Effects of water and sediment variations on estuarine channel evolution: mechanisms and morphological discrimination

This study employed physical experiments to simulate the morphological evolution of a meandering tail channel, a critical river-sea interaction zone, under varying flow and sediment conditions, with a focus on the Yellow River. Results demonstrate distinct evolutionary patterns: during sediment-feeding phases, the non-estuarine reach experiences deposition under low flows, leading to bed aggradation, channel widening, and mid-channel bar development, suggesting a potential shift toward a wandering pattern, while scour dominates under high flows, forming narrow, deep cross-sections. In the estuarine reach, a nascent Lambda-shaped delta forms under low flows, whereas high-flow conditions promote erosion and a W-shaped cross-section. After sediment feeding ceases, the non-estuarine reach maintains a wide, shallow form under low flows but undergoes intense scour under high flows, whereas the estuarine reach develops a multi-distributary fan-shaped deposit under low flows, with high flows triggering channel migration or avulsion. Experiments confirm that sediment transport profoundly influences channel morphology regardless of bed state, and particle size distribution of sediments correlates strongly with the degree of channel evolution. Based on these findings, the resistance law expression was refined, and a channel pattern discrimination method suitable for the lower Yellow River was proposed and validated with measured data, confirming its rationality and reliability.