MODELING WATER EROSION AND THE IMPACT OF WATER REPELLENCY

Three years of weekly measurements of surface runoff and sediment yield from two small plots in a dune terrain along the Dutch coast have been used to model water erosion. The measurements of the third year have been used to validate the regression model based on the first two years of measurements. A major effect on runoff and concomitant erosion is exerted by water repellency of soils, which results in impeded infiltration of dune soils when dry. In a spatial context, water repellency is associated with more runoff and less erosion (per unit area). For a given catchment, however, water repellent conditions generally lead to both more runoff and erosion. This temporal aspect is due to the fact that the degree of water repellency decreases with soil moisture content. Consequently, antecedent rainfall affects the degree of water repellency of dune sands, and taking this into account leads to profoundly distinct predictions of water erosion.