Justifying the Use of a Nonlinear Detachment Model for Cohesive Soil Erosion

Abstract. Cohesive sediment transport is typically modeled for channels, levees, spillways, earthen dams, and internal erosion using a linear excess shear stress approach. However, mechanistic nonlinear detachment models, such as the Wilson Model, have recently been proposed in the literature. Questions exist as to the appropriateness of nonlinear relationships between applied shear stress and the erosion rate. Therefore, the objective of this research was to determine the suitability of linear and nonlinear detachment models for cohesive sediment transport using two applicable data sets: (i) rill erodibility studies across a limited range of applied shear stress (0.9 to 21.4 Pa) and (ii) hole erosion tests across an extended range of applied shear stress (12.6 to 62.0 Pa). Using these two case studies, it was determined that the nonlinear, mechanistic detachment model was more applicable across a wider range of applied shear stress. In situ and laboratory tests sometimes confine the collection of erosion rate data in terms of the applied shear stress, and therefore, users of these measurement techniques should be aware of the nonlinear behavior of cohesive sediment detachment especially at higher shear stress. Nonlinear detachment models should be used in the place of the linear excess shear stress approach in design and predictive models for cohesive sediment detachment.