The linkage between barrier island morphologies and dune topographies, vegetation, and biogeomorphic feedbacks, has been examined. The two-fold stability domain (i.e., overwash-resisting and overwash-reinforcing stability domains) model from case studies in a couple of islands along the Georgia Bight and Virginia coast has been proposed to examine the resilience properties in the barrier dune systems. Thus, there is a need to examine geographic variations in the dune topography among and within islands. Meanwhile, previous studies just analyzed and compared dune topographies based on transect-based point elevations or dune crest elevations; therefore, it is necessary to further examine dune topography in terms of multiple patterns and processes across scales. In this dissertation, I develop and deploy a cross-scale data model developed from resilience theory to represent and compare dune topographies across twelve islands over approximately 2,050 kilometers of the US southeastern Atlantic coast. Three sets of topographic variables were employed to summarize the cross-scale structure of topography (elevational statistics, patch indices, and the continuous surface properties). These metrics differed in their degree of spatial explicitness, their level of measurement, and association with patch or gradient paradigms. Topographic metrics were derived from digital elevation models (DEMs) of dune topographies constructed from airborne Light Detection and Ranging (LiDAR). These topographic metrics were used to construct dune topographic state space to investigate and visualize the cross-scale structure of dune topography. This study investigated (1) dune topography and landscape similarity among barrier islands in different barrier island morphologic contexts, (2) the differences in barrier island dune topographies and their resilience properties across large geographic extents, and (3) how geomorphic and biogeomorphic processes are related to resilience prosperities. The findings are summarized below. First, dune topography varies according to island morphologies of the Virginia coast; however, local controls (such as human modification of the shore or shoreline accretion and erosion) also play an important role in shaping dune topographies. Compared with tide-dominated islands, wave-dominated islands exhibited more convergence in dune topographies. Second, the dune landscapes of the Virginia Barrier Islands have a poorly consistent spatial structure, along with strong collinearity among elevational variables and landscape indices, which reflects the rapid retreat and erosion along the coast. The dune landscapes of the Georgia Bight have a more consistent spatial structure and a greater dimensionality in state space. Thus, the weaker multicollinearity and higher dimensionality in the dataset reflect their potential for resilience. Last, islands of different elevations may have similar dune topography characteristics due to the difference in resistance and resilience. Notwithstanding the geographic variability in geomorphic and biogeomorphic processes, convergence in dune topography exists, which is evidenced by the response curves of the topographic metrics that are correlated with both axes. This work demonstrates the usefulness of different representations of dune topography by cross-scale data modeling. Also, the two existing models of barrier island dune states were integrated to form a conceptual model that illuminates different, but complementary, resilience properties in the barrier dune system. The differences in dune topographies and resilience properties were detected in state space, and this information offers guidance for future study’s field site selections.

A major economic constraint in the Bahamas, and other small carbonates islands world-wide, is the lack of fresh water resources. To combat these socio-economic problems on San Salvador Island I sought to gain a more detailed understanding of the extent, behavior, and controls on the island’s fresh-water lens. DC electrical resistivity tomography and time-series geochemical data are used to study the fresh water lens at the Line Hole well field. Electrical Resistivity profiles are used to image the extent of fresh water resources. Time-series geochemical data provide information on the behavior of the fresh water resources as a function of time. The inversion models of the electrical resistivity profiles illustrate a fresh water lens less than 3 meters thick on average. The mixing zone is diffuse in nature, and substantially thicker than the fresh water lens. The geochemical results corroborate the fresh water lens dimensions predicted by the electrical resistivity model. In addition, mixed semi-diurnal and spring/neap tidal cycles are the primary control on the water level. Statistical analysis of specific conductance and temperature illustrate a positive and negative correlation with water level, respectively. Analysis of precipitation with respect to water level and geochemistry indicate low effective recharge rates during the period of study. The current state of the water resources at the Line Hole well field is strained. Despite moderate levels of freshening since the termination of pumping in December 2006; the system continues to be in a state of disequilibrium. The problem is compounded by abnormal thickening of the mixing zone due to communication of the well field with the ocean, and a limited volume of fresh water. In conclusion, the two techniques used in conjunction provide a non-invasive method of estimating fresh water resources in this type of setting. Conversely, the high RMS and L2 values for the electrical resistivity models and limited time-series data create a high level of uncertainty in the interpretation of results.

