Wednesday, May 14, 2008

Earthquakes and dams

Dams in China are controversial. The costs are already well documented but perhaps the biggest environmental danger is the relationship between earthquakes and dams which is especially pertinent given recent events in China.

This is the first time I have read that dams may be the cause of earthquakes - another point to clock up in the negative column.

TreeHugger have written a good piece on this:

China Earthquake Threatens Nearby Dams, Environment [TreeHugger]

The human impact of China's most devastating natural disaster in three decades, which is estimated to have claimed at least 12,000 lives, may not be fully known for weeks. Thankfully, no damage has been reported at the Three Gorges Dam, the world's largest, situated some 700 km east of the epicenter (map here). If the quake had affected the dam, the human toll would be even harder to imagine.

The dam sits above some 15 million people (some of whom are already suffering from soil erosion that can lead to landslides). Last September, government officials joined the dam's critics in raising the alarm about potential dangers, among them that the dam itself could trigger quakes as it sits near a number of fault lines. A burst at the Three Gorges would, says engineer Philip Williams, former president of the San Francisco-based International Rivers Network, “rank as one of history’s worst man-made disasters.”

More on the link between dams and earthquakes:

Though Monday's disastrous earthquake was a result of tectonic collision, there are fears that the Three Gorges Dam could trigger earthquakes on its own. Its reservoir sits on two major faults, which can be aggravated by changes in water level, and recently relocated residents have reported landslides, mudslides and ominous cracks in the ground. According to a March 2008 article in Scientific American by Mara Hvistendahl,

Engineers in China blame dams for at least 19 earthquakes over the past five decades, ranging from small tremors to one near Guangdong province's Xinfengjiang Dam in 1962 that registered magnitude 6.1 on the Richter scale—severe enough to topple houses.
Surveys show that the Three Gorges region may be next. Chinese Academy of Engineering scholar Li Wangping reports on the CTGPC's Web site that the area registered 822 tremors in the seven months after the September 2006 reservoir-level increase.

Meanwhile, upstream from the Three Gorges along the Jinsha river, a section of the Yangtze, at least a dozen new dams are being built in order to alleviate sedimentation caused by the Three Gorges reservoir. They too lie in the same seismic region as Monday's earthquake. As a geologist told the Guardian in 2003 of the area, "The Jinsha has bad geological conditions, and there is a more severe seismic area upriver from Xiangjiaba [the site of the furthest downstream of the four dams]." Near this site dam projects "should not be encouraged," he said.

Something to think about...

No comments: