Convergence de faciés et pléoenvironnements dans les bassins sédimentaires du Permien supérieur de l'Argentera -Barrot et de Provence orientale

Mémoire HS n° 13 - Géologie Alpine : Le détritisme dans le Sud-Est de la France - Colloque Association des Géologues du Sud-est - Grenoble 11-12 décembre 1986Les series permiennes du Sud Est de la France présentent une forte convergence de faciès lithologiques, associée à une convergence des processus de mise en place. La série stratigraphique du Barrot est choisie pour décrire les trois faciès principaux que l'on observe dans le Permien: faciès silto-argileux des formations du Cians et de la Roudoule (éoliens et lacustres), faciès conglomératiques et gréseux de la formation de Léouvé (coulées boueuses et dépôts fluviatiles). Différents degrés d'analogie peuvent être établis avec les ensembles permiens de l'Argentera et de Provence orientale où des milieux de dépôts similaires donnent des faciès voisins, modulés par des facteurs locaux. Le climat et la tectonique sont les facteurs dominants de la sédimentation. Ils agissent en tant que facteurs d'uniformisation et de différenciation . Le climat, chaud et semi-aride, à périodes sèches et humides alternées, induit des faciès très contrastés tels que les coulées boueuses, très grossières, ou des sédiments très fins, éoliens ,et lacustres . Le régime géodynamique distensif crée des grabens asymétriques et le soulèvement des marges alimente irrégulièrement les bassins subsidents. La dimension des bassins et l'activité différentielle des marges régissent la distribution des corps sédimentaires et modulent la rapidité du comblement

Apports du radar géologique à l'étude de la dynamique sédimentaire à l'Holocène récent dans la plaine interdunaire de Merlimont (Pas-de-Calais).

International audienceA Ground Penetrating Radar (GPR) survey was carried out on the Pas-de-Calais coast in arder la quantify the evolution of sand dunes during the holocene period. 15 km of GPR profiles were recorded with 100 and 500 MHz antennae. Some boreholes were drilled to control the GPR results. Correlation between GPR and boreholes is better than 35 cm. At last, 7 peat layers have been found wilh a north-east dip. It reveals the existence of changes in hydrogeological conditions (variations of water table) during the last 900 years (mast ancient peat in dunes peat layers). Moreover, some ancient dunes features have been outlined between flat peat layers. GPR is a robust tool for sedimentological interpretation in sandy context

Benefits of adapting to sea level rise : the importance of ecosystem services in the French Mediterranean sandy coastline

This article proposes an innovative approach to assess the benefits of adapting to sea level rise (SLR) in a coastal area on a regional scale. The valuation framework integrates coastal ecosystem services, together with urban and agricultural assets. We simulate the impacts of a progressive 1 m rise in sea level in the twenty-first century and an extreme flooding event in 2100 for four contrasted adaptation scenarios (Denial, “Laissez-faire”, Protection and Retreat). The assessment involves coupling the results of hazard-modelling approaches with different economic valuation methods, including direct damage functions and methods used in environmental economics. The framework is applied to the French Mediterranean sandy coastline. SLR will result in major land-use changes at the 2100 time horizon: relocation or densification of urban areas, loss of agricultural land, increase in lagoon areas and modification of wetlands (losses, migration or extension of ecosystems). Total benefits of public adaptation options planned in advance could reach €31.2 billion for the period 2010–2100, i.e. €69,000 per inhabitant (in the study area) in 2010 or €135 million/km of coastline. Our results highlight the importance of (i) raising awareness to ensure that public services and coastal managers can anticipate the consequences of SLR and (ii) incorporating coastal ecosystems into the assessment of the adaptation options. Our findings could provide a basis for participatory foresight approaches to build coastline adaptation pathways.PostprintPeer reviewe

