An army of experts in a WhatsApp group is guiding rescue workers scouring a Nepali valley after a huge flash flood more than a week ago as they desperately search for anyone who may be alive inside tunnels of devastated hydropower plants.

The messaging group was set up by engineers before the wall of water, mud and rock crashed down the Trishuli valley in Nepal on August 26. It has since become a valuable tool alongside helicopters and heavy machinery in the race to find survivors.

The authorities hope some of the about 900 people reported missing from six hydropower plants - at least three of which were under construction - may have escaped the deluge because they worked in or fled into the tunnels.

Even finding entrances to some of the tunnels, which were designed to channel water or used to access hydropower facilities, is tough now after the flood deposited 2.2 million tonnes of mud and debris down the valley.

‘Send me layout drawings’

“Can you send me Chilime layout drawings,” a government official wrote on the engineers’ WhatsApp group on Saturday as rescue workers searched the buried remains of the Chilime hydropower plant high in the Himalayan valley close to the Chinese border.

Minutes afterwards, a member of the group chat, which was expanded to add more experts in support of the rescue effort, responded by sending drawings of ⁠the project’s powerhouse, as well as details of access tunnels.

That exchange and others posted on the group, which has more than 500 members, were seen by Reuters.

No one has yet been found alive in the tunnels at the 22 MW Chilime plant - or in tunnels at any of the power plants further down the valley.

But Nepal’s Independent Power Producers’ Association said on Monday at least eight people could be trapped at Chilime, while an official at the Nepal Electricity Authority said 46 may be trapped at Rasuwagadhi hydropower plant, further south.

Reuters spoke to a dozen people - including government and military officials, engineers, survivors and relatives of missing workers - who described the efforts to search the tunnel networks of ruined hydropower plants, including how real-time guidance was being provided by experts over WhatsApp.

“The flood has altered the terrain around the tunnels and changed their structure, while mud, rocks, soil and other debris had accumulated inside,” Nepal army spokesperson Raja Ram Basnet told Reuters. “This is not a normal closure of tunnels.”

At Chilime, Reuters images on Monday showed a large tunnel entrance with flood debris rising to the ceiling a short way inside.

More than 1,200 people were killed in last week’s deluge caused by a glacier collapse. More than 4,000 people are still missing, including those who might be trapped inside tunnels.

Alongside Chilime, rescue workers are searching five other hydroelectric sites in the valley that were part of an expanding network of plants powering the nation and exporting the surplus. The flood wiped out 10% of ⁠Nepal’s generation capacity.

Seeking advice about tunnel networks via WhatsApp

At Rasuwagadhi hydropower plant, rescue workers reached 250 metres into one tunnel before finding it blocked. But they have not given up the search.

“We are trying to reach there inside again to look for people,” said Amshu Kiran Shahi, a board member of the Nepal Electricity Authority, adding that 46 people may have been trapped in a chamber, where they might have access to food and water.

A manager at the Nepal Electricity Authority, speaking on condition of anonymity, said rescue workers had also asked former plant employees for advice about the tunnel networks via the WhatsApp group. He said drawings posted on the group had been useful.

At the Upper Trishuli 3A hydropower project, rescue workers took almost six days before reaching the tunnel because the entrance was buried, Shahi said, ⁠adding that they had since tried to supply oxygen via pipes into any cavities in case someone was trapped.

A Reuters photographer who flew to the site on Thursday saw excavators trying to move huge boulders from the mouth of a tunnel and seeking to work their way deeper inside.

Jan Jiwan Thakur, a civil engineer at the Upper Trishuli 1 plant, said a colleague warned him of the coming flood moments before it swept down the valley, giving him enough time to climb to higher ground with about 100 others from the facility.

“We just ⁠ran away towards the hillside and, after two to three minutes when we looked down, everything was gone,” he said. “The flood debris had entirely covered our office area.”

Dhan Bahadur Tamang described escaping through a tunnel at the same plant when the flood hit, sending pipes and other equipment rushing inside. With knowledge of the tunnel system, he and several others found a way out but he described seeing dead bodies during his subterranean journey to escape.

On the engineers’ WhatsApp group, members shared names and ⁠mobile phone numbers of missing workers, asking government officials to relay them to telecom authorities in a bid to find their last recorded location.

Meanwhile, family members await news of missing loved ones, like Rajesh Shrestha, whose 30-year-old son, Rajish, is an environmental engineer at Upper Trishuli 1.

“Whenever I look outside, I imagine seeing him carrying a bag and coming home, just as he used to,” said Shrestha, who runs a workshop making window grills.

“I am surviving on the hope that he will return.”