Interaction of Hurricanes and Natural Coastal Features: Implications for Storm Damage Reduction

It is generally acknowledged that wetlands and barrier islands can reduce surge and waves. However, while a general qualitative understanding of these interactions is available in the scientific literature, quantification of these interactions is lacking and has previously been based on limited data of relatively poor quality. The overall aim of this study was to improve the understanding of the interaction between hurricanes and natural coastal features; quantify the potential for natural features to reduce storm surge and waves; and provide a capability to evaluate a holistic approach to hurricane storm damage reduction. A high resolution numerical modelling system capable of representing complicated coastal landscapes and simulating all the primary relevant physical processes, including winds, air-sea momentum transfer, atmospheric pressure, wind-driven waves, riverine flows, tides, and friction due to land cover is applied to better understand the physical interaction of hurricanes and natural features. The focus of the study is restricted to the interaction of hurricanes (and not other coastal storms such as Nor’easters) with wetlands and barrier islands. Other coastal features such as ridges and lakes are part of the natural system, but not specifically addressed. Analyses of model results indicate that the surge attenuation rates estimated by the modelling system are consistent with observations. Both model results and observed data suggest that wetlands do have the potential to reduce surges but that it is dependent on the landscape (bathymetry, structures, and vegetation) and storm characteristics (size, speed, track, and intensity). The effectiveness of wetlands at attenuating surge is primarily dependant on the surrounding coastal landscape and the strength and duration of the relevant forcing. Results from this thesis indicate that barrier islands also have the potential to reduce storm surge and waves. The barrier islands act as a speed bump, blocking and diverting surge propagation around the islands until they become overtopped. Once overtopped, the islands can still slow the surge by bathymetric and vegetation resistance as water flows over the island. The potential of barrier islands to reduce surge and waves at the mainland coast is dependant on barrier island elevation, proximity of the island to the mainland coast, and the size of the passes in the barrier island chain. The potential to reduce surges is lessened if the barrier island is breached during a storms passage as this creates a direct route for water to bypass the island. Natural and man-made protection features like levees, wetlands and barrier islands do not decrease the mass of water driven into the region by the hurricane winds but they do change the momentum and redistribute the storm surge. Water level changes in one part of a system can create unintended consequences somewhere else in the system. The potential for these unintended changes must be considered for effective coastal flood protection design. For these reasons, the effect of proposed project alternatives on storm surge levels and waves must be examined over large spatial and temporal scales, or a systems approach. The importance of taking a holistic systems approach to coastal flood protection and how the modelling system can identify unintended consequences is demonstrated. The knowledge of the interaction of hurricanes and natural coastal features developed within this thesis will lead to better coastal flood protection planning, particularly in deltaic areas. (Less)