Papers by Marie-Hélène Ruz
Une démarche participative Trois ans d'échanges Une enquête par questionnaire Un sondage en ligne... more Une démarche participative Trois ans d'échanges Une enquête par questionnaire Un sondage en ligne 13 14 16 20 DES HABITANTS ATTACHÉS À LEUR TERRITOIRE 32-39 pages Un territoire "attachant" Un territoire de loisirs Les usages passés présents et futurs 34 34 37 UN PARTAGE DE CONNAISSANCES 22-31 pages Recueil d'une documentation mémorielle Production et diffusion de cartes de l'évolution du littoral à différentes échelles de temps Mise en place d'une action collaborative : le suivi du trait de côte Un outil de communication : le site Web 24 26 29 31 DES HABITANTS CONSCIENTS DES RISQUES 40-45 pages Des risques bien localisés par les habitants Dont les causes sont bien identifiées Une bonne information sur les risques littoraux 43 44 45
Science of The Total Environment, 2021
This study examines the role of sediment supply in controlling the formation and the spatial patt... more This study examines the role of sediment supply in controlling the formation and the spatial patterns of nebkha, numbers and sizes, present in foredunes fronting coastal dunefields of the arid northwest African and the Canary Islands coasts. Sediment supply is estimated qualitatively and quantitatively by various measures, and the number and size of nebkhas are obtained on a range of beach-dune systems. In the case of the Canary Islands, LiDAR data and orthophotos with high spatial resolution (0.25 m) are used to measure sediment supply/activity, nebkha numbers and sizes, and vegetation variables, whereas data availability is less on the African coast. Results show that sediment supply exerts a major control on nebkha development such that as sediment supply increases, the number of coastal nebkha decreases, and the size of individual plants/nebkha increases. Once sediment supply is large, nebkha can only form on the immediate backshore if space is available, and a point is reached when the sediment supply is so large that nebkha do not, or cannot form. The data presented here provide two indicators which could be applicable to other dune systems. Firstly, by estimating the number of nebkha and the vegetation cover, the degree of aeolian sedimentary activity or sediment supply might be estimated. Secondly, the type of aeolian landform present provides a qualitative indication of sediment supply and aeolian activity.
Journal of Coastal Research, 2019
ABSTRACT Héquette, A.; Ruz, M.H.; Zemmour, A.; Marin, D.; Cartier, A., and Sipka, V., 2019. Along... more ABSTRACT Héquette, A.; Ruz, M.H.; Zemmour, A.; Marin, D.; Cartier, A., and Sipka, V., 2019. Alongshore Variability in Coastal Dune Erosion and Post-Storm Recovery, Northern Coast of France. In: Castelle, B. and Chaumillon, E. (eds.), Coastal Evolution under Climate Change along the Tropical Overseas and Temperate Metropolitan France. Journal of Coastal Research, Special Issue No. 88, pp. 25–45. Coconut Creek (Florida), ISSN 0749-0208. As along many parts of the world's shoreline, the coastal dunes extending along the macrotidal coast of northern France represent important defenses against marine flooding. The impacts of storms on the upper beach and foredunes and their post-storm recovery were analyzed using nearly 10 years of offshore wave measurements, water level records, wind measurements, and in situ and airborne LiDAR topographic surveys of the beach and foredunes. Our results show that coastal dunes located at a relatively short distance apart along a coastal stretch with the same wave exposure can have significantly different responses to storms. Not only the impacts of storm events were greater on some dunes, but post-storm recovery also varied from one foredune to another. A strong alongshore variability in dune erosion and recovery was observed with a positive eastward gradient in dune volume change, probably related to longshore and onshore-directed sediment supply. Our measurements revealed that even where the foredune underwent significant erosion during the first years of the survey period, progressive full dune recovery took place through the development of a sand ramp at the dune toe that favored landward sediment transport from the upper beach to the foredune. This period was followed by an unusual series of closely spaced storms during fall-winter 2013-2014 that had major impacts on the coasts of Western Europe. Several of these storms were responsible for extreme water levels, which resulted in significant retreat of the dune front and massive volume loss in places. Our analyses show that the maximum water levels reached during storms represent a major factor explaining dune erosion compared to wave energy that is of secondary importance along this macrotidal coast. Our results also suggest that dune volume change during storms and subsequent recovery were largely controlled by the initial dune and upper beach morphology. A strong correspondence was found between dune front volume change and initial upper beach width and with dune toe elevation, but a somewhat weaker relationship was observed between dune volume change and initial dune height.