Multi-risk governance for natural hazards in Naples and Guadeloupe

Technical and institutional capacities are strongly related and must be jointly developed to guarantee effective natural risk governance. Indeed, the available technical solutions and decision support tools influence the development of institutional frameworks and disaster policies. This paper analyses technical and institutional capacities, by providing a comparative evaluation of governance systems in Italy and France. The focus is on two case studies: Naples and Guadeloupe. Both areas are exposed to multiple hazards, including earthquakes, volcanic eruptions, landslides, floods, tsunamis, fires, cyclones, and marine inundations Cascade and conjoint effects such as seismic swarms triggered by volcanic activity have also been taken into account. The research design is based on a documentary analysis of laws and policy documents informed by semi-structured interviews and focus groups with stakeholders at the local level. This leads to the identification of three sets of governance characteristics that cover the key issues of: (1) stakeholders and governance level; (2) decision support tools and mitigation measures; and (3) stakeholder cooperation and communication. The results provide an overview of the similarities and differences as well as the strengths and weaknesses of the governance systems across risks. Both case studies have developed adequate decision support tools for most of the hazards of concern. Warning systems, and the assessment of hazards and exposure are the main strengths. While technical/scientific capacities are very well developed, the main weaknesses involve the interagency communication and cooperation, and the use and dissemination of scientific knowledge when developing policies and practices. The consequences for multi-risk governance are outlined in the discussion

Evolution of coastal zone vulnerability to marine inundation in a global change context. Application to Languedoc Roussillon (France)

The coastal system is likely to suffer increasing costal risk in a global change context. Its management implies to consider those risks in a holistic approach of the different vulnerability components of the coastal zone, by improving knowledge of hazard and exposure as well as analyzing and quantifying present day and future territory vulnerability. The ANR/VMC2007/MISEEVA project (2008-2011) has applied this approach on Languedoc Roussillon region in France. MISEEVA approach relies on several scenarios for 2030 and 2100, in terms of meteorology (driver of coastal hazard), sea level rise, and also considering further trends in demography and economy, and possible adaption strategies Hazard has been modeled (SWAN, MARS and SURFWB), on the base of the presentday situation, sea level rise hypotheses, and existing or modeled data, of extreme meteorological driving f. It allowed to assess the possible surges ranges and map coastal zone exposure to: - a permanent inundation (considering sea level rise in 2030 and 2100, - a recurrent inundation (considering sea level rise and extreme tidal range) - an exceptional inundation (adding extreme storm surge to sea level rise and tidal range). In 2030, exposure will be comparable to present day exposure. In 2100, extreme condition will affect a larger zone. Present days social and economic components of the coastal zone have been analyzed in terms of vulnerability and potential damaging. Adaptation capacity was approached by public inquiries and interviews of stakeholders and policy makers, based on existing planning documents The knowledge of the present day system is then compared to the possible management strategies that could be chosen in the future, so to imagine what would be the evolution of vulnerability to marine inundation, in regards to these possible strategies

Contribution of insurance data to cost assessment of coastal flood damage to residential buildings: insights gained from Johanna (2008) and Xynthia (2010) storm events

International audienceThere are a number of methodological issues involved in assessing damage caused by natural hazards. The first is the lack of data, due to the rarity of events and the widely different circumstances in which they occur. Thus, historical data, albeit scarce, should not be neglected when seeking to build ex-ante risk management models. This article analyses the input of insurance data for two recent severe coastal storm events, to examine what causal relationships may exist between hazard characteristics and the level of damage incurred by residential buildings. To do so, data was collected at two levels: from lists of about 4000 damage records, 358 loss adjustment reports were consulted, constituting a detailed damage database. The results show that for flooded residential buildings, over 75% of reconstruction costs are associated with interior elements, with damage to structural components remaining very localised and negligible. Further analysis revealed a high scatter between costs and water depth, suggesting that uncertainty remains high in drawing up damage functions with insurance data alone. Due to the paper format of the loss adjustment reports, and the lack of harmonisation between their contents, the collection stage called for a considerable amount of work. For future events, establishing a standardised process for archiving damage information could significantly contribute to the production of such empirical damage functions. Nevertheless, complementary sources of data on hazards and asset vulnerability parameters will definitely still be necessary for damage modelling; multivariate approaches, crossing insurance data with external material, should also be investigated more deeply

