Morphological evolution of mid-channel bars in the Middle Yangtze River in response to upstream damming

Since the operation of the Three Gorges Dam, the mid-channel bars (MCBs) in the Middle Yangtze River (MYR) experienced significant deformation, which is crucial to the stability of river regime. However, a systematic understanding of MCB’s morphodynamics and their linkage to upstream damming still remains largely unknown. Therefore, Landsat images were collected to perform an analysis of MCB’s deformation in the MYR. The following conclusions are obtained: (i) the total exposed area of MCBs presented a decreasing trend owing to upstream damming; moreover, the shrinking degree decreased in the longitudinal direction; (ii) the process of MCB’s deformation was consistent with the process of channel degradation during the dam-operation period (erosion, slight erosion and strong erosion); (iii) the deformation of MCBs is mainly attributed to the altered flow-sediment conditions. It can be found that the magnitude of sediment transport capacity changed slightly after the upstream damming, but the concentration of suspended sediment was greatly reduced, which resulted in a general erosion trend of MCBs; moreover, the sediment concentration recovered owing to channel degradation, and the differences between sediment transport capacity and suspended sediment concentration decreased along the MYR, which made the dam effect generally diminish in the longitudinal direction.