AbstractA drainage system was installed in 2008 on the macrotidal beach of Quend-Plage, close to Abbeville (Somme, northern France), following a period of significant erosion of recreational areas. The “Direction départementale des territoires et de la mer” (French Coastal Department Authority) has requested a biannual survey in order to validate the beach drainage setup and its efficiency. This paper presents the methodology used for this survey, and the response of the coastal system to this soft engineering method for preventing erosion. These five years of drainage operation have strongly modified the morphology of the beach. Three main modifications occurred: (i) accretion of the upper beach and foredune, (ii) erosion of the lower and middle beach and (iii) a slight shift in directions of the beach bars and troughs. These morphological changes finally led to the stabilization of the beach

Anne Combaud

Guillaume Villemagne

Olivier Bain

Pascal Barrier

Renaud Toulec

Bain, Olivier

Toulec, Renaud

Combaud, Anne

Villemagne, Guillaume

Barrier, Pascal

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Five years of beach drainage survey on a macrotidal beach (Quend-Plage, northern France) 

Comptes Rendus Géoscience

ForCoan ses14tgisttotaformconstuskiltheEngSeaignbayvercat ueaam reseath qnbti leathintha mpC. R. Geoscience 348 (2016) 409–410http163ewordastal sediment dynamics: Introduction to the thematic issueThis thematic issue of Comptes rendus Geoscience givesoverview of the works presented in the frame of asion dedicated to ‘‘Coastal sediment dynamics’’ at theh Congress of the French Association of Sedimentolo-s, held in Paris, France, from 5 to 7 November 2013. Inl, 23 papers were presented in this session, both in the of oral communications and posters. This nationalference is traditionally a gateway for PhD and Masterdents to share their first results and sharpen their oralls in front of an audience of specialists.The diversity of papers presented in this session reflects natural diversity of the French coasts that open on thelish Channel, the Atlantic Ocean and the Mediterranean, both in terms of morphology (sedimentary andeous rocky coasts, sandy beaches and subtidal prisms,s and estuaries) and hydrodynamic processes (wavesus tide-dominated environments).The main scientific issues addressed in the communi-ions focused on:nderstanding the evolution of constructional androsional coasts at both long (Neogene to Quaternary)nd short-terms (Holocene) through the stratigraphicrchitecture of sedimentary systems and remnantorphology of rocky platforms;fining our vision of modern coastal systems in terms ofdimentary facies and heterogeneity, geomorphologynd hydrodynamic processes, in order to better constraine interpretation of fossil systems;uantifying sedimentary fluxes and relating hydrody-amic processes to morphodynamics of sedimentaryodies in tide-dominated environments (estuaries anddal channels, subtidal platforms);arning from natural hazards (tsunamis, tidal floodingnd storms) by studying the record of extreme events ine sediment archive, and anticipating future evolutions the scope of climate change and rising sea-levelrough refined numerical models of sediment transportnd morphodynamic evolution;onitoring and anticipating the changes in sedimentatterns and transport due to human activities(sediment dredging, installation of marine renewableenergy facilities. . .).The different studies presented gave an interestingoutlook on the variety of tools deployed by the communityof coastal sedimentologists, and raised a number ofquestions on the sensitivity, calibration and limits of useof the measurement systems. Subtidal morphologies aregenerally investigated using multi-swath bathymetry andside-scan sonar, sometimes on vessels specially designedfor shallow water; intertidal and subtidal environmentsare surveyed using air-borne and terrestrial laser scanner,or by man-made surveys using differential GPS (beachprofiles). Hydrodynamics and sediment fluxes are quanti-fied using optic (OBS) and acoustic (ADV, ADCP) probes.While a very high-resolution seismic has proven itsefficiency to investigate the stratigraphy of subtidal bodiesand sediment infilling of bays and estuaries, ground-penetrating radar is becoming increasingly popular in thecommunity to characterize the architecture of dunes andbeach ridges. Finally, original tools such as magneticsusceptibility and X-ray microtomography enrich theclassical package of sedimentological lab analyses.Six papers were selected for this thematic issue, whichillustrate the diversity of methods and objects embracedby the community of sedimentologists working on coastalenvironments.Sandy beaches are subject to erosion, especially duringwinter storms, and the French coasts are globallyretreating under the action of rising sea-level. Due to thisloss of recreational areas and to the damages oninfrastructures on the seaside, engineering solutions aresometimes required to fight against erosion. Bain et al.