Rescuers in Nepal have successfully extracted survivors from a hydropower tunnel that was buried by a massive flash flood, a feat described by a lead tunnelling expert as "layer upon layer of miracles." The Trishuli 3A Hydropower Station was among several facilities hit by severe flooding along the Nepal-Tibet border, which has claimed at least 1,300 lives.
Arnold Dix, president of the International Tunnelling and Underground Space Association, advised Nepalese authorities on the challenging rescue operation. He explained that the first major obstacle was locating the entrance to the tunnel, which had been completely buried by an avalanche caused by the flood. "I've never known a rescue operation where you had to look for an entrance of a tunnel that was previously up the hill, that was now underground," Dix told the BBC. The team used a combination of engineering techniques, old topographic maps, post-disaster satellite imagery, helicopter footage, and surface observations like the position of power poles to pinpoint the likely location of the buried entrance.
Once the entrance was found, the next critical task was to locate the two men trapped inside. Dix noted that the team had to dig in the correct direction, listening for any signs of life. The tunnel was blocked by mud and rocks, some as large as cars. Rescuers had to resort to using explosives to clear the debris, a risky measure given the presence of survivors.
Dix credited the Nepalese army for their precision in managing the explosives to avoid destabilizing the tunnel and endangering the trapped workers or the rescue team. Simultaneously, it was discovered that the tunnel was still filled with water. Nepalese rescuers employed excavators and pumping machines to dig trenches from the tunnel to the nearby river, successfully draining the water.
