Journal
JOURNAL OF COASTAL CONSERVATION
Volume 22, Issue 3, Pages 457-474Publisher
SPRINGER
DOI: 10.1007/s11852-017-0514-8
Keywords
Beach nourishment; Beneficial use of dredged sand; Flood defence; Beach morphodynamics
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Funding
- Port of Dunkirk
- Universite du Littoral Cote d'Opale
- French Association Nationale de la Recherche et de la Technologie (ANRT) through a CIFRE Ph.D. scholarship
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The largest beach replenishment project ever in France was completed in February 2014 in Dunkirk on the coast of northern France. A volume of 1.5 x 10(6) m(3) of sand extracted from a navigation channel was placed on the beach to build up a 150 to 300 m wide supratidal platform in front of a dike, called A << Digue des Alli,s A >>, which protects several residential districts of Dunkirk from marine flooding. High resolution topographic surveys were carried out during 2A 1/2A years to monitor beach morphological changes, completed by a hydrodynamic field experiment conducted in February 2016. Approximately -138,200 m(3) of sand, corresponding to 9.2% of the initial nourishment volume, were eroded over the nourishment area in about 2 years. An obvious decrease in erosion eastward with a shift from erosion to accumulation was observed, suggesting an eastward redistribution of sand. This longshore sand drift is beneficial for the eastward beach of Malo-les-Bains where most of the recreational activities are concentrated. Hydrodynamic measurements showed that waves and wave-induced currents play a major role on the longshore sand redistribution compared to tidal flows. Strong relationships were observed between cumulative offshore wave power and beach volume change during distinct beach survey periods (R-2 = 0.79 to 0.87), with more significant correlations for northerly waves. A slight decrease in erosion during the second year compared to the first year after nourishment suggests that the loss of sand should decrease after an initial phase of rapid readjustment of the beach shape towards equilibrium.
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