Modeling Water Quality Impacts of Off-Road Vehicles in Forested Watersheds

Abstract

Erosion from off-road vehicles can cause negative effects on water quality by impairing fish habitat and shortening reservoir life. Due to an increasing level of off-road vehicle use throughout the country, this impact has risen to a level that has become a cause for concern. Interest has been raised by the USDA Forest Service to quantify sediment loads and determine management practices that may aid in reducing the current sediment delivery rates. A bridged stream trail crossing on the Kentuck ORV trail system in the Talladega National Forest was equipped with water sampling equipment to measure total suspended sediment and flow rates. Equipment was also installed to measure rainfall and traffic volumes. From this data, sediment loads were calculated and used to calibrate the Water Erosion Prediction Project (WEPP) model. The model was then utilized to simulate sediment yields for varying management practices. A total sediment load of 120.9 kg was calculated for the entire data collection period. Sediment yield proved to be only significant from storm events that had a one year return interval or longer. During peak season, traffic volumes reached 180 passes per day with an average throughout the riding season of 25 passes per day. During calibration of the WEPP model, a Nash-Sutcliffe R² of 0.92 was achieved. Using the WEPP model, it was determined that in order to achieve target sediment loads, management practices should have a minimum forest buffer length of 20 m with a minimum water bar spacing of 6 m for slopes between 13 and 20%. The use of proper BMPs , such as water bar spacing, slope grade, and buffer lengths, can aid in minimizing the degradation of water quality.