Development of spatially explicit descriptive models of watershed mass wasting

The Nemadji River contributes 525,000 metric tons of sediment per year to Lake Superior. This sediment results in a number of environmental impacts to the Nemadji/Superior fluvial system. Basin hydrology has been changed through logging, burning, clearing for agriculture and road construction. These activities are hypothesized to have reduced evapotranspiration rates and to have decreased the soil's resistance to shear forces. A GIS was established to analyze landscape data for nine representative subwatersheds within the Nemadji basin. Predictor variables were examined in buffer zones on each side of the stream in each watershed. Output from the GIS was used as input to linear regression models used to quantify the relationships between the frequency of soil mass movement and landscape characteristics. Results show no significant relationships between watershed area, percent coniferous cover, percent of stream channel protected in coniferous cover, channel gradient, time of concentration, road density, mean weighted watershed slope, or number of beaver dams and frequency of mass soil movement. Significant relationships were found between slump frequency and total forested area and percent non-forested land. The results of this investigation have important implications for the maintenance and restoration of forest land in the red clay area.