 

bridge etc.(1% - 2% of Sub 

Total (A) depending upon the 

site conditions & type of 

structure) 

1.50% 105.06 



Total (B) 


(B) 

8.0 Contingencies 3% of Sub -Total 

(B) 



1% 71.09 

2% 142.18 

3% 213.27 

2% 142.18 

Total 7677.89

155 



J -POWER PLANT APPURTENANCES (CIVIL WORKS) 

S. Description Amount (Rs. in Lakhs) 

NO. Civil HM Total 

1 POWER INTAKE STRUCTURE 720.97 236.67 957.64 

2 

DESILTING CHAMBERS 

(INCLUDING S.F.T.) 680.40 

174.30 854.70 

3 ADITS 1403.17 18.48 1421.65 

4 

HEAD RACE, LINK TUNNEL 

AND TAIL RACE TUNNEL 

6314.91 209.58 6524.49 

5 SURGE SHAFT 742.57 27.72 770.29 

6 

PRESSURE SHAFTS AND 

PENSTOCKS 778.25 

2182.95 2961.20 

7 POWER HOUSE COMPLEX 7491.99 7491.99 

8 SWITCHYARD 368.49 368.49 

Total 18500.76 2849.70 21350.46 

Add works tax @ 2% 370.02 56.99 427.01 

GRAND TOTAL 18870.77 2906.69 21777.47

S. 

No. 

POWER INTAKE STRUCTURE 

156 




Rs.) 

Amount 

(Rs. in 

Lakhs) 





3.0 Supports System 

3.1 Rock bolts M 1,500 400 6.00 

3.2 Steel ribs Support T 25 42000 10.50 


3.4 Concrete Lagging if required Cum 100 7000 7.00 

4.0 Concrete 

4.1 M15 Cum 1,000 2930 29.30 

4.2 M25 Cum 8,000 3610 288.80 



Works 


drilling & grouting, 

wiremeshreinforcement, slope 

protection works, other steel works, 


depending upon the site conditions & 

type of structure) 


1.50% 9.96 


7.0 Instrumentation 1% of Sub -Total (B) 1% 6.74 

8.0 Dewatering 1% of Sub -Total (B) 1% 6.74 

9.0 Contingencies 3% of Sub -Total (B) 3% 20.21 

10.0 Work Charged Establishment 2% of 

Sub -Total (B) 

2% 13.48 

Total 720.97

S. 

No. 

DESILTING CHAMBERS (INCLUDING S.F.T.) 


Rs.) 

157 



Amount 

(Rs. in 

Lakhs) 






3.1 Rock bolts M 11,000 400 44.00 



3.4 Concrete Lagging Cum 225 7000 15.75 

4.0 Concrete 

4.1 M15 Cum 3,000 2930 87.90 

4.2 M25 Cum 3,000 3610 108.30 




Works 


like wiremesh/steel 


grouting works, etc.(3% - 4% 

of Sub Total (A) depending 

upon the site conditions & type 

of structure) 

3.50% 21.30 


7.0 Instrumentation (1% of Sub - 

Total (B) 

1% 6.30 

8.0 Dewatering (2% of Sub -Total 2% 12.60 

(B) 

9.0 Contingencies (3% of Sub - 

Total (B) except on L.S. items) 

10.0 Work Charged 

Establishment(2% of Sub -Total 

(B) except on L.S. items) 

3% 18.90 

2% 12.60 

Total 680.40

S. 

No. 

ADITS 

DESCRIPTION UNIT QTY. RATE 

(in 

Rs.) 

158 



Amount 

(Rs. in 

Lakhs) 




2.0 Underground excavation 

2.1 Excavation of adits Cum 50,000 1000 500.00 


3.1 Rock bolts M 30,000 400 120.00 


3.3 Shotcreting Cum 2,600 4000 104.00 

3.4 Concrete lagging if required Cum 800 7000 56.00 

4.0 Concrete 


4.2 M10 Cum 500 2560 12.80 

4.3 M15 Cum 7,000 2930 205.10 

4.4 M20 Cum 1,000 3390 33.90 




Works 


wiremesh/steel reinforcement, 

drilling & grouting, PVC pipes 

for drainage etc.(3% -4% of Sub 

Total (A) depending upon the site 

conditions & type of structure) 

3.50% 43.94 



Total (B) 

1% 12.99 


(B) 

9.0 Contingencies (3% of Sub -Total 



of Sub -Total (B) except on L.S. 

items) 

3% 38.98 

2% 25.98 

Total 1403.17

S. 

No. 

HEAD RACE, LINK TUNNEL AND TAIL RACE TUNNEL 


(in 

Rs.) 

159 



Amount 

(Rs. in 

Lakhs) 






3.1 Rock bolts M 90,000 400 360.00 



3.4 Concrete lagging Cum 6,000 7000 420.00 

4.0 Concrete 


4.2 M15 Cum 22,000 2930 644.60 

4.3 M25 Cum 6,000 3610 216.60 




Works 


wiremesh/steel reinforcement, 

drilling & grouting, PVC pipes 

for drainage etc.(7% - 8% of Sub 

Total (A) depending upon the site 


7.50% 407.94 



Total (B) 

1% 58.47 




3% 175.41 



items) 

2% 116.94 

Total 6314.91

S. 

No. 

SURGE SHAFT 


(in 

Rs.) 

160 



Amount 

(Rs. in 

Lakhs) 


1.1 Common Excavation Cum 50000 125 62.50 

1.2 Rock excavation Cum 10000 300 30.00 

2.0 Underground excavation 

2.1 Surge shaft excavation Cum 10000 1,200 120.00 

2.2 Surge shaft excavation with raise Cum 200 1,500 3.00 

borer 

2.3 Concrete Lagging if required Cum 100 7,000 7.00 

3.0 Support System 

3.1 Rock bolts M 25000 400 100.00 

3.2 Steel ribs Support T 50 42,000 21.00 

3.3 Shotcreting Cum 1000 4,000 40.00 

4.0 Concrete 

4.1 M-20 Cum 3500 3,390 118.65 

4.2 M-25 Cum 2500 3,610 90.25 

5.0 Steel Works 

5.1 Deformed Reinforcement Steel T 250 27,000 67.50 

5.2 Steel liner T 25 70,000 17.50 




drilling & grouting,wiremesh 

reinforcement, airvent pipe, lift 

arrangement, other steel works etc.(1- 

2% of Sub Total (A) depending upon 

the site conditions & type of 

structure) 

1.50% 10.16 


7.0 Instrumentation (1% of Sub -Total 

(B) 

1% 6.88 


9.0 Contingencies (3% of Sub -Total (B) 

except on L.S. items) 

10.0 Work Charged Establishment(2% of 

Sub -Total (B) except on L.S. items) 

3% 20.63 

2% 13.75 

Total 742.57

S. 

No. 

PRESSURE SHAFTS AND PENSTOCKS 


(in 

Rs.) 

161 



Amount 

(Rs. in 

Lakhs) 

1.0 Underground excavation Cum 17500 1200 210.00 


2.1 Rock bolts M 12,500 400 50.00 



3.0 Concrete 

3.1 M15 backfill concrete Cum 12,000 2930 351.60 



works 


like drilling & 

grouting,wiremesh 

reinforcement, swellex anchors 

etc.(2-3% of Sub Total (A) 



2.50% 17.74 



Total (B) 

1% 7.27 


(B) 

7.0 Contingencies (3% of Sub - 

Total (B) except on L.S. items) 

8.0 Work Charged 

Establishment(2% of Sub -Total 


3% 21.82 

2% 14.55 

Total 778.25

S. 

No. 

POWER HOUSE COMPLEX 

162 




(in 

Rs.) 

1.0 Under Ground Excavation 

1.1 Excavation of PH cavern, transformer 

cum MIV cavern and draft tube gate 

Amount 

(Rs. in 

Lakhs) 

Cum 160,000 1000 1600.00 


2.1 Rock bolts M 70,000 400 280.00 



3.0 Concrete 

3.1 M15 backfill concrete Cum 5,000 2930 146.50 

3.2 Concrete lining M20 Cum 2,000 3390 67.80 

3.3 M25 Cum 60,000 3610 2166.00 

4.0 Reinforcement steel T 7,000 27000 1890.00 

5.0 Structural Steel for roof trusses T 300 42000 126.00 

6.0 Masonry 

6.1 Stone Cum 1500 2000 30.00 

6.2 Brick Cum 500 2000 10.00 



7.1 Various Miscellaneous works like site 

clearance, drilling & 

grouting,wiremesh/steel reinforcement, 

flooring, water fpoffing system, 

swellex anchor, doors, window, 

painting, lift arrangement, architectural 

works , other metal works etc.(4-5% of 

Sub Total (A) depending upon the site 

4.50% 298.72 



8.0 Instrumentation (1% of Sub -Total (B) 1% 69.370235 


10.0 Contingencies (3% of Sub -Total (B) 

except on L.S. items) 

3% 208.110705 

11.0 Work Charged Establishment(2% of 

Sub -Total (B) except on L.S. items) 

2% 138.74047 

Total 7491.99

S. 

No. 

SWITCHYARD 


(in 

Rs.) 

163 



Amount 

(Rs. in 

Lakhs) 





2.1 Rock bolts M 1,000 400 4.00 


3.0 Earthwork in filling Cum 25,000 342 85.50 

4.0 Concrete 

4.1 M15 Cum 1,000 2930 29.30 

4.2 M20 Cum 1,000 3390 33.90 

4.2 M25 Cum 1,000 3610 36.10 

5.0 Deformed Reinforcement Steel T 100 27000 27.00 

6.0 Stone/Brick Masonry Cum 300 2000 6.00 




site clearance, PVC pipes, control 

block building works like flooring, 

doors, windowsets including water 

supply and sewerage, boulder 

pitching, metal works, etc.(4-5% of 

Sub Total (A) depending upon the 

site conditions & type of structure) 

4.50% 14.83 





3% 10.3313925 



items) 

2% 6.887595 

Total 368.49

Sl 

No 

1.0 Residential Buildings 

K-BUILDINGS 

Description Plinth 

Area(Sqm). 

164 



Rs. In lakhs 

Rate Unit Amount 

1.1 Residential permanent buildings 4134 0.075 Sqm 310.05 

Service Charges @31% 

1.2 Residential temporary buildings 

96.12 

4514 0.065 Sqm 293.41 

Service Charges @27% 

79.22 

Total (Residential) 8648 778.80 

2.0 Non-Residential Buildings 

2.1 Non residential permanent 

buildings 

4540 0.065 Sqm 295.10 

Service Charges @22.5% 66.40 

2.2 Non residential and other 

purposes temporary buildings 

(Sl No. 1,3&4) 

5090 0.055 Sqm 279.95 

Service Charges @20.5% 57.39 

Total( Non-Residential) 9630 698.84 

Total(1+2) 18278 1477.63 

Add works tax @ 2% 2% 29.55 

Total 1507.19

Sl No 

Description 

1 CAPITAL COST 

1.1 Purchase of Diesel Generator 

Sets (25 KVA) including 

anciliary equipments etc. 

1.2 Cost of transmission line for 

construction power 

1.2 Water Supply, purification & 

distribution arrangements 

including purchase of water 

tankers,filters, cost of tanks & 

chlorination. 

1.4 Providing sewage disposal 

and storm water drains in 

office and residential 

1.5 

complexes. 

Providing & fixing of fire 

fighting equipments. 

1.6 Providing telephone, 

Telegraph office, Post office 

and Wireless equipments. 

1.7 Providing hospital 

equipments. 

1.8 Construction of children park 

and welfare centres for 

officials and labourers. 

1.9 Furnishing and equipping of 

rest houses and field hostels 

of officers and staff. 

1.1 Purchase of furniture and 

other articles for labour 

welfare centres and clubs and 

schools. 

1.11 Purchase of equipment for 

quality control/field 

Laboratories 

165 



O-MISCELLANEOUS 

Rs. In lakhs 

Quantity Rate Unit Amount 

5.00 2.50 Nos 12.50 

10.00 10.00 km 100.00 

LS 25.00 

LS 25.00 

LS 15.00 

LS 20.00 

LS 15.00 

LS 8.00 

LS 5.00 

LS 5.00 

LS 15.00 

Sub Total Item 1 245.50 

2.0 MAINTENANCE & 

SERVICE CHARGES OF 

2.1 R&M of Diesel Generator sets 

4 Nos. for four years. 

16.00 4.00 Nos 64.00

R&M of Transmission line for 

four years. 

2.2 R&M of water supply 

facilities to the staff and 

labour colonies for four years 

2.3 R&M of sanitation and 

drainage facilities for office 

and residential compllex and 

labour colonies. 

2.4 R&M of fire fighting 

2.5 

equipments. 

Maint. Of telecommunication 

system and post offices. 

166 



10.00 4.00 km 40.00 

LS 10.00 

LS 8.00 

LS 4.00 

LS 20.00 

2,6 R&M of hospitals. LS 16.00 

2.7 Maint. of parks and welfare 

centres, clubs and school. 

LS 10.00 

2.8 R&M of Rest houses and field 

hostels. 

2.9 R&M of research & quality 

control laboratories 

2.1 Labour welfare compensation 

and retrenchment benefits. 

LS 8.00 

LS 8.00 

LS 30.00 

2.11 Providing Security & Policing LS 10.00 

2.12 R&M of Inspection vehicles 

and staff cars (25 nos) for four 

year 

25*4 2.50 year 250.00 

2.13 R&M of school buses, 4*4 1.80 year 28.80 

Ambulance Car etc. (4 nos) 

for for four year 


3 MISCELLANEOUS 

3.1 Foundation stone laying 

LS 10.00 

ceremony, inaguration and 

3.2 

visit of Dignitaries. 

Railway siding LS 20.00 

3.3 Installation and maintenance 

of Petrol/Diesel Pumps 

LS 16.00 

3.4 Providing 

measures 

anti malarial 

LS 2.00 

3.5 Procurement 

leterature. 

of technical 

LS 2.00 

3.6 Model Exhibits LS 4.00 

3.7 Canteen facilities and cooperative 

stores. 

LS 20.00

3.8 Photographic and 

Cinemagraphic equipment 

and their maintenance 

167 



LS 8.00 

3.9 Group insurance LS 15.00 

3.1 Publication and pamplets LS 2.00 

3.11 Creches LS 2.00 

3.12 Compensation for accident LS 8.00 

3.13 Training of personnels aboard 

includig study course and visit 

LS 15.00 

3.14 Award to workers LS 1.5 


Grand Total Item (1+2+3) 877.80

SI 

NO. 

R - COMMUNUCATION 

168 



Rs. In lakhs 

Description Quantity Rate Unit Amount 

1 Proposed new roads 

Approach road to Lower dam site, 

DT, Top of Dam 

Approach road to Upper dam site, 

DT, Top of Dam 

15.0 80.00 Km 1200.00 

6.0 80.00 Km 480.00 

Approach road to power house site 2.0 80.00 Km 160.00 

Switch yard 1.0 80.00 Km 80.00 

Surgeshaft,Adit I,II,III 9.0 80.00 Km 720.00 

Colony Roads 2.0 75.00 Km 150.00 

3 Proposed new bailey bridges Cl 30 

At Upper dam site 30.0 2.25 m 67.50 

At Upper dam site 30.0 2.25 m 67.50 

On Pokhram Chu (2 no) 40.0 2.25 m 90.00 

On Rangyong Chu 20.0 2.25 m 45.00 

4 Proposed Culverts 

Culverts( 4nos) 40.0 1.00 m 40.00 

Grand Total 3100.00 

Add works tax @ 2% 2% 62.00 

Total 3162.00

Q-Spl T&P for Infrastructure Development 

S.No. Description of equipment Quantity 

(Nos.) 

169 



Cost 

(Rs in 

Lacs) 

Total 

Cost (Rs 

in Lacs) 

1 Hydraulic Excavator, 1.0 cum. 1 50.00 50.00 

2 Loader cum Excavator, 1.0/0.25 

cum. 

