Mechanisms of hydraulic erosion control in different microrelief patterns of loess sloped farmland under continuous rainfall

Different microrelief patterns of sloped farmland have important effects on soil erosion. However, its hydraulic erosion control mechanism under continuous rainfall is unclear. In this study, the effects of two microrelief patterns (reservoir tillage (RT) and contour tillage (CT)) of sloped farmland on runoff, soil erosion, and hydrodynamic parameters were investigated at the plot scale using simulated rainfall and high-definition photography methods. Smooth slopes (SS) were chosen as a control. The test rainfall intensities (RIs) were selected as 30, 60, 90, and 120 mm h⁻¹. Two continuous rainfall events, each lasting 40 min, were conducted on each type of slope. The results show that the different microrelief patterns have a twofold role in soil erosion on slopes as influenced by rainfall conditions. During the first rainfall, compared to SS, the RT and CT increased the Darcy–Weisbach coefficient and reduced the surface flow velocity. The RT and CT significantly increased the initial runoff time and reduced runoff yield (10.9–69.46 %) and sediment yield (9.87–74.87 %). However, during the second rainfall event, the water-retaining terrain of the RT and CT was destroyed. This resulted in reduced Darcy–Weisbach coefficients and increased flow velocities on the RT and CT. Compared to the SS, the RT reduced the runoff yield (10.59–63.86 %) and sediment yield (19.04–51.17 %) under RIs of 30, 60, and 90mm h⁻¹, but the magnitude of reduction decreased compared to the first rainfall event. The RT increased the runoff yield (11.32 %) and sediment yield (6.08 %) under the RI of 120 mm h⁻¹. The CT increased the runoff yield (19.13–24.88 %) and sediment yield (15.75–46.32 %) under all four RIs. In addition, statistical analysis indicated that stream power could explain 79 % of the changes in runoff and sediment yield on RT and CT, and effective stream power could account for 79 % of the variations in runoff and sediment yield on SS. Stream power served as the optimal indicator for characterizing the runoff and sediment yield rates on RT and CT, whereas effective stream power was the best metric for SS. This study can help us to better explain the mechanism of hydraulic erosion control in different microrelief patterns.