Geospatial contrasts between natural and human-altered barrier island systems: Core Banks and Ocracoke Island, North Carolina, U.S.A

This study investigates differences in geomorphology between two barrier island systems, one considered to be in a pristine or natural geomorphic state, and another in some way geomorphically altered by humans. Alteration here is defined by the presence of a continuous, protective dune wall designed and installed alongshore to arrest island erosion and protect interior infrastructure. In contrasting the two environments we focus on a single question: how does the presence of such a dune wall alter the physical response of an island system to forces that compel change (e.g. storms, sea level rise)? Island widths, and ocean and sound shoreline positions are measured along a series of shore-normal transects on Core Banks and Ocracoke Island, both members of North Carolina’s Outer Banks. Surveys date from the mid-nineteenth century through 2012. Four surveys were retained for Core Banks, five for Ocracoke Island. Findings point to differences in the geomorphic character along both islands. More of Core Banks is narrow with evidence of current overwash and inlet activity. Ocracoke presents more stability, width, limited overwash, and no inlets. Evidence uncovered points to three fundamental conclusions. First: there appears to exist a minimum threshold width about which an island tends to oscillate. Second, differential shoreline retreat along Ocracoke Island has resulted in a counterclockwise (CCW) rotation along the island’s northern half. Finally, the protective dunes along Ocracoke appear to have slowed the rate of shoreline retreat, and the observed CCW rotation, by more than 40%.