ROLE OF GEOLOGIC FRAMEWORK, PHYSICAL DYNAMICS, AND SAND RESOURCE POTENTIAL FOR BEACH NOURISHMENT ON THE NORTH CAROLINA OUTER BANKS

Most North Carolina ocean beaches are in a serious state of erosion with over 120 miles (about 35 miles on the Outer Banks) being considered for immediate beach nourishment projects. Reconnaissance studies of the thick Quaternary section on the continental shelf adjacent to the Outer Banks have demonstrated numerous potential sand resources that occur in paleofluvial deltas and channels, cape-shoal structures, and various stratigraphic lithofacies. The geologic framework (including the geometry and lithology of the framework stratigraphy, paleotopography of the flooding surface, etc.), physical dynamics, and recent human modification dictate the types of barrier islands that constitute the Outer Banks and their evolutionary development. Sediment-rich coastal segments previously formed as complex barriers consisting of multiple seaward prograding beach ridges resulting in high and wide islands. Today, these complex islands are neither migrating landward nor accreting seaward; rather, erosion is the dominant process on both ocean and estuarine shorelines. Sediment-starved coastal segments formed as simple overwash barriers consisting of thin Holocene sand perched on the interstream divides of Pleistocene drainage basins. Due to the geologic inheritance and evolutionary development, some of these sediment-starved barriers are presently collapsing with little chance of surviving in their present form. In addition to basic economic considerations, decisions concerning the use of potential sand resources for long-term beach management on the Outer Banks should also consider some significant scientific parameters. These parameters should include the geologic framework variables controlling individual island formation and evolution, regional high-energy wave and storm climate, cumulative environmental consequences of sand mining and beach nourishment, and the specific response of each coastal segment to ongoing sea-level rise.