Lingza - Ministry of Power

CHAPTER 

I 

TABLE OF CONTENTS 

DESCRIPTION 

Executive Summary 

Preliminary Feasibility Report 

Lingza HE Project (3 x 40 MW) 

PAGE NO. 

1-9 

II Background Information 10-17 

III Project Area 18-25 

IV Topographical & Geo-technical Aspects 26-33 

V Hydrology 34-53 

VI Conceptual Layout and Planning 54-64 

VII Power Potential Studies 65-97 

VIII Power Evacuation 98 

IX Environmental Aspects 99-119 

X Infrastructure 120-123 

XI Construction Planning & Schedule 124-129 

XII Cost Estimate 130-165 

XIII Economic Evaluation 166-173 

Plates 

Annexures

TITLE 

LIST OF DRAWINGS 



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 

Layout Plan-Dam Area 6.3 

Layout Plan-Power House Area 6.4 

Water Conductor System L-Section 6.5 

Dam Upstream Elevation 6.6 

Dam: Spillway & Non-Overflow Cross Section 6.7 

Typical Cross Section Of Constituents Of Water 

Conductor System & Diversion Tunnel 

Single Line Diagram – Power Evacuation 8.1 

6.8

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 Lingza Hydroelectric Project located in North Sikkim district of Sikkim envisages 

utilization of the waters of the river Ringpi a tributary of river Rangyong for power 

generation on a run of river type development, harnessing a head of about 746m. 

The project with a proposed installation of 120MW (3 x 40MW) would afford an annual 

energy generation of 477.51 GWh in a 90% dependable year. The tariff from the project 

at present day cost would be Rs2.62 per KWh(levellised). 

The diversion site is located at Latitude 27º36’ North, Longitude 88º27’20” East. The 

dam site is approachable from Mangan-Lingza road by a footpath of 5km. The dam site is 

at a distance of about 7km from Lingza and about 24km from Mangan, the head quarter 

of North Sikkim district. The nearest railhead is at New Jalpaiguri and airport at 

Bagdogra. 

1.1 GENERAL PROJECT FEATURES 

The Lingza HE Project envisages construction of : 

• a 75 m high concrete Dam across river Ringpi to provide a live storage of 

1.71mcum. with FRL at 1850m and MDDL at 1830m; 

• two intakes and two desilting chambers of size 95m(L)x5m(W)x7.5m(H) to 

remove silt particles of size 0.2mm and above; 

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

• a 40m high, 10m dia surge shaft; 

• 900m long, 2m dia one pressure shaft; 

• an underground power house having an installation of 3 Pelton turbine generating 

units of 40 MW each operating under a net head of 736m; and

2 



• 250m 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 line to be connected at the pooling station, which is assumed to come up 

near Teesta-III HE Project to feed power to the national grid. 

The salient features of the projects are as under: 

LOCATION 

SALIENT FEATURES 

State Sikkim 

District North Sikkim 

River Ringpi 

Location Of Dam Site U/S Of Ishana Village 

Location Of Power House U/S Of Village Lingza 

Nearest Rail Head New Jalpaiguri 

Nearest Airport Bagdogra 

Latitude 27º36’00’’& 27º33’46’’ 

Longitude 88º27’20’’& 88º26’39’’ 

HYDROLOGY 

Catchment Area 198 Km² 

Design Flood (PMF) 940 Cumecs 

DIVERSION TUNNEL 

Diameter & Shape 6 M, Horse-Shoe 

Length 400 M 

Diversion Discharge ±300 Cumecs

Diversion Tunnel Gate 2nos., 3 M X 7.5 M 

COFFER DAMS 

DAM 

3 



Type Rock Fill With U/S Concrete Facing 

Max. Ht Of U/S Coffer Dam 20M 

Max. Ht Of D/S Coffer Dam 10M 

Type Concrete Gravity With Central Spillway 

Dam Top EL 1855 M 

River Bed Level EL 1795M 

Length At The Top 320 M 

Dam Height (Above River Bed 

Level) 

Max. Dam Height (Above Deepest 

Fdn. Level) 

SPILLWAY 

60 M 

75 M 

Type Low Level Orifice Type 

Crest Elevation EL 1810 M 

Number & Size Of Spillway Opening 3 Nos, 4 M (W) X 6 M (H) 

Design Flood 940 Cumecs 

RESERVOIR 

Full Reservoir Level (FRL) EL 1850 M 

Min. Draw Down Level (MDDL) EL 1830 M 

Area Under Submergence At FRL 10.75 Ha 

Gross Storage 2.64MCM

Live Storage 1.71 MCM 

INTAKE 

Invert Level EL 1820 M 

Number Of Intakes 2 NO. 

Size Of Each Gate 3 M (W) X 3 M (H) 

Design Discharge 22.16 Cumecs 

Stoplogs 1 Set Of Stoplog (3 M Wide) 

Trash Rack Steel Trash Rack With M/C 

DESILTING CHAMBERS 

Type & Numbers 2 No;. Dufour Type 

4 



Design Discharge 11.08 Cumecs Each (Including 20% 

Flushing Discharge) 

Particle Size To Be Removed 0.2mm And Above (90% Efficiency) 

Size Of Chamber 95 M(L) X 5 M (W) X 7.5M(H) 

SILT FLUSHING TUNNEL 

HRT 

Shape & Size 1 M X 1.8 M, D-Shaped 

Shape And Size Horse-Shoe, 3.3 Dia 

Length 4 Km 

No. Of Adits 2 (3.3 M Dia, D-Shaped) 

SURGE SHAFT 10 M Diameter & 40 M High 

PRESSURE SHAFT 

Number & Type One, Inclined

Shape Circular, Steel Lined 

Length 900 M (Inclined) 

Diameter 2 M 

No. Of Adits (3.3 M Dia D-Shaped) 

POWER HOUSE 

Type And Location Under Ground; Left Bank 

Design Discharge 18.47 Cumecs 

Type Of Turbine Vertical Pelton 

Power House Size 100 M X 17m X 40m 

Gross Head 746 M 

Rated Net Head 736m 

Centre Line Of M/C 1097m 

Installed Capacity 120 Mw 

TAILRACE TUNNEL 

Shape And Size Horse Shoe, 3.3 M Dia 

Length 250 M 

Tail Water Level El.1095 M 

SWITCHYARD 

Size 200M X 150 M 

POWER GENERATION 

Installed capacity 120 MW 

Annual Energy generation in a 90% 

dependable year & 95% machine 

availability 

5 

477.51MU 


Lingza HE Project (3 x 40 MW)

COST ESTIMATES & FIANANCIAL ASPECTS ( Rs. Crores) 

Civil Works 527.68 

Electro Mechanical Works 97.36 

Sub Total (Generation) 625.04 

Transmission Works 5.01 

Total (Hard Cost) 630.05 at June,2003 Price Level 

Interest During Construction 69.75 

Grand Total 699.80 

Tariff for first year per KWh 

a. with 12% free power 

b. without 12% free power 

Levellised Tariff per KWh 

a. with 12% free power 

b. without free power 

6 

Rs. 3.24 

Rs. 2.85 

Rs. 2.62 

Rs. 2.31 

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 

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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 components of the project. The geological survey of the 

near by area was also carried out to co-relate the geology of the project area. The dam 

location has been fixed after observing the rock exposures on both the banks and in the 

riverbed. 

1.3.2 Hydrology 

The river Ringpi drains a catchment area of about 198sq.km at the proposed dam site. 

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 

Lingza dam site has been derived from the above data on the basis of catchment area 

proportion and applying an overall reduction factor of 0.22. The computed inflow series 

works out has been utilized for Power Potential Studies. The design flood has been 

assessed as 940cumecs. 

1.3.3 Power Potential Studies 

The computed inflow series for 21 years viz June 1976 to May 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 120MW 

comprising 3 generating units of 40MW has been proposed. The energy availability from 

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

Annual Energy Generatio n 

Annual Energy Generation (GWh) 477.51

Annual Load Factor (%) 47.42 

Generation during Lean Flow Season (Sept – JuneI) 

Energy Output (GWh) 225.79 

Load Factor (%) 28.72 

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

worked out at 477.51 GWh. 

A pondage of 1.71 mcum has been provided in the diversion dam which would enable the 

station to operate as peaking station. The pondage is equivalent to 3086.61 MWh which 

sufficient to operate the station for 3 hours. 

1.3.4 Power Evacuation Aspects 

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

circuit line to be connected at the pooling station assumed to come up near Teesta –III 

HE Project to feed power to the 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 112ha. 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 Cost 

The project is estimated to cost Rs. 699.80 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 : 527.68 

Electro Mechanical Works : 97.36 

Sub Total (Generation) : 625.04 

Transmission Works : 5.01 

Total (Hard Cost) : 630.05 

Interest During Construction : 69.75 

Grand Total : 699.80 

1.3.7 Financial Aspects 

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As indicated above, the Lingza HE project with an estimated cost of Rs. 699.80crores 

(including IDC of Rs. 69.75crores) and design energy of 477.51GWh in a 90% 

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

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. 3.24/KWh 

& Rs. 2.62/KWh respectively. 

1.3.8 Conclusion 

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

The project would afford a design energy of 477.51 GWh in a 90% dependable year. The 

cost per MW installed work out Rs.5.21Crore. 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 

10 



Sikkim has elected to join the Indian Union to become 22 nd state 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

11 



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

Besides 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

12 



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 

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

13 



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 

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 Lingza is one of the such scheme 

for PFR. 

2.1.5.2 About The Project 

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

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

construction of a 75m high concrete dam, a 4.0 Km long headrace tunnel and an 

underground powerhouse with an installed capacity of 120 MW. The project shall 

generate 477 MU of energy in a 90% dependable year. The dam site is located about 5.0 

Km u/s of the confluence of river Ringpi Chu and Rangyong Chu.and 6.0Km u/s of 

village Lingza. The underground powerhouse is located about 750 m u/s of the 

confluence of Ranyong Chu and Ringpi Chu near the place called Chhana. The village 

Lingza, nearest to Power house site, is well connected from Mangan by 17 km long state 

PWD road. 

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.

14 



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. 

The proposed Lingza Hydro electric project located in north Sikkim is envisaged to feed 

power at a pooling point near Teesta III H.E. Project (Approx 2 Km from Teesta-III) via 

one double circuit line. 

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 10 th and 11 th Five Year Plans is 

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

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

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 10 th 

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 

15 



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 

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

2.2.3 Load Demand & Power Position of Eastern Grid 

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

2.3 NECESSITY OF THE PROJECT AND RELATED ASPECTS 

16 



The need for Lingza 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 in Teesta basin in North Sikkim District, Sikkim. It will generate 477.51 MU in 

90% dependable year (1976-77) with 95% machine availability. 

The proposed Lingza Hydro Electric project located in north Sikkim is envisaged to feed 

power at a pooling point near Treesta-III H.E. Project (Approx 2 Km from Teesta III) 

through one 220 KV double circuit line.

Region 

Eastern 

POWER SUPPLY POSITION OF EASTERN REGION 

WITHOUT LINGZA HE PROJECT (120 MW) 

10th Plan 11th Plan 

17 


Lingza HE Project, (3 x 40 MW) 

Table 2.1 

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 

18 



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

envisages construction of 75 m high concrete gravity dam near the place Ishana. and an 

under ground powerhouse near the place Chhana. The river water shall be diverted 

through a diversion tunnel of 400 m length and 6.0 m dia for construction of dam. A 

headrace tunnel of 4.0 km length, 3.3m dia shall carry a discharge of 18.47 cumecs of 

water to the powerhouse. Two numbers of desilting chambers of 95mX8mX7.5 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 40m deep along with one inclined pressure shaft of 2.0m 

dia 900 m length shall be constructed. A tailrace tunnel of 250m length and 3.3 m dia 

shall discharge the water back into the river. A switchyard of 200Mx150m size shall also 

be constructed. The powerhouse shall have installed capacity of 120 MW to generate 

477.51MU of energy in a 90% dependable year. 

The river Ringpi Chu is the tributary of the Rangyong Chu originating in the glaciers of 

North Sikkim at an elevation of about 5000 m above mean sea level. he Jumthu Chu, 

Dawathang Chu, Kishong Chu, Pegor Chu and Zong Chu are the main tributary of Ringpi 

Chu. The Ringpi is the tributary of Rangyong Chu and meets Rangyong Chu upstream of 

the confluence of Ringyong Chu and Rangyong Chu. The other tributaries of the 

Rangyong Chu /Tolung Chu are Umram Chu, Passaram Chu, Rangyang Chu , Rangli 

Chu and Rahi Chu. Both the river 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 

19 



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

density of population in the State is 76 per sq. Km. East district is the most populated 

where as North's density 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 

urban population is 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 2001 census is 48.52%. The female participation rate in Sikkim is 

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

economy, as productivity is low and hence all the able-bodied people are employed 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 hold economy of the 

region. There are certain household industries also which substantially adds to house hold 

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. The area in the vicinity of the 

project is populated. The human settlements are scattered and the human population as 

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

Table 3.1: Human settlement and Population around the project vicinity 

Item Up to 2 km from Up to 2-5 km Up to 5-10 km 

Population Nil 527 2369 

Households Nil 118 448

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

20 



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 Lapchas are the original inhabitants of the state. Compared to other ethnic 

groups, the Lapchas 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, espically in urban areas. 

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 

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 

21 



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. 

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

22 



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 

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 

23 



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 

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 

24 



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 

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

25 



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 

26 



TOPOGRAPHIC AND GEOTECHNICAL ASPECTS 


Central Electricity Authority proposed construction of Lingza hydroelectric scheme on 

Ringpi Chu near Ishana in order to generate hydroelectricity from its water potential. The 

scheme envisaged construction of a diversion structure upstream of Ishana, a water 

conductor system in the left bank of Ringpi Chhu and a powerhouse downstream of 

confluence of Ringpi Chu and Rangyong Chu. The scheme was expected to generate 

approximately 160 MW of power. The task of preparation of pre-feasibility report was 

assigned to NHPC. As per the MOU, GSI reports and site visits of experts would form 

major in puts for topographic and geotechnical aspects. The present appraisal is based on 

study of topographic sheet 78 A/6 and reconnaissance traverse that was undertaken by 

mid October. 

A study of the area was undertaken and a few modifications were made in layout of the 

project, because of Panan scheme, which has been proposed in the downstream. Now, a 

diversion structure shall be constructed approximately 700m upstream of Ishana, a 4 km 

long water conductor system in the right hill and an underground powerhouse upstream 

of confluence of Ringpi and Rangyong Chhu. The tail water shall be discharged above 

the FRL of Panan Scheme. The geological report from GSI has been received and placed 

as annexure 4.1. 

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 

and Rangpo Chu, apart from others join the river. The river valleys in this region are u- 

shaped while, as the tributaries had developed deep gorges, which are bound by steep

27 



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 the north. It 

is designated 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 Ringpi Hydroelectric Scheme has been 

brought out hereunder for the purpose of regional geological setup of the area. According 

to this report the region from south to north is occupied by Gondwana, Daling, 

Chungthang and Central Crystalline Gneissic group of rocks. 

Group Lithology 

Gondwana 

Daling 

Grits, pebble cum boulder beds and carbonaceous shale with 

occasional coal seams, pegmatite, quartzite (Tourmaline bearing) 

• Interbedded quartzite and chlorite sericite phyllite / schist 

• Lingza Granite 

• Quartzite/ Biotite schist 

Chungthang • Interbedded quartzite and garnetiferous quart biotite 

schist. 

• Calc-silicate rock/marble. 

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

Central Crystalline 

Gneissic Complex 

28 



Banded gneiss with augen gneiss and quart-biotite gneiss. 

Augen gneiss. 

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

4.3 TOPOGRAPHIC AND GEOTECHNICAL ASPECTS OF COMPONENT 

STRUCTURES 

The region is thickly vegetated and falls within Tolung Reserve Forest. From the peruse 

of topographic sheet 78 A/6 Jumthul Chhu an E-W flowing nala originating from Jumthul 

glacier meets Dwathang Chhu near Tolung and thus give rise to Ringpi Chhu. Beyond 

this confluence Ringpi Chhu flows almost N-S with occasional easterly and westerly 

swings. Upstream of Ishana the nala takes a southwesterly direction till it meets 

Rangyong Chu. Beyond the confluence of jhumthul Chhu and Dwathang Chhu near 

Tolung the nala is joined by few tributaries namely Ludul Chhu, Pegor Chhu, Kangcha 

Chhu and Zong Chhu all left bank tributaries. The area is bound by ridges, which 

generally trend NE-SW and follow the general strike of formations. The river flows in a 

steep gradient. The project area is occupied by Central Crystallines of Higher Himalaya. 

Ringpi Chhu almost flows along the strike of the formations. Entire area has a highly 

rugged terrain with elevation in vicinity varying from 1600 M to 6000 M. Near Shobrung 

and Ishana the topography is approximate as indicated in the topographic map. 

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

reaches Tolung. In general the valley slopes are occupied by slope wash material, while 

rock fromations are exposed as steep ridges. 

4.3.1 Diversion Structure 

The proposed diversion structure is located approximately 700m upstream of Ishana. 

Here, Ringpi takes a westerly swing and flows southwesterly to southerly. The area was

29 



studied in detail to assess the proposed alignment and any possible alternative alignment. 

During the study it was observed that in vicinity of Ishana the river has carved a wide 

valley with gentle to moderate side slopes. From upstream of Ishana and upto Shobrung 

the river flows in a gentler gradient and has deposited a wider terrace, however, 

downstream of Shobrung the nala flows in a steeper gradient. Also, upstream of the 

proposed location the nala flows in cascades within a steep gradient. Further upstream the 

nala section is inaccessible, however it is observed that a thick pile of debris material 

(approximately 15m) comprising boulders, cobbles and pebbles in a silty/sandy matrix 

occupies the riverbed section (Photo-1). The river valley is approximately 300m wide. A 

thick pile of slope wash material occupies both the right and left bank slopes and the 

same is under a thick vegetal cover. The slopes are comparatively steeper while the right 

bank slopes are moderate and become steep towards higher elevation, which show rock 

exposure. The area is under a thick vegetal cover. The right bank slopes are being used 

for cardamom cultivation. The area is occupied by rock exposures of gneisses, which are 

strong to very strong. The rock formations trend NE-SW dipping northwesterly (Plate- 

4.1). Occasional warping in rock types is noticed. Downstream of place Be a massive 

band of yellowish quartzite is noticed. The area is required to be investigated in detail to 

assess the bedrock depth and abutment conditions. 

4.3.2 Water Conductor System 

A 4 Km long head race tunnel has been proposed in the left hill. A recci traverse from 

lingza along the foot track in left bank of Ringpi was undertaken upto place Be. After 

crossing the nala at place Be a traverse was undertaken from place Be to Ishana. The area 

is bound by steep ridges, which trend NE-SW. The slopes along the foot track are 

occupied by a pile of slope wash material. Nevertheless, a few intermittent reaches show 

rock exposures. Also rock exposures are observed towards higher elevations. From a 

study of the topographic map it is seen that the water conductor system is crossed by 

several small drainages. Mostly these drainages are dry. During the field visit a nala 

downstream of Be was seen to carry a little discharge.

30 



This water conductor system shall be housed within the rock types of gneisses with 

occasional bands of augen gneisses. A thick band of quartzite was observed in vicinity of 

place Be. This band appears to be 150-200m thick. Since the contact between the two is 

under a debris its nature could not be ascertained. The gneisses and quartzites are strong 

to very strong and are expected to offer a good tunneling media. The rock types trend 

NE-SW dipping 40-65º towards NW (Plate-4.1). Sufficient superincumbent cover is 

available above the tunnel. Prima-facie no major drainage appears to have deeply incised 

the proposed tunnel alignment. 

4.3.3 Powerhouse 

The powerhouse location was fixed keeping in view the FRL of Panan Scheme. 

Accordingly, it was proposed to keep the tail water above the FRL of Panan Scheme. A 

foot track runs above the proposed powerhouse location and the present appraisal is 

based on the observations made along this foot track. At the proposed powerhouse 

location the formation are exposed as steep rocky escarpments. A thick pile of slope wash 

material occupies the area along the foot track. An underground powerhouse has been 

contemplated since steep ridges bind the area. The underground powerhouse area shall be 

housed within gneisses, which occupy the area. These trend NE-SW dipping towards NW 

(Plate-1). Fair to good rock media is expected during powerhouse excavation. Sufficient 

superincumbent cover is available above the proposed powerhouse cavern. The 

orientation of powerhouse shall be suitably aligned with respect to principal 

discontinuity. 

4.4 SEISMICITY 

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

Technical report on seismic history and seismicity of the teesta basin of sikkim covering 

proposed sites for hydroelectric schemes has been collected from IMD and enclosed as 

annexure 4.2. The report contains a list of earthquake events that have occurred within

31 



the region. The Seismic data for the region covering longitude 86-90º and 25-29º has 

been analyzed. 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-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 occur in the area namely MBT (Main Boundary Thrust) and 

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

earthquakes have been associated with these major lineaments. 

4.5 GEO-PHYSICAL SURVEY 

The area at dam site is covered by heavy boulders and the opposite bank was not 

accessable and is connected by 5 km long hilly footpath. Hence the geophysical survey 

was not feasible at dam location. The rock is fully exposed in the power house area, 

therefore geo-physical survey was not required. 

4.6 CONSTRUCTION MATERIAL SURVEY 

The availability of river shoals may not suffice the requirement of construction material. 

Hence, the alternative arrangements for construction material have to be explored. The 

area is bound by steep rocky ridges, therefore the quarries for construction material can 

be developed. 

4.7 RECOMMENDATIONS 

• At the dam axis and powerhouse area, few drill holes are required to assess 

overburden thickness and its amenability for construction of various structures. 

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

32 



• Availability of construction material may be assessed after detailed survey of the 

quarries and may be got tested for their suitability at FR/PFR stage.

Photo-1 Riverbed at Proposed Dam Site 

33 


Lingza HE Project (3 x 40 MW)



CHAPTER – V 

HYDROLOGY

5.1 GENERAL 

CHAPTER –V 

HYDROLOGY 

34 



Lingza scheme is a run of the river scheme, proposed on Ringpi Chu, one of the 

tributaries of Ryong Chu/Tolung Chu, which is a major right bank tributary of river 

Teesta. The project envisages construction of a 75 m high diversion structure on Ringpi 

Chu with a gross storage capacity of about 2.64 Mcum and area of submergence as 10.75 

Ha at EL 1850 m. The hydrological investigations and analysis have been carried out for 

Lingza 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 

Ringpi Chu is one of the major tributary of Talung chu river which in turn is one of the 

major tributary of river Teesta and meets Teesta at Singhik on its right bank. Ringpi Chu 

intercepts a substantial catchment area and is formed by two streams originating at high 

elevations having snow catchment in their upper reaches. The river has substantial flows 

and a steep gradient. Talung 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. Tolung Chu is fed by a number of 

tributaries having large drainage areas at their confluence.

35 



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 nallah 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 

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

36 



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. 

5.2.2 Catchment Area 

The catchment area of the proposed scheme lies between Longitude 88 o 16′00” E to 

88 o 32′00” E and Latitude 27 o 35′00” N to 27 o 45’00” N. The catchment area upto the 

proposed dam site is about 198 Sq.km. The catchment is both snowfed as well as rainfed. 

The proposed diversion structure lies at Longitude 88 o 28′00” E and latitude 27 o 36′00” N. 

The catchment Plan 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 is about 74 Sq.km and has been assumed to be the snowfed area in the 

catchment. Thus the rainfed and snowfed area in the catchment are 124 Sq.km and 74 

Sq.km respectively. 

5.2.3.1 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

37 



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. 

Month 

& 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 

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 distrib ution, 

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 

%

38 



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 

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

39 



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 

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

40 



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 Feb 03 

11. Pelling May 93 to Dec 96 

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 on Ringpi Chu, at or near the proposed dam site of Lingza H.E

41 



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 

4. Lachung Lachung 

5. Chuba 

Chu 

Yumtha 

6. Zema 

ng Chu 

Zema 

Chu 

Jan 75 to Aug 85, Apr 

90 to Apr 98 

731.25 

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) 

Teesta Jan 84 to Oct 91, 

Nov91 to Mar97, Jan 

00to Oct01, Sep02 to 

Feb 03 

Teesta May 84 to Mar 97, 

2000 

10. Legship (near Rangit Rangit Jan 77 to Dec 79, Apr 

4307

damsite) 87 to Dec 87, Jan 90 

42 

to Dec 91 

11. Teesta Bazar Teesta 1972 to 1994 



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 Ringpi Chu, on which the present project is 

proposed. For the pre feasibility study, water availability for the proposed project has 

been computed based on the following methodologies: 

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

98) 

The proposed diversion structure for Lingza project is located on Ringpi Chu, which is a 

tributary of Tolung Chu. Daily G&D data is available on Tolung Chu from Jan 75 to Aug 

85 and Apr 90 to Apr 98. The 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 dam site using catchment area proportion, 

using a reduction factor of 0.21. 

(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 proposed site using catchment area reduction (catchment reduction 

factor – 0.15). Thus a series for the period 1976 to 1984 has been obtained.

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

43 



G&D data observed at Lachen has been converted at proposed site using catchment area 

reduction (catchment reduction factor – 0.22). 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 proposed damsite using catchment area reduction (catchment reduction 

factor – 0.03). The series from 1976-1996 is the approved series by CWC for Teesa-V 

and from 1997 to Feb 2003 is the observed data at Dikchu where observations are being 

taken by NHPC. 

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

compared. The plot showing this comparison of average 10-daily discharge at Lingza is 

enclosed at Figure -5.1. From the plot 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 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 fe lt necessary. For pre-feasibility stage, the average 

10-daily obtained from G&D data at Lachen is recommended for Lingza 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

44 



done during feasibility/DPR stage. The final 10-daily series at Lingza is enclosed as 

Annexure-5.2. 

5.4 RESERVOIR ELEVATION AREA CAPACITY CURVE 

The reservoir elevation-area-capacity curve for Lingza 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 1800m. The area enclosed within the contours has 

been found using Autocad. Area has been found from elevation 1800m 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 

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

resultant area capacity curve is enclosed as Figure-5.2. The curve may be improved after 

receiving toposheets in scale of 1:25000. The gross capacity at FRL 1850 m is 2.64 

Mcum and submergence area is 10.75 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 

45 



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 

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 = 14 x 198 3/4 

= 739 cumec 

(ii) Ali Nawab Jung formula 

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

Where C = 49 to 60 (55 used) 

Q = 55* (0.386*198) (0.925-1/14log(198)) 

= 1694 cumec 

(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. Lingza H.E project is located

46 



on Ringpi Chu river which is a tributary of Tolung Chu, which in turn 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 dam at Lingza. This transposition has been done by Dicken’s 

formula using a conversion factor of 0.138. 

