Assessment of Infiltration Rate of Water Repellent Dune Sand

Abstract

A water-repellent or a hydrophobic soil does not wet up spontaneously when a drop of water is placed on the surface. The primary effect of water repellency is the reduction of infiltration rates. The purpose of this study was to determine the effect of water repellency on infiltration rate of dune sand in Dry zone of Sri Lanka under thick cover of Casuarina equisetifolia. Infiltration test was conducted in-situ and the water repellency measurements were conducted both in-situ and ex-situ. Water repellency was determined using the water drop penetration time (WDPT) test. Infiltration rate of the dune sand was determined using a double ring infiltrometer. The WDPT of the studied dune sand was > 1 h showing extreme water repellent condition. The water repellent condition in the dune sand was attributed to the water repellent leaf litter of Casuarina equisetifolia. The water repellent condition gradually decreased with the soil depth. The initial infiltration rate was 120 cm h'1 and started to increase with time after about 5 min elapsed time. The highest infiltration rate was 188 cm h~‘, which was achieved 12 min after the starting of the infiltration test. Then, the infiltration rate gradually decreased. The steady state infiltration rate was 164 cm h 1 and achieved within about 40 min from the beginning of the test. Water infiltration started within seconds irrespective of the extreme water repellent condition. This can be considered as governed by the ponding depth.