Three Gorges Dam shrinking Yangtze delta

Chinese scientists have determined how China's Three Gorges Dam -- the world's largest dam -- affects downstream sediment delivery in the Yangtze RiverResearchers from East China Normal University found river damming can damage downstream environments by retaining sediments and nutrients.

Shi-Lun Yang and colleagues at the university's State Key Laboratory of Estuarine and Coastal Research calculated supplies of water and sediment from ungauged areas and combined them with data sets from gauging stations.



They discovered the Three Gorges Dam, which has regulated the waters of the Yangtze River since 2003, retains two-thirds of the upstream sediment each year and, in response to that retention, significant erosion occurs in the riverbed downstream of the dam.



Since the erosion doesn't offset the sediment lost in the reservoir, and because sediment flux to the Yangtze River mouth has decreased by 31 percent per year, the Yangtze delta is shrinking.



The researchers said continued sediment retention at those rates, combined with more dams planned for the watershed, will severely affect the people and various ecosystems in the Yangtze delta.



The study appears in the journal Geophysical Research Letters.



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