Erosion-accretion Spatiotemporal Distribution in the Continuous Sharp Bend of the Lower Jingjiang River and Its Influencing Factors Since the Construction of the Three Gorges Dam

This research analyzed the general morphological changes of Xiongjiazhou-Chenglingji reach, the spatiotemporal changes pattern in different sub-regions and corresponding influencing factors. Data sources included measured topography in five years, water and sediment at Jianli Station from 2002 to 2018. The results show that Xiongjiazhou-Chenglingji reach has undergone significant erosion with 0.1m/a since 2002. The shoal scouring, channel silting occurred from 2002 to 2006 and shoal silting, channel scouring occurred from 2006 to 2013, respectively. The shoal and channel scouring has appeared since 2013. The maximum scouring in the straight transition reach is 0.21m/a in the west of Baxing sandbar. The average annual scouring thickness of straight transition reach is greater than that of bend, and the erosion intensity decreases along the river. Sediment reduction and annual flow process change are the main reasons for the erosion-accretion temporal difference and the role of flow process change is enhanced since 2013. The initial riffle-pool topography is the critical for the erosion-accretion spatial difference. The straight transition reach in the west of Baxing sandbar is longer and the width depth ratio is larger, which has provided sufficient space for the thalweg shift. However, the long-term stability deep pool at the outlet of Qigongling bend, Guanyinzhou bend and rivers and lakes confluence area is conducive to conform to the upstream mainstream change. The findings will deepen the understanding of natural continuous sharp bends evolution rule during erosion, and provide a scientific basis for river pattern control, flood and navigation safety in tail reach of the Lower Jingjiang River.