Field study of high-risk glacial lakes in North Sikkim

SUDIP DHUNGEL

GANGTOK,: The multi-disciplinary glacial lake susceptibility assessment study expedition in North Sikkim was flagged-off on Saturday morning by Lachen Mangan MLA and minister Samdup Lepcha from Gangtok.

The 15-day expedition from August 31 to September 14 will be on six high-risk glacial lakes of Tenchungkha, Khangchung Chho, Lachen Khangtse, Lachung Khangtse, La Tsho and Shako Chho.

The six A-category high risk lakes are located at an average elevation of 5200 meters in the extreme northeastern corner of Sikkim right on the Indo-China border. This region is a trans-Himalayan landscape falls behind the Khangchengyao massif and behind the main Himalayan range. It is the southern-most extremity of the Tibetan plateau and is characterized as a cold desert ecosystem.

The six lakes fall in the Chhombo Chu River's watershed, a tributary of the Teesta River flowing east to west. The origin of the river Teesta from the Teesta Khangtse glacier is also in this landscape. The river originates from the Khangchung Chho glacier lake, the largest lake in the State. This lake is over 3 km long and has an estimated water volume of 106 million cubic meters.

The expedition represents a unique collaboration by 33 officials under six State departments, two Central government agencies (GSI, CWC), the National Disaster Management Authority (NDMA) and the Sikkim State Disaster Management Authority (SSDMA), Sikkim University and the Lachen Dzumsa. The Indian Army 27 Mountain Division and the Indo-Tibetan Border Police (ITBP) are providing essential ground support, including medical assistance.

The objective of expedition is to evaluate the lake's volume, depth, and longitudinal profile to characterize its physical dimensions using a bathymetry survey; to perform a geophysical assessment of the moraine dam to evaluate its stability and potential risk factors using electrical resistivity tomography survey (ERT) and Ground Penetrating Radar (GPR).

The expedition also aims a slope stability assessment of the glacial lake to assess mass movement hazard. The other objectives are to conduct a morphometric survey of the glacial lake and its adjacent landscape; to measure lake discharge and assess the outlet flow dynamics to understand the lake's hydrology, and 3D Terrain Mapping using UAV/Drone to build a high-resolution terrain model.

State Science & Technology secretary Sandeep Tambe is leading the expedition with field-based studies such as bathymetric investigation of high risk glacial lakes which includes study on lake volume and depth estimation, maximum, average and minimum depth, lake bed elevations, longitudinal profile of glacial lake, hydrodynamic modelling of high-risk glacial lakes to identify vulnerable locations and extent of floods downstream.

The entire exercise aims to assess the potential risks associated with GLOF and propose mitigation measures to safeguard the local communities and infrastructure.