Nonlinear Detachment Model for Soil Erodibility: Application and Incorporation into a Streambank Erosion and Stability Model

Abstract

Cohesive sediment transport is typically modeled for channels, levees, spillways, earth 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. The objective of this research was to determine the suitability of linear and nonlinear detachment models for cohesive sediment transport using three applicable data sets: (1) a rill erodibility study across a limited range of shear stress (0 to 10 Pa), (2) a hole erosion test across an extended range of shear stress (10 to 60 Pa), and (3) streambank erodibility as quantified by jet erosion tests for the linear excess shear stress equation and the nonlinear Wilson Model across a small range of shear stress (2.5 to 7.5 Pa). The Wilson Model was incorporated into the Bank Stability and Toe Erosion Model (BSTEM) as an option for simulating fluvial erosion and used to simulate bank retreat in the streambank erodibility study. Using these three case studies, it was determined that the nonlinear, mechanistic detachment model was more applicable across a wider range in applied shear stress. The use of the nonlinear detachment model also alleviates questions about the most appropriate solution technique for jet erosion tests in deriving erodibility parameters. In situ tests may confine the collection of erosion rate data in terms of the applied shear stress, and therefore, users of these techniques should be aware of the nonlinear behavior of cohesive sediment detachment especially at higher shear stress.