| Popis: |
Despite over forty years of research attributing changes in streambank erosion rates over time to freeze-thaw cycling and soil desiccation, little quantitative information is available on the relationships between streambank erodibility and critical shear stress and the environmental conditions and processes that enhance streambank erosion potential. The goal of this study was investigate temporal changes in streambank erodibility and critical shear stress due to subaerial processes. Soil erodibility and critical shear stress were measured monthly in situ using a multi-angle submerged jet test device. Soil and weather data were also collected to determine the number of freeze-thaw cycles, soil moisture, temperature, bulk density, erodibility, and critical shear stress, as well as other atmospheric conditions that could impact bank erosion potential. A nonparametric alternative to ANOVA in combination with Dunn’s nonparametric multiple comparison test showed soil erodibility was significantly higher (p=0.024) during the winter (November - March) than the spring/fall (April - May, September - October). Regression analysis showed 70% of the variability in soil erodibility was attributed to freeze-thaw cycling alone. Study results also indicated that bulk density is highly influenced by winter weather conditions since gravimetric water content and freeze-thaw cycles combined explained as much as 86% of the variance in bulk density measurements. Study results showed significant changes in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes, specifically changes in soil moisture and temperature. These results have potential implications for streambank modeling and restoration projects that assume constant values for soil erodibility. Watershed models and restoration designs should consider the implications of reduced soil erodibility during the winter in model development and stream restoration designs. |
