ANALYZING BACKBARRIER SHORELINE CHANGE ALONG GEORGIA'S BARRIER ISLANDS: LESSONS LEARNED FROM DEVELOPING AND USING AMBUR

Georgia’s barrier coast is composed of standalone islands and multi-barrier complexes that front expansive tidal marsh and are separated by relatively large, positionally stable inlets. The backbarrier shorescape is a mixture of dense to moderately vegetated dunes and sediment banks, maritime forests, and marsh platforms dissected by laterally migrating tidal streams. The shape of the shoreline can range from curvilinear to highly sinuous depending on the processes acting upon the backbarrier shore. Most historical shoreline change studies have concentrated on the oceanfront side of the barriers. Not only because, simply, that is where the built environment is concentrated, but also because the oceanfront shoreline is mostly curvilinear and lacks highly curved segments which are difficult to analyze with currently available GIS-based analysis tools. Recently, the AMBUR (Analyzing Moving Boundaries Using R) package was developed and applied to map shoreline change for each island along the Georgia coast including backbarrier, oceanfront, and inlets. AMBUR’s transect-casting techniques simplify dealing with curved shoreline segments that have proven problematic for the traditional perpendicular-transect method. Furthermore, AMBUR’s output of data tables, graphics, and shapefiles allows for rapid identification of erosion hotspots and other areas of shoreline position flux.

Preliminary results from coast-wide analyses show that approximately 65% of Georgia’s backbarrier shoreline eroded throughout the study period from 1855 to 2004 at a mean rate of -0.35 m/yr. Less than half of the backbarrier of the islands eroded from 1933 to 1974. However, during the most recent period from 1974 to 2004, there was approximately 78% backbarrier erosion coast-wide occurring at a mean rate of -0.39 m/yr. Backbarrier erosion tends to be heightened near the apex of encroaching tidal stream meanders, near the confluence of two tidal streams adjacent to the backbarrier shore, and along shorelines within close proximity to or adjacent to inlets. Furthermore, more than half of the length of the Atlantic Intracoastal Waterway is adjacent to the backbarrier shoreline and has influenced shoreline behavior through dredging activities.