Race against to time to find workers missing in Nepal’s hydropower tunnels. Here’s what we know

By Jessie Yeung, CNN

(CNN) — Rescue crews and foreign specialists are racing to find scores of workers feared trapped alive inside hydropower tunnels in Nepal, after thick mud buried the facilities during last week’s devastating flash floods.

At least 933 workers are missing at various hydropower projects that run along the Trishuli river, which winds through multiple districts in the remote and mountainous area, according to the country’s disaster agency.

It’s not clear how many of those workers were inside the deep and heavily reinforced tunnels when the water hit. It’s also unclear how many of them may be still alive, with search and rescue efforts complicated by poor weather, mud, and the loss of critical infrastructure like roads and bridges.

Nepal and its superpower neighbors – China and India – have invested heavily in hydropower projects across the Himalayas in recent years, hoping to harness the vast energy potential of its raging rivers.

Here’s what we know so far.

Where are the workers?

A list compiled by Nepal’s Independent Power Producers’ Association (IPPAN) on Saturday showed around 900 workers were missing at 11 different hydro projects affected by the flooding.

Each plant presents its own challenges to rescuers who are trying to find the safest way in. Some have internal tunnels stretching several kilometers, meaning any workers inside could be a long way from the portal. Rooms and resources inside the tunnels could theoretically help any trapped workers to survive –– potentially for weeks, though air supply could be another problem.

At the Trishuli 3A hydropower plant, where 42 people were listed as missing, a massive operation is underway to bore into a tunnel so rescuers can search for survivors.

The tunnel that leads to the underground powerhouse there, where dozens of people were working when the flood hit, is more than four kilometers (2.5 miles) long.

It’s not clear how much of the tunnel has been filled with mud or water, said Arnold Dix, a geologist in Australia who has advised rescuers at the Trishuli 3A plant. “So, we might only have to dig 10 meters, or we might have to dig 100 meters.”

There are many other risk factors, said Dix. The turbine room could have filled with water if the emergency shutdown systems failed, potentially drowning anyone inside. And that water could potentially be released by the crews’ drilling, presenting a risk for rescuers.

Six people are believed to be missing inside the Chilime Hydropower Plant, Jenjen Lama, a mountain guide involved in the search-and-rescue operations, told CNN on Monday.

He shared a diagram of the facility, which shows the 250-meter (820-foot) tunnel leading downhill before connecting with a larger facility including a service bay, control room, and the hydropower transformer.

Rescue teams on Sunday found that the tunnel was “completely blocked by deep, muddy sediment and sludge,” which eventually reached up to their chests, said Lama. They only made it 130 meters into the tunnel before they had to stop; the damaged infrastructure also makes it hard for helicopters to land there, he said.

Inside the tunnel “there is the kitchen, there is some food … but I don’t know about the oxygen,” he said.

As many as 27 hydropower plants were damaged in Nepal, with about 12 all but destroyed, according to Dix.

What are rescue teams doing?

Engineers and search-and-rescue teams from the Nepal Army and Nepali police were joined by specialists sent by India and China, who arrived over the weekend.

Teams used thermal cameras on drones to search for survivors, while working to locate the entrance of the tunnels and clear away mud. At the same time, rescuers drilled holes through the top of the heavily fortified tunnels.

At the Trishuli 3A plant, rescuers managed to make a big enough hole that they could rappel inside using ropes and harnesses – but when they called out, they received no response. Earlier, they also pumped air into the tunnel and sent food inside.

But breaking through the top of the hydropower station presents its own difficulties. “We need special equipment to get through the steel and everything that’s surrounding the turbine room. So, it’s layer upon layer of technical difficulties,” Dix said.

Next, they’ll work to send rescuers into the tunnel carrying oxygen, medical supplies, communication equipment and cameras, said officials on Monday.

What survivors have said

At least 279 hydropower workers have been rescued or managed to trudge their way out of the mud and silt riddled tunnels.

But those survivors, who each have harrowing stories of their own, are still searching for answers about their still missing friends, coworkers, and family members.

One such survivor, Bhakti Ram Bohara, estimated that only 100 people had made it out from his and other nearby projects, out of about 1,000 workers.

Among the missing was his brother-in-law. They had worked on the same team, spending weeks away from their families at a time, and sending money back to their home villages.

“His wife is my sister, and she is pregnant,” he told CNN on Sunday, breaking down into tears.

Another survivor, Ram Chandra, described gripping onto rungs of the ceiling to make his way out of the tunnel as water, concrete and debris swirled around him. He and his coworkers took six hours to reach the mouth of the tunnel.

Why are there so many hydropower projects?

The devastation could be a reality check for governments driving a boom in dams, tunnels, highways, railways and bridges across the Himalayas – with China leading the charge.

India, and to a lesser extent Nepal, have been on an infrastructure-building spree in recent years, funneling hundreds of millions of dollars into developments in a region that is acutely vulnerable to natural hazards and climate change.

Despite being one of the most ecologically and seismically sensitive areas in the world, the potential to tame its rivers into major hydropower projects has long enticed engineers. Demand for electricity with the development of AI could see efforts to harness the region’s rivers intensify.

Experts say the severity of the event and its positioning on the Nepal-China border should make state planners think more carefully about how they design, situate and scale projects in the region –– and spark regional discussion about shared risk monitoring systems.

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CNN’s Simone McCarthy contributed reporting