China races to drain barrier lake after deadly Nepal-Tibet floods

China has mobilised an engineering team to assess the risk of another flood at the Gyirong border crossing with Nepal after a flash flood killed hundreds of people on Wednesday. Nepal and China warned of fresh flooding in the Himalayas as debris dams formed two barrier lakes on both sides of the border, raising fears that they could collapse.

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China has sent an eight-member engineering team to conduct aerial surveys and prepare 3D models of the barrier lake, state broadcaster CCTV reported on Friday.


The team is studying whether the lake can be drained safely. Engineer Chen Hanxiao said difficult access to the site was one of the main challenges.

“After the glacier collapse created the lake, many isolated cliffs and steep cliffs appeared along it,” Chen told CCTV on Thursday evening.

Chen said engineers generally reduce the risk from such lakes by excavating a drainage channel at a lower point of the dam. However, they must calculate the channel’s width and depth based on the speed of water flow and the rate at which the lake is filling.

Survey data showed that the lake is about 150 metres long and 40 to 50 metres deep. It holds between 1.5 million and 2 million cubic metres of water.

The team will continue monitoring the lake, collect data from its floor and track weather conditions in the coming days.

The Gyirong border port area has received light to moderate rainfall. The rain has loosened and destabilised soil and rocks around the fragile upstream zone. Forecasts indicate that rainfall may continue over the next week.

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China warned on Thursday that around 3 million cubic metres of water could flow into the blocked lake over the next three days. This is equal to about 1,200 Olympic swimming pools. The inflow could create a high risk of the dam breaking, with the peak flow expected around September 1.

Aerial footage released by Chinese broadcaster CGTN showed brown water collecting in a basin with no visible outlet. The water had already submerged bushes and trees and appeared to be pressing against a barrier made of debris and stones.

Nearly 1,000 people remain missing on both sides of the border, including up to 540 foreign nationals from 31 countries.