Physical Geography, 1994
Many studies have been carried out on coastal dunes of mid-latitude regions, but little is known ... more Many studies have been carried out on coastal dunes of mid-latitude regions, but little is known about cold-climate coastal dunes. Coastal dunes that have developed in arctic and subarctic environments usually are described as minor aeolian accumulation features, but they occur widely along arctic and subarctic coastlines. In the Arctic, aeolian deflation is a common phenomenon and coastal dunes are less developed than in subarctic environments. Short open-water duration, coarse beach sediment, and sparse vegetation cover are factors explaining the limited coastal dune development of arctic regions. In subarctic settings, niveo-aeolian sedimentation is a major process contributing to coastal dune development. Quantitative and qualitative studies still are needed for a better understanding of the mechanisms of coastal-dune development in cold-climate environments. [Key words: coastal dunes, arctic, subarctic, coastal geomorphology].
Journal of Coastal Conservation, 2017
The largest beach replenishment project ever in France was completed in February 2014 in Dunkirk ... more 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 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.
Http Www Theses Fr, 1986
Cette these presente les resultats de recherches geomorphologiques menees sur les littoraux meubl... more Cette these presente les resultats de recherches geomorphologiques menees sur les littoraux meubles du sud-est de l'Irlande. La cote sud-est de l'Irlande possede une cote basse caracterisee par la diversite des constructions meubles littorales qui barrent des lagunes. On y trouve des cordons dunifies a cretes individualisees de type darss, des pouliers dont la progression a entrave l'ecoulement vers la mer de petits fleuves cotiers, des pointes sableuses progressent en vis a vis et s'avancent a l'embouchure d'un estuaire, des cordons de barrage isolent des lagunes. Un suivi pluri-annuel de profils de plages a mis en evidence une evolution saisonniere classique des estrans: demaigrissement apres la periode hivernale et engraissement pendant l'ete. Chaque accumulation evolue actuellement en fonction des reserves sedimentaires disponibles, qui sont tres limitees, et de la derive littorale majeure induite par les houles efficaces. Chaque plage constitue un compartiment sedimentaire independant. Depuis 1840, la comparaison du trait de cote figure sur les cartes anciennes avec la ligne de rivage actuelle a revele une tendance generale au recul des plages. Ce travail montre que cette crise erosive est en grande partie a relier aux amenagements dont ont fait l'objet ces littoraux meubles depuis plus d'un siecle.
This present study aims at assess the effects of fair-weather conditions and storms on the morpho... more This present study aims at assess the effects of fair-weather conditions and storms on the morphodynamic evolution of a low-lying, macrotidal and fetch limited, unconsolidated coast. At short-term and event scale, our results revealed very different morphological responses of two study areas, even located 4 km away, showing distinct morphologies and contrasting behaviors in response to fair-weather conditions and, above all, to storm events, at short-term (some hours, days to weeks) as longer time-scale (up to pluriannual). Under fair-weather and storm conditions, X-BEACH computations accurately predicted respectively the null but realistic simulated morphological response (both sites A and B) and the erosion that commonly occurs only at one site (A, but null at site B). A contrasting response that results from different hydrodynamic conditions at each site depending above all on various topographic and bathymetric parameters (nearshore, beach, foredune).
Cette synthèse de travaux récents menés par des équipes de recherche en collaboration avec des in... more Cette synthèse de travaux récents menés par des équipes de recherche en collaboration avec des institutions locales, repose sur deux approches comparables, l'une focalisée sur l'agglomération du Havre à l'embouchure de la Seine, l'autre sur l'agglomération de Dunkerque dans la plaine maritime flamande. Ces différents travaux, ciblés sur l'analyse et la compréhension du risque de submersion marine, sont basés sur la connaissance historique des processus conduisant à la submersion, la reconstitution des niveaux marins et des évènements extrêmes récents. Ces deux territoires à enjeux ont en commun une forte densité de population, la présence de biens, d'activités et d'infrastructures (administratives, touristiques, portuaires, industrielles), et d'aménagements côtiers. En Mer du Nord méridionale, la majorité de la plaine maritime flamande est constituée de zones basses urbanisées, en grande partie sous le niveau moyen des pleines mers. Ceci est parti...
Marine Geology, 1992
... Our observations provide the basis of a semi-quantitative model of shoreline changes for the ... more ... Our observations provide the basis of a semi-quantitative model of shoreline changes for the barrier coast of the Canadian Beaufort Sea which relates coastal stability to bluff erosion, ground-ice content, sediment texture, offshore sediment supply, wave energy, volume of ...
