Lhonak lake disaster: A deluge of unanswered questions

There are 9,575 glaciers in the Indian section of the Himalayas. Satellite data shows that most of these glaciers are in retreat, having lost 13 per cent of their glacial area between 1960 and 2000. What is of great concern is that this glacial meltdown has resulted in the creation of over 500 lakes that are dammed by loose debris known as moraine.

Many of these lakes are ticking time bombs that can, and have, burst their banks at the slightest trigger. On 13 June 2013, the Chorabari glacial lake (situated at the base of the Chorabari glacier, above Kedarnath town) burst its banks owing to heavy rainfall, resulting in the horrific Kedarnath tragedy where several towns were wiped out and over 6,000 people died.

On 7 February 2021, heavy rainfall over the Nanda Devi glacier precipitated another glacial lake outburst flood (GLOF) — this time in the Rishiganga and Dhauliganga rivers, both tributaries of the Alakananda.

The massive overflow resulted in the complete destruction of the Rishiganga power project at Chamoli and the partial destruction of the Vishnugad-Tapovan power project. Over 200 workers were reported dead, though the number of actual deaths was probably higher.

On 3 October 2023, disaster struck Sikkim when the Lhonak glacial lake, located at 5,200 feet above sea level, broke its moraine banks and surged forward into the Teesta river in Lachen.

The torrent was so turbulent it took a mere 10 minutes to destroy India’s second-largest run-of-the-river hydropower project — the 1,200 MW Teesta-III dam in Chungthang. An exceptionally heavy monsoon, with intense rainfall at the end of September and early October, caused the floods that swept away bridges, roads, houses and army barracks.

Over 100 people are reported dead, with a large number of people still missing.

Could this tragedy have been prevented? Why do these disasters recur despite timely warnings from scientists? Isn’t it high time the government brought out a white paper to address a deluge of unanswered questions?

The earliest warning on Lhonak lake was given way back in 2001 and was highlighted in the Sikkim Human Development Report.

Glaciologist Prof Anil Kulkarni at the Divecha Centre for Climate Change in Bengaluru says, “Periodic warnings about this overflow were given to the government for over two decades. In 2015, I carried out a detailed investigation on the potential for flash floods at Lhonak lake.

“I had predicted then that a disaster could take place at any time, due to cloudbursts or flash floods. It is for this reason that I had suggested we create an outlay where excess water could be directed to smaller dams in order to prevent a massive overflow of water from here. It would have cost less than Rs 50 crore.”

A drop in the ocean, compared to the current loss, “which is running into thousands of crores”.

Kulkarni goes on to add, “In 2021, we did a detailed flood simulation which showed that in case of a flood, the town of Chungthang would be badly affected. We also warned that the Teesta-III dam was at high risk. No action was taken. All I can say is that one is left feeling very helpless because our recommendations went unheeded.”

The other question glaciologists and agencies that monitor glacial lakes are asking is, why no early warning systems were put in place, given the importance of the Teesta-III hydropower project, which supplied electricity to practically the whole of northern Sikkim.

Scientists and government authorities were working on providing an early warning system for glacial floods. Weather instruments and a camera to monitor the water level in the Lhonak lake had been put in place last month, but the installation of the trip wire system was planned for end-October.

Had it been placed earlier, residents would have been warned 90 minutes prior to the actual disaster, ample time for the hydropower station to open its gates and save the dam.

SANDRP (South Asia Network on Dams, Rivers and People) has questioned why senior officials of the Central Water Commission (CWC), which monitors the inflows and outflows of water in these regions, did not play a more proactive role in helping prevent this disaster.

The CWC’s monitoring station at Sankalang showed a water level surge of 19 m above maximum water level at 1.30 am on 4 October 2023. However, the hydrograph of Sankalang station downloaded from the CWC website on 5 October shows no reading after 10.00 pm on 3 October 2023.

“Why did the CWC flood forecasting site not have more data on the floods and why should officials of CWC not be held responsible for disregarding the inputs of scientists who had warned of a GLOF-like scenario?” asked SANDRP activists.

Of the 18 flood monitoring stations on the Teesta river — of which six are in West Bengal — only two of the 12 stations in Sikkim were functioning.

Had the Lachen monitoring site been operative, it could have issued a forewarning of the flood travelling from south Lhonak lake to Chungthang, provided a precious 10 to 20-minute window that would have helped empty the Teesta-III dam, open the spillway gates, save the dam and reduce the disaster that occurred downstream.

In March 2023, a parliamentary committee report had raised serious questions about the severe shortage of meteorological and monitoring stations in the Himalayan regions. There are 14 potentially high-risk lakes in this north-eastern region, where similar disasters could be triggered. The government needs to immediately devise early warning systems as well as build smaller dams around the lakes so their overflow can be siphoned off.

Dr Kalachand Sain, director of the Wadia Institute of Himalayan Geology in Uttarakhand, warns that there are 350 moraine lakes, of which 47 pose a serious threat. These lakes are located across the north-eastern states, Jammu & Kashmir, Himachal Pradesh and Uttarakhand.

The glacial lakes located around the Dhauliganga and Rishiganga rivers are also at risk and can be breached anytime, he says, adding that “They need real time monitoring.”

Prof Anil Kulkarni points out that the Gephang Gath lake in Himachal Pradesh has been growing at an unprecedented rate and is at high risk of breaking its banks and causing a flash flood not only because of its size but also due to the local topography.

“Gephang is in a similar situation as Lhonak and needs careful monitoring and timely mitigation efforts. As a first step, its water levels need to be brought down through controlled breaching, construction of an outlet from which water can be siphoned out. As has happened in Sikkim, the biggest threat is to the public and infrastructure located downstream,” he said.

NGOs like Affected Citizens of Teesta (ACT) describe the Lhonak lake disaster as “a State-sponsored disaster”. They question the systemic response by the government as baffling, given the late arrival of the NDRF (National Disaster Response Force) teams after the Lhonak lake had been breached.

ACT has been advocating against large dams and the huge concretisation of our rivers for the last decade. “The mindless concretisation of Teesta in the last 10 years and the continued negligence of social and environmental laws serves as proof that these disasters are state-led development disasters.”

They have every reason to see Sikkim’s tragedy as another deep wound on the communities living in the Himalayas. These are all-too painful reminders of the reason why locals oppose destructive developmental models, speaking out forcefully against building hydropower stations at such heights.

Climate change is affecting the mountains more visibly and much faster than it is the plains, and the higher the mountains, the greater the impact.

Will the activists’ plea that the scientific community be consulted and taken seriously be heeded? Will it take another catastrophe to make governments see the sense in issuing a blanket ban against the construction of such high-altitude hydro projects?