Evaluation of Road Approaches to Four Different Types of Stream Crossings in the Virginia Piedmont

Erosion potential was estimated for road approaches during 4 phases of a timber harvesting scheduled for 23 stream crossings in the Virginia Piedmont. The objectives of this study were to: (1) examine four different types of stream crossing structures (steel bridges, pole bridges, standard culverts, and reenforced fords) in order to determine if the type of stream crossing affects erosion potential and (2) evaluate the potential erosion associated with the stream crossing approaches using the Water Erosion Prediction Project (WEPP) for forest roads and the forestry version of the Universal Soil Loss Equation (USLE). An unbalanced replication resulted in six replications of each crossing, except pole bridges (7) and fords (4). Results indicate that any of the stream crossings may be appropriate if located, installed, and maintained properly. However, we found that approaches associated with culverts had the potential for the highest soil loss rates as estimated by both WEPP (46.2 tons per acre per year) and USLE (85.8 tons per acre per year). Both of these models showed a general decrease in the potential for erosion from the during harvest phase to the postroad closure phase. INTRODUCTION Stream crossings can produce a number of water-quality pollutants, but sediment is usually the primary concern. Research indicates that roads create more pollution, in the form of sediment, than harvesting activities. Furthermore, stream crossings are the most frequent sources of sediment introduction (Rothwell 1983). Road construction and associated stream crossings are common activities for conventional harvest operations. Sediment produced at stream crossings originates from two primary sources: the stream crossing structure itself and the road approaches to the crossing (Taylor and others 1999). Locating the least steep approaches for stream crossings and choosing good locations are common best management practices (BMP) recommended for minimizing sediment pollution. The potential for water-quality impacts other than sediment also exist at stream crossings. Nutrients attached to sediment particles, which are transported directly to stream systems, may also present additional nonpoint source problems in forested watersheds (Grace 2005).