Abstract
Monitoring of dune erosion and accretion on the high-energy macrotidal Vougot beach in North Brittany (France) over the past decade (2004–2014) has revealed significant morphological changes. Dune toe erosion/accretion records have been compared with extreme water level measurements, defined as the sum of (i) astronomic tide; (ii) storm surge; and (iii) vertical wave runup. Runup parameterization was conducted using swash limits, beach profiles, and hydrodynamic (Hm0, Tm0,–1, and high tide water level—HTWL) data sets obtained from high frequency field surveys. The aim was to quantify in-situ environmental conditions and dimensional swash parameters for the best calibration of Battjes [1] runup formula. In addition, an empirical equation based on observed tidal water level and offshore wave height was produced to estimate extreme water levels over the whole period of dune morphological change monitoring. A good correlation between this empirical equation (1.01Hmoξo) and field runup measurements (Rmax) was obtained (R2 85%). The goodness of fit given by the RMSE was about 0.29 m. A good relationship was noticed between dune erosion and high water levels when the water levels exceeded the dune foot elevation. In contrast, when extreme water levels were below the height of the toe of the dune sediment budget increased, inducing foredune recovery. These erosion and accretion phases may be related to the North Atlantic Oscillation Index.
Highlights
Extreme events such as storms or hurricanes play a major role in dune erosion [2,3,4,5,6,7]
The work presented in this paper extends the analysis of runup on the same study site (Vougot beach in north western Brittany) in order to estimate extreme water levels
Fit analysis between observed runup values and morphodynamic variables was achieved following the same methodological approach as the one used by Cariolet and Suanez [33]. Morphodynamic parameters such as Hm0ξ0 have been used to characterize runup processes in as far as it was demonstrated that these variables were best correlated with runup when using the slope of the active section
Summary
Extreme events such as storms or hurricanes play a major role in dune erosion [2,3,4,5,6,7]. Sallenger et al [18] and Ruggiero et al [19] proposed different models designed to assess the foredune’s sensitivity to erosion generated by the impact of storm waves This methodological approach was used for assessing the vulnerability of barrier islands to hurricanes along the eastern coast of the USA [7,18] and analyzing decadal-scale variations in dune erosion and accretion rates on the Sefton coast in northwest England [20]. Sallenger [18] has defined four storm-impact regimes (swash, collision, overwash, and inundation) related to increased water levels from storms that shift the runup and location of wave attack higher on the profile, making berms or foredunes more vulnerable to erosion and overtopping In this storm-impact scaling model, the borders between the impact regimes represent thresholds across which the magnitudes and processes of dune erosion are substantially different. The aim is to evaluate the frequency with which water can reach the property, providing an evaluation of the susceptibility to potential erosion
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