Bhutan glacial lake burst: Assam's Dhubri on alert over Sankosh surge

Assam's Dhubri district has been put on alert after a glacial lake outburst flood (GLOF) in Bhutan sent a surge of water down the river that enters India as the Sankosh.

The outburst was reported on Thursday evening, October 29, at Shintaphu Lake (also called Shintaphu Tsho) below Wakila Mountain in Bhutan's northern Gasa district. The lake sits in the upper reaches of the Mo Chhu basin and is listed among Bhutan's 17 potentially dangerous glacial lakes.

What the Central Water Commission said

The Flood Forecast Monitoring Directorate of the Central Water Commission (CWC) issued a special advisory for Assam and West Bengal on Thursday. It said a flash flood had been reported in the upper reaches of the Punatsangchhu river in Bhutan, which becomes the Sankosh after crossing into India, and that water was expected to reach the India-Bhutan border within six to eight hours.

The advisory flagged Dhubri in Assam and Alipurduar in West Bengal as the districts that could see a sudden rise in water levels, and asked local authorities along the Sankosh to monitor levels closely and take precautions.

Assam government response

Chief Minister Himanta Biswa Sarma said on X that the state was closely monitoring the situation and that "Team Dhubri" was on the ground and prepared to deal with any downstream effects.

No damage or displacement had been reported from Assam as of Friday morning.

Thousands moved in north Bengal

The bigger evacuation took place across the border in West Bengal. Alipurduar Superintendent of Police Amit Kumar Shaw said about 4,000 to 5,000 people had been moved into shelters, mostly school buildings, and more than 6,000 others had been shifted to safer places. He urged residents not to panic and said the administration was in constant contact with Bhutanese authorities.

NDRF and SDRF teams were deployed at Tufanganj and Boxirhat in Cooch Behar district, both close to the Assam border on the Sankosh. Alerts were also issued for the Darjeeling hills, Jalpaiguri and Cooch Behar. By Friday morning, officials said the period of greatest flash-flood risk had passed and residents in the Indian areas were safe, though preparedness is being maintained.

Damage inside Bhutan

In Bhutan, the flood damaged a solar-powered irrigation system in Punakha district and dumped debris on a stretch of the Punakha-Gasa highway, according to local officials. Bhutan's state broadcaster BBS reported that infrastructure at the Gasa Tshachu hot springs was washed away and that two Bailey bridges may have been lost. No injuries or deaths have been reported.

What is a GLOF?

A glacial lake outburst flood happens when water held in a lake formed by a melting glacier is suddenly released, usually because the natural dam of ice, rock or moraine holding it gives way. The surge can travel fast through mountain valleys, carrying debris that damages roads, bridges, farmland and homes far downstream.

What residents should do

People living along the Sankosh and its tributaries in Dhubri should follow instructions from the district administration, avoid riverbanks and low-lying areas until the all-clear is given, and keep an eye on official alerts from the Assam State Disaster Management Authority (ASDMA).