Uttarakhand: Expert team explains formation of lake in Bhagirathi during Dharali disaster

Uttarkashi: A team of geological experts on Friday explained how a temporary lake was formed in the Bhagirathi river following the recent flash floods in Uttarkashi's Dharali village, which also caused large-scale damage to the neighbouring Harshil town.

Efforts are underway at present to manually puncture the lake to facilitate outflow of water in a phased and controlled manner to prevent flooding downstream.

The team conducted a geological inspection of the disaster-affected areas of both Dharali and Harshil, studied the possible dangers and measures for rescue, an official release here said.

The team observed that a local stream named Telgad in Harshil near the Army camp became active due to heavy rainfall during the August 5 disaster, in which, according to the administration, one person died and 68 others are missing.

The camp bore the brunt of the disaster, which demolished structures besides leaving nine of its personnel missing, including a junior commissioned officer and eight jawans.

A large amount of debris and water came and accumulated in the stream at its point of confluence with the Bhagirathi River and formed a large fan-shaped deposit (alluvial fan) of sediments, the team of experts said.

This fan obstructed the original channel of the Bhagirathi River and formed a temporary lake on the right bank of the river.

The length of the newly formed lake was about 1,500 metres, and its estimated depth was 12 to 15 feet.

The flooding not only submerged a portion of the national highway and a helipad, but also posed a serious threat to Harshil town.

This event also significantly altered the topography of the Bhagirathi River, as the sand dune located on the right bank was eroded, while fresh sediment was deposited on the left side, exposing the northern part of the town.

The continued bedrock erosion in this area had already caused partial structural damage to the camp, including the loss of a portion of the Garhwal Mandal Vikas Nigam Guest House.

Inspection by the geological team on August 12 revealed that the left bank of the Bhagirathi River was blocked by a saturated alluvial fan.

Due to its high moisture content, the fan was weak, which prevented heavy machinery such as JCBs from being deployed — the only equipment available locally.

Based on the field data and available resources, the geologists prepared a plan for debris clearance and partial restoration of water flow.

The plan involved creating small diversion channels of about 9-12 inches deep to gradually release the stagnant water.

During discussions with Uttarkashi District Magistrate Prashant Arya and Inspector General (SDRF) Arun Mohan Joshi, it was emphasised that the lake outflow channels should be opened in three or four stages to avoid sudden flooding downstream.

Work was immediately started by the State Disaster Response Force (SDRF) and the Irrigation Department, Uttarkashi.

Through careful execution of the plan on two successive days, the teams engaged in the exercise were able to facilitate controlled water drainage from the lake.