BARRIER ISLAND MODEL FOR GEOMORPHIC MAPPING OF CAPE HATTERAS AND CAPE LOOKOUT NATIONAL SEASHORES, NORTH CAROLINA

Geomorphic classification and mapping of the NC barrier islands is part of the ongoing USGS-ECU-NCGS cooperative coastal research program in partnership with the USNPS and USFWS. Geomorphic classification is based on a model of barrier island evolution developed from process-response studies and modern field surveys of the NC Outer Banks. The detailed studies utilize time-slice analysis of georeferenced aerial photos (1932-2003) and topographic surveys (1852-2003) of sites between Kitty Hawk and Cape Lookout, NC. The modern data are integrated with historical data to develop the evolutionary responses of geomorphic-ecologic systems to sea-level rise, storms, and human modification. LIDAR data are used to aid in mapping the geomorphic components. The model used in the geomorphic classification is based on a barrier island whose fundamental structure is a sand ramp that evolved in response to storm dynamics. Superimposed on the basic sand ramp are variations due to differences in storm patterns, sand supply, location, age, underlying geology, and human modification. The model barrier island is divided into five main components: beach, overwash-plain, cross-barrier island, back-barrier estuary, and anthropic components. Mapped geomorphic units are sub-categories of these five main components and include the dominant vegetation associated with each geomorphic unit. The model comprises two basic types of barrier islands. Simple barriers are sediment-poor, dominated by inlet and overwash dynamics, with low elevations and narrow widths, and tend to be relatively young. They are dominated by opening and closing of inlets that are shallow and migratory, and by storm-tide overwash with much of the sand incorporated into inlet flood-tide deltas and storm-surge overwash fans, respectively. Complex barriers are sediment rich and consequently wide and high islands consisting of beach ridges and swales and back-barrier dune fields stretching soundward from the ocean front. These barrier segments tend to be relatively older with multiple stages of formation.