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Cumulative Impacts on the Ma'anshan Reach of the Lower Yangtze River Under Varying Water and Sediment Conditions

change of water and sediment condition; Ma'anshan Reach of the Lower Yangtze River; morphological evolution trend; cumulative impacts

Ma'anshan reach is a typical braided reach of the Lower Yangtze River, with numerous bars and complicated evolution. The stability of river regime and waterway conditions have been strengthened and improved under the control of a large number of regulation projects. Following the impoundment of the Three Gorges Reservoir, notable alterations of water and sediment conditions occurred within the Ma'anshan reach of the Yangtze River, leading to pronounced local river regime adjustments. Based on historical in-situ data and results from physical model experiments, morphological pattern analysis and evolution trend prediction were carried out and the cumulative impacts of water and sediment changes on flood control, navigation, and shoreline utilization were assessed. The results show that the river regime adjustments pose potential adverse impacts on the safe functioning of river and waterway regulation projects, water-related engineering projects, and navigation activities. The erosion and undercutting of the near-bank riverbed have led to the continuous scouring and collapse of existing bank protection projects, posing a threat to flood control safety. With a continuous downward shift in the mainstream transitional segment of the left branch of Jiangxinzhou, the deposition and outward expansion of the Niutun Sandbar as well as the deposition of the riverbed in front of the water intake along the section from the Muxia River to the Sunhe River have occurred, leading to decreasing water depth of the Zhengpu Port. Additionally, the decrease of diversion ratio in the transition section of Xiaohuangzhou and the left branch of Xiaohuangzhou threatens the stability of the waterway and the sustainable development of the Ma'anshan Port.