Probabilistic Structure of Events Controlling the After-Storm Recovery of Coastal Dunes

Abstract:

Coastal dunes protect beach communities and ecosystems from rising seas and storm flooding, and influence the stability of barrier islands by preventing overwashes and limiting barrier migration. Therefore, the degree of dune recovery after a large storm provides a simple measure of the resiliency of barrier islands to external stresses. Dune recovery is modulated by low-intensity/high-frequency high water events (HWE), which remain poorly understood compared to the low-frequency extreme events eroding mature dunes and dominating the short-term socio-economic impacts on coastal communities. Here, we define HWEs and analyze their probabilistic structure using time series of still water level and deep-water wave data from multiple locations around the world. We find HWEs overtopping the beach can be modeled as a marked Poisson process with exponentially distributed sizes or marks, and have a mean size that varies surprisingly little with location. This homogeneity of global HWEs is related to the distribution of the extreme values of a wave-runup parameter defined in terms of deep-water significant wave height and peak wavelength. Furthermore, the characteristic beach elevation at any given location seems to be tied to a constant HWE frequency of about one event per month, which suggest a stochastic dynamics behind beach stabilization. Our results open the door to the development of stochastic models of beach, dune and barrier dynamics, as well as a better understanding of wave-driven nuisance flooding.