Q 1 = CA 1 n 

Q 2 = CA 2 n 

Where,A 1 = Catchment area of Lingza project 

A 2 = Catchment area of Teesta-III project 

Q 1 = Design Flood for Lingza project 

Q 2 = Design Flood for Teesta-III project 

C = Dicken’s constant 

n= 0.75 

Q Lingza = Q Teesta-III * (A Lingza/A Teesta-III) 0.75 

= 629 cumec 

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

formula 

The design flood for Lingza 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 Lingza project, having a catchment area of 198 

Sq.km comes out to be 0.099. 

Q Lingza = Q Teesta-V * (A Lingza/A Teesta-V) 0.75 

= 943 cumec 

A comparativ study of flood peak computed from various methods is placed as Table 

5.5.

Table 5. 5 

Comparison Of Various Flood Values 

47 



SSS.No Method used Design Flood (cumec) 

1. Dickens Formula 739 

2. Ali Nawaz Jung Formula 1694 

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. 

For pre-feasibility stage study, a design flood of 940 cumec has been recommended at 

proposed dam site. 

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. Also, design flood has been worked out 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. 

5.6 SEDIMENTATION 

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 Lingza 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. 

629 

943

48 



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 




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 

RELATIVE 

HUMIDITY 

(%) 

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

AVERAGE 10-DAILY DISCHARGE 

49 



Annexure-5.2 

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

I 4.85 4.50 5.27 7.15 8.46 13.44 24.33 20.57 21.84 7.79 6.18 3.72 

1976 II 4.64 4.42 5.65 7.83 6.70 26.23 23.19 22.43 12.60 6.15 5.12 3.18 10.38 

III 4.42 4.61 6.13 9.15 9.40 19.03 17.65 23.98 9.20 6.21 4.57 2.94 

I 2.62 4.39 2.43 4.66 5.08 14.46 21.32 24.53 16.83 14.01 7.31 4.55 

1977 II 2.49 4.28 3.46 4.37 6.28 25.65 25.08 20.64 13.76 8.83 6.67 4.81 10.34 

III 2.38 2.56 3.21 4.65 8.95 18.65 30.04 24.10 11.48 7.05 5.04 5.44 

I 3.74 3.47 3.16 4.50 7.78 21.35 24.87 30.46 16.03 15.09 8.04 5.69 

1978 II 3.35 3.39 3.38 5.76 15.94 22.41 26.66 25.74 20.87 11.77 5.99 4.82 12.20 

III 3.43 3.12 3.74 6.83 18.62 28.33 25.73 19.32 15.69 10.03 5.90 4.33 

I 3.99 3.30 3.67 6.99 13.09 15.21 27.11 26.84 22.11 23.58 12.03 8.79 

1979 II 3.69 3.29 3.85 6.95 16.69 18.20 25.93 21.19 19.29 16.09 9.80 7.24 13.12 

III 3.62 3.58 4.74 8.73 12.77 26.10 29.04 22.48 14.15 12.07 9.22 6.97 

I 6.57 6.01 6.91 10.75 14.98 20.94 33.01 35.77 31.26 15.51 10.49 8.17 

1980 II 6.32 6.30 7.09 13.78 12.81 27.87 33.79 39.28 24.50 13.33 9.55 7.42 16.71 

III 6.26 6.72 9.57 15.71 13.66 31.19 35.40 32.72 19.83 12.42 8.79 6.74 

I 6.50 5.59 6.88 8.61 15.77 18.19 37.72 29.67 29.13 18.25 12.58 7.63 

1981 II 6.09 5.75 7.28 10.90 17.03 21.75 32.35 31.31 24.97 16.89 10.04 6.86 16.04 

III 6.01 6.95 8.60 12.84 16.52 29.53 30.43 30.44 19.90 14.76 8.31 5.38 

I 4.94 5.38 5.66 9.48 13.16 25.34 27.09 24.06 20.56 13.81 8.75 6.53 

1982 II 5.50 5.58 6.33 9.46 14.78 27.91 30.35 22.78 29.74 11.60 7.63 6.02 14.52 

III 5.42 5.43 7.54 10.49 14.36 30.86 35.80 26.73 19.51 11.17 7.39 5.70 

I 5.65 3.21 4.77 8.11 13.36 26.79 41.55 28.71 28.58 26.07 14.32 9.04 

1983 II 5.03 3.19 6.11 6.63 16.01 26.00 35.35 30.44 32.14 25.70 13.16 8.47 17.82 

III 3.53 4.44 5.51 8.30 21.31 36.28 35.07 35.56 37.07 17.52 10.84 7.60

50 




I 6.78 5.72 12.60 14.54 17.60 37.97 47.19 45.14 48.80 31.12 22.66 11.16 

1984 II 6.67 5.94 14.08 15.50 25.72 45.66 47.35 45.26 46.57 39.47 19.58 10.98 25.99 

III 5.94 5.71 13.83 15.51 36.54 41.00 50.05 47.38 36.94 30.41 17.41 11.02 

I 11.12 9.99 14.04 17.05 17.48 18.13 50.58 44.85 23.62 16.25 9.53 6.25 

1985 II 10.56 9.13 15.21 20.57 20.29 22.64 66.00 47.31 22.57 14.25 8.28 5.65 22.47 

III 9.14 11.05 14.16 24.29 28.26 64.15 55.50 57.92 18.91 11.74 7.34 5.20 

I 4.93 4.69 5.89 6.47 8.80 11.98 26.08 26.02 21.74 17.72 9.51 6.54 

1986 II 4.90 4.82 6.41 8.37 9.36 20.32 32.59 22.36 27.00 13.25 8.47 6.03 13.29 

III 4.64 5.52 6.58 9.39 9.86 30.12 29.31 24.76 21.98 10.35 7.31 4.44 

I 3.88 3.25 3.30 8.96 9.35 20.25 28.31 28.66 37.59 17.13 8.85 4.48 

1987 II 3.65 3.22 3.91 6.26 10.40 29.40 27.07 31.26 20.11 12.76 5.40 4.09 13.52 

III 3.43 3.53 4.91 8.27 12.20 24.68 30.26 20.90 27.58 10.91 4.75 3.74 

I 3.65 3.54 4.27 7.44 9.99 16.00 39.42 33.87 22.52 14.34 6.31 5.04 

1988 II 3.65 3.71 6.33 8.40 14.97 23.15 30.96 31.09 15.19 9.51 5.70 4.78 14.13 

III 3.61 4.12 6.51 9.77 19.84 25.36 34.12 47.16 16.99 7.65 5.31 4.52 

I 2.77 2.97 3.28 3.58 9.02 20.16 35.96 28.57 21.32 15.15 6.52 4.20 

1989 II 2.69 2.71 3.35 4.28 9.32 33.39 35.37 22.41 19.31 12.89 5.29 3.64 13.14 

III 2.67 2.89 3.44 5.14 22.70 35.32 32.92 21.99 19.18 10.49 4.81 3.19 

I 2.91 2.40 1.99 1.71 5.16 22.09 27.82 25.85 22.37 12.50 6.41 3.66 

1990 II 2.70 2.26 1.63 2.82 9.09 21.58 35.46 26.26 21.42 12.73 4.79 3.02 11.38 

III 2.44 2.18 1.65 3.50 10.46 25.24 30.35 23.30 14.92 10.47 4.00 2.61 

I 2.64 2.48 2.54 8.03 8.13 11.73 19.45 23.69 22.72 14.84 8.00 4.54 

1991 II 2.59 2.36 2.90 4.58 9.91 18.52 18.95 27.29 24.00 11.77 7.08 3.48 10.64 

III 2.56 2.38 3.06 4.84 10.96 17.03 20.66 22.55 18.59 9.66 5.40 3.06 

I 2.79 2.50 2.47 3.03 3.81 4.92 11.69 14.70 14.08 8.66 3.90 3.13 

1992 II 2.31 2.41 2.49 4.25 4.43 7.02 11.82 14.76 13.85 6.21 3.47 2.71 6.46 

III 2.36 2.31 2.56 3.89 4.46 13.60 13.43 16.05 11.47 5.29 3.16 2.50 

I 2.54 2.33 3.91 4.15 6.89 8.06 27.74 36.49 34.86 24.67 13.02 10.26 

1993 II 2.57 2.48 3.90 4.53 6.20 10.30 27.74 34.59 29.36 18.30 11.47 9.43 13.80 

III 2.41 2.39 4.08 5.43 6.28 13.25 32.53 33.13 27.76 15.69 10.52 7.75

51 




I 7.30 6.77 6.40 7.09 9.12 16.70 21.94 21.79 19.41 13.14 8.80 5.85 

1994 II 6.80 6.48 5.77 8.87 9.40 22.10 23.26 21.28 19.44 11.68 7.26 5.35 12.32 

III 6.87 6.94 7.30 8.14 11.57 25.66 23.71 22.89 16.80 10.70 6.06 5.06 

I 4.80 4.75 4.33 5.53 14.58 25.25 34.72 24.46 19.78 12.59 6.23 5.35 

1995 II 4.85 4.73 4.10 6.85 22.51 27.01 29.13 24.68 17.71 12.25 7.11 4.76 13.47 

III 4.79 4.76 5.65 9.99 21.75 27.36 22.39 21.92 17.04 9.57 7.15 4.42 

I 3.81 4.15 4.11 4.66 12.28 13.97 23.47 21.51 20.18 14.72 10.97 6.25 

1996 II 3.79 3.69 4.75 4.53 10.76 11.83 25.27 20.06 19.26 13.49 10.20 5.65 11.62 

III 4.01 4.04 5.07 10.07 14.89 21.13 22.50 20.21 16.75 12.06 9.07 5.20 

I 5.88 5.67 5.72 6.28 7.50 9.85 21.61 17.91 15.35 11.07 5.25 3.96 

1997 II 5.59 5.65 6.01 6.25 8.63 14.04 18.71 21.85 17.39 7.26 4.85 3.87 9.57 

III 5.69 5.59 6.55 6.43 8.91 17.29 15.63 14.35 14.07 5.73 4.39 3.65 

I 4.76 4.41 5.16 7.22 10.52 17.85 29.68 27.91 24.12 16.27 9.35 6.13 

AVG II 4.57 4.35 5.64 7.81 12.60 22.86 30.11 27.47 22.32 13.92 8.04 5.56 13.77 

III 4.35 4.58 6.11 9.15 15.19 27.32 29.66 27.72 19.35 11.45 7.12 5.07 

Note : 1) All discharge data is in cumec. 

2) Total no. of years -19



CHAPTER – VI 

CONCEPTUAL LAYOUT & 

PLANNING


CHPAPER-VI 

CONCEPTUAL PLANNING AND LAYOUT 

54 



The Lingza H.E. project is located in the North district of Sikkim state near village 

Ishana. It is a run of the river scheme proposed to harness hydel potential of the Ringpi 

Chu, a tributary of river Teesta. The available maximum gross head of 746 m is 

proposed to be utilised for generating 120 MW of Power. A small reservoir of adequate 

capacity has been provided as an operating pool to meet diurnal peaking load demands. 

6.2 PROJECT COMPONENTS 

• 6 m diameter, 400 m long Diversion Tunnel with u/s & d/s coffer dam 

• 75 m high & 320m long concrete Dam with a central spillway 

• Intake Structure leading to 2 Nos. 3 m dia D-shaped intake tunnels. 

• Two Nos. Underground Desilting Chambers of size 95m (L) X 5m (W) X 7.5 m (H). 

• One 3.3m diameter horseshoe shaped concrete lined and 4 kms long Head Race 

Tunnel with three adits. 

• One 10 m diameter & approx. 40 m high semi-Underground Surge Shaft. 

• One circular inclined Pressure Shaft of 2m diameters, 900 m long each further 

bifurcating into 3 numbers steel lined circular penstocks of 1.1 m diameter and length 

50 m each up to Power House. 

• Underground Power House of size 100m x 17m x 40m consisting of 3 Pelton units of 

40 MW each. 

• One no.3.3m diameter Horseshoe shaped tailrace tunnel of about 250 m length. 

The conceptual planning and lay-out of project components have been worked out based 

on S.O.I toposheets of 1:50000 scale (toposheet no. 78A/6) with contour intervals 40 m.

6.2.1 Conceptual Layout 

55 



The choice of location and type of the dam has been made keeping in view the 

topography, geology and water availability at various locations of the diversion structure 

near the one suggested earlier by CEA. The location of the powerhouse has been fixed 

keeping the tailrace outlet at EL 1095 m. This level has been kept same as FRL of the 

proposed Panan H E Project. 

The location of major component of the project, riverbed levels at dam site, 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 Ringpi Chu have been considered 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 sept’03. 

6.2.2 Dam and River diversion works 

Construction of a 75m high concrete Dam has been proposed across river Ringpi Chu. 

The reservoir formed by construction of Dam has a gross storage pre-sedimentation 

capacity of 2.64 M.cum and live storage capacity of 1.71 M cum. After sedimentation, 

the reservoir is likely to have a live storage of adequate capacity for running the power 

station at full capacity for 3-4 hours in a day during the period of lean flows.

56 



Width of the valley at Dam site varies from 50 m at riverbed level to 320 m at EL 1855 

m, which is suitable for a concrete dam. Average bed level at Dam site is EL 1795 m. 

FRL is proposed to be fixed at EL 1850 and MDDL at El.1830 m keeping in view the 

inflow of water in Ringpi Chu during lean period. The top of the dam has been proposed 

to be kept at EL 1855 m and seat of the dam at EL 1780 m after removal of approx. 15.0 

m thick overburden. Near the dam axis, right bank is steep, however left bank rises 

moderately and becomes steeper at higher elevation. The area is thickly forested and the 

slopes are covered by slope wash material. No rock exposure is seen in the dam area. 

However on the basis of exposure in the vicinity. It appears that the rock type expected to 

be encountered shall be gneiss, which is suitable for founding the dam and housing the 

underground structures. The availability of construction material for the dam, cofferdam 

and its suitability has been discussed elsewhere in the report. 

The overflow section is 30 m long and Non –overflow section is 290 m comprising 165 

m on right abutment and 125 m on left abutment. The spillway has three bays each of size 

4 m X 6 m with 3.0 m wide piers. The spillway is designed to pass a probable maximum 

flood of 940 cumecs with one gate inoperative. The crest of spillway has been kept at 

EL1810 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. 

One no. Concrete lined 6 m dia 400 m long diversion tunnel has been proposed on the left 

bank of the river to divert a flood of approx. 300 cumecs of Ringpi chu The design 

diversion discharge has been decided based on the experience of various ongoing NHPC 

projects in Teesta valley and fast track completion of the project. This data shall however 

need 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

57 



of Teesta-V project. In order to divert the river during construction of the dam, an u/s 

cofferdam of approx. height 20m and d/s cofferdam of 10 m height is proposed. 

6.2.3 Power Intake & Desilting Chambers 

The proposed power intake system is on the Left side of the river 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 22.16 cumecs, which is about 20% excess of 

turbine discharge of 18.47 cumecs. The invert level of the intake structure has been kept 

at El. 1820m taking into consideration the water seal requirement to prevent the vortex 

formation and air entrainment. Also, this level being 10m higher than the spillway crest, 

the sediment entry in the water conductor system shall be checked. The intake structure 

shall be provided with the trash racks to prevent the entry of trash in 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.1855m 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 0.2mm-particle size. Two nos. 5 m wide Dufour type Desilting chambers with 

height 7.5 m shall be provided to remove 90% of particles having size greater than or 

equal to 0.2m. Two separate intakes lead the water to two independent desilting chambers 

95 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 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 m x 1.8 m D -shaped and 500 m length which will discharge the sediment

58 



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, as the Teesta- 

V project, which is d/s of this project, has been provided with the desilting chambers. The 

size, alignment, orientation of the chambers can be optimized after more geo-logical, 

topo-graphical and sedimentation data becomes available. 

. 

6.2.4 Head Race Tunnel, Surge Shaft, and Pressure Shaft 

The proposed 3.3 m diameter concrete lined horseshoe shaped headrace tunnel of 4 km 

length, and having a slope of 1 in 300 is designed to carry a design discharge of 18.47 

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. 1820 m near intake. 

The rock cover above headrace tunnel generally varies from +100 m to +400 m. The low 

cover reaches are confined to prominent nalla crossings. The HRT shall be aligned with 

in the rock type of quartzite and gneiss. Three nos. constructions Adits are proposed to 

facilitate excavation of headrace tunnel within the scheduled completion time. The length 

of tunnel between 300 m long adit-1 & 300 m long adit-2 is 2.5 Km. The tunnel is 

proposed to be lined with 225 mm thick plain M-20 concrete. The rock support treatment 

shall consist of grouted rock bolts/anchors and shotcrete with or without wire mesh as per 

geological conditions encountered. 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 40 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 1815 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 

conditions and optimize the surge shaft dimensions. During excavation, rock shall be 

supported with grouted rock bolts/anchors with wire mesh as per geological conditions.

59 



Two no. Steel lined inclined circular Pressure Shaft of 2m diameter and 900 m length 

takes off from the surge shaft each further bifurcating at two points into 3 numbers 

underground steel lined circular penstocks of 1.1 m diameter and 50 m length ach upto 

Power House which will feed water to three units of Pelton turbines each of 40 MW. 

6.2.5 Power House Complex & Tail Race Channel 

The underground Power House is located on the Left bank of Ringpi Chu u/s of Panan 

dam. It will have an installed capacity of 120 MW (3 generating units of 40 MW each). 

The rock type expected to be encountered is gneiss and the support system shall comprise 

of rock bolts and Shotcrete. The centerline of the turbines is proposed at EL 1097m. 

One number electrically operated overhead traveling crane (E.O.T) shall be provided for 

handling the electrical and mechanical equipment. The Main inlet valve chamber is 

proposed on the u/s of the powerhouse. A lift shall be provided near the service bay for 

the transportation of men and material. The overall dimensions of the Power House are 

100m x 17m x 40m. A 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. The 

approx. size is of the transformer cavern is 90mx 14m x 15m. 

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. 200 m x 150 m shall 

be formed in cutting/filling. 

Water from the turbines is discharged through four concrete lined tailrace tunnels, which 

merge into a single tailrace tunnel of diameter 3.3-m & discharge in the Ringpi Chu. This 

tunnel is 3.3 m diameter horseshoe and about 250m long with invert at EL.1095 at 

tailrace outlet. The tailrace outlet level has been kept at El. 1095 m in conformity with the 

FRL of proposed Panan H E Project so as to use the entire available potential. The 

reservoir of Panan H.E. Project shall extend beyond the junction of the Tolung Chu and 

Ringpi Chu on the u/s side.

6.3 FURTHER STUDIES 

6.3.1 Topographical Studies 

60 



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. 

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.

61 



4. Sedimentation analysis for working out the post sedimentation storage capacity of the 

reservoir. 

5. Alternative studies for location, type and layout of main components based on 

detailed topographical and geological studies. 

6. Alternative studies for diversion structure i.e. possibility of other types of dam. 

6.4 HYDRO- MECHENICAL EQUIPMENT 

6.4.1 Diversion Tunnel Gates And Hoists 

After the construction of the dam, for the purpose of plugging the diversion tunnel, two 

numbers fixed wheel type gates will be provided at the inlet of 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 20m and gate is designed for 

operation against 24m water head. 

6.4.2 Spillway Radial Gates, Hoists, Emergency Bulkhead Gate And Gantry Crane 

For flushing and to regulate the water level in the reservoir, three numbers submerged 

type spillway radial gates have been provided. Each gate shall be operated by means of 

suitable capacity hydraulic hoist from a power pack and two double acting cylinders (one 

on each end of the gate) having a provision of 25% pushing force. 

One trolley mounted mobile gasoline engine operated power pack capable of operating 

one gate at 25% of the normal rated speed is envisaged for emergency operation of 

spillway radial gates. 

One portable oil filter unit for filtration, dehydration & degasification of hydraulic oil is 

also being provided.

62 



One number slide type bulkhead gate has been envisaged to cater to the maintenance 

requirement of three nos. spillway radial gates. The bulkhead gate shall be shall be 

operated under balanced head condition by means of a suitable capacity gantry crane with 

the help of a lifting beam. 

6.4.3 Trash Rack And Trash Rack Cleaning Machine 

Upstream face of the intake shall be provided with the trash rack screen, which will be 

cleaned by means of a trash rack-cleaning machine. 

6.4.4 Intake Gates, Intake Bulkhead Gates And Hoists 

Two number fixed wheel type gates shall be provided at the intake. The intake 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 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 electrically operated rope drum hoist under balanced 

head condition. 

6.4.5 Desilting Chamber Gate & Hoist 

One number slide type gate shall be provided at the outlet of desilting chamber for the 

maintenance requireme nt of two nos. desilting chambers. The gate shall be lowered / 

raised under balanced head condition by means of suitable capacity EOT Crane. 

6.4.6 Flushing Tunnel Gates & 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

63 



provided with bonnet structures embedded in the concrete and a watertight bonnet cover 

at the top of the groove. 

6.4.7 Surge Shaft Gate And Hoist 

The intake of pressure shaft is provided with one number slide type gate. The gate shall 

be operated under balanced head condition by means of an electrically operated rope 

drum hoist. 

6.4.8 Tail Race Gate And Hoist 

To isolate powerhouse from the river during flood, one number fixed wheel type tailrace 

gate has been envisaged. The gate shall be operated under balanced head conditions by 

suitable capacity electrically operated monorail hoist placed in the transformer cavern. 

6.4.9 Adit Inspection Gates 

Three nos. adits shall be provided with manually operated hinged type gates in the 

concrete plug at the HRT to give access to the head race tunnel in the event of any 

inspection, repair and maintenance. 

6.4.10 Pressure Shaft Steel Liner 

One no. Pressure Shaft of dia. 2000 mm fully steel lined will take off from Surge Shaft to 

feed the turbines placed in the powerhouse. It comprises horizontal & inclined ferules, 2 

nos. vertical bends, 2 nos. plan bends, 2 nos. bifurcations and branch pipes for feeding 

three nos. turbines. 

The material of Pressure Shaft liner shall conform to ASTM A537 Class - I. However, for 

bifurcation material shall conform to ASTM A517 Gr. F.

6.4.11 Instrument And Remote Control 

64 



Gates shall be provided with PLC based remote control system for Control and operation 

of gates and automatic control of the reservoir level. 

6.4.12 Diesel Generating Set 

One diesel generating set complete with all accessories will be provided for emergency 

operation of gates and hoists.



CHAPTER – VII 

POWER POTENTIAL STUDIES

7.1 GENERAL 

CHAPTER-VII 

POWER POTENTIAL STUDIES 

65 



The Power potential studies of Lingza 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) =1850 m 

MDDL (EL) =1830 m 

TWL = EL 1095 m 

Centre line of M/C =EL 1097 m 

Rated net head = 736 m 

Type of turbine = Vertical Pelton 

Rated Discharge of Plant =18.47 cumecs 

Proposed Plant Capacity =120 MW (3x40 MW) 

Design Energy =477.51 MU in the 90% dependable year with 

95% machine availability 

Minimum Peaking (Hrs) = 3 hrs (approx.) 

Gross Storage = 2.64MCM 

MWhr = 4765.31 

Live storage = 1.71 MCM 

MWHr = 3086.61 

7.2 AVAILABLE FLOW 

The discharge data for the 90% dependable hydrological year is given in table 7.3 and 

power potential in 90% dependable year with 95% machine availability has also been 

shown in this table. For carrying out the power potential and optimisation studies, the 

following statistics have been computed.

Year: 

66 



Each 10-daily period of the year represents the average of the flow recorded for the 

corresponding period of each year. 

90% Dependable Year: 

This is the lower decile of the series of the corresponding 10-daily period of the record 

i.e. (N+1) x 0.9 th 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. Here no reservoir capacity has been selected in order to have 

minimum environmental impact. During lean inflow period (winter season) the firm 

power comes out to be 15.50 MW calculations for this has been shown in table 7.3. 

7.4 FULL RESERVOIR LEVEL (FRL) AND MINIMUM DRAW DOWN 

LEVEL (MDDL) 

FRL and MDDL have been fixed at EL 1850m & EL 1830 m respectively based on civil 

consideration. Justification for FRL, MDDL and TWL has been presented in chapter VI 

“Conceptual Planning and layout”. This project is envisaged as a run of the river scheme. 

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 10 m.

Net operating head =MDDL+2/3 (FRL-MDDL)-TCL-Head losses 

The net operating head comes out to 736 m. 

7.6 INSTALLED CAPACITY 

67 



Installed capacity of 120 MW has been selected based on power potential studies, water 

availability and results arrived as per table 7.4(a).The studies for power output and annual 

energy generation for the 90% dependable year restricted to various MW has been given 

in table 7.4. 

7.7 SIZE OF GENERATING UNITS 

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 with capacity each of 40 

MW with Pelton turbine as prime mover has been envisaged. However detailed 

optimization studies for fixation of installed capacity would have to be done at FR/DPR 

stage. 

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 7.5 (A). It may be seen from table 7.3 

that the total unrestricted energy generation is 543.04 MU. Total energy restricted to 120 

MW comes out to be 489.35MU. Annual energy generation at 120 MW (in 90% 

dependable year and 95% machine availability) comes out to be 477.51 MU. Incremental 

benefits have been shown in table 7.4a which comes out to be 1.79 for this year. Also 

annual energy generation unrestricted has been indicated in table 7.7(A) to 7.7(U) for 21

68 



hydrological years. Energy available at bus bar shall be 471.79 MU after allowing 

auxiliary consumption of 0.7% and transformer losses of 0.5% respectively. 

A table giving the summary of studies indicating yearly inflows, annual energy 

generation, load factor of operation during monsoon and lean flow period has been 

presented in studies as per Table 7.5 Annex-B.

