Settling velocity characteristics of sediment detached from a soil surface by raindrop impact

Abstract

Summary The aim of the study was to ascertain whether the detachment of sediment from a soil surface by raindrop impact is a selective or aselective process. Relationships between particle size and settling velocity were established. Two contrasting soil types with a mean surface water depth of 5 mm were subjected to simulated rainfall at a rate of 56 mm h−1 in modified splash-cups. Mean drop diameter was 2.24 mm. The two soil types were a cracking clay (black earth or vertisol) and a slightly dispersive sandy clay loam (solonchak or aridisol). For both soil types, sediment that was ejected into the air from drop-impact sites had a selective preference for removing sediment with settling velocities corresponding to fine sand-sized primary particles, and fine to coarse sand-sized aggregates. Investigations of the settling velocity distributions of detached sediments sampled from the surface water before ejection or deposition could occur suggested that, within experimental uncertainties, the impact-detachment process is aselective with respect to sediment size or settling velocity for the drop diameter and water depth investigated.