Effects of reservoir group topological structures on the sediment reduction in large river networks – A case study of the Upper Yangtze River Basin

Study region Upper Yangtze River Basin (UYRB), China. Study focus Reservoir construction has profoundly altered sediment transport in large river systems, yet the influence of reservoir-group topological structures on basin-scale sediment redistribution remains poorly understood. This study quantified how reservoir-group topology regulates runoff–sediment relationships and sediment reduction across the UYRB using hydrological observations from 1950 to 2024. A topology-based framework incorporating the effective basin area ratio ( λ ) was developed to improve sediment trapping efficiency estimation for interconnected reservoir systems. New hydrological insights Sediment load at Yichang Station decreased by 98.09% during 1950–2024, primarily due to the rapid expansion of large reservoirs, which account for 88.5% of the basin's total storage capacity. Reservoir-group topology produced pronounced spatial heterogeneity in sediment reduction. The Xiluodu-Xiangjiaba cascade in the Jinsha River Basin contributed 53.7% of the basin-wide sediment reduction, whereas the Wujiang River Basin exhibited substantially lower sediment trapping efficiency despite its large storage capacity. After the Three Gorges Reservoir began operation, the dominant contribution to sediment reduction shifted from the mainstream to upstream tributaries, with the Jinsha River Basin increasing from 30.5% to 54.7%. A revised sediment trapping efficiency equation incorporating λ reduced RMSE by 48.3–75.0% compared with conventional models. These results demonstrate that reservoir connectivity, rather than storage capacity alone, controls basin-scale sediment redistribution, providing a transferable framework for sediment management in regulated river networks.