Month 

JUNE 

JULY 

AUGUST 

SEPTEMBER 

OCTOBER 

NOVEMBER 

DECEMBER 

JANUARY 

FEBRUARY 

MARCH 

APRIL 

MAY 

1976- 

1977 

1977- 

1978 

1978- 

1979 

1979- 

1980 

1980- 

1981 

1981- 

1982 

1982- 

1983 

68 

TABLE 7.1 

HYDROLOGICAL SERIES 

1983- 

1984 

1984- 

1985 

1985- 

1986 

1986- 

1987 

1987- 

1988 

1988- 

1989 

1989- 

1990 

1990- 

1991 

1991- 

1992 

1992- 

1993 

1993- 

1994 



1-10 13.44 14.46 21.35 15.21 20.94 18.19 25.34 26.79 37.97 18.13 11.98 20.25 16.00 20.16 22.09 11.73 4.92 8.06 16.70 25.25 13.97 

11-20 1 26.23 25.65 22.41 18.20 27.87 21.75 27.91 26.00 45.66 22.64 20.32 29.40 23.15 33.39 21.58 18.52 7.02 10.30 22.10 27.01 11.83 

21-30 2 19.03 18.65 28.33 26.10 31.19 29.53 30.86 36.28 41.00 64.15 30.12 24.68 25.36 35.32 25.24 17.03 13.60 13.25 25.66 27.36 21.13 

1-10 Jan-00 24.33 21.32 24.87 27.11 33.01 37.72 27.09 41.55 47.19 50.58 26.08 28.31 39.42 35.96 27.82 19.45 11.69 27.74 21.94 34.72 23.47 

11-20 4 23.19 25.08 26.66 25.93 33.79 32.35 30.35 35.35 47.35 66.00 32.59 27.07 30.96 35.37 35.46 18.95 11.82 27.74 23.26 29.13 25.27 

21-31 5 17.65 30.04 25.73 29.04 35.40 30.43 35.80 35.07 50.05 55.50 29.31 30.26 34.12 32.92 30.35 20.66 13.43 32.53 23.71 22.39 22.50 

1-10 Jan-00 20.57 24.53 30.46 26.84 35.77 29.67 24.06 28.71 45.14 44.85 26.02 28.66 33.87 28.57 25.85 23.69 14.70 36.49 21.79 24.46 21.51 

11-20 7 22.43 20.64 25.74 21.19 39.28 31.31 22.78 30.44 45.26 47.31 22.36 31.26 31.09 22.41 26.26 27.29 14.76 34.59 21.28 24.68 20.06 

21-31 8 23.98 24.10 19.32 22.48 32.72 30.44 26.73 35.56 47.38 57.92 24.76 20.90 47.16 21.99 23.30 22.55 16.05 33.13 22.89 21.92 20.21 

1-10 Jan-00 21.84 16.83 16.03 22.11 31.26 29.13 20.56 28.58 48.80 23.62 21.74 37.59 22.52 21.32 22.37 22.72 14.08 34.86 19.41 19.78 20.18 

11-20 10 12.60 13.76 20.87 19.29 24.50 24.97 29.74 32.14 46.57 22.57 27.00 20.11 15.19 19.31 21.42 24.00 13.85 29.36 19.44 17.71 19.26 

21-30 11 9.20 11.48 15.69 14.15 19.83 19.90 19.51 37.07 36.94 18.91 21.98 27.58 16.99 19.18 14.92 18.59 11.47 27.76 16.80 17.04 16.75 

1-10 Jan-00 7.79 14.01 15.09 23.58 15.51 18.25 13.81 26.07 31.12 16.25 17.72 17.13 14.34 15.15 12.50 14.84 8.66 24.67 13.14 12.59 14.72 

11-20 13 6.15 8.83 11.77 16.09 13.33 16.89 11.60 25.70 39.47 14.25 13.25 12.76 9.51 12.89 12.73 11.77 6.21 18.30 11.68 12.25 13.49 

21-31 14 6.21 7.05 10.03 12.07 12.42 14.76 11.17 17.52 30.41 11.74 10.35 10.91 7.65 10.49 10.47 9.66 5.29 15.69 10.70 9.57 12.06 

1-10 Jan-00 6.18 7.31 8.04 12.03 10.49 12.58 8.75 14.32 22.66 9.53 9.51 8.85 6.31 6.52 6.41 8.00 3.90 13.02 8.80 6.23 10.97 

11-20 16 5.12 6.67 5.99 9.80 9.55 10.04 7.63 13.16 19.58 8.28 8.47 5.40 5.70 5.29 4.79 7.08 3.47 11.47 7.26 7.11 10.20 

21-30 17 4.57 5.04 5.90 9.22 8.79 8.31 7.39 10.84 17.41 7.34 7.31 4.75 5.31 4.81 4.00 5.40 3.16 10.52 6.06 7.15 9.07 

1-10 Jan-00 3.72 4.55 5.69 8.79 8.17 7.63 6.53 9.04 11.16 6.25 6.54 4.48 5.04 4.20 3.66 4.54 3.13 10.26 5.85 5.35 6.25 

11-20 19 3.18 4.81 4.82 7.24 7.42 6.86 6.02 8.47 10.98 5.65 6.03 4.09 4.78 3.64 3.02 3.48 2.71 9.43 5.35 4.76 5.65 

21-31 20 2.94 5.44 4.33 6.97 6.74 5.38 5.70 7.60 11.02 5.20 4.44 3.74 4.52 3.19 2.61 3.06 2.50 7.75 5.06 4.42 5.20 

1-10 Jan-00 2.62 3.74 3.99 6.57 6.50 4.94 5.65 6.78 11.12 4.93 3.88 3.65 2.77 2.91 2.64 2.79 2.54 7.30 4.80 3.81 5.88 

11-20 22 2.49 3.35 3.69 6.32 6.09 5.50 5.03 6.67 10.56 4.90 3.65 3.65 2.69 2.70 2.59 2.31 2.57 6.80 4.85 3.79 5.59 

21-31 23 2.38 3.43 3.62 6.26 6.01 5.42 3.53 5.94 9.14 4.64 3.43 3.61 2.67 2.44 2.56 2.36 2.41 6.87 4.79 4.01 5.69 

1-10 Jan-00 4.39 3.47 3.30 6.01 5.59 5.38 3.21 5.72 9.99 4.69 3.25 3.54 2.97 2.40 2.48 2.50 2.33 6.77 4.75 4.15 5.67 

11-20 25 4.28 3.39 3.29 6.30 5.75 5.58 3.19 5.94 9.13 4.82 3.22 3.71 2.71 2.26 2.36 2.41 2.48 6.48 4.73 3.69 5.65 

21-28 26 2.56 3.12 3.58 6.72 6.95 5.43 4.44 5.71 11.05 5.52 3.53 4.12 2.89 2.18 2.38 2.31 2.39 6.94 4.76 4.04 5.59 

1-10 Jan-00 2.43 3.16 3.67 6.91 6.88 5.66 4.77 12.60 14.04 5.89 3.30 4.27 3.28 1.99 2.54 2.47 3.91 6.40 4.33 4.11 5.72 

11-20 28 3.46 3.38 3.85 7.09 7.28 6.33 6.11 14.08 15.21 6.41 3.91 6.33 3.35 1.63 2.90 2.49 3.90 5.77 4.10 4.75 6.01 

21-31 29 3.21 3.74 4.74 9.57 8.60 7.54 5.51 13.83 14.16 6.58 4.91 6.51 3.44 1.65 3.06 2.56 4.08 7.30 5.65 5.07 6.55 

1-10 Jan-00 4.66 4.50 6.99 10.75 8.61 9.48 8.11 14.54 17.05 6.47 8.96 7.44 3.58 1.71 8.03 3.03 4.15 7.09 5.53 4.66 6.28 

11-20 31 4.37 5.76 6.95 13.78 10.90 9.46 6.63 15.50 20.57 8.37 6.26 8.40 4.28 2.82 4.58 4.25 4.53 8.87 6.85 4.53 6.25 

21-30 32 4.65 6.83 8.73 15.71 12.84 10.49 8.30 15.51 24.29 9.39 8.27 9.77 5.14 3.50 4.84 3.89 5.43 8.14 9.99 10.07 6.43 

1-10 Feb-00 5.08 7.78 13.09 14.98 15.77 13.16 13.36 17.60 17.48 8.80 9.35 9.99 9.02 5.16 8.13 3.81 6.89 9.12 14.58 12.28 7.50 

11-20 34 6.28 15.94 16.69 12.81 17.03 14.78 16.01 25.72 20.29 9.36 10.40 14.97 9.32 9.09 9.91 4.43 6.20 9.40 22.51 10.76 8.63 

21-31 35 8.95 18.62 12.77 13.66 16.52 14.36 21.31 36.54 28.26 9.86 12.20 19.84 22.70 10.46 10.96 4.46 6.28 11.57 21.75 14.89 8.91 

1994- 

1995 

1995- 

1996 

1996- 

1997

YEAR 

UNRESTRICTED 

ENERGY 

GENERATION 

MU 

TABLE NO.-7.2 

CALCULATION OF 90% DEPENDABLE YEAR 

YEAR 

UNRESTRIC 

TED 

ENERGY IN 

DESCENDIN 

G ORDER 

69 

RANK 

OF 

THE 

YEAR 

1976-1977 543.04 1984-1985 1531.95 1 

1977-1978 637.97 1983-1984 1159.62 2 

1978-1979 710.22 1985-1986 1078.12 3 

1979-1980 820.67 1980-1981 951.00 4 

1980-1981 951.00 1981-1982 887.89 5 

1981-1982 887.89 1993-1994 876.18 6 

1982-1983 818.15 1979-1980 820.67 7 

1983-1984 1159.62 1982-1983 818.15 8 

1984-1985 1531.95 1987-1988 806.52 9 

1985-1986 1078.12 1988-1989 766.48 10 

1986-1987 740.20 1986-1987 740.20 11 

1987-1988 806.52 1995-1996 722.59 12 

1988-1989 766.48 1994-1995 719.50 13 

1989-1990 706.28 1978-1979 710.22 14 

1990-1991 677.88 1989-1990 706.28 15 

1991-1992 569.80 1990-1991 677.88 16 

1992-1993 391.47 1996-1997 666.10 17 

1993-1994 876.18 1977-1978 637.97 18 

1994-1995 719.50 1991-1992 569.80 19 

1995-1996 722.59 1976-1977 543.04 20 

1996-1997 666.10 1992-1993 391.47 21 



CALCULATION OF 90% 

DEPENDABLE YEAR 

N= No. of year 

90% Dependable Year 

=(N+1)*0.9th year 

=(21+1)*0.9th year 

=19.8th year 

=20th year (say) 

90% Dependable year is 

1976-1977 

90% Dependable energy 

(unrestricted) 

is543.04MU 

90% Dependable energy 

whenpower is restricted 

to 120 MW is 489.35MU 

90% DEPENDABLE 

YEAR IS 1976-1977

TABLE 7.3 

70 



POWER POTENTIAL IN 90% DEPENDABLE YEAR WITH 95% m/c AVAILABILITY 

Net Head 736 m Design Discharge 18.47 RESTRICTED MW 120 

1976-1977 overall Efficiency 90% 

Period 

Inflow 

Cumecs 

Unrestricted Power 

Potential Mw 

Unrestricted 

Energy(Mu) 

Restricted 

Energy (Mu) 

95% M/C 

Availability 

10 1-10 13.44 87.34 20.96 20.96 20.96 

Jun-76 10 11-20 26.23 170.46 40.91 28.80 27.36 

10 21-30 19.03 123.69 29.68 28.80 27.36 

10 1-10 24.33 158.12 37.95 28.80 27.36 

Jul-76 10 11-20 23.19 150.68 36.16 28.80 27.36 

11 21-31 17.65 114.69 30.28 30.28 30.10 

10 1-10 20.57 133.70 32.09 28.80 27.36 

Aug-76 10 11-20 22.43 145.74 34.98 28.80 27.36 

11 21-31 23.98 155.81 41.13 31.68 30.10 

10 1-10 21.84 141.94 34.06 28.80 27.36 

Sep-76 10 11-20 12.60 81.85 19.65 19.65 19.65 

10 21-30 9.20 59.76 14.34 14.34 14.34 

10 1-10 7.79 50.63 12.15 12.15 12.15 

Oct-76 10 11-20 6.15 39.99 9.60 9.60 9.60 

11 21-31 6.21 40.37 10.66 10.66 10.66 

10 1-10 6.18 40.15 9.64 9.64 9.64 

Nov-76 10 11-20 5.12 33.24 7.98 7.98 7.98 

10 21-30 4.57 29.72 7.13 7.13 7.13 

10 1-10 3.72 24.16 5.80 5.80 5.80 

Dec-76 10 11-20 3.18 20.66 4.96 4.96 4.96 

11 21-31 2.94 19.09 5.04 5.04 5.04 

10 1-10 2.62 17.03 4.09 4.09 4.09 

Jan-77 10 11-20 2.49 16.19 3.88 3.88 3.88 

11 21-31 2.38 15.50 4.09 4.09 4.09 

10 1-10 4.39 28.54 6.85 6.85 6.85 

Feb-77 10 11-20 4.28 27.81 6.67 6.67 6.67 

8 21-28 2.56 16.66 3.20 3.20 3.20 

10 1-10 2.43 15.76 3.78 3.78 3.78 

Mar-77 10 11-20 3.46 22.50 5.40 5.40 5.40 

11 21-31 3.21 20.89 5.51 5.51 5.51 

10 1-10 4.66 30.29 7.27 7.27 7.27 

Apr-77 10 11-20 4.37 28.43 6.82 6.82 6.82 

10 21-30 4.65 30.21 7.25 7.25 7.25 

10 1-10 5.08 33.03 7.93 7.93 7.93 

May-77 10 11-20 6.28 40.79 9.79 9.79 9.79 

11 21-31 8.95 58.13 15.35 15.35 15.35 

365 543.04 489.35 477.51 

Restricted Energy generated in 90% dependable year with 95% machine availability with installed 

capicity of 120 MW = 

477.51 MU 

% MU 

Auxiliary consumptions 0.7 0.007 

Transformer losses 0.5 0.005 

Energy available at Bus 471.79 MU

Period 

Jun-76 

Jul-76 

Aug-76 

Sep-76 

Oct-76 

Nov-76 

Dec-76 

Jan-77 

Feb-77 

Mar-77 

Apr-77 

May-77 

TABLE 7.4 

POWER POTENTIAL IN 90% Dependable Year 

1976-1977 

Net Head 736.00 Incremental Steps 10 Overall Efficiency 90% 

Inflow 

(Cumecs) 

Power Potential 

(MW) 

Unrestricted Energy 

Generation (MU) 

71 

ENERGY GENERATION IN MU RESTRICTED TO VARIOUS MW 

80 90 100 110 120 130 140 150 160 170 180 

1-10 13.44 87.34 20.96 19.20 20.96 20.96 20.96 20.96 20.96 20.96 20.96 20.96 20.96 20.96 

11-20 26.23 170.46 40.91 19.20 21.60 24.00 26.40 28.80 31.20 33.60 36.00 38.40 40.80 40.91 

21-30 19.03 123.69 29.68 19.20 21.60 24.00 26.40 28.80 29.68 29.68 29.68 29.68 29.68 29.68 

1-10 24.33 158.12 37.95 19.20 21.60 24.00 26.40 28.80 31.20 33.60 36.00 37.95 37.95 37.95 

11-20 23.19 150.68 36.16 19.20 21.60 24.00 26.40 28.80 31.20 33.60 36.00 36.16 36.16 36.16 

21-31 17.65 114.69 30.28 21.12 23.76 26.40 29.04 30.28 30.28 30.28 30.28 30.28 30.28 30.28 

1-10 20.57 133.70 32.09 19.20 21.60 24.00 26.40 28.80 31.20 32.09 32.09 32.09 32.09 32.09 

11-20 22.43 145.74 34.98 19.20 21.60 24.00 26.40 28.80 31.20 33.60 34.98 34.98 34.98 34.98 

21-31 23.98 155.81 41.13 21.12 23.76 26.40 29.04 31.68 34.32 36.96 39.60 41.13 41.13 41.13 

1-10 21.84 141.94 34.06 19.20 21.60 24.00 26.40 28.80 31.20 33.60 34.06 34.06 34.06 34.06 

11-20 12.60 81.85 19.65 19.20 19.65 19.65 19.65 19.65 19.65 19.65 19.65 19.65 19.65 19.65 

21-30 9.20 59.76 14.34 14.34 14.34 14.34 14.34 14.34 14.34 14.34 14.34 14.34 14.34 14.34 

1-10 7.79 50.63 12.15 12.15 12.15 12.15 12.15 12.15 12.15 12.15 12.15 12.15 12.15 12.15 

11-20 6.15 39.99 9.60 9.60 9.60 9.60 9.60 9.60 9.60 9.60 9.60 9.60 9.60 9.60 

21-31 6.21 40.37 10.66 10.66 10.66 10.66 10.66 10.66 10.66 10.66 10.66 10.66 10.66 10.66 

1-10 6.18 40.15 9.64 9.64 9.64 9.64 9.64 9.64 9.64 9.64 9.64 9.64 9.64 9.64 

11-20 5.12 33.24 7.98 7.98 7.98 7.98 7.98 7.98 7.98 7.98 7.98 7.98 7.98 7.98 

21-30 4.57 29.72 7.13 7.13 7.13 7.13 7.13 7.13 7.13 7.13 7.13 7.13 7.13 7.13 

1-10 3.72 24.16 5.80 5.80 5.80 5.80 5.80 5.80 5.80 5.80 5.80 5.80 5.80 5.80 

11-20 3.18 20.66 4.96 4.96 4.96 4.96 4.96 4.96 4.96 4.96 4.96 4.96 4.96 4.96 

21-31 2.94 19.09 5.04 5.04 5.04 5.04 5.04 5.04 5.04 5.04 5.04 5.04 5.04 5.04 

1-10 2.62 17.03 4.09 4.09 4.09 4.09 4.09 4.09 4.09 4.09 4.09 4.09 4.09 4.09 

11-20 2.49 16.19 3.88 3.88 3.88 3.88 3.88 3.88 3.88 3.88 3.88 3.88 3.88 3.88 

21-31 2.38 15.50 4.09 4.09 4.09 4.09 4.09 4.09 4.09 4.09 4.09 4.09 4.09 4.09 

1-10 4.39 28.54 6.85 6.85 6.85 6.85 6.85 6.85 6.85 6.85 6.85 6.85 6.85 6.85 

11-20 4.28 27.81 6.67 6.67 6.67 6.67 6.67 6.67 6.67 6.67 6.67 6.67 6.67 6.67 

21-28 2.56 16.66 3.20 3.20 3.20 3.20 3.20 3.20 3.20 3.20 3.20 3.20 3.20 3.20 

1-10 2.43 15.76 3.78 3.78 3.78 3.78 3.78 3.78 3.78 3.78 3.78 3.78 3.78 3.78 

11-20 3.46 22.50 5.40 5.40 5.40 5.40 5.40 5.40 5.40 5.40 5.40 5.40 5.40 5.40 

21-31 3.21 20.89 5.51 5.51 5.51 5.51 5.51 5.51 5.51 5.51 5.51 5.51 5.51 5.51 

1-10 4.66 30.29 7.27 7.27 7.27 7.27 7.27 7.27 7.27 7.27 7.27 7.27 7.27 7.27 

11-20 4.37 28.43 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 6.82 

21-30 4.65 30.21 7.25 7.25 7.25 7.25 7.25 7.25 7.25 7.25 7.25 7.25 7.25 7.25 

1-10 5.08 33.03 7.93 7.93 7.93 7.93 7.93 7.93 7.93 7.93 7.93 7.93 7.93 7.93 

11-20 6.28 40.79 9.79 9.79 9.79 9.79 9.79 9.79 9.79 9.79 9.79 9.79 9.79 9.79 

21-31 8.95 58.13 15.35 15.35 15.35 15.35 15.35 15.35 15.35 15.35 15.35 15.35 15.35 15.35 

543.04 400.23 424.51 446.59 468.67 489.35 507.28 522.80 534.49 540.53 542.93 543.04 


Lingza HE Project, (3 x 40 MW)

S. 

No. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

TABLE 7.4a 

72 



AVAILABILITY OF UNITS IN KWH/KW FOR INCREMENTAL INSTALLATION IN 90% 

DEPENDABLE YEAR 

Net Head 736.00 

Installed 

Capacity 

Mw 

Annual 

Energy Mu 

Load 

Factor % 

80 400.23 57.11% 

90 424.51 53.84% 

100 446.59 50.98% 

110 468.67 48.64% 

120 489.35 46.55% 

130 507.28 44.54% 

140 522.80 42.63% 

150 534.49 40.68% 

160 540.53 38.57% 

170 542.93 36.46% 

180 543.04 34.44% 

1976-1977 

Overall 

Efficiency 

Incremental 

Energy Mu 

90% 

Incremental 

Energy 

Kwh/Kw 

Load Factor 

For 

Additional 

Capacity % 

24.29 2428.74 27.73% 

22.08 2208.00 25.21% 

22.08 2208.00 25.21% 

20.68 2067.79 23.60% 

17.92 1792.49 20.46% 

15.53 1552.70 17.72% 

11.68 1168.24 13.34% 

6.05 604.55 6.90% 

2.40 240.00 2.74% 

0.11 11.06 0.13%

Table 7.5(A) 

1976-1977 

73 



Net Head 736 m Restricted MW 120 Overall Efficiency 90% 

Period 

Jun-76 

Jul-76 

Aug-76 

Sep-76 

Oct -76 

Nov-76 

Dec-76 

Jan-77 

Feb-77 

Mar-77 

Apr-77 

May-77 

Inflow 

(Cume 

cs) 

Head 

(M) 

Unrestr 

icted 

Power 

(Mw ) 

Unrestrict 

ed 

Energy 

(Mu) 


Restricted 

To 

120mw 

Restricted 

Energy At 

120 Mw 

(Mu) 

Restricted 

Energy at 120 

MW With 95% 

m/c availability 

Energy 

during 

high 

inflow 

period 

Energy 

during 

lean 

inflow 

period 

10 1-10 13.44 736.00 87.34 20.96 87.34 20.96 20.96 0.00 20.96 

10 11-20 26.23 736.00 170.46 40.91 120.00 28.80 27.36 27.36 0.00 

10 21-30 19.03 736.00 123.69 29.68 120.00 28.80 27.36 27.36 0.00 

10 1-10 24.33 736.00 158.12 37.95 120.00 28.80 27.36 27.36 0.00 

10 11-20 23.19 736.00 150.68 36.16 120.00 28.80 27.36 27.36 0.00 

11 21-31 17.65 736.00 114.69 30.28 114.69 30.28 30.10 30.10 0.00 

10 1-10 20.57 736.00 133.70 32.09 120.00 28.80 27.36 27.36 0.00 

10 11-20 22.43 736.00 145.74 34.98 120.00 28.80 27.36 27.36 0.00 

11 21-31 23.98 736.00 155.81 41.13 120.00 31.68 30.10 30.10 0.00 

10 1-10 21.84 736.00 141.94 34.06 120.00 28.80 27.36 27.36 0.00 

10 11-20 12.60 736.00 81.85 19.65 81.85 19.65 19.65 0.00 19.65 

10 21-30 9.20 736.00 59.76 14.34 59.76 14.34 14.34 0.00 14.34 

10 1-10 7.79 736.00 50.63 12.15 50.63 12.15 12.15 0.00 12.15 

10 11-20 6.15 736.00 39.99 9.60 39.99 9.60 9.60 0.00 9.60 

11 21-31 6.21 736.00 40.37 10.66 40.37 10.66 10.66 0.00 10.66 

10 1-10 6.18 736.00 40.15 9.64 40.15 9.64 9.64 0.00 9.64 

10 11-20 5.12 736.00 33.24 7.98 33.24 7.98 7.98 0.00 7.98 

10 21-30 4.57 736.00 29.72 7.13 29.72 7.13 7.13 0.00 7.13 

10 1-10 3.72 736.00 24.16 5.80 24.16 5.80 5.80 0.00 5.80 

10 11-20 3.18 736.00 20.66 4.96 20.66 4.96 4.96 0.00 4.96 

11 21-31 2.94 736.00 19.09 5.04 19.09 5.04 5.04 0.00 5.04 

10 1-10 2.62 736.00 17.03 4.09 17.03 4.09 4.09 0.00 4.09 

10 11-20 2.49 736.00 16.19 3.88 16.19 3.88 3.88 0.00 3.88 

11 21-31 2.38 736.00 15.50 4.09 15.50 4.09 4.09 0.00 4.09 

10 1-10 4.39 736.00 28.54 6.85 28.54 6.85 6.85 0.00 6.85 

10 11-20 4.28 736.00 27.81 6.67 27.81 6.67 6.67 0.00 6.67 

8 21-28 2.56 736.00 16.66 3.20 16.66 3.20 3.20 0.00 3.20 

10 1-10 2.43 736.00 15.76 3.78 15.76 3.78 3.78 0.00 3.78 

10 11-20 3.46 736.00 22.50 5.40 22.50 5.40 5.40 0.00 5.40 

11 21-31 3.21 736.00 20.89 5.51 20.89 5.51 5.51 0.00 5.51 

10 1-10 4.66 736.00 30.29 7.27 30.29 7.27 7.27 0.00 7.27 

10 11-20 4.37 736.00 28.43 6.82 28.43 6.82 6.82 0.00 6.82 

10 21-30 4.65 736.00 30.21 7.25 30.21 7.25 7.25 0.00 7.25 

10 1-10 5.08 736.00 33.03 7.93 33.03 7.93 7.93 0.00 7.93 

10 11-20 6.28 736.00 40.79 9.79 40.79 9.79 9.79 0.00 9.79 

11 21-31 8.95 736.00 58.13 15.35 58.13 15.35 15.35 0.00 15.35 

Energy obtained on 95% machine availibility 489.35 477.51 251.71 225.79 

LOAD FACTOR 45.42 95.00 28.72

Period 

Yearly 

inflow 

(M Cum) 

Annual 

Energy 

Generation 

(MU) 

Table 7.5 

Annual 

Load Factor 

(%) 

74 

Load Factor 

during high in 

flow period 

(%) 



Annexure-B 

Load Factor during 

lean inflow period 

(%) 

1976-1977 300.85 477.51 45.42 95.00 28.72 

1977-1978 353.44 555.73 52.87 93.89 34.47 

1978-1979 393.47 599.02 56.98 92.45 34.40 

1979-1980 454.65 711.68 67.70 92.32 50.13 

1980-1981 526.86 704.05 66.98 93.19 45.82 

1981-1982 491.90 690.15 65.65 94.26 45.24 

1982-1983 453.26 635.53 60.46 94.42 38.58 

1983-1984 642.43 797.29 75.85 93.92 52.94 

1984-1985 848.71 882.95 83.99 94.35 60.29 

1985-1986 597.28 627.60 59.70 94.71 39.87 

1986-1987 410.07 597.98 56.89 95.08 37.71 

1987-1988 446.82 619.88 58.97 93.94 33.73 

1988-1989 424.63 548.05 52.14 93.19 28.60 

1989-1990 391.28 523.25 49.78 94.02 24.71 

1990-1991 375.55 536.56 51.04 93.83 29.56 

1991-1992 315.67 504.63 48.01 93.57 25.13 

1992-1993 216.88 391.47 37.24 86.90 35.70 

1993-1994 485.41 663.31 63.10 94.44 47.17 

1994-1995 398.60 630.92 60.02 94.40 37.88 

1995-1996 400.32 594.40 56.54 93.68 35.26 

1996-1997 369.02 609.25 57.96 94.58 43.75

Period 

TABLE 7.6 

POWER GENERATION IN 90% DEPENDABLE YEAR (1976-77) 

90% 

Dependable 

Inflow 

Cumecs 

Unrestricted 

Power Potential 

Mw 

Power In Mw Energy In Mu 

75 

Restrictedto 

Installed 

Capacity 

Unrestricted 

Energy(Mu) 



Restricted 

Energy 

(Mu) 

Monthly 

Energy In 

Gwh 

1 2 3 4 5 6 7 8 

10 1-10 13.44 87.34 89.36 20.96 20.96 

Jun-76 10 11-20 26.23 170.46 120.00 40.91 28.80 78.56 

10 21-30 19.03 123.69 120.00 29.68 28.80 

10 1-10 24.33 158.12 120.00 37.95 28.80 

Jul-76 10 11-20 23.19 150.68 120.00 36.16 28.80 87.88 

11 21-31 17.65 114.69 117.34 30.28 30.28 

Aug- 

76 

Sep-76 

Oct -76 

Nov- 

76 

Dec-76 

Jan-77 

Feb-77 

Mar- 

77 

Apr-77 

May- 

77 

10 1-10 20.57 133.70 120.00 32.09 28.80 

10 11-20 22.43 145.74 120.00 34.98 28.80 89.28 

11 21-31 23.98 155.81 120.00 41.13 31.68 

10 1-10 21.84 141.94 120.00 34.06 28.80 

10 11-20 12.60 81.85 83.75 19.65 19.65 62.79 

10 21-30 9.20 59.76 61.14 14.34 14.34 

10 1-10 7.79 50.63 51.80 12.15 12.15 

10 11-20 6.15 39.99 40.92 9.60 9.60 32.41 

11 21-31 6.21 40.37 41.31 10.66 10.66 

10 1-10 6.18 40.15 41.08 9.64 9.64 

10 11-20 5.12 33.24 34.01 7.98 7.98 24.75 

10 21-30 4.57 29.72 30.40 7.13 7.13 

10 1-10 3.72 24.16 24.72 5.80 5.80 

10 11-20 3.18 20.66 21.14 4.96 4.96 15.80 

11 21-31 2.94 19.09 19.53 5.04 5.04 

10 1-10 2.62 17.03 17.42 4.09 4.09 

10 11-20 2.49 16.19 16.56 3.88 3.88 12.06 

11 21-31 2.38 15.50 15.86 4.09 4.09 

10 1-10 4.39 28.54 29.20 6.85 6.85 

10 11-20 4.28 27.81 28.45 6.67 6.67 16.72 

8 21-28 2.56 16.66 17.05 3.20 3.20 

10 1-10 2.43 15.76 16.13 3.78 3.78 

10 11-20 3.46 22.50 23.02 5.40 5.40 14.70 

11 21-31 3.21 20.89 21.37 5.51 5.51 

10 1-10 4.66 30.29 30.99 7.27 7.27 

10 11-20 4.37 28.43 29.08 6.82 6.82 21.34 

10 21-30 4.65 30.21 30.91 7.25 7.25 

10 1-10 5.08 33.03 33.79 7.93 7.93 

10 11-20 6.28 40.79 41.74 9.79 9.79 33.06 

11 21-31 8.95 58.13 59.47 15.35 15.35 

365 543.04 489.35 #REF! 

