Nepal’s Dangerous Dams

Among the more sketchily reported rescues in the aftermath of the weekend's catastrophic earthquake in Nepal was the successful extraction of some two hundred and eighty Chinese workers and engineers from the construction site of the Rasuwagadhi hydropower dam, on the upper reaches of the Trishuli river, a tributary of the Narayani

The construction site sits high in the mountains in the north of Nepal, close to the Tibetan border, eighty-six miles northwest of the capital Kathmandu and forty-one miles from the epicenter of the 7.9-magnitude quake. Two Chinese dam workers died as the earthquake struck the site.

Even before the earthquake, Rasuwagadhi was remote and inaccessible: a ten-mile road had to be built to the nearest highway before work could begin on the dam. When the earthquake struck, it triggered rockslides that cut the roads on both sides of the border. Aftershocks sent repeated showers of fresh rocks down onto rescuers on the Chinese side, who were trying to clear them.

By Tuesday, three days after the initial quake, Chinese military helicopters had evacuated twenty-five Chinese citizens, engineers and their families, across the border. Most of the remaining Chinese were flown out twenty-four hours later, leaving twenty engineers to keep an eye on the dam. Three hundred and fifty Nepali workers, who were running low on food and water, were reportedly left to walk to a container terminus under construction at Kyirong. The dam itself, according to the Chinese state-owned behemoth that was building it, the Three Gorges Corporation, was "severely damaged."

It is difficult to imagine a worse tragedy for Nepal than the one that has unfolded in the past few days: four days after the first quake struck, the death toll reached five thousand. With rescue efforts outside the relatively well-off and accessible Kathmandu Valley barely begun, and an already dysfunctional government buckling under the weight of the task ahead, it will certainly continue to rise.

Other deadly earthquakes will almost certainly strike the region, and the damage at Rasuwagadhi raises the question of whether a future quake in the Himalayas might precipitate a dam collapse that could send thousands of tons of water and rubble crashing downstream, piling horror upon catastrophe. The likelihood of such an event is growing because, simply put, more and more dams are being built in one of the world's most active earthquake zones. More than four hundred dams are planned or are under construction in steep Himalayan valleys in China, India, Pakistan, and Bhutan, in one of the biggest waves of dam construction the world has ever seen.

The Rasuwagadhi dam is one of three contracts won in the area by the Three Gorges Corporation, and one of thirteen planned along this stretch of river. The company, which has been repeatedly implicated in corruption in China, has also won the contract to build the controversial seven-hundred-and-fifty-megawatt West Seti dam, which, at $1.6 billion, will be Nepal's biggest-ever foreign investment. A South Korean company is building one of the other Trishuli River dams, and Nepal has signed deals with India to build eighteen hundred megawatts of hydropower. India is also building cascades of big dams in Bhutan as well as in its own Himalayan region.

Nepal, which has an abundance of as-yet-undammed rivers, a chronic shortage of energy (nineteen-hour blackouts are routine across the country), no spare cash, and little engineering expertise, is an obvious target for these regional investors. But then, there are the earthquakes. The Himalayas are the world's highest and youngest mountains, the product of a slow-motion collision, fifty million years ago, between India—then an island—and the Eurasian landmass that forced what became the spectacular mountains upwards. India still pushes several inches northward a year, and stresses on the mountain region's multiple fault lines regularly result in severe earthquakes that send avalanches crashing into steep river valleys, carrying away precarious roads, bridges, and other infrastructure.

Geologists argue that the risks of building dams in earthquake zones go well beyond an earthquake-induced collapse. Earthquakes trigger landslides that can block rivers or change their course, which would also impact the operation of a hydrodam. But the most fiercely debated risk, since the 7.9-magnitude Sichuan earthquake in 2008, which killed seventy thousand people and left nearly twenty thousand missing, is that of "reservoir-induced seismicity"—the theory that the weight of water behind a dam, coupled with the seeping of water into fissures in rocks below, can produce shearing stress strong enough to worsen, or trigger, an earthquake. The Zipingpu dam, a five-hundred-and-eleven-foot-high structure on the Min River and the largest dam in Sichuan Province, was implicated in the 2008 earthquake. Work on the dam began in 2001; it was built just five hundred and fifty yards from the Longmenshan fault line and three miles from the epicenter of the quake.

Source: The New Yorker

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• Hydropower
• Dams
• Design & Construction