Sikkim Floods: Research Group Highlights Factors Leading to Dam Breach
Chungthang Dam, part of Sikkim’s biggest hydropower project on the Teesta river was washed away in a Glacial lake outburst flood on October 3. In its blog, South Asia Network on Dams, Rivers and People (SANDRP) discussed what could have triggered the disaster.
गाँव कनेक्शन 7 Oct 2023 1:49 PM GMT
From cloudburst, to glacial lake outburst and excessive rainfall, a host of factors are being held responsible for the breach of the Chungthang Dam which flooded areas in north Sikkim on October 4.
A research group that specialises in dams, rivers and their impact on the environment mentioned in a blog that the outburst in south Lhonak Glacial lake washed away a 60 metres high 1,200 megawatts project named Teesta 3.
“The flood has brought unprecedented disaster all along the river in Sikkim and further downstream in West Bengal and then Bangladesh,” South Asia Network on Dams, Rivers and People [SANDRP] mentioned in the blog.
It noted that the lake had an area of 17.54 hectares in 1977 but between 1977 and 2008, the lake’s surface area rose by 81.1 hectares.
The lake is one of the fastest expanding lakes in the Sikkim Himalaya region, and one of the 14 potentially dangerous lakes susceptible to Glacial lake outburst flood.
“The lake is rapidly growing in an abnormally rapid manner due to the melting of the lake’s associated South Lhonak glacier and additional melt water from the adjacent North Lhonak and main Lhonak glaciers. The lake possibly burst at 12.40 am. According to the Sikkim State Disaster Management Authority, the water flowed out at the rate of 15 metres per second,” it added.
“The dam at Chungthang got washed away in ten minutes just after 12 midnight. We also saw that the 200-metre-long bridge connecting the powerhouse has been washed away. The entire powerhouse has been submerged under water,” Sunil Saraogi, the executive chairman of Sikkim Urja Limited was quoted.
Informing about the reasons behind the dam breach, it stated that initially, some officials including some from Central Water Commission [CWC] talked about cloud burst leading to the floods.
“...but even CWC officials now quoted by the media are rejecting this. If we look at the rainfall reported in Sikkim in 24 hours ending at 0830 hrs on October 4, 2023, as reported in IMD’s daily district wise rainfall, we see that it is not the North Sikkim (Mangan) dish that had the high rainfall but it was East Sikkim and South Sikkim,” it mentioned.
It further added that another theory being explored for further investigation is if an earthquake in west Nepal Bajhang district on October 3 caused the floods, but the highest magnitude earthquake (6.2) happened around 3 pm, whereas the GLOF happened past midnight.
“Let us see what conclusion the scientists arrive at about this,” the blog stated.
Meanwhile, India’s National Disaster Management Authority stated that excessive rainfall caused the floods.
A disaster waiting to happen?
Twenty years ago, in an inventory carried out of the glacial lakes in Sikkim, 266 lakes were mapped of which 14 were deemed as potentially dangerous. Following reports on these lakes in 2013 and again in 2017 reiterated the warning, said Ashim Sattar, scientist, Divecha Centre for Climate Change, Indian Institute of Science, Bangalore. Sattar has published two papers — the latest in 2021 being a study of six avalanche scenarios leading to glacial lake outburst floods (GLOFs).
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The Chungthang Dam was swept away in no more than ten minutes and the waters also washed away the 200-meter long bridge that connected the powerhouse to the dam, said Sunil Saraogi, executive chairman of Sikkim Urja Limited. The powerhouse is also completely submerged, he added.
A Himalayan glacial lake in India probably burst its banks this week after chunks of ice fell into it in an apparent avalanche following heavy rains, triggering The deadly flash floods in the Teesta river could have been been triggered by chunks of ice falling into the glacial lake following torrential rains, causing the lake to burst its banks, experts told Reuters.
About 14 bridges in Sikkim have either been washed away or are submerged in the flooding. Many habitations near the river have been destroyed or washed away. According to the Gangtok District Administration, connectivity to Sikkim, including its capital Gangtok, has been affected and the Teesta river has washed away parts of NH-10 that connects the state to the rest of the country.