Assessment of Proglacial Lakes in Sikkim Himalaya, India for Glacial Lake Outburst Flood (GLOF) Risk Analysis using HEC-RAS and Geospatial Techniques

Abstract

Existence and expansion of glacial lakes from Sikkim Himalaya enhances the susceptibility of the region to glacial lake outburst floods (GLOF) causing destruction of infrastructures and loss of life in the downstream region. Apart from the expanding glacial lake, various topographic factors play important role in its susceptibility to GLOF. This study aims to find out the GLOF susceptibility of a relatively stable lake, Shako Cho in terms of areal expansion using different topographic parameters. The lake volume has been estimated using area-based scaling method. Using Sentinel-2A satellite imagery and ALOS- PALSAR digital elevation model, probable avalanche pathway, steep lakefront area (SLA) have been mapped. Estimating the potential lake lowering height from the digital elevation model, potential flood volume (PFV) has been quantified. A band-ratio method has been employed to extract the debris-cover around the glacial lake. This lake has a PFV of 45.478*106 m3 water. Sikkim being a hilly terrain, some of its glacial lakes are located in highly avalanche prone zone. Excessive snowfall often causes snow avalanche in those region. Thus a snow-avalanche triggered GLOF simulation in HEC-RAS 5.0.6, using 2D dam breach scenario has been performed to evaluate its impact on the downstream region.