Yann Balouin

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A monitoring-based management approach for Natech-related risks: reflection from a case study

Le Centre pour la Communication Scientifique Directe - HAL - memSIC, Sep 22, 2022

Impact du changement climatique sur les événements de tempête affectant les littoraux européens, le projet MICORE

Journées de l'hydraulique, 2012

Climate change impact on storminess along Europe coastlines. Within the European project MICORE (... more Climate change impact on storminess along Europe coastlines. Within the European project MICORE (Morphological Impacts and COastal Risks induced by Extreme storm events Project FP7 n° 202798), an analysis of historical storm events was performed along 9 European coastlines. Physical characteristics of storms (meteorology, Oceanography) were studied to assess if the magnitude of storms, their duration and frequency has changed in the last decades. Despite the wish ans effort to apply the same methology for all countries, several differences can be highlighted on the approaches chosen by the MICORE partners, mainly due to a variable availability to the datasets, and the variable quality of backward modeling of historical events. The periods considered for wind analysis range from 46 years (Netherlands) to 105 years (Andalusia – Spain), for surge analysis range from 45 years (Poland) to 100 years (Netherlands), while for wave analysis range from 30 years (Belgium) up to 60 years (Bulgaria). Results of the analysis of 58 different proxies indicate an absence of significant trend on storminess (62% of cases). 19% of the indicators suggest an increase of storminess, but only 5% and statistically significant. Based on the chosen indicators and the available data, the main conclusion derived from the table analysis is that a clear trend of storminess change at European level is not evident. The results express a large variability of trends from coastal region to coastal region. A decrease in storminess in Southern coast of Portugal as well as Bulgaria in observed but remains poorly significant. A significant increase in the frequency of storm is however observed along the polish coastline. Despite the absence of significant trends in these analyses, the obtained results do not imply that global climate change consequences (e. g., sea temperature increase, sea level rise) will not have an influence on European storminess and storminess impacts. It mainly means that for the existing and available data sets, those impacts have not been detected or do not have a visible and strong signal at European level.Dans le cadre du projet européen MICORE (Morphological Impacts and COastal Risks induced by Extreme storm events), une analyse des événements historiques de tempêtes ayant affecté les littoraux européens a été réalisée. Elle concerne 12 régions littorales réparties dans 9 pays d’Europe. Les caractéristiques physiques des tempêtes marines (hydrodynamique, météorologie) ont été étudiées pour évaluer les évolutions éventuelles de la fréquence, l’intensité et la durée de ces événements au cours des dernières décennies. Bien que la méthodologie initiale se voulait commune à toutes les régions d’Europe, une grande disparité a été observée concernant la disponibilité de séries de mesures à long-terme et la qualité des reconstitutions numériques des événements passés. Les périodes d’analyses de la houle s’étendent de 30 ans (Belgique) à 60 ans (Bulgarie). Les résultats obtenus mettent en évidence la difficulté de comparer entre eux les résultats obtenus dans différents pays. Toutefois, les résultats de l’analyse de 58 critères différents indiquent en majorité l’absence d’une tendance significative d’évolution des tempêtes (62% des cas). Dans 19% des cas une tendance à l’augmentation des tempêtes est observée, toutefois, seul 5 % des critères analysés présentent une augmentation statistiquement significative. Sur la base des critères et des jeux de données analysés dans cette étude, on peut conclure qu’il n’existe pas de modification globale du régime de tempêtes en Europe lors des dernières décennies. Quelques régions côtières présentent toutefois des tendances spécifiques : la côte sud du Portugal et la Bulgarie présentent une diminution du régime de tempête, peu significative, l’Aquitaine montre une légère augmentation des tempêtes, peu significative, la Pologne présente une augmentation significative de la fréquence de ses tempêtes. Malgré l’absence de tendance dominante dans ces analyses, les résultats obtenus n’impliquent pas que des tendances à plus long-terme n’existent pas, ni que les changements climatiques actuels et futurs n’auront pas d’effets sur les régimes de tempêtes dans le futur.Balouin Yann, Ferreira Oscar, Ciavola Paolo. Impact du changement climatique sur les événements de tempête affectant les littoraux européens, le projet MICORE. In: Evénements extrêmes fluviaux et maritimes. Leurs variabilités spatiales et chronologiques dans l'ouest de l’Europe. 34èmes journées de l’hydraulique Paris, 1 et 2 février 2012. 2012

Effect of offshore winds and storm waves on the efficiency of beach nourishment behind detached breakwaters, The Barcarès beach, France

