Mechanism of runoff generation on the sloped land of purple soil with different thicknesses in the Three Gorges Region

Soil thickness is one of the most important factors determining the hydrological process on hillslopes. Using a portable rainfall simulator, file experiments were conducted on three sloped land sites along a hillslope to investigate the mechanism of runoff generation under artificial rainfall intensities of 60 mm/h. The sites contain purple soil with different depths (23 cm, 45 cm, and 76 cm). The results show that saturation excess runoff contributes a large portion of overland flow on the 23 cm soil site; it is in contrast with the domination of infiltration excess runoff generation found on other two sites. As for interflow, preferential flow is generated from the 23 cm soil site, while matrix flow dominates in the 76 cm soil site; two types of interflow zones are observed on the 45 cm soil site. And preferential flow is generated in upper soil horizon AC, while lower soil horizon A contains mainly matrix flow. The experiments reveal that the thickness of soil horizons and their hydrogeological properties play major roles in runoff generations.