Stages of sedimentary infilling in a hypertidal bay using a combination of sedimentological, morphological and dynamic criteria (Bay of Somme, France) Charlotte Michel, Sophie Le Bot, Flavie Druine, Stéphane Costa, Franck Levoy, Carole Dubrulle-Brunaud, Robert Lafite To cite this version: Charlotte Michel, Sophie Le Bot, Flavie Druine, Stéphane Costa, Franck Levoy, et al.. Stages of sedimentary infilling in a hypertidal bay using a combination of sedimentological, morphological and dynamic criteria (Bay of Somme, France). Journal of Maps, Taylor & Francis, 2017, 13 (2), pp.858-865. 10.1080/17445647.2017.1389663. hal-02119165 HAL Id: hal-02119165 https://hal.archives-ouvertes.fr/hal-02119165 Submitted on 3 May 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Journal of Maps ISSN: (Print) 1744-5647 (Online) Journal homepage: http://www.tandfonline.com/loi/tjom20 Stages of sedimentary infilling in a hypertidal bay using a combination of sedimentological, morphological and dynamic criteria (Bay of Somme, France) Charlotte Michel, Sophie Le Bot, Flavie Druine, Stéphane Costa, Franck Levoy, Carole Dubrulle-Brunaud & Robert Lafite To cite this article: Charlotte Michel, Sophie Le Bot, Flavie Druine, Stéphane Costa, Franck Levoy, Carole Dubrulle-Brunaud & Robert Lafite (2017) Stages of sedimentary infilling in a hypertidal bay using a combination of sedimentological, morphological and dynamic criteria (Bay of Somme, France), Journal of Maps, 13:2, 858-865, DOI: 10.1080/17445647.2017.1389663 To link to this article: http://dx.doi.org/10.1080/17445647.2017.1389663 © 2017 The Author(s). Published by Informa View supplementary material UK Limited, trading as Taylor & Francis Group on behalf of Journal of Maps Published online: 26 Oct 2017. Submit your article to this journal Article views: 24 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tjom20 Download by: [Rouen University] Date: 06 November 2017, At: 04:01 JOURNAL OF MAPS, 2017 VOL. 13, NO. 2, 858–865 https://doi.org/10.1080/17445647.2017.1389663 SCIENCE Stages of sedimentary infilling in a hypertidal bay using a combination of sedimentological, morphological and dynamic criteria (Bay of Somme, France) Charlotte Michela, Sophie Le Bot a, Flavie Druinea, Stéphane Costa b, Franck Levoyc, Carole Dubrulle- Brunaud c and Robert Lafite a aNormandie University, UNIROUEN, UNICAEN, CNRS, M2C, 76000 Rouen, France; bNormandie University, UNICAEN, CNRS, LETG, 14000 Caen, France; cNormandie University, UNICAEN, UNIROUEN, CNRS, M2C, 14000 Caen, France ABSTRACT ARTICLE HISTORY In the context of rising sea level, many estuaries and bays show an overall trend to sedimentary Received 10 January 2017 infilling. Among these coastal environments, the Bay of Somme is a hypertidal tide and wave- Accepted 4 October 2017 dominated estuary, filled in by marine sands, with a superficy of 70 km2. This study proposes a KEYWORDS spatial zonation of the intertidal area of the bay based on the combination of information on Sedimentary infilling; sediments, seabed morphology and dynamics. Data come from a surficial sediment sampling – sediment dynamics; campaign and six airborne LiDAR topographic surveys, acquired over the period 2011 2013, sediment grain-size; providing information on grain size, carbonate content, bedform occurrence and seabed hydraulic dunes; hypertidal dynamics. The Main Map shows the morpho-sedimentary and -dynamic zonation used as a estuary; intertidal; LiDAR; basis to describe infilling stages in the bay. Bay of Somme 1. Introduction Littoral Picard, 2011), is located on the French coast Currently, many estuaries and bays are being filled with of the Eastern English Channel. It is the biggest estuar- sediment since the Holocene transgression (Anthony, ine bay of Picardy (70 km²), with a mixed energy 2002; Davis & Fitzgerald, 2004; Dyer, 1986; Gibbard regime, influenced by both tides and waves: the tide & Lautridou, 2003; Green & MacDonald, 2001; Harris, has a hypertidal range (8.5 m in mean spring con- 1988; Jago, 1980; Moore, Wolf, Souza, & Flint, 2009; ditions, up to 10.55 m in case of exceptional tides) Nichols & Biggs, 1985; Paphitis, Bastos, Evans, & and prevailing waves are of west provenance (75% of Collins, 2010; Psuty & Silveira, 2009; Tessier, Billeaud, the time) with mean significant wave height and period Sorrel, Delsinne, & Lesueur, 2012). The characteriz- around 2 m and 7 s, respectively, along the littoral of ation of the degrees of sedimentary infilling and the Cayeux-sur-Mer. These weather-marine forcings con- quantification of its rates constitute an important trol the infilling of the bay by marine sands (Dupont, information in order: (i) to better understand