Edition 4, Split, Croatie, 2017

In 2014, 3 detached breakwaters were implemented at the wave-dominated beach of Le Barcarès, S Fr... more In 2014, 3 detached breakwaters were implemented at the wave-dominated beach of Le Barcarès, S France, to fight against erosion and submersion hazards. Additionally, beach nourishments are undertaken every summer. Daily video images from Oct 2014 to July 2016 covering an alongshore distance of 1.6 km are used to analyse the response of the shoreline to the structure implementation and to the main forcing factors (SE storms and Tramontane winds). Results show that the breakwaters clearly modified the shoreline shaped by the formation of salient. However, in contrast with the adjacent southern beach, the shoreline is not stabilised and shows rapid short-term variations as well as a great seasonal variability. Nourishment efficiency appears to be clearly linked with the occurrence of storm events that generate a loss of sediment northwards and tramontane winds that favours a southwards sediment transport and an increase of sediment volume in the area.

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Apport de la géophysique terrestre (géo-radar, sismique) pour l’aide à la gestion du trait de côte

XVèmes Journées, La Rochelle, 2018

Le système dunaire de Torreilles (Pyrénées Orientales) a été choisi comme site test pour réaliser... more Le système dunaire de Torreilles (Pyrénées Orientales) a été choisi comme site test pour réaliser une campagne de géophysique terrestre combinant géo-radar et sismique ondes de surface. L'objectif est d'apporter une expertise de l'utilisation de ce type de technologie afin de i) comprendre la construction et l'évolution du système et, ii) estimer le stock sédimentaire terrestre en place. Ces résultats démontrent l'avantage qu'il y a de coupler les deux méthodes pour identifier et cartographier les unités sédimentaires constitutives du prisme littoral. Les données géo-radar permettent d'obtenir une image détaillée de l'architecture interne des dépôts jusqu'à 9m de profondeur (pendage des dépôts et sens de progradation, informations sur les phases de construction/destruction, toit de la nappe…). La donnée sismique présente l'avantage de pouvoir cartographier l'ensemble des unités jusqu'à 30 m de profondeur, toutefois sans détail architectural. Le volume des dépôts dunaires et de la plage fossile imagée atteint 8.5 m 3 /m 2. La combinaison des résultats de la sismique et du forage permet de pouvoir identifier la limite sable/argile (13 m de profondeur) et d'estimer le volume de l'ensemble de l'unité sableuse entre 13 et 17 m 3 /m 2. Ces données sont susceptibles d'apporter des éléments de réflexion sur l'évolution du système à des fins de gestion du trait de côte.

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Stratégie de modélisation des phénomènes de submersion par franchissement de paquets de mer

XVèmes Journées, La Rochelle, 2018

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Video monitoring framework in support of sargassum management

The waters off Caribbean islands have seen large amounts of Sargassum seaweed during the last yea... more The waters off Caribbean islands have seen large amounts of Sargassum seaweed during the last years (Wang and Hu, 2016). This record-breaking events of algae blooms and mass stranding started in earnest in 2011, then 2015 saw the next large-scale event and in January 2018, unusually large aggregations of Sargassum have been spotted on satellite imagery (Optical Oceanography Laboratory, n.d.). Normally, when floating offshore Sargassum provide important habitat and refuge to a large diversity of animals. However, while weeds approach nearshore and beach, due to currents and winds actions, in such massive quantities, they start to be deathtrap for many animals and contribute to the degradation of important coastal habitats, threatening coastal activities and ecosystems. The decomposing mass, which can be several meters high, creates oily slicks in its wake and releases a foul odor, damaging tourism activities since the sight and smell left beaches highly unappealing. Both satellite an...

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Video monitoring of Posidonia oceanica banquettes on pocket beaches, Northern Corsica

Fragments of Posidonia oceanica accumulate on beaches and can form structures composed of seagras... more Fragments of Posidonia oceanica accumulate on beaches and can form structures composed of seagrass and sediments of variable heights and extents, called banquettes. Coastal video-monitoring tools were used on pocket beaches of the Cape Corse to investigate the dynamics of these banquettes and evaluate their role against beach erosion. On Pietracorbara beach and Meria beach, these banquette dynamics reflect those of pocket beaches: beach and banquette rotations are monitored. On the three sites, the dynamics of the banquette is thus controlled by wave direction and wave energy, i.e. when a threshold of wave height is reached, the banquette is destroyed. On Ostriconi beach, the P. oceanica litter is moved back and forth from the water to the shore by waves through rip current channels. The banquette is thus building on specific areas of the beach corresponding to the exit of the channels. P. oceanica litter has a protective role when ashore (buffer between the beach sediments and the ...

