Changes in riverbed morphology in the middle Yangtze River (Yichang–Chenglingji) after the construction of the Three Gorges Dam

The present study investigates the impact of the Three Gorges Dam (TGD) construction on riverbed morphology in the middle Yangtze River (YR). We analyse data collected on sand wave morphology, shallow surface topography, and section morphology after the completion of the dam. Specifically, we examine the spatial distribution characteristics of sand wave morphology and the riverbed evolution process in the Yicheng reach. Results reveal significant changes in the morphology of sand waves in the middle reach of the YR, with wavelengths ranging from 5.2124.15 to 5.0915.33 m in the upper and lower Jingjiang River, respectively. Additionally, sediment incipient velocity was found to be smaller than that of the sand wave, making it difficult for the sand wave to start as the bedload continued to coarsen. After impoundment, the riverbed is strongly scoured, the undercutting is serious, and the bed morphology changes dramatically.