1 18.00 18.00 

3 Mini excavator 0.3 cum 1 25.00 25.00 

4 Multi utility (Skid Steer loader) 1 40.00 40.00 

5 Front End loader 2 cum 1 24.00 24.00 

6 Crawler Dozer, 100 FHP 2 50.00 100.00 

7 Crawler Dozer, 200 FHP 1 85.00 85.00 

8 Wheel Dozer, 130 FHP 1 95.00 95.00 

9 Motor Grader, 145 FHP 1 60.00 60.00 

10 Diamond Core Drill (Mechanical) 2 15.00 30.00 

11 Diamond Core Drill (Hyd) 1 60.00 60.00 

12 Air Track/Wagon Drill 2 15.00 30.00 

13 Jack Hammer/Pavement Breaker 5 0.35 1.75 

14 Compressed Air(cfm) 2000 0.0125 25.00 

15 Mobile Crane, 10 t Pick & Carry 2 10.00 20.00 

16 Mobile Crane, 20 t (rough Terrain) 1 70.00 70.00 

17 Road Roller, 8/10 t 1 10.00 10.00 

18 Dewatering Pump L.S 10.00 10.00 

19 Tipper 4.5/6.0 cum. 10 9.50 95.00 

20 Truck, 8/10 t 4 7.50 30.00 

21 Low Bed Tractor Trailor, 20 t 1 30.00 30.00 

22 Concrete Mixer, 14/10 cft 2 1.50 3.00 

23 Explosive Van, 5/7 t 1 10.00 10.00 

24 Water Tanker/Sprinkler, 10 KL 1 12.00 12.00 

25 Petrol/Diesel Tanker, 10 KL 1 12.00 12.00 

26 Bus/Mini Bus 5 8.00 40.00 

27 Car/MUV 2 4.00 8.00 

28 Jeep (Petrol/Diesel) 20 4.00 80.00 

29 Ambulance 2 8.00 16.00 

30 Workshop Equipt. L.S 20.00 20.00 

31 Fire Tender 1 15.00 15.00 

32 Recovery Van 1 5.00 5.00 

33 Pick up Van/L.C.V 2 5.00 10.00 

34 Motor Boat 2 5.00 10.00 

Total 1149.75

170 



DISTRIBUTION OF COST UNDER HEAD Q - SPECIAL T & P AND V - 

RECEIPT & RECOVERIES 

Cost of equipments excluding inspection 

vehicles 

(Rs. In lakhs) 

Cost Q R&R 

990.75 247.69 185.77 

Cost of inspection vehicles 159.00 159.00 31.80 

Provision under head Q - Spl. T&P 1149.75 406.69 

Recoveries to be shown under V- Receipt and 

Recoveries 

217.57

V - RECEIPT & RECOVERIES 

171 



S. No. Item Amount 

(Rs. In Lakhs) 

1. Recovery from the Sale of Equipments 217.57 

2 Recovery from the DG sets 2.50 

3 Recovery from Temporary Buildings 106.50 

Total 326.56

COST ESTIMATE OF E&M WORKS 

Generator, Turbine and Accessories 

S.No. Item Particulars Qty Unit Rate Amount Excise 

Duty* 

172 



Annex-I (page 1 of 2) 

Total 

(Rs % Amou (Rs 

Lakh) 

nt Lakh) 

1 2 3 3(a) 4 5 6 7 5+7 

1 (a) Generating units and 

Bus Ducts 3 X 47 MW, 

500 rpm, Head 723.18 

meters 

2 Step up transformer 

11/220 KV, 20MVA, 

single phase bank 

3 Auxiliary Electrical 

Equipment for Power 

Stations (Except 

Transformer) (5% of 

item 1) 

3 no. 3500 

Rs/KW 

10 no. 250 

Rs/KVA 

4 Auxiliary Equipment & 

Services for Power 

stations (5% of Item 1) 

5 Switchyard (220KV) 6 bays 120 

6 Spares (5% of item 1 

and 3% of item 2 to 5 ) 

4935.00 16 789.60 5724.60 

500 16 80 580 

246.75 16 39.48 286.23 

246.75 16 39.48 286.23 

720.00 16 115.20 835.20 

247 

lacs/bay 

51.41 298.16 16 47.70 345.86 

7 Subtotal(1-6) 8058.12 

8 Central Sales tax** 4% 

of item 7 

9 Transportation & 

Insurance 6% of item 7 

10 Erection & 

commissioning 8% of 

item 7 except spares 

277.87 322.32 

483.49 

616.98 

11 Subtotal (7-10) 9480.91 

12 

13 

14 

15 

16 

17 

Total of FC (XLPE 

Cable and Termination 

kit) in INR (As per 

Annexure-II) 

Custom Duty @22% of 

item 12 

Marine frieght and 

insurance @6% Approx 

of 12 

Inland Frieght and 

insurance 6% of item 12 

Erection & 


item 12 excluding spares 

Subtotal of FC ( item 

12-16 in INR) 

included in above item 12 

826.73 

49.60 

49.60 

65.12 

991.06

18 

Subtotal of item no 

11+17(Foreign plus 

indian component) 

19 Establishment, 

Contingency, other 

charges 11% of Item 18 

Excluding duties 

GRAND TOTAL (In 

Lakh) 

S.No. 

173 



10471.98 

838.70 

11310.67 

Annex-II 

Dec 2003 price level 

Item Particulars Qty Rate Amount 

Custom 

Duty* 

Amou 

nt( 

Total 

( Lakh 

Lakh (Lakh 

( USD) USD) Rate% USD) USD) 

1 

2 3 4 5 6 7 5+7 

2 

XLPE Cable (220 kV) 2750 m 

280 

USD/m 7.70 22 1.69 9.39 

3 

XLPE Cable termination 

Kit 20 no. 35000 7.00 22 1.54 8.54 

4 

Spares for above @ 3% 

of 2 0.23 22 0.05 0.28 

Total 18.21 

*Custom duty in case of imported Items 

**Not applicable for Imported Items 

1 USD conversion rate as on 23/12/03= Rs. 45.400

S.No. Item Particulars Qty Un 

it 

Power Evacuation system 

Rate Amount E xcise 

Duty* 

(Rs 

Lakh) 

174 

(Rs 

Lakh) 



Annex-III (page 1 of 1) 

Rate Amou 

nt 

Total 

(Rs 

Lakh) 

1 2 3 4 5 6 7 5+7 

1 1 no 220kV Double 

Circuit line (of 

approximately 30 kms) 

30 km 30 

lacs/km 

900.00 16 144.00 1044.00 

2 Spares ( 3% of 1) 27 16 4.32 31.32 

3 Subtotal(1) 1075.32 

4 Central Sales tax 4% of 

item 3 

5 Transportation & 

Insurance 6% of item 3 

7 Erection & 


item 3 except spares 

37.08 43.01 

64.52 

83.52 

8 Subtotal(2) 1266.37 

9 Establishment, 

Contingency, other 

charges 11% of Item 3 

excluding duties 

GRAND TOTAL (In 

Lakh) 

101.97 

1368.34



CHAPTER – XIII 

ECONOMIC EVALUATION

13.1 GENERAL 

CHAPTER – XIII 

ECONOMIC EVALUATION 

175 



The Project has been contemplated as a run-off the river scheme on river Rangyong 

Chu. The project is estimated to cost Rs. 799.50 crores excluding IDC at June 2003 

Price Level. Sale price of energy generated at powerhouse bus bars has been worked 

out as 3.07 Rs. per unit with free power to home state (Table 13.2) & Rs. 2.70 per unit 

without free power to home state (Table 13.2-A). 

13.2 ECONOMIC JUSTIFICATION 

The energy generation of the project with an installed capacity of 3X47 MW has been 

estimated at 639.52 MU in a 90% dependable year. 

13.3 COST ESTIMATES AND PHASING OF EXPENDITURES 

The cost of construction of the project has been estimated at June 2003 price level with a 

construction schedule of 5.5 years including 1.5 years for Infrastructure works. 

The estimated Present Day Cost of the project is Rs. 799.50 Crores without IDC at June 

2003 Price level. 

13.4 PHASING OF EXPENDITURE 

The phasing of expenditure has been worked out on the basis of anticipated construction 

programme.

176 



The phasing of expenditure without IDC for present day cost is shown as below: 

Year Estimated Cost at June 2003 P.L. 

(Rs. in Crores) 

1 st 79.95 

2 nd 111.93 

3 rd 

159.90 

4 th 223.86 

5 th 159.90 

5.5 th 63.96 

Net Cost 799.50 

13.5 INTEREST DURING CONSTRUCTION (IDC) 

Based upon above phasing of expenditure the interest during construction (IDC) have 

been calculated with 70:30 debt equity ratio and 10.0% interest on loan for estimated 

Present Day cost of the project. 

The estimated IDC with estimated present cost is Rs. 91.32 Crores 

13.6 COST OF ENERGY GENERATION 

The cost of energy generation has been calculated for the annual energy generation in a 

90% dependable year based upon following assumptions. 

1. Debt-equity ratio 70 : 30 

2. Annual interest rate on loan 10.0% 

3. Return on equity 16% 

4. Annual interest rate on working capital 10.0% 

5. O&M Charges 1.5% of Project Cost 

6. Free power to Home State 12% of the energy 

available after losses

177 



7. Depreciation considered 1/12 th of loan amount 

during loan repayment 

period. 

The levellised tariff of the Project at present day cost works out to be Rs. 2.49 Per Unit 

with free power to home state (Table 13.3) & Rs 2.19 per unit without free power to 

home state. (Table 13.3-A).

178 


Rangyong HE Project (3 x 47MW) 

STATEMENT SHOWING IDC CALCULATION AT PRESENT DAY COST (APRIL 2003 LEVEL) 

Table-13.1 

PRESENT DAY COST 799.50 Crs. Transmission Works 13.68 Crores 

Civil Works 672.71 Crs. Electrical Works 113.11 Crs. 

INTEREST RATE PER ANNUM 10% Transmission cost 13.68 Crs. 

(Rs. in Crs.) 

Present Day Amount Receivable I.D.C Loan Outstanding Amount Receivable 

Year Cost Equity Loan at the end of Equity Loan 

year (for the year) 

1 2 3 4 5 6 7 8 

1 79.95 79.95 79.95 

2 111.93 111.93 111.93 

3 159.90 75.37 84.53 2.23 86.77 75.37 86.77 

4 223.86 223.86 19.87 330.50 243.73 

5 159.90 159.90 41.05 531.45 200.95 

5.5 63.96 63.96 28.17 623.58 92.13 

Total 799.50 267.25 532.26 91.32 267.25 623.58 

IDC 91.32 Crs. Equity 267.25 Crs. 

Net cost of the project 890.82 Crs. Loan 623.58 Crs.

179 



TABLE-13.2 

UNIT COST OF ENERGY AT BUS BAR AT CURRENT PRICE LEVEL 

(June 2003 P.L.) 

(Based on 16% return on equity & 10% interest on loan, 10% interest on working capital) 

1 Installed capacity 141 MW 

2 Cost of the Project (Net) Rs. 799.50 Crores 

3 Interest During Construction Rs. 91.32 Crores 

4 Total Cost of Project Rs. 890.82 Crores 

(Including IDC) 

a) Equity 30% Rs. 267.25 Crores 

b) Loan 70% Rs. 623.58 Crores 

5 Annual Energy Generation 639.52 MU 

6 0.7% As Auxiliary Consumption of No. 5 0.70% 4.48 MU 

7 Energy Available After Auxiliary Consumption 635.04 MU 

8 0.5% As Transformer Loss of No. 7 0.50% 3.18 MU 

9 Energy Available After Transformer Loss 631.87 MU 

10 Free Power to Home State 12% 75.82 MU 

11 

Energy Available After Allowing Free 

Power 556.04 MU 

12 Fixed and Running Charges 

A) Capacity Charges 

a) Interest on Loan 10.00% 59.76 Crores 

b) Depreciation Charges 

(Limited to 1/12 th of Loan Amount) 

51.96 Crores 

SUB- 

TOTAL 111.72 Crores 

B) Energy Charges 

a) O&M Charges 1.50% 13.36 Crores 

b) Return on Equity 16.00% 42.76 Crores 

SUB-TOTAL 56.12 Crores 

c) Interest on Working Capital 10.00% 2.96 Crores 

I) O&M Charges for 1 month 1.11 

II) 2 Months Average Billing 28.47 

TOTAL Rs. 170.80 Crores 

13 Sale Price at Bus Bar/Unit 3.07 Rs. 

14 Cost of Generation at Bus Bar/Unit 2.03 Rs. 

(Without Allowing Free Power to Home State and Return on Equity) 

Note : This unit rate is excluding water cess, income tax incentive, penalties etc.

180 



TABLE-13.2 A 

UNIT COST OF ENERGY AT BUS BAR AT CURRENT PRICE LEVEL 

(June 2003 P.L.)WITHOUT FREE POWER TO HOME STATE 

(Based on 16% return on equity & 10% interest on loan, 10% interest on working capital) 

1 Installed capacity 141 MW 

2 Cost of the Project (Net) Rs. 799.50 Crores 

3 Interest During Construction Rs. 91.32 Crores 

4 Total Cost of Project Rs. 890.82 Crores 

(Including IDC) 

a) Equity 30% Rs. 267.25 Crores 

b) Loan 70% Rs. 623.58 Crores 

5 Annual Energy Generation 639.52 MU 

6 0.7% As Auxiliary Consumption of No. 5 0.70% 4.48 MU 

7 Energy Available After Auxiliary Consumption 635.04 MU 

8 0.5% As Transformer Loss of No. 7 0.50% 3.18 MU 

9 Energy Available After Transformer Loss 631.87 MU 

10 Free Power to Home State 0% 0.00 MU 

11 

Energy Available After Allowing Free 

Power 631.87 MU 

12 Fixed and Running Charges 

A) Capacity Charges 

a) Interest on Loan 10.00% 59.76 Crores 

b) Depreciation Charges 

(Limited to 1/12 th of Loan Amount) 

51.96 Crores 

SUB- 

TOTAL 111.72 Crores 

B) Energy Charges 

a) O&M Charges 1.50% 13.36 Crores 

b) Return on Equity 16.00% 42.76 Crores 

SUB-TOTAL 56.12 Crores 

c) Interest on Working Capital 10.00% 2.96 Crores 

I) O&M Charges for 1 month 1.11 

II) 2 Months Average Billing 28.47 

TOTAL Rs. 170.80 Crores 

13 Sale Price at Bus Bar/Unit 2.70 Rs. 

14 Cost of Generation at Bus Bar/Unit 2.03 Rs. 

(Without Allowing Free Power to Home State and Return on Equity) 

Note : This unit rate is excluding water cess, income tax incentive, penalties etc.

181 



Table 13.3 

CALCULATION OF ENERGY RATE WITH PRESENT COST (JUNE 2003 PRICE LEVEL) AS PER TARIFF NOTIFICATION 

Annual Generation in a 90% dependable 639.52 MU O&M Charges 1.50% 

Annual Generation after allowing losses & free Rate of increase of O&M Charges after 1st Year (Compounded) 6% 

power to home state in a 90% dependable year 556.04 MU Interest rate on Loan 10.0% 

Total cost including IDC Rs. 890.82 Crores Interest rate on Working Capital 10.00% 

Equity 30% Rs. 267.25 Crores Return on Equity 16% 

Loan 70% Rs. 623.58 Crores Discounting rate 12% 

Year Capacity Charges Charges Per Unit Discounting Discounted 

Out- (Rs.in Cr.) (Rs.in Cr.) (Rs. per Unit) Factor Tariff 

standing 

Loan 

(Rs.in Cr.) 

Interest on 

loan 

Depre- 

ciation 

Total Return on 

equity 

O&M 

Charges 

O&M 

for1 

month 

Interest on 

Working 

Capital 

Interest Total Capacity 

charges 

Energy 

charges 

Total (Paisa per 

Unit) 

2 months 

Average 

Billing 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 

1 623.58 59.76 51.96 111.72 42.76 13.36 1.11 28.47 2.96 59.08 2.01 1.06 3.07 1.0000 3.07 

2 571.61 54.56 51.96 106.53 42.76 14.16 1.18 27.72 2.89 59.81 1.92 1.08 2.99 0.8929 2.67 

3 519.65 49.37 51.96 101.33 42.76 15.01 1.25 26.99 2.82 60.60 1.82 1.09 2.91 0.7972 2.32 

4 467.68 44.17 51.96 96.13 42.76 15.91 1.33 26.26 2.76 61.43 1.73 1.10 2.83 0.7118 2.02 

5 415.72 38.97 51.96 90.94 42.76 16.87 1.41 25.54 2.69 62.32 1.64 1.12 2.76 0.6355 1.75 

6 363.75 33.78 51.96 85.74 42.76 17.88 1.49 24.84 2.63 63.27 1.54 1.14 2.68 0.5674 1.52 

7 311.79 28.58 51.96 80.55 42.76 18.95 1.58 24.14 2.57 64.29 1.45 1.16 2.60 0.5066 1.32 

8 259.82 23.38 51.96 75.35 42.76 20.09 1.67 23.45 2.51 65.36 1.36 1.18 2.53 0.4523 1.14 

9 207.86 18.19 51.96 70.15 42.76 21.30 1.77 22.78 2.46 66.51 1.26 1.20 2.46 0.4039 0.99 

10 155.89 12.99 51.96 64.96 42.76 22.58 1.88 22.12 2.40 67.73 1.17 1.22 2.39 0.3606 0.86 

11 103.93 7.79 51.96 59.76 42.76 23.93 1.99 21.47 2.35 69.04 1.07 1.24 2.32 0.3220 0.75 

12 51.96 2.60 51.96 54.56 42.76 25.37 2.11 20.83 2.29 70.42 0.98 1.27 2.25 0.2875 0.65 

13 0.00 0.00 7.75 7.75 42.76 26.89 2.24 13.16 1.54 71.19 0.14 1.28 1.42 0.2567 0.36 

14 0.00 0.00 7.75 7.75 42.76 28.50 2.38 13.43 1.58 72.84 0.14 1.31 1.45 0.2292 0.33 

15 0.00 0.00 7.75 7.75 42.76 30.21 2.52 13.72 1.62 74.59 0.14 1.34 1.48 0.2046 0.30 

16 0.00 0.00 7.75 7.75 42.76 32.02 2.67 14.03 1.67 76.45 0.14 1.37 1.51 0.1827 0.28 

17 0.00 0.00 7.75 7.75 42.76 33.95 2.83 14.36 1.72 78.42 0.14 1.41 1.55 0.1631 0.25 

18 0.00 0.00 7.75 7.75 42.76 35.98 3.00 14.71 1.77 80.51 0.14 1.45 1.59 0.1456 0.23 

19 0.00 0.00 7.75 7.75 42.76 38.14 3.18 15.08 1.83 82.73 0.14 1.49 1.63 0.1300 0.21 

20 0.00 0.00 7.75 7.75 42.76 40.43 3.37 15.47 1.88 85.07 0.14 1.53 1.67 0.1161 0.19 

21 0.00 0.00 7.75 7.75 42.76 42.85 3.57 15.88 1.95 87.56 0.14 1.57 1.71 0.1037 0.18 

22 0.00 0.00 7.75 7.75 42.76 45.43 3.79 16.32 2.01 90.20 0.14 1.62 1.76 0.0926 0.16 

23 0.00 0.00 7.75 7.75 42.76 48.15 4.01 16.79 2.08 92.99 0.14 1.67 1.81 0.0826 0.15 

24 0.00 0.00 7.75 7.75 42.76 51.04 4.25 17.28 2.15 95.95 0.14 1.73 1.86 0.0738 0.14 

25 0.00 0.00 7.75 7.75 42.76 54.10 4.51 17.81 2.23 99.09 0.14 1.78 1.92 0.0659 0.13 

26 0.00 0.00 7.75 7.75 42.76 57.35 4.78 18.36 2.31 102.42 0.14 1.84 1.98 0.0588 0.12 

27 0.00 0.00 7.75 7.75 42.76 60.79 5.07 18.95 2.40 105.95 0.14 1.91 2.04 0.0525 0.11 

28 0.00 0.00 7.75 7.75 42.76 64.44 5.37 19.57 2.49 109.69 0.14 1.97 2.11 0.0469 0.10 

29 0.00 0.00 7.75 7.75 42.76 68.30 5.69 20.23 2.59 113.66 0.14 2.04 2.18 0.0419 0.09 

30 0.00 0.00 7.75 7.75 42.76 72.40 6.03 20.93 2.70 117.86 0.14 2.12 2.26 0.0374 0.08 

31 0.00 0.00 7.75 7.75 42.76 76.75 6.40 21.68 2.81 122.31 0.14 2.20 2.34 0.0334 0.08 

32 0.00 0.00 7.75 7.75 42.76 81.35 6.78 22.46 2.92 127.04 0.14 2.28 2.42 0.0298 0.07 

33 0.00 0.00 7.75 7.75 42.76 86.23 7.19 23.30 3.05 132.04 0.14 2.37 2.51 0.0266 0.07 

34 0.00 0.00 7.75 7.75 42.76 91.41 7.62 24.18 3.18 137.35 0.14 2.47 2.61 0.0238 0.06 

35 0.00 0.00 7.75 7.75 42.76 96.89 8.07 25.12 3.32 142.97 0.14 2.57 2.71 0.0212 0.06 

TOTAL 9.1566 22.82 

(A) (B) 

Note: The charges per unit is exclusive of water cess, spares, incentive & Income Tax etc. Levellised Tariff =(B)/(A) 2.49

CALCULATION OF ENERGY RATE WITH PRESENT COST (JUNE 2003 PRICE LEVEL) AS PER TARIFF NOTIFICATION 

182 



Table 13.3A 

WITHOUT FREE POWER TO HOME STATE 

Annual Generation in a 90% dependable year 639.52 MU O&M Charges 1.50% 

Annual Generation after allowing losses Rate of increase of O&M Charges after 1st Year (Compounded) 6% 

in a 90% dependable year 631.87 MU Interest rate on Loan 10.0% 

Total cost including IDC Rs. 890.82 Crores Interest rate on Working Capital 10.00% 

Equity 30% Rs. 267.25 Crores Return on Equity 16% 

Loan 70% Rs. 623.58 Crores Discounting rate 12% 

Year Capacity Charges(Rs.in Cr.) (Rs.in Cr.) Charges Per Unit (Rs. per Unit) Discounting Discounted 

Out- standing 

Loan(Rs.in 

Cr.) 