(2016) report a 5-year monitoring of a sandy beach innorthern France following the installation of a beachdrainage system. This soft engineering solution lowers thebeach watertable, and reduces the erosive potential of thebackwash. The survey reveals a landward displacement ofthe sediment stock and a stabilization of the beach profile,although the system is vulnerable to damages by strongwinter storms.Contents lists available at ScienceDirectComptes Rendus Geoscienceww w.s c ien c edi r ec t . c om://dx.doi.org/10.1016/j.crte.2016.05.0011-0713/ 2016 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.Foreword / C. R. Geoscience 348 (2016) 409–410410Duperret et al. (2016) present a new dataset of high-resolution shallow-water bathymetry coupled with aeriallidar topography. The digital elevation models of land–seatransition zones offer a unique opportunity to study thedevelopment of rocky shore platforms. A comparisonbetween a chalky coast along the English Channel and agranitic coast in Brittany highlights the role of lithologyand of the tectonic heritage as control factors of shoreplatform development in response to past sea-levelfluctuations.Quantifying sediment fluxes is essential to understandlong-term evolution and infilling of estuaries. However,measuring suspended sediment concentration in highlyturbid and turbulent flow is not straightforward. Furgerotet al. (2016) address this issue by performing a detailedcomparison of suspended sediment concentration valuesduring the passage of a tidal bore using: (i) in-situsampling, (ii) optical back-scatter sensor measurements.The quantification of the tidal bore hydrodynamicsperformed with ADV and ADCP measurements, coupledwith turbidity measurements, allowed them to calculateinstantaneous vertical sediment concentration profilesduring the passage of a tidal bore, which plays a significantrole in resuspended sediments from the channel bed.Lesourd et al. (2016) present a new map of superficialsediments in and around the mouth of the Seine estuary,based on an interpolation of 561 grab samples. Thecomparison of these data with four other superficialsediment maps gives an overview of the sedimentaryevolution of the Seine estuary since the late 19th century.The observations reveal an increasing content of muddysediment in the mouth of the estuary. Although in a mega-tidal context, the man-induced alteration of the estuary byengineering works for navigation has transformed theestuary from a sandy tide-dominated environment to amuddy river-dominated system.The silting of the Seine estuary requires a continuousdredging of the channels to ensure a minimum waterdepth for navigation. The dredged material is generallydumped on specific sites in the bay of Seine. Nizou et al.(2016) propose an original method to monitor thedispersal of the dredge material. Because terrigenoussediment contains a higher fraction of ferromagneticminerals than marine sediment does, magnetic suscepti-bility analysis of grab samples is an efficient tool to mapthe dispersion of dredge-dumped sediment on the seafloor, in complement to classical grain size analysis.Van Vliet-Lanoë et al. (2016) investigate the historicaldevelopment of coastal dunes in Brittany. Dune building isconditioned by the sediment budget, which increased inthe Late Holocene due to the slowing down of the marinetransgression and the development of agriculture, and tostormy conditions that are more favourable duringdominantly negative NAO periods. However, modernconditions of rising sea-level and sediment starvationmight weaken coastal dunes that protect lowlands frommarine submersion.AcknowledgementsWe wish to thank the authors for their contributions,and all the participants in the ‘‘Coastal sediment dynam-ics’’ session during the conference.We are indebted to the numerous referees for theirconscientious and constructive reviews of the manu-scripts: Rémi Belon (BRGM, France), Benoı̂t Camenen(IRSTEA, France), Christian Crouzet (Savoie Mont-BlancUniversity, France), Daidu Fan (Tongji University China),Christine Franke (MINES ParisTech, France), Sophie Lebot(University of Rouen, France), Barbara Mauz (University ofLiverpool, UK), Steve Mitchell (University of Portsmouth,UK), Christophe Morhange (Aix-Marseille University,France), Cherith Moses (Univ. of Sussex, UK), AldoSottolichio (University of Bordeaux), and Wayne Stephen-son (University of Otago, New Zealand).We are grateful to Sylvie Bourquin, associate editor ofComptes rendus Geoscience, who offered us the opportunityto publish this thematic issue, and who helped us in thereviewing and editorial processes.ReferencesBain, O., Toullec, R., Combaud, A., Villemagne, G., Barrier, P., 2016. Fiveyears of beach drainage survey on a macrotidal beach (Quend-Plage,northern France). C. R. Geoscience 348, (this issue).Duperret, A., Raimbault, C., Le Gall, B., Authemayou, C., van Vliet-Lanoë, B.,Regard, V., Dromelet, E., Vandycke, S., 2016. High-resolution onshore–offshore morpho-bathymetric records of modern chalk and graniticshore platforms in NW France. C. R. Geoscience 348, (this issue).Furgerot, L., Mouazé, D., Tessier, B., Perez, L., Haquin, S., Weill, P., Crave, A.,2016. Sediment transport induced by tidal bores. An estimation fromsuspended matter measurements in the Sée River (Mont-Saint-Michel Bay, northwestern France). C. R. Geoscience 348, (this issue).Lesourd, S., Lesueur, P., Fisson, C., Dauvin, J.-C., 2016. Sediment evolutionin the mouth of the Seine estuary (France): A long-term monitoringduring the last 150 years. C. R. Geoscience 348, (this issue).Nizou, J., Demory, F., Dubrulle-Brunaud, C., 2016. Monitoring of dredged-dumped sediment dispersal off the Bay of the Seine (northern France)using environmental magnetism. C. R. Geoscience 348, (this issue).Van Vliet-Lanoë, B., Goslin, J., Hénaff, A., Hallégouët, B., Delacourt, C., LeCornec, E., Meurisse-Fort, M., 2016. Holocene formation and evolutionof coastal dunes ridges, Brittany (France). C. R. Geoscience 348, (thisissue).Pierre Weill*, Bernadette TessierMorphodynamique continentale et côtière, CNRS, Universitéde Caen Normandie, 24, rue des Tilleuls, 14000 Caen, France*Corresponding authorE-mail address: pierre.weill@unicaen.fr (P. Weill)Available online 1 June 2016

Five years of beach drainage survey on a macrotidal beach (Quend-Plage, northern France)

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Five years of beach drainage survey on a macrotidal beach (Quend-Plage, northern France)

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