A glacial lake outburst flood (GLOF) in Bhutan has prompted flood alerts across parts of West Bengal and Assam, with the Central Water Commission (CWC) warning of a possible sudden rise in water levels along the Sankosh River system. The advisory, issued on October 29, 2026, identified Alipurduar in West Bengal and Dhubri in Assam as vulnerable districts, urging local administrations to monitor river conditions and take precautionary measures.
The incident was reported at Shintaphu Lake in Bhutan's Gasa district. According to the CWC, information about the outburst was received from the Indian Embassy in Bhutan. The resulting flash flood in the upper reaches of the Punatsangchhu River, which enters India as the Sankosh, was expected to reach the international border within six to eight hours of the advisory.
How The Outburst Triggered Downstream Flood Alerts
Shintaphu Lake, also spelt Sintaphu, is located near Wakila Mountain in the Lungo area of Bhutan's Laya Gewog, in Gasa district. According to estimates cited by the International Centre for Integrated Mountain Development (ICIMOD), the lake held approximately six to seven million cubic metres of water before the breach. The actual volume released during the outburst is still being assessed. The floodwaters travelled through the Mo Chhu river system, which joins the Pho Chhu at Punakha to form the Punatsangchhu. The river flows into India as the Sankosh, making downstream settlements in North Bengal and western Assam vulnerable to a sudden surge.
Evacuations And Emergency Measures In India
In West Bengal, the Alipurduar district administration moved thousands of residents living along the Sankosh to safer locations. Around 10,000 people from vulnerable settlements, including Kumargram tea estate, Kumargram forest village, Pakriguri and Bholka, reportedly took shelter in temporary relief centres. Eighteen shelters were opened in the Kumargramduar block, with food, drinking water and other essential supplies arranged for evacuees. National Disaster Response Force (NDRF) and State Disaster Response Force (SDRF) teams were also mobilised.
In Assam, Chief Minister Himanta Biswa Sarma said that authorities were monitoring vulnerable areas in Dhubri and Kokrajhar districts. Rescue and evacuation teams were kept on standby, while residents were advised to follow official instructions and avoid riverbanks.
Floodwaters Recede, But Bhutan Faces Secondary Risks
By the afternoon of October 30, the immediate flood threat in parts of North Bengal had eased. The Sankosh had risen approximately 1.5 metres above its normal level before beginning to recede. No major damage or casualties were reported in the affected Indian areas, and residents began returning home. Bhutan, however, reported considerable infrastructure damage. The flood swept away facilities at the Gasa Tshachu natural hot springs, damaged sections of the Punakha-Gasa highway and affected bridges and roads leading to the remote village of Laya. No casualties were reported, as the affected area had been evacuated before the floodwaters arrived.
A further concern emerged after Bhutan's National Centre for Hydrology and Meteorology (NCHM) reported the formation of a temporary lake at Taktsemakhang, near the confluence of Sintaphu Chhu and Lungu Chhu. Authorities are monitoring the new water body for the possibility of another outburst and have advised residents in the Mochhu and Punatsangchhu valleys to stay away from riverbanks and low-lying areas.
A GLOF occurs when water stored in a glacial lake is suddenly released, often following the breach of a natural barrier made of ice, rock or accumulated glacial debris. Such events can generate powerful flash floods carrying water, sediment and debris over considerable distances. The Bhutan incident highlights how hazards originating in high-altitude Himalayan catchments can have consequences across international borders, making early-warning systems, river monitoring and coordination between neighbouring countries essential for downstream communities.
FAQs
1. Why did the CWC issue a flood advisory for West Bengal and Assam?
The Central Water Commission issued the advisory following a glacial lake outburst at Shintaphu Lake in Bhutan on October 29, 2026, which triggered concerns about rising water levels along the Sankosh River.
2. Which areas in India were placed under a flood alert?
Alipurduar district in West Bengal and Dhubri district in Assam were identified as vulnerable areas due to their proximity to the downstream Sankosh River system.
3. What is a Glacial Lake Outburst Flood (GLOF)?
A GLOF occurs when water accumulated in a glacial lake is suddenly released, often due to the breach of a natural barrier made of ice, rocks or glacial debris. It can cause sudden flooding downstream.
4. How did authorities respond to the flood warning?
Authorities in West Bengal evacuated residents from vulnerable settlements and opened temporary relief shelters. Assam placed disaster response teams on standby and monitored vulnerable riverbank communities.
5. Why does the Bhutan glacial lake outburst pose a risk beyond the immediate flood event?
The outburst led to the formation of a temporary lake at Taktsemakhang in Bhutan, raising concerns about a possible secondary flood event. Authorities continue to monitor the water body and downstream river valleys.