NOTE : The energy is calculated taking into consideration 95% machine availability

INCREMENTAL MW?MU/?MW 

2.50 

2.00 

1.50 

1.00 

0.50 

0.00 

2.43 

2.21 2.21 

INCREMENTAL BENEFIT FOR 90% DEPENDABLE 

YEAR(1976-1977) 

2.07 

76 

1.79 

80 90 100 110 120 130 140 150 160 170 

CAPACITY(MW) 

1.55 

1.17 

0.60 

0.24 



0.01

TABLE 7.7(A) 

ENERGY GENERATION IN YEAR 

1976-1977 

UNRISTRICTED 

PERIOD FLOW 

ENERGY 

MONTH CUMECS MU 

JUNE 1-10 13.44 20.96 

11-20 26.23 40.91 

21-30 19.03 29.68 

JULY 1-10 24.33 37.95 

11-20 23.19 36.16 

21-31 17.65 30.28 

AUGUST 1-10 20.57 32.09 

11-20 22.43 34.98 

21-31 23.98 41.13 

SEPTEMBER 1-10 21.84 34.06 

11-20 12.60 19.65 

21-30 9.20 14.34 

OCTOBER 1-10 7.79 12.15 

11-20 6.15 9.60 

21-31 6.21 10.66 

NOVEMBER 1-10 6.18 9.64 

11-20 5.12 7.98 

21-30 4.57 7.13 

DECEMBER 1-10 3.72 5.80 

11-20 3.18 4.96 

21-31 2.94 5.04 

JANUARY 1-10 2.62 4.09 

11-20 2.49 3.88 

21-31 2.38 4.09 

FEBRUARY 1-10 4.39 6.85 

11-20 4.28 6.67 

21-28 2.56 3.20 

MARCH 1-10 2.43 3.78 

11-20 3.46 5.40 

21-31 3.21 5.51 

APRIL 1-10 4.66 7.27 

11-20 4.37 6.82 

21-30 4.65 7.25 

MAY 1-10 5.08 7.93 

11-20 6.28 9.79 

21-31 8.95 15.35 

77 



543.04

TABLE 7.7(B) 

78 




1977-1978 

PERIOD FLOW 

UNRISTRICTED 

ENERGY 


JUNE 1-10 14.46 22.55 

11-20 25.65 40.00 

21-30 18.65 29.09 

JULY 1-10 21.32 33.24 

11-20 25.08 39.11 

21-31 30.04 51.53 

AUGUST 1-10 24.53 38.25 

11-20 20.64 32.19 

21-31 24.10 41.34 

SEPTEMBER 1-10 16.83 26.25 

11-20 13.76 21.46 

21-30 11.48 17.90 

OCTOBER 1-10 14.01 21.84 

11-20 8.83 13.77 

21-31 7.05 12.10 

NOVEMBER 1-10 7.31 11.41 

11-20 6.67 10.41 

21-30 5.04 7.86 

DECEMBER 1-10 4.55 7.10 

11-20 4.81 7.51 

21-31 5.44 9.34 

JANUARY 1-10 3.74 5.84 

11-20 3.35 5.23 

21-31 3.43 5.88 

FEBRUARY 1-10 3.47 5.41 

11-20 3.39 5.29 

21-28 3.12 3.89 

MARCH 1-10 3.16 4.93 

11-20 3.38 5.27 

21-31 3.74 6.42 

APRIL 1-10 4.50 7.02 

11-20 5.76 8.99 

21-30 6.83 10.65 

MAY 1-10 7.78 12.13 

11-20 15.94 24.86 

21-31 18.62 31.93 

637.97

TABLE 7.7 ( C ) 


1978-1979 

PERIOD FLOW UNRISTRICT ED ENERGY 


JUNE 1-10 21.35 33.30 

11-20 22.41 34.94 

21-30 28.33 44.18 

JULY 1-10 24.87 38.79 

11-20 26.66 41.58 

21-31 25.73 44.14 

AUGUST 1-10 30.46 47.50 

11-20 25.74 40.14 

21-31 19.32 33.15 

SEPTEMBER 1-10 16.03 25.00 

11-20 20.87 32.55 

21-30 15.69 24.47 

OCTOBER 1-10 15.09 23.53 

11-20 11.77 18.35 

21-31 10.03 17.21 

NOVEMBER 1-10 8.04 12.53 

11-20 5.99 9.35 

21-30 5.90 9.20 

DECEMBER 1-10 5.69 8.87 

11-20 4.82 7.52 

21-31 4.33 7.43 

JANUARY 1-10 3.99 6.23 

11-20 3.69 5.75 

21-31 3.62 6.21 

FEBRUARY 1-10 3.30 5.14 

11-20 3.29 5.13 

21-28 3.58 4.47 

MARCH 1-10 3.67 5.73 

11-20 3.85 6.00 

21-31 4.74 8.12 

APRIL 1-10 6.99 10.91 

11-20 6.95 10.85 

21-30 8.73 13.61 

MAY 1-10 13.09 20.42 

11-20 16.69 26.03 

21-31 12.77 21.90 

79 

710.22 



TABLE7.7 (D) 


1979-1980 

PERIOD FLOW UNRISTRICTED ENERGY 


JUNE 1-10 15.21 23.73 

11-20 18.20 28.39 

21-30 26.10 40.71 

JULY 1-10 27.11 42.27 

11-20 25.93 40.44 

21-31 29.04 49.83 

AUGUST 1-10 26.84 41.86 

11-20 21.19 33.05 

21-31 22.48 38.56 

SEPTEMBER 1-10 22.11 34.48 

11-20 19.29 30.09 

21-30 14.15 22.07 

OCTOBER 1-10 23.58 36.78 

11-20 16.09 25.10 

21-31 12.07 20.71 

NOVEMBER 1-10 12.03 18.77 

11-20 9.80 15.28 

21-30 9.22 14.39 

DECEMBER 1-10 8.79 13.70 

11-20 7.24 11.29 

21-31 6.97 11.95 

JANUARY 1-10 6.57 10.24 

11-20 6.32 9.86 

21-31 6.26 10.75 

FEBRUARY 1-10 6.01 9.38 

11-20 6.30 9.83 

21-29 6.72 9.43 

MARCH 1-10 6.91 10.78 

11-20 7.09 11.05 

21-31 9.57 16.41 

APRIL 1-10 10.75 16.76 

11-20 13.78 21.50 

21-30 15.71 24.49 

MAY 1-10 14.98 23.36 

11-20 12.81 19.98 

21-31 13.66 23.43 

80 

820.67 



TABLE 7.7 (E) 


1980-1981 



JUNE 1-10 20.94 32.66 

11-20 27.87 43.46 

21-30 31.19 48.64 

JULY 1-10 33.01 51.48 

11-20 33.79 52.70 

21-31 35.40 60.73 

AUGUST 1-10 35.77 55.79 

11-20 39.28 61.27 

21-31 32.72 56.13 

SEPTEMBER 1-10 31.26 48.75 

11-20 24.50 38.21 

21-30 19.83 30.93 

OCTOBER 1-10 15.51 24.19 

11-20 13.33 20.79 

21-31 12.42 21.31 

NOVEMBER 1-10 10.49 16.36 

11-20 9.55 14.90 

21-30 8.79 13.72 

DECEMBER 1-10 8.17 12.74 

11-20 7.42 11.58 

21-31 6.74 11.57 

JANUARY 1-10 6.50 10.13 

11-20 6.09 9.50 

21-31 6.01 10.31 

FEBRUARY 1-10 5.59 8.72 

11-20 5.75 8.97 

21-28 6.95 8.68 

MARCH 1-10 6.88 10.72 

11-20 7.28 11.36 

21-31 8.60 14.75 

APRIL 1-10 8.61 13.43 

11-20 10.90 17.00 

21-30 12.84 20.03 

MAY 1-10 15.77 24.60 

11-20 17.03 26.57 

21-31 16.52 28.34 

81 

951.00 



TABLE 7.7 (F) 


1981-1982 



JUNE 1-10 18.19 28.36 

11-20 21.75 33.92 

21-30 29.53 46.05 

JULY 1-10 37.72 58.83 

11-20 32.35 50.45 

21-31 30.43 52.20 

AUGUST 1-10 29.67 46.27 

11-20 31.31 48.83 

21-31 30.44 52.21 

SEPTEMBER 1-10 29.13 45.44 

11-20 24.97 38.94 

21-30 19.90 31.04 

OCTOBER 1-10 18.25 28.46 

11-20 16.89 26.34 

21-31 14.76 25.32 

NOVEMBER 1-10 12.58 19.62 

11-20 10.04 15.65 

21-30 8.31 12.96 

DECEMBER 1-10 7.63 11.90 

11-20 6.86 10.70 

21-31 5.38 9.23 

JANUARY 1-10 4.94 7.71 

11-20 5.50 8.58 

21-31 5.42 9.30 

FEBRUARY 1-10 5.38 8.39 

11-20 5.58 8.71 

21-28 5.43 6.77 

MARCH 1-10 5.66 8.82 

11-20 6.33 9.87 

21-31 7.54 12.94 

APRIL 1-10 9.48 14.78 

11-20 9.46 14.76 

21-30 10.49 16.37 

MAY 1-10 13.16 20.52 

11-20 14.78 23.04 

21-31 14.36 24.63 

82 

887.89 



TABLE7.7 (G) 


1982-1983 

83 





JUNE 1-10 25.34 39.53 

11-20 27.91 43.53 

21-30 30.86 48.12 

JULY 1-10 27.09 42.25 

11-20 30.35 47.34 

21-31 35.80 61.42 

AUGUST 1-10 24.06 37.52 

11-20 22.78 35.52 

21-31 26.73 45.85 

SEPTEMBER 1-10 20.56 32.07 

11-20 29.74 46.38 

21-30 19.51 30.43 

OCTOBER 1-10 13.81 21.54 

11-20 11.60 18.09 

21-31 11.17 19.16 

NOVEMBER 1-10 8.75 13.64 

11-20 7.63 11.90 

21-30 7.39 11.53 

DECEMBER 1-10 6.53 10.18 

11-20 6.02 9.39 

21-31 5.70 9.78 

JANUARY 1-10 5.65 8.81 

11-20 5.03 7.85 

21-31 3.53 6.05 

FEBRUARY 1-10 3.21 5.01 

11-20 3.19 4.97 

21-28 4.44 5.54 

MARCH 1-10 4.77 7.44 

11-20 6.11 9.53 

21-31 5.51 9.46 

APRIL 1-10 8.11 12.65 

11-20 6.63 10.34 

21-30 8.30 12.95 

MAY 1-10 13.36 20.84 

11-20 16.01 24.97 

21-31 21.31 36.55 

818.15

TABLE7.7 (H) 


1983-1984 

PERI OD FLOW UNRISTRICTED ENERGY 


JUNE 1-10 26.79 41.78 

11-20 26.00 40.55 

21-30 36.28 56.59 

JULY 1-10 41.55 64.80 

11-20 35.35 55.13 

21-31 35.07 60.17 

AUGUST 1-10 28.71 44.77 

11-20 30.44 47.47 

21-31 35.56 61.01 

SEPTEMBER 1-10 28.58 44.58 

11-20 32.14 50.12 

21-30 37.07 57.82 

OCTOBER 1-10 26.07 40.65 

11-20 25.70 40.08 

21-31 17.52 30.05 

NOVEMBER 1-10 14.32 22.33 

11-20 13.16 20.52 

21-30 10.84 16.90 

DECEMBER 1-10 9.04 14.10 

11-20 8.47 13.22 

21-31 7.60 13.03 

JANUARY 1-10 6.78 10.57 

11-20 6.67 10.40 

21-31 5.94 10.18 

FEBRUARY 1-10 5.72 8.92 

11-20 5.94 9.26 

21-29 5.71 8.01 

MARCH 1-10 12.60 19.65 

11-20 14.08 21.96 

21-31 13.83 23.73 

APRIL 1-10 14.54 22.68 

11-20 15.50 24.18 

21-30 15.51 24.18 

MAY 1-10 17.60 27.44 

11-20 25.72 40.11 

21-31 36.54 62.68 

84 

1159.62 



TABLE7.7 (I) 


1984-1985 



JUNE 1-10 37.97 59.21 

11-20 45.66 71.20 

21-30 41.00 63.94 

JULY 1-10 47.19 73.60 

11-20 47.35 73.84 

21-31 50.05 85.87 

AUGUST 1-10 45.14 70.40 

11-20 45.26 70.59 

21-31 47.38 81.28 

SEPTEMBER 1-10 48.80 76.11 

11-20 46.57 72.63 

21-30 36.94 57.61 

OCTOBER 1-10 31.12 48.53 

11-20 39.47 61.56 

21-31 30.41 52.17 

NOVEMBER 1-10 22.66 35.34 

11-20 19.58 30.54 

21-30 17.41 27.14 

DECEMBER 1-10 11.16 17.40 

11-20 10.98 17.12 

21-31 11.02 18.91 

JANUARY 1-10 11.12 17.34 

11-20 10.56 16.47 

21-31 9.14 15.68 

FEBRUARY 1-10 9.99 15.58 

11-20 9.13 14.24 

21-28 11.05 13.79 

MARCH 1-10 14.04 21.90 

11-20 15.21 23.72 

21-31 14.16 24.30 

APRIL 1-10 17.05 26.59 

11-20 20.57 32.08 

21-30 24.29 37.89 

MAY 1-10 17.48 27.27 

11-20 20.29 31.64 

21-31 28.26 48.48 

85 

1531.95 



TABLE7.7 (J) 


1985-1986 



JUNE 1-10 18.13 28.28 

11-20 22.64 35.30 

21-30 64.15 100.04 

JULY 1-10 50.58 78.88 

11-20 66.00 102.93 

21-31 55.50 95.20 

AUGUST 1-10 44.85 69.94 

11-20 47.31 73.78 

21-31 57.92 99.36 

SEPTEMBER 1-10 23.62 36.84 

11-20 22.57 35.19 

21-30 18.91 29.49 

OCTOBER 1-10 16.25 25.35 

11-20 14.25 22.22 

21-31 11.74 20.14 

NOVEMBER 1-10 9.53 14.86 

11-20 8.28 12.91 

21-30 7.34 11.44 

DECEMBER 1-10 6.25 9.75 

11-20 5.65 8.81 

21-31 5.20 8.92 

JANUARY 1-10 4.93 7.69 

11-20 4.90 7.65 

21-31 4.64 7.96 

FEBRUARY 1-10 4.69 7.31 

11-20 4.82 7.52 

21-28 5.52 6.89 

MARCH 1-10 5.89 9.18 

11-20 6.41 9.99 

21-31 6.58 11.29 

APRIL 1-10 6.47 10.09 

11-20 8.37 13.05 

21-30 9.39 14.64 

MAY 1-10 8.80 13.72 

11-20 9.36 14.59 

21-31 9.86 16.91 

86 

1078.12 



TABLE7.7 (K) 


1986-1987 



JUNE 1-10 11.98 18.69 

11-20 20.32 31.70 

21-30 30.12 46.97 

JULY 1-10 26.08 40.68 

11-20 32.59 50.83 

21-31 29.31 50.28 

AUGUST 1-10 26.02 40.57 

11-20 22.36 34.88 

21-31 24.76 42.47 

SEPTEMBER 1-10 21.74 33.90 

11-20 27.00 42.10 

21-30 21.98 34.27 

OCTOBER 1-10 17.72 27.64 

11-20 13.25 20.67 

21-31 10.35 17.76 

NOVEMBER 1-10 9.51 14.84 

11-20 8.47 13.20 

21-30 7.31 11.40 

DECEMBER 1-10 6.54 10.21 

11-20 6.03 9.40 

21-31 4.44 7.62 

JANUARY 1-10 3.88 6.05 

11-20 3.65 5.70 

21-31 3.43 5.88 

FEBRUARY 1-10 3.25 5.06 

11-20 3.22 5.02 

21-28 3.53 4.40 

MARCH 1-10 3.30 5.14 

11-20 3.91 6.10 

21-31 4.91 8.42 

APRIL 1-10 8.96 13.97 

11-20 6.26 9.76 

21-30 8.27 12.90 

MAY 1-10 9.35 14.58 

11-20 10.40 16.22 

21-31 12.20 20.94 

87 

740.20 



TABLE 7.7 (L) 


1987-1988 



JUNE 1-10 20.25 31.57 

11-20 29.40 45.86 

21-30 24.68 38.49 

JULY 1-10 28.31 44.15 

11-20 27.07 42.21 

21-31 30.26 51.92 

AUGUST 1-10 28.66 44.69 

11-20 31.26 48.76 

21-31 20.90 35.85 

SEPTEMBER 1-10 37.59 58.63 

11-20 20.11 31.36 

21-30 27.58 43.01 

OCTOBER 1-10 17.13 26.71 

11-20 12.76 19.89 

21-31 10.91 18.71 

NOVEMBER 1-10 8.85 13.80 

11-20 5.40 8.42 

21-30 4.75 7.40 

DECEMBER 1-10 4.48 6.98 

11-20 4.09 6.39 

21-31 3.74 6.42 

JANUARY 1-10 3.65 5.70 

11-20 3.65 5.70 

21-31 3.61 6.19 

FEBRUARY 1-10 3.54 5.52 

11-20 3.71 5.78 

21-29 4.12 5.78 

MARCH 1-10 4.27 6.66 

11-20 6.33 9.87 

21-31 6.51 11.16 

APRIL 1-10 7.44 11.60 

11-20 8.40 13.11 

21-30 9.77 15.24 

MAY 1-10 9.99 15.59 

11-20 14.97 23.35 

21-31 19.84 34.04 

88 

806.52 



TABLE 7.7 (M) 


1988-1989 



JUNE 1-10 16.00 24.96 

11-20 23.15 36.11 

21-30 25.36 39.56 

JULY 1-10 39.42 61.47 

11-20 30.96 48.29 

21-31 34.12 58.54 

AUGUST 1-10 33.87 52.82 

11-20 31.09 48.48 

21-31 47.16 80.91 

SEPTEMBER 1-10 22.52 35.12 

11-20 15.19 23.68 

21-30 16.99 26.49 

OCTOBER 1-10 14.34 22.36 

11-20 9.51 14.84 

21-31 7.65 13.13 

NOVEMBER 1-10 6.31 9.84 

11-20 5.70 8.88 

21-30 5.31 8.28 

DECEMBER 1-10 5.04 7.86 

11-20 4.78 7.46 

21-31 4.52 7.76 

JANUARY 1-10 2.77 4.32 

11-20 2.69 4.20 

21-31 2.67 4.58 

FEBRUARY 1-10 2.97 4.63 

11-20 2.71 4.23 

21-28 2.89 3.61 

MARCH 1-10 3.28 5.12 

11-20 3.35 5.22 

21-31 3.44 5.90 

APRIL 1-10 3.58 5.58 

11-20 4.28 6.68 

21-30 5.14 8.01 

MAY 1-10 9.02 14.07 

11-20 9.32 14.53 

21-31 22.70 38.95 

89 

766.48 



TABLE 7.7 (N) 


1989-1990 

UNRISTRICTED 

PERIOD FLOW 

ENERGY 


JUNE 1-10 20.16 31.44 

11-20 33.39 52.08 

21-30 35.32 55.08 

JULY 1-10 35.96 56.08 

11-20 35.37 55.16 

21-31 32.92 56.48 

AUGUST 1-10 28.57 44.56 

11-20 22.41 34.96 

21-31 21.99 37.73 

SEPTEMBER 1-10 21.32 33.24 

11-20 19.31 30.11 

21-30 19.18 29.91 

OCTOBER 1-10 15.15 23.63 

11-20 12.89 20.11 

21-31 10.49 17.99 

NOVEMBER 1-10 6.52 10.17 

11-20 5.29 8.26 

21-30 4.81 7.51 

DECEMBER 1-10 4.20 6.55 

11-20 3.64 5.68 

21-31 3.19 5.47 

JANUARY 1-10 2.91 4.54 

11-20 2.70 4.20 

21-31 2.44 4.19 

FEBRUARY 1-10 2.40 3.74 

11-20 2.26 3.52 

21-28 2.18 2.72 

MARCH 1-10 1.99 3.10 

11-20 1.63 2.53 

21-31 1.65 2.84 

APRIL 1-10 1.71 2.67 

11-20 2.82 4.40 

21-30 3.50 5.45 

MAY 1-10 5.16 8.05 

11-20 9.09 14.18 

21-31 10.46 17.95 

90 

706.28 



TABLE 7.7 (O) 


1990-1991 

91 





JUNE 1-10 22.09 34.46 

11-20 21.58 33.66 

21-30 25.24 39.36 

JULY 1-10 27.82 43.38 

11-20 35.46 55.30 

21-31 30.35 52.06 

AUGUST 1-10 25.85 40.31 

11-20 26.26 40.96 

21-31 23.30 39.98 

SEPTEMBER 1-10 22.37 34.88 

11-20 21.42 33.40 

21-30 14.92 23.26 

OCTOBER 1-10 12.50 19.49 

11-20 12.73 19.85 

21-31 10.47 17.97 

NOVEMBER 1-10 6.41 10.00 

11-20 4.79 7.47 

21-30 4.00 6.24 

DECEMBER 1-10 3.66 5.71 

11-20 3.02 4.71 

21-31 2.61 4.47 

JANUARY 1-10 2.64 4.12 

11-20 2.59 4.04 

21-31 2.56 4.40 

FEBRUARY 1-10 2.48 3.87 

11-20 2.36 3.68 

21-28 2.38 2.97 

MARCH 1-10 2.54 3.97 

11-20 2.90 4.52 

21-31 3.06 5.25 

APRIL 1-10 8.03 12.52 

11-20 4.58 7.14 

21-30 4.84 7.55 

MAY 1-10 8.13 12.68 

11-20 9.91 15.45 

21-31 10.96 18.80 

677.88

TABLE 7.7 (P) 


1991-1992 

92 





JUNE 1-10 11.73 18.29 

11-20 18.52 28.88 

21-30 17.03 26.56 

JULY 1-10 19.45 30.34 

11-20 18.95 29.56 

21-31 20.66 35.44 

AUGUST 1-10 23.69 36.94 

11-20 27.29 42.56 

21-31 22.55 38.68 

SEPTEMBER 1-10 22.72 35.43 

11-20 24.00 37.43 

21-30 18.59 28.99 

OCTOBER 1-10 14.84 23.14 

11-20 11.77 18.35 

21-31 9.66 16.57 

NOVEMBER 1-10 8.00 12.48 

11-20 7.08 11.04 

21-30 5.40 8.42 

DECEMBER 1-10 4.54 7.08 

11-20 3.48 5.43 

21-31 3.06 5.25 

JANUARY 1-10 2.79 4.35 

11-20 2.31 3.61 

21-31 2.36 4.05 

FEBRUARY 1-10 2.50 3.89 

11-20 2.41 3.75 

21-29 2.31 3.24 

MARCH 1-10 2.47 3.86 

11-20 2.49 3.89 

21-31 2.56 4.39 

APRIL 1-10 3.03 4.72 

11-20 4.25 6.63 

21-30 3.89 6.06 

MAY 1-10 3.81 5.94 

11-20 4.43 6.92 

21-31 4.46 7.65 

569.80

TABLE 7.7 (Q) 


