Subsurface flow aggravates the soil erosion on steep slopes in karst post-mining areas

On karst steep slopes, subsurface flow frequently emerges at the rock-soil interface, thereby exacerbating soil erosion. However, there have been few studies that quantitatively assess the impact of subsurface flow on soil erosion in this region. We conducted indoor artificial rainfall experiments to observe runoff and sediment yield under two conditions: with subsurface flow (SF) and without subsurface flow input (WSF). We considered various rainfall intensities (30 mm h-1, 60 mm h-1, 90 mm h-1) and slope gradients (30 degrees, 35 degrees, 40 degrees). The results demonstrated that the presence of subsurface flow significantly amplified both surface runoff and sediment yield, while also intensifying the influence of rainfall intensity and slope gradient on runoff and sediment yield. Compared to WSF, under SF conditions, surface runoff increased by 1.55 to 4.43 times, and sediment yield increased by 4.60 to 8.72 times. Slope gradient played a substantial role in soil loss, while rainfall intensity primarily impacted surface runoff. Under WSF conditions, soil loss only occurred at a 40 degrees slope gradient or under a rainfall intensity of 90 mm h-1, whereas under SF conditions, soil loss could occur at a 30 degrees slope gradient or under a rainfall intensity of 30 mm h-1. This research provides a scientific foundation for a more profound understanding of the mechanisms driving soil erosion on karst slopes, particularly in the context of subsurface flow.