Can we reliably estimate dune erosion without knowing pre-storm bathymetry?

Abstract

Pre-storm bathymetry is a required boundary condition for processed-based dune erosion models but is often out of date, extremely coarse resolution, or in the worst case, non-existent. Despite these limitations, coastal engineers and managers are being called upon to provide estimates of dune erosion to vulnerable coastal communities in light of changes in storm conditions and longer term climate projections. Here we calibrate and then use a state of the art dune erosion model (XBeach) to predict a range of possible erosion volumes for the May 2009 East Coast Low that impacted the Gold Coast, Australia. Using pre-storm bathymetry surveys the model required minimal calibration. Predicted erosion volumes, as well as shoreline retreat were in good agreement with observations. To account for errors in nearshore bathymetry, the suite of available surveys was used to estimate a range of erosion volumes. The model results were relatively insensitive to the range of available bathymetry. Milder sloping and terraced/barred profiles resulted in less dune erosion, while steeper foreshores and non-barred profiles were more vulnerable.