Interest on 

loan 

Depre- 

ciation Total 

Return 

on 

equity 

O&M 

Charges 

O&M 

for1 

month 

Interest on 

Working 

Capital Interest Total 

Capacity 

charges 

Energy 

charges Total Factor 

(Paisa 

Tariff per 

Unit) 

2 months 

Average 

Billing 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 

1 623.58 59.76 51.96 111.72 42.76 13.36 1.11 28.47 2.96 59.08 1.77 0.94 2.70 1.0000 2.70 

2 571.61 54.56 51.96 106.53 42.76 14.16 1.18 27.72 2.89 59.81 1.69 0.95 2.63 0.8929 2.35 

3 519.65 49.37 51.96 101.33 42.76 15.01 1.25 26.99 2.82 60.60 1.60 0.96 2.56 0.7972 2.04 

4 467.68 44.17 51.96 96.13 42.76 15.91 1.33 26.26 2.76 61.43 1.52 0.97 2.49 0.7118 1.77 

5 415.72 38.97 51.96 90.94 42.76 16.87 1.41 25.54 2.69 62.32 1.44 0.99 2.43 0.6355 1.54 

6 363.75 33.78 51.96 85.74 42.76 17.88 1.49 24.84 2.63 63.27 1.36 1.00 2.36 0.5674 1.34 

7 311.79 28.58 51.96 80.55 42.76 18.95 1.58 24.14 2.57 64.29 1.27 1.02 2.29 0.5066 1.16 

8 259.82 23.38 51.96 75.35 42.76 20.09 1.67 23.45 2.51 65.36 1.19 1.03 2.23 0.4523 1.01 

9 207.86 18.19 51.96 70.15 42.76 21.30 1.77 22.78 2.46 66.51 1.11 1.05 2.16 0.4039 0.87 

10 155.89 12.99 51.96 64.96 42.76 22.58 1.88 22.12 2.40 67.73 1.03 1.07 2.10 0.3606 0.76 

11 103.93 7.79 51.96 59.76 42.76 23.93 1.99 21.47 2.35 69.04 0.95 1.09 2.04 0.3220 0.66 

12 51.96 2.60 51.96 54.56 42.76 25.37 2.11 20.83 2.29 70.42 0.86 1.11 1.98 0.2875 0.57 

13 0.00 0.00 7.75 7.75 42.76 26.89 2.24 13.16 1.54 71.19 0.12 1.13 1.25 0.2567 0.32 

14 0.00 0.00 7.75 7.75 42.76 28.50 2.38 13.43 1.58 72.84 0.12 1.15 1.28 0.2292 0.29 

15 0.00 0.00 7.75 7.75 42.76 30.21 2.52 13.72 1.62 74.59 0.12 1.18 1.30 0.2046 0.27 

16 0.00 0.00 7.75 7.75 42.76 32.02 2.67 14.03 1.67 76.45 0.12 1.21 1.33 0.1827 0.24 

17 0.00 0.00 7.75 7.75 42.76 33.95 2.83 14.36 1.72 78.42 0.12 1.24 1.36 0.1631 0.22 

18 0.00 0.00 7.75 7.75 42.76 35.98 3.00 14.71 1.77 80.51 0.12 1.27 1.40 0.1456 0.20 

19 0.00 0.00 7.75 7.75 42.76 38.14 3.18 15.08 1.83 82.73 0.12 1.31 1.43 0.1300 0.19 

20 0.00 0.00 7.75 7.75 42.76 40.43 3.37 15.47 1.88 85.07 0.12 1.35 1.47 0.1161 0.17 

21 0.00 0.00 7.75 7.75 42.76 42.85 3.57 15.88 1.95 87.56 0.12 1.39 1.51 0.1037 0.16 

22 0.00 0.00 7.75 7.75 42.76 45.43 3.79 16.32 2.01 90.20 0.12 1.43 1.55 0.0926 0.14 

23 0.00 0.00 7.75 7.75 42.76 48.15 4.01 16.79 2.08 92.99 0.12 1.47 1.59 0.0826 0.13 

24 0.00 0.00 7.75 7.75 42.76 51.04 4.25 17.28 2.15 95.95 0.12 1.52 1.64 0.0738 0.12 

25 0.00 0.00 7.75 7.75 42.76 54.10 4.51 17.81 2.23 99.09 0.12 1.57 1.69 0.0659 0.11 

26 0.00 0.00 7.75 7.75 42.76 57.35 4.78 18.36 2.31 102.42 0.12 1.62 1.74 0.0588 0.10 

27 0.00 0.00 7.75 7.75 42.76 60.79 5.07 18.95 2.40 105.95 0.12 1.68 1.80 0.0525 0.09 

28 0.00 0.00 7.75 7.75 42.76 64.44 5.37 19.57 2.49 109.69 0.12 1.74 1.86 0.0469 0.09 

29 0.00 0.00 7.75 7.75 42.76 68.30 5.69 20.23 2.59 113.66 0.12 1.80 1.92 0.0419 0.08 

30 0.00 0.00 7.75 7.75 42.76 72.40 6.03 20.93 2.70 117.86 0.12 1.87 1.99 0.0374 0.07 

31 0.00 0.00 7.75 7.75 42.76 76.75 6.40 21.68 2.81 122.31 0.12 1.94 2.06 0.0334 0.07 

32 0.00 0.00 7.75 7.75 42.76 81.35 6.78 22.46 2.92 127.04 0.12 2.01 2.13 0.0298 0.06 

33 0.00 0.00 7.75 7.75 42.76 86.23 7.19 23.30 3.05 132.04 0.12 2.09 2.21 0.0266 0.06 

34 0.00 0.00 7.75 7.75 42.76 91.41 7.62 24.18 3.18 137.35 0.12 2.17 2.30 0.0238 0.05 

35 0.00 0.00 7.75 7.75 42.76 96.89 8.07 25.12 3.32 142.97 0.12 2.26 2.39 0.0212 0.05 

TOTAL 9.1566 20.08 

(A) (B) 

Note: The charges per unit is exclusive of water cess, spares, incentive & Income Tax etc. Levellised Tariff =(B)/(A) 2.19



PLATES

ELEVATION IN METERS 

SCHEMATIC DIAGRAM SHOWING CASCADE DEVELOPMENT OF TEESTA RIVER BASIN (SIKKIM) 

3500 

3000 

2500 

2000 

1500 

1000 

500 

000 

TEESTA PROJECT 

STAGE -VI 

SALENTFEATURES:- 

1. CATCHMENT AREA 4874sqkm 

2. DISCHARGE(Dependable) 93CUMECS 

3. F.R.L. 341m. 

4. TYPE OF DAM(Conc.GravityDam) 

5. T.W.L. 253.5om. 

6. AVERAGE GROSS HEAD 84.50m. 

7. LENGTH OF TUNNEL 3.50km. 

8. FIRM POWER 55.50MW. 

9. PROPOSED INSTALLED 

CAPACITY 360MW. 

11O 

UNDER CONST.BY NHPC 


STAGE -V 


1. CATCHMENT AREA 4336sqkm 

2. DISCHARGE(Dependable) 60cumecs 

3. F.R.L. 579m. 

4. TYPE OF DAM-Conc.GravityDam 

5. T.W.L. 359.5m. 

6. AVERAGE GROSS HEAD 216.73m. 

7. LENGTH OF TUNNEL 18km. 

8. FIRM POWER 100mw. 


CAPACITY 510mw. 

100 90 80 70 


STAGE -II 


1. CATCHMENT AREA 1772sqkms 

2. DISCHARGE(Dependable)9.29cumecs. 

3. F.R.L. 2287m. 


5. T.W.L. 1592m. 

6. AVERAGE GROSS HEAD 683m. 


8. FIRM POWER 57.38mw. 




STAGE -III 


1. CATCHMENT AREA 2787sqkm. 

2. DISCHARGE(Dependable)31cumecs 

3. F.R.L. 1585m. 

4. TYPE OF DAM(Conc.GravityDam) 

5. HEIGHT OF DAM 103m. 

6. T.W.L. 779m. 


8. LENGTH OF TUNNEL 12.93m. 

9. FIRM POWER 180mw. 



60 50 

DISTANCE IN KILOMETER 


STAGE-IV 


1. CATCHMENT AREA 3859sqkms 

2. DISCHARGE(Dependable)56cumecs. 

3. F.R.L. 722m. 


5. T.W.L. 589m. 


7. LENGTH OF TUNNEL 11km. 




40 

LACHEN PROJECT 


1. CATCHMENT AREA 1604sq.km. 

2. DISCHARGE(Dependable)9.25 cumecs. 

3. F.R.L. 2650m. 


5. T.W.L. 2290m. 






30 20 


STAGE -I 

10 0 

3500 

3000 

2500 


1. CATCHMENT AREA 1461sq.km. 

2. DISCHARGE(Dependable)10.8 cumecs. 

3. F.R.L. 3258m. 

4. TYPE OF DAM(Conc.GravityDam) 2Nos. 

5. T.W.L. 2675m. 






500 

000 

2000 

1500 

1000 

PLATE-2

27° 

45' 

40' 

35' 

27° 

30' 

88° 15' 

6200 

6200 

6400 

5200 

4200 

5000 

4600 

88° 15' 

6539 

4800 

4000 

6671 

3720 

4850 

4600 

4400 

4000 

4400 

4800 

5485 

4000 

5000 

RUKEL CHHU 

4000 

3690 

4565 

4600 

5215 

5508 

4400 

4890 

4600 

5000 

4600 

5000 

4340 

3400 

3200 

4200 

4600 

4440 

4200 

4425 

3000 

3600 

3800 

4000 

RUKEL H.E PROJECT 

F R L 2395 

R B L 2355 

M D D L 2385 

3800 

4525 

5288 

4600 

3190 

3400 

3800 

4000 

4400 

4200 

4400 

3000 

6888 

2810 

2600 

3000 

DAM AXIS 

4000 

6345 

5259 

8425 

2800 

3200 

20' 25' 

UMRAM CHHU 

RANGYONG H.E PROJECT 

F R L 1845 

R B L1795 

M D D L1825 

RANGYONG CHHU 

T W L 1845 

AVG. GROSS HEAD 541.1 

P.H. CAPACITY 3 X 11 

4200 

4600 

2600 

2800 

6065 5643 

3800 

3000 

5600 

5718 

3800 

3600 

3400 

3200 

3000 

3580 

5200 

4800 

5000 

5200 

4600 

4800 

3775 

2600 

4934 

4000 

3200 

4180 

4000 4200 

3400 

4400 

3800 

5070 

4200 

4600 

4800 

4390 

4885 

DAM AXIS 

3200 

4200 

5200 

4000 

4925 

4600 

PASSAM CHHU 

CANE BRIDGE 

T W L 1098 

JUMTHUL CHU 

F R L 1845 

R B L1795 

M D D L1825 

DAM AXIS 

2200 

2400 

2800 

4200 

2000 

4000 

4400 

POKHRAM CHU 

AVG GROSS HEAD 738.2 


3800 

4660 

3400 

2600 

4800 

4600 

2800 

3600 

3000 

4800 

3580 

2600 

2400 

5000 

4135 

5000 

4115 

1800 

2800 

3000 

3200 

3400 

RINGPI H.E PROJECT 

F R L 2966 

R B L 2940 

M D D L2933 

4640 

LINGZA H.E PROJECT 

F R L 1850 

M D D L 1830 

R B L 1795 

RINGYONG CHU 

3370 

2600 

2400 

2600 

RGVINGRUM CHU 

2000 

2400 

4940 

1400 

2800 

2200 

2400 

3000 

1800 

3200 

3355 

2900 

2600 

2800 

2600 

2800 

3000 

4060 

KISHONG CHU 

DAM AXIS 

1600 

2200 

DAM AXIS 

PANAN H.E PROJECT 

F R L 1095 

R B L 1050 

M D D L 1085 

3000 

2800 

2600 

2400 

4000 

4235 

DAWATHANG CHHU 

RINGPI CHHU 

RANGYONG CHHU 

LUDUI CHHU 

PEGAR CHHU 

T W L 1095 

AVG. GROSS HEAD 746 


DAM AXIS 

1200 

1800 

4200 

4200 

2000 

1600 

4400 

3000 

1400 

2200 

4400 

1200 

2200 

2400 

4600 

4600 

2725 

1800 

1600 

2800 

4800 

5000 

3200 

KONGCHA CHU 

ZONG CHHU 

2600 

2800 

3000 

3200 

1200 

1000 

4965 

2400 

2503 3065 

5060 

3000 

3400 

88° 30' 

3600 

4600 

4800 

3000 

3200 

SUSPENSION BRIDGE 

1800 

2600 

2400 

5615 

4400 

4460 

4195 

2200 

2000 

TW L 770 

27° 

30' 

3400 

3800 

2008 

88° 30' 

1800 

4600 

3400 

3600 

3400 

3200 

3800 

3400 

3200 

2800 

2600 

2200 

1400 

1600 

27° 

45' 

TW L 1853 

AVG GROSS HEAD 1110 


2400 

1600 

1400 

1400 

1000 

1600 

AVG. GROSS HEAD 322 

1200 

2400 

TOLUNG CHU 

1000 

2485 

1000 

1200 

800 

800 

2000 

1000 

RAHI CHU 

1000 

1400 

TEESTA RIVER 

TEESTA H.E. PROJECT 

(STAGE-IV) 

1200 

DAM AXIS 

1400 

1600 

1430 

1800 

2845 

2000 

3200 

3400 

3000 

2800 

2600 

2400 

2200 

1800 

1800 

1600 

1400 

1200 

1000 

1000 

1200 

1400 

1600 

1800 

2000 

NOTES 

1. NO DIMENSION SHALL BE MEASURED FROM 

THIS DRAWING . 

2. CONTOURS AND OTHER FEATURES HAVE 

BEEN TRACED FROM THE S.O.I. TOPO-SHEET 

NO. 78A/6 & 78A/10 (SCALE:- 1:50000). 

FEB.2004 

PLATE-3 

F/DCE730/01/02

SCHEMATIC DIAGRAM SHOWING CASCADE DEVELOPMENT 

OF TOLUNG RIVER BASIN (SIKKIM) 

ELEVATION IN METERS 

3000 

2750 

2500 

2250 

2000 

1750 

1500 

1250 

PANAN HE PROJECT 

LINGZA HE PROJECT 

o 2 4 6 8 

RANGYONG HE PROJECT 

DISTANSE IN KILOMETER 

RINGPI HE PROJECT 

RUKEL HE PROJECT 

10 12 14 16 18 20 22 

3000 

2750 

2500 

2250 

2000 

1750 

1500 

1250 

PLATE-4

Hot spring 

LEGEND:- 

Falls 85m 

Rukel chhu 

S A K K Y O N G RF 

Dense mixed jungle 

QUARTZITE 

GNEISS 

Indragram 

DAM 

Open scrub 

Sing Gamringa 

88°20' 

Falls 150m 

Riyot Potam 

SCALE:- 1:50,000 

Open scrub 

Falls 90m 

falls 

Shophyak 

2440 Payongchu 

(Lingmlum) 

Rangyong 


0 1 2 3 Kilometres 

Umram chhu 

chhu 

27°35' 27°35' 

RUKEL HE SCHEME 

88°20' 

Passamphyaku 

1795 

Singnok 


Date: 

Passaram chhu 

DAM 

DAM 

Lam 

RANGYONG HE SCHEME 

Pokhram Chhu 

Cune bridge 

Sakkyong 

S A K K Y O N G R F 

Ravingrum chhu 

Falls 71m 

Falls 25m 

88°25' 

88°25' 

Phontong 

Log bridge 

? 

