Spatio-temporal analysis of barrier island shoreline change
Jackson, Chester W.
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Deficiencies exist in the study of shoreline dynamics of Georgia’s barrier islands and the processes that influence change. Previously unexamined shoreline localities that were difficult to assess using existing techniques and software programs provide a basis for the development of new tools and methods for analyzing change. AMBUR (Analyzing Moving Boundaries Using R) was developed to analyze shoreline change along barrier islands with complex shapes and highly curved coastlines. Built using the R programming environment, AMBUR provides a suite of functions for quantifying the rate and magnitude of shoreline movement and performs additional statistical, graphical, and geospatial analyses. The reliability of transect-based analyses is improved using new techniques for curved shorelines too problematic for the traditional perpendicular-transect method. Application of AMBUR to Georgia’s barrier islands provides a robust dataset for island-wide shoreline change and assists with classifying the modern behavior of the coast. Historical shorelines from 1855 to 2004 were analyzed and partitioned into oceanfront, backbarrier, and inlet-facing zones. Throughout the 1855 to 2004 era, 41 % of Georgia’s oceanfront shoreline eroded at a mean rate of -1.66 m/yr EPR (± 0.06 m/yr) and the remaining shoreline accreted at 2.25 m/yr EPR (± 0.06 m/yr). The backbarrier eroded along 65 % of the shore at a mean rate of -0.35 m/yr EPR (± 0.07 m/yr) throughout the period. More than half of the islands exhibit a net seaward shift in area and regressive behavior, whereas Wolf and St. Catherines Islands are thinning and shortening and are transgressive, erosional hotspots. Reversals of longshore transport currents, primarily due to inlet dynamics and seasonal shifts in climate regimes, promote periods of accretion and erosion along the northern and southern ends of some islands. Stable, migrating, and ephemeral inlet processes at the local level exert the greatest influence over oceanfront shorelines. Backbarrier shorelines are primarily influenced by tidal creek migration, proximity to inlets and confluences of other streams. Human activities are influencing shoreline erosion and accretion rates through uses of hard/soft stabilization and dredging activities.