April 8, 2008
Read this feature article by Mara Hvistendahl in the March 25th issue of Scientific American available online at http://www.sciam.com. Here are a few excerpts:
Fan Xiao, a geologist at the Bureau of Geological Exploration and Exploitation of Mineral Resources in Sichuan province, is quoted saying recent landslides in the Three Gorges area are directly linked to filling the reservoir. Water first seeps into the loose soil at the base of the area’s rocky cliffs, destabilizing the land and making it prone to slides. Then the reservoir water level fluctuates—engineers partially drain the reservoir in summer to accommodate flood waters and raise it again at the end of flood season to generate power—and the abrupt change in water pressure further disturbs the land.
A study published in the Chinese journal Tropical Geography in 2003, is cited predicting that tinkering with the Three Gorges reservoir water levels could trigger activity in 283 landslide-prone areas.
One of the greatest fears is that the dam may trigger severe earthquakes, because the reservoir sits on two major faults: the Jiuwanxi and the Zigui–Badong. According to Fan Xiao, changing the water level strains them.
“When you alter the fault line’s mechanical state it can cause fault activity to intensify and induce earthquakes,” he says.
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.
Chinese Academy of Engineering scholar Li Wangping reports on the CTGPC’s website that the Three Gorges area registered 822 tremors in the seven months after the September 2006 reservoir-level increase. So far, none have been severe enough to cause serious damage. But by 2009, the dam’s water level is set to be raised to its full 175-metre capacity and then lowered about 30 metres during flood season. That increase in water pressure, in water fluctuation and in land covered by the reservoir, Fan says, makes for a “very large possibility” that the situation will worsen.
China’s original goal was to fill the reservoir to its maximum level by 2013. Despite all the trouble, that target was moved up to 2009, Fan says, to boost hydropower output by an additional 2.65 billion kilowatt-hours each year.
Raising the reservoir level is very important “for the economic interests and profit of the Three Gorges Project Development Corporation,” he says. “But the function of any river, including the Yangtze, is not only to produce power. At the very least, a river is also important for shipping, alleviating pollution, sustaining species and ecosystems, and maintaining a natural evolutionary balance.”
“The Yangtze doesn’t belong to the Three Gorges Project Development Corporation,” Fan adds. “It belongs to all of society.”
Read full article here or here [PDFver here]
Categories: Dams and Landslides, RIS, Three Gorges, Three Gorges Probe
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