Ringyong Chhu 

? 

? 

40 

? ? 

Ringpi chhu 

Falls 40m Log bridge 

? ? 

? 

45 

45 

45 65 

80 

50 

45 

70 

65 

40 

? 

? ?

TALAM HYDRO ELECTRIC PROJECT 

( 2 X 35 MW ) 

RINGPI HYDRO ELECTRIC PROJECT 

( 2 X 35 MW ) 

RANGYONG HYDRO ELECTRIC PROJECT 

( 3 X 47 MW ) 

RUKEL HYDRO ELECTRIC PROJECT 

( 3 X 11 MW ) 

N E P A L 

LINGZA HYDRO ELECTRIC PROJECT 

( 3 X 40 MW) 

YANGSS CHHU 

RAMAM OR 

RANGBONG KHOLA 

C H I N A 

CHAUNRIKHIANG 

TIKIPCHHU 

RIYONG KHOLA 

RIMBI CHHU 

T I B E T 

PHUTHUNG CHHU 

TONGSHIONG GLACIER 

TALUNG GLACIER 

CHOKCHURANG CHHU 

PREK CHHU 

LAMBI 

KHUNGME 

RATHANG CHHU 

KALEJ KHOLA 

TINGCHEN KHANG 

REFLI CHHU 

RISHI KHOLA 

GOMA CHHU 

RUKEL CHHU 

RONGDUNG CHHU 

GEZING 

REATHOK KHOLA 

SOMBARE NAYA BAZAR 

KHORA CHHU 

LUNGMA CHHU 

UMMRAM CHHU 

RANGYONG CHHU 

RANGIT RIVER 

KAYAM CHHU 

NAMCHI 

RINGYONG CHHU 

RANGPO CHHU 

GREAT RANGIT RIVER 

NACHUNGTHANGKHA 

THANG CHHO 

NAKU CHHU 

LANGBO CHHU 

THOMPHYAK CHHU 

POKE CHHU 

LHONAK CHHU 

RINGPI CHHU 

MONMU CHHU 

RANGPHAP CHHU 

ZEMU CHHU 

TOLUNG CHHU 

RUN CHHU 

SINGTAM 

TEESTA RIVER 

MANGKHA 

SIRWANI 

RONGNI CHHU OR RANI K 

TEESTA RIVER 

RAHI CHHU 

LASHA CHHU 

KALEP 

MANGAN 

DIKCHU 

TEESTA RIVER 

GYAMTHANG CHHU 

BURUM CHHU 

GEY CHHU 

TEESTA RIVER 

RANGPO CHHU 

RANGPO 

CHHU 

TARUM CHHU 

RABOM CHHU 

RI CHHU 

RISHI KHOLA 

BAKCHA 

DIK CHHU 

YUMRHANG CHHU 

CHUNGTHANG 

GANGTOK 

CHAKUNG CHHU 

CHHU 

RORA CHHU 

TAKCHOM CHHU 

RANGLI KHOLA 

W E S T B E N G A L 

DONGKYA CHHU 

TOKLUNG CHHU 

RATE CHHU 

BYU CHHU 

SEBOZANG CHHU 

LUNGZE CHHU 

RANGPO CHHU 

C H I N A 

T I B E T 

B H U T A N 

PANAN HYDRO ELECTRIC PROJECT 

(4 X 50MW) 

RONGNI STORAGE PROJECT 

( 3 X 65 MW) 

NOTES 

1. NO DIMENSION SHALL BE MEASURED FROM THIS DRAWING. 

PRE- FEASIBILITY REPORT DRAWING 

VICINITY MAP 

PLATE NO.- 6.1 

TEESTA HYDRO ELECTRIC PROJECT(STAGE-I) 

( 4 X 80 MW ) 

LACHEN HYDRO ELECTRIC PROJECT 

( 3 X 70 MW ) 

TEESTA HYDRO ELECTRIC PROJECT(STAGE-V) 

( 3 X 170 MW ) 

DIKCHU HYDRO ELECTRIC PROJECT 

( 3 X 35 MW ) 

LEGEND 

INTERNATIONAL BOUNDARY 

STATE BOUNDARY 

RIVER 

TRIBUTARY 

ROAD 

DAM SITE 

F/DCE730/01/02

27° 

35' 

2600 

2200 

2400 

2600 

2800 

3000 

3200 

2400 

OPEN SCRUB 

RANGYONG CHU 

2000 

UMRAM CHHU 

3400 PAYONGCHU 

3600 

(LINGMIUM) 

INTAKE TUNNEL 

3MØ 

DESILTING 

CHAMBER 

3400 

LINK TUNNEL 

3.3MØ 

DAM AXIS 

1800 

3200 

3600 

2200 

2400 

1800 

PASSARAM CHHU 

SINGNAK 

2000 

2000 

DAM AXIS 


3.3MØ H.S. 


3.3 MØ H.S. 


ADIT-1 

3400 

2200 

2400 

3200 

1600 

2400 

2600 

2800 

RANGYONG CHU 

ADIT-2 

2000 

2200 

1800 

3000 

1600 

1400 

CANE BRIDGE 

SOKKYONG 

HEADRACE TUNNEL 3.3MØ H.S. 

PAKHRAM CHHU 

LOG BRIDGE 

ADIT-3 

2800 

RAVINGRUM CHHU 

2800 

2600 

88° 

25' 

2600 

2400 

88° 

25' 

FARD 

2000 

2400 

2200 

1400 

1800 

PHANTONG 

1200 

SWITCH YARD 

LOG BRIDGE 

POWER HOUSE 

INCLINED PRESSURE 

SHAFT 2.5M Ø 

1600 

SURGE SHAFT 10M Ø 

2200 

2000 

1800 

RINGYONG CHHU 

1400 

TRANSFORMER 

CAVERN 

1600 

VAWL 

SHABRUNG 

RINGPI CHHU 

1600 

1800 

T.R.T. 3.3 M Ø 

M.A.T. 

1800 

ISHANA 

FORD 

LOG BRIDGE 

MYONG 

2200 

RANGYONG CHU 

LOG BRIDGE 

1600 

1800 

2000 

2200 

2000 

1800 

1600 

1400 

1200 

1200 

1400 

1600 

27° 

35' 

NOTES 


2. CONTOURS AND OTHER FEATURES HAVE BEEN TRACED 

FROM THE S.O.I. TOPO- SHEET NO. 78A/6 (SCALE 1:50000) . 


PROJECT LAY-OUT PLAN 

PLATE NO.-6.2 

F/DCE730/01/02

2000 

1800 

2600 

SINGNAK 

2400 


2M.X 3M. D- SHAPE 

1600 

D/S COFFERDAM 

H.R.T. 3.3M.Ø H.S.SHAPE 

RANGYONG CHHU 

2200 

1800 

27° 

35' 

2000 

1600 

RANGYONG CHU 

DESILTING CHAMBER 

( 125 X 6 X 9M.) 

INTAKE TUNNEL 

3MØ 

U/S COFFERDAM 


3.3 MØ H.S.SHAPE 

(LINGMIUM) 

3400 PAYONGCHU 

LINK TUNNEL 

3.3MØ H.S. SHAPE 

D/S COFFERDAM 


3.3MØ H.S.SHAPE 

2400 

DAM AXIS( UPPER ) 

1800 

2200 

2400 

2000 

UMRAM CHHU 

U/S COFFERDAM 

PASSARAM CHHU 

NOTES 



FROM THE S.O.I. TOPO-SHEET NO. 78A/6 (SCALE 1:50000) . 


DAM AREA 

LAY-OUT PLAN 


F/DCE730/01/02

H.R.T. 3.3M Ø H.S.SHAPE 

1600 

1800 

SURGE SHAFT 10M Ø 

2000 

1800 

CABLE TUNNEL 

1400 

POWER HOUSE 

(100M. X 22.5M. X 40 M.) 

INCLINED PRESSURE 

SHAFT 2.5M Ø 

TRANSFORMER 

CAVERN 

SWITCH YARD 

(100M. X 155M.) 

1200 

1600 

RINGYONG CHHU 

T.R.T. 3.3 M Ø H.S. SHAPE 

M.A.T. 

RANGYONG CHHU 

1200 

1400 

1200 

NOTES 



FROM THE S.O.I. TOPO-SHEET NO. 78A/6 (SCALE 1:50000) . 


POWER HOUSE AREA 

LAY-OUT PLAN 


F/DCE730/01/02

FRL 1845.00 

MDDL 1825.00 

EL 1815.00 

EL 1810.00 

TRESTLE 

EL 1850.00 

? 

? 

DESILTING CHAMBER 

(125M. X 6M.X 9M.) 


(2M.X 3M. D-SHAPED) 

? 

? 

GATE OPERATION ? 

CHAMBER 

EL 1850.00 

EL1860 

1 

? ? 

250 

HRT 3.3M. Ø H.S. SHAPE 

STEEL LINED PRESSURE SHAFT 2.5M. Ø 

SURGE SHAFT 

10M. Ø 

ADIT TO P.S. 

3.3M.Ø D-SHAPE 

EL 1783.85 

EL. 1100.15 

C L - OF MACHINE 

? 

? 

ADIT TO P.S. 

3.3M.Ø D-SHAPE 

22500 

EL.1132.00 

BUS DUCT 

30000 

? 

POWER HOUSE CAVERN 

14000 

TRANSFORMER CAVERN 

CABLE TUNNEL 

EL.1114.55 

? 

T.R.T. 3.3M.Ø H.S.SHAPE 

NOTES: 

MAR.2004 

C.C. BLOCKS 

TWL1098.00 

COFFERWALL 

1 ALL DIMENSIONS ARE IN MILLIMETERS AND LEVELS IN METERS. 

WATER CONDUCTOR SYSTEM 

L-SECTION 

PLATE NO.-6.5 

2 NO DIMENSION SHALL BE MEASURED FROM THIS DRAWING. 

F/DCE730/01/02

L6 

? 

L5 

? 

L4 

107000 27000 166000 

3000 (TYP.) 

3000(TYP.) 

DAM TOP EL 1850.00 

L3 

? 

L2 

L1 

S3 

S2 

S1 

UPSTREAM ELEVATION 

? 

300000 

R1 R2 R3 R4 R5 R6 

RADIAL GATE 3000 X 6000 

? 

N.S.L. 

ANTICIPATED ROCK PROFILE 

? 

R7 

NOTES: 

1 ALL DIMENSIONS ARE IN MM AND LEVELS IN METRES. 


MAR.2004 

RAILING 

R8 

R9 

UPPER DAM 



R10 


? 

F/DCE730/01/02

L6 

? 

L5 

? 

L4 

118000 

L3 

? 


L2 

250000 

27000 

3000(TYP.) 3000(TYP.) 

L1 

RADIAL GATE 3000 X 6000 

105000 

S3 S2 S1 R1 R2 R3 R4 

? 

? 

RAILING 

NSL 

ANTICIPATED ROCK PROFILE 

? 

NOTES: 



MAR.2004 

LOWER DAM 




R5 

F/DCE730/01/02

STOPLOG GATE GROOVE 

1 

STOPLOG GANTRY 

CRANE 


FRL EL. 1845.00 

MDDL EL. 1825.00 

1 

CREST EL 1805.00 

RBL ±EL 1795.00 

EL ±1785.00 

STEEL LINER 

GROUT CURTAIN HOLES 

? 

3500 

DAM AXIS 

8000 

ROAD 

BREAST WALL 

AIR VENT PIPE 

EL. 1811.00 

R9600 

FOUNDATION 

GALLERY 

DRAINAGE HOLE 

RADIAL GATE(3M. X 6M.) 

TRUNION BEAM 

HIGH PERFORMENCE CONC. 

70000 

FLIP BUCKET 

BUCKET INVERT EL 2353.00 

? ? ? ? ? ? 

SPILLWAY- MAXIMUM SECTION 

15° 

R25000 

30° 

1 

1 

1 1 

12250 

7000 LONG ROCK ANCHORS 

@1500 c/c STAGGERED 

MAX. T W L 

NORMAL T W L 

CONCRETE APRON 


FRL EL 1845.00 

MDDL EL 1825.00 

0.1 

1 

EL. VARIES ? 

DAM AXIS 

8000 

NON- OVERFLOW SECTION 

COMPACTED BACKFILL 

NOTES: 

? ? 


2 NO DIMENSION SHALL BE MEASURED FROM THIS 

DRAWING. 


MAR.2004 

0.8 

1 

DAM 

SPILLWAY & NON-OVER FLOW 

CROSS-SECTION 

PLATE NO.-6.8 

F/DCE730/01/02

HRT3.3 M. Ø 

Ø3300 

Ø10000 

TYP. SECTION - SURGE SHAFT 

2000 LONG 25 Ø ROCK BOLTS/ 

ANCHORS 1000 c/c 

Ø1650 

Ø3300 

TYP. SECTION - HRT 

CONC. LINING 225 THK. 

50 THK. 

SHOTCRETE 

4M LONG 25 Ø ROCK BOLTS/ 


100 THK. SHOTCRETE 

WITH WIREMESH 

CONC.LINING 750 THK. 

PRESSURE SHAFT 

Ø3300 

TYP. SECTION - DIVERSION TUNNEL 

12000 



Ø1650 

Ø3300 

CONC. LINING 225 THK. 

50 THK. 

SHOTCRETE 

10000 

1.5 

1 

SECTION - DESILTING CHAMBER 

Ø2500 

32Ø 5000 LONG ROCK BOLTS / 

ANCHORS @ 2000 c/c 


ANCHORS 1000 c/c(IF REQUIRED) 

BACK FILL 750 THK. 

STEEL LINER 

50THK. 

SHOTCRETE 

TYP. SECTION - PRESSURE SHAFT 

100 THK. SHOTCRETE 

WITH WIREMESH 

R.C.C. LINING 300 THK. 

32Ø 5000 LNG ROCK BOLTS/ 

ANCHORS @ 1500 c/c 

NOTE :- 

1 ALL DIMENSIONS AREIN MILIMETRES AND LEVELS 

IN METRE UNLESS OTHERWISE SPECIFIED. 

2 NO DIMENSION SHALL BE MEASURED FROM THIS 

DRAWING. 

PRE-FEASIBILITY REPORT DRAWING 

TYPICAL CROSS SECTION 

OF CONSTITUENTS OF WATER 

CONDUCTOR SYSTEM & DIVERSION TUNNEL 

MAR.2004 


00 

F/DCE/730/01/02

220KV 

BUS1 

BUS CVT-1 

220kV 

BUS-II 

BUS CVT-2 

EX. Tr. 

NGT 

S.A. 

XLPE CABLE 

GSU Tr. 

G-III 

UNIT -III 

SC 

SA 

PT 

PT 

UAT 

64G1 

64G2 

PTSP 

FUTURE 

CVT 

EX. Tr. 

NGT 

UNIT -II 

S.A. 

XLPE CABLE 

GSU Tr. 

SC 

SA 

G-II 

PT 

PT 

UAT 

64G1 

64G2 

TO 220KV 

FEEDER-1 

PTSP 

CVT 

BUS 

COUPLER 

EX. Tr. 

NGT 

UNIT -I 

S.A. 

XLPE CABLE 

GSU Tr.1Ø,20 MVA 

11/ 220/ 3 KV 

SA 

PT 

PT 

G-I 

47 MW,11 KV 

64G1 

64G2 

FOR 

TO 220KV 

FEEDER-2 

UAT 

11 / 0.415KV,800KVA 

SC PTSP 

FOR 

METERING & 

PROTECTION 

DVR DUPLICATE 

PROTECTION 

CVT 

AUTO Tr. 14 MVA 

132/220 KV, 1Ø CVT 

SA 

S.A. 

VED PAL 

MAR, 2004 

FROM RUKEL 

SINGLE LINE DIAGRAM 

BHU DEV 

V.K.SINGH 

NH/DEM/RYG/SLD/01 

PLATE-8.1 

00



ANNEXURES

GEOLOGY OF THE AREA AROUND THE PROPOSED 

Annexure 4.1 

RANGYONG HYDROELECTRIC PROJECT, TEESTA BASIN, 

INTRODUCTION 

SIKKIM 

The Central Electricity Authority (CEA), as a part of an exercise to assess the 

balance hydroelectric potential in the county have identified 399 schemes with installed 

capacity of 1,50,000 MW in various river basins. The schemes thus identified were 

subjected to ranking studies based on different parameters. As a resulted of ranking 

studies, 162 schemes located in the different river basins in 16 states were selected to 

be taken up for preparation of Pre-Feasibility Reports (PFR’s) in first phase. The 

schemes thus found feasible are proposed to be taken up for further development during 

X and XI Five Year Plans. Out of 162 schemes selected to be taken up for preparation 

of PFR’s in first phase, 10 are located in Teesta Basin in Sikkim. The proposed 

Rangyong Hydroelectric Project located in north Sikkim is one of the ten schemes that 

are being taken up for preparation of PFR’s in first phase. As per the layout provided by 

NHPC Ltd. the scheme envisages construction of two diversion dams, one across 

Umram Chhu just downstream of its confluence with Passaram Chhu (27 O 36’ 00” N: 88 O 

22’ 24” E, 78 0/6 ) with a view of diverting its water to Rangyong Chhu through 2 km long 

diversion tunnel and another across Rangong Chhu just downstream of powerhouse of 

upstream Rukel Hydroelectric Project (27 O 35’ N: 88 O 21’ E, 78 0/6 ). The water 

conductor system includes approximately 7.5 km. long headrace tunnel aligned on right 

bank of Rangyong Chhu and underground powerhouse with probable installed capacity 

of 175 MW just upstream of powerhouse of the proposed Lingza Hydroelectric Project 

(27 O 33’ 00” N: 88 O 26’ 00” E, 78 0/6 ). 

REGIONAL GEOLOGY 

The area around the proposed project is located in North Sikkim in Central 

Crystalline axial region and is characterised by sharp crested snow bound mountains.

The ridges trend both in E-W and N-S directions. Teesta River, main draining agency of 

Sikkim flows almost N-S in the area. The important tributaries of Teesta are Lach Chhu, 

Toloung Chhu Chakung Chu, Ringpi Chu and their numerous tributaries. The valleys of 

rivers are U-shaped and small streams have formed deep gorges. Vegetation is 

observed up to EI . 3.900 m and many lakes are present at high altitudes. 

The area around the proposed project has been mapped by Raina (1966) 

Chakraborti and Banerjee (1982), Kumar et al (1984), Neogi et al (1984) and Neogi et al 

(1986). The stratigraphic sequence established by the officers of GSI on the basis of 

geological mapping is given below: 

GROUP LITHOLOGY 

Gondwana Grits, pebble cum boulder beds and 

2 

carbonaceous shales with occasional 

coal seams, pegmatite, quartzite 

(Tourmaline bearing) 

Daling Inter bedded quartzite and chlorite 

sericite phyllite / schist. 

Lingza Granite 

Quartzite/Biotite schist 

Chungthang Interbedded quartzite and 

Central Crystalline Gneissic 

Complex 

garnetiferous quartz biotite schist . 

Calc – silicate rock / marble. 

Garnet – kyanite – sillimanite – biotite 

– quartz – schist. 

Banded gneiss with augen gneiss and 

quartz – biotite gneiss. 

Augen gneiss

The area falls within axial belt of Central Crystalline Zone of the North Sikkim 

Himalayas where the rock types are mainly high grade gneisses (CCGC) having 

interbands of metasedimentaries represented by calc – silicate / quartzite, high grade 

schists and their fine inter laminations. The metasedimentaries occur as enclaves in the 

high-grade gneisses in the area around the proposed project. All these rock types are 

often intruded by discordant tourmaline bearing quartz veins and pegmatite. 

The higher grade gneisses belonging to the Central Crystalline Gneissic 

Complex (CCGC) Group vary in composition from a gneiss in which feldspar is 

predominant with respect to quartz to quartz biotite gneiss in which feldspar is almost 

absent (Chakraborti & Banerjee, 1982 and Neogi et al, 1986) with frequent association 

of garnet, tourmaline and sillimanite / kyanite depending up on bulk chemical 

composition. While the former type is well foliated with streaks of biotite, the latter is 

compact and poorly foliated. The different types of these gneisses occurring at different 

structural levels are banded gneiss, augen gneiss and streaky gneiss. A gradual 

passage from one type to other type, both vertically and laterally, is rather common. 

The banded type is characterized by alternate bands of quartz feldspar and biotite. 

These bands are at places stretched giving rise to augens which are composed 

predominantly of single grains of feldspar or occasionally quartz or their aggregate. The 

latter may be the result of metamorphic differentiation. The augens are both deformed 

or undeformed and are invariably warped around by biotite flakes defining the gneissic – 

foliation. The augens are stretched in the direction of regional schistosity. The high 

grade gneisses are often intruded by tourmaline granite at places and are associated 

with interbands of calc silicate – quartzite and garnetiferous biotite schist and various 

other schists belonging to Chungthang Group. These have locally been mapped as 

Kanchendzonga Gneiss, Chungthang Gneiss and Darjeeling Gneiss by various workers 

earlier. According to Neogi et al (1986), there exists a complete gradation both laterally 

and in down dip direction amongst above mentioned gneisses. Their repetition is due to 

normal morphological variation and unlinked with folding and thrusting. Various 

structural/textural types of these gneisses stated above have also been observed in all 

the so called gneissic groups of Central Crystalline axial region and have been referred 

as “High Grade Gneisses” of Central Crystalline Belt which are also comparable to 

Darjeeling Gneisses of Lesser Himalayas. 

3

The metasedimentaries of the area belonging to the Chungthang Group are 

represented by a sequence of lithounits varying from calcareous to arenaceous and 

argillaceous lithofacies. These comprise calc silicate rocks, quartzite, high grade 

micaceous schists occasional amphibolites and their fine grained interlaminations. 

Neogi et al (1986) have clubbed together calc silicate rocks and quartzites as 

these invariably occur together. Prominent bands of these rocks have been observed 

near Be and Myong, north of Talung gompa and near Phygn and south of Kishong. 

These have NE-SW trend are locally folded. Calcareous bands are easily identified by 

their greenish colour within banded calc silicate / quartzite assemblage. Apart from 

carbonates and quartz, stumpy diopside and needle shaped tremolite have also been 

observed in these. Garnet is generally leached giving rise to ferruginous staining. The 

quartzite is sericite quartzite. Thin laminations of biotite are observed in quartzite at 

places. The rocks are occasionally boudinaged. Carbonaceous biotite schist is found 

associated with southern west calc silicate / quartzite band. Tourmaline bearing silica 

veins and pegmatites have been observed occasionally intruding these rock types. 

Daling Series of Raina (1966) having two zones viz phyllite zone and schistose 

zone has been mapped as low grade metamorphites of Daling Group by Kumar et al 

(1984). Daling Group comprises quartz – chlorite – sericite schist phyllite, quartz – 

sericite schist, quartz chlorite phyllite often associated with thin interbands of quartzite. 

The low grade sedimentaries belonging to Daling Series from southern part of the area 

structurally underlie the Lingtze Granite Gneiss. Near Gyathang and at some other 

places, the frequency of presence of garnet is slightly higher and its grain size is 

controlled by the original bulk composition of the rock. According to Kumar et al (1984) 

these metasedimentaries typically resemble the Gorubathan Formation of Daling Group 

and hence been named “low Grade Daling” . 

The granite gneiss which crops out near north of Senkhalang with an E-W trend 

and northerly dips is also observed NW of Kendong and north of Karsang to form the 

western limb of major antiformal closure. It occupies a unique position between low- 

grade and high-grade metasedimentaries and is conformable to both. This granite is a 

well foliated, coarse grained, sheared streaky biotite gneiss and occasionally contains 

4

garnets. At places, augens of quartz and feldspar stretched parallel to the foliation plane 

are recorded within this unit. 

Tourmaline and biotite bearing granites are the younger granites having 

discordant relationship with high-grade gneisses and high-grade metasedimentaries. 

Compositionally, these are mainly quartz-feldspar rich leucogranite varying from coarse 

grained to fine grained aplitic variety and shows disseminated flakes of biotite. 

Tourmaline grains are observed generally in structural highs. 

Gondwanas, according to Raina (1966) include grits, pebble cum boulder beds 

and carbonaceous shales with occasional coal seams. Pebble cum boulder bed forms 

the marker horizon for Gondwana. Arkosic sandstone (feldspathic grit) forms the other 

main rock type. It is light yellow to dark grey coloured and is infolded within pebble 

beds. 

STRUCTURE AND TECTONICS 

The area exposes a sequence of gneissic rocks and associated 

metasedimentary rocks of Central Crystalline Belt of North Sikkim and the structural 

fabric elements observed pertain to features in the area predominated by high grade 

litho-facies which have undergone polyphase deformation and metamorphism. The 

primary structures include compositional banding. The gneisses show lithological 

banding which can be attributed to metamorphic differentiation. Bedded characters are 

observed only in calc silicate – quartzite multilayers. The high-grade schists also show 

compositional banding of alternate quartz rich and calc silicate rich bands. There is no 

evidence however to indicate that these bandings are relict of primary sedimentary 

banding. However, broad parallelism of the bandings and later imposed pervasive 

planes, S2, indicates that these could be transposed. 

The secondary structures include planar surfaces like gneisses foliation, 

schistosity which include bedding schistosity (S1), regional schistosity (S2) and fracture 

cleavage (S3). Bed Gneissic foliation forms the most prominent fabric element of high 

grade metamorphic tectonics. These ‘S’ surfaces are marked by parallel lithological 

5

layering and preferred dimensional orientation of minerals. The gneissic foliation in the 

area generally trends NE-SW with moderate NW dips. 

The metasedimentaries associated with the gneisses show a pervasive 

schistosity where lithological layering is absent. The fabric is defined by preferred 

orientation of tabular mica crystals. Bedding schistosity (S1) is incipient and is parallel to 

the compositional banding in metasedimentaries. This ‘S’ surface could not be related to 

any tectonic structure in the area and could be described as another inherited fabric 

element along with bedding. The regional schistosity (S2) is most pervasive structural 

element in metasedimentaries. The axial plane schistosity is symmetrically oriented with 

respect to axial planes of folds (F1). The trend of regional schistosity is parallel to the 

gneissic foliation. The fracture cleavage (S3) is defined by discrete parallel fractures 

and are also axial plane cleavages related to F2 crenulation. Due to varying styles of the 

F2 folds the orientation of the S3 surfaces varies with respect to regional schistosity ‘S2’. 

The linear structures include striping lineation, pucker axis lineation and mineral 

lineation. 

The area comprises a sequence of high-grade metasedimentaries and gneisses 

that show evidence of having undergone polyphase deformation with complex pattern of 

folds due to repeated super-imposition of successive fold forms. Grouping of different 

generations of folds on the basis of styles and spatial attitudes has not been possible 

due to their complex forms. Broadly three generations of fold movement could be 

deciphered. F1 folds, the earliest recognizable folds have compositional banding and 

bedding schistosity as their form surface and are of tight isoclinal reclined to inclined 

folds. Their style and spatial orientation as observed in the area is comparable to these 

observed in Daling Group of rocks exposed south of present area. The F2 folds have 

involved all the above mentioned surfaces. These show a variety of styles ranging from 

appressed isoclinal folds to open warps, small-scale chevron folds or multi-hinged 

disharmonic folds. The calc silicate / marble quartzite bands show regional warps along 

NW-SE axis due to this phase of folding. The effects of F3 folds have been observed 

mainly on regional scale. On macro scale they are of the nature of minor broad warps 

that have folded the weakly developed S3 planes. No planar surface related to this 

phase of folding are apparent. F3 warps are only locally developed in high-grade 

metasedimentaries and have N-S oriented axis. 

6

Zones of intense mylonitisation have been observed in the gneisses but there is 

no basis to conclude that these could represent planes of thrusting on the basis of 

evidence like distinct truncation of lithounits reorientation of major folds (F2), 

development of small scale faults etc.. Chakraborty and Banerjee (1982) have marked 

NNW-SSE trending thrust near Manual and NW-SE trending thrust near Naga. Neogi et 

al (1984) observed minor slips and faults occurring commonly within gneisses and 

metasedimentaries along S3 planes near hinge zone of F2 folds. The slips are more 

common where folds are tight. A meso scale normal vertical fault trending N-S has been 

found with in low grade metasedimentaries about 2 km north of Brang village. 

Silicification, chloritization and mylonitization are found along this fault plane. 

SEISMOTECTONICS AND SEISMICITY 

Seismotectonically the area under reference is located in Axial Belt of Central 

Crystalline Zones of North Sikkim. According to Narula at al (2000) the northern part of 

the area is occupied by poorly metamorphosed sequence (Tethyan) folded during 

Himalayan Orogeny. Similar tectonic pockets representing Gondwana sequence crop 

out within Rangit Window as well as lenticular tectonic wedge along the Main Boundary 

Thrust (MBT). The northern Tethyan Belt is followed successively to the south by high- 

grade complex of Central Crystallines and low-grade complex of Lesser Himalayan rock 

worked during Himalayan Orogeny. The latter packet is exposed within tectonic 

windows as well as linear belt between Main Central Thrust (MCT) and MBT. South of 

MBT the foot hill region is occupied by sequence of frontal belt affected by the terminal 

phase of the Himalayan Orogeny. Adjacent Peninsular tract is covered by Quaternary 

alluvial fill along the foredeep. In the southwestern part, Peninsular element is 

represented by small inliers of gneissic complex and Rajmahal Trap. The basement 

gneissic complex, representing a part of Shillong massif along with marine transgressive 

cover are present in south eastern part. Like other parts of Himalayas, this area is the 

high grade Central Crystallines from comparatively lower grade Lesser Himalayan 

packages which are separated from the Siwalik Belt by MBT. At places, particularly 

towards east, several subsidiary thrust are presented between MCT and MBT. Besides 

these, several approximately N-S trending gravity faults are present particularly within 

northern Tethyan Belt and the southern foot hill belt. Within northern Tethyan Belt these 

7

N-S faults define some well knows graben structures, viz. Pum Qu Graben and Yadong 

Gulu Graben. In the former, the faults affecting the Quaternary glacial deposits are 

clearly evident. The latter graben is considered to be longest one in Tibetan Plateau and 

is segmented into several N-S smaller grabens. The foredeep tract east of Munger – 

Saharsha Ridge is known as Purnia Basin where Gondwana sequence has developed 

over the rifted basement. The structural configuration of this foredeep region is 

architectured by a set of almost N-S trending faults resulting in development of alternate 

horst and graben structures. The westernmost is the Munger – Saharsha Ridge which 

alternates towards east by Purnia Basin. The western and eastern boundaries of Purnia 

Basin are defined by the Munger - Saharsha Ridge Morginal Fault (MSRF) and Malda 

Kishanganj Fault (MKF). The former fault known as Sainthia – Brahmani Fault further 

south, along which cluster of earthquakes have been recorded by the Geological Survey 

of India, has been found seismically active. Further east the prominent tectonic feature 

is the Rangpur Ridge bound by MKF and Jangipur – Goribandha Fault, Teesta Fault and 

Katihar – Nailphamari Fault. Several subsidiary faults, parallel to Teesta Fault forming 

grabens are reported from ridge. Gondwana sequence is found to have developed 

within these grabens. Along with transverse faults, several lineaments cutting across the 

Himalayan belt are also present. These exhibit NE and NW trends. The NE trending 

Azun Lineament considered to be trace of northern extension of East Patna Fault, 

Kanchanjunga Lineament and NW-SE trending Teesta and Purnia lineaments are other 

prominent transverse lineaments. The basement contours corroborate the presence of 

Purnia Saddle and Rangpur Ridge. 

Most of the earthquakes in this area are shallow focus (40 km. The depth of focus for one event, that of 

21.05.1935, has been interpreted to be 140 km. As such observed seismic events are 

mostly concentrated in Main Himalayan Belt. Keeping in view the seismotectonic set up 

8

and seismicity, the area has been kept in Zone – IV as per Map of India Showing 

Seismic Zones (IS - 1893 (part –I) : 2002). 

GEOTECHNICAL APPRAISAL 

The proposed Rangyong Hydroelectric Project is located downstream of Rukel 

Hydroelectric Project in valley of Rangyong Chhu. This scheme involves diversion of 

discharges of Umram Chhu and Passasam Chu with a view to augment discharge of 

Rangyong Chhu through a diversion structure proposed to be located just downstream 

of confluence of both the tributaries near Pussamphyaku. The site of the diversion 

structure exposes banded and augen gneisses and quartzite – biotite gneisses 

belonging to CCGC. The rocks are foliated and jointed. It is suggested that thickness of 

overburden in the river bed and on the abutments be assessed and availability of bed 

rock on the abutments be assured before finalizing the type of structure and location. 

The discharge is proposed to be diverted to the main diversion structure through a 2 km 

long diversion tunnel. This diversion tunnel is expected to encounter the gneisses of 

CCGC. These are expected to provide good tunneling media. The main diversion 

structure on Rangyong Chhu is proposed just downstream of powerhouse of upstream 

Rukel Hydroelectric Project. Similar studies are suggested for the diversion structure. 

The water conductor system comprising about 7.5 km long HRT for conveying 

combined discharge to powerhouse is proposed on the right bank of Rangyong Chhu. 

The proposed HRT is expected to encounter the high grade gneisses belonging to 

CCGC on major portion and garnet – kyanite – sillimanite – biotite quartz schist and 

interbedded quartzite and garnetiferous quartz biotite schist belonging to Chhungthang 

Group. The rocks belonging to CCGC and Chhunghang Group are interbanded and are 

expected to provide good to fair tunneling media in general except for reaches where 

local faults and shears are encountered where poor rock conditions can be expected. 

The preliminary layout of the project indicates that no intermediate construction adit has 

been included along this 7.5 km long HRT. It is suggested that tunnel be shifted towards 

river in the middle reaches and a kink be provided so that at least one construction adit 

is provided to facilitate construction. However, adequate lateral and top covered be 

ensured so that structure is safe. Patches of Lingtse Granite may also be encountered 

9

in HRT. The proposed underground powerhouse with installed capacity of 175 MW is 

envisaged on the right bank of Rangyong Chhu just upstream of powerhouse of the 

proposed Lingza Hydroelectric Project near Lingza. It is expected to encounter 

interbedded quartzite and garnetiferous quartz biotite schist. The rock conditions are 

expected to be fair in general. The tailrace may also encounter high grade schists which 

are kyanite – sillimanite schist. The Project is located in zone-IV as per Map of India 

Showing Seismic Zones (BIS : 1893 (Part-I) : 2002). Therefore proper seismic 

coefficient be incorporated in the designs of appurtenant structures of the project. This 

preliminary geotechnical appraisal is without field visit to the project site. 

REFERENCE 

Chakraborti, B., and Banerjee, H., (1982). Geology and Structure of the Area around 

Chungthang - Mangan – Tolung, North Sikkim. Unpubl. Prog. Rep. Geological Survey of 

India, F.S. 1980-81. 

Kumar, J.P., and Mitra, P.K. (1984). Geology and Structure of the Area Around 

Sakkyong, Mangan, Dikchu, Lingi and Mangka Covering Parts of North South and East 

Sikkim. Unpubl. Prog. Rep. Geological Survey of India, F.S. 1982-83. 

Narula, P.L. Acharayya, S.K., and Banerjee, J., (Eds) (2000). Seismotectonic Atlas of 

India and its Environs, GSI Publication. 

Neogi S., Purkaint, B. and Samaddar, A.K. (1984). Geology of the Area Around 

Tashiding – Lapdang – Maidang La-Karshang – Lampokhari – Khungre, West District, 

Sikkim. Unpubl. Prog. Rep. Geological Survey of India, F.S. 1982-83. 

