Off-Road Vehicle Impact on Sediment Displacement and Disruption at Assateague Island National Seashore, Maryland

摘要

The National Park Service (NPS) monitors off-road vehicle (ORV) use in National Seashores across the United States. The sediment disturbance that is caused by ORVs is believed to have a large impact on erosion (by wind or waves), which there by affects the morphology of the foredunes. With greater knowledge of ORV impacts, the NPS can better manage ORV use and minimize anthropogenic affects to the coastal environment. There remains considerable uncertainty about the disturbance and its larger-scale impact.This study quantifies the sediment disturbance made by tire tracks, as well as the tire track form, width, depth, and evolution with relation to the number of vehicle passes and location on the beach at Assateague Island National Seashore (ASIS), Maryland. To measure ORV impact, ground-based LiDAR was used to collect detailed profiles across a three by three meter test plot at each site. Based on the quantification of the displaced sediment and redistribution of that sediment from the tracks, a recommendation to the NPS can be made as to where along the beach traffic should be limited to, in order to minimize impact to the physical environment at ASIS. Tire tracks were found to widen after the first pass, as a result of the imperfections of driving. Compaction of the sediment in the center of the tire track accounts for only a minimal amount of the sediment lost from the tire tracks. Sediment removal accounted for greater than 75% of the sediment lost from the tire tracks at all sites. It was concluded that sediment removal is the most dominant factor in the creation and evolution of a tire track. The width, depth, and evolution of a tire track were also found to be controlled by the imperfections of driving. Despite the amount of sediment disturbance, it is found that there is no net downslope displacement of sediment. This conclusion counters previous ORV impact studies and suggests that ORVs are not directly responsible for beach erosion. It is also recommended that to minimize the impact of OVRs on the beach at ASIS, the NPS should limit driving to the backshore.