Fluvial processes of meandering channels in the Lower Jingjiang River reach after the impoundment of Three Gorges Reservior

The sediment discharge has been reduced sharply since the operation of Three Gorges Project in 2003, leading to the severe erosion of Lower Jingjiang Reach (LJR), a representative meandering channel located in the middle of Yangtze River. Some sharp bends in LJR are unusually undergoing convex bank erosion and concave bank deposition resulting in submerged shoal, which are contrary to the basic fundamentals of curved riverbed evolution. These abnormal riverbed deformations induce changes in flood control, waterway condition and the relationship between Yangtze River and Dongting Lake, and indeed the corresponding mechanism needs to be investigated. In the paper, based on a number of field data, the characteristics of riverbed evolution and channel morphology adjustments are fully demonstrated by quantitative statistics of erosion-deposition distribution and channel morphology for selected curved reaches. The results indicate that the annual redistribution of flow, the reduction of sediment discharge and mutation of sediment gradation are the dominant causes.