Neogi, S., Kumar, J.P., Mitra, N.D., Samaddar, A.K. and Dawande, A.K. (1986). 

Geology of the Area Around Tolung – Thijp, - Kishong, North Sikkim District, Sikkim. 

Unpubl. Geological Survey of India Prog. Preg., F.S. 1983-84. 

Raina, U.K. (1966). Geological Mapping in the western part of Sikkim. Unpubl. 

Geological Survey of India, Rep., F.S. 1965-66. 

10

1 

Annexure-4.2 

TECHNICAL REPORT ON SEISMIC HISTORY AND SEISMICITY OF THE 

TEESTA BASIN OF SIKXKIM COVERING PROPOSED SITES FOR 

HYDROELECTRIC SCHEMES 

Historical and instrumentally recorded data on earthquakes show that the whole area of 

the proposed sites for hydroelectric schemes at Dikchu, Rongni Storage, Panan, 

Namlum, Zedang, Teesta St-I, Ringpi, Lingza, Rukel and Rangyong in Sikkim lies in a 

region liable to damage due to moderate to great earthquakes. Noteworthy earthquakes 

which affected the region in the past are (i) the Cachar earthquake of 10.01.1869 

(Magnitude= 7.5 on Richter scale), (ii) the Shillong plateau earthquake of 12.06.1897 

(Magnitude= 8.7), (iii) the Dhubri earthquake of 02.07.1930 (Magnitude= 7.1), (iv) the 

Bihar-Nepal Border earthquake of 15.01.1934 (Magnitude= 8.3), (v) the Assam 

earthquake of 15.08.1950 (Magnitude= 8.5) and (vi) the Nepal-India Border earthquake 

of 21.08.1988 (Magnitude= 6.4). The 1897 earthquake had its epicentral tract in and 

around Shillong where there was considerable damage to lives and property, in addition 

to other effects of very strong ground shaking. One of the significant observations made 

on this earthquake was that boulders were thrown out vertically upwards from their 

original places showing that the force of earthquake motion exceeded the force due to 

gravity, at least momentarily. The earthquake was followed by a large number of 

aftershocks. 

In addition to the above significant earthquakes, the region has experienced 

several earthquakes of lesser intensity originating within a radius of 450 km around 

Shillong and neighbouring regions. A list of important earthquakes from I.M.D. 

catalogue occurred in the region bounded by Lat. 25.00 to 30.00°N and Long. 86.00 to 

91.00°E for the period 1505 to 2001 is enclosed. 

The occurrence of earthquakes in Sikkim region is broadly associated with the 

tectonic activity along the well-known faults in the Himalayas such as the Main 

Boundary Thrust (MBT) and the Main Central Thrust (MCT). Besides, earthquakes 

occurring along some other faults namely Malda-Kishanganj Fault, Tista Fault, Purnia- 

Everest Lineament, Katihar-Nailphamani Fault, Dhubri Fault etc. have also affected the 

region. 

In the seismic zoning map of India prepared by a committee of experts under the 

auspices of Bureau of Indian Standards (BIS: 1893: Part I 2002), the entire area of 

Sikkim has been placed in the zone IV. The seismic zone IV is broadly associated with 

a seismic intensity VIII on Modified Mercalli (MM) scale. It may be mentioned that the 

seismic intensity VIII corresponds to a horizontal ground acceleration range of 51- 

350cm/sec 2 or an average acceleration of 172cm/sec 2 in any direction. The ground 

acceleration and hence the intensity of an earthquake at a place depends on magnitude 

of earthquake, distance from the focus, duration of earthquake, type of underlying soil 

and its damping characteristics and liquefaction potential. The damage to the buildings

founded on sandy soil is higher than that in the similar type of buildings having their 

foundation on hard bedrock. Also, the damage will be higher for higher magnitude and 

long duration earthquakes, less epicentral distance soft soil conditions and area with 

high liquefaction potential. 

Presently, there is no scientific technique available anywhere in the world to predict 

occurrence of earthquakes with reasonable degree of accuracy with regard to space, 

time and magnitude. It is, therefore suggested that appropriate steps may be taken to 

ensure that the dwellings and other structures in the region are designed and constructed 

as per guidelines laid down by Bureau of Indian Standards (BIS) to minimize the losses 

caused by earthquakes. Suitable seismic design parameters may be adopted as per 

recommendations of National Committee on Seismic Design Parameters (NCSDP) 

for designing and engineering Hydroelectric Projects. 

EXPLANATION OF COMPUTER OUTPUT (IMD CATALOGUE) 

1. “O” – Time means time of Origin of Earthquake in UTC. 

2. “Depth” means Focal Depth in Kilometers. If depth is reported as 33, it means 

that the earthquake is located in the crust but its focal depth could not be 

determined. 

3. “MAG” means magnitude on Richter scale. 

4. “Zero” under any column means that the parameters have not been determined. 

2

MODIFIED MERCALLI INTENSITY SCALE (ABRIDGED) 

CLASS OF REMARKS 

EARTHQUAKE 

I Not felt except by a very few under specially favourable circumstances. 

II Felt only by a few persons at rest, specially on upper floors of buildings; and 

delicately suspended objects may swing. 

III Felt quite noticeably indoors, specially on upper floors of buildings but many 

people do not recognize it as an earthquake; standing motor cars may rock 

slightly; and vibration may be felt like the passing of a truck. 

IV During the day felt indoors by many, outdoors by a few, at night some 

awakened; dishes, windows, doors disturbed; walls make creaking sound, 

sensation like heavy truck striking the building; and standing motor cars rocked 

noticeably. 

V Felt by nearly everyone; many awakened; some dishes, windows, etc. broken; a 

few instances of cracked plaster; unstable object overturned; disturbance of 

trees; polls and other tall objects notices sometimes; and pendulum clocks may 

stop. 

VI Felt by all, many frightened and run outdoors; some heavy furniture moved; a 

few instances of fallen plaster or damaged chimneys and damaged slight. 

VII Everybody runs outdoors, damage negligible in buildings of good design and 

construction; slight to moderate in well built ordinary structures; considerable 

in poorly built or badly designed structures; and some chimneys broken, noticed 

by person driving motor cars. 

VIII Damage slight in specially design structures; considerable in ordinary but 

substantial buildings with partial collapse; very heavy in poorly build structures; 

panel walls thrown out of framed structured; falling of chimney, factory stacks, 

columns, monuments and walls; heavy furniture overturned, sand and mud 

ejected in small amounts; changes in well water; and disturbs person driving 

motor cars. 

IX Damage considerable in specially designed structures: well designed framed 

structures thrown out of plumb; very heavy in substantial buildings with partial 

collapse; buildings shifted off foundations; ground cracked conspicuously; and 

underground pipes broken. 

3

X Some well built wooden structures destroyed; most masonry and framed 

structures with foundations destroyed; ground badly cracks; rails bent; 

landslides considerable from river banks and steep slopes; shifted sand and mud; 

and water splashed over banks. 

XI Few, if any, masonry structures remain standing; bridges destroyed; broad 

fissures in ground, underground pipelines completely out of services; earth 

slumps and landslips in soft ground; and rails bent greatly. 

XII Total damage; waves seen on ground surfaces; lines of sight and levels distorted; 

