Sikkim Proposes Three Measures to Mitigate GLOF Risks
Solar pumping, flood-retention structure and safety wall proposed for vulnerable glacial lake systems
GG News Bureau
Gangtok, 2nd Sept: Sikkim has proposed three major engineering interventions aimed at reducing the potential impact of Glacial Lake Outburst Floods (GLOFs), including solar-powered pumping at Shako Chho, a flood-retention structure at Dolma Sampa in the Lhonak Valley and a safety wall at the outlet of the Gurudongmar lake complex.
The proposals signal a shift from assessing glacial hazards towards implementing concrete mitigation measures. Principal Secretary of the Science and Technology Department Sandeep Tambe said the state was increasingly focusing on reducing the risks associated with vulnerable glacial lakes.
“Studying glaciers is one thing, but we are mostly working towards glacial hazard mitigation,” Tambe said.
Solar pumping proposed at Shako Chho
At Shako Chho, located at around 17,000 feet and about 12 km from Thangu on the route to Gurudongmar, the state has proposed lowering the lake level through solar-powered pumping.
The lake is estimated to contain around 27 million cubic metres of water. Its terminal moraine is high but permeable, while the lake has no natural outlet. The National Disaster Management Authority (NDMA) has advised against directly disturbing the fragile moraine.
Under the proposal, around 8 million cubic metres of water would initially be pumped out using eight solar-powered pumps, potentially lowering the lake level by about 20 to 40 metres.
Chief Engineer Ashim Basnett said reducing the lake’s volume could reduce the force of water released during a possible future avalanche, landslide or similar event.
“The best way to stop it is at the lake itself,” Basnett said, explaining that reducing the depth and volume could lessen the impact of a potential outburst.
Conventional pumping has been considered impractical because the site has no electricity supply and transporting fuel to such a high-altitude location would be difficult. A Detailed Project Report (DPR) has been prepared and submitted through the state disaster management authorities, with the proposal currently being examined at the Government of India level.
Retention structure planned for Lhonak Valley
The second proposal concerns the Lhonak Complex, comprising the South Lhonak, North Lhonak and Changsang lakes. Instead of intervening directly at the lakes, Sikkim is studying the construction of a flood-retention structure at Dolma Sampa, around 24 km downstream near Muguthang.
The site is significant because it played a role during the October 2023 South Lhonak GLOF. The outburst released nearly 30 million cubic metres of water and lowered the lake level by around 20 to 25 metres.
The flood reached Dolma Sampa, where the naturally wider valley allowed water, boulders and debris to spread across a larger area, reducing the flood’s momentum.
The latest assessment found South Lhonak to be presently stable. The lake is currently about 2.70 km long and covers around 148 hectares, compared with approximately 2.60 km and 155 hectares before the 2023 disaster. The combined water volume of South and North Lhonak lakes is estimated at around 70 to 80 million cubic metres.
“We will not do something at the lake level. We will do it at a location called Dolma Sampang where the valley suddenly broadens out and the flood actually slows down there,” Tambe said.
Safety wall proposed at Gurudongmar
The third intervention is proposed for the Gurudongmar Lake complex, which comprises three lakes. While one is accessible to tourists and pilgrims, the other two are considerably larger. The complex has also expanded significantly over the past three decades.
The proposed measure involves constructing a moraine-plug safety wall or stone-masonry structure at the lake outlet to regulate water release and reduce the force of a potential outburst.
“Once it starts rolling down the valley, it gains momentum and picks up boulders and debris. Then it is almost impossible to do anything about it,” S&T Secretary Dhiren Shrestha said.
16 high-risk lakes classified as Category-A
Of the 40 high-hazard glacial lakes identified by NDMA in Sikkim, 16 have been classified as priority Category-A lakes. Detailed assessments have been completed for 13 of these lakes.
The state is now evaluating which engineering interventions are technically viable while continuing monitoring and hazard assessments of vulnerable glacial lake systems.
