ESTIMATING POTENTIAL VOLUMES AND ONSHORE COMPATIBILITY OF SURFICIAL AND SHALLOW SAND RESOURCES ON THE NEAR (3-8 NM) OUTER CONTINENTAL SHELF OFFSHORE OF SOUTH CAROLINA

Since 2014, the Bureau of Ocean Energy Management (BOEM) has worked with cooperative partners in 11 states along the Atlantic Coast of the US to investigate and evaluate sand resources located on the near (3-8 nautical miles offshore) Outer Continental Shelf (OCS). These cooperative efforts seek to enhance the capacity of coastal communities in these states to recover from the damaging impacts of storms by providing information about the location and character of potentially beach-compatible offshore sand resources for renourishment.

Geophysical (sidescan sonar, Chirp subbottom profiler) and geological (vibracore and grab sample) data collected offshore of South Carolina in 2015 for the BOEM Atlantic Sand and Gravel Assessment Project (ASAP) were processed and interpreted by cooperative partners at the South Carolina Department of Natural Resources (SCDNR), College of Charleston (CofC), and Coastal Carolina University (CCU). These ASAP datasets are concentrated in four areas: Hilton Head, Folly Beach-Kiawah Island, Cape Romain, and North Myrtle Beach. Potential sand resources were identified in three of the compartments using remotely-sensed Chirp subbottom profiler data sea-truthed with five vibracores. Areas with 5-foot or greater sand thickness were delineated by digitizing reflectors identified in the seismic data. Horizontal x and y data and vertical z data were exported to provide thickness estimates for shallow (<3 meters) sand deposits.

Offshore of Folly Beach and Kiawah Island, volumetric estimates calculated using kriging analyses in GIS identified three areas containing enough sand (> 1.15 million cubic meters, the volume required for a 2014 renourishment effort) to serve as potential options for beach renourishment needs at Folly Beach. In addition to volumetric analyses based on the interpretation of shallow seismic facies, detailed lithological, grain-size, and mineralogical data produced for the vibracore sediments are used to assess the potential compatibility of the sand in these deposits with sediments found on nearby modern onshore systems. Shallow samples collected from these five cores include major amounts of quartz, with minor to trace apatite, feldspars, calcite, ilmenite, epidote, amphibole, garnet, and zircon.