Study of simulated soil erosion on a bare karst slope

Karst is widely distributed in China where carbonate rocks, including buried karst, account for up to 3,463,000 km2. Strata with carbonate rock formations comprise 2,060,000 km2, while carbonate rocks outcrop over 907,000 km2.The karst system, which is faces serious soil erosion problems, is an ecologically fragile system due to its high sensitivity, low catastrophe capacity and small environmental capacity. Therefore, study of soil erosion in karst areas is important. The impacts of fissure porosity, bedrock outcrop percentage and rainfall intensity on underground runoff and sediment yield were evaluated using simulated rainfall. The results provide a theoretical basis for future evaluation and prevention of soil erosion in karst areas. The results showed; (1) Soil erosion has a high correlation with porosity or fracture aperture; (2) Soil infiltration rate is dependent on rainfall. Surface and subsurface suspended sediment decrease with rainfall duration, while surface bed material load increases; (3) In general, the amount of surface runoff and sediment decreases with the bedrock outcrop rate, while the amount of underground runoff and sediment increases; (4) Only suspended sediment loss took place on the surface. No bed material load loss occurred with rainfall intensity of 30 mm/h. The runoff and sediment yield increase with rainfall intensity. For instance, when rain intensity increased from 30 mm/h to 150 mm/h, the cumulative surface runoff was 538.5 L, cumulative surface sediment yield 2,393.81 g, cumulative underground runoff 207.8 L and cumulative underground sediment yield 687.83 g. The rate of increase in the cumulative sediment yield is greater than the rate of increase in the cumulative runoff, and the rate of increase in the surface runoff and sediment yield is greater than that of the underground runoff and sediment yield; (5) The correlation between soil erosion and each individual factor indicates that the relative impact of each factor on soil erosion is, rainfall duration ＞ rainfall intensity ＞ underground porosity ＞ bedrock outcrop.