Detachment of Soil by Flowing Water Under Turbulent and Laminar Conditions

Abstract

Abstract Fluid turbulence of water flowing over soil surfaces imparts instantaneous and localized levels of shear stress to the fluid‐solid interface that are much greater than the average shear stress of flow. It has been hypothesized that these high levels of instantaneous shear are the driving mechanism for detachment of cohesive soil by flowing water. The purpose of this study was to test the hypothesis that detachment of soil by flowing water at a given shear stress is dependent on turbulence. Detachment rates of three soils were measured in a hydraulic flume at seven combinations of flow depth and bed slope under both turbulent and laminar flow conditions. For all soils and all slope/depth treatments, detachment was dramatically greater for the turbulent case compared with the laminar case. Detachment that occurred under laminar flow conditions was thought to be due in part to localized turbulence associated with pitting of some of the samples.