Stability of Root Reinforced Streambanks: Numerical Modeling and Laboratory Experiments

Abstract

The scope of this study includes the effects of vegetation and root reinforcement on seepage erosion and undercutting as they regard streambank stability. An in-depth analysis of the effects of vegetation used in a current streambank stability software package, the Bank Stability and Toe Erosion Model, developed by the USDA-ARS National Sedimentation Laboratory was performed on previously studied streambanks. Laboratory experiments were then performed in a three-dimensional soil block in which steady heads were induced to cause subsurface flow events and seepage out of the simulated bank face. The laboratory experiments were performed with and without switchgrass (Panicum virgatum), after which the shape and properties of the seepage undercutting wereanalyzed.Findings and Conclusions: The Bank Stability and Toe Erosion Model revealed, as expected, significant increases in streambank stability when all forms of vegetation were added to the streambank; however, this software is more significantly influenced by pore-water pressure distribution than root cohesion and seepage undercutting. Undercut formations of the seepage blocks varied between the unvegetated and vegetated three-dimensional soil block experiments. This can be explained by soil weathering patterns which may have occurred over the vegetation growth period; however, future replications of the vegetation experiments should be performed for a more in-depth analysis. Modeling of the vegetated soil block experiments revealed the need for the incorporation of both seepage undercutting and seepage force in future streambank stability software.