Future Glacial Lake Outburst Flood (GLOF) hazard of the South Lhonak Lake, Sikkim Himalaya

Sattar, A and Goswami, A and Kulkarni, AV and Emmer, A and Haritashya, UK and Allen, S and Frey, H and Huggel, C (2021) Future Glacial Lake Outburst Flood (GLOF) hazard of the South Lhonak Lake, Sikkim Himalaya. In: Geomorphology, 388 .

Preview	PDF geo_388_2021.pdf - Published Version Download (9MB) | Preview
	Microsoft Word 1-s2.0-S0169555X21001914-mmc1.docx - Published Supplemental Material Download (281kB)

Abstract

The Teesta basin in Sikkim Himalaya hosts numerous glacial lakes in the high altitude glacierized region, including one of the largest and the fastest-growing South Lhonak Lake. While these lakes are mainly located in remote and unsettled mountain valleys, far-reaching glacial lake outburst floods (GLOFs) may claim lives and damage assets up to tens of kilometers downstream. Therefore, evaluating GLOF hazard associated with current and potential future glacier-retreat-driven changes is of high importance. In this work, we assess the future GLOF hazard of the South Lhonak Lake by integrating glacier and hydrodynamic modeling to calculate the lake's future volume and hydraulic GLOF characteristics and impacts along the valley. We identify the increased susceptibility of the lake to potential avalanche impacts as the lake grows in the future. Here we model six avalanche scenarios of varying magnitudes to evaluate the impact-wave generated in the lake and overtopping flow at the dam. Avalanche simulations indicate that the frontal moraine is susceptible to overtopping. The overtopping flow hydraulics is evaluated along the channel assuming no erosion of the moraine. Further, we consider three lake-breach scenarios to model GLOFs originating from the lake, flow propagation, and its downstream impacts. The uncertainty in the breach parameters including breach width and time of failure are calculated to estimate the upper and the lower hydraulic limits of potential future GLOF events. Further, the uncertainty in the flow hydraulics was evaluated using dynamic flood routing of six GLOFs that originate from the lake. Hydrodynamic GLOF modeling resulted in a predicted peak discharge of 4311 m3s�1, 8000 m3s�1, and 12,487 m3s�1 for breach depths of 20 m, 30 m, and 40 m respectively. The large-potential scenario suggests that maximum flow depth and flow velocity at Chungthang, a town proximally located to a major hydropower station built-in 2015, could reach up to 25�30 m and 6�9 m s�1, respectively. Mapping infrastructure exposed to GLOFs in the Teesta valley shows that many settlements and assets located along the river channel at Chungthang are potentially exposed to future GLOFs, indicating the need to conduct a full environmental impact assessment and potentially undertake GLOF risk mitigation measures. © 2021 The Authors

Item Type:	Journal Article
Publication:	Geomorphology
Publisher:	Elsevier B.V.
Additional Information:	The copyright for this article belongs to Authors
Department/Centre:	Division of Mechanical Sciences > Divecha Centre for Climate Change
Date Deposited:	24 Aug 2021 06:54
Last Modified:	24 Aug 2021 06:54
URI:	http://eprints.iisc.ac.in/id/eprint/69232

Actions (login required)

View Item