The Role of Bedrock Topography in the Runoff Process and Soil Erosion on Karst Steep Slopes

ABSTRACT The micro‐scale distribution patterns of rocks and soils are crucial to the hydrological processes of karst slopes. However, current research has provided detailed reports only on the aboveground rock–soil patterns, neglecting the role of underground rock–soil patterns. To address this, our study conducted simulated rainfall experiments and runoff supply tests to observe surface runoff, sediment yield and the migration characteristics of subsurface runoff under three types of bedrock topographies: mosaic bedrock topography (MBT), horizontal‐strip bedrock topography (HBT) and smooth bedrock topography (SBT), at rainfall intensities of 30, 60 and 90 mm/h. The results indicated that undulating bedrock topography significantly increases surface runoff and exacerbates surface erosion. The surface runoff yields in HBT and MBT were 184.68% and 131.77% higher, respectively, than in SBT, and their average surface soil losses were 4.56 and 3.35 times greater than those of SBT, respectively. The undulating bedrock topography impeded the movement of subsurface runoff; the average subsurface runoff yield in SBT was 42.36% and 82.86% greater than in MBT and HBT, respectively. The movement of subsurface runoff followed the ‘fill‐and‐spill’ theory, where the undulating bedrock topography controls subsurface runoff transport. Additionally, preferential pathways between bedrock depressions affected the rate of subsurface runoff movement. Similar to rock outcrops, underlying bedrock, influenced by its characteristics and other factors, may play two opposing roles in the erosion process. Therefore, it warrants as much attention as rock outcrops.