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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #171181
Title: ESTIMATING THE MECHANICAL EFFECTS OF RIPARIAN VEGETATION ON STREAM BANK STABILITY USING A FIBER BUNDLE MODEL

Author
item POLLEN, NATASHA - UNIVERSITY OF MISSISSIPPI
item Simon, Andrew

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2005
Publication Date: 7/23/2005
Citation: Pollen, N., Simon, A. 2005. Estimating the mechanical effects of riparian vegetation on stream bank stability using a fiber-bundle model. Water Resources Research 41, W07025, doi: 10.1029/2004WR003801.

Interpretive Summary: Riparian vegetation protects streambanks from erosion by the stream, and from bank failure. This paper investigates ways of quantifying the reinforcing effect provided to streambanks by the root networks of plants and trees growing on the banks. First, the assumptions made by existing root-reinforcement models were investigated, and the results compared to a newly constructed root-reinforcement model, based on models used in materials science. Results of the two root models were compared to direct-shear tests of soil samples with and without roots. Second the root reinforcement values obtained from the two root-reinforcement models were input to a streambank stability model in order to calculate streambank factor of safety with each of the two models. The results show that the more simple existing root-reinforcement model overestimated the actual root reinforcement provided to a streambank. The new model (RipRoot) provided more accurate estimates of root reinforcement through its inclusion of progressive root-breaking during failure of a streambank. In cases where the forces acting on the streambank were great to enough to break all of the roots, the existing root-model overestimated root reinforcement by up to 50%, with overestimation increasing greatly in model runs where streambank forces could be supported by the roots. For the highest banks modeled (3 meters) the difference in factor of safety values between the runs with the two models varied from 0.13 to 2.39 depending on the streambank species considered.

Technical Abstract: Riparian vegetation plays a number of roles in protecting stream banks from erosion by particle entrainment and mass wasting. This paper investigates ways of quantifying mechanical reinforcement provided to the soil matrix of the banks by riparian plant-root networks. First, the assumptions made by perpendicular root-reinforcement models were investigated, and the results compared to a newly constructed root-reinforcement model, based on the fiber-bindle models used in materials science. Results of the two root models were compared to direct-shear tests of root-permeated and non-root-permeated soil samples. Second the root reinforcement values obtained from the two root-reinforcement models were input to a streambank stability model in order to assess the impact of the differences between the root models on streambank factor of safety values. The results show that the simple perpendicular root-reinforcement model overestimated the actual root reinforcement provided to a streambank. 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 to 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 modelled (3 meters) the difference in factor of safety values between the runs with the two models varied from 0.13 to 2.39 depending on the riparian species considered.