A conceptual morphodynamic model including storm impacts for microtidal barred beaches

International audienceThis paper introduces the main results of a large dataset concerning the impacts of storm events and recovery period on a microtidal double barred beach of the NW Mediterranean Sea (Lido de Sète, Gulf of Lions, South France). The objective is to discuss of the key control parameters among both the forcing conditions and the morphological state of the bar/beach system. Our new dataset (high frequency topo-bathymetries and ARGUS video) clearly demonstrates the importance of the morphological variations in bar pattern along the beach. The steady alongshore difference in the outer bar depth and distance (maintained by the N.O.M. variations) has a concrete influence on the modal inner bar state and sensitivity of bar and beach profile face to the erosive processes

Swash platform morphology in the ebb-tidal delta of the Barra Nova inlet, South Portugal

A fieldwork study of an artificially created inlet cut in the barrier island system of the Ria Formosa (South Portugal) was carried out from January to March 1999. This study focused on the updrift swash platform associated with the ebb-tidal delta. The area was monitored during a month with fair weather conditions studying morphodynamics, sedimentary dynamics and hydrodynamic measurements. The results were used to establish a sedimentary budget of the swash platform and to quantify the morphodynamics. A strong accretion was observed on the swash platform, which corresponded to the volume of sediment provided by the longshore drift on the adjacent updrift coast. A redistribution of sediment was observed on the platform, changing the orientation of the main swash platform axis. The swash bars forming this area are very dynamic (20 m migration in 8 days), and the entire swash platform migrated toward the inlet resulting in progressive closure of the system. Characteristics of the inlet and morphodynamics of the swash platform were used to validate a conceptual model of by-passing by ebb-tidal delta breaching for this system

Risk assessment required in the framework of new french regulation on dams. Methodology developped by INERIS

The new French dam safety regulation classifies each dam in four classes depending on its height and the volume of water it stores. The first two classes require each owner to establish a safety report for an authority review. A main objective of this report is to demonstrate that all hazardous scenarios have been taken into account by the dam owner in assessing the risk level and also that sufficient safety measures have been specified to reach a global risk as low as reasonably possible. First, considering all existing data and characteristics of the dam, the owner has to carry out a risk analysis to identify all failure modes that may occur on dam structure and hydraulic equipment. Every potential accident is then characterised in terms of severity of consequences and annual occurrence probability. The severity level is assessed quantitatively or qualitatively, using a combination of maps representing the effects of the flood waves and the Population At Risks. The probability is assessed using a semi-quantitative method analyzing all scenarios and safety measures involved in prevention and protection: the bow-tie approach. This cross analysis implements an iterative approach to highlight complementary measures and recommendations and therefore enhance global safety level

Assessment of a Smartphone-Based Camera System for Coastal Image Segmentation and Sargassum monitoring

International audienceCoastal video monitoring has proven to be a valuable ground-based technique to investigate ocean processes. Presently, there is a growing need for automatic, technically efficient, and inexpensive solutions for image processing. Moreover, beach and coastal water quality problems are becoming significant and need attention. This study employs a methodological approach to exploit low-cost smartphone-based images for coastal image classification. The objective of this paper is to present a methodology useful for supervised classification for image semantic segmentation and its application for the development of an automatic warning system for Sargassum algae detection and monitoring. A pixel-wise convolutional neural network (CNN) has demonstrated optimal performance in the classification of natural images by using abstracted deep features. Conventional CNNs demand a great deal of resources in terms of processing time and disk space. Therefore, CNN classification with superpixels has recently become a field of interest. In this work, a CNN-based deep learning framework is proposed that combines sticky-edge adhesive superpixels. The results indicate that a cheap camera-based video monitoring system is a suitable data source for coastal image classification, with optimal accuracy in the range between 75% and 96%. Furthermore, an application of the method for an ongoing case study related to Sargassum monitoring in the French Antilles proved to be very effective for developing a warning system, aiming at evaluating floating algae and algae that had washed ashore, supporting municipalities in beach management

Les embouchures Mesotidales (tidal inlets) et leur relation avec les littoraux adjacents - Exemple de la Barra Nova, Sud Portugal.

L'évolution d'une embouchure tidale dépend de l'équilibre dynamique entre les processus littoraux sur les côtes adjacentes et la barrière hydraulique que représente le chenal de marée. L'objectif de ce travail était de quantifier l'influence de ces différents paramètres afin de comprendre et prédire la morphodynamique du site de la Barra Nova sur le système d'îlesbarrières de la Ria Formosa (Sud Portugal). Les mesures de morphodynamique (bathymétries, vidéo), d'hydrodynamique et de dynamique sédimentaire (traçages) ont permis de quantifier l'évolution de cette embouchure en déterminant les processus hydrosédimentaires sur le littoral adjacent, et la réponse du système aux variations climatiques. Un schéma conceptuel est proposé, basé sur la compréhension de la morphodynamique à court terme et sur l'enregistrement vidéo à moyen terme. Ce nouveau concept, qui explique l'évolution saisonnière de la Barra Nova, met en évidence les facteurs responsables de la migration historique de cette embouchure.Tidal inlets are among the most dynamic morphological features along the world coastlines. Their evolution and stability, frequently critical to the local environment, are dependent on the relative influence of longshore transport along adjacent coasts and tidal flows in the inlet. Main objective of this study was to quantify the processes involved in the inlet morphodynamics in order to determine the key parameters of these systems and to predict medium to long-term evolution. Morphology evolution (bathymetry, remote sensed video data), hydrodynamics and sediment transport measurements were analyzed to quantify the inlet dynamics. Our approach was based on the study of hydrosedimentary processes along the adjacent coastline, and inlet responses to environmental variations (mainly seasonal). A conceptual model is proposed, based on the understanding of short-term morphodynamics of the system, and medium to long-term video information. This new model, explaining the seasonal evolution of the Barra Nova, points out the processes responsible for the historical migration of this tidal inlet

