China: dam nation

China has more hydroelectric dams than any other nation, and the presence of so many near the epicenter in Sichuan province could prove a huge risk in the aftermath of last month's earthquake.

Sichuan's position in the most easterly mountainous part of China, where the rivers cascade from high elevations, is understandably a tempting location for genrating hydropower. Yet nowhere on Earth has more dams in an area of such high seismic risk, and it will make the government decidedly more cautious when selecting sites for further hydroelectric projects -- and nuclear power stations.

The earthquake triggered extensive landslides that blocked river valleys; monsoon rains are also swelling river flow in the region, putting unprecedented pressure on the dams. Failure of one dam increases the probability of failure for the others. In 1975, a dam burst during a monsoon in Henan province, causing a tidal wave that destroyed a larger dam downstream. The floods killed between 80,000 and 200,000 people. The hazard is somewhat lessened for the cities on the Chengdu Plain to the south-east, because the water can spread laterally across the flat plain, but flood peaks of over ten metres are still possible in the event of a rapid and catastrophic dam failure.

Efforts by the authorities to dig diversion channels to avert catastrophic failure have been impressive, and represent the best possible strategy to deal with this hazard. The dams survived this time, but the country's extensive network of dams may be vulnerable in future. The New Scientist writes that Beijing has plans to quadruple Sichuan's hydroelectric power exports to the rest of China by 2020.

Yet it points out that if major structural damage is discovered at any of the existing dams, the quake could put those plans in jeopardy. The quake will also raise questions about the wisdom of plans announced this year to build nuclear power stations in Sichuan, already home to secret labs at Mianyang, dubbed China's Los Alamos.