MORPHOLOGICAL EVOLUTION OF A SEDIMENT-STARVED LOW-LYING BARRIER BEACH: FT. MYERS BEACH, SOUTHWEST FLORIDA

Florida has more barrier islands than any other states in the United States. Low lying Barrier island dynamics are expected to modify in response to accelerated sea-level rise and increased storminess. Along the Estero Island, home to the city of Fort Myers Beach, longshore sediment transport shows north and southward directions, due to the sheltering of energetic northerly and north-westerly waves by the Sanibel and Captiva barrier system. This study documented the morphological evolution of a 1.6 km stretch of the barrier beach, located with the center of its 11 km length, since 1982. Repeated Beach profiles collected using a Trimble RTK GPS were analyzed along with LiDAR data from 1998, 2004 and 2010 and archived beach profile data from Florida Department of Environmental Protection. Beach volume changes were estimated for different consecutive observation pairs using SANDS^® software, developed by CH2M. Also, net beach volume change between 2004 and 2010 was computed for the northern and southern sectors using ArcGIS 3D Analyst tool. Barrier beach evolution during the 33 year period was dominated by the passage of hurricanes and tropical storms as well as the presence of a divergent cell towards the center of the study area. The medially located transect corresponds well with this sediment divergent center. Profiles since 1982 show patterns of persistent erosion and consistently represent the narrowest beaches, indicating the position of the divergent cell has remained stable. Hurricanes Charley and Ivan were responsible for significant erosion of both the backshore and foredune. More extensive erosion occurred in front of the seawall-armored beaches in the southern half. All profiles recovered naturally between 2005 and 2010, with beach widening occurred towards the northern and southern end of the study area. Since 2010, the beach profiles showed that the divergent cell has experienced renewed erosion, while the convergent regions have received much of the translocated sand. Tropical Storm Debby (2012) and numerous cold front disturbances could be the driving force for this recent morphological evolution of the beach. The study outcome calls for beach nourishment at the divergent center because sand will be transported locally to neighboring convergent zones by the long shore currents and waves.