Impact of boundary conditions on soil water and subsurface flow in shallow purple soil slope

By applying mathematical statistics methods,the parameters of the water-content wave and subsurface flow hydrograph which derived from in-situ simulated rainfall were analyzed,and the effects of rainfall intensity and surface soil bulk density (0～5mm depth) on subsurface flow of a shallow purple soil slope was studied.The results show that the wetting front velocities are in the range from 0.28 to 1.63mm/s with obvious features of preferential flow,which are much higher than the velocities expected from flows that are driven by the combined gradients of gravity and capillarity.Rainfall intensity and surface soil bulk density are major factors affecting the soil water movement and subsurface flow.The increase of rainfall intensity facilitates the occurrence and development of preferential flow,while surface seal is the main reason impedes preferential flow.