Effects of upslope inflow rate, tillage depth, and slope gradients on hillslope erosion processes and hydrodynamic mechanisms

Inflow rate, tillage depth and slope gradient play vital roles in hillslope soil erosion processes. However, the effects of these factors and their interactions on hillslope soil erosion processes, particularly on long slopes in the Chinese Mollisol region, are still lacking to date. Thus, a set of laboratory experiments, including six upslope inflow rates (0, 50, 100, 150, 200 and 300 L min−1), two tillage depths (5 and 20 cm) and two slope gradients (5° and 10°), were conducted to quantify the impacts of these factors and their interactions on hillslope soil erosion processes. The results showed that soil erosion rates increased as a power function with increase of inflow rate and slope gradient, while they decreased as a power function with an increase in tillage depth. The slope gradient had a greater impact on soil erosion rates than inflow rate and tillage depth. Moreover, inflow rate, slope gradient, and their pairwise interaction mainly governed hillslope soil erosion. Compared with hillslope soil erosion, hillslope runoff rate was dominantly affected by inflow rate. The inflow rate and slope gradient affected the hydrodynamic characteristics and erosion rates by shifting erosion patterns; while tillage depth mainly influenced them by converting surface flow to seepage flow. In addition, the dimensionless effective stream power was the optimal index (R2 = 0.884, NSE = 0.861) affecting soil erosion rates, followed by the dimensionless stream power (R2 = 0.879, NSE = 0.848). The dimensionless soil erosion rates were correlated with the dimensionless hydrodynamic parameter following a power function. Therefore, soil erosion in the Chinese Mollisol region could be effectively prevented by dispersing runoff, increasing deep tillage and reducing the impact of slope gradient through soil conservation measures.