Sediment Concentrations Resulting from Flow Depth/Drop Size Interactions in Shallow Overland Flow

Abstract

Flow depth influences the erosive stress applied by raindrop impact to the surface under shallow flow. An analysis of data from laboratory experiments shows the sediment concentration associated with drops of a given size to decrease exponentially with flow depth within two regimes when the susceptibility of the surface to erosion remains constant. In the first regime, raindrop size has a non-significant effect because the height of the water surface above the bed constrains the height to which particles are lifted in the flow. In the second regime, which occurs when flows are deeper than a critical depth that varies with the energy of the impacting drops, drop size and velocity influence sediment concentration from the sediment transport perspective. These effects need to be considered in experiments designed to evaluate the susceptibility of soil to erosion when raindrop impact is a dominant force in the erosion process. They also need to be considered in models designed to predict raindrop-driven erosion.