Barrier islands serve as valuable resources for coastal communities by reducing backbarrier flooding, providing wildlife habitat, and creating local economic activity through opportunities for recreation and tourism. Because the benefits of these islands are linked to their morphology, coastal resource planners must consider what management alternatives will maximize these benefits, considering both short- and long-term goals. Recent advances in long-term computational modeling of barrier island, marsh, and lagoon systems have created opportunities for gaining additional insights into the morphodynamics of these systems, which may help planners make better-informed coastal management decisions. In this series of studies, a recently developed long-term barrier-marsh-lagoon model is evaluated to better understand system morphodynamics and applied to a real barrier island system in the mid-Atlantic to understand its vulnerabilities and the potential impacts of management alternatives. In the first study, a comprehensive review of advances in barrier island morphodynamic modeling was presented. In the second study, a global sensitivity analysis method, the Sobol method, was used to explore the parameter space of the barrier-marsh-lagoon model. The significant influence of initial barrier geometry, the combination of parameters required for short-term drowning to occur, and the significant role of tidal dispersion on backbarrier sediment dynamics were morphodynamic insights drawn from this study. In the third study, five global sensitivity analysis methods were evaluated based on their ability to rank parameters, converge to stable results, and their reliability. Groups of the most significant parameters were generally identified by all methods; however, the Morris method exceeded all others in terms of performance, especially its ability to converge and its reliability. VARS performed second best, on average, with better convergence and reliability results than the Sobol method, and with lower simulation counts. In the fourth study, the long-term model was applied to a mid-Atlantic barrier island and used to assess the island's vulnerabilities to sea level rise, overwash, and the impact of coastal management alternatives. Thin-layer placement and beach nourishment were found to be effective at sustaining the marsh and minimizing island retreat, respectively. / Doctor of Philosophy / Barrier islands help coastal communities by reducing flooding, providing wildlife habitat, and creating local economic activity through opportunities for recreation and tourism. Because the benefits of these islands are linked to their form, decision-makers must think about how to manage these islands to help the community both now and in the future. Recent advances in computer modeling of barrier islands, and the adjacent marshes and lagoons, over decades to hundreds of years, have created opportunities for us to learn more about how these systems behave over time, which may help planners make better-informed coastal management decisions. In this series of studies, a recently developed computer model of the barrier island, marsh, and lagoon is evaluated to learn how the system changes over time and applied to a real barrier island system in the mid-Atlantic to understand its vulnerabilities and the potential impacts of management alternatives. In the first study, a comprehensive review of advances in computer modeling of barrier island changes over time was presented. In the second study, the impact of the model parameters and their combinations with one another was explored using the Sobol global sensitivity analysis method, which is widely considered to be the standard method in practice. The significant influence of initial barrier geometry, the combination of parameters required for the barrier to be overcome by sea level in the short-term, and the significant role of sediment delivered behind the island through tidal inlets were significant insights into the system behavior that were drawn from this study. In the third study, five global sensitivity analysis methods were evaluated based on their ability to rank parameters, the number of computer simulations that were required, the ability of a method to arrive at a conclusive answer, and the consistency of a method in providing an answer. Groups of the most significant parameters were generally identified by all methods; however, the Morris method exceeded all others in terms of its ability to find conclusive and consistent answers due to its ability to identify unimportant parameters. VARS performed second best, on average, with better ability to find conclusive and consistent answers with fewer computer simulations than Sobol. In the fourth study, the long-term computer model was applied to a mid-Atlantic barrier island and used to assess the island's vulnerabilities to sea level rise, overwash (when water flows over the dunes), and the impact of coastal management alternatives. Placing thin layers of additional sediment on top of the marsh platforms and extending the shoreline toward the ocean by placing additional sediment on the beach were found to be effective at sustaining the marsh and minimizing movement of the barrier island landward, respectively.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/121266 |
| Date | 02 October 2024 |
| Creators | Hoagland, Steven William Harvey |
| Contributors | Civil and Environmental Engineering, Irish, Jennifer L., Weiss, Robert, Strom, Kyle Brent, Vitousek, Sean |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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