Glof Study in Tawang River Basin, Arunachal Pradesh, India

Abstract. Glacial lake outburst flood (GLOF) is one of the major unexpected hazards in the high mountain regions susceptible to climate change. The Tawang river basin in Arunachal Pradesh is an unexplored region in the Eastern Himalayas, which is impending to produce several upcoming hydro-electric projects (HEP). The main source of the river system is the snow melt in the Eastern Himalayas, which is composed of several lakes located at the snout of the glacier dammed by the lateral or end moraine. These lakes might prove as potential threat to the future scenario as they have a tendency to produce flash flood with large quantity of sediment load during outbursts. This study provides a methodology to detect the potential lakes as a danger to the HEP sites in the basin, followed by quantification of volume of discharge from the potential lake and prediction of hydrograph at the lake site. The remote location of present lakes induced the use of remote sensing data, which was fulfilled by Landsat-8 satellite imagery with least cloud coverage. Suitable reflectance bands on the basis of spectral responses were used to produce informational layers (NDWI, Potential snow cover map, supervised classification map) in GIS environment for discriminating different land features. The product obtained from vector overlay operation of these layers; representing possible water area, was further utilized in combination with Google earth to identify the lakes within the watershed. Finally those identified lakes were detected as potentially dangerous lakes based on the criteria of elevation, area, proximity from streamline, slope and volume of water held. HEC-RAS simulation model was used with cross sections from Google Earth and field survey as input to simulate dam break like situation; hydrodynamic channel routing of the outburst hydrograph along river reach was carried out to get the GLOF hydrograph at the project sites. It was concluded from the results that, the assessed GLOF would be a lead for the qualitative approximation of the amount of bed load transported along the river reach and thus hydropower project sites.