Phased Responses in Gully Water-Sediment Regulation Throughout Check Dam Lifecycles

To address the unclear mechanisms of water-sediment regulation during different stages of check dam lifecycles,this study coupled the distributed hydrological model MIKE SHE with the one-dimensional hydrodynamic model MIKE 11 to establish a slope-gully hydrological-hydrodynamic model.By integrating dynamic sedimentation processes,historical retrospection and future projections quantitatively analyze the differential impacts of check dam systems on flood process characteristics and erosion dynamics during three stages:pre-construction (S1),initial operation (S2),and sediment-filled maturity (S3).Check dams exhibit phased regulatory effects:shifting from “rigid regulation” dominated by physical interception in the initial operation stage (S2) to “resilient regulation” relying on gully geomorphology in the sediment-filled stage (S3).The initial operation stage (S2) exhibits optimal runoff regulation,with the smallest average flow,flood volume,and peak discharge among the three stages.Under a 200-year rainfall event,the reduction rates for outlet flow,flood volume,and peak discharge reached 80.96%,89.85%,and 89.81% in S2,and 11.09%,2.51%,and 24.04% in S3,respectively.Mature check dam systems primarily attenuate flow energy,achieving reduction rates of 145.64% for average velocity and 66.37% for shear stress.Peak shear stresses in the main channel predominantly occur near tributary confluences and dam sites,yet check dam construction effectively reduces the overall shear stress levels.These findings provide theoretical support for the dynamic optimization of check dam systems on the Loess Plateau.