Soil surface roughness impacts erosion behavior through selective regulation of flow properties in rainfall-seepage scenarios

Soil surface roughness (SSR) impacts runoff dynamics of surface-subsurface and the magnitude of soil erosion, limited attention has been paid to how SSR governs runoff hydrodynamics to affect erosion behavior and the effectiveness of erosion reduction under rainfall-seepage scenarios on low-permeability purple soil slopes. Herein the seepage rates of 2, 4, and 8 L min⁻¹ were sequentially simulated under a rainfall intensity of 1.0 mm min⁻¹ among different microrelief treatments (CT: conventional tillage; AD: artificial digging; RT: ridge tillage) on purple soil slopes with gradients of 5°, 10°, and 15°. These simulations aimed to investigate the mechanisms underlying the erosion reduction benefits associated with flow properties due to microrelief. The results showed that increased SSR altered erosion kinetic energy under rainfall-seepage conditions. The benefits of rough slopes to control erosion decreased as rainfall-seepage intensity and slope gradient increased. During rainfall-seepage events, the variation in runoff behavior was regulated positively by the effect of SSR on unit stream power. However, the increasing net output power of runoff due to flow turbulence altered sediment output, thereby affecting sediment control benefits. Overall, the impact of rainfall-seepage intensity on surface roughness became more significant with increasing slope gradient. Our findings suggest the capable of integrating for interrelated microrelief and runoff processes in factors analysis of driving soil erosion at rainfall-seepage hydrologic states to elucidate erosion effect.