USING A LONG-TERM SURFACE ELEVATION TABLE (SET) NETWORK TO INVESTIGATE LANDSCAPE-SCALE UPLIFT AND SUBSIDENCE THROUGH HEIGHTMOD, RTK, AND GNSS

The South Carolina Geological Survey (SCGS) has installed and monitored a coast-wide array of Surface Elevation Tables (SETs) in South Carolina’s salt marshes since 1998. In addition to using the technique to measure and quantify surface elevation changes to the marsh platform and to assess whether marshes are maintaining their vertical elevation with regards to relative sea-level rise (RSLR), another long-term goal of the project has been to collect geodetic elevation data to quantify subsidence or uplift.

The South Carolina Geodetic Survey worked with SCGS to produce a high-resolution elevation survey on the original stations in the array, using the Height Modernization (HeightMod) standard’s base station and rover technique in 1998. Since 2011, geodetic control has been obtained by SCGS through global navigation satellite system (GNSS) surveying using a Trimble R8 system connected to South Carolina’s Virtual Reference Station (VRS) Network. This method has been repeated in 2018 and 2021. Through ellipsoidal values, data collected through survey methods in 1998 were compared to RTK-GNSS derived data.

The long-term (20+ year) vertical elevation dataset collected on the original SET array indicates subsidence at rates of − 2.24 ± 0.09 to − 3.57 ± 0.10. We present this dataset, along with a short-term vertical elevation dataset (2018-2024) on a more spatially extensive section of the array. Results have implications for carrying datasets through changes in technology and methodology, and also support stratigraphic relationships recorded in SCGS auger borings indicating that faulting may have impacted both the geologic record and modern subsidence rates in areas around the ACE Basin.