No early warning system and insufficient dam safety turned Sikkim flood deadly

  • A glacial lake outburst flood at South Lhonak lake and the failure of the Teesta III Hydroelectric Project together killed at least 30 people and damaged over a thousand homes in Sikkim.
  • Scientists say the risk of GLOFs occurring in Sikkim is well known, but mitigative action hasn’t been consistent.
  • The Affected Citizens of Teesta, an organisation advocating for environmental protection, says that questions raised about the Teesta III’s inability to handle a GLOF situation were ignored by authorities.

Every year, September 18 is observed as a day of disaster risk reduction in Sikkim, in remembrance of the 6.9 magnitude earthquake that shook the state in 2011. This year was no different, with a focus on preparedness should a flood come cascading down the mighty Teesta river. And yet, when a few weeks later it did, the state and dam authorities did not anticipate the scale of the disaster – among the worst flood events to have ever taken place since 1968 – proving its preparedness efforts to be too incremental.

In the early hours of October 4, the glacier-fed South Lhonak Lake in North Sikkim breached, causing a Glacial Lake Outburst Flood (GLOF) that destroyed the state’s largest hydropower plant and left at least 35 people dead and around 104 missing as on October 9.  “Even though we’ve studied the possibility of this occurring, I was numb with shock when I first heard the news,” said Ashim Sattar, a researcher with the Divecha Centre for Climate Change at the Indian Institute of Science, Bengaluru, who projected a GLOF would occur at the lake in a 2021 modeling study.

Scientists and citizens affected by the damming of the Teesta river have warned about the dangers of a GLOF event since 2005. The state and central governments have been aware of the risks and made piecemeal attempts to mitigate the threat of a flood in the past. But authorities were not immediately alerted that the lake had breached on October 4 because there was no Early Warning System (EWS) installed at the lake. The Indo Tibetan Border Police, which has a presence along the river’s course, sounded the alarm first which initiated evacuation efforts downstream, where the 1200 megawatt Teesta III Hydroelectric Project was located.

The Teesta III HEP’s reservoir was reportedly full when the flood hit, magnifying impacts as the water from the lake came gushing down. Questions are now being raised about the neglect by dam authorities and the state and central governments to ensure adequate dam safety measures were in place, which would have cushioned the blow of the floods’s impacts. Damages were recorded in four districts, sweeping away 13 bridges and affecting over 60,000 people in total.

After South Lhonak lake breached, it destroyed Sikkim’s largest hydropower plant, the Teesta III Hydroelectric Project, located downstream. Map from Google Earth Pro.

The Affected Citizens of Teesta (ACT), an organisation of indigenous peoples advocating for environmental protection in the state, said the destruction of the Rs. 14,000 crore dam would further push Sikkim into indebtedness. “ACT condemns the project authority, the Teesta Urja Limited and the private financiers seeking profits for ignoring the environment, social concerns and disaster risks potential raised by affected communities and environmentalists,” they said in a statement on October 7.

GLOF events are set to become more common, particularly in Himalayan states like Sikkim that are vulnerable to the effects of global warming. A second glacial lake, Shako Cho in northern Sikkim, was on high alert and nearby villages evacuated just a day after the flood, due to fears that it, too, would breach.

The Sikkim government has nurtured large-scale hydroelectric generation since the 1990s, and it has grown to become a steady revenue stream for the state.  The Central Water Commission estimates the state’s hydro power potential to be around 8000 MW, of which over 5,284 MW had awarded to developers as of 2018. But experts that Mongabay India spoke to state the state’s hydroelectric ambitions need to be tempered in light of its fragile ecology, which hosts 644 glacial lakes.

Flood preceded installation of early warning

On September 8, almost a month before the flash floods, the Sikkim State Disaster Management Authority (SSDMA) organised a “pre-expedition” workshop, where scientists with the Swiss Agency for Development and Cooperation (SDC) handed over two monitoring stations to the government in order to “establish the monitoring stations, develop a prototype Early Warning System, assess the hazards and dangers related to GLOFs, and make decisions regarding appropriate mitigating measures.”

The expedition was a 10-day trip to South Lhonak and Shako Cho lakes with around 30 experts from Indian and Swiss agencies, intended to install the devices. But the EWS systems were not fully installed. “We were in discussions with the SDC about how to set up a sustainable monitoring system, given the terrain and past attempts. The plan was to stabilise the system in one lake before installing it in the other,” said Vinod Sharma, vice chairman of the Sikkim State Disaster Management Authority. But the deluge arrived before the EWS system started functioning.

Glaciologist Anil Kulkarni said it was “deeply disappointing” that efforts to install EWS had not been consistent. In 2015, Kulkarni chaired a committee investigating the possibility of a GLOF at South Lhonak lake. The committee recommended setting up EWS and preparing a map with vulnerable locations “that may get inundated due to extreme GLOF event” in order to plan evacuation and mitigation efforts.

