SEDIMENT PROCESSES IN BARRIER ISLAND SYSTEMS IN GEORGIA, USA: STATUS AND IMPLICATIONS FOR FUTURE PERSISTANCE

Barrier island systems are composed of two different environments that provide protection to the island: sacrificial beaches and dunes on the seaward side of the island, and extensive salt marshes that decrease energy on the back side of the island. Beaches and dunes are highly dynamic, responding to energetic oceanic forcing, eroding and accreting at rates averaging meters per year, up to 100 m/y in some areas of the Georgia coast. In developed settings, these dynamic changes are managed routinely by beach renourishment and dune building to protect upland infrastructure. The magnitude of change, under sea level rise, requires active monitoring of beaches to identify erosional hotspots for proactive planning for mitigation. In contrast, salt marshes respond more slowly to two dominant forces: tidal creek migration (10’s of cm/y), and the slow rise of sea level, documented at about 3 mm/y in Georgia. Dated marsh cores demonstrate that accretion rates (1-2 mm/y) are less than the rate of sea level rise in Georgia marshes, when away from accreting creek bank margins and muddy tidal flats. These observations suggest that active management of marsh systems (e.g., thin-layer placement or other measures) may be necessary to provide the sediments required for long-term persistence.