Erosion of Channel Beds covered by Cohesive Sediments

A physically based model is developed for estimation of surface erosion of cohesive bed channels. Advantage of the model is application of new approaches for estimation of erosion flux coefficient and critical shear stress, and accounts for stochastic behavior of the actual bed shear stress. The critical shear stress has also taken to be proportional to bed shear strength. Rayleigh probability function is proposed as the distribution of bed shear stress. The model requires four physical and one statistical scale parameters. The physical parameters are effective cohesion, volumetric concentration, entrainment velocity and gelling concentration. To correlate the model, the scale parameter of the Rayleigh function is applied. The experiments were conducted in 2m of a 12m long straight flume with natural sediments collected in order to verify model results with field measurments. Regardless of degree of consolidation, the scale parameter has shown to have a strong power relation with relative critical shear stress. Thus it can be determined with only two fast erosion tests. The erosion rate simulated by the proposed model has shown well agreement with laboratorial measurements.