Coastal vulnerability assessment based on video wave run-up observations at a mesotidal,steep-sloped beach |
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| Authors: | Michalis Ioannis Vousdoukas Dagmara Wziatek Luis Pedro Almeida |
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| Institution: | 1.Forschungszentrum Küste,Hannover,Germany;2.CIMA,University of Algarve,Faro,Portugal;3.Leibniz University Hannover,Hannover,Germany |
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| Abstract: | Coastal imagery obtained from a coastal video monitoring station installed at Faro Beach, S. Portugal, was combined with topographic
data from 40 surveys to generate a total of 456 timestack images. The timestack images were processed in an open-access, freely
available graphical user interface (GUI) software, developed to extract and process time series of the cross-shore position
of the swash extrema. The generated dataset of 2% wave run-up exceedence values R
2 was used to form empirical formulas, using as input typical hydrodynamic and coastal morphological parameters, generating
a best-fit case RMS error of 0.39 m. The R
2 prediction capacity was improved when the shore-normal wind speed component and/or the tidal elevation η
tide were included in the parameterizations, further reducing the RMS errors to 0.364 m. Introducing the tidal level appeared
to allow a more accurate representation of the increased wave energy dissipation during low tides, while the negative trend
between R
2 and the shore-normal wind speed component is probably related to the wind effect on wave breaking. The ratio of the infragravity-to-incident
frequency energy contributions to the total swash spectra was in general lower than the ones reported in the literature E
infra/E
inci > 0.8, since low-frequency contributions at the steep, reflective Faro Beach become more significant mainly during storm
conditions. An additional parameterization for the total run-up elevation was derived considering only 222 measurements for
which η
total,2 exceeded 2 m above MSL and the best-fit case resulted in RMS error of 0.41 m. The equation was applied to predict overwash
along Faro Beach for four extreme storm scenarios and the predicted overwash beach sections, corresponded to a percentage
of the total length ranging from 36% to 75%. |
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