A MODEL OF STREAMBANK STABILITY INCORPORATING HYDRAULIC EROSION AND THE EFFECTS OF RIPARIAN VEGETATION

Abstract: Sediment is one of the principle pollutants of surface waters of the United States and 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 1990’s at the USDA-ARS National Sedimentation Laboratory and has undergone substantial enhancements since that time. The original model (Simon et al. 1999) 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 4.1) includes a sub-model to predict bank-toe erosion and undercutting by hydraulic shear. This is based on an excess shear-stress approach that is linked to the geotechnical algorithms. Complex geometries resulting from simulated bank-toe are used as the new input geometry for the geotechnical part of the bank-stability model. The enhanced bank-stability submodel allows the user to select between cantilever and planar failure modes. In addition, the mechanical effects of riparian vegetation are included in Version 4.1, based on the RipRoot model developed by Pollen and Simon (2005). The model has been successfully tested in a diverse range of environments to predict bank failures and to investigate the effects of riparian vegetation on critical conditions for bank stability