The Proceedings of the Coastal Sediments 2011, 2011
ABSTRACT Along the southwestern coast of the North Sea a large proportion of the Flemish coastal ... more ABSTRACT Along the southwestern coast of the North Sea a large proportion of the Flemish coastal plain consists of densely populated reclaimed land, much of which lying below mean sea level. This sandy coast is exposed to fetch-limited, relatively low-energy waves punctuated by storm activity and experiences tidal range of 5.6 m at spring tides. A number of recent studies suggested medium term (10 years) gross stability of the beach-dune system. This stability was related to moderate wind regime and efficient dune management practices. In March 2007, a storm event resulted in major foredune retreat. This episodic erosive event was induced by moderate direct onshore winds blowing during more than 48 hours associated with a spring tide. Our results show that along this macrotidal coast, erosive events are not necessarily associated with strong winds. Wind direction and duration combined with a spring tide appear to hold the key to understanding the relative importance of processes controlling medium term foredune evolution.
XIIèmes Journées, Cherbourg, 2012
La digue du Braek est un ouvrage de défense contre la mer du port de Dunkerque. Cette digue en en... more La digue du Braek est un ouvrage de défense contre la mer du port de Dunkerque. Cette digue en enrobé bitumineux de 6 km de long borde une plage macrotidale orientée OSO-ENE. Le transport éolien a été évalué le long d'un profil transversal allant du haut de plage au sommet de la digue à l'aide de pièges à sédiment, pour des conditions de vent obliques. Les vitesses de vent associées ont été déterminées grâce à des anémomètres à coupelles placés à différentes hauteurs sur des mâts. Les résultats montrent une accélération du vent sur le versant de la digue exposé, similaire à l'effet de rampe observé sur les versants dunaires, ainsi que des quantités de sable piégé supérieures sur l'asphalte que sur le sable. Mots-clés : Transport éolien-Mesures in situ-Digue en enrobé
Géomorphologie : relief, processus, environnement, 2002
... Catherine Meur-Férec et Marie-Hélène Ruz. ... pièges verticaux de type Leatherman modifié (d&... more ... Catherine Meur-Férec et Marie-Hélène Ruz. ... pièges verticaux de type Leatherman modifié (d'après Goldsmith et al, 1988) qui captent le sable jusqu'à 46 cm de hauteur et des pièges horizontaux de type Owens (1927) qui ne piègent les sédiments que jusqu'à 17 cm du sol (fig. ...
An objective method is used to evaluate the sensitivity of Canadian coasts to a rise in sea level... more An objective method is used to evaluate the sensitivity of Canadian coasts to a rise in sea level of 0.65 m by the end of next century. Based on the assumption that the intensity of impact is related to seven quantifiable variables - relief, geology, coastal landform, coastal retreat rate, sea-level trend, wave energy, and tidal range - a dimensionless index is determined for each of 2899 NTS map sheets (1:50 000 scale) that include parts of Canada's coast. Scores range from 0.8 to 57, with a mean of 5.1, and a strong mode between 2 and 4. Areas of low sensitivity (scores below 5) constitute 67% of the total, of moderate sensitivity (scores of 5 - 15) make up 30%, and of high sensitivity, only 3%. No large areas are susceptible to catastrophic inundation by the sea but any sea-level rise would cause an increase in the rates of change. The most sensitive region includes much of the coasts of Nova Scotia, Prince Edward Island, and New Brunswick. The major impacts would be higher r...
Coastal Engineering Proceedings, 2012
The shoreline of Dunkirk Seaport partly consists of a macrotidal beach oriented WSW-ENE backed by... more The shoreline of Dunkirk Seaport partly consists of a macrotidal beach oriented WSW-ENE backed by a 6 km long coated dike called “digue du Braek”. Aeolian sand transport was estimated on asphalt by means of sand traps. Also, time-averaged wind speed profiles were measured using cup anemometers under various wind velocities and directions along a transversal profile on the dike and the upper beach. High rates of sand transport enabled the setup of different kinds of experimental windbreaks on asphalt, in order to test potential dune formation on this kind of substrate. Under oblique onshore winds, it was regularly observed that amounts of sand captured in the traps placed on the dike were more important than those in traps placed on the upper beach. These results were related to sand sources: windblown sand captured on the dike originated from the coastal dunes developed at the dike toe, while sand trapped on the upper beach came from the tidal zone were aeolian transport is limited ...
