GLACIAL LAKE OUTBURST FLOOD (GLOF) ANALYSIS OF GLACIER AND GLACIAL LAKE IN A HIMALAYAN BASIN

Abstract

A great number of glacial lakes have appeared in many mountains of the world during the last half century due to global warming. Several floods have been caused by frequent outburst from the glacial lakes. These glacial lake outburst flood (GLOF) have also occurred in Himalayan Mountains. In the present study, GLOF risk assessment has been carried out in the Teesta river basin located in the Sikkim state of India. The study includes accurate mapping of the glaciers and glacial lakes using multispectral satellite images of LANDSAT and IRS. For glaciers mapping NDSI image and slope map of the area have been prepared. NDSI maps can identify glacier covered with snow cover debris covered glaciers cannot be mapped using NDSI, with the help of NDSI and slope maps glaciers have been delineated manually. Inventory of lakes has been prepared by supervised maximum likelihood classification and NDWI followed by intense manual editing after wards using Google earth images. Proper inventory of glacial lakes in the basin has been created and information of 143 lakes has been prepared. Detail analysis of these lakes has been carried out for identification of potentially dangerous lakes. Vulnerable lakes have been identified on the basis of area, position with respect to glacier, growth since 2009, slope, distance from the outlet of the basin, presence of supraglacial lakes, presence of other lakes in downstream, condition of moraine, condition of the terrain around them etc.. From these criterions, total 18 lakes have been identified. Out of these 18 lakes, further analysis has been carried out for the identification of most vulnerable lake. Lake-140 comes out to be the most vulnerable. For this potentially dangerous lake, different parameters have been generated using satellite data and DEM (Digital Elevation Model). The volume and depth have been computed using empirical formulae, other parameters such as cross sections from the lake to outlet etc. have been prepared in Arc GIS. The GLOF which can be caused by Lake-140 was modeled and simulated using MIKE-11 software and flood values have been obtained. The flood at lake site comes out to be 10251.71 cumec which get mitigated to 5068.59 cumec at the