THE HYDROGEOMORPHOLOGY OF ASSATEAGUE ISLAND: LANDFORMS, HYDROLOGY, AND VEGETATION

A recently completed hydrogeomorphic map of Assateague Island National Seashore in Maryland interprets the land surface of the island as a result of the predominant storm and inlet processes that have shaped the island, and relates the geomorphology to the ground-water hydrology and dominant plant communities. The map subdivides the land surface into six primary map units: island core, zone of overwash, former inlets, washarounds, tidal marsh, and ponds. The primary map units are further divided to identify smaller features, such as ridges and swales, and to reflect the distribution of fresh, brackish, and saline ground water in the surficial aquifer. The magnitude and frequency of seawater input to the island surface by storm overwash from the ocean and high-water flooding from the bay largely affect the zonation within each primary map unit. The interpretation presented in the map was developed from extensive geophysical surveys of key sites on the island that represent end-member settings and environmental gradients within and between those end members. Geophysical surveys included ground-penetrating radar and electrical resistivity to characterize the surficial aquifer, specifically the thickness of the fresh ground-water lens, with complementary borehole logs of a few deep wells. Additional supporting information includes a previous general geomorphology of the island by Morton et al. (2007), a study of ponds on Assateague by Hall (2005), and observations of overwash following two moderate storms. The actual map interpretation was done on a color infrared photomosaic provided by the National Park Service, in conjunction with a lidar DEM from the US Geological Survey. The map has substantial value for explaining the distribution and density of individual plant species and plant communities on the island as a response to the average and dynamic salinity characteristics of the shallow ground water. The explanatory report that accompanies the hydrogeomorphic map is available at www.eeescience.utoledo.edu/Faculty/Krantz/Research/research.htm.