Around 80% of homes in Chungthang town in north Sikkim have been severely hit by Wednesday’s flash floods caused by Lhonak Lake over flow , a senior state government official said on Thursday, following the first assessment of the damage to the town adjacent to Teesta-III dam that collapsed.

“Nearly 80% of the Chungthang town has been severely hit. Several houses and establishments in the entire Mangan district have been rendered unsafe because of the erosion caused by the flood,” said the senior official of the state disaster management authority.

Around 80% of homes in Chungthang town in north Sikkim have been severely hit by Wednesday’s flash floods caused by Lhonak Lake over flow , a senior state government official said on Thursday, following the first assessment of the damage to the town adjacent to Teesta-III dam that collapsed.

“Nearly 80% of the Chungthang town has been severely hit. Several houses and establishments in the entire Mangan district have been rendered unsafe because of the erosion caused by the flood,” said the senior official of the state disaster management authority.

Experts warned that Chungthang could be hit if Lhonak lake bursts. A report prepared by the Sikkim’s disaster management authority in 2020 hinted that in case of a Glacial Lake Outburst Flood (GLOF) at Lhonak Lake, towns lower down in the Teesta Valley such as Chungthang, Dikchu, Singtam and Rangpo may be hit.

Satellite images showed that the town developed rapidly at the confluence of Lachen and Lachung rivers, where the Teesta dam was built, and has grown faster since the dam construction started in 2009. The images show that the entire green buffer zone on the banks of two rivers vanished and was replaced by residential and commercial establishments.

In a research paper titled “Future Glacial Lake Outburst Flood (GLOF) Hazard of the South Lhonak Lake, Sikkim Himalayas” published in ScienceDirect in September 2021, scientists projected how the town could be hit if there was a GLOF in Lhonak Lake.

“Mapping infrastructure exposed to GLOFs in the Teesta valley shows that many settlements and assets located along the river channel at Chungthang are potentially exposed to future GLOFs, indicating the need to conduct a full environmental impact assessment and potentially undertake GLOF risk mitigation measures,” the paper stated.

Chungthang, a major town, is located around 62 km downstream of the lake and is the site of the Teesta Stage III hydropower dam.

“Our study included future modelling of lake breach and understanding potential GLOF’s impact on the rapidly increasing downstream infrastructures because of the new hydropower site at Chungthang,” said Ashim Sattar, corresponding author of the research paper and a scientist with IISc Bengaluru, who has been studying the lake and the glacier for many years.

According to the 2011 census the population of Chungthang was around 10,038, as compared to 3,766 in 2001.

Government officials said that the town has further expanded since 2015 when the dam construction gained momentum.

Researchers said that the hydropower plant, commissioned in 2017, was expected to foster economic development in the region.

“However, as reflected in the recent constructions, it could also lead to building houses and other facilities on slopes closer to the river valley, thus increasing the risk. The increasing infrastructure in the region is leading to loss of vegetated river banks, reducing this natural buffer to flooding,” the researchers said in their findings in the paper.

An official of the Sikkim disaster management department said there is sludge all over the town and several homes have been damaged. “As the roads and communication lines are snapped, the town now remains virtually cut off from the rest of the state. The exact assessment of the damage will be done in a few days,” the official said.

Another official said as people were evacuated soon after the water level in the Teesta started rising in the early hours of Wednesday, there haven’t been too much human casualties.