ENGINEERING GEOLOGICAL EVALUATION OF KOTLIBHEL HYDROELECTRIC PROJECT STAGE 1A, GARHWAL HIMALAYA

Abstract

Kotlibhel Hydroelectric Project Stage-1A is situated on Bhagirathi River near Muneth village, 3.8 Km upstream of Devprayag in Tehri Garhwal District. The Project consist of 82.5 M high and 129 M long concrete gravity dam with 195 MW (3 X65 MW) capacities and underground power house. For the construction of dam, a regional and local geological study of the area is required. For detail study of the surface geology of dam site area, a geological map is prepared on the scale of 1:2,000 which contain lithology, structural variation. For sub-surfaces geology, drifts and drill holes are needed. Uniaxial Compressive Strength (UCS), Point Load Index, Triaxial Compressive Strength (TCS) and Density etc are some laboratory test used to know the strength of the rocks. Rocks like quartzite, phyllitic-quartzite are good for foundation rock. Further horizontal foliation/bedding plane is good for foundation rock Reservoir of the Project extends from Muneth village to Koteshwar Dam. Length of the reservoir will be 18.4 Km, while FRL expected to be 530.0 M where as MDDL is expected to be same as FRL. A geological map is prepared for detail study of reservoir area on the scale of 1:13,000. For stability of rim of reservoir, kinematic analysis and landslide investigation is used. Further forests/vegetation and step by step cultivated lands are increases the stability of rim of reservoir. Due to water level fluctuation, in case of Full Reservoir Level (FRL), the rim of reservoir will be saturated with water. During drawdown condition, these water saturated slopes would become unstable and this would cause instability of the rim of reservoir.