Slow Lateral Migration Rates of the Gravel-Bedded South River, Virginia: the Influence of Bedrock, Riparian Vegetation, and Bend Geometry.

Shorelines mapped on orthorectified aerial photographs from 1937 and 2005 demonstrate that the South River is unusually stable: rates of lateral migration from 1937-2005 range from 0 to 0.3 m/yr with a median of 0.02 m/yr. Shoreline changes are barely resolvable at some locations on aerial photographs despite rectification errors that are typically less than 1m. Field surveys indicate that only 12.4 percent of the entire shoreline is currently actively eroding. Lateral shifting of the channel appears to occur where riverbanks are composed of alluvium, rather than bedrock. In some areas, mid-channel bars and tributary confluences are areas of significant bank erosion, as the bars and tributary-mouth deltas deflect the main flow into the opposite banks. Erodibility values computed using the model of Johanneson and Parker (1989) are distinctly different for bends with different geologic setting and riparian vegetation.