Water repellent soils

Abstract

Capillary forces in unsaturated soils depend on the surface tension of water, the dimensions of soil pores and on the contact angle of the interfaces of the solid phase of soil (soil matrix) and liquid water. The contact angle (angle of wetting) is assumed to be zero, but in real soils is higher, depending on the properties of the thin surface layer (organic) covering soil particles. There are some classes of soils with limited affinity for soil water. Soils are classified as wettable with contact angles φ < 90°; water-repellent soils are characterized by contact angles of φ ≥ 90°. The occurrence of water-repellent soils is rare and usually their repellency is temporary (dry soils). This chapter defines the characteristics of soil-water repellency: contact angle, severity of water repellency, persistence of soil water repellency and index of water repellency. It also presents the hydrophobic compounds in soils and the influence of soil-water repellency on hydrological processes in soil (infiltration, preferential flow, evaporation).