Effects of rainfall intensity, underlying surface and slope gradient on soil infiltration under simulated rainfall experiments

Knowledge of infiltration patterns and process is very important in understanding and managing slope hydrological processes, crop irrigation, soil erosion, and so on. This paper describes a study in which simulated rainfall events were used to study the effects of various factors (vegetation cover, rainfall intensity, and slope angle) on the soil moisture increase after rainfall and the infiltration recharge coefficient. Soils hosting three different plants (purple medic, PM; spring wheat, SW; and ryegrass, RS) were considered, along with bare soil (BL). These soil surfaces were tested with four different slopes (8.8, 17.6, 26.8 and 36.4%) and subjected to five different rainfall intensities (0.5.0.75, 1.0, 1.5 and 2.0 mm min(-1)). The following key results were obtained: (1) The water distribution in BL boxes differed significantly from that in boxes with vegetation cover, but all boxes with vegetation cover exhibited similar distributions. Vegetation cover significantly increased the depth of the wetting front: under very similar conditions, the wetting front in the RS box reached a depth of more than 35 cm, while that in the BL box reached only 25 cm. (2) Vegetation cover (especially ryegrass) yielded a greater soil moisture increase than did bare land. The overall average soil moisture increase for RS boxes was 36.7 +/- 5.1 mm, about twice than that of BL (3) The water storage after rain across the whole soil profile initially increased and then decreased as the rainfall intensity rose. No differences in the average soil water content increase were found between various rainfall intensities. (4) As the slope increased from 8.8% to 36.4%, the water storage increase initially rose but then fell sharply. There were significant differences (p = 0.05) between the water storage increases for gradual slopes (8.8 and 17.6%) and steep slopes (26.8 and 3.4%). (5) The recharge coefficient increased with increasing vegetation cover but decreased with increasing rainfall intensity, slope gradient, and initial soil water content. The average value for boxes with vegetation cover was 1.5 times that for BL boxes. The vegetation cover was the most important factor in determining the recharge coefficient. (C) 2012 Elsevier B.V. All rights reserved.