past evol- 1981), derived from the sedimentary prism of Picardy ution of estuaries, and (ii) to forecast future landscape, (Ferret, Le Bot, Tessier, Garlan, & Lafite, 2010), and habitat and usage modifications for an adapted by an important endemic bioclastic production management. (Desprez, Olivesi, Duhamel, Loquet, & Rybarczyk, Downloaded by [Rouen University] at 04:01 06 November 2017 Sea-level rise rate, bedrock morphology, sediment 1998). A sand bulge occupies the bay, which is fully supply and sediment transport rate are the main con- located in the intertidal domain. The seabed of the trolling factors of the general infilling pattern of estu- Bay of Somme is characterized by: (1) a uniform and aries and bays (Tessier et al., 2012). According to relatively flat beach (almost devoid of bedforms) con- Harris (1988), bedforms (e.g. sandbanks, hydraulic necting the Pointe de St-Quentin to the Crotoy; (2) dunes, tidal flats) can constitute a source of infor- tidal channels; (3) sand banks; (4) sedimentary bars mation on the stages of sedimentary infilling of bays systems and (5) more than 4200 hydraulic dunes and on the directions of sediment transport. Estuary arranged in fields and usually covered with ripples evolution is mainly driven by bedform evolution, (Michel, 2016). Two rivers flow into the bay: the which is strongly controlled by sediment dynamics Somme river (mean flow rate of 32 m3/s) to the east on the estuarine bed, itself dependent on sediment of the bay, channeled from Abbeville to Saint-Valery- characteristics (Boyd, Dalrymple, & Zaitlin, 1992; sur-Somme, and the Maye river (mean flow rate of Green & MacDonald, 2001; Jarvis & Riley, 1987). 1.5 m3/s) leading to the north of the bay. They bring − The Bay of Somme, ranked 10th ‘Grand Site de low amounts of fine particles (67 800 T year 1 from France®’ (Syndicat Mixte Baie de Somme Grand the Somme river; Loquet, Rybarczyk, & Elkaim, CONTACT Sophie Le Bot [email protected] Normandie University, UNIROUEN, UNICAEN, CNRS, M2C, 76000 - Rouen, France © 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of Journal of Maps This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. JOURNAL OF MAPS 859 2000), which deposit on salt marshes (altitude beyond altimeter system IGN69. They cover the intertidal area + 4 m NGF-IGN69). with a vertical accuracy of ±0.15 m for the February– In this study, an interpretative map of the morpho- March 2011 data and ±0.08 m for the other surveys sedimentary and -dynamic characteristics of the Bay of (28 September 2011 to 11 April 2013), except in Somme is proposed, based on the combination of data water areas in which the LiDAR signal does not pene- on seabed dynamics and bedform occurrence, obtained trate (e.g. bottom of tidal channels, hunting ponds in from airborne LiDAR topographic surveys, and refined salt marshes, lowest areas of the intertidal zone, subti- with sedimentary data (grain-size parameters, carbon- dal areas). These topographic LiDAR data have been ate content) derived from surficial sediment sampling used to perform the mapping of the morphology and (Main Map). On the basis of these sedimentological, the dynamics of the bay. morphological and dynamic criteria, the definition of sectors with homogeneous morpho-sedimentary and 2.2. Cartography and computer graphics -dynamic characteristics allows to propose a zonation of the Bay of Somme, which can be then used as a Maps were realized from the sediment and topographic spatial framework to describe the different infilling data by means of ArcGIS10 (© ESRI) and Adobe® Illus- stages in the bay. trator® CS6 Tryout (© Adobe Systems Inc.) softwares. The sedimentary facies map (Figure 1), established according to the classification of Folk (1965), was 2. Methods built as a shapefile of polygons drawn by hand. All other sedimentary maps (mean grain size on Main 2.1. Data Map; mud and fine sand contents, sorting, CaCO3 A total of 246 surficial sediment samples were realized content on Figure 1) correspond to rasters created on the sandy seabed of the bay, between 13 February using kriging interpolation proposed in ArcGIS10 2013 and 22 August 2013, at a mean sampling interval (© ESRI), with a resolution of 1 m. On the Sediment of 500 m. Most of the areas were reached by foot and Map (Main map), sedimentary zones were delimitated samples were collected by hand in the first 4 cm. For on the basis of the distribution of mean grain size, the water areas (tidal channels, the western border of which is a synthetic sediment parameter, and content the intertidal domain), samples were collected with in fine sands, which is the most represented sedimen- an Ekman grab from a zodiac.