Mass failure is one of the most common failures of low-volume roads in mountainous terrain. Current methods for evaluating stability of these roads require a geotechnical specialist. A stability analysis program, XSTABL, was used to estimate the stability of 3,696 combinations of road geometry, soil, and groundwater conditions. A sensitivity analysis was carried out to find the most important site-specific variables in estimating slope stability, and two regression equations were developed to predict the factor of safety (FS) for a given road, one with the groundwater below the road fill and one with the groundwater in the road fill. The resulting equations predicted failures on road segments where failures were observed to have occurred. A comparison of the predicted FSs from the regression equations with the FS values predicted by the infinite slope equation showed that both methods predicted similar FSs.

In the years following a major forest disturbance, such as fire, the erosion rate is greatly influenced by variability in weather, in soil properties, and in spatial distribution. This paper presents a method to incorporate these variabilities into the erosion rate predicted by the Water Erosion Prediction Project model. It appears that it is not necessary to describe both the soil and the vegetation effects of the disturbance. Incorporating the vegetation effects on soil erodibility, and its associated variability, is sufficient-when combined with weather and spatial variability-to predict the probabilities of single storm and annual soil erosion rates in the years following the disturbance. By redefining the probability distributions of the soils, erosion during the recovering years, and impacts of mitigation on erosion can be determined from the same initial set of computer runs.

The Water Erosion Prediction Project (WEPP) model was found to be too time-consuming for Forest Service specialists to learn and apply. To make the WEPP technology available to these specialists, interfaces to run the WEPP erosion model and CLIGEN weather generator were developed to run on the World Wide Web with a web browser. These interfaces include the X-DRAIN program, a lookup table for sediment delivery from forest roads; WEPP:Road, a WEPP interface for forest roads; Disturbed WEPP, a WEPP interface for disturbed forests and rangelands; and Rock:Clime, an interface to the CLIGEN weather generator with an expanded database to complement our WEPP interfaces.

Summary: To develop a simple road sediment delivery tool, the WEPP program modeled sedimentation from forest roads for more than 50,000 combinations of distance between cross drains, road gradient, soil texture, distance from stream, steepness of the buffer between the road and the stream, and climate. The sediment yield prediction from each of these runs was stored in a data file. Two computer interfaces were developed to access the results either from a Windows operating system or over the Internet. Methods are presented to apply these results to road planning and environmental analysis.