Sediment transport pattern at the Barra Nova inlet, south Portugal: a conceptual model

The Barra Nova inlet, in south Portugal, is known to migrate progressively southeastwards under wave action. The morphodynamics of this system during a representative year suggests that this long-term evolution is dependent on a seasonal behavior of the tidal inlet which can be described through a three-stage model of post-storm, transition and extended fair-weather conditions. Processes involved in this evolution indicate that the historical migration of the Barra Nova is not dependent on the longshore drift forcing constricting the channel on the updrift coast, but rather on the adjustment of the system to a major erosion of the downdrift coast during short storm events

Longshore sediment movements from tracers and models, Praia de Faro, South Portugal

This work aims to improve the knowledge of sediment circulation in the coastal zone, focusing on the quantification of sediment movement due to longshore drift. The studied field site is the Praia de Faro beach on the Peninsula do Ancão in Algarve (Portugal), which is located on the updrift coast of the Barra Nova tidal inlet. The main objective of the study was to quantify the sediment transport rate that will enter in the inlet system.Measurements were undertaken during low hydrodynamic conditions prevailing in this area and permitted to estimate a longshore transport rate of 2.6–4.2 m/s, consistent with other transport estimations in Algarve. Four theoretical models for longshore transport rate calculation were confronted to tracer results to choose a extrapolation tool. Kamphuis (1991) formula appeared to be the more appropriate in this area. It was used to extrapolate the results in order to be compared to the observed morphological evolution. The calculated short term sediment flux (10500 m3/month) corresponds to the accretion on the updrift swash platform of the Barra Nova tidal inlet and is thus considered to be the contribution of the adjacent coast to this system. Moreover, the estimated longshore transport rate permit us to predict a spit progradation of 60–70 m/year. This result is consistent with the observed migration rate of the Barra Nova inlet during the last 25 years. This study shows that, with a good knowledge of the environmental context, sediment fluxes obtained by sand tracers are accurate enough to estimate the long term longshore transport and long term morphological response of a stretch of shoreline

Tidal inlet function: field evidence and numerical simulation in the INDIA project

In recognition of the environmentally sensitive nature of inlets and of a requirement to improve present knowledge of their function, the INDIA project has studied a small natural tidal inlet located in the Ría Formosa, Algarve, Portugal. The project has used state-of-the-art field equipment to study present day processes, and a range of numerical models to extend the spatial and temporal range of the measurements. Underpinned by knowledge of inlet evolution over several years, and by knowledge of other inlet systems, a conceptual model describing the medium-to long-term evolution of the inlet is presented. Key elements of the model are then examined with reference to field observations and to numerical simulations of tides, waves, sediments and morphology. Supported by historical evidence of inlet evolution in the Ría Formosa, the picture that emerges of inlet dynamics is essentially one of relative simplicity and predictability in the short-to medium-term

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

De la compréhension de la dynamique sédimentaire littorale à la gestion des risques côtiers

Mes travaux depuis 1998 ont portés sur l’hydrodynamique et la dynamique sédimentaire littoralespar des approches d’expérimentation in-situ reposant sur le suivi des évolution morphologiques,l’évaluation par traçages sédimentaires des flux sableux et la télédétection par vidéo numériquepermettant un suivi à haute fréquence des réponses morhologiques, en particulier pendant lestempêtes. Mes études ont porté sur des échelles spatiales et temporelles variées allant du transportinstantanné à l’évolution pluri-annuelle. Je me suis particulièrement intéressé aux domainesd’embouchures tidales, lagunaires ou fluviatiles où les interactions sont complexes et fortement nonlinéaires.Un deuxième sujet important de ma recherche concerne les barres d’avant-côte et lescouplages barres-plages qui constituent également un challenge scientifique dans la mesure où lesmodèles numériques peinent encore à simuler les évolutions observées, notamment en raison dumanque de données pendant les épisodes les plus morphogènes. Enfin, mon travail a comporté unvolet plus appliqué destiné à améliorer la compréhension et la prévisions des risques côtiers, parplusieurs approches complémentaires alliant l’analyse historique, la modélisation numérique et lamise en oeuvre de réseaux d’observation dédiés aux tempêtes et à leurs impacts sur le littoral. Cestravaux collectifs ont été réalisés par des collaborations et avec des étudiants que j’ai pu encadrer etont donné lieu à un nombre conséquent de publications (40), conférences (45) et rapports publics(52)