A second suggestion, made by the committee, was to use engineering techniques to reduce the load of the lake. In 2016, the Sikkim government teamed up with the Students’ Educational and Cultural Movement of Ladakh (SECMOL), led by scientist and inventor Sonam Wangchuk, to “siphon” water away from the lake in 2016. Reducing the height of the lake by siphoning water away reduces its volume and can act as a mitigative measure because there’s less pressure in the event of a breach. Water was drawn from pipes and a sensor to monitor the lake’s water levels installed, but the system did not last. “We had only set up a prototype sample, which we proposed to be scaled up to roughly eight systems. We couldn’t do all eight because it was very difficult physically,” Wangchuk told Mongabay India.

Rescue efforts underway in Sikkim. Photo by Press Information Bureau, Government of India.

According to Sharma of the SSDMA, two more siphoning efforts were made to lower the height of the lake but did not endure on account of the harsh terrain. “Wind velocity is so high, sensors were destabilised, other times the pipes were washed away. It’s a difficult task at 18,000 feet. Expeditions like this are also extremely expensive, costing crores of rupees, which is expensive for a state like ours where funding is a constraint,” he said.

The National Disaster Management Authority, in a statement on October 4, said it would “expedite” the deployment of EWS at at-risk glacial lakes across India in light of the Sikkim disaster.

Spillways and dam construction added to hazard

Two years before it became commercially operational, a 2015 study by the Central Water Commission said that dams along the Teesta – including the 1200 MW Teesta III HEP – were vulnerable to GLOF events. Activists say aspects of the dam’s vulnerability have been known much before – since 2005 – and systematically ignored or overlooked by the government and the erstwhile Teesta Urja Limited (now Sikkim Urja Limited), the company that owns the dam.

The Affected Citizens of Teesta wrote in their recent statement that WAPCOS, the consulting company that conducted the Environmental Impact Assessment of the plant, had acknowledged the risk of GLOFs on the dam in a meeting in 2005, but that it “deliberately or otherwise, chose not to assess the risk of GLOFs at all in the Environmental Impact Assessment it was parallelly working on specifically for the 1200 MW Teesta III project. Nor did the Ministry of Environment, Forests, and Climate Change insist on such a study being done.”

The ACT had also approached the then National Environmental Appellate Authority about their concerns, but their petition was ultimately dismissed. “In the counter-affidavits by MoEFCC and the company, not a single line was written about the threat of GLOFs we had raised. The Appellate Authority dismissed our appeal. Not a single line was written about the threat of GLOFs…in the Appellate Authority order of July 2007,” they said in their statement.

Experts also say the dam was not designed to withstand a GLOF-like event – evidenced by the fact that it was reportedly swept away within 10 minutes of the flood hitting. “The Teesta III project is a rock filled concrete dam, which is structurally more vulnerable to flooding compared to a concrete dam,” said Himanshu Thakkar, convener of the South Asia Network on Dams, Rivers and People (SANDRP). “The Teesta V dam, which is further downstream, was able to survive the deluge partly because it’s a concrete dam and sturdier.”

Public records show that in 2008, Teesta Urja Limited made changes to the design of the Teesta III dam without seeking prior permission. The Central Electricity Authority (CEA), after a field visit, cautioned that some of those changes had the potential to endanger the safety of the dam. The CEA’s observations are noted in the minutes of a meeting by the Expert Appraisal Committee of the River Valley and Hydroelectric Projects in Sikkim in 2009.

“The CEA found that the company planned to reduce the dam’s spillway capacity from 7000 cumecs to 3000 cumecs. A spillway capacity of 7000 cumecs is itself a conservative figure, based on a probable maximum flood due to rainfall and not accounting for a GLOF event, even though the risk of one occurring was well known,” said Neeraj Vagholikar, member of environmental NGO Kalpavriksh who brought the CEA’s observations to the notice of the Expert Appraisal Committee on river valley and hydroelectric projects of the Environment Ministry. “The government accepted some of the design changes, but rejected the proposal to reduce the spillway capacity further.”

The spillway is one of the most important safety features of a dam, because it controls the release of water from the reservoir.

Teesta running through Mangan district in Sikkim, which bore the brunt of the destruction. Photo by Pratap Chakma/Wikimedia Commons.

Both Thakkar and Vagholikar say that the spillway capacity was too insufficient to withstand the force of the October 4 flood. “But had an EWS been in place, dam authorities would have had sufficient time to drain the water from the reservoir, which would have reduced impacts downstream,” said Thakkar. In a recent interview with the publication, Hindustan Times, Teesta Urja Limited’s CEO said the spillway gates could not be opened in time. An investigation is on to determine why the spillway gates could not be opened in time.

Kulkarni is of the view that large infrastructural projects located in fragile ecosystems like the Himalayas must undertake a separate climate impact assessment, apart from the already mandatory environmental impact assessment. “The problem is that the Environmental Impact Assessment process doesn’t always factor in impacts in a changing environment. Governments should insist on climate impact assessments which include modeling studies, so tragedies like this can be avoided,” he said.

Read more: [Explainer] What is a GLOF and how does it affect the Himalayas?

Banner image: Rescue efforts in the aftermath of the GLOF event in Sikkim on October 4. Photo by Press Information Bureau, Government of India.

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