Vulnérabilité des plages du Languedoc-Roussillon face au risque de submersion marine lié au changement climatique

National audienceCet article rend compte de la vulnérabilité des plages du Languedoc-Roussillon au risque de submersion marine liée au changement climatique. Il présente en premier lieu quelques résultats des enquêtes de perceptions menées auprès d'un échantillon de résidents locaux, de résidents secondaires, de touristes et d'excursionnistes, soit un total de 881 personnes enquêtées. Une simulation des effets de la submersion permanente des plages en 2100 permet ensuite d'évaluer la surface de plage perdue du fait d'une augmentation d'un mètre du niveau de la mer. Selon que l'on tient compte ou pas des processus d'érosion, les pertes s'élèvent à 240 ou 450 hectares, soit respectivement 14 % et 27 % de la surface actuelle. A partir de ces pertes physiques et des consentements à payer obtenus par enquête, une évaluation monétaire de ces dommages est proposée. Les pertes directement liées à la submersion s'élèvent à 1,3 milliards d'euros (coût 2010 non actualisé). Enfin, dans la dernière partie, des indicateurs de vulnérabilité sont élaborés et mesurés pour l'ensemble des communes de la région. Ils combinent quatre critères : le taux de perte de surface de plage rend compte de l'exposition à l'aléa, la surface initiale des plages exprime leur sensibilité au risque tandis que le taux d'érosion et le taux d'urbanisation en première ligne permettent de mesurer la capacité d'adaptation. A partir de ces indicateurs, trois classes de vulnérabilité des plages permettent de caractériser les communes du Languedoc-Roussillon

Coastal flooding of urban areas by overtopping: dynamic modelling application to the Johanna storm (2008) in Gâvres (France)

International audienceRecent dramatic events have allowed significant progress to be achieved in coastal flood modelling over recent years. Classical approaches generally estimate wave overtopping by means of empirical formulas or 1-D simulations , and the flood is simulated on a DTM (digital terrain model), using soil roughness to characterize land use. The limits of these methods are typically linked to the accuracy of overtopping estimation (spatial and temporal distribution) and to the reliability of the results in urban areas, which are places where the assets are the most crucial. This paper intends to propose and apply a methodology to simulate simultaneously wave overtopping and the resulting flood in an urban area at a very high resolution. This type of 2-D simulation presents the advantage of allowing both the chronology of the storm and the particular effect of urban areas on the flows to be integrated. This methodology is based on a downscaling approach, from regional to local scales, using hydrodynamic simulations to characterize the sea level and the wave spectra. A time series is then generated including the evolutions of these two parameters, and imposed upon a time-dependent phase-resolving model to simulate the overtopping over the dike. The flood is dynamically simulated directly by this model: if the model uses adapted schemes (well balanced, shock capturing), the calculation can be led on a DEM (digital elevation model) that includes buildings and walls, thereby achieving a realistic representation of the urban areas. This methodology has been applied to an actual event, the Johanna storm (10 March 2008) in Gâvres (South Brittany, in western France). The use of the SURF-WB model, a very stable time-dependent phase-resolving model using non-linear shallow water equations and well-balanced shock-capturing schemes, allowed simulating both the dynamics of the over-topping and the flooding in the urban area, taking into account buildings and streets thanks to a very high resolution (1 m). The results obtained proved to be very coherent with the available reports in terms of overtopping sectors, flooded area, water depths and chronology. This method makes it possible to estimate very precisely not only the overtopping flows, but also the main characteristics of flooding in a complex topography like an urban area, and indeed the hazard at a very high resolution (water depths and vertically integrated current speeds). The comparison with a similar flooding simulation using a more classical approach (a digital terrain model with no buildings, and a representation of the urban area by an increased soil roughness) has allowed the advantages of an explicit representation of the buildings and the streets to be identified: if, in the studied case, the impact of the urbanization representation on water levels does indeed remain negligible, the flood dynamics and the current speeds can be considerably underestimated when no explicit representation of the buildings is provided, especially along the main streets. Moreover, on the seaside, recourse to a time-dependent phase-resolving model using non-stationary conditions allows a better representation of the flows caused by overtopping. Finally, this type of simulation is shown to be of value for hazard studies, thanks to the high level of accuracy of the results in urban areas where assets are concentrated. This Published by Copernicus Publications on behalf of the European Geosciences Union. 2498 S. Le Roy et al.: Coastal flooding of urban areas by overtopping methodology, although it is currently still quite difficult to implement and costly in terms of calculation time, can expect to be increasingly resorted to in years to come, thanks to the recent developments in wave models and to the increasing availability of LiDAR data

