Final Report on the Effects of Off-Road Vehicles on Beach and Dune Systems, Fire Island National Seashore

Anders, Fred; Leatherman, Stephen

A three year investigation was undertaken to examine the effects of off-road vehicles (ORVs) on the beach and dunes of Fire Island National Seashore, New York. Over 45,000 vehicle trips per year are concentrated in the zone seaward of the dune crest along this shoreline. The experimental approach was adopted in order to assess the environmental effects of ORVs. Specially developed instrumentation was used to measure the direct displacement of sand by vehicles on a daily basis. Adjacent impacted and unimpacted beaches were surveyed to examine differential profile changes. Swash and tracer tests were conducted to determine if swash interaction with vehicle tracks on the beach face contributed to additional erosion. Two experimental sites were monitored to evaluate the impacts of vehicles on the foredune vegetation and topography. The results of the direct displacement studies showed that slope, sand compaction, and number of passes in the same track, were the principal factors controlling the measured net downslope displacement of sand. ORV tracks can lead to some increased mobility of beach sand as shown by the swash and tracer tests. This increased mobility could lead to accelerated erosion. However, there are no substantial yearly differences between natural and impacted beaches, except on and just in front of the dunes. Foredune vegetation was rapidly destroyed by low level ORV impacts, which resulted in a marked alteration in the cross-sectional profile of the dune zone. These changes signal increased dune instability during storm attack.