Particle travel distances and bed and sediment compositions associated with rain-impacted flows

Laboratory experiments were performed with rain of uniform drop size (2.7 nun, 5.1 mm) impacting flows over noncohesive beds of uniform sized sand (0.11-0.9 mm) and coal (0.2-0.9 mm) particles with flow velocities (20 nun s(-1), 40 mm s(-1)) that were insufficient for the flow to entrain the particles without the aid of raindrop impact. Measurement of particle travel distance under rain made up of 2.7 mm drops confirmed a theoretical relationship between settling velocity and the distance particles travel after being disturbed by drop impact. Although, in theory, a relationship between settling velocity and particle travel distance exists, settling velocity by itself was unable to account for the effect of changes in both particle size and density on sediment discharge from beds of uniform non-cohesive material. Particle density was also a factor. Further study of how particle characteristics influence sediment discharge will aid modelling of the impact of the soil in process-based models of erosion by rain-impacted flow. Copyright (C) 2001 John Wiley Sons, Ltd.