A New Approach to Modeling the Mechanical Effects of Riparian Vegetation on Streambank Stability: A Fiber-Bundle Model

Abstract

Riparian vegetation plays a number of roles in protecting stream banks from erosion by particle entrainment and mass wasting, with the impacts generally separated into those that are mechanical, hydraulic, or hydrological. This paper investigates the quantification of mechanical root-reinforcement of streambanks using established perpendicular root-reinforcement models and a newly constructed root-reinforcement model, RipRoot. The root-reinforcement estimates were tested against direct-shear tests with root-permeated and non-root permeated soil samples and were then input to a streambank stability model to assess the impact of the differences between the root models on streambank factor of safety values. The new fiber-bundle model, RipRoot, provided more accurate estimates of root reinforcement through its inclusion of progressive root breaking during mass failure of a streambank. In cases where bank driving forces were great enough to break all of the roots, the perpendicular root model overestimated root reinforcement by up to 50 %, with overestimation increasing an order of magnitude in model runs where streambank driving forces did not exceed root strength. For the highest banks modeled (3 m) the difference in factor of safety values produced by the two models varied from 0.13 to 2.39 depending on the riparian species considered.