Modeling sediment transport from an off-road vehicle trail stream crossing using WEPP model
There is a limited information available pertaining to the adverse effects of Off-Road-Vehicle (ORV) use and trail impacts. As a result, this study was initiated in 2003 to (a) quantify water quality impacts of an ORV trail stream crossing through monitoring of total suspended solids, and (b) conduct WEPP (Water Erosion Prediction Project) simulations to determine long-term sediment loads contributed by the ORV trail stream crossing. To collect suspended sediment samples from the ORV trail stream crossing, ISCO6 6700 water samplers were installed. Data was collected from November 2003 through July 2004. During this time suspended sediment samples were collected for three different operational conditions (open, closed, maintenance). When the study began the trail was open to traffic. The trail was then closed to traffic on January 1, 2004 and went through a two-week maintenance regime in early March. The trail was then opened to ORV traffic on April 1, 2004. The largest suspended sediment load contributed by the stream crossing during this study occurred during the trail closed condition. This storm event had a recorded rainfall of 49 mm, and contributed a suspended sediment load of 109 kg. Since there were no storm events sampled with return intervals of more than one year, the WEPP model was used to estimate the potential long term effects of ORV trail stream crossing. A thirty-year synthetic weather data (generated by CLIGEN) was used to predict sediment yield from the ORV trail stream crossing. The WEPP model suggested that average annual sediment load from the stream crossing is about 126.8 tons/ ha, which is much higher than what is allowed by the USDA Forest Service-National Forests in Alabama for temporary roads. The model also suggested that most of the sediment load to the stream is contributed by a steep hillslope section that flows directly to the stream. Hence the modeling study suggests that a BMP needs to be implemented to control sediment loss from ORV trail section that contributes sediment directly to the stream. In addition, the ORV trail stream crossing should be located on as flat a slope as possible.