Abstract
There is an increasing interest in the broad-scale implementation of coastal erosion early warning systems (EWS) with the goal of enhancing community preparedness to extreme coastal storm wave events. These emerging systems typically rely on process-based models to predict the storm-induced morphological change. A key challenge with incorporating these models in EWSs is the need for up-to-date nearshore and surf zone bathymetry data, which is difficult to measure routinely, but potentially important for accurate erosion forecasting. This study evaluates the degree to which up-to-date bathymetry is required for accurate coastal erosion predictions using the morphodynamic model XBeach and, subsequently, whether a range of “representative” and/or “synthetic” bathymetries can be used for the bottom boundary, when a survey of the immediate pre-storm bathymetry is not available. Twelve storm events at two contrasting sites were modelled using six different bathymetry scenarios, including the expected “best case” bathymetry surveyed immediately pre-storm. These results indicate that alternative bathymetries can be used to obtain sub-aerial erosion predictions that are similar (and in some cases better) than those resulting from the use of an immediately pre-storm surveyed bathymetry, provided that rigorous model calibration is undertaken prior. This generalized finding is attributed to specific parametrizations in the XBeach model structure that are optimized during the calibration process to match the particular bottom boundary condition used. This study provides practical guidance for the selection of suitable nearshore bathymetry for use in operational coastal erosion EWSs.
Highlights
Coastal hazard early warning systems (EWS) are an evolving disaster risk reduction tool that can provide information several days in advance of an impending storm, potentially providing a “window of opportunity” to implement a range of emergency responses.These systems typically incorporate coastal numerical models within their workflow to simulate nearshore hydrodynamic and morphodynamic processes, with the goal of predicting the location and magnitude of coastal flooding and erosion along coastlines [1,2,3,4,5]
Six different bathymetries were tested for XBeach sensitivity, ranging from the benchmark “best case” scenario of the bathymetry having been surveyed immediately pre-storm, to time-invariant scenarios based on temporal averages of available historic survey measurements, or simple beach equilibrium profile formulae
Following extensive calibration of each bathymetry using a rigorous generalized likelihood uncertainty estimation (GLUE) methodology, model performance was assessed both against storm events used in the model calibration, as well as a number of “unseen” storm events
Summary
Coastal hazard early warning systems (EWS) are an evolving disaster risk reduction tool that can provide information several days in advance of an impending storm, potentially providing a “window of opportunity” to implement a range of emergency responses. These systems typically incorporate coastal numerical models within their workflow to simulate nearshore hydrodynamic and morphodynamic processes, with the goal of predicting the location and magnitude of coastal flooding and erosion along coastlines [1,2,3,4,5]. Coastal erosion hazards are relevant along wave-dominated, sandy coastlines [8], and the dynamic nature of these nearshore systems may result in additional forecasting challenges
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