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High-resolution wave forecasts are of critical importance for coastal safety, hazard prevention, and energy transition. Examples that benefit from detailed information of coastal sea states range from the adaptation of coastal protection to beach goer and marine safety and even include the growing market of marine renewable energy. While regional and global wave forecasts exist, local high-resolution details are often not accessible due to the associated computational cost.In our work we use a neural network to apply a so-called super-resolution approach that can turn wave forecasts computed over coarse grids into substantially higher resolution at very low computation cost and with only little loss of overall quality. The idea is to train the neural network with pairs of coarse and fine-grid computations, so that later on wave computations over coarse grids can be converted into a higher resolution. While the amount of saved computation time varies with the level of resolution between coarse and fine grid, the super-resolution approach can be more than 50-times faster than a direct high-resolution computation and still provide good accuracy.Here we will present a case study on a 44-year hindcast of the French Basque coast, with which we trained and tested multiple networks. We will comment on the dependency of model performance on the amount of training data and the difficulties of an unstructured grid, compared to a structured one. More specifically, structured grids can be handled as regular images, which makes the adaptation of classical and powerful convolutional neural networks to the problem relatively easy. The application to irregular grids, however, is not trivial and requires different approaches like graph neural networks or multi-layer perceptrons. Lastly, we will compare the performance of a surrogate model, that is, a neural network that simply replaces completely a spectral wave model like SWAN, with our super-resolution approach, that uses coarse wave model computations as an input. We argue that both approaches are complementary and have their advantages and disadvantages in specific settings.

A wave resource characterisation is presented for the French Basque coastal region, with a specific focus on Bayonne nearshore area. The study is derived from a 10-year hindcast computation performed with a very high-resolution coastal implementation of a SWAN model. After a detailed validation of the model in intermediate and shallow water, the spatial, temporal, and spectral distributions of the local nearshore wave energy climate are characterized. Refraction over a local submarine canyon splits the coastal domain into two main regions with different general characteristics. In the southern Basque region, the spatial fluctuations of the wave resource increase drastically in shallow water. Variability nearshore was shown to be significantly higher than over the deeper part of the shelf. Noticeable hot-spots are found in the nearshore area around Bayonne, where the local wave resource substantially exceeds the outer shelf incident energy flux. Seasonal to hourly temporal fluctuations are also characterized at different nearshore locations and found to be very pronounced. The major wave resource variations found at reduced space-time scales highlight the strong influence of local small-scale bathymetry features in the Basque nearshore region.

International audience; This paper presents a multi-fluid Navier-Stokes modelling of the waves generated by two granular slides (subaerial and submarine) which were previously studied experimentally and a pure synthetic submarine case used for results interpretation. In the numerical model, air and water are considered as Newtonian fluids. The slide is modelled as a Newtonian fluid whose viscosity is adjusted to fit the experimental results. Once the viscosity is adjusted, the first and the second waves are shown to be accurately reproduced by the model even though the computed slide is slower. For the subaerial case, the viscosity value found is shown to be consistent with the granular µ(I) rheological law. The second part of this work focuses on the energy transfers between a slide and its generated waves. Energy balance is computed in each phase. The wave energy is evaluated in the wave propagation zone. Energy dissipation, kinematic and potential energies are taken into account in the computation of energy transfer ratio allowing for a better understanding of the phenomena. In light of these results, the wave train generation process is discussed as well as the importance of the slide dynamics in the wave generation stage. The amount of energy transferred to wave is not constant with time and the transfer rate depends strongly on the definition of this rate as well as the case considered. For instance, in the subaerial case simulated, the energy transferred to surface waves is 30 % of the energy transferred to water at the time the transfer stops, but this conversion rate is only equal to 4 % of the overall available potential slide energy at the end of the process. For the two submarine cases simulated, the corresponding values, equal in both cases, are 2 % and 1 %, respectively. The simulation results also show that the slide energy is transferred to the water in a short period of time at the beginning whatever the case considered. This observation may be related to the initial nil slide velocity (subaerial case) and the relatively large slope values considered (both cases). Nevertheless, the results illustrate the importance of accurate simulation of the slide dynamics within the wave generation process.

