ARCHITECTURE OF BARRIER ISLAND SHORE FACE IN RESPONSE TO HARD STRUCTURES, BEACH NOURISHMENT, AND SUBSIDENCE: INVESTIGATIONS ALONG GALVESTON AND FOLLET’S ISLANDS, UPPER TEXAS COAST

High resolution swath bathymetry, side scan sonar and CHIRP seismic profiling data along with sediment coring and surface grab samples were collected within select grids off of Galveston and Follet’s Island. Sites were both along the seawall, where armoring and nourishment has been conducted and along natural sections of the beach. Each survey site extends from 3 m of water out to 10 m. The lower shore face and inner shelf along each of the survey sites reveal a tripartite division of shore-parallel sedimentary facies at the surface. The innermost “toe-of-the-beach” facies is the seaward-thinning sand wedge of the barrier island. Seaward of the island toe is a facies consisting of a belt of outcropping relict island shoreface that formed during progradation of this island prior to 1,200 yBP. Further offshore, the relict units are buried below a burrowed mud facies that thickens offshore. Radioisotope age dates (137Cs and 210Pb) from sediment cores indicate most of the mud layer has accumulated in the last 40-50 years. Proximal to areas where beach nourishment has occurred, there is a thin veneer of sand (<5 cm) at the surface of the offshore mud facies. Near-shore, along sections of the beach where the seawall exists, beach scarps are present. Bathymetric change maps show little significant seasonal alteration in the shoreface profile between winter and summer conditions. However, comparison with historical bathymetric data indicates that with enhanced subsidence, significant ravinement of the shoreface has occurred in the last century. CHIRP profiles reveal significant buried incised paleochannels proximal to the Seawall as well as below both San Luis Pass and the Brazos River channel suggesting significant potential sources of beach sand. All of these results and data will be available on the Texas Coastal Erosion Data Network website, http://coastal.tamug.edu/.