Teesta - Ministry of Power

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Preliminary Feasibility Report
Teesta (I) HE Project (4 x 80 MW)
4.2 REGIONAL TOPOGRAPHIC AND GEOTECHNICAL FEATURES
This regional geological setup is based on literature studies and geological report of
GSI for the Scheme. River Teesta in Sikkim is a major river originating from Zemu
glaciers and generally flows in north-south direction, at a steeper gradient. The river is
joined by several tributaries major amongst them being Yumthang Chu, Zemu Chu,
Talung Chu, Dik Chu , Rangpo Chu and Rangit chu, apart from others join the river.
The river valleys in this region are u-shaped while, as the tributaries had developed
deep gorges, which are bound by steep slopes. A thick vegetal cover occupies the hill
slopes. A study of available literature was undertaken to have an overview of the
regional geology of this area. 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 set-up 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.