International audience; This paper presents a method to include damage at the initial stage of coastal flooding events definition and in return periods computation. The methodology is illustrated within a local study carried out in Biarritz Grande Plage, a meso-tidal, wave dominated beach located on the french basque coast in the south west of France. The work is based on two datasets covering the period 1949-2015 : a first one, consisting of observation and synthetic data on wave characteristics and water level, and a second one, gathering storm dates and related damage intensities obtained through investigations in the press and in archives. A statistical analysis was first carried out to find the best combination of source variables explaining the reported damages for the identified storms. Maximal, mean and accumulated values were calculated over storm duration, considering source and aggregated variables based on the empirical run-up formula or the wave energy flux. Most rules combining a wave parameter and water level are found to provide satisfactory damage prediction as soon as maxima variables are considered. Rules based on mean variables are less accurate and those based on accumulated variable values are not relevant. The best results are obtained with the wave energy flux and water level maxima over the storm duration. The ability of the rules to be used as generic event definition rules is then tested by performing a retrospective analysis on the whole dataset, checking their efficiency in detecting historical storms (i.e., with damages) without finding too many false positives. Most of the rules formerly studied, except the ones using wave period only as wave parameter, were able to correctly perform this task. Coastal flood event return periods (RP) were then calculated by applying three of the best rules identified previously. The rule using non simultaneous maxima of wave energy flux and water level gives encouraging results for the RP values. Nevertheless, the discrepancy still observed among the different rules calls for further work in this direction.

In the literature, OpenFOAM has been used to simulate landslide tsunamis, modeling the landslide as a solid or a two-phase flow. Here we present an approach using three phases (air, water and sediment) modeled as Newtonian fluids. This 3D model is validated against two benchmarks with deformable landslides: one subaerial (Viroulet et al. 2016) and one submarine (Grilli et al. 2017). These benchmarks are also run by a 2D depth-integrated model, AVALANCHE, recently used to reproduce the 2017 Karrat Fjord, Greenland and the 2018 Anak Krakatau, Indonesia events. Both models are able to reproduce either the water waves or the landslide behavior but not both at the same time.Considering OpenFOAM as a reference code, sensitivity studies on the slope angle, the landslide viscosity and the landslide initial submergence showed that AVALANCHE produces similar results for slope angles between 10 and 45°, for subaerial or close to the surface landslide and/or for low viscosity values. In the other cases (submarine landslides and higher viscosity values) results indicated that OpenFOAM should be preferred to a 2D depth-integrated model. References:Grilli, S., Shelby, M. & Kimmoun, O. (2017), ‘Modeling coastal tsunami hazard from submarine mass failures: effect of slide rheology, experimental validation, and case studies off the US East Coast’, Natural Hazards 86, 353-391.Viroulet, S., Sauret, A., Kimmoun, O. & Kharif, C. (2016), Tsunami waves generated by cliff collapse: comparison between experiments and triphasic simulations, in E. Pelinovsky & C. Kharif, eds, ‘Extreme Ocean Waves’, Springer International Publishing, Cham, pp. 173-190.

Tsunami waves are often very energetic and therefore pose a significant threat to coastal structures. However, most coastal defenses such as detached breakwaters are designed to protect ag...

