*2.1. Coastline Changes*

Satellite images taken by GeoEye-1 and SkySat-1 platforms with 5 and 3 m ground pixel resolutions, respectively, were used to trace coastlines between 2010 and 2020. Using this imagery, past coastlines were visually delineated along the limit between wet and dry sediment. This well-established methodological approach [36–38] provides a proxy for the mean high water line (MHWL). Once a set of coastlines were established, changes were quantified using DSAS [35]. From the various statistics that DSAS produces, the average-ofrates (AOR) method, obtained by averaging the values resulting from the distance between each pair of available coastlines divided by the time between surveys, was selected to assess the rates of coastline changes over time. The AOR values were processed for transects spaced at 100 m intervals, perpendicular to a reference baseline traced parallel to the coastline. Accordingly, for two consecutive years, the accuracy of the coastline position depends on the image resolution (5 or 3 m), the georeferencing error (estimated to be 1 m), and a physical component of the error related to the magnitude of the tidal changes and slope of the beach (as intertidal range/tan (slope)) [17,39]. The latter was assessed by using an average beach slope of 9.0◦ (pers. obs. June/2019), and a maximum intertidal range of 0.4 m. Determining the quadratic sum of each of these components yielded an annual maximum uncertainty for coastline change estimates of ±5.0 m/yr.
