SOUTH CAROLINA SURFACE ELEVATION TABLE (SET) PROJECT: PROGRESS REPORT AND INTERPRETATIONS

The South Carolina Geological Survey maintains an array of twenty-two Surface Elevation Table (SET) stations along the coast of South Carolina that is designed to address the question of whether SC’s coastal marshes are, or are not, maintaining themselves against possible effects of relative sea-level change. The array is spread from Little River Inlet, at the North Carolina state line, south along the coast to Hunting Island, with the highest concentration of stations in the ACE Basin NERR. Locations were chosen to compare effects of relative sea-level change in different marsh environments, comparing such parameters as periods and elevations of tidal inundation, proximity to open water, sediment composition and thickness, vegetation type and density, and responses to storm events.

Collection of SET data started in 1998 with surface measurements made at least quarterly and 2^nd-order GPS locational data collected at least every 5 years. In 2009, SET locations were upgraded from the limited life-span aluminum pipe-attached design to the longer life-span stainless steel rod design (Rod Set) with the measurements transferred from the older to the newer design.

Repeated geodetic observations indicate no significant vertical elevation changes to date, outside the sphere of geodetic uncertainty. Therefore no measureable deep vertical motion is interpreted at any SET location.

SET data record effects from seasonal vegetation growth and decay, drought, tidal wrack, slope failure, creek migration, and damage from wildlife. To help identify long-term trends in surface elevation, a simple linear regression was applied to the data. Rates of surface-elevation change range from highly negative, ACEFC1 at -8.42 mm/yr (wave scour at mean-high tide), to highly positive, ACEWI1 at 9.62 mm/yr (long inundation period and protected from waves). Many locations record 0.00 to 1.5 mm/yr elevation gains. Wave energy and proximity to open water is the major destructive factor, and tidal inundation period is the major constructive factor for SC’s coastal marshes.