Erodibility of Channels with Cohesive Boundary

Results of laboratory investigations on the erodibility of cohesive soils by water were critically reviewed, summarized and compared with similar field results and with older empirical information. There is strong experimental evidence, substantiated by physical reasoning, that the bed shear stress strongly controls both the erosion and the deposition of cohesive sediments. The net attractive physicochemical interparticle forces in the soil provide the main resistance to erosion. For low values the soil shear strength itself does not have any measurable effect on soil erodibility, while for medium to high strength clays, the resistance to erosion seems in general to increase with the macroscopic strength. Under certain conditions erosion may stop completely after some scouring. The depth of this scouring and the final bed roughness increase with increasing shear stress and decreasing shear strength of the bed. A mechanistic model about the interaction between the surface of the bed and the flow is described which explains the observed phenomena. A set of tentative rules is suggested for design of stable channels with cohesive boundaries.