New Delhi: Almost a year after the bursting of a glacial lake in North Sikkim caused devastating floods that killed 50 people, damaged infrastructure worth thousands of crores and washed away the 60-metre high Chungthang dam, a report by a high-level government panel—that concluded the extreme flood event last October was caused by a glacial lake outburst flood (GLOF)—has become a bone of contention between the Ministry of Jal Shakti, National Dam Safety Authority (NDSA) and the Sikkim government, ThePrint has learnt.
The Sikkim government has contested the findings of the 10-member committee constituted last November by the NDSA, which comes under the Ministry of Jal Shakti, and said that the 3 October incident was not caused by GLOF but a “cloudburst”.
The committee, headed by former Central Water Commission (CWC) chairman R.K. Jain was mandated to examine the causes leading to the bursting of South Lhonak Lake and consequent failure of Teesta-III Chungthang dam and damages to other downstream dams, and submitted its report to the ministry in June 2024. But the ministry is yet to accept the report and make its findings public.
The reason, according to three senior central government officials, who spoke to ThePrint on condition of anonymity, is because the Prem Singh Tamang-led Sikkim government has made multiple representations to the Jal Shakti Ministry, claiming that their observations based on data show last October’s flood was a result of “cloudburst”. The latest representation from the state government was sent to the ministry on 4 September, one of the officials said.
In the aftermath of the disaster, senior state government officials, including chief secretary V.B. Pathak had in media briefings said that India Meteorological Department (IMD) data does not support a cloudburst as a probable cause. But the state government soon changed their stand, notifying the incident as a cloudburst.
The central government officials quoted earlier said there is a reason the Sikkim government is pushing for the disaster to be considered a cloudburst by the Jal Shakti ministry.
Among the infrastructure that got damaged in the flood that originated in the South Lhonak Lake on 3 October, 2023, was the 1,200 MW Teesta Stage-III Hydro Power Project, built at a cost of approximately Rs 14,000 crore. While the power station got submerged, the 60-metre high Chungthang dam was completely washed away.
Though the dam, built and run by Sikkim Urja Limited, is fully insured by a consortium of insurers led by IFFCO-Tokio General Insurance (the total sum assured is to the tune of Rs 11,400 crore), there’s a catch. While there is a 100 percent coverage of the sum assured for losses resulting from flash floods or cloudburst-induced floods, the coverage for damages by GLOF is capped at Rs 500 crore, a senior Sikkim government official told ThePrint.
Two of the central government officials also told ThePrint that the Sikkim government’s insistence that it was not GLOF could be on account of this particular clause that will restrict the insurance claim to Rs 500 crore.
“Sikkim Urja Limited (SUL) has filed an insurance claim of over Rs 2,500 crore. But if the heavy floods were caused by GLOF and not cloudburst, SUL could get only upto Rs 500 crore,” explained a Sikkim government official who wished to not be named.
The state government had a 60.08 percent stake in Sikkim Urja through its investment company, Sikkim Power Investment Corporation Limited (SPICL). On 2 February, 2024, the Sikkim cabinet, in a controversial move, decided to divest the entire 60.08 percent stake of SPICL to Greenko Energies Private Limited, part of the Greenko Energy Holdings.
But that will not affect the insurance clause, a second Sikkim government official added.
ThePrint reached V.B. Pathak, Sikkim Chief Secretary, via calls and messages. This report will be updated if and when a response is received.
A senior Jal Shakti Ministry official confirmed that the Sikkim government has written to them on this matter. “The State Dam Safety Organisation has submitted a representation, which is being considered. The ministry will finalise the committee’s report after that.”
Tamang’s Sikkim Krantikari Morcha, which won 31 of the 32 assembly seats in June in the strategic Himalayan state and formed the government, is an ally of the ruling BJP-led National Democratic Alliance at the Centre.
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All signs point to GLOF, says central committee
The central committee—formed on 20 November, 2024, and comprising senior officials from NDSA, Central Water Commission, Geological Survey of India, National Remote Sensing Centre (NRSC), and Central Electricity Authority of India—has, in its report, said that all scientific data and satellite images from that period points to GLOF and not a cloudburst.
Durga Kamla Rai, Chairman, Sikkim State Dam Safety Organisation (SDSO) is also part of the committee.
In its report, the committee said that it found the disaster was a GLOF event after it went through all relevant data, including from the IMD and the NRSC. The report, which ThePrint has seen, said that rainfall data from IMD during that period does not show heavy rainfall in the higher reaches of south Lhonak lake.
A senior official in the Jal Shakti ministry said that in scientific parlance, a cloudburst is defined as one where more than 100 mm rainfall occurs in one hour.