1992-1993 

93 





JUNE 1-10 4.92 7.68 

11-20 7.02 10.95 

21-30 13.60 21.21 

JULY 1-10 11.69 18.22 

11-20 11.82 18.44 

21-31 13.43 23.04 

AUGUST 1-10 14.70 22.93 

11-20 14.76 23.02 

21-31 16.05 27.53 

SEPTEMBER 1-10 14.08 21.95 

11-20 13.85 21.61 

21-30 11.47 17.89 

OCTOBER 1-10 8.66 13.51 

11-20 6.21 9.69 

21-31 5.29 9.07 

NOVEMBER 1-10 3.90 6.09 

11-20 3.47 5.41 

21-30 3.16 4.93 

DECEMBER 1-10 3.13 4.88 

11-20 2.71 4.22 

21-31 2.50 4.29 

JANUARY 1-10 2.54 3.96 

11-20 2.57 4.00 

21-31 2.41 4.13 

FEBRUARY 1-10 2.33 3.63 

11-20 2.48 3.86 

21-28 2.39 2.98 

MARCH 1-10 3.91 6.10 

11-20 3.90 6.08 

21-31 4.08 7.00 

APRIL 1-10 4.15 6.46 

11-20 4.53 7.07 

21-30 5.43 8.46 

MAY 1-10 6.89 10.74 

11-20 6.20 9.67 

21-31 6.28 10.77 

391.47

TABLE 7.7 (R) 


1993-1994 



JUNE 1-10 8.06 12.57 

11-20 10.30 16.06 

21-30 13.25 20.66 

JULY 1-10 27.74 43.27 

11-20 27.74 43.27 

21-31 32.53 55.81 

AUGUST 1-10 36.49 56.90 

11-20 34.59 53.95 

21-31 33.13 56.84 

SEPTEMBER 1-10 34.86 54.36 

11-20 29.36 45.78 

21-30 27.76 43.29 

OCTOBER 1-10 24.67 38.47 

11-20 18.30 28.54 

21-31 15.69 26.91 

NOVEMBER 1-10 13.02 20.30 

11-20 11.47 17.89 

21-30 10.52 16.40 

DECEMBER 1-10 10.26 16.01 

11-20 9.43 14.71 

21-31 7.75 13.29 

JANUARY 1-10 7.30 11.38 

11-20 6.80 10.60 

21-31 6.87 11.78 

FEBRUARY 1-10 6.77 10.56 

11-20 6.48 10.10 

21-28 6.94 8.66 

MARCH 1-10 6.40 9.97 

11-20 5.77 9.00 

21-31 7.30 12.52 

APRIL 1-10 7.09 11.06 

11-20 8.87 13.83 

21-30 8.14 12.69 

MAY 1-10 9.12 14.23 

11-20 9.40 14.66 

21-31 11.57 19.84 

94 

876.18 



TABLE 7.7 (S) 


1994-1995 



JUNE 1-10 16.70 26.04 

11-20 22.10 34.47 

21-30 25.66 40.01 

JULY 1-10 21.94 34.22 

11-20 23.26 36.28 

21-31 23.71 40.67 

AUGUST 1-10 21.79 33.98 

11-20 21.28 33.19 

21-31 22.89 39.26 

SEPTEMBER 1-10 19.41 30.28 

11-20 19.44 30.32 

21-30 16.80 26.20 

OCTOBER 1-10 13.14 20.49 

11-20 11.68 18.22 

21-31 10.70 18.35 

NOVEMBER 1-10 8.80 13.73 

11-20 7.26 11.32 

21-30 6.06 9.46 

DECEMBER 1-10 5.85 9.12 

11-20 5.35 8.34 

21-31 5.06 8.68 

JANUARY 1-10 4.80 7.48 

11-20 4.85 7.56 

21-31 4.79 8.22 

FEBRUARY 1-10 4.75 7.41 

11-20 4.73 7.38 

21-28 4.76 5.94 

MARCH 1-10 4.33 6.75 

11-20 4.10 6.40 

21-31 5.65 9.70 

APRIL 1-10 5.53 8.62 

11-20 6.85 10.68 

21-30 9.99 15.59 

MAY 1-10 14.58 22.74 

11-20 22.51 35.10 

21-31 21.75 37.31 

95 

719.50 



TABLE 7.7 (T) 


1995-1996 



JUNE 1-10 25.25 39.39 

11-20 27.01 42.12 

21-30 27.36 42.67 

JULY 1-10 34.72 54.15 

11-20 29.13 45.43 

21-31 22.39 38.41 

AUGUST 1-10 24.46 38.15 

11-20 24.68 38.49 

21-31 21.92 37.61 

SEPTEMBER 1-10 19.78 30.85 

11-20 17.71 27.63 

21-30 17.04 26.58 

OCTOBER 1-10 12.59 19.63 

11-20 12.25 19.11 

21-31 9.57 16.42 

NOVEMBER 1-10 6.23 9.71 

11-20 7.11 11.09 

21-30 7.15 11.15 

DECEMBER 1-10 5.35 8.34 

11-20 4.76 7.43 

21-31 4.42 7.59 

JANUARY 1-10 3.81 5.95 

11-20 3.79 5.91 

21-31 4.01 6.87 

FEBRUARY 1-10 4.15 6.47 

11-20 3.69 5.76 

21-29 4.04 5.68 

MARCH 1-10 4.11 6.40 

11-20 4.75 7.41 

21-31 5.07 8.69 

APRIL 1-10 4.66 7.27 

11-20 4.53 7.06 

21-30 10.07 15.70 

MAY 1-10 12.28 19.14 

11-20 10.76 16.78 

21-31 14.89 25.55 

96 

722.59 



TABLE 7.7 (U) 


1996-1997 

UNRISTRICTED 

PERIOD FLOW 

ENERGY 


JUNE 1-10 13.97 21.78 

11-20 11.83 18.45 

21-30 21.13 32.95 

JULY 1-10 23.47 36.61 

11-20 25.27 39.42 

21-31 22.50 38.60 

AUGUST 1-10 21.51 33.54 

11-20 20.06 31.28 

21-31 20.21 34.68 

SEPTEMBER 1-10 20.18 31.47 

11-20 19.26 30.03 

21-30 16.75 26.12 

OCTOBER 1-10 14.72 22.96 

11-20 13.49 21.04 

21-31 12.06 20.69 

NOVEMBER 1-10 10.97 17.11 

11-20 10.20 15.91 

21-30 9.07 14.15 

DECEMBER 1-10 6.25 9.75 

11-20 5.65 8.81 

21-31 5.20 8.92 

JANUARY 1-10 5.88 9.17 

11-20 5.59 8.72 

21-31 5.69 9.75 

FEBRUARY 1-10 5.67 8.85 

11-20 5.65 8.82 

21-28 5.59 6.97 

MARCH 1-10 5.72 8.93 

11-20 6.01 9.37 

21-31 6.55 11.24 

APRIL 1-10 6.28 9.80 

11-20 6.25 9.74 

21-30 6.43 10.03 

MAY 1-10 7.50 11.70 

11-20 8.63 13.46 

21-31 8.91 15.29 

97 

666.10 





CHAPTER – VIII 

POWER EVACUATION

8.1 GENERAL 

CHAPTER-VIII 

POWER EVACUATION 

98 



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 Lingza 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 Lingza 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 (2 

km from Teesta –III H E Project) Teesta III H.E.P. Teesta – III H.E.P. is situated in the 

close vicinity of Lingza Hydro Electric Project. The length of this 220 kV double circuit 

line would be approximately 15 km.



CHAPTER – IX 

ENVIRONMENTAL ASPECTS

.CHAPTER - IX 

ENVIRONMENTAL ASPECTS 

99 




9.1.1 General 

The State of Sikkim has abundant snow and monsoon fed rivers with immense hydro 

potential. The proposed run-of-the-river Lingza Hydroelectric Power Scheme involves 

construction of diversion structures immediately downstream of Ringpi Power Station at 

a riverbed elevation of about 1795 m on river Ringpi chu (fig. 9.1). Ringpi chu is a 

tributary of Toulong chu which is a major right bank tributary of river Teesta. The water 

from the diversion structure shall be conveyed to the powerhouse through a 4 km long 

headrace tunnel situated on the bank of main Tolung chu. The riverbed elevation at the 

tailrace shall be about 1095 m and would utilise a net head of 736 m. The proposed 

project is envisaged to have generation capacity of about 120 MW. 

9.1.2 Location 

The proposed project is located on Ringpi Chhu in the North district of Sikkim between 

longitude 88°27’20’’E & 88° 26’ 39’’ and latitude 27°36’00’’N & 27° 33’ 46’’, just u/s of 

Panan reservoir. New Jalpaiguri is the nearest railhead and Bagdogra is the nearest 

airport. The dam site is to be located near the Myong village under Lingza-Tolung 

Revenue Block about 4.9 km upstream of the confluence of Rangyong Chhu and Ringpi 

Chhu (Fig. 9.2). 

9.2 PHYSICAL ENVIRONMENT 

9.2.1 Climate/Meteorology 

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

100 



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 

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 

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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 

9.2.4 Geology 

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 (

102 



The physical configuration of Sikkim is partly due to its geological structure. Major 

portion of the State is covered by Precambrian rocks and is of much younger age. The 

northern, eastern and western portions of the State are constituted of hard massive gneiss 

rocks capable of resisting denudation. The rock type in this region belongs to Lesser and 

Higher Himalayas, the former being represented by low grade meta-sedimentaries and 

granite gneiss whereas the central crystalline in the axial zone of the north Sikkim are 

represented by high grade meta-sedimentary and granite intrusive. 

The main lithounits exposed in the area include Daling meta-volcano sedimentaries, 

Lingtse sheared granite gneisses and high grade Central Crystallines. The Daling Group 

of rocks comprises (schistose) metawacke, chlorite-muscovite phyllite intercalated with 

chlorite, quartz and their metamorphic equivalents upto garnet-staurolite kyanite grade. 

The metawacke units are highly sheared and are found to be associated with Lingtse 

gneiss and meta porphyroid bands with bluish pa lescent quartz clasts. 

The Central Crystalline Gneiss comprise of mica bearing quartz, feldspar gneiss, banded 

gneiss. Migmatite gneiss, garnet bearing psammitic gneiss and higher grade kyanite 

sillimannite garnet gneiss are found to crop out in the eastern part of the area. Apart from 

these major litho units in the area there are metabasite bodies and some leucogranites 

which show pegmatitic character at places. The metabasic rocks occur as concordant 

bodies within the country rock. These bands are found to be of varying thickness and are 

present both within the gneisses and the Daling meta-sedimentaries. 

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 

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 

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The direct draining catchment of the project is 198 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 

Ringpi Chhu rises as Jumthul Chhu from Jumthul Phuk glacier at the base of Siniolchu 

peak (6,888 m). Along its eastward course, Jumthul Chhu is joined by Kishong Chhu on its 

left bank to form Ringpi Chhu (Fig 9.3). Kishong Chhu rises in the northeastern part of the 

catchment and drains Kishong Chho, a glacial lake and contributes significantly to Jumthul 

Chhu. Thereafter, up to the proposed dam site Ringpi Chhu receives drainage mainly on its 

left bank from a number of streams like Ludui Chhu, Pegor Chhu, Kongcha Chhu and 

Zong Chhu. There are a number of small and big glacial lakes in the eastern part of the 

catchments, which contribute to the main river through these streams. Ringpi Chhu 

descends from an altitude of 4,000 m to 1,800 m within a distance of about 17.5 km with a 

gradient of 128 m/km. 

9.2.8 Submergence 

The proposed project is likely to inundate a 10.75 ha of land, which is confined to the 

river valley. The predominant landuse in the submergence area is degraded and open 

forest and does not involve inundation of any village or human habitation. Thus no 

displacement is anticipated. 

9.2.9 Landuse pattern (including land requirement of the project) 

The landuse/landcover pattern within the 7 km radius of the proposed Lingza 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

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categories is given in Table 9.2 and the percent representation of each of the 

landuse/landcover type is shown in Figure 9.7. Based on the data generated from remote 

sensing compiled with ground checks, it is clear that Dense Mixed Broadleaf forests 

constitute about half (50%) of the total land area, therefore form the predominant landuse 

around the proposed project site. The degraded types of forests, which are mostly scrub, 

constitute 29% of the area covering about 56.62 ha of land. It is evident from the results 

that the area is not significantly disturbed, as the area under human intervention around 

the project vicinity (within 7 km radius) comprises only 2% of the cultivation/settlement 

area. A sizeable portion of the area is under rocky land and cliffs comprising about 14% 

of land area. In addition, some fragile moraines also comprise about 4% land area. Area 

under snow is small constituting less than 1% land area. The analysis of the 

landuse/landcover indicates that the area is mostly under natural ecosystems with only 

limited human intervention. Natural landscape features also include areas under snow and 

water bodies. The dense forests in the catchment are present towards north, northeast and 

west. These forests are represented by Tolung Reserve Forest in the north and northeast, 

Sakyong Reserve Forest in the west and southwest and Lingdem Reserve Forest in the 

south and southeast. These forests are mostly broad-leaf forests with occasional 

representation of local bamboo species in them, particularly in the warmer areas. 

Table 9.2: Area (ha) under different landuse/landcover categories in 7km radius 

of Lingza H.E. Scheme 

Landuse/landcover Area (ha) 

Dense Mixed Forest 100.33 

Scrub 56.52 

Rockyland 26.69 

Cultivation/Settlements 4.08 

Moraines 8.59 

Snow 0.01

105 



Figure 9.7 Percent area under various landuse/landcover categories in 7 km 

radius of th proposed Lingza H.E. Scheme. 

9.2.10 Infrastructure 

The existing facilities in the project area are as follows: 

Road communication Network 

The project area falls in the North district of Sikkim and the project area is not very easily 

accessible. The road is metalled upto Sakkyong and Lingsha. Beyond this there is trek 

route to the project site. There is also a well-deve loped trek route up to Toulng Gompa. 

Bank 

Branches SBI are present at Tolung, Chungthang and Mangan. 

Post office 

29% 

Post and telegraph office exist at Mangan, HQ of North District. 

14% 

2% 

4% 

50% 

Dense Mixed Forest Scrub Rockyland Cultivation/Settlements Moraines Snow 

1%

Educational Facilities 

106 



Higher secondary school exists at Tingbong Sec. School, Tingbong. Primary school is 

situated at Namprick. Community Information Centre (CIC) is there at Tingbong and 

Mangan and provides education in information technology to the students of the school. 

For higher education, students go to Sikkim Govt. College, Tadong, Gangtok, Manipal 

Institute of Technology Sikkim, Majitar and Sikkim Manipal University of Health 

Technology & Medical Sciences, Gangtok. 

Communication 

The communication network is very poor in the area. However there are telephone 

exchange s at locaed far away Gangtok, Phodong and Mangan. Community Information 

Centre (CIC) is present in Mangan, which provides internet facilities to the locals. 

Government Department 

Government department offices exist at block level in the project area. There is a District 

centre at Mangan. 

Hospitals/ Primary health Centers 

Primary health centres are available at Sankalang. Central Referral hospital and Sikkim 

Manipal University of Health Technology & Medical Sciences (Referral Hospital) are at 

Tadong, Gangtok. 

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

107 



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 Vegetation (details of forest types, etc.) 

Its extreme altitudinal variation brings in tremendous change in climatic conditions that 

in turn supports the biodiversity of different heights. With only 0.22% geographical area 

of the country, Sikkim harbors 1/3 rd of the country’s flowering plants. There are 4500 

species of flowering plants, 362 species of ferns and its allies, 11 species of oaks, 8 

species of tree ferns, 448 species of orchids, 30 species of Primula and 20 species of 

bamboos. Many medicinal plants/herbs/and important shrubs are found in low and high 

altitude areas. 

9.3.2 Flora 

The dam site is located in warm temperate hilly terrain and the area of in the vicinity of 

the project is mainly comprised of dense mixed forests. This area experiences warm and 

humid summers and relatively cold winters. There is warm to cool humid climate 

throughout the year with a short dry spell during winter months starting from October to 

February. Owing to extended spell of humidity and cool to moderate temperatures at 

these altitudes the vegetation is constituted mostly by the warm temperate deciduous and 

evergreen plant species. In those areas where forests are present these are densely 

vegetated by all the physiognomic forms – trees, shrubs and herbaceous flora. The woody 

elements in these mixed forests comprises of Albizia lebbek, Alnus nepalensis, Annona 

squamosa, Callicarpa arborea, Canarium bengalense, Erythrina arborescens, Ficus spp., 

Lithocarpus sp., Litsea sp., Macaranga denticulata, Rhus wallichii and Toona ciliata. 

Shrubby bamboo and some other associates like Abroma anguistifolia, Artemisia 

nilagirica, Boehmeria platyphyla, Girardiana diversifolia , Rhamnus virgatus and Rubus 

ellipticus form second storey. Cissus repens, Piper sp., Raphidophora decursiva, Rubia 

sikkimensis, Smilax sp., Trichosanthes lepiniana, etc. are important climbers in these

108 



forests. Herbaceous flora is represented by Ageratum conyzoides, Arenaria 

neelagheriensis, Arthraxon hispedus, Begonia spp., Commelina bengalensis, Lecanthus 

peduncularis, Oplismenus compositus, Pilea scripta, Polygonum barbadens, Setaria 

palmifolia and Thysanolaena latifolia. 

9.3.3 Fauna and Wildlife 

As the project site falls in the vicinity of dense forests a good presence of wildlife is 

expected in and around the project site. The upper part of catchments of Ringpi Chhu and 

Rangyong Chhu harbour several faunal species like 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). These animals are generally found in the vicinity of agricultural 

fields. In addition there are also species like Civets (Viverra zibetha), porcupines (Hystrix 

brachyura), Grey musk shrew (Suncus murinus), the house mouse (Mus musculus) and 

Bandicoot rat (Bandicota bengalensis). The upper reaches, i.e. the alpine areas of the 

catchment harbour other mammalian species, which include Nayan, Bha ral, Snow 

leopard, Himalaya brown bear, Himalayan tahr, Barking Deer, Himalayan marmot and 

pikas. These animals however are rarely seen descending down to lower altitudes like 

2,000 m. The avifaunal elements are comprised of bird groups like bulbuls, thrushes, 

eagles, partridges, pigeons, doves, koels, owls, kingfishers, nightjars, woodpeckers, 

orioles, drongos, mynas, flycatchers, babblers, robins, etc. Among the reptiles Python 

molurus, Naja naja and Dendrelaphis sp. are important species found in the vicinity of 

project area. 

Among the various faunal species present in the catchment Panthera pardus, Neofelis 

nebulosa, Felis bengalensis, Macaca assemensis and Cervus duvaucelli are the 

Scheduled as threatened animals of India while Panthera tigris, Selenarctos thibetanus 

and Cervus duvaucelli are considered to be globally threatened species.

9.3.3 Aquatic life 

109 



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 dam structure and the powerhouse lies within 7km boundary of the of 

Kanchendozenga Biosphere reserve. However, 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 

Sufficient amount of land will be required for construction of the proposed dam, 

powerhouse, colonies & approach roads etc. About 10.75 ha of land would also 

come under submergence. All these activities would mean some disturbance in 

the soil 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 

110 



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 10.75 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 

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

111 



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 

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.

112 



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 

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 FACIL ITIES 

10.1.1 Road Communication 

120 



The road from Mangan to lingza is the approach to the Project . The Power house is 

located on the left bank of Ringpi Chu u/s of confluence of Rangyong Chu and Ringpi 

Chu near the Place called Chhana about 3.0Km u/s of village Lingza. The Powerhouse is 

approachable from Lingza by a road of 2.0 km and a foot path of 1.0km length from the 

road. Lingza is 17 Km from Magan, the head quater of North Sikkim District 0f Sikkim, 

62 Km from Singtam (NH31A), 162 Km from NJP railway station and 163 Km from 

Bagdogra airport. The Lingza village is well connected form Mangan by a PWD road. 

The Siliguri-Gangtok (NH-31A) and Singtam-Mangan-Sanklan state highways are being 

maintained by BRO. while the Lingza-Sanklan road are being maintained by state PWD. 

The dam site is located near the place called Ishana and is approachable by a hilly foot 

path of about 5.0 Km length from the end of road. The road is available for a length of 

2.0Km beyond Lingza Village. 

10.1.2 Housing And Community Facilities 

Chhana is the name of the place near to powerhouse and Ishana to Dam site 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

121 



Ltd. Teesta (V) HE Project, 510 MW being executed by NHPC in central sector is also 

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 Lingza 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 Lingza H.E. Project has been worked out. 

10.2.1 Improvement Of Existing Road And Bridges 

The Powerhouse is located on the u/s of confluence of Rangyong Chu and Ringpi 

near the village Chhana . The state highway ha ving a length of 17km from Sanklan to 

Lingza connects the power house by a foot path of 10 Km and dam site by a foot path of 

5.0 Km. Since the Lingza H.E. Project is on u/s of the Panan H.E. Project, therefore it has 

been presumed that all the roads and bridges shall be ready upto damsite of Panan H.E. 

Project. 

10.2.2 Construction Of Roads & Bridges 

The power house shall be approached from Mangan - Lingza road from left bank for 

which a new project road of 3.0 Km is to be constructed from the dam site of Panan H.E. 

Project. The Dam site shall be approached from right bank through a bridge at Vawl. 

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 for Power house

122 



shall be at Lingza and for dam site at Ishana where suitable land is available. 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 3960Sq.m of permanent 

built up area and 3970 Sq.m of temporary builtup area would be required. Total plinth 

area for residential accommodation worked out to be 7930Sq.m, 

10.2.4 Accommodation For Non-Residential Purposes 

The office complexes are proposed at Lingza and Ishana. 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 7590 

Sq.m of which about 40% 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.

123 



Therefore, an internal telephone exchange would be provided at the project for 

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 constructio n of 

the project and it is presumed that till the 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 20Km may be required for arranging construction power.



CHAPTER – XI 

CONSRUCTION PLANNING & 

SCHEDULE


CHAPTER –XI 

CONSTRUCTION PLANNING & SCHEDULE 

123 



The Equipment Planning & Construction Methodology of Lingza H.E. Project (3x40 

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 6 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, Motor 

Grader, Air compressor, Road Roller etc. are proposed for deployment during 

infrastructure stage. 

11.2.2 Diversion of River 

The construction of 6.0 m finished diameter, Horse shoe shaped 400 m long diversion 

tunnel would be carried out by full face method. Excavation of Diversion Tunnel will be

124 



carried out with 2 Boom drill jumbo, Air Track/Wagon Drill, Jack hammer, 0.24 cum 

skid steer loader &10 T Tippers. However 1.0 cum hyd. excavator would also be required 

for portal excavation. Excavation & concreting of diversion tunnel (including portal) 

would be completed in 10 months. The concreting equipment proposed are 38 cum 

Concrete pump, Transit mixer, shotcrete machine, Grout pump, shutters etc. Concreting 

requirement would be catered by the same batching & mixing Pla nt and Aggregate 

processing Plant, being proposed for Dam . U/s & D/s Coffer dam would be constructed 

immediately after construction of diversion tunnel in 5 months to divert the river. 

However river bed excavation would be taken up after completion of Ist stage coffer dam 

in three months. 

11.2.3 Concrete Dam 

Dam abutment stripping is proposed to be carried out in 15 months. The excavation of 

river bed & foundation treatment would be carried out in 4 month. 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 18 months. Concreting would be 

done by deploying 2 nos. Tower crane (6.9 T at 60 m radius), 1 No. 120 cum/hr 

Batching& Mixing plant and 250TPH Aggregate Processing plant. 

11.2.4 Intake Structure, Desilting Chamber , Silt Flushing tunnel & HRT 

2 nos. Intake structure having gate size of 3 m x3m , 2 Nos. Dufour type Desilting 

chambers of size 95m X5mX7.5m each and HRT of 3.3 m dia. would be excavated in 20 

months . After excavation of intake structure, 2 nos. intake tunnels of 3m dia 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.

125 



The equipment to be deployed are Jack hammers, wagon drills, air compressors, skid 

steer loader, excavators, tippers, concrete pump, transit mixers etc. 

Excavation of 4.0 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 intermediate adits. The excavation of adits would be carried out in 5 months. 

Excavation would be carried out by deploying three set of equipment i.e 2 boom drill 

jumbo, 0.24 cum Skid Steer Loader 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. 

11.2.5 Surge Shaft : 

For Construction of 10 m diameter, 40 m high Surge Shaft, an adit to surge shaft bottom 

would be excavated in four months. After completion of construction adit, pilot shaft of 

3.0m dia.(approx.) would be excavated by deploying raise climber, jack hammers from 

bottom to top through bottom adit. Thereafter, Pilot hole would be further enlarged to 

excavated diameter & shaft will be lowered up to full length of surge shaft with the help 

of Wagon Drill, Jack Hammer, crawler dozer etc.. Mucking will be done through the 

bottom adit. Concreting would be completed employing 2 m shutter, concrete pump, 

Transit Mixer & batching &mixing plant (installed at dam site). Construction of surge 

shaft would be completed in 32 months. 

11.2.6 Pressure Shaft: 

Initially construction of approaches & adit would be done in 8 months. One no. 900 m 

long inclined pressure shaft, will be excavated in the same wa y as surge shaft by 

deploying Raise climber, Jack hammer etc. However intermediate adit can be used to 

handle the muck. Steel liner (2m dia) erection & concreting will be carried out by

126 



deploying 10/20 t winches, Slipform liner etc. Construction of Pressure shaft would take 

around 29 months. 

11.2.7 Power House 

4 X 30 MW (120 MW) underground power house (100 m X 17 m X 40 m size), 

Transformer Cavern & MIV would be excavated in 20 months. For excavation of Power 

House, a construction adit would be excava ted 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 4 

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, 

winches etc. Concreting of Powerhouse would be carried out in 24 months with the help 

of concrete pump, transit mixer etc. Concreting requirement would be catered by 

deploying 30 cum/hr batching & mixing plant and 50 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. 

11.2.8 Tail Race Tunnel 

1 Nos. 250m 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 2 boom Drill Jumbo, Wagon drill, 0.24 cum skid steer loader , 10 t tipper etc. 

The TRT will be excavated from 10 th 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 

127 



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.