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Video Depth Inversion at a Microtidal Site Exposed to Prevailing Low-energy Short-period Waves and Episodic Severe Storms

Journal of Coastal Research, 2020

ABSTRACT Bouvier, C.; Balouin Y.; Castelle B., and Valentini N., 2020. Video depth inversion at a... more ABSTRACT Bouvier, C.; Balouin Y.; Castelle B., and Valentini N., 2020. Video depth inversion at a microtidal site exposed to prevailing low-energy short-period waves and episodic severe storms. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1021–1026. Coconut Creek (Florida), ISSN 0749-0208. Over the last decades, a wide range of depth inversion algorithms have been developed, which aim to infer local water depth from remotely-sensed wave parameters based on physical relations. Particularly, the depth inversion algorithm named cBathy (Holman, Plant, and Holland, 2013) showed good results for a range of wave conditions and environments but the method was only applied to beaches exposed to moderate or highly energetic wave climate, with wave peak period often larger than 8 s. This paper applies the cBathy algorithm for the very first time on a Mediterranean Sea beach, Sète, southeast France, a semidiurnal microtidal environment exposed to a moderate-energy modal wave climate and episodic severe storms. The objective of the paper is to assess the ability of the cBathy algorithm to estimate the nearshore bathymetry for waves with large energy spread in both direction and frequency. After a comparison between the remotely sensed bathymetry and a ground truth bathymetric survey, we use a non-linear, depth-averaged morphodynamic model, 2DBeach (Dubarbier et al., 2017), on remotely sensed bathymetries to determine the sensitivity of nearshore waves and horizontal circulations to the estimated morphology. The depth inversion technique estimates the nearshore bathymetry with good accuracy (RMSE = 0.39 m) for a beach area extending respectively 1600 m and 600 m in the longshore and cross-shore directions, respectively, suggesting the technical feasibility of coupling remotely-sensed bathymetry to 2DH numerical model, even at short-waves exposed Mediterranean beaches.

Suivis Vidéo de la dynamique hydro-sédimentaire côtière : exemples d’applications sur le littoral méditerranéen

Le suivi video de la dynamique littorale s’est developpe depuis les annees 80 (Holman et Stanley,... more Le suivi video de la dynamique littorale s’est developpe depuis les annees 80 (Holman et Stanley, 1997), et de nombreux outils ont ete mis en place pour analyser les signatures optiques des morphologies cotieres et de l’hydrodynamique. L’interet majeur du suivi video reside dans l’acquisition a haute frequence et en continu, y compris lors des tempetes, fournissant des donnees originales quantitatives inaccessibles a l’heure actuelle avec les moyens de suivi classiques dont on dispose (leves bathymetriques, mesures de houle, courant). Differents systemes sont actuellement a disposition : des appareils time-lapse bon marche a des systemes eprouves comme ARGUS, VM4GIS, CAM-ERA, … On peut ainsi avoir rapidement acces a des indicateurs qualitatifs de l’etat du littoral, ou par des traitement plus complexes a des indicateurs quantitatifs tels que les vagues, les courants, la bathymetrie. En mediterranee, des dispositifs a differentes resolutions ont ete utilises ces dernieres annees pour...

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Observation and Modelling of Shoreward Propagating Accretionary Waves (Spaws) on Microtidal Beaches

INTRODUCTION At straight sandy coasts, wave-induced processes often lead to intriguing alongshore... more INTRODUCTION At straight sandy coasts, wave-induced processes often lead to intriguing alongshore-variable morphology on spatial scales from 10s – 1000s of meters. The alongshore alternation in depth of crescentic nearshore bars, with landward-protruding shallower areas known as horns, is often reflected in the shoreline and beach morphology (e.g. Castelle et al., 2015). Observations have shown that the horns of crescentic bars may separate from the bar during storms and subsequently migrate onshore towards the beach during calmer periods as a spatially coherent structure, termed Shoreward Propagating Accretionary Wave, or SPAW (Wijnberg and Holman, 2007). Consequently, it is thought that such SPAWs play a role in the cross-shore exchange of sand, and the development of alongshore-variable morphology (Price et al., 2017). Here, we aim to (1) quantify the morphological evolution of a SPAW and (2) unravel the physical processes underlying its onshore migration and spatial coherence. T...

