QUANTITATIVE SHORELINE CHANGE ANALYSIS OF BARRIER ISLANDS ALONG THE ATLANTIC AND GULF COASTS OF FLORIDA

The ability to accurately quantify shoreline variability along sandy beaches is essential in order to establish aggressive mitigation strategies, based on recent global climate change predictions. This study employs two shoreline change methodologies –the Digital Shoreline Analysis System (DSAS) and a more recent technique, Analyzing Moving Boundaries Using R, (AMBUR) to analyze historic shoreline change and forecast future shoreline movement. Approximately two dozen historic shoreline positions covering the time period from 1856 to 2013 were used to summarize shoreline change trends, with special emphasis on rates of change during the 1995-2013 period of active storm conditions. Two sandy barrier island regions on Florida’s Gulf and Atlantic coasts were chosen for this analysis. The overall average rate of change over the 157-year period along Little St. George Island was -1.8 m/yr, with approximately 65 percent of the shoreline segments eroding and 35 percent advancing. For transects displaying only erosive characteristics along Little St. George Island, the rate of retreat over the long term period (1856 to 2013) returned a value of -3.4 m/yr. During the periods of high tropical storm activity (1995-2013), retreat rates along eroding portions of the coast accelerated to -10.1 m/yr. Along the northern portion of Merritt Island on Florida’s Atlantic coast, the overall average rate of change, erosion and accretion included was 0.1 m/yr. In direct contrast to Little St. George Island, the majority of transects (65 percent) evaluated along the shoreline of Merritt Island over the long-term displayed a seaward advance. Results indicate that severe storms generally produce dramatic morphological alteration of the coast and in some cases can result in shoreline retreat in excess of 50 m for a single event. Additionally, the data show that shoreline orientation, along with engineering projects, act over a variety of spatial and temporal scales to influence shoreline evolution. Further, the trends of shoreline movement observed in this study indicate that nearshore bathymetry and tidal inlet dynamics in both locations caused increased shoreline fluctuations and more notably, accelerated rates of erosion, especially immediately downdrift from the inlets.