INFRASTRUCTURE 

Acquisition of private & forest land Ha 8 

Construction of roads & buildings LS 12 

AWARD OF CONTRACTS 

Tendering, Award & Mobilization LS 5 

DIVERSION TUNNEL ( 

400 m long, 6 m dia horseshoe) 

Excavation m 3 50,000 6 

Erection of shutters & Conc. Lining m 3 9,500 4 

HM Works Job LS 4 

Plugging of tunnel Job LS 2 

COFFER DAMS (U/s & D/s) 

Const.of Coffer Dams & River Diversion m 3 CONCRETE DAM (60 

m High & 320 m Long at top) 

Filling-60,000 

Conc.-4,500 

Dam abutments stripping 

m 3 3,46,000 

Excavation and foundation treatment 4 

Mass Concreting m 3 5,30,500 16 

Hyromechanical Works Job LS 12 

Reservoir filling Job 2 

Head Race Tunnel of 3.3m dia 4 km long 

(including Intakes & Desilting chambers-2 nos. ) 

Excavation of adits Job LS 5 

Excavation m 3 1,36,500 20 

Concrete Lining m 3 38,200 18 

Grouting Job LS 10 

HM Works Job LS 15 

Cleanning, Adits plugging etc. Job LS 1 

Water conductor charging Job LS 1 

POWER HOUSE COMPLEX 

Name of Work Unit Quantity 

Const. of Adits Job LS 3 

Excavation of Power House m 3 1,60,000 20 

Concreting in sub & super structures m 3 67,000 24 

Erection of EOT crane Job LS 2 

SURGE SHAFT (10 m dia., 40m height) 

Const. of approches Job LS 4 


Concreting & HM Works m 3 4,200 12 

STEEL LINED PRESSURE SHAFT 

(2m dia, 900m long inclined ) & PENSTOCKS 

Const.of approaches & adit Job LS 8 


Erection of steel liners & Concreting m 3 11,000 15 

TAILRACE TUNNEL 

(3.3m dia, 250m long) 


Concreting & HM Works m 3 2,000 10 

POT HEAD YARD 

Civil & Elect. Works of Pot Head Yard Job Exc-1,04,000m 3 

ELECTRO-MECHANICAL WORKS 

Conc-3000m 3 

Erection, Testing & Commisioning of all four Units Job 28 

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. 

5 

15 

15 

CONSTRUCTION SCHEDULE 

Duration 

Schedule of Constructiom 

(months) Ist year IInd year IIIrd year IVth year 

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 

A M J J A S O N D J F M A M J J A S O N D J J F M A M J J A S O N D J F M A M J J A S O N D J F M 

129 

Annexure-11.2



CHAPTER – XII 

COST ESTIMATE

CHAPTER –XII 

COST ESTIMATES 

130 



12.1 PRELIMINARY COST ESTIMATES FOR CIVIL, HYDRO- 

MECHANICAL, ELECTRO-MECHANICAL AND TRANSMISSION 

WORKS 

The estimate has been prepared to arrive at the capital cost of Lingza 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: - 

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

131 



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

132 



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 

133 



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 have been considered. 

12.6 ELECTRICAL & TRANSMISSION 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 

134 



S.No Description Amount 

(Rs. in Crores) 

( June 2003 

P.L.) 

A CIVIL WORKS 

1. DIRECT CHARGES 

I - Works 

A - Preliminary 4.49 

B - Land 11.22 

C - Works 225.11 

J - Power Plant Civil Works 172.35 

K - Buildings 12.92 

O - Miscellaneous 10.01 

P - Maintenance 4.39 

Q-Special Tools & Plants 3.14 

R - Communication 28.25 

X - Environment & Ecology 9.65 

Y - Losses on Stock 1.10 

Total of I-Works 482.63 

II - Establishment @ 8% of cost of I-Works less B-Land 37.71 

III - Tools and Plants @ 1% of cost of I-Works 4.83 

IV - Suspense 0.00 

V - Receipt & Recoveries (-) -2.44 

Total Direct Charges 522.73 

2. INDIRECT CHARGES 

a) Capitalised Value of Abatement of Land Revenue 0.12 

b) Audit and Account Charges @1% of cost of I-Works 4.83 

Total Indirect Charges 4.95 

Total Of Direct & Indirect Charges 527.68 

ABSTRACT : 

A Civil Works 527.68 

B Electrical Works 97.36 

C Transmission Works 5.02 

TOTAL COST 630.05 

C IDC 69.75 

D Total Cost With IDC 699.80

Sl 

No. 

A-PRELIMINARY 

135 



Rs. In lakhs 

Description of Work Unit Qty Rate 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 locationof project componenets LS 20.00 

2.2 Aerial survey, contour survey for reservoir basin 

including establishment of permanent benchmarks. 

2.3 Geological and geophyical surveys and investigation 

LS 10.00 

I) 

Drifting m 400 0.10 40.00 

ii) 

Geophysical LS 20.00 

iii) 

Core drilling m 300 0.10 30.00 

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 8.00 

2.5 Investigations for foundation and rock testing LS 6.00 

2.6 Investigation for availability of construction materials. LS 3.50 

2.7 Construction of access roads to facilitate investigations LS 7.00 

2.8 Model experiment. LS 8.00 

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. 

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 6.00 

LS 15.00 

LS 4.00 

2.15 Ground water studies. LS 6.00 

2.16 Environment and ecological s tudies. LS 10.00 

2.17 Preparation and printing of DPR LS 10.00

3.0 Pre-Construction Stage Investigations 

136 



Total( I+II) 247.50 

3.1 Topographical Surveys LS 15.00 

3.2 Geological Investigation 

I) Diamond Core Drilling m 100 0.1 10.00 

ii) Exploratory Drift m 100.00 0.1 10.00 

iii) Excavation in trenches & pits LS 0.75 

iv) Testing of Samples LS 4.00 

3.3 Hydrological and Silt data collection - 2 sites for 4 

years 

8.00 2.00 16.00 

3.4 Meteorological Data Collection 2 sites for 4 years Year 8.00 0.40 3.20 

3.5 Construction material survey 

I) Topographical Survey LS 4.00 0.05 0.20 

ii) Collection and Transportation of samples LS 3.00 

iii) Laboratory Testing of Samples including charges for 

6.00 

all T&P and Machineries LS 

3.6 Model studies LS 10.00 

3.7 Seismological data collection for 4 years Year 4.00 1 4 

3.8 Survey for layout of colonies and roads 

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 

4.00 2 8.00 

4.0 Design & Consultancy 

4.1 Cost of Design Establishement including procurement 

of printing stationery and preparation of comp letion 

25.00 

report, History of Project etc. LS 

4.2 Cost of Special Studies and Designs LS 15.00 

4.3 Fees for Consultant and specialists LS 15.00 

4.4 Training of Engineers LS 5.00 

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 10.00 

Grand Total :( I+II+III) 449.40

Sl. 

No. 

1.0 Private land Requirement 

137 



B-LAND 

Description Qty. 

Rs. In lakhs 

Rate Unit Amount 

Permanent residential and non residential 

buildings 

6.00 5.50 Ha 33.00 

Diversion tunnel 3.00 5.50 Ha 16.50 

Submerged in the reservior area 12.00 5.50 Ha 66.00 

Construction of dam/ wier 4.00 5.50 Ha 22.00 

Construction material 2.00 5.50 Ha 11.00 

Constrution of approach Roads 54.00 5.50 Ha 297.00 

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 2.40 5.50 Ha 13.20 

Sub Total (1) 90.40 497.20 

2.0 Forest land 

River bed 10.00 0.00 Ha 0.00 

Underground 2.00 0.00 Ha 0.00 

Sub total (2) 12.00 0.00 

3 Other Compensation 

Cost of crops standing on cultivated land 

required @ 30% of cultivated land 

80 1.65 Ha 132.00 

Buildings with brick walls and GGI sheet 3.00 3.00 

9.00 

roofing 

Nos 

Compensation for trees LS 10.00 

4 Misc. Compensation 

Compensation for relocating electric and 

telephone poles 

2.00 

Crop Compensation for submergence LS 200.00 

Sub total (3+4) 353.00 

Total (1+2+3+4) 850.20 

5 Land on lease/ hire for 4 Years 

Dumping area 0.50 2.40 Ha 1.20

138 



Dumping area for batching and mixing plant 0.50 2.40 Ha 1.20 

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 

Electro - Mechanical Works 1.00 2.40 Ha 2.40 

Hydro -Mechanical Works 1.00 2.40 Ha 2.40 

Total (5) 24.00 

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 

29.83 

acquisition for two years 

Solatium charges for compulsary 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 acquision 

Establishment charges @6.25% of cost of 

total compensation 

149.16 

8.742 

4.972 

54.64 

Total 1121.54

ABSTRACT OF COST OF C - WORKS 

139 



S. N. Description Amount (Rs. In Lakhs) 

Civil HM Total 

1. River Diversion Works 865.98 117.60 983.58 

2. Coffer Dam 848.62 848.62 

3 Dam 14764.24 120.75 14884.99 

4 Spillway 4993.30 359.42 5352.72 

Total 21472.13 597.77 22069.90 

Add Work Tax @ 429.44 11.96 441.40 

Total 21901.58 609.72 22511.30

S. 

N. 

DIVERSION TUNNELS 

140 



Description Unit Quantity Rate Amount 

in Rs. Rs. in 

Lakhs 

1 Surface Excavation 

1.1 Common excavation Cum 25000 125 31.25 

1.2 Rock excavation Cum 5000 300 15.00 

2 Underground excavation Cum 20000 1000 200.00 

3 Rock Support System 

3.1 Rock bolts m 10000 400 40.00 

3.2 Steel Supports MT 50 42000 21.00 

3.3 Shotcreting Cum 1000 4000 40.00 

3.4 Concrete lagging Cum 150 7000 10.50 

4 Concrete 

4.1 Cement Concrete Lining M20 Cum 3900 4000 156.00 

4.2 M15 Cum 3500 2930 102.55 

4.3 M20 Cum 100 3390 3.39 

4.4 M25 Cum 2000 3610 72.20 

5.0 Reinforcing steel MT 200 27000 54.00 

Sub Total A 745.89 

6 Miscellaneous and ancillary works @ 7.5% of 

sub-total A 

7.5% 55.94 

Sub Total B 801.83 

7 Instrumentation @ 1% of sub-total B 1% 8.02 

8 Dewatering @ 2% of sub total B 2% 16.04 

9 Contingency @ 3% of sub-total B 3% 24.05 

10 Work Charged establishment @ 2% of 

Sub-total B 

2% 16.04 

Total Civil 

Cost 

865.98

S. 

N. 

COFFER DAMS 

141 




In Rs. Rs. in 

Lakhs 

1 Surface excavation 


2 Embankment Construction and 

Backfill 

2.1 Earth/Rock fill Cum 40000 518.00 207.20 

2.2 Impervious Core Cum 15000 354.00 53.10 

2.3 Filter Cum 5000 901.00 45.05 

3 Concrete including Formwork 

3.1 M10 Cum 2500 2560 64.00 

3.2 Concrete cut off wall Sqm 2000 20000 400.00 


4 Miscellaneous and ancillary works @ 

0.5% sub-total A 

0.5% 3.91 




7 Work Charged establishment @ 2% of Subtotal 

B 

2% 15.72 

Total Civil 

Cost 

848.62

DAM 

142 



S. 

N. Description Unit Quantity Rate Amount 

Rs. in 

in Rs. Lakhs 




2 Rock Stabilization and Supports 

2.1 Rock bolts M 1500 400 6.00 

2.2 Shotcrete Cum 500 4000 20.00 


3.1 M10 Cum 500 2560 12.80 

3.2 M15 Cum 400000 2930 11720.00 

3.3 M20 Cum 20000 3390 678.00 

3.4 M25 Cum 5000 3610 180.50 

4 Reinforcing Steel MT 500 27000 135.00 


5 

Miscellaneous and ancillary works 

@2-3% sub-total A 2.5% 330.37 

Sub Total (1-6) 13545.17 




9 

Work Charged establishment @ 2% of Subtotal 

B 2% 270.90 

Total Civil Cost 14764.24

S. 

N. 

SPILLWAY 

143 




In Rs. Rs. in 

Lakhs 





2.1 M15 Cum 65000 2930 1904.50 

2.2 M20 Cum 2000 3390 67.80 

2.3 M25 Cum 38000 3610 1371.80 


4 Structural Steel MT 150 42000 63.00 


5 Miscellaneous and ancillary works @1- 

2% sub-total A 

1.5% 68.33 





9 Work Charged establishment @ 2% of Sub-total 

B 

2% 92.47 


J-POWER PLANT APURTENANCE (CIVIL WORKS) 

144 



S. Description Amount (Rs. in Lakhs) 

NO. Civil HM Total 

1 Power Intake 784.94 347.13 1132.07 

2 Desilting Basins 793.25 151.83 945.08 

3 Adits 1275.24 21.42 1296.66 

4 Head Race Tunnel & Tail Race Tunnel 3054.82 14.28 3069.10 

5 Surge Shaft 474.54 18.48 493.02 

6 Pressure Shaft 684.70 1367.10 2051.80 

7 Power House Co mplex 7505.75 7505.75 

8 Civil Works of Switchyard 403.43 403.43 

Total 14976.68 1920.24 16896.92 

Add Work Tax @ 6.8% 299.53 38.40 337.94 

Total 15276.21 1958.64 17234.86

S. 

N. 

INTAKE STRUCTURE 

145 




In Rs. Rs. in 

Lakhs 





3 Supports System 

3.1 Rock bolts M 1500 400 6.00 

3.2 Steel Rib Supports MT 15 42000 6.30 

3.3 Shotcreting Cum 100 4000 4.00 


4 Concrete 

4.1 M15 Cum 500 2930 14.65 

4.2 M25 Cum 8000 3610 288.80 

5 Reinforcement Steel MT 1200 27000 324.00 


6 Miscellaneous and ancillary works @ 2- 

3% of sub-total A 

1.5% 10.84 





10 Work Charged establishment @ 2% of Sub-total 

B 

2% 14.67 


S. 

N. 

DESILTING CHAMBER (INCLUDING SFT) 

146 




In Rs. Rs. in Lakhs 





3 Rock Supports System 

3.1 Rock bolts M 14000 400 56.00 

3.2 Structural steel Rib MT 50 42000 21.00 

3.3 Shotcrete Cum 1000 4000 40.00 

3.4 Concre Lagging Cum 200 7000 14.00 

4 Concrete 

4.1 M15 Cum 2500 2930 73.25 

4.2 M20 Cum 500 3390 16.95 

4.3 M25 Cum 2000 3610 72.20 



6 Miscellaneous and ancillary works 

@3.5% sub-total 

3.5% 24.84 


7 Instrumentation @ 1% of sub-total 

B 

1% 7.34 



10 Work Charged establishment @ 2% of 

Sub-total B 

2% 14.69 


S. 

N. 

ADITS 

147 




In Rs. Rs. in 

Lakhs 






3.1 Rockbolts M 25000 400 100.00 

3.2 Steel Ribs Support MT 200 42000 84.00 

3.3 Shotcrete Cum 2500 4000 100.00 


4 Concrete 


4.2 M15 Cum 5000 2930 146.50 

4.3 M20 Cum 1000 3390 33.90 

4.4 M25 Cum 2000 3610 72.20 

5 Reinforcment steel MT 200 27000 54.00 



@ 3-4% of sub-total A 

3.5% 39.93 





10 Work Charged establishment @ 2% 

of Sub-total B 

2% 23.62 


S. 

N. 

HEAD RACE AND TAIL RACE TUNNEL 

148 




In Rs. Rs. in 

Lakhs 






3.1 Rockbolts M 45000 400 180.00 


3.3 Shotcrete Cum 4600 4000 184.00 


4 Concrete 


4.2 M15 Cum 12000 2930 351.60 

4.3 M25 Cum 1000 3610 36.10 

5 Reinforcement steel MT 250 27000 67.50 


6 Miscellaneous and ancillary works @ 7- 

8% of sub-total A 

7.5% 197.34 





10 Work Charged establishme nt @ 2% of 

Sub-total B 

2% 56.57 


S. 

N. 

SURGE SHAFT 

149 




In Rs. Rs. in 

Lakhs 




2 Underground excavation 

2.1 Surge shaft Cum 5500 1200 66.00 

2.2 Surge shaft With Raise Borer Cum 125 1500 1.88 



3.1 Rockbolts m 12000 400 48.00 


3.3 Shotcrete Cum 450 4000 18.00 

4 Concrete 

4.1 M20 Cum 3000 3390 101.70 

4.2 M25 Cum 1200 3610 43.32 

5 Reinforcement steel MT 150 27000 40.50 




1.5% 6.49 

Sub Total (1- 

7) 

439.39 


B 

1% 4.39 



10 Work Charged establishment @ 

2% of Sub-total B 

2% 8.79 


S. 

N. 

PRESSURE SHAFTS AND PENSTOCKS 

150 




In Rs. Rs. in 

Lakhs 



2.1 Rockbolts M 11000 400 44.00 


2.3 Shotcrete Cum 1200 4000 48.00 

3 Concrete 

3.1 M15 Backfill concrete Cum 11000 2930 322.30 




2.5% 15.61 



B 

1% 6.40 





2% 12.80 


S. 

N. 

POWER HOUSE COMPLEX 

151 




Rs. in 

Lakhs 

1 Under Ground Excavation Cum 160000 1000 1600.00 

2 Rock Stabilization and Supports 

2.1 Rock bolts M 70000 400 280.00 

2.2 Structural steel Rib MT 100 42000 42.00 

2.3 Shotcrete Cum 7000 4000 280.00 


3.1 M15 backfill concrete Cum 5000 2930 146.50 

3.2 Concrete linning M20 Cum 2000 4000 80.00 

3.3 M25 Cum 60000 3610 2166.00 


5 Structural steel for roof trusses MT 300 42000 126.00 

6 Masonary 

6.1 Stone Cum 500 2000 10.00 

6.2 Brick Cum 1500 2000 30.00 




4.5% 299.27 

Sub Total (1- 

7) 

6949.77 


B 

1% 69.50 



11 Work Charged establishme nt @ 2% 

of Sub-total B 

2% 139.00 


S. 

N. 

SWITCH YARD 

152 




Rs. in 

Lakhs 


1.1 Common Excavation Cum 100000 125 125.00 



2.1 Rock bolts M 1000 400 4.00 

2.2 Shotcrete Cum 50 4000 2.00 

3 Earthwork in filling Cum 25000 342 85.50 

4 Concrete 

4.1 M15 Cum 1000 2930 29.30 

4.2 M20 Cum 1000 3390 33.90 

4.3 M25 Cum 1000 3610 36.10 


6 Stone/ Brick Masonary Cum 300 2000 6.00 




4.5% 16.24 






2% 7.54 


S. 

N. 

HYDRO MECHANICAL EQUIPMENT 

Detail of Items Nos. Wt./Set Total 

(MT) Wt. 

/ set 

(MT) 

1 Diversion tunnel gate & hoist 

Gate(Fixed wheel type)including 

ballast 

153 



Rate in 

Rs. 

Amount 

in Lakh 

2 30 60 60000 36.00 

Embedded Parts 2 10 20 50000 10.00 

Ropedrum hoist 80 T Capacity 2 25 50 100000 50.00 

Hoist platform and trestle 2 16 32 50000 16.00 

2 Spillway structure 

a) Radial Gates 3 40 120 100000 120.00 

Embedded Parts (including 

anchorages, hoist structure) 

including breast wall liners 

3 25 75 50000 37.50 

Hydraulic Cylinders 40T capacity 

(with provision of 25% pushing 

force) 

6 LS 1200000 72.00 

Power packs 3 LS 500000 15.00 

b) Bulkhead Gate( Slide type) 1 28 28 60000 16.80 


Lifting Beam 1 5 5 50000 2.50 

Gantry crane 55 T capacity 1 LS 5500000 55.00 

Portable oil filter unit along with 

Contamination checking kit & Low 

vacuum dehydration and 

degassification unit 

Portable trolley mounted gasoline 

engine operated power pack 

1 LS 500000 5.00 

1 LS 500000 5.00 

3 Intake structure 

a) TrashRacks (including racking 

guides) 

1 200 200 50000 100.00 

Embedded Parts 1 60 60 50000 30.00

154 



Trash rack cleaning machine 1 LS 10000000 100.00 

b) Intake gate(fixed wheel type) 

including ballast 

2 25 50 60000 30.00 


Rope drum hoist 45T Cap. 2 14 28 100000 28.00 


C) Bulkhead Gate (Slide Type) 2 8 16 60000 9.60 




4 Desilting Chamber Gates 

Desilting Chamber Gate (Slide 

Type) 

1 11 11 60000 6.60 

Embedded parts 2 4 8 50000 4.00 

EOT Crane 20T Cap. 1 LS 1800000 18.00 

5 Silt Flushing Gates (Slide Type) 

Gates (Service & Emergency) 4 1.5 6 100000 6.00 

Embedded parts (including bonnet, 

bonnet cover, gate body liner etc.) 

4 30 120 50000 60.00 

Hydraulic Cylinders 105T Cap. (Double acting) 4 

Power Pack 2 LS 1000000 20.00 

6 Surge shaft gate & hoist 

Gate(Slide Type) 1 11 11 60000 6.60 

Embedded parts 1 6 6 50000 3.00 



7 Tailrace channel gate & hoist 

Gate (Slide type) 1 6 6 60000 3.60 


Monorail Hoist 10 T capacity 1 - LS 750000 7.50

8 Pressure shaft steel Liner (ASTM 

A 537 Class I ) 

155 



Steel Liner 1 1750 1750 70000 1225.00 

Bifurcation (ASTM A 517 Gr.F ) 2 50 100 77000 77.00 

9 Adit Gates 

Adit gates 3 8 24 60000 14.40 


10 Instruments and Remote Control 1 LS 10000000 100.00 

11 D G Set 250 KVA 1 LS 1500000 15.00 

Sub Total 2398.10 

12 Spare parts & contingency @ 5% 

for Spares Airvents, By Pass 

Arrangements etc. 

5% 119.91 

Total 2518.01

Sl 

No 

K-BUILDINGS 

Description Plinth 

Area(Sqm). 

156 

Rate 

(Rs) 



Rs. In lakhs 

Unit Amount 

(Rs) 

1.0 Residential Buildings 

1.1 Residential permanent 

buildings 

3960 0.075 Sqm 297.00 

Service Charges @ 31% 92.07 

1.2 Residential temporary 

buildings 

3970 0.065 258.05 

Service Charges @ 27% 69.67 

Total (Residential) 7930 716.79 

2.0 Non-Residential Buildings 

2.1 Non residential permanent 

buildings 

3485 0.065 Sqm 226.53 

Service Charges @ 22.5% 50.97 

2.2 Non residential and other 

purposes temporary 

buildings 

4105 0.055 Sqm 225.78 

Service Charges @ 20.5% 46.28 

Total( Non-Residential) 7590 549.55 

Total(1+2) 23450 1266.35 

Add for Works Tax @ 2% 25.33 

Grand Total 1291.67

O-MISCELLANEOUS 

157 



Rs. In lakhs 

Sl 

No 

Description Quant. Rate Unit Amount 

1 CAPITAL COST 

1.1 Purchase of Diesel Generator Sets (25 KVA) 

including anciliary equipments etc. 

3.00 2.50 Nos 7.50 

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 complexes. 

20.00 10.00 km 200.00 

LS 30.00 

LS 25.00 

1.5 Providing & fixing of fire fighting equipments. LS 20.00 

1.6 Providing telephone, Telegraph office, Post 

office and Wireless equipments. 

LS 20.00 

1.7 Providing hospital equipments. LS 15.00 

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. 

1.10 Purchase of furniture and other articles for 

labour welfare centres and clubs and schools. 

1.11 Purchase of equipment for quality control/field 

Laboratories 

LS 8.00 

LS 5.00 

LS 5.00 

LS 15.00 

Sub Total Item 1 350.50 

2.0 MAINTENANCE & SERVICE CHARGES 

OF 

2.1 R&M of Diesel Generator sets 3 Nos. for four 

years. 

12.00 4.00 Nos 48.00 

R&M of Transmission line for four years. 15.00 4.00 km 60.00 

2.2 R&M of water supply facilities to the staff and 

labour colonies for four years 

LS 10.00 

2.3 R&M of sanitation and drainage facilities for 

office and residential compllex and labour 

colonies. 

LS 8.00 

2.4 R&M of fire fighting equipments. LS 4.00 

2.5 Maint. Of telecommunication system and post 

offices. 

LS 20.00

158 



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. LS 8.00 

2.9 R&M of research & quality control laboratories LS 8.00 

2.10 Labour welfare compensation and retrenchment 

benefits. 

LS 40.00 

2.11 Providing Security & Policing LS 8.00 

2.12 R&M of Inspection vehicles and staff cars (25 

nos) for four year 

2.13 R&M of school buses, Ambulance Car etc. (4 

nos) for for four year 

25*4 2.50 year 250.00 

4*4 1.80 year 28.80 

Sub Total Item 2 518.80 

3 MISCELLANEOUS 

3.1 Foundation stone laying ceremony, inaguration 

and visit of Dignitaries. 

LS 20.00 

3.2 Railway siding LS 20.00 

3.3 Installation and maintenance of Petrol/Diesel 

Pumps 

LS 16.00 

3.4 Providing anti malarial measures LS 2.00 

3.5 Procurement of technical leterature. LS 2.00 

3.6 Model Exhibits LS 4.00 

3.7 Canteen facilities and co-operative stores. LS 16.00 

3.8 Photographic and Cinemagraphic equipment 

and their maintenance 

LS 8.00 

3.9 Group insurance LS 15.00 

3.10 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 

Sub Total Item 3 

131.50 

Grand Total Item (1+2+3) 1000.80

Q-Spl T&P for Infrastructure Development 

Sl.No. Description of equipment Quantity 

(Nos.) 

159 

Rate 

(Rs in 

Lacs) 



Amount 

(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 Crawler Dozer, 100 FHP 1 50.00 50.00 

4 Wheel dozer 130 FHP 1 95.00 95.00 

5 Motor Grader, 145 FHP 1 60.00 60.00 

6 Diamond Core Drill (Mechanical) 1 15.00 15.00 

7 Diamond Core Drill (Hyd) 1 60.00 60.00 

8 Air Track/Wagon Drill 2 15.00 30.00 

9 Jack Hammer/Pavement Breaker 5 0.35 1.75 

10 Compressed Air (cfm) 2000 0.0125 25.00 

11 Mobile Crane, 10 t Pick & Carry 1 10.00 10.00 

12 Mobile Crane, 20 t (Rough terrain) 1 70.00 70.00 

13 Road Roller, 8/10 t 1 10.00 10.00 

14 Dewatering Pump L.S 10.00 10.00 

15 Tipper 4.5/6.0 cum. 2 9.50 19.00 

16 Truck, 10 t 2 7.50 15.00 

17 Low Bed Tractor Trailor, 30 t 1 40.00 40.00 

18 Concrete Mixer, 14/10 cft 2 1.50 3.00 

19 Explosive Van, 10 t 1 12.00 12.00 

20 Water Tanker/Sprinkler, 10 KL 1 12.00 12.00 

21 Petrol/Diesel Tanker, 10 KL 1 12.00 12.00 

22 Bus/Mini Bus 4 8.00 32.00 

23 Car/MUV 2 4.00 8.00 

24 Jeep (Petrol/Diesel) 20 4.00 80.00 

25 Ambulance 2 8.00 16.00 

26 Workshop Equipment L.S 20.00 20.00 

27 Fire Tender 1 15.00 15.00 

28 Recovery Van 1 5.00 5.00 

29 Pick up Van/L.C.V 2 5.00 10.00 

803.75

DISTRIBUTION OF COST UNDER HEAD Q - SPECIAL T & P AND V - 

RECEIPT & RECOVERIES 

160 

(Rs. In lakhs 

Cost Q R&R 



Cost of equipments excluding inspection vehicles 652.75 163.19 122.39 

Cost of inspection vehicles 151.00 151.00 30.20 

Provision under head Q - Spl. T&P 803.75 314.19 

Recoveries to be shown under V- Receipt and 

Recoveries 

152.59

SI 

NO. 

