Mapping Sand Resources on the Near (3-8 Nautical Mile) Outer Continental Shelf of the Southeastern US: Investigating Regional Trends in Sediment Thicknesses, Age Estimates, and Geologic Evolution

Since 2014, the Bureau of Ocean Energy Management (BOEM), has worked with collaborative partners in 11 states along the Atlantic coast of the US to inventory offshore sand resources in the 3-8 nautical mile (nm) Outer Continental Shelf (OCS) through the Atlantic Sand Assessment Project (ASAP). The purpose of ASAP is to augment the ability of coastal states to recover from the damaging impacts of hurricanes and other storms by providing information about offshore sand resources for beach renourishment projects. The geospatial inventory compiled for the first phase of the state cooperative projects (2014-2016) enhanced the overall state of knowledge regarding the type, quantity, and quality of data that exist within this area of the near OCS, and also facilitated the identification of gaps in data coverage. A needs assessment was also performed in order to better project the renourishment requirements of beach communities, based on historic trends. The first phase of the project revealed that the distance between renourished beaches and corresponding borrow sites is increasing. Because of this trend, exploitation of beach-compatible sand in the OCS is anticipated into the future as resources closer to the shoreline become depleted or are protected for habitat. More recently, the project has focused on processing and interpreting backscatter and shallow seismic data collected for the ASAP in 2015. Data were collected in targeted locations where historical data were lacking or where potential need for beach-compatible renourishment sand is high. In NC, reconnaissance data extend from near Bogue Banks to the SC border. In SC, these targeted areas are located offshore of North Myrtle Beach in Long Bay, Cape Romain, Folly and Kiawah Islands, and Hilton Head Island. The GA data are largely concentrated in a northern compartment offshore of Wassaw National Wildlife Refuge and Ossabaw Island, extending south to Little St. Simons Island, Sea Island, and Cumberland Island. The marine seismic data, vibracores, and grab samples are being used to delineate shoal areas and calculate associated sand volumes on the 3-8 nautical mile outer continental shelf (OCS). Understanding the distribution and composition of sand shoals in the offshore marine environment can provide information relating to benthic habitats, paleoenvironmental features, and economically significant beach-compatible renourishment sands. Mapping efforts are currently underway to consider the role that bathymetry plays in the occurrence and distribution of sand shoals on the seafloor and compare those results with analyses of trends in textural data, specifically grain size, of samples collected from ASAP vibracores. The spatial distribution and average relief of the sand-shoal data are presented with consideration given to other features identified in the seismic data, such as paleochannels, and placed in the context of paleolandscapes offshore of the Southeastern United States.