Annales de Géographie, 1998
La cote est de la baie d'Hudson (Canada) est caracterisee par un relevement glacio-isostatiqu... more La cote est de la baie d'Hudson (Canada) est caracterisee par un relevement glacio-isostatique postglaciaire de l'ordre de 1 m/siecle. Situe a 15 km de l'embouchure de la grande riviere de la Baleine, le detroit de Manitounuk est un des rares secteurs cotiers abrites le long de la cote orientale de la baie d'Hudson. Une etude de l'evolution recente des estrans de sediments fins situes le long de la rive continentale du detroit a revele de nombreux secteurs en erosion. Dans certaines baies une micro-falaise limitant la partie superieure des estrans est en effet en voie de recul a un rythme moyen de 1 m/an et ce, depuis pres d'un demi-siecle. Une telle erosion le long d'un littoral en emersion est d'autant plus surprenante que ce secteur cotier est tres abrite. Plusieurs facteurs ont ete analyses afin d'expliquer cette erosion. Cette etude montre que le recul du rivage est le resultat de plusieurs phenomenes. Le processus initial est le gel-degel saisonnier des sediments fins de la basse terrasse auquel viennent se greffer des processus azonaux comme les vagues et les crues de tempete. Les changements climatiques survenus au debut du siecle contribuent aussi a l'evolution littorale le long de cette cote subarctique.
Sedimentology, 1995
A study of sedimentary structures of cold-climate coastal dunes along Eastern Hudson Bay, Canada,... more A study of sedimentary structures of cold-climate coastal dunes along Eastern Hudson Bay, Canada, showed that in areas of very sparsely vegetated surfaces, tractional sedimentary processes are dominant while in partly and well vegetated areas, grainfall deposition is the dominant sedimentary process. Alternating fine and coarse sand strata are characteristic of the vegetated foredune ridge. Coarse strata are interpreted to be mainly related to niveo-aeolian deposition. In poorly vegetated areas deformed strata associated with the melting of snow were preserved. A vaguely stratified strata interpreted as a dimpled surface as well as coarse lenses with irregular basal contact were found. Such distinctive sedimentary structures may represent good indicators of cold-climate conditions and could serve as criteria to identify aeolianites that may have been deposited in similar cold-climate environments in palaeoenvironmental reconstructions.
Permafrost and Periglacial Processes, 1993
The landscape of the Tuktoyaktuk Peninsula coastal plain, Northwest Territories, has been strongl... more The landscape of the Tuktoyaktuk Peninsula coastal plain, Northwest Territories, has been strongly affected by thermokarst processes. Along thermokarst lakes developed in glaciofluvial sands lake-shore dunes are common. Their formation seems related to complete or partial lake drainage. During the Holocene the rise of relative sea level has induced the submergence of the coastal plain that extended offshore of the present-day coastal lowlands, Today coastal retreat rates in excess of 1 m/yr result in thermokarst lakes breaching and landward migration of spits and barrier-islands. A unique type of coastal dune has been observed along two coastal sections. Late Holocene lake-shore dunes are eroded alongshore and capped by modern coastal dunes. These coastal dunes developed in a thermokarst environment are indicators of lake drainage probably induced by late Holocene sea level rise. RESUME La Peninsule de Tuktoyaktuk, Territoires du Nord Ouest, a CtC grandement affectke par des processus thermokarstiques. Le long des rives des lacs de thermokarst qui se sont formes dans des sables fluvioglaciaires, il est frequent d'observer des dunes de bord de lac. Leur formation semble Ctre en relation avec le drainage partiel ou complet des lacs. Pendant l'Holoc&ne, la hausse du niveau relatif de la mer a provoque la submergence de la plaine cbtiere qui s'etendait en avant de la plaine c6tikre actuelle. Actuellement, la c6te recule a une vitesse de plus de 1 m/an, ce qui induit I'ouverture des lacs de thermokarst qui sont transformis en lagunes ainsi que la migration vers la terre des flirches sableuses et des Iles-barrieres. Un type unique de dunes c6tieres a ktC observe le long de la c6te. I1 s'agit d'anciennes dunes de bord de lac, formees a la fin de I'Holocirne, qui se retrouvent en position littorale du fait de I'erosion marine et qui sont sumontees par des dunes cbtikres actuelles. Ce nouveau type de dunes cbtikres est un bon indicateur du drainage des lacs de thermokarst qui, le long de la c6te est vraisemblablement lie a la hausse du niveau relatif de la mer.
Uploads
Papers by Marie-Hélène Ruz