Impact de l'élévation du niveau marin sur l'évolution future d'un cordon littoral lagunaire : une méthode d'évaluation.: Exemple des étangs de Vic et de Pierre-Blanche (littoral méditerranéen, France)

International audienceAssuming a 22 cm sea level rise by 2050, a map was elaborated, which shows the expected changes which probably will affect the barrier-lagoon system in the Vic and Pierre-Blanche area. The research was supported by the French Conservatoire du littoral and the Procter and Gamble Foundation. According to the linear regression method and using aerial photographs dating back to 1937, the shoreline position in 2050 was predicted. The barrier surface loss due to a 22 cm elevation of the lagoon water level was calculated using a SIG software and accurate topographic data supplied by a GPS survey with sub-centimetric precision. As a result, it is forecasted -within the limits inherent to the methods which were used- that a landward migration of the shoreline over a distance up to 70 m will occur by 2050 as well as a loss of the barrier surface of about 15,76 hectares. Such an evolution which started several centuries ago is likely to be enhanced by the expected sea level rise. The present continuous barrier probably would be transformed in a string of islands through inlet opening.Une cartographie prévisionnelle de l'évolution du système cordon littoral – lagune de Vic et de Pierre Blanche a été réalisée dans la cadre d'un programme lancé par le Conservatoire du Littoral. Elle a reposé sur un scénario d'élévation du niveau marin de + 22 cm d'ici 2050. L'originalité de la démarche employée tient dans l'association de deux types d'approche. D'une part, sur la face externe du lido, la position future de la ligne de rivage a été extrapolée par régression linéaire à partir des données d'évolution historique du trait de côte depuis 1937, obtenues par photo-interprétation . D'autre part, sur la face interne du lido, les pertes en surfaces qu'entraînerait une simple élévation statique du plan d'eau lagunaire de 22 cm ont été simulées au moyen d'un logiciel de S.I.G, à partir de levés topographiques de précision infra-centimétrique réalisés au GPS différentiel. En dépit des incertitudes inhérentes à toute démarche de ce type, il ressort de notre étude que le lido subirait très probablement des pertes en surface non négligeables (estimées à 15,76 ha) sur sa face interne et que, parallèlement, il reculerait en roulant sur lui-même de plusieurs dizaines de mètres (jusqu'à 70 m dans sa partie centrale). Il poursuivrait en cela une évolution entamée depuis plusieurs siècles, et observée aux USA sur des littoraux similaires dans un contexte d'élévation rapide du niveau de la mer. En outre, il risquerait d'être de plus en plus souvent morcelé par l'ouverture de brèches lors des tempêtes et de se transformer à terme en îles-barrières, séparées par des graus permanents reliant la mer aux étangs situés en arrière

Modélisation et observation de submersion de dunes en Languedoc-Roussillon

The « coastal squeeze », which basically results in less beach area and more concrete, fortunately does not yet concern the entire Mediterranean coast. It is thus important, while there are still coastal barrier islands, to study and understand the overwash phenomenon, in order to help anticipate the hydrodynamic and sedimentary processes that drive the responses of dunes to important meteorological events. This article first defines and describes the overwash processes that affect coastal dune behaviour, and then presents the analysis carried out by the EID Méditerranée on the beach of Villeneuve les Maguelone, located between Sète and Montpellier in the region of Languedoc Roussillon, France. This analysis allowed us to construct a schema of the responses of the barrier island of Villeneuve les Maguelonne to the meteorological conditions present during the storms of December 3rd and 4th, 2003 and February 21st, 2004. A hydrodynamic model that integrates the radiation stresses (Berkhoff equations) into the Saint-Venant equations was then attempted with the help of the ARTEMIS and TELEMAC calculation codes, in order to characterize the hydrodynamic properties of the system. Finally, a critique of the results is offered and suggestions for improvement are proposed

La Camargue, terre d’enjeux, première étape d’une gestion intégrée des zones côtières

