The Union Ministry of Environment’s expert panel has raised concerns over the redesign of the 1,200 MW Teesta-III Chungthang Dam in Sikkim. The dam was washed away following a glacial lake outburst flood (GLOF) in October 2023. As a result, the panel has deferred approval for restarting the project with a new dam.
The Expert Appraisal Committee (EAC) reviewing hydroelectric projects expressed doubts about the dam’s design and stability. They questioned whether it could withstand future natural disasters. Before making any recommendations, the EAC decided to conduct a site visit.
Sikkim Urja Limited, the government enterprise responsible for the project, has requested an amendment to the dam’s environmental clearance. They propose replacing the washed-away concrete-faced rockfill dam with a concrete gravity dam. Additionally, they aim to increase the spillway capacity from 7,000 to 19,946 cumecs, claiming it can handle both GLOF and the probable maximum flood.
However, the EAC was not satisfied and decided to consult the Central Electricity Authority (CEA) on the proposed changes. The committee emphasized the need for a thorough review of the modifications. This is done to ensure that the dam’s structural safety, given the region’s vulnerability to extreme hydrological events.
To further assess the situation, the EAC formed a sub-committee consisting of two of its members, as well as representatives from the CEA, the Central Water Commission, and the Union Ministry of Environment. This team will visit the project site.
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On the night of October 3-4, an ice avalanche struck South Lhonak Lake, located at 5,200 meters. The breach caused a massive glacial lake outburst flood, triggering flash floods downstream in the Teesta River. The floodwaters overwhelmed the Chungthang dam, causing widespread devastation and killing 40 people across Sikkim. Over 100 villages in Mangan, Gangtok, Pakyong, and Namchi districts were affected, and 76 people went missing.
The Teesta-III project, located in Mangan district, utilizes a drop of around 800 meters in the Teesta River between Chungthang and Sankalang. The GLOF-triggered flash floods overtopped the dam, flooding the underground powerhouse and halting power generation. Sikkim Urja Limited and their environmental consultants, R S Envirolinks, claim the underground powerhouse and electro-mechanical equipment can be restored in a year.
The company has also proposed partial power generation by constructing a coffer dam upstream. Moreover it plans to restore the main dam within three years, with an estimated restoration cost of Rs 4,189.51 crore.
In response to the GLOF event. The Centre and Sikkim government are working to reduce the risks posed by potentially hazardous glacial lakes in Mangan district. The Centre has approved a Rs 150 crore National GLOF Risk Mitigation Programme. So far, 189 high-risk glacial lakes have been identified for risk reduction.
The Sikkim government has launched high-altitude expeditions this year to assess lakes like Khangchung Chho, Gurudongmar Lakes A, B, and C, and Shako lakes. Khangchung Chho, located at 5,320 meters, has a surface area of 183 hectares and an estimated volume of 106 million cubic meters.