Simulating overtopping and coastal flooding in urban areas: Perspectives to quantify sea level rise effects

International audienceSimulating overtopping and coastal flooding in urban areas: Perspectives to quantify sea level rise effects Recent progresses in numerical modelling and data acquisition have allowed significant improvements in coastal flooding simulations, with a maturity of numerical tools that now allows very precise results in urban areas. Essentially used for hazard studies, their reliability now offers the perspective to estimate the impact of sea level rise on coastal flooding hazards. Thepresented methodis based on simultaneous simulation of wave overtopping and resulting flood in urban areas. This type of two-dimensional simulationscan afford reproducingboth the chronology and the effect of urban areas on flood dynamics. The method consists in elaborating,from larger simulations, a time-series of instantaneous water levels, including waves. This time-series is imposed upon a time-dependent phase-resolving model to simulate dynamically wave overtopping and the resulting flood, using a Digital Elevation Model that includes buildings. This method has been applied to the Johanna storm (2008) in Gâvres (France). SURF-WB, a NLSW model, allowed simulating both overtopping dynamics and flooding, taking into account buildings thanks to a 1m-resolution. Obtained results proved to be very consistent with available reports (overtopping sectors, flooded area, water heights and chronology). This method allows reproducingvery realistically overtopping andflooding dynamics in an urban area (water heights and velocities), with an increased accuracy and very realistic results compared to more classical approaches. This type of simulations can be used to estimate the potential evolutions of coastal flooding processes in a context of sea level rise due to climate change, supposing nevertheless a non-modified morphology. Preliminary simulations realized on the site of Gâvres showed how sea level rise could increase overtopping for a storm like Johanna. For example, a rise of 20 cm of the sea water level may lead to a slightly larger flooded area, but with water heightsincreasing of about 28 cm, due to the modifications in overtopping flows and chronology

Modélisation de la submersion marine lors de la tempête Johanna (2008) à Gâvres (Morbihan) : phénomène de franchissement en zone urbaine

National audienceLa méthodologie présentée dans le présent article vise à simuler de manière la plus réaliste possible les franchissements par paquets de mer et la submersion qui en résulte en milieu urbain. Elle s'appuie sur des simulations régionales à locales de niveaux d'eau et de vagues pour établir des conditions de forçage pour un modèle à résolution de phase ("vague-à-vague") utilisant des schémas numériques adaptés. Ce modèle est alors utilisé sur un Modèle Numérique d'Elévation (MNE), intégrant les bâtiments, de manière à simuler simultanément le franchissement et la propagation de l'inondation. Cette méthodologie a été appliquée avec le modèle SURF-WB à la submersion survenue à Gâvres (Morbihan) lors de la tempête Johanna (10 mars 2008). Les résultats obtenus s'avèrent tout à fait cohérents avec les observations disponibles (zones de franchissement, étendue de l'inondation, hauteurs d'eau et chronologie). Cette méthode permet d'améliorer la qualité des résultats en milieu urbain par rapport aux approches plus classiques, notamment vis-à-vis de la vitesse des courants à terre. Le développement rapide et récent de ce type de modèle devrait permettre la généralisation de ce type d'approche dans les années à venir. Ce travail a été réalisé dans le cadre du projet JOHANNA (partenariat BRGM-UBO, cofinancé par la Fondation MAIF)