International audience; Wave resource assessment is the first step toward the installation of a wave energy converter (WEC). To support initiatives for wave energy development in the southwest of France, a coastal wave database is built from a 44-year hindcast simulation with the spectral wave model SWAN (Simulating WAve Nearshore) run on a high-resolution unstructured grid. The simulation includes shallow-water processes such as refraction, shoaling, and breaking. The model is validated against a five-year coastal wave buoy recording. The study shows that most of the resource is provided by sea states with wave heights ranging from 2 to 5 m, with wave periods from 10 and 15 s, and coming from a very narrow angular sector. The long hindcast duration and the refined unstructured grid used for the simulation allow assessment of the spatiotemporal distribution of wave energy across the coastal area. On the one hand, large longshore variations of the resource caused by steep bathymetric gradients such as the Capbreton submarine canyon are underlined. On the other hand, the study highlights that no specific long-term trend can be extracted regarding the coastal wave energy resource evolution. The provided downscaled local wave resource information may be used to optimize the location and design of a future WEC that could be deployed in the region.

International audience; A coastal storm damage database covering 64 years was built based on press and archives investgations. Flooding of Biarritz La Grande Plage sea front and related damages were characterized with a three level index along with binary reliability indicator. Damages to breakwaters protecting Saint Jean de Luz bay were also documented. Building such a database appeared to be extremely time consuming and also implies some limitations mainly due to the heterogeneity and incompleteness of the data sources. 30 flooding events were reported for Biarritz among which the five most destructive ones were December 28-29, 1951, November 9-10, 2010 and January 4-7, February 1-2, March 3-5, 2014. This clearly shows the extreme character of winter 2014. \textcopyright Coastal Education and Research Foundation, Inc. 2018.

Larroque, B.; Arnould P.; Luthon F.; Poncet, P.A.; Rahali, A., and Abadie, S., 2018. In-situ measurements of wave impact pressure on a composite breakwater: preliminary results. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1086–1090. Coconut Creek (Florida), ISSN 0749-0208.A detached horizontally composite breakwater protecting the Saint Jean de Luz bay (French Basque Coast, Bay of Biscay, France) has been equipped with two pressure sensors displayed vertically onto the vertical wall. The two sensors recorded wave impact pressure in ten minute burst each hour at 10 kHz. In parallel, incoming waves were also recorded about 1 km off the structure with a directional wave buoy giving access to spectral wave parameters as well as raw data. Finally water level, wind magnitude and direction were also acquired. The whole dataset covers winter 2015–2016 from January to March.The results show first the statistical distribution of the measured parameters confirming preceding similar studies in which significantly lower impact pressure values were obtained compared to physical experiments or numerical simulations. A linear multivariate model has then been adjusted showing the overwhelming influence of wave heights to explain maximum pressure variability, followed by water level. Nevertheless this result has still to be confirmed for data reduced to impulsive impacts. Finally, interesting events supposedly corresponding to, or approaching flip-through impact type, have been identified and need further investigations.

Two approaches are proposed to simulate tsunamis generated by granular landslides: a depth-averaged model, AVALANCHE, and laminar Navier–Stokes simulations using the OpenFOAM model. Both models are validated against two 2D benchmarks, a subaerial and a submerged one involving a triangle initial slide shape. In both models, the landslide is defined as a viscous fluid flowing downslope. Except in the first instants, both models can reproduce either the landslide behavior or the generated first water waves but cannot reproduce simultaneously both the landslide and the water surface. There is an overlap in the optimal viscosity range between both models. Sensitivity studies are carried out by varying the slope angle and the landslide submergence for the subaerial benchmark. The largest waves are obtained for initial landslide position close to the free surface. The height of the generated waves increases linearly with the slope angle and the landslide Reynolds number in the depth-averaged model. The relationships are more complex in the Navier–Stokes model. For low slide Reynolds numbers and with an initial slide close to the free surface, both models produce similar waves. Nine additional cases are performed with a k − e turbulence closure model and varying the submergence and the slope angle.

