Water pending depths affect temporal infiltration rates in a water-repellent sand

Water-repellent soils exhibit a positive water entry pressure head, h(p). T he effects of imposing differing water pressure head values, by using diffe ring water pending depths, h(0), on infiltration into repellent soils was i nvestigated. A sand, with particulate size between 0.05 and 20 mm, was trea ted with two concentrations of octadecylamine to create a sand with h(p) va lues of 8.4 and 3.5 cm, The hydraulic conductivity, K, of the water-repelle nt sands increased with increasing values of h(0). The K of the treated san d was equal to K of unheated sand when the ratio h(0)/h(p), was approximate to3.1 for each treated sand. The infiltration rate increased with increase d time for lower h(0) values, but decreased with increased time for higher h(0) values. The transition from increasing to decreasing infiltration rate s with time occurred when h(0)/h(p), was approximately equal to 2.6, The in filtration rate behavior of an aqueous ethanol solution was consistent with theoretical relationships based on liquid surface tension, A positive hydr aulic head was created at the interface of an overlying wet table and under lying water-repellent layer that affected the infiltration rate consistent with the effects of h(0) on a nonlayered water-repellent sand. The followin g mechanism is proposed to explain the increase in infiltration rate with t ime. In water-repellent materials, positive hydraulic heads can be created within the profile during infiltration, which can increase as the depth to the wetting front increases. The higher hydraulic head induces an increase in hydraulic conductivity, which contributes to increased infiltration rate . Alternatively, it the depth of ponded water is sufficient to cause a hydr aulic conductivity equal to that of the wettable material, the infiltration rate behavior is the same as traditionally observed for wettable soils.