Enhancements of a Bank-Stability and Toe-Erosion Model and the Addition of Improved Mechanical Root-Reinforcement Algorithms

Sediment eroded from streambank failures has been found to be the single largest contributor to suspended-sediment loads to streams draining unstable systems in the mid - continent. With the recent focus on stream restoration, a quantitative means was needed to predict critical conditions for stability and the effects of riparian vegetation on attaining stable bank geometries. A deterministic bank-stability model was developed in the late 1990s at the USDA-ARS National Sedimentation Laboratory and has undergone substantial enhancements since that time. The original model allowed for 5 unique layers, accounted for pore-water pressures on both the saturated and unsaturated parts of the failure plane, and the confining pressure from streamflow. The enhanced Bank Stability and Toe Erosion Model (BSTEM Version 5.0) includes a sub-model to predict bank-toe erosion and undercutting by hydraulic shear, and allows the user to select between cantilever or planar failure modes. Riparian vegetation is now accounted for by adding cohesion due to individual layers due to the mechanical reinforcement of the soil by plant roots. The BSTEM (Version 5.0) includes a direct link to an improved root-treinforcement model (RipRoot), where users enter an approximate root density. Individual species or assemblages of common North American riparian species, each with differing root densities can be accounted for. Estimates of root-reinforcement are then input directly into BSTEM 5.0 for use in the stability algorithms. The integration of these two models represents a significant advance in the way that riparian vegetation is accounted for in bank-stability analyses.