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INTRODUCTION
HYDRO POWER SCHEMES
There are basically two types of hydro-power schemes, "run of the river" and "storage" schemes". A storage schemes makes use of a dam to stop river flow, building up reservoir of water behind the dam, the advantage of this approach is that rainfall can accumulate during the wet season and release power during the drier period. A run of the river scheme does not stop the river flow but instead diverts part of the flow. Small hydro schemes are almost always run of the river. The advantage is that the scheme can be built locally at low cost and its simplicity gives rise to better long-term reliability. Run of the river schemes are also preferable from the point of view of environmental damages since seasonal river flow patterns downstream of the installations are not affected and there is no need for reservoirs. The proposed project is a "run of the river" type scheme.
SIKKIM - GEOGRAPHY
Sikkim, though having an area of only 7096 sq.km is unique from the point of view of geographical aspect and the topography is characterized by great variation in elevation. Sikkim is of strategic importance to India and shares three international boundaries i.e. with China, Nepal and Bhutan. The elevation ranges from a low of 250 m from MSL to a high of 8500 m and the state lies in the lesser Himalayan zone so the topography is out and out mountainous. Sikkim has its own climatic peculiarities caused by its geographical location, relief and altitude. The most important factor that determines rainfall at a place is the altitude of the place. About 58 - 76% of the total annual rainfall is received during the Southwest monsoons followed by 16 - 30% in pro-monsoon season and the least rainfall occurs during winter. The rainfall varies from 2500 mm in the southern parts to a low of 65 mm in the northern parts of the state. Teesta and Rangit are the two main rivers of the State.
HYDRO-POWER IN SIKKIM
Based on the study "Reassessment of Hydro Electric Power Potential" by the CEA the total Hydro-Electric power potential of India was assessed as 84044 MW at 60% load factor, out of this more than 70% potential is yet to be harnessed, The total potential of Sikkim is assessed to be about 8000 MW.
As per survey conducted in 1996 small hydro contribute more than 47000 MW representing about 5% of the total installed capacity world wise. In India development of small hydro has been taking place steadily since its first hydro installation of 130 kW at Darjeeling in 1897. The first generation station in Sikkim was commissioned in 1927 on the banks of Ranikhola at lower Sichey busty with an installed capacity of 50 kW.
The present peak demand of Sikkim is around 60 MW with the demand increasing three fold in winter when due to lean flow the generating capacity is reduced to half. In 1998-99 the total installed capacity of the state was 38 MW out of which 33 MW was from hydro and 5 MW from diesel. The present Government has accorded top priority to the development of Hydro-Power generation and various new projects are under planning/construction stage at this time.
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