Abstract
This study presents sand activation depth (SAD) measurements recently obtained on two contrasting beaches located along the Atlantic coast of France: the gently sloping, high-energy St Trojan beach where wave incidence is usually weak, and the steep, low-energy Arçay Sandspit beach where waves break at highly oblique angles. Comparisons between field measurements and predictions from existing formulae show good agreement for St Trojan beach but underestimate the SAD on the Arçay Sandspit beach by 40–60%. Such differences suggest a strong influence of wave obliquity on SAD. To verify this hypothesis, the relative influence of wave parameters was investigated by means of numerical modelling. A quasi-linear increase of SAD with wave height was confirmed for shore-normal and slightly oblique wave conditions, and a quasi-linear increase in SAD with wave obliquity was also revealed. Combining the numerical results with previously published relations, both a new semi-empirical and an empirical formula for the prediction of SAD were developed which showed good SAD predictions under conditions of oblique wave breaking. The new empirical formula for the prediction of SAD (Z 0) takes into account the significant wave height (H s), the beach face slope (β) and the wave angle at breaking (α), and is of the form \( Z_{0} = 1.6\tan {\left( \beta \right)}H^{{0.5}}_{{\text{s}}} {\sqrt {1 + \sin {\left( {2\alpha } \right)}} } \). The use of a dataset from the literature demonstrates the predictive skill of these new formulae for a wide range of wave heights, wave incidence and beach gradients.
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Acknowledgements
The first author is funded by the European Commission through a Marie Curie Intra-European Fellowship (contract IMMATIE MEIF-CT-2006-041171). Eric Chaumillon, Jonathan Allard, Stéphane Recoura, Pascal Tiphaneau, Robin Quique and Antoine Deshouilieres are thanked for their help during fieldwork. Jacques Marquis from the ONCFS has allowed us to work within the Arçay nature reserve. This work is a contribution to the Andalusia PAI Research Group RNM-328. Óscar Ferreira participated under the scope of the BERNA (POCTI/CTA/45431/2002) project.
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Bertin, X., Castelle, B., Anfuso, G. et al. Improvement of sand activation depth prediction under conditions of oblique wave breaking. Geo-Mar Lett 28, 65–75 (2008). https://doi.org/10.1007/s00367-007-0090-2
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DOI: https://doi.org/10.1007/s00367-007-0090-2