Updated on Oct 10 at 8.10 p.m

Dr Navin Juyal, a former scientist at the Physical Research Laboratory (PRL), Ahmedabad, said, “The tragedy in Sikkim was not only due to flash floods, it was due to the Teesta hydro power project as it was not designed to accommodate or handle the extra water of the glacial lake.”

“In 2013, Lhonak lake in Sikkim’s Lhonak glacier was predicted to be unstable. But we never took cognisance of it. The hydro projects are being made only for carrying water and electricity but are not flood-friendly,” he said.

He expressed these views at a special lecture titled ‘Significance of geoscience and its societal implications in the Himalayan region’ at the Birbal Sahni Institute of Palaeosciences’s centre for promotion of geoheritage and geotourism (CPGG) on Oct 9.

Updated on Oct 7 at 9.10 a.m. 

On Oct 4, flash floods in Sikkim claimed 26 lives and left 142 missing, including 22 army personnel, according to the State Disaster Management Authority. 

On Oct 6, the Sikkim CM Prem Singh Tamang has said the Chungthang dam on Teesta River was washed away due to substandard construction. 

In an interview with a leading media house on Oct 6, Sikkim CM Prem Singh Tamang said that the construction of the dam, built by the previous government, was ‘substandard’, he further added that the dams built by NHPC (National Hydroelectric Power Corporation) have not been as damaged by the floods. 

He said that the GLOF from the South Lhonak Lake, and the subsequent demolition of the Teesta Dam brought the violent damage downstream. According to CM Tamang, 22,465 people have been affected, with 103 missing (as of Oct 6). 

2500 people have been evacuated from the flood-affected areas. The floods have washed out 13 bridges, and according to the CM Tamang, North Sikkim has completely been isolated because of the washouts.

From the 22 army personnel missing from Oct 4, seven have been declared dead, with 15 still missing.

The flash floods are believed to be the result of a Glacial Lake Outburst Flood (GLOF) at South Lhonak Lake, triggered by a cloud-burst, according to the Central Water Commission (CWC).

What happened on Oct 4? 

Shocking images showed the swift destruction of Teesta III, Sikkim's largest dam. A flood monitoring system failure possibly contributed to this catastrophe.

Amidst the flash floods, the videos showed the washing away of the 60-feet high dam on the Teesta River, Teesta III, the largest dam in the state with hydroelectric capacity of 1,200 MW.

The construction of the dam began in 2008 and concluded in 2017, costing a substantial amount of ₹14,000 cr.

A combination of factors had led to this infrastructural failure of the mammoth scale.

A flood-monitoring system failure?

A statement released on the cloudburst and flash-flooding of Sikkim by National Disaster Management Authority (NDMA) stated that on Oct 4 at 1.30 p.m. the water levels at Sankalang station showed the water level surge to 19 m, however, no readings can be seen on the CWC website on Oct 3 after 10 p.m.

According to reports, there is a flood monitoring site 20 km upstream the Teesta III dam. 

If proper monitoring had been carried out on Oct 3-4, the CWC might have been able to predict the impending disaster and subsequently alerted dam operators to initiate the opening of spillway gates, potentially preventing the catastrophic destruction of the dam.

On the other hand, the CWC’s forecasting website showed no reading on the website, which could have possibly prevented the massive failure of the dam, but also would have helped people in the path of the Teesta flash floods.

Destruction due to flash floods in Sikkim

Delhi-based advocacy group, SANDRP – South Asia Network on Dams, Rivers and People which is an informal network of organisations and individuals working on issues related to water, took to X with a detailed analysis.

Chungthang, located approximately 90 km north of Gangtok, reportedly faced significant infrastructure damage. The defence ministry reported that two bridges in North Sikkim were severely damaged.

The flooding of the Teesta River disrupted connectivity to Sikkim, including its capital, Gangtok, as parts of NH-10, the vital link to the rest of the country, were washed away by flash floods. 

The Indreni bridge in Singtam and a connecting bridge in the Balutar hamlet were both swept away around 4 a.m., according to the Gangtok District Administration.

A relief camp has been set up at Namphing Sai Mandir, where 500 people are accommodated. Permanent relief efforts are established at Pranami Mandir.

Pakyong district reported the highest number of casualties, with 7 deaths and 59 people missing, including 22 Army personnel. 

The ZEEMA-III and BSD Bridges have also been destroyed, as per reports.

In West Bengal, the Teesta River, carrying sludge from Sikkim, entered homes near the state border, particularly in the Teesta Bazaar area of Kalimpong district. 

The control room of the Teesta V dam near Dikchu suffered severe damage. Water release from Dikchu was delayed, occurring approx 1.5 hours after the lake burst at 12:40 a.m., say reports.

Further downstream, the Teesta River also reportedly washed away sections of NH-10 in Melli, a Sikkim-West Bengal border town, affecting Teesta Low Dam III and IV of NHPC in West Bengal. One bridge in this area was already washed away.

A danger that was always looming

In 2014, the US-based Pulitzer Center on Crisis Reporting, had published an article ‘Chungthang, Sikkim: A New Dam's Potential Impact’ raising concerns about glacial flooding, earthquake risks, and environmental impacts loom large, with the project’s consequences hitting the most vulnerable members of the community the hardest. 

A study conducted in 2021 by the researchers from Indian Institute of Technology, Roorkee, and the Indian Institute of Science, Bangalore stated that the need for a flood warning system becomes more imperative on the South Lhonak Lake, highlighting the growing hazard of GLOFs in remote mountain valleys.

The researchers specifically focused on South Lhonak Lake, and revealed that as the lake expands, it becomes increasingly susceptible to avalanche impacts, especially as it encroaches upon steep slopes, which are potential avalanche-prone areas.

South Lhonak Lake, situated at 5,200 metres above sea level in Sikkim’s northwestern region, is among the 14 potentially dangerous lakes prone to GLOFs. It has expanded significantly due to the melting of the Lhonak glacier, and the adjacent North Lhonak and main Lhonak glaciers contribute to its growth.

Glacier retreats have added to the lake’s size over the years significantly.

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