ASABE Technical Library - Abstract

Abstract. The design of a forest road is important in controlling runoff flow paths and hence erosion from the road surface. When applying a process based erosion model, WEPP (Water Erosion Prediction Project) to forest roads, it was discovered that predicted erosion was much greater from roads that tended to concentrate water in eroding ditches or wheel ruts than roads that did not concentrate water on the surface, or had ditches that were armored with gravel to prevent ditch erosion. In order to validate these predictions, a study was installed on two road designs in Fort Benning, Georgia. One design followed the recent practice of starting with a native material road and adding gravel and grading as required. Rutting on the road surface and erosion were common occurrences on this type of road. The other design was a graded aggregate base (GAB) design, built in compacted layers, with rocked ditches. The GAB roads tended to shed water to rocked ditches. Runoff and sediment delivery were measured from ten plots ranging in size from 65 to 200 m². Runoff depths up to 50 mm occurred from daily rainfall amounts up to nearly 70 mm. Delivered sediment ranged from zero to more than 20 Mg ha^-1 from individual storms. Both road designs had similar runoff coefficients, but the unimproved roads generated more than ten times as much sediment per mm runoff. Calibration and validation work for the WEPP model is ongoing. Initial results suggest that the hydraulic conductivity is similar to newly constructed roads and rill erodibility higher for these two road designs than had been measured on road erosion studies in the western U.S.