ON THE FORMATION OF FUTURE GLACIAL LAKES AND THEIR POTENTIAL GLOF VOLUME AND PEAK DISCHARGE ON THE BED TOPOGRAPHY OF THE GANGOTRI GLACIER

Abstract

The Himalayan glaciers are rapidly retreating. With the increasing loss of glacial mass, the glacial lakes are also increasing in number, increasing the potential threat of GLOF (Glacial Lake Outburst Flood). We aim to identify the sites for future glacial lake formation over the bed-topography of the Gangotri Glacier (Uttarakhand, India) and check the vulnerability of the outburst of those glacial lakes to the downstream hydropower stations. As the glacier melts and loses its mass, the glacier bed gets exposed, and any possible over-deepening, if available in the thereby exposed bed-topography, shall act as a bedrock dam to hold the meltwater forming a moraine-dammed lake. The present research aims to identify the sites for such glacial lake formation. We first prepare the bed topography of the Gangotri glacier using the GlabTop2_IITB model. The sites for future lakes are identified by detecting the over-deepening of the bedrock topography of the glacier. GlabTop2_IITB model has a self-calibration feature that can calibrate its parameters without field measurements. The study results show that there are 65 potential sites for future glacial lakes formation on the Gangotri glacier bed topography, having an area greater than 0.02 km2. The estimated total water storage volume on the identified glacial lakes is 68.46x106m3. The glacial lakes thus identified are checked for their outburst volume and peak discharge using a physical model by incorporating a Monte Carlo simulation to quantify the uncertainties in the dam breach parameters. The peak discharge at the breach sites of the glacial lakes ranged in the span of 67 m3s-1 to 1235 m3s-1. The knowledge of future glacial lakes and their outburst potential during a GLOF event shall help plan the construction of upcoming downstream structures and give an idea of the vulnerability of the present structures to the futuristic GLOF events.