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Regional-scale washover deposits along the Florida Gulf and Atlantic coasts induced by multiple hurricanes in 2004 and 2005 were studied through coring, trenching, ground-penetrating radar imaging, aerial photography, and prestorm and poststorm beach-profile surveys. Erosional and depositional characteristics in different barrier-island sub-environments, including dune field, interior wetland and back-barrier bay were examined. Over the eroded dune fields, the washover deposits are characterized by an extensive horizontal basal erosional surface truncating the old dune deposits and horizontal to slightly landward-dipping stratification. Over the marshes in the barrier-island interior, the washover deposits are characterized by steep tabular bedding, with no erosion at the bottom. Overwash into the back-barrier bay produced the thickest deposits characterized by steep, prograding sigmoidal bedding. No significant erosional feature was observed at the bottom. Washover deposits within the dense interior mangrove swamp demonstrate both normal and reversed graded bedding. The washover deposits caused by hurricanes Frances (2004) and Jeanne (2004) along the southern Florida Atlantic coast barrier islands are substantially different from those along the northern Florida barrier islands caused by Ivan (2004) and Dennis (2005) in terms of regional extension, erosional features and sedimentary structures. These differences are controlled by different overall barrier-island morphology, vegetation type and density, and sediment properties. The homogeneity of sediment along the northern Florida coast makes distinguishing between washover deposits from Ivan and Dennis difficult. In contrast, along the Atlantic coast barrier islands, the two overwash events, as demonstrated by two phases of graded bedding of the bimodal sediments, are easily distinguishable.

Transforming surveyed elevations and water depths to desired vertical datums is an essential step in building a regional coastal management plan. Regional coastal management plans are based on sediment volume changes and numerical simulations of regional coastal change. Computation of sediment volume changes are possible only if the survey data sets compared share the same vertical datum. Some numerical simulations of regional coastal change require a baseline data set that is referenced to a particular stage of the tide.Until recently, hydrographic and topographic surveys covered areas that were sufficiently small to require only a simple vertical shift to convert the survey data to the desired vertical datum based on local established benchmarks. Data sets that cover large areas are now available through rapid survey techniques like airborne lidar, and through digital publishing of data, like that found on nautical charts. These data sets are not easily converted to a common datum. The magnitude of this problem for regional applications is being recognized only now. The vertical location of tidal, geodetic, and ellipsoidal datums can vary widely over the large areas that these data sets cover. The datums are derived at discrete points distributed sparsely through an area. This paper outlines methodologies for developing and applying regional datum conversions. The methods presented are designed both to realistically represent vertical datums as surfaces instead of discrete points within a region and to minimize error in volume computations and numerical simulations for regional coastal management.

ABSTRACT. An examination of eogenetic karst along supratidal coastal and tidally-influenced inland-lake shoreline sites was conducted on San Salvador Island, Bahamas in order to gain insight into the karst forming processes active along the land-marine interface. Based on proximity to marine aerosols and the spatial distribution patterns of surficial karst morphologies and biotic populations, four shore-parallel geomorphic zones are identified. Spatial affinities suggest haloclastic, bioerosional, and to a lesser degree, mixing dissolution/corrosion processes dominate the seaward-most region of the coastal platform, the region regularly wetted by sea spray and most deeply dissected. Further landward, where the platform remains largely free of marine aerosol, surficial karst development is more subdued and appears to be dominated by meteoric dissolution processes. The observed meso-and microkarst morphologies and associated geomorphic zoning patterns are the combined products of biological, chemical, and physical processes unique to the supratidal zone, and are largely controlled by position relative to the landmarine interface and sea level.