Coastal vulnerability assessment based on video wave run-up observations at a mesotidal, steep-sloped beach

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 shorenormal wind speed component is probably related to the wind effect on wave breaking. The ratio of the infragravityto-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%.

Understanding epistemic uncertainty in large-scale coastal flood risk assessment for present and future climates

“…4c). It is noteworthy that the 10 m lidar DEM is comparable with the EAD from SRTM, but this is only due to the site-specific calibration of the coastal protection based on previous studies (Vousdoukas et al, 2012). For most areas such datasets are not available and deviations in the estimated losses can be substantially higher.…”

“…It combines oceanic waves and a tidal range of up to 3 m (Vousdoukas, 2014). Apart from the complex topography (Vousdoukas, 2012), it faces socio-economic challenges, with dense infrastructure and conflicting uses, such as an airport and tourist and wildlife areas. Ria Formosa also provides a test bed for sensitivity analysis due to the availability of a variety of in situ measurements, including high-resolution topographic data from a lidar survey.…”

“…To appraise the above uncertainties we use high-quality 0.5 m resolution lidar nearshore elevation data available for Faro Beach (Vousdoukas et al, 2012). In order to quantify the effect of DEM resolution on CFR assessment, we create four alternative DEMs by resampling the lidar dataset in 10, 20, 50, and 100 m resolution and we compare against the SRTM DEM in terms of both vertical elevation and the resulting EADs.…”

“…Flood risk estimation exhibits methodological differences depending on the scale of application (Apel et al, 2009;Ferreira et al, 2017;de Moel et al, 2015). Local studies benefit from high-quality digital elevation models (DEMs) (Vousdoukas et al, 2012) and exposure data (Christie et al, 2017), as well as detailed numerical models, resolving several scales (Bertin et al, 2014;Giardino et al, 2018) and including complex processes like dune or dike breaching de Moel et al, 2012). Large-scale assessments, however, are based on lower-resolution DEMs and exposure data and more abstract conceptualizations of physical processes: principally the hydrology and hydraulics, as well as flood damage processes.…”

Wave Run-Up Observations on Revetments With Different Porosities

“…After Hunt (1959) several other formulations combining H and L in different ways have been suggested for natural slopes like beaches, (Holman, 1986;Synolakis, 1987;Mase, 1989;Nielsen, 1989;Ruggiero et al, 2004;Stockdon et al, 2006;Vousdoukas et al, 2009;Vousdoukas et al, 2012). However, all these formulations only take the wave parameters and the slope itself into account, neglecting other influencing factors like friction or porosity.…”