China report: Three Gorges causes downstream erosion

Chinese researchers report China’s Three Gorges Dam, the world’s largest hydropower project, is retaining huge amounts of sediment and nutrients and causing significant erosion in the downstream reaches of the Yangtze River.

In a paper published in the latest volume of Geophysical Research Letters, Chinese scientists said the hydro project retained 151 million tons of sediment each year since 2003. The project is to be completed at its initial 18,200-MW capacity by the end of 2008. (HNN 3/26/07)

“The Three Gorges Dam, which has regulated the waters of the Yangtze River since 2003, retains two-thirds of the upstream sediment each year,” researchers from East China Normal University in Shanghai wrote.

The report said researchers calculated amounts of water and sediment at places along the river that previously had not been monitored and combined them with the regular gauging stations.

“In response to this retention, significant erosion occurs in the riverbed downstream of the dam…� the report said. �Sediment flux to the Yangtze River mouth has decreased by 31 percent per year. The Yangtze delta is shrinking.�

“Continued sediment retention at these rates, combined with more dams planned for the watershed, will severely affect people and the ecosystems on the Yangtze delta,” it added.

Official Chinese press reports say the build-up of silt in Three Gorges Reservoir is under control. Huge gates at the bottom of the 185-meter-tall dam are opened between June and September to lower water levels and flush away sediment collected in the reservoir during floods.

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