Sediment Transport Induced by Raindrops Impacting Shallow Flows

Abstract

A theory for RIFT, the transport process that results from raindrops impacting shallow flows, is presented. The theory relies on the observation that, after being lifted from the soil surface, a particle moves downstream a distance that depends on flow velocity and the time the particle remains suspended in the flow. The theory indicates that sediment transport rates increase linearly with rainfall intensity and flow velocity when entrainment by flow is absent. Laboratory experiments where sand was eroded by rain-impacted flow provide support for the theory. In addition to influencing the downstream motion of particles detached by raindrop impacts, surface-water flows absorb raindrop energy. Consequently, interactions between flow depth and drop size were also examined through the laboratory experiments. This resulted in a mathematical model of RIFT that accounts for the interactions between raindrops and flow on the sediment transport rate. When applied to experimental data, the model showed that the time-averaged effect of rainfall on sediment transport by rain-impacted flow is independent of the manner by which the rain is applied.