Water repellency and its role in forming preferred flow paths in soils

The role of water-repellency in forming preferred flow paths and in accelerating solute transport is explained on the basis of extensive field measurements in a grass-covered water-repellent sandy soil in the Netherlands. When the 9 cm thick humous topsoil was wetted to 20-25 vol.%, preferred flow paths, or fingers, were formed in the sandy subosil. The fingers started at the layer interface at `weak' spots with a relatively low degree of potential water-repellency, and protruded vertically into the sandy subsoil. The fingers disappeared during dry periods and recurred at the same locations during new rain events