Au 19ème siècle, l’expression "territoire du vide" s’appliquait fort bien à la terre de Camargue ; au 20ème siècle celle de "littoral d’empoigne" la remplace aisément. L’objectif est de concilier sur ce territoire la conservation de la nature, des paysages et des traditions avec les activités touristiques. Il est donc indispensable d’éviter sur ce site emblématique la compression côtière qui aboutit à moins de plage et plus de béton. Dans cette optique, nous verrons comment des principes stratégiques de gestion de la bande côtière ont été définis à la demande du Parc Naturel Régional de Camargue. La démarche originale est fondée sur la gouvernance : tous les acteurs locaux identifiés ont été rencontrés lors d’entretiens bilatéraux. La synthèse de ces entretiens a permis d’établir une liste de grands principes stratégiques, discutés, amendés et validés par l’ensemble de ces mêmes acteurs locaux regroupés au sein d’un comité de pilotage. Toutes les étapes de la genèse de ce processus sont développées, critiquées et analysées.In the 19th century, the expression “empty land ” applied extremely well to Camargue land ; in the 20th century that of “littoral of seizure” (territoire d’empoigne)” replaced it easily. The objective is to reconcile on this land, in integrated coastal zone management reasoning, the conservation of nature, landscape and traditions with tourism activities. It is thus absolutely necessary to prevent a "Coastal squeeze" on this emblematic land which would lead to less beach and more sprawl of concrete (groynes, hard rocks to hold the line). In this perspective, we will see how strategic principles of the coastal management were defined at the request of the Camargue Regional Natural Park. The original reasoning is founded on the governorship: all the identified local actors have been met during bilateral interviews. The synthesis of these interviews made it possible to draw up a list of strategic principles, discussed, amended and validated by the totality of the local actors gathered within a steering committee. All this process genesis stages are developed, examined and analyzed

Une approche alternative de la gestion des risques côtiers, l’exemple de la petite Camargue

The « petite Camargue » coast is located between the Espiguette sandy spit -Port Camargue- on the west, and the -Rhône vif- on the East. It is a strip of 11 km of sandy beaches, a real mosaic of meadows (Sand dunes with Juniperus phoenica, Mediterranean salt steppes ...).However, on this listed site, the part of artificialized coastal areas has increased from 0% in 1960 to almost 50% in 1990 (46 groynes have been erected, each spaced 100 m, on the oriental coast), this was a decision guided by the proximity of Le Grau du Roi town and flood risks.As a matter of fact these structures are expensive to upkeep as well as ineffective in the “Petite Camargue” context and this leads us to question the relevance of their maintenance. This questioning stems from policies of integrated coastal zone management, and adaptive coastal protection (strategic retreats or making space for water).This process is implemented at territorial level and is meant to leave a proper place for alternative solutions

Evaluating the impacts of sea level rise on coastal wetlands in Languedoc-Roussillon, France

Sea-level rise due to climate change creates new risks of submersion in coastal areas that must be taken into account. Although these are long-term risks for 2100, it is important to anticipate possible consequences in order to identify the most vulnerable areas or issues and develop the appropriate adaptation policies. The aim of this paper is to examine the consequences of such sea-level rise for wetlands in the Languedoc-Roussillon region (France) which is particularly at risk of submersion. The analysis is based on the worst case scenario of a one meter sea level rise by 2100, with a variety of adaptive strategies: denial, laissez-faire and strategic retreat of infrastructure and buildings. This latter strategy assumes that the retreat wetlands is unconstrained. The evaluation examines the losses and transformations of ecological habitats, depending on their distance from salt water. Estimating damages and benefits requires first, to study the evolution of the services supplied by different habitats and second, to estimate the value of the economic impact. This approach demonstrates the superiority of a strategic retreat policy which would halve the damages resulting from submersion.</p

Evaluating the impacts of sea level rise on coastal wetlands in Languedoc-Roussillon, France

Sea-level rise due to climate change creates new risks of submersion in coastal areas that must be taken into account. Although these are long-term risks for 2100, it is important to anticipate possible consequences in order to identify the most vulnerable areas or issues and develop the appropriate adaptation policies. The aim of this paper is to examine the consequences of such sea-level rise for wetlands in the Languedoc-Roussillon region (France) which is particularly at risk of submersion. The analysis is based on the worst case scenario of a one meter sea level rise by 2100, with a variety of adaptive strategies: denial, laissez-faire and strategic retreat of infrastructure and buildings. This latter strategy assumes that the retreat wetlands is unconstrained. The evaluation examines the losses and transformations of ecological habitats, depending on their distance from salt water. Estimating damages and benefits requires first, to study the evolution of the services supplied by different habitats and second, to estimate the value of the economic impact. This approach demonstrates the superiority of a strategic retreat policy which would halve the damages resulting from submersion.</p

Vers des stratégies de gestion de l'érosion des côtes : l'évaluation de la vulnérabilité comme outil d'aide à la gestion des risques.

National audienc

SUBDUNE tool: quasi-explicit formulation of the water level along the shoreline

SUBDUNE v0.6 is a very preliminary version of an exploratory model designed tocompute the sea level to the shoreline, combining the effects of various physics, from run-up to tides. It aims at providing an easy-to-use and quick way to estimate water elevation to the beach, assuming morphology is known. Combined with accurate beachdata, such as LIDAR, this engineering tool may provide with end-users an efficient way to quantify submersion