The breach occurred around 1:30 p.m. on Tuesday near the spillway.
A day after the dam breach, water continues to flow down a stream, though the reservoir level has dropped by more than one meter.
The broken section of the dam shoulder is 4–5 meters wide and 3 meters deep, originally built on natural rock. According to local authorities, surveys have confirmed there is no longer a risk of further collapse.
The spillway system remains operational, releasing water downstream and reducing pressure on the dam body. To build the spillway, part of a mountain had been leveled.
The broken shoulder also caused a slab of concrete at the intake gate to collapse, destroying the central control room and flooding its equipment.
The initial cause of the dam failure is believed to be prolonged heavy rain, which sent water inflows into the reservoir reaching 1,572 cubic meters per second by Tuesday noon, while the spillway was designed to discharge only 24 cubic meters per second.
Doan Thanh Son, Vice Chairman of Lang Son Province People’s Committee, spoke about the Bac Khe 1 dam incident. Video by Huy Manh
The entrance to the hydropower plant is now fenced off, with electricity cut.
Located on the Bac Khe River, a tributary of the Ky Cung River, Bac Khe 1 is a small hydropower plant with a capacity of 2.4 MW, a reservoir volume of 4.7 million cubic meters, and a catchment area of 325 square kilometers. The plant sits in isolation, about 400 meters from the nearest main road. On the day of the breach, more than 50 nearby households were evacuated to safety.
Large amounts of wood and debris carried by the flood have piled up at the dam. Vice Chairman Son said that once the weather improves and water levels are safe, the incident will be dealt with.
Some local households have been using the reservoir for fish cages and duck farming.
According to Hoang Ngoc Hung, Chairman of Tan Tien Commune, home to the dam, the reservoir had been included in plans for an ecotourism site, but after the dam collapse, this project may have to be reconsidered.
The reservoir, holding 4.7 million cubic meters of water at an altitude of about 500 meters, is surrounded by mountains and often covered in mist.
Authorities have put up warning signs and fences to prevent residents from approaching the dam. The commune has also assigned two people to guard the site around the clock in case of emergencies.
