Water repellency and its measurement by using intrinsic sorptivity

Abstract

Measurements of intrinsic sorptivity (S*) by using both ethanol and water were used to indicate the extent of water-repellency in soil. Experiments with initially dry, acid-purified sand verified that in a non-repellent, nonswelling porous medium S' was indeed intrinsic to the medium, and independent of the sorbing liquid. For initially water-moist, non-repellent sand, the measured S* was different when ethanol and water were the invading fluids. But a bound can be put on this difference. It was concluded that in structurally stable soils, the ratio of S* from ethanol to that for water may be used as an index of water-repellency. In the laboratory, disturbance of repellent soil by sieving or shaking effectively removed the repellency. Subsequent incubation restored it. Field measurements of sorptivity, at a scaled negative surface potential, into an initially moist, fine, sandy loam were made. While the soil appeared to absorb water normally, the sorptivity for water was an order of magnitude lower than expected from the ethanol data. This was due, we suggest, to repellency. Some possible implications of this unexpected result are discussed.