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Coastal sediment dynamics: Introduction to the
thematic issue
Pierre Weill, Bernadette Tessier
To cite this version:
Pierre Weill, Bernadette Tessier.
Coastal sediment dynamics:
Introduction to the
the-matic issue.
Comptes Rendus Géoscience, Elsevier Masson, 2016, 348 (6), pp.409 - 410.
Foreword
Coastal
sediment
dynamics:
Introduction
to
the
thematic
issue
ThisthematicissueofComptesrendusGeosciencegives an overview of the works presented in the frame of a sessiondedicatedto‘‘Coastalsedimentdynamics’’atthe 14thCongressoftheFrenchAssociationof Sedimentolo-gists,heldinParis,France,from5to7November2013.In total,23paperswerepresentedinthissession,bothinthe formof oral communicationsand posters.Thisnational conferenceistraditionallyagatewayforPhDandMaster studentstosharetheirfirstresultsandsharpentheiroral skillsinfrontofanaudienceofspecialists.
Thediversityofpaperspresentedinthissessionreflects thenaturaldiversityoftheFrenchcoaststhatopenonthe EnglishChannel,theAtlanticOceanandtheMediterranean Sea, both in terms of morphology (sedimentary and igneousrockycoasts,sandybeachesandsubtidalprisms, bays and estuaries) and hydrodynamic processes(wave versustide-dominatedenvironments).
Themainscientificissuesaddressedinthe communi-cationsfocusedon:
understanding the evolution of constructional and erosionalcoastsatbothlong(Neogene toQuaternary) and short-terms (Holocene) through the stratigraphic architecture of sedimentary systems and remnant morphologyofrockyplatforms;
refiningourvisionofmoderncoastalsystemsintermsof sedimentary facies and heterogeneity, geomorphology andhydrodynamicprocesses,inordertobetterconstrain theinterpretationoffossilsystems;
quantifying sedimentary fluxes and relating hydrody-namic processes to morphodynamics of sedimentary bodies intide-dominated environments(estuaries and tidalchannels,subtidalplatforms);
learningfromnaturalhazards(tsunamis,tidalflooding andstorms)bystudyingtherecordofextremeeventsin thesedimentarchive,andanticipatingfutureevolutions in the scope of climate change and rising sea-level throughrefinednumericalmodelsofsedimenttransport andmorphodynamicevolution;
monitoring and anticipating the changes in sediment patterns and transport due to human activities
(sediment dredging, installation of marine renewable energyfacilities...).
The different studies presented gave an interesting outlookonthevarietyoftoolsdeployedbythecommunity of coastal sedimentologists, and raised a number of questionsonthesensitivity,calibrationandlimitsofuse ofthemeasurementsystems.Subtidalmorphologiesare generallyinvestigatedusingmulti-swathbathymetryand side-scansonar,sometimesonvesselsspeciallydesigned for shallowwater;intertidaland subtidal environments aresurveyedusingair-borneandterrestriallaserscanner, or by man-made surveys using differential GPS (beach profiles).Hydrodynamicsandsedimentfluxesare quanti-fiedusingoptic(OBS)andacoustic(ADV,ADCP)probes. While a very high-resolution seismic has proven its efficiencytoinvestigatethestratigraphyofsubtidalbodies and sediment infilling of bays and estuaries, ground-penetratingradarisbecomingincreasinglypopularinthe communitytocharacterizethearchitectureofdunesand beach ridges. Finally, original tools such as magnetic susceptibility and X-ray microtomography enrich the classicalpackageofsedimentologicallabanalyses.
Sixpaperswereselectedforthisthematicissue,which illustratethediversityofmethodsandobjectsembraced bythecommunityofsedimentologistsworkingoncoastal environments.
Sandybeachesaresubjecttoerosion,especiallyduring winter storms, and the French coasts are globally retreatingundertheactionofrisingsea-level.Duetothis loss of recreational areas and to the damages on infrastructureson theseaside, engineeringsolutions are sometimesrequired tofight against erosion. Bain etal. (2016) reporta 5-year monitoring of a sandy beachin northern France following the installation of a beach drainagesystem.Thissoftengineeringsolutionlowersthe beachwatertable,andreducestheerosivepotentialofthe backwash.Thesurveyrevealsalandwarddisplacementof thesedimentstockandastabilizationofthebeachprofile, althoughthesystemisvulnerabletodamagesbystrong winterstorms.
C.R.Geoscience348(2016)409–410
ContentslistsavailableatScienceDirect
Comptes
Rendus
Geoscience
w ww . sc i e nce d i re ct . co m
http://dx.doi.org/10.1016/j.crte.2016.05.001
Duperretetal.(2016)presentanewdatasetof high-resolutionshallow-waterbathymetrycoupledwithaerial lidartopography.Thedigitalelevationmodelsofland–sea transitionzonesofferauniqueopportunitytostudythe development of rocky shore platforms. A comparison betweenachalkycoastalong theEnglishChannelanda graniticcoastinBrittany highlightstheroleoflithology and of the tectonicheritage as control factors of shore platform development in response to past sea-level fluctuations.
