Bhutan GLOF: Sankosh stays below danger mark in Assam; new lake watched

The flash flood unleashed by a glacial lake outburst in Bhutan passed through without harming western Assam, district officials said on Friday, though authorities on both sides of the border are now keeping watch on a new lake formed by flood debris in Bhutan's Gasa district.

The outburst at Shintaphu Lake, at the head of the Mo Chhu river, on the evening of Thursday, October 29 had prompted the Central Water Commission (CWC) to issue a special advisory warning that the Sankosh could rise suddenly in Dhubri district of Assam and Alipurduar district of West Bengal within six to eight hours.

What happened in Dhubri and Kokrajhar

Dhubri Deputy Commissioner Dibakar Nath said that 12 to 15 hours after the outburst there had been no abnormal rise in the Gangadhar, as the Sankosh is known in the district. The river was more than two metres below the danger level and falling, he told The Times of India. About 8,000 people in the district had been identified as vulnerable.

The district administration had restricted boat movement, asked people not to let children bathe or play in the river, and positioned Indian Reserve Battalion boats under the Golakganj and Tamarhat police stations, with more boats brought in from Goalpara and Bongaigaon, The Assam Tribune reported.

In Kokrajhar, where the Sankosh first enters Assam, Deputy Commissioner Pankaj Chakravarty said about 4,750 people in some 20 riverside villages were considered at risk, but that the water appeared to be receding and no inundation was expected. NDRF and SDRF teams were kept in position in both districts. Chief Minister Himanta Biswa Sarma said the state was monitoring all vulnerable revenue circles of Dhubri and Kokrajhar.

Across the border in West Bengal, around 12,000 people were shifted to safety in Alipurduar. The Sankosh rose about 1.5 metres there on Friday morning before receding, and residents began returning home by the afternoon, with no damage reported.

The worry now: a new lake in Bhutan

Bhutan's National Centre for Hydrology and Meteorology has confirmed that debris from the flood blocked a channel near Taktsemakhang, about 20 km downstream of Shintaphu, creating a temporary artificial lake. Residents of the Mo Chhu and Punatsangchhu valleys have been told to stay away from riverbanks.

Prime Minister Tshering Tobgay inspected the blockage on Friday. According to the river research network SANDRP, he described the lake as not highly dangerous and said controlled blasting to drain it was being considered.

In Bhutan, the flood damaged roads in Gasa, washed away most facilities at the Gasa Tshachu hot springs and swept away a Bailey bridge in Punakha that was built in 2022 with Indian support. No casualties have been reported.

Why it matters for Assam

The Mo Chhu joins the Pho Chhu at Punakha to form the Punatsangchhu, which flows into India as the Sankosh and meets the Brahmaputra in Dhubri. Any sudden release from the new lake would follow the same route. Officials say the wide channel and the start of the dry season leave the river with enough capacity for now, but advise riverside residents to keep following official updates.