A number of researchers have found strong relations between the kinetic energy of water drops and the change in physical properties of the soil surface. Thompson and James (1985) analyzed the increase in hydraulic resistance of the soil surface layer as the drop kinetic energy per unit soil surface area increased. These authors also reported a decrease in soil infiltration with increasing rainfall intensity, kinetic energy per water droplet, and water droplet energy flux. Kohl et al. (1985) reported an increase in kinetic energy per unit volume of discharged water when the operating pressure was reduced. Similar results were obtained by Basahi et al. (1998), when determining the specific power of experimental
water drops impacting on a surface. Mohammed and Kohl (1987), discussed previous experiments performed by Duley (1939) and Ellison (1947), whose results showed that water drops destroyed surface aggregates and gradually formed a surface seal characterized by much lower hydraulic conductivity than the original soil surface.