SLOPE MOVEMENT ANALYSIS USING SENTINEL-1 SAR DATA: A CASE STUDY OF KOTESHWAR RESERVOIR RIM REGION.

Abstract

The ability of PSI (Persistent Scatterer Interferometry) was assessed for monitoring slopes bounding the Koteshwar reservoir, Tehri Garhwal, Uttarakhand, India. Along with the rainfall events, reservoir water fluctuation is considered as main factors that initiated a number of slope failures in the study area. Koteshwar reservoir area is prone to landslides, due to steep slopes and vulnerable slope forming material (belonging to lesser Himalaya Formation). In the last decade, this area has seen development of 18 km long reservoir in Bhagirathi valley. During the reservoir operation, water fluctuation to the tune of 6 meters has been observed in the reservoir water level and consequently several slope portions have subsided. Such slope movements have damaged the Tehri-Koteshwar Road, several houses and one of the ancillary facility ( DG-Pump house) of Koteshwar power plant.

            This paper is focussed on the monitoring of slopes for the post reservoir impoundment period. In particular, several slow-moving rotational and translational slides occurred in the area, making it suitable to monitor ground instability through different InSAR techniques. PS-InSAR (permanent scatterers SAR interferometry) techniques, using Sentinel-1 SAR data were applied to analyse ground displacements post reservoir impoundment. During the reservoir impoundment phase, Sentinel -1A & 1B sensor was able to acquire data for every 12 days gap (2015-2018). Through the PS-InSAR processing of 58 scenes, ground deformation velocity maps were obtained, providing displacement in millimetre/year. A detailed field investigation was carried out to validate the ground deformation results obtained on the basis of PS-InSAR processing.