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

Since operation of the Three Gorges dam, the mid-channel bars (MCBs) in the Middle Yangtze River (MYR) have experienced significant deformation, thus crucially affecting the stability of the river regime. However, systematic understanding of the morphodynamics of the MCBs and their linkage to upstream damming still remains largely unknown. In this work, Landsat images were collected to perform an analysis of the deformation of the MCBs in the MYR. The following conclusions are obtained. The total exposed area of MCBs presented a decreasing trend owing to upstream damming; moreover, the shrinking degree decreased in the longitudinal direction. The process of deformation of the MCBs was consistent with the process of channel degradation during the dam operation period (erosion, slight erosion and strong erosion). The deformation of the MCBs is mainly attributed to altered flow–sediment conditions. The magnitude of sediment transport capacity changed slightly after 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.