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The Northern Gulf of Mexico and coastal Louisiana are experiencing accelerated relative sea level rise rates; therefore, the region is ideal for modeling the global affects of sea level rise (SLR) on estuarine dynamics in a transgressive barrier island setting. The field methods and numerical modeling in this study show that as barrier islands are converted to inner shoals, tidal exchange increases between the estuary and coastal ocean. If marshes are unable to accrete at a pace comparable to SLR, wetlands will deteriorate and the tidal exchange and tidal prism will further increase. Secondary to hurricanes, winter storms are a primary driver in coastal morphology in this region, and this study shows that wind direction and magnitude, as well as atmospheric pressure change greatly affect estuarine exchange. Significant wetland loss and winter storm events produce changes in local and regional circulation patterns, thereby affecting the hydrodynamic exchange and resulting transport.

Barrier island restoration and nourishment is necessary for sustaining coastal systems worldwide. In the Mississippi River Delta Plain, the lack of sediment supply, relative sea level rise, and reworking of abandoned delta lobes promote rapid disintegration of barriers, which can contribute to mainland storm impacts. Barrier island restorations that utilize higher quality sediments (Outer Continental Shelf- OCS) are expected to exhibit higher resiliency, withstanding coastal erosion, event-induced erosion, and ongoing transgression when compared to barriers nourished using lower quality nearshore (NS) sands. Additionally, use of OCS sediments increases sediment supply by adding material to the system supporting increased barrier longevity by maintaining a subaerial footprint longer compared to NS sediments. We used the Delft3D modeling suite to study barrier geomorphic trajectories nourished using OCS/NS sands, compared with control simulations with no nourishment. Resulting morphologies from 18 simulations with forcing that included annualized forcing, storms, and SLR are evaluated and compared.

Title from PDF of title page. / Document formatted into pages; contains 113 pages. / Thesis (M.S.)--University of South Florida, 1983. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Bunces Key, a narrow, linear, barrier island on the west-central coast of Florida, was formed in 1961. Its growth and development since that time is well documented by aerial photography. Cores taken from the Key and surrounding areas reveal a stratigraphic succession of facies reflecting rapid vertical aggradation. Sedimentation began on a gently sloping platform through the landward migration of large scale bedforms (sand waves) during fair weather periods. Migration of these bedforms ceased when emergence and lack of continued overwash precluded further movement. / Vertical accretion to supratidal levels resulted from the continued onshore transport of sediment and subsequent welding to the previously formed bars. Stratigraphically, the barrier exhibits a "layer-cake" type of stratigraphy, with nearshore sediments overlain by foreshore, backbeach, and dune deposits. The backbarrier generally exhibits muddy lagoon sediments intercalated with washover and channel margin sediments.Fining upward washover sequences reflect the unstable nature of the island. / Low pressure systems commonly cause overtopping of the barrier, with the subsequent formation of tidal inlets and washover fans. Aerial photographs document the formation of an initial barrier that was breached twice prior to 1973. A second barrier formed in late 1973 just seaward of the initial island and subsequently grew through littoral drift to a length of 1.8 km. A narrow inlet (30 m) formed through the northern end of the island in 1982. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

Gen. John Adams Dix, the Union commander of the Department of Maryland, wrote in an 1861 letter to Francis Blair of President Lincoln's administration that "we are in the most danger on the Eastern Shore [of Virginia]." Dix did not exaggerate when he implied that Accomac and Northampton County embodied secessionist sentiment on the Delmarva Peninsula in 1861. Dix knew that the Eastern Shore of Virginia, the most southern region of Delmarva, heavily influenced its neighbors to the north. If it made a strong demonstration in favor of the Confederacy, the Eastern Shore of Maryland might go spiraling toward secession. It could also decrease Union sentiment and progress in lower Delaware. With this in mind, Dix decided to make a preemptive strike on the Eastern Shore of Virginia in late 1861. Although this campaign describes only part of the question that this thesis entails it embodies the overarching importance of what occurred in the area.¹ 1. Delmarva is a modern connotation denoting the peninsula made up by parts of Delaware, Maryland, and Virginia. Susie M. Ames, "Federal Policy Toward the Eastern Shore of Virginia." Virginia Magazine of History and Biography, 69 (1961) : 432-459. / Master of Arts