This report was the 13th in a series of beach monitoring reports CSE has performed for Seabrook Island following the April 1996 relocation of Captain Sams Inlet. It also follows ~25 years of annual beach surveys covering Seabrook Island. The focus of this report is on the condition of the beach; the present report summarizes the condition of the beach along Seabrook Island as of January 2008- December 2008 and provides updated survey results.
CSE performed a complete survey of the shorelines and inshore area from Camp St. Christopher to Captain Sams Inlet between 3 and 11 December 2008. Surveys were performed using a Trimble Model R8 GNSS RTK-GPS for backshore, intertidal, and surf zone work. Bathymetry seaward of the surf zone was obtained using the GPS linked to a precision fathometer mounted on CSE’s shallow-draft research vessel, the RV Congaree River. Raw data were collected at ~5 points per second. The seaward limit of the survey was generally greater than 0.5 mile offshore.
Summary – Camp St. Christopher to Oystercatcher
Overall, the section of Seabrook’s shoreline from Camp St. Christopher to Oystercatcher beach access experienced minor accretion between December 2007 and December 2008, gaining ~ 6,000 cy (~0.5 cy/ft). The surveyed volume change in April 1990 compared with prenourishment conditions was ~660,000 cy (~58 ct/ft). By December 2008, the comparative total was ~1,915,000 cy (~169 cy/ft), suggesting that there is almost three times as much sand on the beach today compared with conditions after the 1990 nourishment project.
Conditions along Seabrook Island’s beach remain very healthy compared with conditions from 1975 to 1995.
Changes around Captain Sams Inlet
In April 1996, Captain Sams Inlet was relocated for the second time. Detailed, early winter surveys are available for each year for the period December 1995 through December 2008 (present survey). During the past 12.7 years (April 1996 to December 2008), the Seabrook edge of the new inlet has migrated ~2,250ft (measured at CSE’s project baseline). This equates to an average migration rate of ~180 ft/yr. Captain Sams Inlet migrated ~325 ft between December 2007 and December 2008, shifting the terminus of the ebb-tidal delta closer to Oystercatcher beach access.
The shoreline trends of the past year confirm CSE’s and the Environmental Committee’s recommendation for inlet relocation at the earliest time.