Engineers led by tunnelling expert Arnold Dix, president of the International Tunnelling and Underground Space Association, have been working with Nepal’s hydropower authorities to clear a tunnel at Trishuli 3A Hydropower Station that was buried by last week’s flash flood on the Nepal‑Tibet border. The flood, which has killed 1,300 people, buried the tunnel entrance under avalanche debris, forcing rescuers to locate the entrance from the ground level of the mountain.
Using a combination of old topographic maps, satellite imagery, helicopter footage and surface markers such as power poles, Dix’s team triangulated the likely position of the entrance and began excavation. They eventually found the entrance, but the tunnel was still filled with mud, rocks and water. Rescuers had to use explosives—carefully managed by the Nepalese army—to clear the debris, a move rarely employed in rescue operations because of the risk of detonating trapped people or destabilising the tunnel.
Once the entrance was cleared, rescuers dug a series of trenches from the tunnel to the river outside to drain the water, and then created a narrow passageway the size of a person through the debris at the tunnel’s mouth. This “tiny tunnel” used the original tunnel roof as a protective cover, reducing the risk of flooding. In the early hours of Friday, rescuers heard faint voices and were able to pull out Sanjaya Shah and Kabir Maharjan, both alive.
Despite the successful rescue, the operation is far from over. Dix estimates that about 60 m of the tunnel has been cleared, with an additional 150 m needed to reach the hydropower station deep inside the mountain. The team fears that flood debris could have reached the station, potentially endangering any remaining survivors with rocks, mud or water. The risk of water entering from both ends of the tunnel remains a constant threat, as does the possibility of another flood outside.
Buoyed by the rescue, the team is now focused on reaching the “Goldilocks zone” at the uppermost level of the station, where survivors might still be located. “We got two people out. If we were playing at a casino, some might say it’s time to walk away, but we say game on,” Dix said, signalling renewed determination to continue the operation.
