On Barrier Islands: Drivers and Controls

Abstract

Barrier islands are complex dynamic environments that support unique ecosystems and protect human developments on the mainland from the impacts of storms. Therefore, it is essential to assess their current and future state in terms of the processes driving barrier evolution and of the controls of barrier morphology, critically including the elevation and alongshore extent of coastal foredunes. This Dissertation examines the vulnerability of barrier islands through a stochastic framework addressing both short and long timescales. Chapter 1 offers a stochastic characterization of the water-driven nuisance flooding affecting the after-storm recovery of coastal dunes by analyzing time series of still-water level and deep-water wave data. This short to mid-term driver of barrier dynamics can be modeled as a marked Poisson process with exponentially distributed marks. Furthermore, a constant frequency of about 1 event per month seems to define a characteristic beach elevation suggesting a causal relationship between this driver and beach morphology. Chapter 2 investigates the role of the main controls of the stochastic barrier dynamics, namely elevation capital (defined as sand budget over an island) and barrier width. Through an analysis of Digital Elevation Models, critical thresholds of 100-200m in width and 0.5m in elevation are found to capture the transition from resilient to vulnerable barrier state. In Chapter 3 a reference stochastic model that ties drivers (Chapter 1) and controls (Chapter 2) of barrier steady state is first validated and then used to quantify the transition regime. Finally, the study of the role of barrier width as main control of elevation capital provides an insight into the long-term effects of Sea Level Rise and the onset of vulnerable barrier state. This Dissertation, therefore, should serve researchers, managers and policy-makers in the identification of the key drivers and controls of barrier vulnerability and provide an understanding of the future of barrier islands.