Quantifyingsedimentfluxesisessentialtounderstand long-termevolution and infillingof estuaries. However, measuringsuspended sediment concentration in highly turbidandturbulentflowisnotstraightforward.Furgerot etal.(2016)addressthis issuebyperformingadetailed comparisonofsuspendedsedimentconcentrationvalues during the passage of a tidal bore using: (i) in-situ sampling,(ii)opticalback-scatter sensormeasurements. The quantification of the tidal bore hydrodynamics performed withADV and ADCPmeasurements,coupled withturbiditymeasurements,allowedthemtocalculate instantaneous vertical sediment concentration profiles duringthepassageofatidalbore,whichplaysasignificant roleinresuspendedsedimentsfromthechannelbed.
Lesourdetal.(2016)presentanewmapofsuperficial sedimentsinandaroundthemouthoftheSeineestuary, based on an interpolation of 561 grab samples. The comparison of these data with four other superficial sediment maps gives an overview of the sedimentary evolutionoftheSeineestuarysincethelate19thcentury. Theobservationsrevealanincreasingcontentofmuddy sedimentinthemouthoftheestuary.Althoughina mega-tidalcontext,theman-inducedalterationoftheestuaryby engineering works for navigation has transformed the estuaryfroma sandy tide-dominated environment toa muddyriver-dominatedsystem.
ThesiltingoftheSeineestuaryrequiresa continuous dredging of the channels to ensure a minimum water depth for navigation.The dredgedmaterial is generally dumpedonspecificsitesinthebayofSeine.Nizouetal. (2016) propose an original method to monitor the dispersal of the dredge material. Because terrigenous sediment contains a higher fraction of ferromagnetic mineralsthanmarinesedimentdoes,magnetic suscepti-bilityanalysisofgrabsamplesisanefficienttooltomap the dispersion of dredge-dumped sediment on the sea floor,incomplementtoclassicalgrainsizeanalysis.
VanVliet-Lanoe¨ etal.(2016)investigatethehistorical developmentofcoastaldunesinBrittany.Dunebuildingis conditionedbythesedimentbudget,whichincreasedin theLateHoloceneduetotheslowingdownofthemarine transgressionandthedevelopmentofagriculture,andto stormy conditions that are more favourable during dominantly negative NAO periods. However, modern
conditions of rising sea-level and sediment starvation mightweaken coastaldunesthatprotectlowlandsfrom marinesubmersion.
Acknowledgements
Wewishtothanktheauthorsfortheircontributions, andalltheparticipantsinthe‘‘Coastalsediment dynam-ics’’sessionduringtheconference.
We are indebtedto the numerous refereesfor their conscientious and constructive reviews of the manu-scripts: Re´mi Belon (BRGM, France), Benoıˆt Camenen (IRSTEA, France), Christian Crouzet (Savoie Mont-Blanc University,France), DaiduFan(Tongji UniversityChina), ChristineFranke(MINESParisTech,France),SophieLebot (UniversityofRouen,France),BarbaraMauz(Universityof Liverpool,UK),SteveMitchell(UniversityofPortsmouth, UK), Christophe Morhange (Aix-Marseille University, France), Cherith Moses (Univ. of Sussex, UK), Aldo Sottolichio(UniversityofBordeaux),andWayne Stephen-son(UniversityofOtago,NewZealand).
WearegratefultoSylvieBourquin,associateeditorof ComptesrendusGeoscience,whoofferedustheopportunity topublishthisthematicissue,andwhohelpedusinthe reviewingandeditorialprocesses.
References
Bain,O.,Toullec,R.,Combaud,A.,Villemagne,G.,Barrier,P.,2016.Five yearsofbeachdrainagesurveyonamacrotidalbeach(Quend-Plage, northernFrance).C.R.Geoscience348,(thisissue).
Duperret,A.,Raimbault,C.,LeGall,B.,Authemayou,C.,vanVliet-Lanoe¨,B., Regard,V.,Dromelet,E.,Vandycke,S.,2016.High-resolutiononshore– offshoremorpho-bathymetricrecordsofmodernchalkandgranitic shoreplatformsinNWFrance.C.R.Geoscience348,(thisissue).
Furgerot,L.,Mouaze´,D.,Tessier,B.,Perez,L.,Haquin,S.,Weill,P.,Crave,A., 2016.Sedimenttransportinducedbytidalbores.Anestimationfrom suspended matter measurements in the Se´e River (Mont-Saint-MichelBay,northwesternFrance).C.R.Geoscience348,(thisissue).
Lesourd,S.,Lesueur,P.,Fisson,C.,Dauvin,J.-C.,2016.Sedimentevolution inthemouthoftheSeineestuary(France):Along-termmonitoring duringthelast150years.C.R.Geoscience348,(thisissue).
Nizou,J.,Demory,F.,Dubrulle-Brunaud,C.,2016.Monitoringof dredged-dumpedsedimentdispersalofftheBayoftheSeine(northernFrance) usingenvironmentalmagnetism.C.R.Geoscience348,(thisissue).
VanVliet-Lanoe¨,B.,Goslin,J.,He´naff,A.,Halle´goue¨t,B.,Delacourt,C.,Le Cornec,E.,Meurisse-Fort,M.,2016.Holoceneformationandevolution ofcoastaldunesridges,Brittany(France).C.R.Geoscience348,(this issue).
PierreWeill*,BernadetteTessier
Morphodynamiquecontinentaleetcoˆtie`re,CNRS,Universite´ deCaenNormandie,24,ruedesTilleuls,14000Caen,France
*Correspondingauthor
E-mailaddress:[email protected](P.Weill)
Availableonline1June2016
Foreword/C.R.Geoscience348(2016)409–410 410