Geospatial Analysis of Glacial Lake Outburst Flood (GLOF)

Abstract

AbstractThe Himalayan region is a fragile ecosystem with a steep landscape where natural disasters such as the Glacial Lake Outburst Floods (GLOFs) event have been frequently observed that cause significant damage in valleys downstream areas. GLOF is one of the major unexpected serious hazards that can release a large volume of water with debris cover in a very short interval of time that caused loss of lives, properties, and severe damage to downstream infrastructures. In the present study, lake-terminating South Lhonak lake (Lat 27° 54′ 41.88″ N and Long 88° 11′ 44.65″ E) is located at an altitude of 5205 m above mean sea level (a.s.l.) in the Teesta basin, Sikkim has been identified as highest potentially dangerous glacial lake based on the criteria of area, elevation, slope, distance from the glacier and volume of water held, with maximum surface area 1.39 km2 acquired on October 2020. Spatio-temporal analysis of the glacial lake using Landsat 5 and Landsat-8 satellite imagery shows that the glacial lake has been grown from 0.48 to 1.39 km2 over the past 30 years. The depth of South Lhonak glacial lake is 39.54 m which has been calculated by using Huggle’s formula. This study evaluates the one-dimensional hydrodynamic modeling for GLOF simulation at different downstream sites from the glacial lake. The HEC-GeoRAS has been used for the creation of river geodatabase. Consequently, simulation was carried out using HECRAS model at multiple sections along the river. The GLOF scenario was revealed due to overtopping failure of the frontal moraine, producing peak discharge, and releasing water volume of 54.96 × 106 m3. The result of this study reveals that the predicted peak discharges of the lake have been estimated for breach widths of 30, 40, and 60 m, and breach formation time has also been considered as 40, 30, and 20 min, respectively. The estimated flood peak was 14,658.60 m3/s at the GLOF site, and the same got mitigated to 11,978.77 m3/s at the downstream end, respectively. The study’s findings will aid in the formulation of risk management plans and risk reduction strategies in the event of a GLOF hazard.KeywordsSouth Lhonak lakeGlacial Lake outburst floodsHEC-RAS modelHEC-GeoRASRiver cross-sectionFlood hydrograph