For nearly 24 hours, engineers from South Korea and Laos raced to save the Xe-Pian Xe-Nomnoy dam before it cracked on Monday night, unleashing waters that state media says killed at least 19 people and prompting a rescue operation for thousands of stranded villagers.
The unfinished dam, envisioned as one of the jewels in the tiny communist-run nation’s bid to become the hydroelectric hub of Asia, proved unable to withstand torrential rains that had pounded the region for days, raising questions over safety standards. The dam is a joint venture largely owned by power companies from South Korea and Thailand, with a smaller stake held by a Laos state holding company.
South Korea’s SK Engineering & Construction, the main contractor with a 26% stake, said it is still assessing the cause of the collapse. Laos government ministries didn’t respond to requests for comment.
SK Engineering & Construction, whose account of the accident was corroborated by Thai partner Ratchaburi ElectricityGenerating Holdings, said the first worrying signs began at around 9 p.m. on Sunday.
Construction managers found that one of the so-called saddle dams designed to hold diverted river water had shown signs of damage. They began emergency repairs, although they were hampered by the heavy rains.
At 3 a.m. the following the morning, engineers deployed an emergency tube to siphon out water from the subsidiary dam to ease the pressure on its embankment.
At noon that day, SK Engineering & Construction said, engineers warned Laos authorities that there was extensive damage and that nearby villages should be evacuated. Soon after, a letter purportedly from the hydropower project to local officials was shared on social media warning that the dam had already begun to overflow and that there was an imminent danger that 5 billion cubic meters could soon breach the dam walls.
At 8 p.m. that night the dam burst, flooding nearby villages and swamping residents who weren’t evacuated in time.
The following day, officials confirmed that eight villages had been flooded. Pictures of stranded villagers wading through muddy water or perched on rooftops began to emerge in Laotian media.
Rescue services are now beginning to make their way into the Attapeu region, which borders northern Cambodia. State media have reported that at least 19 people have drowned and quoted district governor Bounhom Phommasane saying 3,000 people are still stranded. He later said only one person was confirmed to have died, the state-run Vientiane Times reported. Prime Minister Thongloun Sisolouth, meanwhile, told a press briefing that 131 people are still missing.
The Red Cross and the U.N. are mobilizing support, with the Red Cross sending packs of sticky rice and instant noodles along with blankets and water-purification equipment. SK Engineering & Construction has dispatched helicopters, boats and medical equipment and Ratchaburi Electricity has sent its own support teams.
“We will do our best to normalize the situation as soon as possible,” Cho Khi-haeng, SK Engineering & Construction’s chief executive, said Wednesday.
A spokesman for South Korean President Moon Jae-in said that while the cause of the incident is still under investigation, Seoul would contribute to the relief effort because a South Korean company is involved.
The aftermath of the dam’s collapse, and the failure to evacuate nearby villagers in time, are set to focus unwelcome attention on Laos’s bold plans to sculpt its hillsides and rivers into a battery to meet its neighbors’ growing energy demands. Laos’s Foreign Ministry has warned foreign media not to attempt to enter the secretive nation country.
Brian Eyler, a director at the Stimson Group research center in Washington, said the dam operator should have known that intense rains were approaching and taken appropriate action. “Beyond any doubt, this was a man-made disaster,” he said.
The plant on the Xe Pian and Xe Nomnoy rivers was earmarked to sell 90% of its output to Thailand. Much of the financing for the project, which was set to be finished later this year, was provided by Thai banks. Other hydro plants being built along the Mekong River and its tributaries supply power to meet growing demand to the east, in Vietnam.
In all, more than 70 plants are either ready, under construction, or are being planned in Laos, where officials say hydropower will soon account for up to a third of its economy.
Mr. Eyler said the dam’s failure could further set back Laos’s hydropower ambitions. Thailand has already suspended plans to buy power from another hydropower plant because of environmental concerns, while other power sources such as solar and biogas have become viable alternatives.
Until now critics had focused on the dams’ impact on the environment. The Mekong is one of the world’s most valuable sources of freshwater fish. Nongovernment organizations often describe how villagers were displaced or point out how some species might find it harder to swim upstream to their spawning grounds. Laos, they argue, is giving up its natural wealth to construct dams that would primarily benefit people in faraway cities such as Bangkok and Ho Chi Minh City.
The accident is also is also raising questions about the safety standards of dam-building programs along the length of the Mekong, which runs from China down through Thailand and Laos to Cambodia before exiting to the South China Sea in Vietnam. The main concern is over whether the dams can absorb the massive rainstorms during South East Asia’s monsoon season.
Worse, the problem is becoming more urgent because of climate change, said Pianporn Deetes, a field researcher with U.S.-based activist group International Rivers.
“Unpredictable and extreme weather events are becoming more frequent in Laos and the region,” she said.
Write to James Hookway at james.hookway@wsj.com and Eun-Young Jeong at Eun-Young.Jeong@wsj.com
