Overflowing lake adds new danger to desperate rescue efforts following China-Nepal disaster

By Simone McCarthy, Yong Xiong, CNN

Beijing (CNN) — Already harrowing rescue efforts along the China-Nepal border are being complicated by the risk of new flooding or landslides, with authorities in China and Nepal pausing rescue efforts Friday due to those fears.

A barrier lake – holding enough water to fill an estimated 1,000 Olympic swimming pools – began overflowing on the China-Nepal border, where it formed after a powerful landslide and torrential flooding devastated the area on Wednesday. A barrier lake is a body of water created by debris damming up a river.

Helicopter rescue operations in Nepal’s flood-hit Rasuwa district were stopped and locals were seen rushing up a hill after reports that the lake had begun to overflow, the Reuters news agency reported, citing a witness.

Chinese state broadcaster CCTV reported late Friday morning the newly formed lake has begun overflowing non-stop, posing such a great risk that rescue teams cannot proceed to the hard-hit land port.

“There is a very real possibility that it could trigger new flash floods or landslides, so it is extremely dangerous to proceed to the areas that have been identified as priorities for search and rescue operations,” CCTV reported Friday.

That’s left rescue teams in China waiting at a village several kilometers from Gyirong border port – a critical disaster zone – as they assess the situation – in the latest blow to an already challenging operation that saw rescue teams contend with roads leading to the port blocked for kilometers by thick mud and debris.

Authorities have been closely monitoring the upstream barrier lake, which is some 10 kilometer upstream of the port, with teams dispatched to monitor the lake and others working on analyzing the risks to adapt rescue plans.

A top government official in Nepal’s Rasuwa district confirmed on Friday that Chinese authorities had shared information about the lake overflowing.

The volume of water in the lake was continuing to expand Friday morning, forming a lake with a storage capacity of approximately over 2.5 million cubic meters, CCTV said Friday afternoon. Around midnight on Friday morning, a member of a team dispatched to monitor the lake told CCTV the barrier forming the lake stretched about 150 meters long and 40 or 50 meters high.

“The rocks and soil along the area are currently loose. During the assessment operation, secondary collapses occurred several times above the barrier,” Chen Hanxiao, a member of the team dispatched by China Anneng Engineering Rescue Lhasa Base, told CCTV in the midnight interview.

Chen said safety personnel would monitor the area and “immediately withdraw” when they detected signals of significant displacement.

Compounding risks

Of key concern is how the lake changes amid on-going rain, which could add significant amounts of water volume – putting more pressure on the dam and creating further risk of breach. Such a breach could be a slow or sudden release, experts have said

Austin Lord, a senior fellow in the energy, water and sustainability program at the Stimson Center think tank, said that experts were currently monitoring two barrier lakes. He referenced an additional lake that had formed just below the fracture in a glacier that broke on Wednesday, causing the initial disaster.

CNN has geolocated that lake, which Chinese authorities appear to also be monitoring and referring as an “impact crater,” according to state media reports. Authorities were also assessing how a breach there would impact the lower lake, one report said.

Lord said breaches of either lake could trigger a small flood in the same flow path as the initial event, rather than a major event like on Wednesday.

“They’re growing in volume. They’re not insignificant – but they’re not to the extent that if they failed that they could trigger an event on the scale that we saw,” Lord told CNN’s Anderson Cooper on Thursday night ET, citing current conditions.

“There is a concern for those doing search and rescue who are operating in the river corridor itself,” he said. The challenge in the coming days would be if weather systems continue to increase the volume behind the lakes, he added.

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CNN’s Fred He contributed to this report.