and objects thrown upward 

4

LIST OF EARTHQUAKES FROM IMD CATALOGUE OCCURING BETWEEN LAT25 . 00 TO 30 . 00 

DEG. AND LONG 86 . 00 TO 91 . 00DEG. E FOR THE PERIOD 1505 TO 2001 

DATE 

O-TIME LAT LONG DEPTH MAG 

Y M D Hr Mn Sec Deg-N Deg-E Km 

1833 8 26 0 0 . 0 27 . 50 86 . 50 0 . 7 . 5 

1834 7 8 0 0 . 0 25 . 80 89 . 40 0 . 6 . 3 

1834 7 21 0 0 . 0 25 . 80 89 . 40 0 . 6 . 0 

1842 2 5 21 15 . 0 25 . 00 87 . 00 0 . 5 . 5 

1842 11 11 0 0 . 0 25 . 00 90 . 00 0 . 6 . 5 

1843 8 10 0 0 . 0 27 . 00 88 . 30 0 . 5 . 5 

1849 2 27 0 0 . 0 27 . 00 88 . 30 0 . 6 . 0 

1852 5 0 0 0 . 0 27 . 00 88 . 00 0 . 6 . 5 

1897 6 12 11 6 . 0 25 . 90 91 . 00 0 . 8 . 7 

1899 9 25 0 0 . 0 27 . 00 88 . 30 0 . 6 . 0 

1909 2 17 0 0 . 0 27 . 00 87 . 00 0 . 5 . 0 

1918 2 4 17 54 49 . 0 29 . 60 87 . 80 0 . 6 . 0 

1923 4 24 22 3 6 . 0 29 . 60 87 . 80 0 . 5 . 5 

1923 9 9 22 3 42 . 0 25 . 30 91 . 00 0 . 7 . 1 

1926 12 4 11 15 23 . 0 29 . 60 87 . 80 0 . 6 . 0 

1930 7 2 21 3 34 . 0 25 . 80 90 . 20 0 . 7 . 1 

1930 7 3 0 19 5 . 0 25 . 80 90. 20 0 . 5 . 5 

1930 7 4 18 54 44 . 0 25 . 80 90 . 20 0 . 5 . 5 

1930 7 4 21 34 . 0 25 . 80 90. 80 0 . 5 . 5 

1930 7 8 4 32 24 . 0 25 . 80 90 . 80 0 . 5 . 5 

1930 7 8 9 43 . 0 25 . 80 90. 80 0 . 5 . 5 

1930 7 13 14 0 12 . 0 25 . 80 90 . 80 0 . 5 . 5 

1932 3 24 16 8 44 . 0 25 . 80 90 . 20 0 . 5 . 5 

1932 3 25 4 29 32 . 0 30 . 00 89 . 20 0 . 5 . 5 

1933 3 6 13 5 38 . 0 25 . 70 90 . 50 0 . 5 . 8 

1934 1 15 8 43 25 . 0 26 . 60 86. 80 0 . 8 . 3 

1934 1 16 4 59 22 . 0 28 . 00 86 . 00 0 . 5 . 6 

1934 7 21 0 0 . 0 25 . 80 89 . 40 0 . 5 . 5 

1935 5 21 4 22 31 . 0 28 . 80 89 . 30 140 . 6 . 3 

1936 5 30 7 8 38 . 0 25 . 70 90 . 50 0 . 5 . 3 

1936 6 9 0 2 42 . 0 27 . 50 87 . 00 0 . 5 . 5 

1936 6 18 14 56 27 . 0 26 . 60 90 . 30 0 . 5 . 8 

1936 9 7 2 30 49 . 0 27 . 50 87 . 00 0 . 5 . 7 

1937 8 15 11 36 48 . 0 30 . 00 90 . 00 0 . 5 . 8 

1938 1 29 4 13 8 . 0 27 . 50 87 . 00 0 . 5 . 8 

1938 2 26 12 10 43 . 0 28 . 00 90 . 50 0 . 5 . 7 

1938 4 13 1 10 17 . 0 26 . 00 91 . 00 0 . 5 . 2 

1939 6 4 22 36 . 0 28 . 50 86 . 50 0 . 5 . 7 

5

1940 8 2 3 3 59 . 0 28 . 00 90 . 50 0 . 5 . 2 

1945 5 19 5 2 53 . 0 25 . 10 90 . 90 0 . 6 . 1 

1949 12 10 19 37 14 . 0 26 . 00 89 . 00 0 . 6 . 0 

1950 2 26 3 35 48 . 0 28 . 00 90 . 50 0 . 6 . 0 

1951 4 7 20 29 12 . 0 25 . 90 90 . 50 0 . 6 . 8 

1951. 5 28 15 59 19 . 0 29 . 00 87 . 00 0 . 6 . 0 

1952 3 6 9 11 23 . 0 29 . 60 90 . 80 0 . 5 . 5 

1952 11 19 10 23 28 . 0 29 . 80 86 . 60 0 . 6 . 0 

1955 3 27 14 38 43 . 0 29 . 90 90 . 20 0 . 6 . 3 

1958 11 23 20 15 48 . 0 28 . 79 86 . 94 0 . 5 . 5 

1959 6 10 4 25 15 . 0 30 . 00 91 . 00 0 . 5 . 7 

1960 7 29 10 42 44 . 6 26 . 90 90 . 30 11 . 6 . 5 

1960 8 21 3 29 4 . 9 27 . 00 88 . 50 29 . 5 . 5 

1961 9 29 22 36 30 . 0 28 . 00 87 . 00 0 . 5 . 5 

1961 12 25 11 19 10 . 0 27 . 00 90 . 00 0 . 5 . 5 

1963 2 22 1 32 30 . 0 27 . 20 87 . 10 0 . 5 . 2 

1964 2 1 11 28 19 . 2 27 . 30 87 . 78 33 . 4 . 8 

1964 3 27 23 3 41 . 1 27 . 13 89 . 36 29 . 5 . 0 

1964 4 13 3 19 57 . 3 27 . 52 90 . 17 1 . 5 . 2 

1964 8 30 2 35 7 . 3 27 . 36 88 . 21 21 . 5 . 1 

1964 11 9 16 12 51 . 9 29 . 53 86 . 04 33 . 5 . 0 

1965 1 12 13 32 24 . 1 27 . 40 87 . 84 23 . 5 . 8 

1965 1 12 13 55 18 . 1 27 . 31 87 . 68 18 . 5 . 2 

1967 3 2 11 47 13 . 0 28 . 70 86 . 38 20 . 4 . 8 

1968 8 18 14 18 58 . 0 26 . 42 90 . 62 22 . 5 . 1 

1968 10 28 17 48 30 . 1 27 . 57 86 . 03 37 . 4 . 9 

1969 11 5 20 25 13 . 7 27 . 66 90 . 24 13 . 5 . 0 

1970 7 25 1 35 26 . 0 25 . 72 88 . 58 32 . 5 . 1 

1971 10 24 8 59 6 . 3 28 . 30 87 . 19 57 . 4 . 8 

1971 10 31 15 54 48 . 2 26 . 18 90 . 65 33 . 4 . 7 

1971 12 4 8 38 . 2 27 . 92 87 . 95 29 . 5 . 2 

1972 8 21 14 4 34 . 2 27 . 33 88 . 01 33 . 4 . 5 

1972 11 6 10 56 13 . 5 26 . 88 88 . 43 59 . 4 . 4 

1973 3 22 1 6 57 . 4 28 . 12 87 . 15 33 . 5 . 0 

1973 8 1 14 5 15 . 5 29 . 59 89 . 17 63 . 4 . 9 

1974 3 24 14 16 1 . 1 27 . 66 86 . 00 0 . 5 . 4 

1974 3 24 16 17 35 . 3 27 . 63 86 . 01 3 . 4 . 7 

1975 1 23 1 37 42 . 6 27 . 44 88 . 37 33 . 4 . 5 

1975 2 6 6 39 48 . 7 27 . 95 87 . 67 63 . 4 . 7 

1975 4 24 1 35 51 . 2 27 . 44 87 . 04 26 . 4 . 9 

1975 6 24 15 38 28 . 1 27 . 74 87 . 50 33 . 4 . 8 

1975 11 21 13 49 27 . 9 26 . 96 86 . 54 0 . 4 . 9 

1975 11 26 15 2 31 . 1 28 . 15 87 . 80 33 . 5 . 0 

1976 9 14 6 43 51 . 6 29 . 81 89 . 57 75 . 5 . 4 

1977 6 5 19 21 37 . 4 26 . 07 88 . 43 0 . 4 . 7 

1978 10 14 18 48 48 . 9 27 . 66 87 . 33 0 . 4 . 8 

1978 10 23 14 36 50 . 4 28 . 56 86 . 78 33 . 4 . 4 

1979 4 2 1 16 46 . 5 26 . 46 90 . 68 33 . 4 . 4 

1979 4 11 16 8 12 . 6 25 . 98 88 . 84 33 . 4 . 7 

1979 6 19 16 29 8 . 4 26 . 74 87 . 48 1 . 5 . 2 

6

1979 10 17 1 44 22 . 2 27 . 97 87 . 62 33 . 4 . 6 

1979 11 16 19 17 27 . 4 27 . 95 88 . 69 39 . 4 . 6 

1980 6 11 5 25 15 . 4 25 . 79 90 . 31 68 . 4 . 9 

1980 11 19 19 0 44 . 5 27 . 40 88 . 80 1 . 6. 0 

1980 12 22 4 36 8 . 0 26 . 67 89 . 59 33 . 4 . 4 

1980 12 26 5 19 44 . 9 29 . 08 88 . 88 66 . 4 . 5 

1981 2 9 15 49 21 . 6 27 . 20 89 . 76 16 . 4 . 9 

1981 11 21 4 25 5 . 6 29 . 52 89 . 12 50 . 4 . 8 

1982 1 28 7 18 7 . 6 25 . 47 90 . 89 33 . 4 . 4 

1982 2 26 0 5 47 . 5 25 . 79 90 . 62 48 . 4 . 6 

1982 4 5 2 19 41 . 1 27 . 38 88 . 84 9 . 5 . 0 

1982 6 20 15 29 19 . 8 26 . 24 89 . 97 33 . 4 . 5 

1982 7 6 6 13 32 . 0 25 . 88 90 . 31 8 . 5 . 0 

1982 8 18 18 1 7 . 6 27 . 04 89 . 26 51 . 4 . 6 

1983 10 16 22 3 14 . 5 29 . 51 90 . 31 33 . 4 . 5 

1983 12 16 15 15 40 . 1 28 . 37 86 . 65 116 . 4 . 2 

1983 12 23 19 35 44 . 2 25 . 87 87 . 91 33 . 4 . 3 

1984 1 25 23 49 44 . 6 27 . 49 86 . 10 11 . 4 . 6 

1985 5 25 0 28 18 . 7 27 . 60 88 . 48 33 . 4 . 6 

1985 6 7 18 23 59 . 0 26 . 87 90 . 21 33 . 4 . 8 

1985 6 17 21 52 49 . 0 25 . 65 90 . 20 22 . 4 . 6 

1985 10 2 16 33 50 . 3 27 . 19 89 . 73 45 . 4 . 4 

1986 1 7 20 20 . 4 27 . 40 88 . 43 41 . 4 . 7 

1986 1 10 3 46 30 . 9 28 . 65 86 . 56 63 . 5 . 5 

1986 2 2 0 13 50 . 7 27 . 92 86 . 45 33 . 4 . 5 

1986 2 10 12 56 23 . 0 28 . 15 87 . 86 87 . 4 . 7 

1986 4 12 12 44 2 . 2 28 . 63 86 . 57 33 . 4 . 8 

1986 10 25 21 25 30 . 4 26 . 12 88 . 26 33 . . 0 

1986 12 1 19 14 29 . 0 28 . 30 87 . 80 10 . . 0 

1987 4 23 9 5 56 . 8 27 . 93 87 . 01 48 . 4 . 7 

1987 4 25 22 13 47 . 0 25 . 30 88 . 46 10 . . 0 

1987 5 10 5 10 42 . 3 28 . 99 87 . 26 33 . 4 . 5 

1987 6 22 23 6 53 . 5 28 . 40 87 . 17 33 . 4 . 1 

1987 9 25 23 16 29 . 0 29 . 84 90 . 37 19 . 5 . 1 

1987 9 26 1 3 3 . 0 29 . 82 90 . 45 33 . 4 . 4 

1987 9 29 17 30 28 . 3 29 . 91 90 . 41 33 . 4 . 6 

1987 9 29 21 12 30 . 0 29 . 70 90 . 41 46 . 4 . 5 

1987 10 6 22 18 17 . 2 29 . 90 90 . 42 10 . 4 . 7 

1987 10 22 21 23 56 . 0 27 . 07 89 . 06 19 . 4 . 2 

1987 11 25 19 20 40 . 0 27 . 70 86 . 17 33 . 4 . 5 

1987 12 6 23 29 44 . 0 27 . 00 88 . 52 42 . . 0 

1987 12 11 6 39 40 . 0 26 . 04 90 . 92 57 . 4 . 6 

1987 12 12 5 49 . 0 29 . 80 90 . 40 45 . 4 . 8 

1988 1 10 6 18 35 . 0 29 . 75 90 . 29 50 . 4 . 7 

1988 1 10 6 31 42 . 7 29 . 89 90 . 44 10 . 4 . 7 

1988 1 19 11 23 51 . 0 27 . 80 88 . 80 33 . 4 . 3 

1988 3 27 5 56 30 . 0 27 . 10 88 . 42 70 . 4 . 1 

1988 4 9 12 57 55 . 7 29 . 84 86 . 87 33 . 4 . 4 

1988 4 20 6 40 25 . 8 27 . 02 86 . 72 55 . 5 . 4 

1988 4 25 16 4 3 . 7 26 . 90 86 . 54 79 . 4 . 7 

7

1988 5 10 7 16 16 . 1 25 . 32 90 . 88 33 . 4 . 4 

1988 5 26 16 30 5 . 5 27 . 45 88 . 61 42 . 4 . 7 

1988 5 28 23 13 12 . 0 28 . 00 89 . 70 33 . . 0 

1988 8 20 23 9 10 . 1 26 . 72 86 . 63 65 . 6 . 4 

1988 8 20 23 38 56 . 0 26 . 90 86 . 70 38 . . 0 

1988 8 22 11 34 34 . 7 26 . 61 86 . 74 33 . 4 . 3 

1988 8 24 9 55 34 . 3 26 . 77 86 . 44 41 . 4 . 7 

1988 8 29 12 12 17 . 0 26 . 39 87 . 50 33 . 4 . 5 

1988 9 1 22 4 11 . 3 26 . 80 86 . 53 33 . 4 . 5 

1988 9 2 6 35 34 . 3 26 . 56 86 . 48 33 . 4 . 3 

1988 9 27 19 10 10 . 0 27 . 19 88 . 37 28 . 5 . 0 

1988 12 10 15 24 31 . 4 26 . 38 86 . 68 33 . . 0 

1988 12 13 6 29 17 . 3 27 . 14 87 . 97 52 . 4 . 4 

1988 12 24 13 32 22 . 0 26 . 90 88 . 00 41 . 4 . 4 

1988 12 27 2 56 1 . 8 27 . 98 87 . 86 38 . 4 . 6 

1989 2 12 23 44 57 . 0 30 . 00 89 . 86 53 . . 0 

1989 4 9 2 31 36 . 3 29 . 11 90 . 02 10 . 5 . 1 

1989 4 16 0 2 33 . 0 29 . 20 89 . 70 33 . . 0 

1989 5 10 23 20 34 . 0 27 . 70 87 . 20 33 . . 0 

1989 5 22 19 24 31 . 0 27 . 38 87 . 86 4 . 5 .0 

1989 6 11 13 42 45 . 7 26 . 39 90 . 70 50 . 4 . 5 

1989 7 30 21 4 44 . 0 30 . 00 90 . 50 33 . . 0 

1989 10 10 4 10 56 . 0 28 . 36 87 . 49 38 . 4 . 7 

1989 11 19 22 11 34 . 0 29 . 00 89 . 70 33 . 4 . 4 

1990 1 9 2 29 21 . 8 28 . 15 88 . 11 35 . 5 . 7 

1990 1 10 23 1 21 . 7 26 . 52 86 . 67 66 . 4 . 4 

1990 2 18 18 12 48 . 3 29 . 39 89 . 95 10 . 4 . 5 

1990 2 22 13 33 16 . 6 29 . 14 90 . 02 54 . 4 . 9 

1990 2 23 14 25 19 . 3 29 . 38 90 . 02 10 . 4 . 3 

1990 3 1 18 47 28 . 0 28 . 70 88 . 40 33 . 4 . 2 

1990 5 6 10 30 9 . 0 29 . 99 89 . 98 33 . 4 . 2 

1990 5 19 2 18 57 . 0 25 . 40 90 . 93 33 . . 0 

1990 7 13 11 50 11 . 0 28 . 20 86 . 90 33 . 4 . 5 

1990 10 29 12 6 28 . 0 27 . 60 89 . 10 33 . . 0 

1991 1 5 14 50 8 . 0 28 . 90 87 . 92 33 . . 0 

1991 3 4 0 55 38 . 0 28 . 10 89 . 20 33 . . 0 

1991 3 15 4 28 18 . 2 28 . 34 87 . 55 64 . 4 . 7 

1991 6 8 18 59 57 . 8 26 . 30 90 . 37 33 . 4 . 0 

1991 8 7 11 36 29 . 1 25 . 27 88 . 66 10 . 4 . 7 

1991 8 19 22 28 41 . 0 26 . 80 90 . 70 10 . . 0 

1991 9 25 19 26 49 . 3 26 . 70 88 . 40 33 . . 0 

1991 9 27 11 56 40 . 8 29 . 90 90 . 40 33 . . 0 

1991 10 30 13 13 57 . 0 26 . 00 88 . 60 33 . . 0 

1991 12 21 19 52 45 . 1 27 . 79 87 . 96 65 . 4 . 7 

1992 3 7 22 41 50 . 8 29 . 40 89 . 40 113 . 4 . 3 

1992 4 1 13 41 3 . 9 27 . 40 87 . 10 33 . 4 . 3 

1992 4 4 17 43 20 . 7 28 . 10 88 . 00 33 . 4 . 9 

1992 4 20 19 22 59 . 7 25 . 80 90 . 60 55 . 4 . 2 

1992 7 24 6 24 17 . 6 29 . 30 90 . 20 33 . 4 . 8 

1992 7 30 8 24 46 . 6 29 .60 90 . 20 14 . 5 . 9 

8

1992 7 30 9 7 39 . 1 29 . 90 90 . 30 33 . 4 . 2 

1992 7 30 13 36 42 . 0 29 . 80 90 . 30 33 . 4 . 4 

1992 7 30 17 28 53 . 9 30 . 00 90 . 40 33 . 4 . 5 

1992 7 30 19 6 13 . 3 29 . 80 90 . 20 33 . 4 . 3 

1992 8 4 22 50 3 . 0 29 . 90 90 . 40 10 . 4 . 2 

1992 8 8 19 50 42 . 6 29 . 90 90 . 30 33 . 4 . 3 

1992 8 9 22 34 46 . 4 28 . 70 86 . 50 37 . 4 . 3 

1993 2 15 14 29 40 . 8 25 . 90 87 . 50 30 . 5 . 0 

1993 3 3 5 17 31 . 0 25 . 40 90 . 20 33 . 4 . 5 

1993 3 20 14 51 59 . 7 29 . 10 87 . 30 12 . 5 . 8 

1993 3 20 21 26 39 . 4 29 . 00 87 . 40 21 . 5 . 0 

1993 3 31 13 44 10 . 1 29 . 10 87 . 30 20 . 5 . 1 

1993 7 3 2 0 22 . 2 28 . 30 86 . 60 33 . 4 . 7 

1993 7 9 16 23 17 . 3 26 . 80 86 . 00 33 . 4 . 6 

1993 9 5 6 5 54 . 6 27 . 20 87 . 30 33 . 4 . 5 

1993 12 14 2 27 44 . 4 28 . 40 86 . 80 33 . 4 . 8 

1993 12 14 2 27 44 . 4 28 . 40 86 . 80 33 . 4 . 8 

1994 1 16 14 22 38 . 3 26 . 40 89 . 10 33 . 3 . 9 

1994 4 15 14 28 48 . 7 25 . 90 90 . 50 33 . 4 . 2 

1994 5 25 7 38 53 . 7 26 . 60 87 . 80 48 . 4 . 6 

1995 1 1 19 36 13 . 6 27 . 80 87 . 60 33 . 4 . 9 

1995 1 12 23 39 51 . 0 29 . 40 88 . 20 33 . 4 . 9 

1995 8 8 16 52 48 . 8 26 . 40 90 . 40 33 . 4 . 4 

1995 12 6 0 50 33 . 0 25 . 20 91 . 00 33 . 4 . 5 

1995 12 11 9 49 36 . 0 27 . 60 87 . 50 33 . 4 . 0 

1996 1 25 7 15 19 . 3 28 . 00 87 . 00 33 . 5 . 2 

1996 1 25 7 15 13 . 0 28 . 40 86 . 90 33 . 4 . 4 

1996 3 23 16 7 34 . 2 27 . 20 88 . 30 33 . 4 . 0 

1996 4 26 16 31 3 . 0 27 . 80 87 . 60 33 . 5 . 2 

1996 5 10 9 7 1 . 8 30 . 00 88 . 10 0 . 4 . 8 

1996 5 11 3 58 50 . 2 29 . 90 88 . 10 0 . 4 . 8 

1996 5 11 7 27 11 . 2 29 . 90 88 . 10 0 . 4 . 3 

1996 5 14 5 41 8 . 9 29 . 70 87 . 90 0 . 4 . 1 

1996 7 3 7 0 28 . 9 29 . 90 88 . 10 0 . 4 . 1 

1996 7 3 10 10 33 . 8 29 . 90 88 . 20 0 . 5 . 0 

1996 7 3 10 19 42 . 9 30 .00 88 . 20 0 . 4 . 3 

1996 7 3 10 49 50 . 5 29 . 90 87 . 80 0 . 4 . 1 

1996 7 4 18 11 4 . 6 30 . 00 88 . 10 0 . 4 . 9 

1996 7 6 8 12 39 . 4 29 . 90 87 . 90 0 . 3 . 8 

1996 7 13 8 29 4 . 0 29 . 90 88 . 10 0 . 4 . 3 

1996 7 22 15 54 7 . 0 30 . 00 88 . 00 0 . 4 . 5 

1996 8 3 7 12 6 . 0 30 . 00 88 . 20 0 . 4 . 1 

1996 8 18 2 48 . 0 25 . 80 90 . 10 0 . 4 . 4 

1996 9 13 3 41 8 . 6 27 . 00 88 . 20 33 . 4 . 5 

1996 9 25 17 41 17 . 2 27 . 40 88 . 50 33 . 5 . 0 

1996 10 3 1 29 3 . 1 28 . 20 87 . 50 33 . 4 . 5 

1996 10 14 14 49 12 . 7 29 . 90 88 . 20 33 . 4 . 4 

1996 12 30 11 8 18 . 9 27 . 43 86 . 63 37 . 5 . 0 

1996 12 30 15 16 29 . 5 27 . 23 86 . 50 33 . 3 . 6 

1997 1 22 11 12 4 . 4 25 . 60 90 . 30 33 . . 0 

9

1997 1 25 20 8 28 . 7 30 . 00 88 . 00 33 . 4 . 4 

1997 3 3 9 29 40 . 0 27 . 24 86 . 00 45 . 4 . 7 

1997 3 22 21 16 4 . 8 29 . 89 88 . 15 33 . 4 . 4 

1997 4 4 10 8 41 . 0 25 . 50 90 . 80 33 . 3 . 8 

1997 4 7 13 0 42 . 0 27 . 40 86 . 50 33 . 4 . 4 

1997 5 26 0 45 32 . 1 27 . 70 86 . 90 33 . . 0 

1997 7 5 6 22 53 . 5 28 . 80 86 . 86 33 . 4 . 8 

1997 7 8 21 16 49 . 8 29 . 83 88 . 31 33 . 3 . 7 

1997 7 9 7 18 52 . 9 29 . 90 88 . 40 33 . 4 . 1 

1997 7 12 23 41 9 . 7 29 . 90 88 . 40 33 . . 0 

1997 8 10 11 53 17 . 2 29 . 16 89 . 49 33 . 3 . 4 

1997 8 17 20 3 32 . 8 28 . 13 87 . 56 33 . . 0 

1997 9 18 7 37 10 . 0 28 . 87 86 . 15 33 . 4 . 6 

1997 10 11 10 11 10 . 3 27 . 70 86 . 40 33 . 4 . 3 

1997 10 12 19 45 25 . 8 30 . 00 88 . 00 33 . . 0 

1997 10 30 2 2 52 . 0 29 . 50 89 . 70 33 . 5 . 3 

1997 10 30 20 3 . 0 29 . 20 89 . 40 0. 4 . 9 

1997 11 14 12 30 23 . 9 25 . 30 87 . 70 33 . . 0 

1997 11 27 16 11 57 . 0 27 . 60 87 . 34 33 . 5 . 1 

1997 11 27 16 55 52 . 1 27 . 70 87 . 76 33 . 4 . 2 

1997 12 8 2 3 55 . 8 27 . 48 87 . 17 33 . 5 . 0 

1997 12 8 6 37 57 . 8 27 . 48 87 . 16 33 . . 0 

1998 1 16 18 6 42 . 5 30 . 00 86 . 00 33 . 4 . 0 

1998 2 1 17 32 48 . 2 28 . 10 87 . 10 33 . 4 . 5 

1998 2 12 2 40 29 . 1 26 . 50 88 . 10 33 . 4 . 6 

1998 2 28 4 59 30 . 7 27 . 00 87 . 50 33 . 4 . 4 

1998 3 15 20 35 29 . 3 28 . 55 86 . 88 33 . 4 . 4 

1998 3 16 10 35 2 . 0 26 . 90 89 . 68 33 . 3 . 8 

1998 3 18 18 12 18 . 9 27 . 36 88 . 33 33 . 4 . 0 

1998 5 13 1 24 55 . 6 28 . 18 89 . 80 10 . 4 . 9 

1998 7 31 17 50 18 . 3 28 . 01 87 . 73 33 . 4 . 1 

1998 8 18 4 10 20 . 6 27 . 55 90 . 98 22 . 5 . 2 

1998 8 24 7 32 21 . 5 30 . 00 87 . 92 33 . . 0 

1998 8 25 9 43 6 . 0 29 . 99 88 . 09 33 . 4 . 1 

1998 8 25 9 56 44 . 0 29 . 83 87 . 91 33 . 4 . 4 

1998 8 25 10 25 6 . 0 29 . 98 88 . 10 33 . 4 . 4 

1998 8 25 12 43 4 . 3 29 . 96 88 . 09 33 . 4 . 4 

1998 8 25 13 39 49 . 5 29 . 92 88 . 12 33 . 3 . 8 

1998 8 25 15 16 2 . 7 29 . 97 88 . 10 33 . 4 . 4 

1998 8 30 3 49 48 . 1 29 . 90 87 . 98 33 . 4 . 0 

1998 9 3 18 15 56 . 5 27 . 85 86 . 94 33 . 5 . 6 

1998 9 3 18 22 19 . 2 27 . 97 87 . 04 33 . . 0 

1998 9 3 18 51 38 . 6 27 . 65 86 . 80 33 . 4 . 4 

1998 9 3 21 0 53 . 5 27 . 72 86 . 88 33 . 4 . 1 

1998 9 3 23 2 28 . 3 27 . 60 86 . 73 33 . 4 . 6 

1998 9 4 0 36 17 . 9 27 . 45 86 . 46 33 . 4 . 1 

1998 9 4 1 10 18 . 4 27 . 77 86 . 79 33 . 4 . 2 

1998 9 4 21 16 13 . 7 27 . 65 86 . 72 33 . . 0 

1998 9 6 21 35 49 . 4 27 . 86 86 . 89 33 . 4 . 6 

1998 9 10 22 57 16 . 9 27 . 20 88 . 34 33 . 4 . 7 

10

1998 9 12 5 8 52 . 1 27 . 85 86 . 90 33 . 4 . 2 

1998 9 21 23 24 40 . 6 29 . 94 88 . 00 33 . 4 . 1 

1998 9 26 20 48 44 . 1 27 . 52 86 . 13 33 . 3 . 9 

1998 9 30 2 29 55 . 1 29 . 94 88 . 11 33 . 5 . 1 

1998 10 11 22 0 49 . 9 26 . 35 86 . 40 90 . 4 . 4 

1998 10 13 14 47 51 . 9 29 . 74 87 . 88 33 . . 0 

1998 10 16 14 17 16 . 7 30 . 00 88 . 19 33 . . 0 

1998 11 26 10 14 27 . 6 27 . 75 87 . 89 73 . 5 . 1 

1998 12 1 5 35 9 . 2 27 . 93 87 . 64 33 . 4 . 8 

1999 1 28 16 10 33 . 9 28 . 22 87 . 31 41 . 4 . 0 

