Effects of combined vegetation and terrace configurations on rill erosion in the slope-gully systems of the Loess Plateau

Abstract: Rill erosion serves as a crucial transitional stage in water erosion, bridging sheet erosion and gully erosion, and constitutes a major form of soil erosion. Existing research has mainly focused on the impacts of vegetation patterns or vegetation coverage on rill erosion processes; however, the regulatory mechanisms of vegetation, terraces, and their combined configurations on rill erosion remain understood. To address this research gap, this study established slope-gully system models under six slope management scenarios: a control group (CK, bare slope), Measure A (upper-slope grass), Measure B (mid-slope grass), Measure C (lower-slope grass), Measure D (mid-slope terrace), Measure E (upper-slope grass + mid-slope terrace), and Measure F (mid-slope terrace + lower-slope grass). Employing simulated rainfall experiments and 3D laser scanning technology, this study clarified the developmental process of rill erosion and its responses to different management configurations, quantified variations in slope hydrological connectivity, and elucidated the regulatory mechanisms of different management measures on rill erosion. The results indicated that the combined Measure F exerted a significant regulatory effect on rill erosion processes in the slope-gully system. Specifically, this measure reduced the total rill length by 79.76%, delayed the initial occurrence of distinct rills by approximately 18 minutes, and minimized the average rill elongation rate to 1.32 cm/min. Additionally, it decreased the rill erosion mass, rill erosion volume, and the proportion of rill erosion by 50.14%, 50.06%, and 44.22%, respectively, exhibiting the optimal erosion control efficiency. Simultaneously, Measure F most effectively blocked surface runoff pathways, reducing the proportion of longer runoff path lengths by 4.99% and 4.81% compared to the control group after two rainfall events. Topographic analysis revealed that the slope topography was predominantly concave (characterized by negative skewness of the topographic convergence index), and the topographic wetness index increased post-rainfall, facilitating runoff generation. Compared with single measures, Measure F exerted a significant synergistic effect, enhancing the reduction rates of rill erosion mass, volume, and area by 18.82%, 20.51%, and 18.02%, respectively. In conclusion, the combined configuration of “mid-slope terrace + lower-slope grass” effectively inhibits rill erosion and optimizes slope hydrological connectivity, serving as an optimal integration of vegetative and engineering measures. This study provides a scientific basis for soil and water conservation management on the Loess Plateau.