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Application and implementation of the RESPONSE methodology to evaluate the impact of climate change on the Aquitaine and Languedoc Roussillon coastlines

Proceedings of the International Conference on Landslides and Climate Change, Ventnor, Isle of Wight, UK, 21–24 May 2007, 2007

MISEEVA : Set up of a transdisciplinary approach to assess vulnerability of the coastal zone to marine inundation at regional and local scale, within a global change context

Littoral 2010 – Adapting to Global Change at the Coast: Leadership, Innovation, and Investment, 2011

MISEEVA (2008-2011) aims to assess coastal zone vulnerability to marine inundation by integrating... more MISEEVA (2008-2011) aims to assess coastal zone vulnerability to marine inundation by integrating the physical and socio-economical aspects at different temporal (2010, 2030 and 2100) and spatial (local to regional) scales. The Languedoc Roussillon (France) region was chosen as a pilot site, focusing on local sites from Villeneuve-lès-Maguelone to Carnon, in Hérault. It required the development of a transdisciplinary methodology to enable transfers of knowledge and promote interdisciplinary iteration of methods throughout the project.

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Seasonal and episodic runup variability on a Caribbean reef-lined beach

Tidal inlets and adjacent coasts - Example of the Barra Nova inlet, south Portugal

Tidal inlets are among the most dynamic morphological features along the world coastlines. Their ... more 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 evolutio...

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Video Monitoring of soft coastal defenses at the Lido of Sete, France

The feedback on soft techniques against erosion is still limited nowadays, and does not allow to ... more The feedback on soft techniques against erosion is still limited nowadays, and does not allow to determine if such techniques are efficient or not, and if they are applicable to similar environments. The site of the Lido of Sete is currently evaluating these techniques and thus provided an outstanding natural setting to analyze coastal behavior associated with soft defenses. An Argus video monitoring system was deployed in 2011 to survey this area. The monitoring before, during and after the management works permitted to describe the natural evolution of the beach and nearshore area, and the morphological response following the deployment of a submerged geotextile wave breaker. The bar system, characterized by well-developed crescentic patterns was linearized and progressively rotated to become parallel to the geotextile. Consequently, the beach began the same rotation, inducing a shoreline advance of 15m. After this period of adaptation, the system of bar/shoreline remained quite s...

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Impacts of Human Activities on Dynamic Coastal Processes

In this paper we present the first results of beach profile hindcasting with XBeach using recentl... more In this paper we present the first results of beach profile hindcasting with XBeach using recently measured coastal data acquired under storm conditions at eight European sites, including a comparison to model results obtained with off-the-shelf models. The results show consistently that the XBeach has skill in predicting the coastal profile, albeit that in most cases the erosion around the mean water line is overpredicted and the depositions at the lower beach face are overpredicted. The causes for this model effect are under active investigation but not resolved yet. Likely candidates are the modeling of onshore (asymmetry) transports which reduces the offshore transports due to undertow (currents) or the modeling of sediment motion in the swash zone.

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Investigation on the Capabilities of Low-Cost and Smartphone-Based Coastal Imagery for Deriving Coastal State Video Indicators: Applications on the Upper Mediterranean

Coastal Sediments 2019, May 1, 2019

This work deals with the implementation and operational use of lowcost and smartphone-based camer... more This work deals with the implementation and operational use of lowcost and smartphone-based camera system for the purpose of coastal video monitoring. Capability of such system for coastal remote sensing is described in this study. Particularly, a small network of ©Solarcam has been implemented in Corsica Island (France) for purposes of coastline evolution, sandbar(s) detections and to investigate the influence of the Posidonia banquettes on morphological evolution. A new coastal indicator derived from video observation is presented. Furthermore, the second part deals with the description and application of image semantic segmentation procedures, developed in order to regionalize the main morphologies framed by web-cams. Such techniques can be apply for a range of applications: from shoreline evolution, sandbar(s) detection, algae identification and development of a warning system.

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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 ... more 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 Rifa 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 Ria Formosa, the picture that emerges of inlet dynamics is essentially one of relative simplicity and predictability in the short-to medium-term.

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CARIB-COAST caribbean network for coastal risks related with climate change

International audienc

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

Mes travaux depuis 1998 ont portes sur l’hydrodynamique et la dynamique sedimentaire littorales p... more Mes travaux depuis 1998 ont portes sur l’hydrodynamique et la dynamique sedimentaire littorales par des approches d’experimentation in-situ reposant sur le suivi des evolution morphologiques, l’evaluation par tracages sedimentaires des flux sableux et la teledetection par video numerique permettant un suivi a haute frequence des reponses morhologiques, en particulier pendant les tempetes. Mes etudes ont porte sur des echelles spatiales et temporelles variees allant du transport instantanne a l’evolution pluri-annuelle. Je me suis particulierement interesse aux domaines d’embouchures tidales, lagunaires ou fluviatiles ou les interactions sont complexes et fortement nonlineaires. Un deuxieme sujet important de ma recherche concerne les barres d’avant-cote et les couplages barres-plages qui constituent egalement un challenge scientifique dans la mesure ou les modeles numeriques peinent encore a simuler les evolutions observees, notamment en raison du manque de donnees pendant les episo...

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