“Cloudburst happens when there is a very intense spell of rain in a small area and over a small period of time,” the official said, adding that IMD data shows that heavy rainfall never occurs in the higher reaches of the Himalayas. “…Heavy precipitation is only in the form of snowfall. There will never be heavy rainfall. That is why it’s a GLOF event,” the official said.
The committee members visited Sikkim—including Chungthang, where the dam was located—in February-March this year for a week. The report states that according to available scientific data, the total volume of water that was released on the night of 3 October from the south Lhonak lake was 40 million cubic metre (mcm). Due to an unprecedented volume of water, high waves were generated, leading to the breach of the moraine dam—a structure of unconsolidated boulders, sediments, debris, and ice. The moraine had fallen and pushed into the deepest portion of the lake, resulting in overflow of a large volume of water from the outlet.
The Teesta-III project’s Chungthang dam’s volume was around 5 mcm. This means that eight times more water than the installed capacity of the Chungthang dam was released on that fateful night, the report said.
According to the report, because of this sudden high discharge, there was approximately 10,000 cubic metre per second inflow of water from the South Lhonak Lake—much higher than the 7,500 cubic metre per second capacity of the dam’s spillway. The volume of water discharged from South Lhonak Lake was so huge that it toppled the Chungthang dam. The water flowed 7-8 metre over the top of the dam, the report said, adding that it was “inevitable” that the dam would break away.
The committee, however, added that if an Early Warning System (EWS) was installed and operational, the loss of lives could have been minimised. It also observed that “had it been a concrete dam, it would have survived”. Chungthang was a concrete faced rock-fill dam. It has recommended that in future, concrete dams should be considered in the area.
The dam at the Teesta-V hydropower project survived because it was a concrete dam. The dam was partially damaged in the disaster.
Besides the Teesta-III project, the committee also examined the damages suffered by NHPC’s 510 MW Teesta-V and an independent power producer’s 96 MW Dikchu project. Five spillways of Teesta-V also got washed away in the flood.
What Sikkim govt is saying
However, the Sikkim government in its representation has said that the report of the central committee is “based upon the hypothesis that the event was a GLOF event and then interpreting data to align with this conclusion”.
The state government further states that the Sikkim Disaster Management Authority (SDMA) had notified the 3 October, 2023, event as “cloudburst” and the matter of damage due to flash floods was taken suo moto cognizance by the National Green Tribunal on 26 October. The Sikkim government is a respondent in the case and they have submitted an affidavit on the causes of the incident.
Citing the report of North Eastern Space Applications Centre, the Sikkim government has said that it is indicative of a cloudburst event or, at least, more than usual heavy rainfall in the region preceding the incident.
Prabhakar Rai, Sikkim SDMA Director, told ThePrint, “Both the SDMA and state government’s presumption is that it was a flash flood induced by heavy rain and landslide.”
In its representation, the Sikkim government has said that the event (extreme flood) appears to have resulted from a confluence of factors—”significant rainfall leading to avalanches and secondary flooding, formation of temporary hydraulic blockages along the downstream flood wave path created by sudden debris accumulation, which caused localised water retention and increased flow volume”.
The SDSO chairman Durga Kamla Rai has also submitted his comments to the Jal Shakti Ministry, where he said that intense precipitation in the catchment or tributary led to water accumulation.
ThePrint reached via calls. This report will be updated if and when a response is received.
“The cumulative effect of these factors resulted in a flood event of unprecedented magnitude, surpassing the discharge capacity of the dams and spillways. These analyses highlight that flooding was due to complex interplay of multiple hydrological and geomorphological patterns rather than a single event,” Rai, who was also a member of the central committee, said in his comments.
Rai added that an “orange alert” was issued by IMD on 3 and 4 October and satellite imagery and input from local residents confirm the presence of two glaciers on the northern side of the south Lhonak lake. “Between these glaciers, avalanches frequently descend into the lake. This kind of avalanche activity, observed over a prolonged period indicates that it’s a long-standing natural process rather than recent development,” the state government has said.
The state government has said that before reaching any conclusion about the causes of the flash flood, a comprehensive field investigation should be conducted.
“The report should only be finalised after completing a current bathymetric survey (measuring the depth of the lake and volume of the lake using sonar) of the lake and a thorough study of the breached areas capacity. The impact of the Nepal earthquake and the heavy rainfall in the areas should also be duly evaluated,” the representation states.
It adds that an in-depth analysis of the river’s geomorphology is necessary, including any temporary hydraulic blockages along the downstream floodway path that could have caused localised water retention and increased the volume.
(Edited by Zinnia Ray Chaudhuri)
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