R - COMMUNUCATION 

Description Quantity Rate 

(Rs.) 

1 Proposed new roads 

3 

Approach road to dam site.,DT, 

Top of Dam 

161 



Rs. In lakhs 

Unit Amount(Rs.) 

18.0 80.00 Km 1440.00 

Approach road to power house site 3.0 80.00 Km 240.00 

Switch yard 1.0 80.00 Km 75.00 

Surgeshaft 8.0 80.00 Km 640.00 

Colony Roads 2.0 75.00 Km 150.00 

Proposed new bailey bridges Cl 

30 

At Dam site 50.0 2.25 M 112.50 

At Vawl across the river 50.0 2.25 M 112.50 

Total 2770.00 

Add for Works Tax @ 2% 55.4 

Grand Total 2825.40

S. 

No. 

V - RECEIPT & RECOVERIES 

Item Amount 

162 

(Rs. In Lakhs) 

1. Recovery from the Sale of Equipments 152.59 

2. Recovery from the sale of DG Sets and 

Transformers used for generating Construction 




1.50 

3. Recovery towards Temporary Buildings 

(@ 15% of Amount for Temporary Buildings) 89.97 

Total 244.06

ELECTRO MECHANICAL WORKS 

Generator, Turbine and Accessories 

163 



Annex-I Page 1 of 2 

S.No. Item Particulars Qty Unit Rate 

DEC 2003 PRICE LEVEL 

Excise Duty* 

Amount 

(Rs 

Lakh) % Amount 

Total 

(Rs 

Lakh) 

1 2 3 3(a) 4 5 6 7 5+7 

1 

(a) Generating units and Bus 

Ducts 3X40 MW, 3 no. 3700.00 4440.00 16 710.40 

5150.40 

2 

3 

4 

600 rpm, Head 736 meters 

Step up transformer,3 phase 

Rs/KW 

11/220 KV, 49 MVA, 3 no. 220.00 323.40 16 51.74 

Rs/KVA 

Auxiliary Electrical Equipment 

for Power Stations 

(Except Transformer) (5% of 

item 1) 

Auxiliary Equipment & Services 

222 16 35.52 

for Power stations 222 16 35.52 

(5% of Item 1) 

375.14 

257.52 

257.52 

5 Switch yard(220 Kv) 

Bays 120.00 720 16 115.200 835.20 

6 Lacs/Bay 

6 

Spares (5% of 1 and 3% of 2 to 

6) ) 222 26.62 248.62 16 39.78 

288.40 

7 SUB TOTAL(1-6) 

8 

Central Sales tax **4% of item 7 

Transportation & Insurance 6% 

9 

of item 7 

Erection & commissioning 8% 

10 

of item 7 Excluding 

spares 

7164.19 

286.57 

429.85 

550.06 

11 Sub total item 7,8,9,10 8430.67 

12 

Total of FC(XLPE Cable and 

Termination kit) in INR(As per 

Annexure-I) 

13 Custom Duty @22% of item 12 

included 

in above 

item 12 

484.84

14 

15 

S.No. 

Marine frieght and insurance 

@6% Approx of 12 

Inland Frieght and insurance 6% 


16 Erection & commissioning 8% 

of item 12 Excluding spares 

17 

SUB TOTAL of FC ( item 

12,13,14,15,16 in INR) 

164 



29.09 

29.09 

38.78 

581.80 

18 

Subtotal of item no 

17+12(Foreign plus indian 

component) 

9012.47 

19 Establishment,Contingency,other 

charges 

11% of Item18 excluding duties 

723.08 

GRAND TOTAL (In Lacs) 9735.54 

Annex-I Page 2 of 2 

DEC 2003 price level 

Item Particulars Qty Rate Amount 

Custom 

Duty* Total 

( Lcs 

Amount'( (Lcs 

( USD) USD) Rate% Lcs USD) USD) 

1 2 3 4 5 6 7 5+7 

2 XLPE Cable (220 kV) 600 m 280.00 1.68 22 0.37 2.05 

USD/m 

3 XLPE Cable termination Kit 20 no. 35000.00 7.00 22 1.54 8.54 

4 Spares for above @ 3% of 2 0.05 22 0.01 0.06 

Total 8.73 10.65 

*Custom duty in case of imported Items 

**Not applicable for Imported Items 

1 USD conversion rate as on 

22/12/03= 

45.52 

each

POWER EVACUATION SYSTEM 

S.No. Item Particulars Qty Rate Amount 

165 

(Rs Lcs) 



Annex-II (page 1 of 1) 

Dec 2003 Price level 

Excise 

Duty* Total 

(Rs 

Lcs) Rate Amount 

1 2 3 4 5 6 7 5+7 

1 220kV Double Circuit line 15 km 22.00 330.00 16 52.80 382.80 

per km 

3 Spares ( 3% of 1 ) 9.9 16 1.584 11.48 

4 Subtotal(1) 394.28 

5 Central Sales tax **4% of item 4 

15.77 

6 

Transportation & Insurance 6% 


Erection & commissioning 8% 

23.66 

7 of item 4 except spares 30.62 

8 Subtotal(2) 

Establishment,Contingency,other 

464.34 

9 charges 37.39 

11% of Item 8 

(Rs 

Lcs) 

GRAND TOTAL (In Lacs) 501.73 

*Custom duty in case of imported Items 

**Not applicable for Imported Items



CHAPTER – XIII 

ECONOMIC EVALUATION

13.1 GENERAL 

CHAPTER – XIII 

ECONOMIC EVALUATION 

166 



The Project has been contemplated as a run-off the river scheme on river Ringpi. The 

project is estimated to cost Rs. 630.05 crores excluding IDC at June 2003 Price Level. 

Sale price of energy generated at power house bus bars has been worked out as 3.24 Rs. 

per unit with free power to home state (Table 13.2) & Rs. 2.85 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 3X40 MW has been 

estimated at 477.51 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 includ ing 1.5 years for Infrastructure works. 

The estimated Present Day Cost of the project is Rs. 630.05 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.

167 



The phasing of expenditure without IDC for present day cost is shown as below: 

Year Estimated Cost at June 2003 P.L. 


1 st 63.00 

2 nd 88.21 

3 rd 

126.01 

4 th 176.41 

5 th 94.51 

5.5 th 81.91 

Net Cost 630.05 

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. 69.75Crores 

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

168 



available after losses 

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. 2.62 Per Unit 

with free power to home state (Table 13.3) & Rs 2.31 per unit without free power to 

home state. (Table 13.3-A).

169 


Lingza HE Project (3 x 40MW) 

Table-13.1 

STATEMENT SHOWING IDC CALCULATION AT PRESENT DAY COST (JUNE 2003 LEVEL) 

PRESENT DAY COST 630.05 Crores 

Civil Works 527.68 Crores 

Electrical Works 97.36 Crores 

INTEREST RATE PER ANNUM 10% 

EQUITY 30% 

LOAN 70% 

Present Day Amount Receivable I.D.C Loan Outstanding Amount 


Receivable 

Year Cost Equity Loan at the end of Equity Loan 

half year (for the half year) 

1 2 3 4 5 6 7 8 

1 63.00 63.00 63.00 

2 88.21 88.21 88.21 

3 126.01 58.73 67.28 1.80 69.08 58.73 69.08 

4 176.41 176.41 15.73 261.22 192.14 

5 94.51 94.51 30.85 386.58 125.35 

5.5 81.91 81.91 21.38 489.86 103.28 

Total 630.05 209.94 420.11 69.75 209.94 489.86 

IDC 69.75 Crores Equity 209.94 Crores 

Net cost of the project 699.80 Crores Loan 489.86 Crores

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) 

170 



Table 13.2 

1 Installed capacity 120 MW 

2 Cost of the Project (Net) Rs. 630.05 Crore 

3 Interest During Construction Rs. 69.75 Crore 

4 Total Cost of Project (Including IDC) Rs. 699.80 Crore 

a) Equity 30% Rs. 209.94 Crore 

b) Loan 70% Rs. 489.86 Crore 

5 Annual Energy Generation 477.00 MU 

6 0.5% As Auxiliary Consumption of No. 5 0.70% 3.34 MU 

7 Energy Available After Auxiliary Consumption 473.66 MU 

8 0.5% As Transformer Loss of No. 7 0.50% 2.37 MU 

9 Energy Available After Transformer Loss 471.29 MU 

10 Free Power to Home State 12% 56.56 MU 

11 

Energy Available After Allowing Free 

Power 414.74 MU 

12 Fixed and Running Charges 

A) Capacity Charges 

a) Interest on Loan 10.00% 46.94 Crore 

b) Depreciation Charges 

(Limited to 1/12 th of Loan Amount) 

40.82 Crore 

SUB-TOTAL 

B) Energy Charges 

87.76 Crore 

a) O&M Charges 1.50% 10.50 Crore 

b) Return on Equity 16.00% 33.59 Crore 

SUB-TOTAL 44.09 Crore 

c) Interest on Working Capital 10.00% 2.32 Crore 

I) O&M Charges for 1 month 0.87 

II) 2 Months Average Billing 22.36 Crore 

TOTAL Rs. 134.18 Crore 

13 Sale Price at Bus Bar/Unit 3.24 Rs. 

14 Cost of Generation at Bus Bar/Unit 2.13 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.

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) 

171 



1 Installed capacity 120 MW 

2 Cost of the Project (Net) Rs. 630.05 Crore 

3 Interest During Construction Rs. 69.75 Crore 

4 Total Cost of Project (Including IDC) Rs. 699.80 Crore 

a) Equity 30% Rs. 209.94 Crore 

b) Loan 70% Rs. 489.86 Crore 

5 Annual Energy Generation 477.00 MU 

6 0.5% As Auxiliary Consumption of No. 5 0.70% 3.34 MU 

7 Energy Available After Auxiliary Consumption 473.66 MU 

8 0.5% As Transformer Loss of No. 7 0.50% 2.37 MU 

9 Energy Available After Transformer Loss 471.29 MU 

10 Free Power to Home State 0% 0.00 MU 

11 Energy Available After Allowing Free Power 471.29 MU 

12 Fixed and Running Charges 

A) Capacity Charges 

a) Interest on Loan 10.00% 46.94 Crore 

b) Depreciation Charges 40.82 Crore 

(Limited to 1/12 th of Loan Amount) 


B) Energy Charges 

a) O&M Charges 1.50% 10.50 Crore 

b) Return on Equity 16.00% 33.59 Crore 


c) Interest on Working Capital 10.00% 2.32 Crore 

I) O&M Charges for 1 month 0.87 Crore 

II) 2 Months Average Billing 22.36 Crore 

TOTAL Rs. 134.18 Crore 

13 Sale Price at Bus Bar/Unit 2.85 Rs. 

14 Cost of Generation at Bus Bar/Unit 2.13 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. 

Table-13.2 a

172 



Table 13.3 

CALCULATION OF ENERGY RATE WITH PRESENT DAY COST AS PER TARIFF NOTIFICATION 

Annual Generation in a 90% dependable year 477 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 414.74 MU Interest rate on Loan 10.0% 

Total cost including IDC Rs. 699.80 Crores Interest rate on Working Capital 10.00% 

Equity 

Loan 

30% 

70% 

Rs. 

Rs. 

209.94 

489.86 

Crores 

Crores 

Return on Equity 

Discounting rate 

16% 

12% 

YEAR Out- CAPACITY CHARGES 

CHARGES Discounting Discounted 

standing (Rs.in Cr.) (Rs.in Cr.) (Rs. per Factor Tariff 

Loan Interest Depre - Total Return O&M O&M Interest on Working Total Capacity Energy Total (Paisa per 

(Rs.in on loan ciation on Charges for 1 2 months Capital Interest charges charges Unit) 

Cr.) 

equity 

month 

Average Billing 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 

1 489.86 46.94 40.82 87.77 33.59 10.50 0.87 22.36 2.32 46.41 2.12 1.12 3.24 1.0000 3.24 

2 449.04 42.86 40.82 83.68 33.59 11.13 0.93 21.78 2.27 46.99 2.02 1.13 3.15 0.8929 2.81 

3 408.22 38.78 40.82 79.60 33.59 11.79 0.98 21.20 2.22 47.60 1.92 1.15 3.07 0.7972 2.45 

4 367.39 34.70 40.82 75.52 33.59 12.50 1.04 20.63 2.17 48.26 1.82 1.16 2.98 0.7118 2.12 

5 326.57 30.62 40.82 71.44 33.59 13.25 1.10 20.07 2.12 48.96 1.72 1.18 2.90 0.6355 1.84 

6 285.75 26.53 40.82 67.36 33.59 14.05 1.17 19.51 2.07 49.71 1.62 1.20 2.82 0.5674 1.60 

7 244.93 22.45 40.82 63.27 33.59 14.89 1.24 18.96 2.02 50.50 1.53 1.22 2.74 0.5066 1.39 

8 204.11 18.37 40.82 59.19 33.59 15.78 1.32 18.42 1.97 51.35 1.43 1.24 2.67 0.4523 1.21 

9 163.29 14.29 40.82 55.11 33.59 16.73 1.39 17.89 1.93 52.25 1.33 1.26 2.59 0.4039 1.05 

10 122.46 10.21 40.82 51.03 33.59 17.73 1.48 17.37 1.89 53.21 1.23 1.28 2.51 0.3606 0.91 

11 81.64 6.12 40.82 46.94 33.59 18.80 1.57 16.86 1.84 54.23 1.13 1.31 2.44 0.3220 0.79 

12 40.82 2.04 40.82 42.86 33.59 19.93 1.66 16.36 1.80 55.32 1.03 1.33 2.37 0.2875 0.68 

13 0.00 0.00 6.09 6.09 33.59 21.12 1.76 10.33 1.21 55.92 0.15 1.35 1.50 0.2567 0.38 

14 0.00 0.00 6.09 6.09 33.59 22.39 1.87 10.55 1.24 57.22 0.15 1.38 1.53 0.2292 0.35 

15 0.00 0.00 6.09 6.09 33.59 23.73 1.98 10.78 1.28 58.60 0.15 1.41 1.56 0.2046 0.32 

16 0.00 0.00 6.09 6.09 33.59 25.16 2.10 11.02 1.31 60.06 0.15 1.45 1.59 0.1827 0.29 

17 0.00 0.00 6.09 6.09 33.59 26.67 2.22 11.28 1.35 61.61 0.15 1.49 1.63 0.1631 0.27 

18 0.00 0.00 6.09 6.09 33.59 28.27 2.36 11.56 1.39 63.25 0.15 1.52 1.67 0.1456 0.24 

19 0.00 0.00 6.09 6.09 33.59 29.96 2.50 11.85 1.43 64.99 0.15 1.57 1.71 0.1300 0.22 

20 0.00 0.00 6.09 6.09 33.59 31.76 2.65 12.15 1.48 66.83 0.15 1.61 1.76 0.1161 0.20 

21 0.00 0.00 6.09 6.09 33.59 33.67 2.81 12.48 1.53 68.78 0.15 1.66 1.81 0.1037 0.19 

22 0.00 0.00 6.09 6.09 33.59 35.69 2.97 12.82 1.58 70.86 0.15 1.71 1.86 0.0926 0.17 

23 0.00 0.00 6.09 6.09 33.59 37.83 3.15 13.19 1.63 73.05 0.15 1.76 1.91 0.0826 0.16 

24 0.00 0.00 6.09 6.09 33.59 40.10 3.34 13.58 1.69 75.38 0.15 1.82 1.96 0.0738 0.14 

25 0.00 0.00 6.09 6.09 33.59 42.50 3.54 13.99 1.75 77.84 0.15 1.88 2.02 0.0659 0.13 

26 0.00 0.00 6.09 6.09 33.59 45.05 3.75 14.42 1.82 80.46 0.15 1.94 2.09 0.0588 0.12 

27 0.00 0.00 6.09 6.09 33.59 47.75 3.98 14.89 1.89 83.23 0.15 2.01 2.15 0.0525 0.11 

28 0.00 0.00 6.09 6.09 33.59 50.62 4.22 15.38 1.96 86.17 0.15 2.08 2.22 0.0469 0.10 

29 0.00 0.00 6.09 6.09 33.59 53.66 4.47 15.89 2.04 89.28 0.15 2.15 2.30 0.0419 0.10 

30 0.00 0.00 6.09 6.09 33.59 56.88 4.74 16.45 2.12 92.59 0.15 2.23 2.38 0.0374 0.09 

31 0.00 0.00 6.09 6.09 33.59 60.29 5.02 17.03 2.21 96.08 0.15 2.32 2.46 0.0334 0.08 

32 0.00 0.00 6.09 6.09 33.59 63.91 5.33 17.65 2.30 99.79 0.15 2.41 2.55 0.0298 0.08 

33 0.00 0.00 6.09 6.09 33.59 67.74 5.65 18.30 2.39 103.73 0.15 2.50 2.65 0.0266 0.07 

34 0.00 0.00 6.09 6.09 33.59 71.81 5.98 19.00 2.50 107.89 0.15 2.60 2.75 0.0238 0.07 

35 0.00 0.00 6.09 6.09 33.59 76.11 6.34 19.73 2.61 112.31 0.15 2.71 2.85 0.0212 0.06 

TOTAL 9.1566 24.03 

(A) (B) 

Note: The charges per unit is exclusive of water cess, spares, incentive & Income Tax etc. Levellised Tariff =(B)/(A) 2.62

173 



Table 13.3 a 

CALCULATION OF ENERGY RATE WITH PRESENT DAY COST AS PER TARIFF NOTIFICATION 

WITHOUT FREE POWER TO HOME STATE 

Annual Generation in a 90% dependable year 477 MU O&M Charges 1.50% 

Annual Generation after allowing losses & free Rate of increase of O&M Charges after 1st Year (simple) 6% 

power to home state in a 90% dependable year 471.29 MU Interest rate on Loan 10.0% 

Total cost including IDC Rs. 699.80 Crores Interest rate on Working Capital 10.00% 

Equity 30% Rs. 209.94 Crores Return on 16% 

Loan 70% Rs. 489.86 Crores Discounting rate 12% 

YEAR CAPACITY CHARGES Discounting Discounted 

Out- (Rs.in Cr.) (Rs.in Cr.) (Rs. per Factor Tariff 

standing Interest Depre- Total Return O&M Interest on Total Capacity Energy Total (Paisa per 

Loan on loan ciation on Charges O&M 2 months Interest charges charges Unit) 

(Rs.in equity 1 month Average 

Billing 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 

1 489.86 46.94 40.82 87.77 33.59 10.50 0.87 22.36 2.32 46.41 1.86 0.98 2.85 1.0000 2.85 

2 449.04 42.86 40.82 83.68 33.59 11.13 0.93 21.78 2.27 46.99 1.78 1.00 2.77 0.8929 2.48 

3 408.22 38.78 40.82 79.60 33.59 11.79 0.98 21.20 2.22 47.60 1.69 1.01 2.70 0.7972 2.15 

4 367.39 34.70 40.82 75.52 33.59 12.50 1.04 20.63 2.17 48.26 1.60 1.02 2.63 0.7118 1.87 

5 326.57 30.62 40.82 71.44 33.59 13.25 1.10 20.07 2.12 48.96 1.52 1.04 2.55 0.6355 1.62 

6 285.75 26.53 40.82 67.36 33.59 14.05 1.17 19.51 2.07 49.71 1.43 1.05 2.48 0.5674 1.41 

7 244.93 22.45 40.82 63.27 33.59 14.89 1.24 18.96 2.02 50.50 1.34 1.07 2.41 0.5066 1.22 

8 204.11 18.37 40.82 59.19 33.59 15.78 1.32 18.42 1.97 51.35 1.26 1.09 2.35 0.4523 1.06 

9 163.29 14.29 40.82 55.11 33.59 16.73 1.39 17.89 1.93 52.25 1.17 1.11 2.28 0.4039 0.92 

10 122.46 10.21 40.82 51.03 33.59 17.73 1.48 17.37 1.89 53.21 1.08 1.13 2.21 0.3606 0.80 

11 81.64 6.12 40.82 46.94 33.59 18.80 1.57 16.86 1.84 54.23 1.00 1.15 2.15 0.3220 0.69 

12 40.82 2.04 40.82 42.86 33.59 19.93 1.66 16.36 1.80 55.32 0.91 1.17 2.08 0.2875 0.60 

13 0.00 0.00 6.09 6.09 33.59 21.12 1.76 10.33 1.21 55.92 0.13 1.19 1.32 0.2567 0.34 

14 0.00 0.00 6.09 6.09 33.59 22.39 1.87 10.55 1.24 57.22 0.13 1.21 1.34 0.2292 0.31 

15 0.00 0.00 6.09 6.09 33.59 23.73 1.98 10.78 1.28 58.60 0.13 1.24 1.37 0.2046 0.28 

16 0.00 0.00 6.09 6.09 33.59 25.16 2.10 11.02 1.31 60.06 0.13 1.27 1.40 0.1827 0.26 

17 0.00 0.00 6.09 6.09 33.59 26.67 2.22 11.28 1.35 61.61 0.13 1.31 1.44 0.1631 0.23 

18 0.00 0.00 6.09 6.09 33.59 28.27 2.36 11.56 1.39 63.25 0.13 1.34 1.47 0.1456 0.21 

19 0.00 0.00 6.09 6.09 33.59 29.96 2.50 11.85 1.43 64.99 0.13 1.38 1.51 0.1300 0.20 

20 0.00 0.00 6.09 6.09 33.59 31.76 2.65 12.15 1.48 66.83 0.13 1.42 1.55 0.1161 0.18 

21 0.00 0.00 6.09 6.09 33.59 33.67 2.81 12.48 1.53 68.78 0.13 1.46 1.59 0.1037 0.16 

22 0.00 0.00 6.09 6.09 33.59 35.69 2.97 12.82 1.58 70.86 0.13 1.50 1.63 0.0926 0.15 

23 0.00 0.00 6.09 6.09 33.59 37.83 3.15 13.19 1.63 73.05 0.13 1.55 1.68 0.0826 0.14 

24 0.00 0.00 6.09 6.09 33.59 40.10 3.34 13.58 1.69 75.38 0.13 1.60 1.73 0.0738 0.13 

25 0.00 0.00 6.09 6.09 33.59 42.50 3.54 13.99 1.75 77.84 0.13 1.65 1.78 0.0659 0.12 

26 0.00 0.00 6.09 6.09 33.59 45.05 3.75 14.42 1.82 80.46 0.13 1.71 1.84 0.0588 0.11 

27 0.00 0.00 6.09 6.09 33.59 47.75 3.98 14.89 1.89 83.23 0.13 1.77 1.90 0.0525 0.10 

28 0.00 0.00 6.09 6.09 33.59 50.62 4.22 15.38 1.96 86.17 0.13 1.83 1.96 0.0469 0.09 

29 0.00 0.00 6.09 6.09 33.59 53.66 4.47 15.89 2.04 89.28 0.13 1.89 2.02 0.0419 0.08 

30 0.00 0.00 6.09 6.09 33.59 56.88 4.74 16.45 2.12 92.59 0.13 1.96 2.09 0.0374 0.08 

31 0.00 0.00 6.09 6.09 33.59 60.29 5.02 17.03 2.21 96.08 0.13 2.04 2.17 0.0334 0.07 

32 0.00 0.00 6.09 6.09 33.59 63.91 5.33 17.65 2.30 99.79 0.13 2.12 2.25 0.0298 0.07 

33 0.00 0.00 6.09 6.09 33.59 67.74 5.65 18.30 2.39 103.73 0.13 2.20 2.33 0.0266 0.06 

34 0.00 0.00 6.09 6.09 33.59 71.81 5.98 19.00 2.50 107.89 0.13 2.29 2.42 0.0238 0.06 

35 0.00 0.00 6.09 6.09 33.59 76.11 6.34 19.73 2.61 112.31 0.13 2.38 2.51 0.0212 0.05 

TOTAL 9.1566 21.15 

(A) (B) 

Note: The charges per unit is exclusive of water cess, spares, incentive & Income Tax etc. Levellised Tariff =(B)/(A) 2.31



PLATES

DIVERSION 

BED LEVEL : 1055 m. 

PANAN 

POWER HOUSE 

T.R.L. : 1060 m. 

AV.GROSS HEAD : 740 M 

FIRM POWER : 19.7 MW 

INST. CAPACITY : 160 MW 

PANAN H.E. SCHEME 

LAVEN 

POWER HOUSE 

LINGZA 

T.R.L. : 780 m. 




LINGZA H.E. SCHEME 

DIVERSION 


POWER HOUSE 

T.R.L. : 1800 m. 




RINGPI H.E. SCHEME 

DIVERSION 


N 

SCALE- 1:50000 

PLATE - 1 

MAY, 1983 

PANAN, LINGZA & RINGPI 

H.E. SCHEMES 

ON TOLUNG RIVER 

(TISTA RIVER SYSTEM) 

DRG.NO. HEPR-PS-BHM-784

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

LINGZA H.E. SCHEME - SIKKIM 

PLATE 4.1

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 

TINGCHEN KHANG 

RATHANG CHHU 

KALEJ KHOLA 

RONGDUNG CHHU 

REFLI CHHU 

RISHI KHOLA 

GOMA CHHU 

RUKEL CHHU 

GEZING 

REATHOK KHOLA 

SOMBARE NAYA BAZAR 

KHORA CHHU 

LUNGMA CHHU 

UMMRAM CHHU 

RANGYONG CHHU 

RANGIT RIVER 

KAYAM CHHU 

NAMCHI 

RINGYONG CHHU 

NAKU CHHU 

RANGPO CHHU 

GREAT RANGIT RIVER 

NACHUNGTHANGKHA 

THANG CHHO 

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 

RORA CHHU 

TAKCHOM CHHU 

W E S T B E N G A L 

RANGLI KHOLA 

DONGKYA CHHU 

TOKLUNG CHHU 

CHAKUNG CHHU 

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

2000 

2000 

2200 

2400 

2600 

2800 

RINGPI CHU 

INTAKE TUNNEL 3MØ 

DIVERSION TUNNEL 6MØ 

H.S SHAPE 

2200 

DAM AXIS 

2400 

2600 

DESILTING CHAMBER 

2 Nos. (95 X 5X 7.5 M) 

SILT FLUSHING 

TUNNEL 

1800 

2000 

1800 

ADIT-1 

1600 

2400 

1600 

PROPOSED ROAD 

27°35' 

RINGPI CHU 

2200 

2800 

2600 

2400 

HEAD RACE TUNNEL 3.3 M Ø HORSE-SHOE 

2000 

1600 

2200 

2000 

ADIT-2 

1800 

1800 

2200 

1800 

1400 

1600 

1600 

M.I.V. 

