Evolution of a beach nourishment project using dredged sand
from navigation channel, Dunkirk, northern France
Alexandra Spodar
1
&
Arnaud Héquette
1
&
Marie-Hélène Ruz
1
&
Adrien Cartier
2
&
Pascal Grégoire
3
&
Vincent Sipka
1
&
Nicolas Forain
3
Received: 15 December 2016 /Revised: 5 April 2017 / Accepted: 17 April 2017 / Published online: 29 May 2017
#
Springer Science+Business Media Dordrecht 2017
Abstract 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 × 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 « Digue des Alliés », which protects several
residential districts of Dunkirk from marine flooding. High
resolution topographic surveys were carried out during
2½ 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 off-
shore wave power and beach volume change during distinct
beach survey periods (R
2
= 0.79 to 0.87), with more signifi-
cant 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.
Keywords Beach nourishment
.
Beneficial use of dredged
sand
.
Flood defence
.
Beach morphodynamics
Introduction
Coastal zones are exposed to a range of coastal hazards in-
cluding erosion and marine flooding that are likely to worsen
in the next decades with predicted sea level rise (Nicholls and
Cazenave 2010; Rahmstorf et al. 2012) and possible changes
in storminess (Bertin et al. 2013;Ruggiero2013)associated
with climate change (IPCC 2013). The likely increase in fre-
quency of extreme water levels during the next decades due to
rising sea level (Haigh et al. 2011; Weisse et al. 2012)should
result in increasing shoreline retreat and storm-induced
flooding along low-elevated areas (Brown et al. 2013;Kruel
2016). Due to the increasing vulnerability of the coastal zones
to coastal hazards, the need for coastal protection will neces-
sarily increase in the future, especially in densely populated
areas (Neumann et al. 2015).
Coastal engineering structures such as seawalls, dikes and
breakwaters have been extensively used for decades for shore-
line stabilization all over the world (Charlier et al. 2005;
Kamphuis 2010), but these types of hard coastal protections
commonly induce adverse effects on beaches and adjoining
shorelines by altering hydrodynamics and sediment transport
processes (Sánchez-Badorrey et al. 2008; Guimaraes et al.
2016). Therefore, alternate adaptive strategies involving soft
* Alexandra Spodar
alexandra.spodar@univ-littoral.fr
1
Laboratoire d’Océanologie et de Géosciences, UMR CNRS 8187,
Université Littoral Côte d’Opale, 32 Avenue Foch,
62930 Wimereux, France
2
GEODUNES, 79 rue Pasteur, 59240 Dunkirk, France
3
Dunkirk Port, 2505 route de l’écluse Trystram,
59386 Dunkirk, France
J Coast Conserv (2018) 22:457–474
DOI 10.1007/s11852-017-0514-8
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