Rainfall Infiltration Pattern in an Unsaturated Silty Sand

One-dimensional infiltration tests were conducted to investigate the effects of rainfall intensity and initial water content on the transient infiltration pattern of unsaturated silty sand. For a constant rainfall intensity greater than the saturated permeability but smaller than the maximum infiltration capacity of soil, the infiltration curve is divided into preponding and postponding stages. The time to ponding reduces with increasing rainfall intensity and initial water content. After ponding, the infiltration rate reduces with time and its reducing rate increases with rainfall intensity but does not vary significantly with initial water content. The infiltration pattern can be simulated qualitatively by solving Richard’s equation numerically with the use of the flux and head type boundary conditions at the soil surface in the preponding and postponding stages, respectively.