1999 3 25 5 4 54 . 3 28 . 51 88 . 28 33 . 3 . 8 

1999 3 25 20 47 57 . 4 28 . 50 87 . 63 13 . 4 . 2 

1999 3 31 22 32 57 . 8 28 . 57 86 . 81 21 . . 0 

1999 4 10 20 42 39 . 7 28 . 04 87 . 85 33 . 4 . 2 

1999 5 7 17 53 52 . 3 27 . 22 90 . 64 33 . . 0 

1999 5 9 8 8 57 . 7 27 . 40 89 . 45 15 . . 0 

1999 6 13 7 38 6 . 4 28 . 14 86 . 64 33 . 4 . 4 

1999 7 4 6 5 15 . 2 25 . 42 90 . 28 33 . 3 . 8 

1999 8 1 8 24 51 . 2 28 . 37 86 . 79 40 . 5. 0 

1999 9 5 2 28 22 . 8 28 . 07 87 . 53 33 . 4 . 5 

1999 9 8 18 8 27 . 9 27 . 90 87 . 91 19 . 3 . 7 

1999 9 16 12 20 9 . 8 27 . 55 87 . 71 33 . . 0 

1999 9 20 7 28 5 . 6 27 . 24 87 . 98 23 . 4 . 1 

1999 9 21 13 54 39 . 8 25 . 16 88 . 86 2 . 3 . 9 

1999 10 15 7 33 1 . 0 29 . 61 90 . 06 33 . 4 . 4 

1999 10 18 16 12 55 . 7 26 . 68 87 . 22 33 . . 0 

1999 11 5 15 57 21 . 4 28 . 59 87 . 08 23 . 3 . 7 

1999 11 17 5 27 14 . 0 28 . 09 89 . 18 33 . 3 . 6 

1999 1 28 16 10 33 . 9 28 . 22 87 . 31 41 . 4 . 0 

1999 3 25 5 4 54 . 3 28 . 51 88 . 28 33 . 3 . 8 

1999 3 25 20 47 57 . 4 28 . 50 87 . 63 12 . 4 . 2 

1999 4 10 20 42 39 . 7 28 . 04 87 . 85 33 . 4 . 2 

1999 6 13 7 38 6 . 4 28 . 14 86 . 64 33 . 4 . 4 

1999 7 4 6 5 15 . 2 25 . 42 90 . 28 33 . 3 . 8 

1999 8 1 8 24 51 . 2 28 . 37 86 . 79 40 . 5 . 0 

1999 9 5 2 28 22 . 8 28 . 07 87 . 53 33 . 4 . 5 

1999 9 8 18 8 27 . 9 27 . 90 87 . 91 19 . 3 . 7 

1999 9 20 7 28 5 . 6 27 . 24 87 . 98 22 . 4 . 2 

1999 9 21 13 54 39 . 8 25 . 16 88 . 86 2 . 3 . 9 

1999 10 15 7 33 1 . 0 29 . 61 90 . 06 33 . 4 . 4 

1999 11 5 15 57 21 . 4 28 . 59 87 . 08 23 . 3 . 7 

1999 11 7 5 11 57 . 6 27 . 10 89 . 13 14 . 3 . 8 

1999 11 17 5 27 13 . 8 28 . 04 89 . 22 33 . 3 . 3 

2000 1 20 12 54 27 . 5 27 . 78 86 . 02 33 . 5 . 0 

2000 1 25 12 7 33 . 3 29 . 94 89 . 72 0 . 5 . 0 

2000 2 21 18 21 43 . 2 28 . 36 86 . 56 33 . 4 . 7 

2000 3 13 20 44 38 . 3 27 . 43 87 . 85 108 . 4 . 1 

2000 4 18 7 53 45 . 2 26 . 55 90 . 26 33 . 3 . 3 

2000 6 20 7 16 43 . 8 26 . 04 90 . 31 33 . 4 . 3 

2000 9 6 7 19 8 . 9 28 . 52 86 . 86 33 . 4 . 2 

11

2000 10 3 17 8 22 . 4 26 . 88 89 . 8 33 . 2 . 8 

2001 1 16 8 6 57 . 4 26 . 42 90 . 24 33 . . 0 

2001 2 9 10 20 55 . 7 27 . 24 89 . 67 13 . 3 . 9 

2001 2 27 1 46 7 . 0 26 . 48 90 . 55 20 . 4 . 7 

2001 2 27 16 21 25 . 6 28 . 38 86 . 97 33 . 4 . 9 

2001 4 3 23 8 38 . 0 27 . 74 86 . 13 33 . 4 . 6 

2001 4 3 23 26 4 . 4 27 . 82 86 . 18 18 . 3 . 5 

2001 4 8 18 35 49 . 3 28 . 16 88 . 57 20 . 3 . 9 

2001 4 20 18 35 2 . 7 26 . 13 90 . 67 33 . 4 . 6 

2001 4 28 10 37 59 . 1 28 . 55 87 . 14 33 . 5 . 0 

2001 4 29 10 39 9 . 1 28 . 70 87 . 14 33 . 4 . 5 

2001 5 3 16 2 59 . 6 27 . 63 90 . 47 33 . 3 . 8 

2001 5 21 21 55 7 . 8 28 . 54 86 . 72 33 . 3 . 8 

2001 6 12 10 47 46 . 6 28 . 46 86 . 57 20 . 3 . 9 

2001 7 3 19 16 18 . 4 26 . 15 89 . 20 6 . 3 . 6 

2001 7 6 23 4 3 . 4 27 . 65 88 . 64 10 . 2 . 7 

2001 8 6 6 23 32 . 7 27 . 47 87 . 47 9 . 4 . 3 

2001 9 4 22 8 3 . 7 25 . 37 90 . 96 15 . 3 . 7 

2001 9 27 22 40 11 . 1 26 . 99 87 . 76 2 . 4 . 1 

2001 12 2 22 41 14 . 8 27 . 18 88 . 33 15 . 4 . 8 

NO. OF EARTHQUAKES = 358 

12

PRELIMINARY RANKING STUDY REPORT- BY CEA 

Rangyong Hydro Electric Scheme (Org. No. HEPR-PS-BHM-764) 

Annexure 6.1 

The water of Talung Chhu rivers and also its tributaries the Umaram and Passaram can 

possibly be utilized for power generation by constructing (i) two diversion structures one 

on the main Talung Chhu immediately downstream of confluence of Umaram and 

Passaram tributaries and the other across the Rukel Chhu (ii) a small tunnel connecting 

two diversions (iii) a tunnel diverting the waters of Talung Chhu and droping the same to 

a power house & (iv) a power house on the main Talung Chhu at a site where the river 

bed level is of the order of +1085 m. Between the diversion level as + 1795 m. and the 

tailrace level as +1085 m. a gross head of 710 m. would be available enabling a firm 

power output of about 22 MW. The schemes would have an installed capacity of about 

175 MW. And would enable annual energy generation of 785 GWH and 853 GWH 

respectively in 90% and 50% dependable years.

TITLE 

ANNEXURES 6.2 



No. 

Reply on CWC’s Comments on Hydrology 1-3 

Summary of Discussions on Power Potential 

studies 

4-5 

Reply on Comments of SP&PA Division CEA 6-7 

Reply on comments on CMDD(E&NE), CWC 8

REPLY ON CWC’s COMMENTS ON HYDROLOGY OF 


1 

Annexure 6.2 

In reference to your letter no. NH/CON-229 dt. 5-1-2004. Point wise reply to the CWC observations for the 

project is placed as below: 

CWC Observations Reply of NHPC 

Data availability Rainfall - The report has quoted the paper 

of Sh. Biswas and Bhadram in which data 

of 42 raingauge stations, 24 of which is 

equipped with SRRG have been stated to 

be available. However rainfall data has 

not been furnished in the report and only 

the period of data availability of 11 

raingauge stations located u/s of the 

Teesta-V HEP is given in the report. 

Though the rainfall data of 11 raingauge 

stations are lying in the project catchment 

area under consideration, the project 

authorities may put their efforts to verify 

whether any of the rain gauges out of the 

remaining 31 raingauges as mentioned in 

the report lies in the catchment area under 

consideration and to explore the 

possibilities of utilization of this data in 

the study. 

Discharge – It is stated in the report that 

discharge data is available for the period 

Jan 75 to Aug 85 and April 90 to Apr 98 

on Tolung Chu, which is located d/s of 

the proposed project site having a 

catchment area of 731 Sq.km. But the 

discharge data and the methodology 

adopted for collection have not been 

furnished. 

Consistency of 

data 

The project authorities may verify 

whether any of the rain gauges out of the 

remaining 31 raingauges as mentioned in 

the report of C.V.V Bhadram are located 

in the sub-basin under consideration and 

to collect the rainfall data of these sites 

None of the raingauge stations out of the 

remaining 31 raingauges as mentioned in the 

report of C.V.V Bhadram are located in the 

sub-basin under consideration. 

Similarly, the discharge data at on Tolung Chu 

has been used only for comparison purpose and 

not adopted finally for water availability, hence 

the basic data not given in report. However, the 

discharge data at Tolung Chu has been taken 

from the report of Teesta H.E Project Stage-III 

& VI submitted by CWC itself. 

None of the raingauge stations out of the 

remaining 31 raingauges as mentioned in the 

report of C.V.V Bhadram are located in the 

sub-basin under consideration.

Water 

availability 

studies 

and to utilize the same. The data and the 

consistency check done on it may be 

furnished. 

c) Before discarding the G&D data of 

Tolung Chu site the project authorities are 

advised to verify whether any of the 

remaining 31 rain gauges mentioned in 

the report of the Bhadram are located in 

the sub-basin and to collect the data of 

these sites and to utilize the same after 

applying consistency check. 

(d) The approved series of Lachen G&D 

used for converting to the present project 

may also be appended. 

(e) The basis of deriving the catchment 

reduction factor is not given. 

(f) Integrated studies on water availability 

may be done incorporating the likely 

releases from the u/s power house and 

independent catchment contributions. 

Design Flood (a) The design flood studies done by 

NHPC are too empirical to be relied 

upon. 

(b) In the absence of short interval 

concurrent rainfall runoff data the design 

flood may be calculated using relevant 

sub zonal report of CWC taking into 

account the recommendations of 1993 

workshop and by collecting PMP/SPS 

values from IMD. The results may be 

compared before recommending the 

design flood. 

Sedimentation Sedimentation rate for the projects in the 

region given in the compendium on 

siltation published by CWC is higher than 

the value adopted by the project 

authorities. The rate given in the 

2 

(c) As stated earlier also, none of the remaining 

31 rain gauges mentioned in the report of the 

Bhadram are located in the sub-basin of the 

proposed project. 

(d) The available average 10-daily series at 

Lachen is enclosed as Annexure (I). 

(e) The catchment reduction factor has been 

obtained on the basis of rainfed area at both the 

sites. Rainfed catchment of Lachen site is 574 

Sq.km and of Rangyong is 92 and 102 Sq.km 

for the two diversion structures. 

(f) Cascade development need to be done at a 

later stage. 

As already explained in our earlier reply also, 

for such detailed studies as suggested for this 

stage i.e PFR, neither the database is at all 

sufficient nor necessacity felt by us. During 

feasibility stage, deterministic/probabilistic 

approach will be used, based on more observed 

data. 

As per report of “Compendium on silting of 

reservoirs in India”, the sediment rate varies 

from 0.05658 to 0.2785 Ham/Sq.km/year for 

Indus, Ganga and Brahmaputra basin. But the

compendium on siltation will be the most 

likely value after construction of projects 

and the same may be incorporated in the 

proposal stage. As stated in the report 

detailed study may be done. 

As per the terms of preparation of PFRs 

and as emphasized in the meetings 

conducted by CEA sedimentation studies 

are required to be carried out and 

incorporated in the PFRs. However such 

studies have not been given to HSO/CWC 

for vetting. 

General The PFR must bring out the limitations of 

the hydrological studies carried out for 

the PFR and suggest improvements, 

specific recommendations for opening 

new hydrological stations, method of 

observations, data to be collected etc. 

may be given which will help us as 

guidance to the agency taking up the 

detail investigations/DPR must review the 

network in consultation with HSO, 

CWC.The hydrological studies for the 

PFR may be revised incorporating the 

above observations and resubmitted. 

3 

silt rate adopted for this particular project has 

been calculated on the basis of observed 

sediment data at Dikchu and is more region 

specific than that given in the report. Also silt 

rate is usually calculated based on the observed 

sediment data at or near the proposed site. The 

necessity of detailed sedimentation study 

showing the new zero elevation, revised area 

capacity curve etc. is not felt during PFR stage. 

The PFR has pointed out the limitation of the 

studies after each study and establishment of 

G&D site, rainfall stations etc. are also 

highlighted in the PFR. 

Moreover, all the CWC comments along with 

their replies are also being appended in the 

PFR’s for future reference.

SUMMARY RECORD OF DISCUSSIONS OF MEETING TAKEN BY 

DIRECTOR (HP&I), CEA WITH NHPC ON 24.12.2003 REGARDING 

POWER POTENTIAL STUDIES OF PFRS OF RINGPI & RANGYONG HE 

PROJECTS IN SIKKIM. 

(Letter no 7/9/2003/HP&I/1581-1582 dated 24.12.2003) 

Power potential studies of Ringpi & Rangyong H.E. Projects in Sikkim were 

discussed in detail and summarized as under : 

1 Ringpi HE Project : 

i. Only power potential studies without any write up was presented by NHPC 

officers and the same was discussed. 

ii. Hydrology may be got cleared by CWC. 

iii. NHPC have furnished studies considering FRL at +2940 m. and tail water 

level of +1853 m. (+3 m. above the FRL of proposed Lingza HE 

Project). NHPC Officers indicated that sufficient pondage is available 

for peaking operation. NHPC was advised to furnish basis of FRL, 

MDDL and tail water level in the concerned chapter of PFR. 

iv. Based on the studies presented by NHPC an installed capacity of 70 MW 

was considered to be in order subject to approval of hydrology by CWC. 

It was suggested that two units of 35 MW each could be installed in case 

there is no problem of transportation. 

v. NHPC may prepare summary of the studies indicating yearly inflow, annual 

energy generation, load factor of operation during monsoon and lean flow 

period. 

vi. NHPC may indicate recommendation for further studies at the time of 

FR/DPR. 

2. Rangyong HE Project : 

i. Only power potential studies without any write up was presented by NHPC 

officers and the same was discussed. 

ii. Hydrology may be got cleared by CWC. 

4

iii. NHPC was advised to keep the tail water level of the project about 3 m. 

above FRL of the downstream project. NHPC Officers indicated that 

sufficient pondage is available for peaking operation. NHPC was advised 

to furnish basis of FRL, MDDL and tail water level in the concerned 

chapter of PFR. 

iv. NHPC has proposed an installation of 150 MW. The power potential studies 

presented by NHPC are generally in order subject to compliance of the above 

comment and approval of hydrology by CWC. 

v. NHPC may prepare summary of the studies indicating yearly inflow, annual 

energy generation, load factor of operation during monsoon and lean flow 

period. 

vi. NHPC may indicate recommendation for further studies at the time of 

FR/DPR. 

5

REPLY ON COMMENTS OF SP&PA DIVISION ON DRAFT PFR OF 


(CEA Letter No.7/9/(NHPC)/2003/HP&I/111 dated 20.01.2004 ) 

Sr.No. Comments Reply 

7.1 

General 

Rangyong HEP is a run of the river 

scheme and situated in the Dzongu 

area of North district of Sikkim. The 

project envisages construction of 65m 

high two concrete gravity dam. The 

underground power house is just 

It is general description of the 

project and no reply is required. 

upstream of the confluence of 

Rangyong chu and Rangyong chu. 

7.2 

7.3 

Construction Power 

The construction power will get from 

existing 2X2.5 MVA 66/11 KV 

Phadong near Mangan. 

Switchyard 

No details of switchyard are given. 

7.4 Power Evacuation: 

Power will be generated at 11KV and 

stepped up to 220KV through 10no 

20MVA 11/220KV single phase unit 

transformer. Evacuation of power 

generated at Rangyong HEP can be 

done through 1 no 220KV double 

circuit 30km line to be connected at 

the pooling point which can be 

assumed to come up near Teesta-II 

6 

This is already discussed in Chapter 

–X of the PFR 

6 nos. of bays have been taken at 

switchyard which have been 

indicated in the cost estimate based 

on the tentative scheme envisaged at 

this stage. However, 8 nos of bays 

have been envisaged in dimension of 

170 X 100m switchyard taking into 

account 132/220KV bay for power 

coming from Rukel HEP and a 

future bay. Further details of 

switchyard are normally worked out 

during FR/DPR stage. 

No reply is required.

HEP, which is in order. 

7.5 Cost: 

According to PFR 6 no of 220KV line 

bays has been taken: 

Generator bays -3 

220KV line bays – 2 

Bus Coupler bays – 1 

Which is in order. 

7 

No reply is required.

REPLY ON COMMENTS OF CMDD DIRECTORATE, CWC ON PFR OF 


(Letter No CWC P.U. No. 20/2/03-CMDD(E&NE)/136 dated 26.2.2004) 

Comments of CEA/CWC Replies of Design Division 

1. It should be mentioned in the report 

that the PMF value has been vetted by 

hydrology (NE) 

Dte. CWC. 

8 

Hydrology adopted is as per 

decisions taken in the progress 

review meeting with CEA.

Rangyong - Ministry of Power

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