P.H. 

M.A.T. 

TRANSFORMER 

CAVERN 

1600 

1800 

2000 

1400 

SURGE SHAFT 10 M Ø 


2 M Ø INCLINED 

T.R.T. 3.3 M. Ø H.S.SHAPE 

1200 

1400 

SWITCHYARD 

(200M. X 150M.) 

TOLUNG CHU 

88°27'30'' 

NOTES 

PLATE :- 6.2 

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 (SCALE:- 1:50000) . 


PROJECT LAY-OUT PLAN 

F/DCE730/01/02

RINGPI CHU 

U/S COFFER DAM 

DIVERSION TUNNEL 6MØ H.S. 

DAM AXIS 

INTAKE TUNNEL 3MØ 

2000 

165000 

2000 

30000 

125000 

DAM TOP EL. 1855.0 M. 

SPILLWAY BAY 

3NOS. 4.0M. X 6.0M. 

1800 


2 Nos. (95 X 5X 7.5 M) 

2400 

GATE OPERATION CHAMBER 


1.0X1.8M.D-SHAPED 

D/S COFFER DAM 

PROPOSED ROAD 

2400 

HRT 3.3M. Ø H.S. 

1800 

2200 

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 (SCALE:1:50000) . 



LAY-OUT PLAN 

DAM AREA 

F/DCE730/01/02

2000 

PROPOSED ROAD 

1800 

1600 

1400 

1400 

RINGPI CHU 

HRT 3.3 Ø H.S.SHAPE 

M.A.T. 7M.Ø 

D- SHAPE 

POWER HOUSE 

(110M. X 17M. X 40M.) 

M.I.V. 

TRANSFORMER 

CAVERN 

2000 

T.R.T. 3.3 M Ø H.S. 

H.S. SHAPE 

SURGE SHAFT 10 M Ø 

1800 


2 M Ø INCLINED 

1200 

PENSTOCKS 3NOS. 1.1M. Ø 

SWITCH YARD 

(200M. X150M. ) 

1600 

1400 

1200 

TOLUNG CHU 

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 (SCALE:- 1:50000). 


LAY-OUT PLAN 

POWER HOUSE AREA 

F/DCE730/01/02

FRL 1850.00 

MDDL 1830.00 

EL 1820.00 

EL 1815.00 

TRESTLE 

EL 1855.00 

? 

? 


(95M. X 5M.X7.5M.) 

? 

? 

GATE OPERTATION 

CHAMBER 

HRT 3.3M. Ø H.S. 


(1.0M.X1.80M. D-SHAPED) 

? 

STEEL LINED 


2 M. Ø 

SURGE SHAFT 

10 M. Ø 

EL 1860 M. 

EL.1097.00 

? 

ADIT TO P.S. 

3.3M. Ø D-SHAPE 

MIV CAVERN 

ASSUMED N.S.L. 

8000 

? 

EL.1133.00 

? 

POWER HOUSE CAVERN 

17000 

? 

BUS DUCT 

14000 

TRANSFORMER CAVERN 

CABLE TUNNEL 

EL.1110.00 

? 

T.R.T. 

NOTES: 


MAR.2004 

C.C. BLOCKS 

TWL1095.00 

COFFERWALL 

1 ALL DIMENSIONS ARE IN MILLIMETERS AND LEVELS IN METERS. 

UNLESS OTHERWISE SPECIFED. 

WATER CONDUCTOR SYSTEM 

L-SECTION 

PLATE NO.:- 6.5 

2 NO DIMENSION SHALL BE MEASURED FROM THIS DRAWING. 

F/DCE730/01/02

L7 

L6 

? 

L5 

L4 

125000 

L3 

? 

L2 

? 

30000 

320000 

4000(TYP.) 3000(TYP.) 

L1 S1 S2 S3 R1 

R2 

R3 

R4 

R5 R6 

R7 

UPSTREAM ELEVATION 

STOPLOG GANTRY 

CRANE 

RADIAL GATE 4000 X 6000 

? 

165000 

NSL 

ANTICIPATED ROCK PROFILE 

? 

R8 

NOTES: 

MAR.2004 

R9 

? 

DAM 

UPSTREAM ELEVATION 


1 ALL DIMENSIONS ARE IN MM AND LEVELS IN METRES. 

UNLESS OTHERWISE SPECIFIED. 

2. NO DIMENSION SHALL BE MEASURED FROM THIS 

DRAWING. 


F/DCE730/01/02

STOPLOG GATE GROOVE 

1 

1 

STOPLOG GANTRY 

CRANE 

DAM TOP EL 1855.00 

FRL EL 1850.00 

MDDL EL 1830.00 

CREST EL 1810.00 

RBL ±EL 1795.00 

EL ±1780.00 

GROUT CURTAIN HOLES 

? 

DAM AXIS 

8000 

ROAD 

3500 

EL 1816.00 

BREAST WALL 

AIR VENT PIPE 

STEEL LINER 

R9000 

FOUNDATION 

GALLERY 

DRAINAGE HOLE 

RADIAL GATE 

TRUNION BEAM 

HIGH PERFORMANCE CONC. 

90000 

FLIP BUCKET 

? ? ? ? 

SPILLWAY- MAXIMUM SECTION 

15° 

R25000 

30° 

1 

1 

1 

1 

12250 

7000 LONG ROCK ANCHORS 

@1500 c/c STAGGERED 

MAX. T W L 

BUCKET INVERT EL 1798.25 

CONCRETE APRON 

DAM TOP EL 1855.00 

EL. VARIES ? 

NORMAL T W L 

FRL EL 1850.00 

MDDL EL 1830.00 

COMPACTED BACKFILL 

0.1 

1 

DAM AXIS 

8000 

NOTES: 

NON- OVERFLOW SECTION 


MAR.2004 

0.8 

1 

? ? 

DAM 

SPILLWAY & NON-OVER FLOW 

CROSS-SECTION 


1 ALL DIMENSIONS ARE IN MM AND LEVELS IN METRES. 

UNLESS OTHERWISE SPECIFIED. 

2 NO DIMENSION SHALL BE MEASURED FROM THIS 

DRAWING. 

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 



100 THK. SHOTCRETE 

WITH WIREMESH 

CONC.LINING 750 THK. 


7500 

5000 

SECTION - DESILTING CHAMBER 

Ø2000 

1.5 

1 


ANCHORS 1000 c/c(IF REQUIRED) 

TYP. SECTION - PRESSURE SHAFT 

32Ø 5000 LONG ROCK BOLTS / 

ANCHORS @ 2000 c/c 

BACK FILL 750 THK. 

STEEL LINER 

50THK. 

SHOTCRETE 

100 THK. SHOTCRETE 

WITH WIREMESH 

R.C.C. LINING 300 THK. 

32Ø 5000 LNG ROCK BOLTS/ 

ANCHORS @ 1500 c/c 

Ø6000 

Ø3000 

Ø6000 

4000 LONG 25Ø ROCK BOLTS/ 


TYP. SECTION - DIVERSION TUNNEL 

NOTE :- 

DRAWING. 

CONC.LINING 225THK. 

50/75 THK. SHOTCRETE 

1 ALL DIMENSIONS AREIN MILIMETRES AND LEVELS 

IN METRE UNLESS OTHERWISE SPECIFIED. 

2 NO DIMENSION SHALL BE MEASURED FROM THIS 

PRE-FEASIBILITY REPORT DRAWING 

TYPICAL CROSS SECTION 

OF CONSTITUENTS OF WATER 

CONDUCTOR SYSTEM & DIVERSION TUNNEL 

MAR.2004 


00 

F/DCE/730/01/02

220KV 

BUS-1 

BUS CVT-1 

220KV 

BUS-II 

BUS CVT-2 

EX. Tr. 

NGT 

G-III 

UNIT -III 

S.A. 

GSU Tr. 

SC PTSP 

SA 

PT 

64G1 

64G2 

TO 220KV 

FEEDER-1 

CVT 

BUS 

COUPLER 

EX. Tr. 

NGT 

UNIT -II 

GSU Tr. 

SC 

SA 

PT 

G-II 

64G1 

64G2 

PTSP 

TO 220KV 

FEEDER-2 

XLPE CABLE XLPE CABLE XLPE CABLE 

CVT 

EX. Tr. 

PT PT PT 

S.A. 

NGT 

UNIT -I 

GSU Tr.3Ø,49 MVA 

11/ 220/ 3 KV 

UAT UAT UAT 

11 / 0.415KV,500KVA 

S.A. 

SC PTSP 

SA 

PT 

G-I 

40MW,11 KV 

64G1 

64G2 

FOR 

METERING & 

PROTECTION 

FOR 

DVR DUPLICATE 

PROTECTION 

FUTURE BAY 

CVT 

MANJIT 

SA 

S.A. 

SINGLE LINE DIAGRAM 

BINOD 

V.K.SINGH 

PLATE 8.1 

MAR, 2004 NH/DEM/LIN/SLD/01 00



ANNEXURES

GEOLOGY OF THE AREA AROUND THE PROPOSED LINGZA 

INTRODUCTION 

HEDROELECTIRIC PROJECT, TEESTA, BASIN, SIKKIM 

Annexure-4.1 

The Central Electricity Authority (CEA), as a part of an exercise estimate balance 

hydroelectric potential in the county have identified 399 schemes with installed capacity 

of about 1,50,000 MW in various river basins. The schemes thus identified were 

subjected to ranking studies by applying different parameters. With result of ranking 

studies, 162 schemes with probable installed capacity of 50,600 MW have been 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 Lingza Hydroelectric Project is one of the ten schemes that are 

being taken up in first phase. This run of river scheme envisages construction of 

diversion dam/weir across Ringpi Chhu just down stream of powerhouse of Ringpi 

Hydroelectric Project (27 O 37’ 20” N: 88 O 27’ 09” E; 78 0/6), a water conductor system 

comprising 4 km long HRT and an underground powerhouse with probable installed 

capacity of 160 MW located on left bank of Rangyong Chhu downstream of its 

confluence with Ringpi Chhu and just north of proposed powerhouse of the Rangyong 

Hydroelectric Project (27 O 33’ 30” N: 88 O 26’ 30” E, 78 0/6) upstream of Lingza. 

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 occassionally 

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 structura/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. 

The metasedimentaries of the area belonging to the Chungthang Group are 

represented by a sequence of lithounits varying from calcareous to arrnaceous and 

argillaceous lithofacies. These comprise calc silicate rocks, quartzite, high grade 

micaceous schists occasional amphibolites and their fine grained interlaminations. 

3

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 

garnets. At places, augens of quartz and felspar 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. 

4

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 ocassional coal seams. Pebble cum boulder bed forms the 

marker horizon for Gondwana. Arkosic sandstone (felspathic 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 

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 

5

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 

structurs 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. 

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) 

6

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 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 

7

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 

and seismicity, the area has been kept in Zone – IV as per Map of India Showing Seismic 

Zones (IS - 1893 (part –I) : 2002). 

8

GEOTECHNICAL APPRAISAL 

The proposed Lingza Hydroelectric Project is located downstream of Ringpi 

Hydroelectric Project. As per geological map, the area around the proposed diversion 

structure exposes Banded Gneisses with augen gneisses and quartzite and biotite gneisses 

belonging of Central Crystalline Gneissic Complex. The rocks are well foliated and 

jointed. Keeping in view the general topography of the area It is suggested that type of 

structure and its final site be selected after assessing the thickness of overburden the 

riverbed and on the abutment and availability of bed rock for locating intake structure for 

the water conductor system. The water conductor system comprising 4 km long HRT is 

aligned on the left bank of Rinpgi Chhu. The rocks expected to be encountered in the 

proposed HRT include banded gneisses with augen gneiss belonging to CCGC in initial 

and final reaches and calc silicate / marble and quartzite / biotite quartzite schist 

belonging to Chungthan Group of metasediments along with augen gneisses of CCGC in 

middle reaches. The rocks of CCGC and Chungthang Group are interbanded. These are 

well foliated and jointed. One suspected thrust fault between rocks of CCGC and 

Chungthang Group may be encountered in downstream reaches. The tunneling 

conditions are likely to be good to fair in general excepted in the influence zone of the 

thrust or where local faults and shear / mylonitised zones are encountered where poor 

conditions can be expected. Similarly water ingress along with poor conditions can be 

expected in calc silicate / marble rock is these are cavernous and water charged. The 

powerhouse with probable installed capacity is proposed as an underground structure on 

the left bank of Rangoyong Chhu upstream of Lingza. The rocks exposed around the site 

of proposed structure are banded and augen gneisses and quartz – biotite gneisses of 

CCGC. These are expected to provide fair tunneling media and supports be designed 

accordingly. However, presence of local poor rock zones can not be ruled out. The 

proposed project is located in Zone IV as per Map of India Showing Seismic Zones (IS – 

1893 (part-I) : 2002). Therefore, required seismic coefficient will have to be 

incorporated in the designs of appurtenant structures of the project. This preliminary 

geotechnical appraisal is without field visit to site. 

9

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 

Lingza Hydro Electric Scheme (Org. No. HEPR-PS-BHM-784): 

Annexure 6.1 

The Ringpi appear to permit another run-of-the-river type hydro electric 

scheme utilizing the river waters available downstream of Ringpi power 

house for power generation. The scheme would involve construction of a 

diversion structure immediately downstream of the power house under 

Ringpi hydro electric scheme at a site where the river bed level is +1795 m., 

a tunnel about 4 Km. long for carrying the waters to a power house to be 

located on the main Talung Chhu river at a site where the river bed level is 

1055 m. The power house would operate under a gross head of 740 MW. 

and have an optimum generating capacity of about 160 MW enabling firm 

power generation of about 20 MW. The scheme would enable annual energy 

of 715 GWH and 780 GWH respectively in 90% and 50% dependable years.

TITLE 

ANNEXURES 6.2 



No. 

Reply on CWC’s Comments on Hydrology 1-3 

Reply on CEA (HP&I) General Comments & 

Comments on Power Potential Studies. 

4-5 

Reply on Comments of SP&PA Division CEA 6-7 

Reply on comments on CMDD(E&NE), CWC 8-9

REPLY ON CWC’s COMMENTS ON HYDROLOGY OF 


1 

Annexure 6.2 

In reference to letter no. 7/9/(NHPC)/2003/HPI/1500 dt. 20-1-2004, point wise reply to the CWC 

observations are placed as below: 

Data 

availability 

Consistenc 

y of data 

Water 

availability 

CWC Observations Reply of NHPC 

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. 

(i) Though the rainfall data of 11 raingauge 

stations available with NHPC could not be 

utilized in the study due to the reason that 

none of the stations are within the project 

catchment, the project authorities may put in 

their effort to verify whether any of the 

remaining stations as mentioned in the report 

lies in the project catchment and to explore 

the possibilities of utilization of the data in 

the study. 

(ii) A complete list of all rainfall and 

discharge stations of Teesta Basin may be 

furnished. 

(i) Only graphical presentation comparing 

the avg. 10-daily discharges of the four 

As explained in earlier meetings and 

correspondences, the paper of Biswas and 

Bhadram has been quoted in the report to explain 

the precipitation characteristics. At present, 

NHPC has rainfall data of only the 11 raingauge 

stations whose data availability status is shown in 

the report. As desired, the annual rainfall at these 

11 stations for the available period is enclosed as 

Annexure-I. 

(i) 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. 

(ii) The list of rainfall stations lying upto the 

catchment of Teesta-V has already been shown in 

the data availability status given in report. 

However, as referred by the paper 42 raingauge 

stations exist in the entire Teesta Basin. Rainfall 

and discharge stations lying in the entire Teesta 

basin are of not relevant for the present projects. 

The available average 10-daily series at Lachen 

has already been sent along with the replies of

studies methodologies has been furnished in the 

Design 

Flood 

report. The data and the analysis of Lachen 

adopted for the project has not been 

furnished without which checking is not 

possible. In the absence of site-specific data, 

the use of Tolung Chu data would be more 

reliable. The snowfed area covers a major 

portion of the project catchment and without 

establishing hydro-meteorological similarity 

transfer of data from other sub-basin would 

be unjustified. Before discarding Tolung Chu 

data the project authorities are advised to 

verify whether any of the remaining 31 rain 

gauges are located in the sub-basin and to 

utilize the same after applying consistency 

checks and results incorporated. Rainfall- 

runoff factor based on Tolung Chu data may 

be evaluated before discarding the data. The 

results obtained may be compared with the 

series obtained from Lachen before 

recommending the yield series. Efforts may 

be made to collect site specific data and 

water availability studies may be reviewed 

based on observed data. 

(ii) The basis of deriving the catchment 

reduction factor is not given. 

(iii) A series of projects is bieng planned in 

Teesta Basin and Integrated studies on water 

availability need to be done incorporating the 

likely releases from the u/s power house and 

independent catchment contributions. 

(i) The design flood studies done by NHPC 

are too empirical to be relied upon even for 

PFR. The project authorities may also 

calculate the PMF value using SUH 

2 

Rukel and Rangyong projects. Tolung Chu data 

has not been used as the series obtained using this 

data was on a much higher side as compared to 

other three series and no consistency checks 

could be applied to check the reliability of the 

data. Hence for the time being Lachen G&D data 

has been used. 

It has been verified that 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. 

(ii) 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 Lingza is 124 Sq.km. 

(iii) Cascade development need to be done at a 

later stage. 

(i) As already explained in our earlier replies 

also, for such detailed studies as suggested for 

this stage i.e PFR, neither the database is at all 

sufficient nor necessity felt by us. During

Sedimentati 

on 

approach as suggested in North Brahmaputra 

Basin (Sub Zone-2(a) report published by 

CWC by obtaining the PMP/SPS value and 

temporal distribution of rainfall from IMD 

and following 2 bell per day approach and 

incorporate this value also in the comparative 

study to get a more realistic value. 

(ii) Short interval data may be collected and 

the design flood should be reviewed based on 

observed data. 

The sedimentation rate for the region is about 

0.1765 Ham/Sq.km/year as per CWC studies 

published in the Compendium on Silting of 

Reservoirs In India which is higher than the 

rate proposed for the project. As stated in the 

report more detail study is required. Data 

may also be collected from the completed 

projects of the basin. 

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. 

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. 

3 

feasibility stage, deterministic/ probabilistic 

approach will be used, based on more observed 

data. 

(ii) It is not felt necessary to perform such 

detailed study during PFR stage. 

We are aware of the findings of CWC studies 

published in the Compendium on silting of 

reservoirs in India. As per that report, the 

sediment rate varies from 0.05658 to 0.2785 

Ham/Sq.km/year for Indus, Ganga and 

Brahmaputra basin. But the 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 

“Compendium on silting of reservoirs in India”. 

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.

REPLY ON COMMENTS OF CEA (HP & I ) ON DRAFT PFR OF LINGZA H E 

PROJECT, (120MW) SIKKIM. 

(CEA Letter No.7/9/(NHPC)/HP&I/2003/1552 dated 12.12.2003 ) 

Sr.No. CEA (HP&I)’s Comments 

GENERAL COMMENTS : 

NHPC’s reply 

1 It may be ensured that the Initial 

Environmental studies incorporated 

in the PFR are as per scope of work 

for PFR. 

This has been considered. 

2 The Financial Parameters may be 

taken as per guidelines sent vide our 

Lr. No. 7/9/HPI-2003/1118-1123, 

dated 21 st October, 2003. 

3 It may be ensured that the Cost 

Estimates is prepared as per the 

Guidelines sent vide our Lr. 

No.7/9/HP&I/2003/1163-1172, dated 

24.10.2003. 

4 NHPC may indicate 

recommendations for further studies 

required wherever necessary in the 

relevant chapters of PFRs for 

consideration during Feasibility 

Report/DPR stage. 

. 

5 It may be ensured that the Installed 

Capacities & assessment of power 

benefits takes into account various 

comments and advise given in this 

regard. 

6 It may be ensured that the hydrology 

adopted is approved by CWC. 

7 The power evacuation arrangements 

considered in the PFR should take 

into account views and suggestions of 

SP&PA Division of CEA. 

4 

The Financial Parameters may be 

taken as per guidelines of CEA 

Cost Estimates have been prepared 

as per the Guidelines of CEA 

Recommendation for further studies 

required for preparation of FR/DPR 

has been indicated wherever 

necessary 

The installed capacities and 

assessment of power benefits require 

no change. 

Hydrology adopted is as discussed 

and decided in the meetings with 

CEA 

The power evacuation arrangements 

considered in the PFR has taken into 

account views and suggestions of 

SP&PA Division of CEA.

8 Cost of Projects etc has been 

mentioned in lakhs where as it should 

be in crores in cost of energy 

statements. 

POWER POTENTIAL STUDIES: 

1 Gross storage and live storage in 

terms of Mcum and MWhr may 

please be indicated in the power 

potential studies chapter. 

2 Justification for FRL, MDDL, TWL, 

Proposed installed capacity of 

120MW has not been brought out 

properly in text portion of Chapter 

VII studies carried out and presented 

in tables need also to be explained in 

the chapter. 

3 A table giving the summary of 

studies indicating yearly inflows, 

annual energy generation, load factor 

of operation during monsoon and 

lean flow period may be presented in 

studies. 

. 

4 NHPC may indicate 

recommendations for further studies 

required for preparation of FR/DPR. 

5 

Necessary correction has been 

incorporated. 

Gross storage and live storage in 

terms of Mcum and MWhr has been 

indicated in the power potential 

studies chapter. 

Justification for FRL, MDDL, 

TWL, Proposed installed capacity of 

120MW has been modified as per 

Civil Design recommendations and 

brought out in text portion of 

Chapter VII studies carried out, and 

also explained in the chapter. 

Annual energy generation in 90% 

dependable year and design energy 

(with 95% availability has been 

indicated separately in the text and 

in table 7.5A. In table 7.5A energy 

with 95% machine availability has 

been modified and presented in text 

and table form. 

A table giving the summary of 

studies indicating yearly inflows, 

annual energy generation, load 

factor of operation during monsoon 

and lean flow period has been 

presented in studies as per annex-B 

Table 7.5. 

Recommendation for further studies 

required for preparation of FR/DPR 

has been indicated wherever 

necessary

REPLY ON COMMENTS OF SP&PA DIVISION ON DRAFT PFR OF 


(CEA Letter No.7/9/(NHPC)/HP&I/2003/9 dated 02.01.2004 ) 

Comment Reply 

4.1 General 

The project is located in the river 

Ringpi Chu in Dzongu area of North 

District of Sikkim. The project 

involves construction of a 75m high 

concrete dam, a 4.0km long Head 

Race Tunnel and an underground 

power house with an installed capacity 

of 120MW. This power house will be 

runoff river type and well connected 

from Mangan by 17km long state 

PWD road. 

4.2 Construction Power 

The necessary construction power 

shall be availed from Phodong 2x2.5 

MVA, 66/11 kV substation or from 

Mangan S/s which will be decided at 

the time of DPR. 

4.3 Switchyard 

A cable tunnel of size 2.0m x 3.0m 

will take off from transformer area 

and shall carry cable to a surface 

switch yard. The switchyard 

measuring approximate 200m x 150m 

shall be formed in cutting and filling. 

No details of switchyard are available 

in PFR. 

4.4 Power evacuation 

NHPC proposed power will be 

generated at 11 kv and stepped up to 

220 kv through 49 MVA 11/220 kv 

unit transformer. Power will be 

evacuated through 11km 220KV S/C 

to Teesta III. 

6 

As this is only general description of the 

project. No reply is required. 

This has been already been considered in 

the draft PFR. 

The required information will be taken 

care of during preparation of FR/DPR 

stage. 

This has been incorporated in the final 

PFR.

In the consultation with NHPC 

officers the schemetic transmission 

system to evacuate power generated in 

the various hydro projects proposed 

inTeesta basin has been evolved and is 

enclosed. Accordingly it is also 

advised that power generated at 11 kv 

and be stepped up to 220 kv and 

evacuated through 220 kv D/C line to 

pooling point of Teesta Stg-III. In 

view of this, following no. of bays 

may be provided in the switchyard. 

Generator bays – 3 

220kv line bays –2 

Bus coupler bay – 1 

4.5 Cost 

In the PFR, cost of 5 no of bays and 

220KV D/C line has been taken. 

Accordingly in the PFR cost of 6 no of 

bays and transmission network may be 

revised. 

7 

This has been incorporated in the final 

PFR.

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. The report should indicate the The study on alternative layouts and 

alternative layouts and alternative 

locations of project components 

examined during the preparation of 

PFR to bring out their merits and 

demerits of each including the finally 

adopted in PFR. The reasons for 

rejecting the particular alternative 

should be elucidated justifying the 

rejection. 

2. Preliminary survey should be made 

to ensure the quality and quantity 

regarding availability of construction 

material. 

3. The PFR should include some 

geophysical information about the 

project location, which should be 

ensured by field study. 

alternative locations has been included in 

further studies during FR/DPR stage 

when more information on topography, 

geology, construction material etc. shall 

be available. 

Availability of Construction material has 

been addressed in revised Chapter–IV 

(Topo-graphical & Geo-technical aspect 

of PFR). The construction material 

testing shall be done during FR/DPR 

stage for ensuring quality of construction 

material. 

The right bank of the dam site was not 

approachable. Therefore geo-physical 

survey was not feasible. Sufficient rock 

exposure was available in the power 

house area, hence geo-physical survey 

was not required at this stage. 

8

4. For river diversion purpose non- 

Monsoon flood of 300 cumecs has 

been considered. But reason for 

considering this value has not been 

furnished. 

5. It should be mentioned in the report 

that the PMF value has been vetted by 

hydrology (NE)Dte. CWC. 

6. The GSI report has not been 

incorporated in the PFR. 

7. The reason for providing concrete 

dam over rock fill dam please may 

incorporated in PFR. 

8. Schematic plan of all schemes in 

one basin should be furnished. 

Reasons have been detailed in revised 

chapter-VI (conceptual layout and 

planning of PFR). 

This is as per decision taken in the 

progress review meeting on PFR with 

CEA. 

GSI report is included as annexure 4.1. 

This has been discussed in ‘conceptual, 

layout and planning’ chapter of PFR. 

The same has been incorporated in the 

PFR. 

9

Lingza - Ministry of Power

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