China quake weakens Sichuan dams, cuts off river

By Lucy Hornby

BEIJING (Reuters) - A devastating earthquake that struck China this week has raised concerns over the stability of dams and infrastructure in the afflicted mountainous area, while landslides have blocked a river that flows to the region.

More than 13,000 people have been confirmed dead and at least the same number remain missing or buried by the 7.9-magnitude earthquake, which struck to the northwest of Sichuan's provincial capital Chengdu on Monday.

Heavy rains could compound the damage by hindering rescue work, triggering mudslides and adding to pressure on weakened dams, officials and state media said on Wednesday.

The quake left a swathe of collapsed buildings in the steep, rainy mountain range that runs from southwest to the northeast. The dramatic shelf where the Tibetan plateau collides with the Sichuan basin is ideal for hydropower, while doubling the challenges of building roads, bridges and railways.

One of the worst-damaged cities is Dujiangyan, site of multiple dams and weirs that irrigate about 3 million hectares in the fertile Sichuan plain. The Dujiangyan irrigation works date from the 3rd century BC, when engineers split the Min river where it spills from the mountains, and diverted it to irrigation channels along the plain.

"Upstream on the Min river is an important reservoir called Tulong which is already imperiled. If the danger intensifies, this could affect some power stations downstream," He Biao, deputy party chief of Aba prefecture, told reporters.

"This is an extremely dangerous situation." The quake caused the 760-megawatt hydropower generating unit at Zipingpu, 9 kilometers upstream of Dujiangyan, to collapse, the provincial government said. It began operations in 2006, as part of China's program to develop its poorer western regions.

Water has been released at 50 percent more than average levels, to lower water levels in the Zipingpu reservoir and relieve pressure on the cracked dam, the Ministry of Water Resources said on its Web site (www.mwr.gov.cn).