Modeling Study on Enhancing Overall Sediment Transport Efficiency in a Reservoir‐River Coupled System of the Middle and Lower Yellow River

Abstract Effective sediment management in reservoir–river coupled systems remains a global challenge due to the conflicting objectives of sediment evacuation from reservoirs and deposition reduction in downstream reaches. This study proposed a physics‐based modeling framework oriented to a reservoir–river coupled system, which integrates morphodynamic calculation and reservoir operation simulation via a two‐way feedback mechanism. Unlike simplified approaches, this framework captures complex transient flow‐sediment processes at the system scale. The study region covers the 1,000‐km Tongguan–Lijin reach in the Middle and Lower Yellow River, encompassing the Sanmenxia–Xiaolangdi cascade reservoirs. This region represents a typical reservoir–river coupled system facing an urgent need to balance the conflicting objectives. The validation results demonstrated that the proposed model achieved high‐fidelity modeling of flow‐sediment fluxes in reservoirs and downstream reaches. Multi‐scenario simulations and sensitivity analyses provide quantitative insights into how the overall sediment transport efficiency responds to varying reservoir operation parameters during the period of Water‐Sediment Regulation Scheme, including replenishing discharge and regulation water volume. In addition, this study identifies distinct optimal operation strategies for different deposition reduction targets: a sharp and short‐duration flushing mode can maximize the reservoir sediment evacuation, while a low‐discharge but long‐lasting release process can maximize the downstream channel erosion. Further simulations across various flow‐sediment regimes demonstrate the universality of the proposed operation strategies. The findings provide insights for adaptive selection of reservoir operation strategies when addressing the conflicts between different stakeholders at a flood‐event scale.