Borrow Area Surveys - Offshore Sediment Identification and Classification
Geodynamics was contracted by the USACE Wilmington District to perform three high-resolution surveys of the seafloor surface and sub-bottom for potential borrow areas offshore Topsail Beach, North Carolina. The survey area is comprised of twelve individual sites approximately 14.25 sq nmi in size, and located approximately 1.5 to 5 nmi offshore Topsail Island, NC. This offshore area is a potential target borrow-area for sediments to be dredged for renourishment purposes. To accurately assess the nature of sediments at these locations, multibeam bathymetry, multibeam backscatter, and high-resolution Chirp seismic (sub-bottom) data were collected. The multibeam bathymetry data was collected in accordance with IHO Special Order, USACE standards for navigation and dredging requirements and the State Regulation 15A NCAC 07H .0312 – Technical Standards for Beach Fill Projects to provide accurate seafloor elevations and details needed to evaluate discrete sand resources. The multibeam backscatter was used to identify areas of possible hard bottom/rock outcrops, areas of possible archaeological concern, bedforms, and likely surface sediment type that can be used to interpolate ground truth data being collected across the survey areas. Geodynamics provided the USACE and BOEM with final GIS maps of precise bathymetry, and seafloor characterization for each of the 12 potential borrow areas, including detailed descriptions of the coastal geologic features identified.