The effect of pre-detached particles on soil erodibilities associated with erosion by rain-impacted flows

Abstract

In shallow rain-impacted flows, particles detached from the soil matrix will produce a layer of pre-detached particles on an eroding surface when entrainment by flow is absent. This layer provides a degree of protection to the underlying soil matrix and material from the layer also contributes to the discharge of sediment across the downstream boundary of an eroding area. The development and effects of the layer are dynamic. The layer tends to be more protective at low flow velocities and with coarse particles than at high velocities and with fine particles. The ease by which particles can be detached from the soil matrix also influences the development of the layer. The dynamic nature of the layer results in the susceptibility of a surface to erosion by rain-impacted flow varying in time and space. The consequence of this is examined with respect to erodibilities associated with an erosivity index that is based on the product of runoff rate and the rate of expenditure of rainfall kinetic energy.