Effects of cascade reservoir dams on the streamflow and sediment transport in the Wujiang River basin of the Yangtze River, China

Numerous cascade dams built on the Wujiang River have caused significant problems, including increased sediment deposition and a change in the relationship between sediment discharge and runoff. To detect the damming effects, we used nearly 60 years of hydrologic data including rainfall, runoff, and sediment discharge as well as dam construction data in a runoff and sediment discharge analysis. The mean annual rainfall and runoff series did not change significantly; however, the sediment discharge decreased significantly due to cascade dam construction. The change points detected in the accumulative curves and the correlation analysis between the runoff and sediment discharge corresponded to the timing of the construction of the dams. In the entire watershed, the sediment yield at the upstream Yachihe station decreased by 37.7% after construction of the Dongfeng Dam, and the sediment yield decreased by 55.3% at the Wujiangdu station after construction of the Wujiangdu Dam in 1979.The sediment yield at the downstream Wulong station decreased by 11.7% from 2004 to 2015 following the completion of hydropower projects in the 2000s.This analysis provides important and relevant information to the operation of the engineering projects and environmental protection in the Wujiang River Basin.