China assesses barrier lake breach risk near Nepal border after deadly flash flood

Gyirong, China. China has mobilised engineers to assess a barrier lake near the border with Nepal after a flash flood on Wednesday killed hundreds of people. Authorities in both countries have warned of further flooding risks in the Himalayas.

Survey and mitigation work

Chinese authorities dispatched an eight-member engineering team to carry out aerial surveys and 3D modelling of the barrier lake, state broadcaster CCTV reported on Friday.

Engineer Chen Hanxiao said access to the site was difficult after a glacier collapse formed the lake and created isolated and steep cliffs along its perimeter.

Chen said the general approach to reducing the threat was to excavate a drainage channel at a lower point of the dam. The channel’s width and depth would need to be calculated based on the expected water flow and the rate at which the lake would fill.

Water levels and rainfall risk

Survey data showed the lake was about 150 metres long and 40 to 50 metres deep, with an estimated reservoir volume of 1.5 million to 2 million cubic metres of water.

The team’s next tasks include monitoring the lake, collecting data from the lake floor and tracking weather conditions in the coming days.

The Gyirong border port area has experienced light to moderate rainfall, loosening and destabilising soil and rock around the upstream danger zone. Rain is forecast to continue over the coming week.

China warned on Thursday that 3 million cubic metres of water, equivalent to about 1,200 Olympic swimming pools, were expected to flow into the still-dammed lake over the next three days. Authorities said this created a high risk of a breach, with peak flow expected around September 1.