As parts of the dam washed away due to glacial lake outburst, it reportedly released an alarming 5.08 million cubic metres of water from its reservoir
Photo: X (formerly Twitter) @ Prem Singh Tamang (Golay)
A devastating glacial lake outburst triggered flash floods in north Sikkim’s Mangan district on October 4, 2023. The burst also led to the breach of Sikkim’s Chungthang dam (Teesta 3 HEP), the biggest hydropower project in the state.
As parts of the dam washed away, it reportedly released an alarming 5.08 million cubic metres of water from its reservoir. Visuals from the state showed a large part of the dam wall missing and water rushing down the mountains.
The dam is part of the 1,200 megawatts (MW) Teesta Stage III Hydro Electric Project. The dam breach in the Himalayan state has raised serious concerns about a deluge in the downstream areas.
Hydropower projects are mushrooming in the Himalayan region. As of September 2023, the 10 states and two Union Territories in the region had 81 large hydropower projects (above 25 MW), 32 projects under execution and another 320 large projects in the pipeline, according to the Central Electricity Authority under the Union Ministry of Power.
Five of these 32 under-execution projects are in Sikkim.
The Himalayan region is part of a seismically active zone and the breach on the Chungthang hydro dam once again reminds of the importance of reviewing such large hydro projects in the region.
Government estimates show that the Himalayas, with an installed capacity of 46,850 MW, have the potential to generate 115,550 MW.
Even after the enactment of the Dam Safety Act 2021, which aims to prevent dam failure-related disasters through regular surveillance, inspection, operation and maintenance, disasters linked to hydropower projects in the Himalayan region have become more frequent.
Recently, a series of disasters have marred construction works at the 2,000 MW Lower Subansiri Hydro Electric Project in Arunachal Pradesh, whose waters have the country’s highest hydropower potential (34 per cent), according to the India Hydropower Policy 2008.
This project, being built by public-sector undertaking National Hydro Power Corporation, is the country’s largest run-of-the-river hydropower project under construction. In 2022, following heavy rains in June, water overflowed from the dam and inundated about 100 villages in the downstream state Assam.
A compilation report by South Asia Network on Dams, Rivers and People in 2022 showed that hydropower projects act as force multipliers when disasters like cloud bursts happen close to them.
In 2021, at least 11 hydropower projects (four each in Uttarakhand and Himachal, two in Jammu and Kashmir and one in Ladakh) had faced cloud burst-induced deluge and damages in lesser or greater degrees.
Most of the existing or under-construction projects in the Himalayas were envisaged 10-15 years ago and there is a dire need to revaluate them based on current scientific data.
Experts have time and again called for slope stability maps to be created by project developers. This map will identify vulnerable portions and demarcate the reservoir area.
Meanwhile, India has over 5,000 dams and 234 of these are more than 100 years old (constructed in or before 1922).
By the government’s own admission, dams in India are normally designed for approximately 100 years of useful age. The functional life of the dams gets decreased with progressive reservoir sedimentation, concurrently reducing project’s benefits.
However, there is no mechanism to assess the viable lifespan and performance of these dams, the government mentioned in a response to a parliamentary standing committee on water resources, tabled in the Lok Sabha on March 17, 2023.
“However, no information / recommendation from the dam owners has been submitted for de-commissioning of any of their dams,” it said.
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