In an unusually discordant move, the president of the Bharatiya Janata Party’s Sikkim cadre wrote a letter to the Prime Minister on February 2 urging the Centre to withhold its approval to rebuild the Teesta III Hydro Electric Project dam, which was destroyed in a deluge over a year ago and the effects of which continue to be felt in the state.
“The people of Sikkim deeply value your commitment to environmental conservation and disaster resilience. The Teesta river is the lifeline of Sikkim, and any decision regarding hydropower infrastructure must be based on the scientific data, risk assessments, and inclusive public participation,” reads the letter, signed by state party president DR Thapa.
The letter’s urgency was brought on by the fact that only a few weeks prior, a centrally-appointed Expert Appraisal Committee approved plans to rebuild the dam just 14 months after it was swept away. The final approval is granted by the Union environment ministry, generally on the recommendation of the Expert Appraisal Committee.
In October 2023, a glacial lake outburst flood, or GLOF, originating from the South Lhonak glacial lake destroyed the 1200-megawatt Teesta III Hydro Electric Project in minutes, killing 55 people along the way and displacing 7,025 others. The destruction was described as one of the worst disasters the Himalayan state had ever seen and spotlighted the need to account for the region’s fragile ecology.
Both environmental experts and opposition parties in the state have raised concerns about the project’s renewed approval for clearance. A study published in the journal Science warned that the region remains highly susceptible to GLOF events and that the 2023 disaster “prompts urgent reflection on the role of climate change and human activities in exacerbating such disasters”.
The BJP Sikkim cadre letter demanded that approval be withheld until further studies on the dam’s Probable Maximum Flood limits are completed. It also demanded a new Environmental Impact Assessment with “recent climate data, GLOF risks, and Sikkim’s evolving ecological challenges,” as well as fresh public hearings to “uphold the principles of democratic participation…in this crucial decision”.
Opposition parties in the state such as the Sikkim Democratic Front and the Citizen’s Action Party echo these demands too and challenge the “hasty clearance”, to the project. The ruling Sikkim Krantikari Morcha, which had sold the government’s majority stake in the company operating the Teesta III HEP, has so far remained silent on the matter.
Dam acquisition and clearance
In February 2024, four months after the glacial lake outburst flood destroyed the Teesta III HEP, the Sikkim cabinet decided to sell the entirety of the state government’s 60.08% stake in Sikkim Urja Limited – the company operating the dam – to Greenko, a fast-growing renewable energy company based in Andhra Pradesh. At the time, the chief minister had justified the sale, saying it would transfer the dam’s liabilities and loans to the company and save the state from bearing losses made worse by the flood.
The transition was approved by the Competition Commission of India in May 2024. In the state, however, the Opposition cried foul over the nature of the sale, which did not include public consultations, independent scrutiny, or discussion in the state assembly. “The government’s decision to sell its equity appears arbitrary and lacks transparency. We have demanded a white paper on the acquisition,” Passang Sherpa, Sikkim’s BJP spokesperson, told Mongabay India.
Mongabay India sent queries about the acquisition to a Greenko spokesperson, but no response was received at the time of publishing this story.
In November 2024, Sikkim Urja Limited submitted its proposal to rebuild the dam to the Union environment ministry, which referred the project to the Expert Appraisal Committee. “Other than the dam, most of the components can be restored in a year’s time. As most of the components would be ready in a year, there is a case for restoring the dam and bringing back the project in operation at the earliest,” Sikkim Urja Limited told the Expert Appraisal Committee.
The revised proposal includes an upgraded design to a sturdier concrete gravity dam in place of the concrete-faced rockfill dam which could not withstand the flood. The new design also proposes increasing the dam’s spillway capacity from 7,000 cumecs to 19,946 cumecs. Sikkim Urja Limited said the revised spillway capacity was based on assessments taking into account Probable Maximum Flood levels (7,000 cumecs) as well as GLOF possibilities (12,946 cumecs) but did not provide details about how the assessments were done, and by whom.
