The effects of vegetation and soil type on streambank erosion, southwestern Virginia, USA

The goal of this research was to evaluate the relative effects of root density, freeze/thaw cycling, and soil properties on the erodibility and critical shear stress of streambanks. The erodibility and critical shear stress of rooted bank soils were measured in situ at 25 field sites using a submerged jet test device; several soil, vegetation, and stream chemistry characteristics shown to influence soil erosion were also assessed. Multiple linear regression analysis was conducted to determine those factors that most influenced streambank erodibility and the relative impact of riparian vegetation. Study results indicated that soil erosion is a complex phenomenon that depends primarily on soil bulk density. Freeze/thaw cycling, soil antecedent moisture content, the density of roots with diameters of 2 to 20 mm, soil texture, and the interaction of soil pore water and stream water had a significant impact on soil erodibility and critical shear stress, depending on soil type. Riparian vegetation had multiple significant effects on soil erodibility. In addition to reducing soil erodibility through root reinforcement, the streamside vegetation affected soil moisture and altered the local microclimate, which in turn affected freeze/thaw cycling (FTC). This study represents the first in situ testing of the erodibility of vegetated streambanks and provides a quantitative analysis on the effects of vegetation on streambank erosion, relative to other soil physical and chemical parameters.