The 12th International Conference on Scour and Erosion (ICSE 2025)

The middle and lower reaches of the Yangtze River constitute a large alluvial plain river system. Following the sequential operation of upstream cascade reservoirs, the downstream channels have undergone prolonged and extensive erosion-deposition adjustments. As the reach closest to the dam, the Jingjiang Reach has been significantly impacted by altered flow-sediment regimes, becoming the most severely eroded section since the impoundment of the Three Gorges Reservoir(TGR). This study investigates the spatiotemporal characteristics of erosion and deposition in the Jingjiang Reach following TGR impoundment, utilizing extensive measurement data. The results show that the reach has experienced long-term morphological adjustments, transitioning from a near-equilibrium state under natural conditions to a predominantly erosional regime, with scour concentrated in middle and low-flow channels. Under the combined effects of flood peak attenuation, prolonged moderate discharge durations, and substantial sediment supply reduction, unprotected mid-channel bars exhibited systematic erosion patterns, characterized by headward retreat of bar fronts and areal shrinkage. The 175m trial impoundment in 2008 intensified bar erosion, while the diminished supply of medium-fine sediments from upstream has hindered the recovery of eroded bars. These results highlight the profound and persistent geomorphic impacts of large reservoir operations on downstream alluvial systems, providing critical insights for sustainable river management.