Flood sedimentation dynamics in dam-regulated river channels: A case study of the Lower Yellow River

The Lower Yellow River (LYR), China. The construction and operation of large dams can significantly alter runoff and sediment transport processes in downstream river channels, resulting in long-term and long-distance adjustments in river sedimentation. Since the Xiaolangdi Reservoir began impoundment in late 1999, the runoff and sediment transport processes in the LYR have experienced significant changes. To comprehend the response of sedimentation in the LYR to the reservoir’s operation, this study provides a detailed analysis of the spatiotemporal variations in sedimentation and examines the effects of 159 floods released from the Xiaolangdi Reservoir during 2000–2023. The LYR reached dynamic equilibrium following a long period of erosion, the magnitude of channel erosion increased rapidly from 2000 to 2004, then gradually decreased from 2004 to 2017. Floods were categorized into three types based on average sediment concentration ( S av ), which varied under different reservoir regulation modes. During 2000–2023, the low ( S av <1 kg/m 3 ) and medium (1 ≤ S av ≤10 kg/m 3 ) sediment concentration floods yielded erosion, while the high sediment concentration floods ( S av >10 kg/m 3 ) caused either aggradation or erosion. For a stable dynamic equilibrium (both erosion and aggradation are minor) to be maintained in the LYR, it is recommended that the sediment concentration of floods released from the Xiaolangdi Reservoir be kept below 40 kg/m 3 . • Flood sedimentation dynamics in the Lower Yellow River was studied using a long-series dataset. • Due to dam regulations, floods into the Lower Yellow River differed dramatically in sediment concentration. • The Lower Yellow River eroded for 17 years, initially increasing rapidly and then decreasing gradually. • All low and medium sediment concentration floods yielded erosion, but high sediment floods caused aggradation or erosion. • All sub-reaches achieved equilibrium concurrently with the entire LYR, but they followed distinct adjustment trajectories.