“Calculating the PMF [Probable Maximum Flood] is essential to determine a dam’s spillway capacity, which in turn affects dam safety. The PMF is calculated using rainfall data to make accurate projections about floods,” explained Himanshu Thakkar, coordinator of South Asia Network on Dams, Rivers and People (SANDRP).
Initially, the Expert Appraisal Committee “expressed serious concerns regarding the dam’s design and stability”, and constituted a sub-committee to carry out field visits to inspect the project site. Deliberations after the field visit revealed that the Central Water Commission, a technical expert body, had said a revised study on the Probable Maximum Flood (PMF) level needed to be done and subsequently approved by the CWC. “Further, design aspects of Dam and other components are yet to be approved by the Central Water Commission, Geological Survey of India and Central Soil and Materials Research Station,” the minutes of the meeting say.
The Expert Appraisal Committee approved the project for clearance despite these deficiencies on January 10, after three sittings. The committee also said a public hearing was not necessary since no additional land needed to be acquired for the dam. This, even though impacts of the GLOF went beyond the dam site in the Changthang region and were felt as far downstream as Bangladesh.
“In the revised plan, the PMF [Probable Maximum Flood] has stayed the same at 7,000 cumecs, which is a figure based on old data from 2006. Rainfall patterns have changed drastically in recent decades, and the PMF doesn’t appear to have taken this into account. This could have implications on dam safety,” said Thakkar. “It’s shocking the EAC [Expert Appraisal Committee] approved the project for clearance without asking for more details about the PMF assessment. Given the scale and history of this project, a fresh clearance, with fresh impact assessments and fresh public hearings should have happened.”
Hazards remain
Weeks after the decision of the Expert Appraisal Committee, a scientific analysis on the impacts of the GLOF event found that the area wasn’t entirely out of harm’s way.
On the intervening night of October 3-4, 2023, the collapse of South Lhonak’s lateral moraine (a ridge formed along the side of the glacier as it retreated) into the glacial lake caused a 20-meter-high tsunami which came cascading down the Teesta river.
The high velocity flood carried 270 million cubic metres of sediment along with it, magnifying impacts as it came crashing downstream. Deposits from the GLOF have since “raised the riverbed by several meters, heightening the risk of early onset of bank-full conditions during future floods, increasing the probability of flooding in adjacent floodplains, and exposing populations and infrastructure to greater risks,” says the study, published in the journal Science.
A series of complex interactions, including permafrost warming deep below the surface and glacier retreat, added to the hazard risk. The study also found that, despite the GLOF draining the South Lhonak glacial lake of 50 million cubic metres of water, it still “remains highly susceptible to future GLOF events, including repeat triggers from northern lateral moraine failures.”
“The breach of the South Lhonak glacial lake was triggered by the collapse of the lateral moraine. As long as it remains unstable, the potential of another collapse cannot be ruled out. It needs to be monitored,” Ashim Sattar, lead author of the study, told Mongabay India.
In its presentation to the Expert Appraisal Committee, Sikkim Urja Limited said it carried out a “criticality analysis” to determine adequate spillway capacity, and identified 13 high risk glacial lakes whose breach could cause a GLOF. A simultaneous breach by two lakes was modelled to have an outflow of 12,946 cumecs, which was added to the Probable Maximum Flood (PMF) level to come up with a revised spillway capacity of 19,946 cumecs. However, no documents of the studies or details about how the analysis was done were made available. There was also no mention of the impacts of increased sediment along the riverbed.
“If the spillway capacity for the Teesta III HEP is nearly 20,000 cumecs, that means the spillway capacities for dams further downstream, like the Teesta V and Teesta VI, must be enhanced too, so they can also withstand GLOF like events,” said Thakkar.
According to Sattar, their study demonstrates the shortcomings in current modelled hazard assessments. “From the transportation of sediments to the permafrost warming conditions that contributed to moraine’s collapse, to the meteorological conditions at that time – all these factors can be made part of future hazard assessments, so the results are precise and help mitigate disasters.”
This article was first published on Mongabay.
