Correlation Between Water Erosion and Hydraulics of Slope–Gully Systems According to Check Dam Siltation Depth

The loess hilly area consists of a slope–gully system, which promotes erosion; as such. it is one of the most intensely eroded areas in the world. The construction of check dams can effectively control water and soil loss of slope gullies. However, existing studies focus on the benefits of intercepting runoff and sediments at dam sites, while ignoring the change law of hydrological processes with respect to progressing dam land sedimentation. Moreover, past studies focus on the “runoff–sediment” or “flood–sediment” relationships, but rarely consider the “hydrodynamics–runoff” and “hydrodynamics–sediment” dynamics. Therefore, in this study, we developed five physical models of slope–gully systems for dam land sedimentation depths of 0, 1, 2, 3, and 4 m, in order to explore the effects of sedimentation on runoff–sediment–hydrodynamic processes. The runoff and sediment yield of the slope–gully system decreased with increasing siltation depth. The spatial and temporal distributions of the hydrodynamic parameters were different. The Reynolds number ( Re ), runoff energy consumption ( ΔE ), and runoff power ( P ) increased with rainfall time, whereas runoff shear stress ( τ ) and Froude number ( Fr ) did not show a significant trend over time. Re and ΔE could better describe the runoff process of the slope–gully system, while P and ΔE could better simulate the sedimentation process. Notably, our study can provide a scientific basis for establishing effective erosion prediction models to estimate the water erosion process of slope–gully systems.