Relationships between drainage area, slope length, and slope gradient for riparian slopes in Virginia

Surface runoff and interflow generated on riparian hillslopes concentrate along rills or topographic depressions as they move downslope. This runoff concentration is an important factor that determines the effectiveness of conservation practices such as vegetated filter ships and riparian buffers and needs to be accounted for while designing such practices. Currently, routinely available DEMs are not detailed enough to capture the runoff concentration that occurs at the hillslope scale. This article investigated the possibility of developing simple relationships that could be used to quantify specific or total contributing areas in terms of hillslope attributes such as slope length or gradient. Riparian hillslopes in the Ridge and Valley region of Virginia were surveyed. The bounds of the survey were defined by the size of dissected hollows and spurs for these hillslopes. Surface elevations were recorded at a resolution of 0.5 to 2 m. Catchment areas which were used as a surrogate for runoff concentration were determined using digital elevation models. Results from this study suggest that although some of the measures of runoff concentration could be expressed in terms of slope length and gradient, it is unlikely that complete probability distribution of catchment areas could be derived based simply on slope gradients and lengths.