International audience; The storm impact scale of Sallenger (J Coast Res 890-895, 2000) was tested on a partially engineered beach. This scale is supposed to provide a convenient tool for coastal managers to categorize the storm impact at the shore. It is based on the relation between the elevation of storm wave runup and the elevation of a critical geomorphic or man-made structures in the present study. Two different approaches were tested to estimate the elevation of extreme storm wave runup: (1) a parametric model based on offshore wave conditions and local beach slope and (2) the XBeach process-based model that solves implicitly the runup. The study shows comparisons between impact regimes computed with the two methods and those derived from video observations acquired during 2 weeks while the site was battered by three consecutive storms. Storms scenario including wave conditions with higher return periods and different tidal range were also investigated. The advantages and disadvantages of the two methods used to compute extreme water level are then compared, and guidelines for the development of early warning system are drawn.

International audience; On the evening of December 22, 2018, the coasts of the Sunda Strait, Indonesia, were hit by a tsunami generated by the collapse of a part of the Anak Krakatau volcano. Hundreds of people were killed, thousands were injured and displaced. This paper presents a preliminary modeling of the volcano flank collapse and the tsunami generated based on the results of a 2D depth-averaged coupled model involving a granular rheology and a Coulomb friction for the slide description and dispersive effects for the water flow part. With a reconstructed total volume (subaerial and submarine) of the landslide of 150 million m 3 inferred from pre and post-collapse satellite and aerial images , the comparison of the simulated water waves with the observations (tide gauges located all around the strait, photographs and field surveys) is satisfactory. Due to the lack of information for the submarine part of the landslide, 2 Alexandre Paris et al. the reconstructed submarine slope is assumed to be approximately constant. A significant time delay on the results and particularly in the Bandar Lampung Bay could be attributed to imprecisions of bathymetric data. The sensitivity to the basal friction and to dispersive effects is analyzed through numerical tests. Results show that the influence of the basal friction angle on the simulated wave heights decreases with distance and that a value of 2°gives consistent results with the observations. The dispersive effects are assessed by comparing water waves simulated by a shallow water model and a Boussinesq model. Simulations with frequency dispersion produce longer wave periods and smaller wave amplitudes in the Sunda Strait and particularly in deep waters.

d'Amico, D.; Larroque, B.; Luthon, F.; Poncet, P.A., and Abadie, S., 2020. Continuous measurement and automatic processing of in-situ wave impact pressure data. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 214-219. Coconut Creek (Florida), ISSN 0749-0208.Although wave impact has been extensively studied in laboratories, field studies are comparatively rare. However, as real wave impacts are influenced by numerous environmental factors, complementing physical studies with in-situ data is necessary to better understand the processes at stake and provide reliable tools for coastal engineers. One of the main reasons for the lack of field data is the extreme conditions usually met on site. Nowadays, technology allows to set up stations able to resist those conditions and record data over long periods. In this context, the so-called Artha breakwater, in the French Basque coast, was equipped with an in-situ laboratory to record wave impact pressures. This station enables to collect long term wave impact pressure data therefore covering any weather conditions. In the present paper, the use of computer engineering based methods to process the large amount of wave impact data is described. It involves signal pre-processing, impact automatic segmentation, automatic computation of impact parameters, and artificial intelligence to classify the impacts. Impact automatic segmentation allows to have a big database of impacts available. This database has been used to make a first classification of the strongest impacts. The classification was performed thanks to the parameters automatically computed for each impact. As preliminary results for the classification, several wave impact pressure classes have been established. The approach is encouraging since the obtained results can be compared with the existing laboratory classification. However, the results can still be improved by computing other impact parameters and considering all impacts.

In this paper, we present a new source assessment of the La Palma collapse scenario previously described and studied in Abadie et al. (2012). Three scenarios (i.e., slide volumes of 20, 40 and 80 km3) are considered, from the initiation of the slide to the water waves generation, using THETIS, a 3D Navier–Stokes model. The slide is considered as a Newtonian fluid whose viscosity is adjusted to approximate a granular behavior. After 5 minutes of propagation with THETIS, the generated water wave is transferred into FUNWAVE-TVD for 15 minutes of Boussinesq model simulation. Then, four different depth-averaged codes are used to propagate the wave to the Guadeloupe area, Europe and French coasts. Finally, the wave impact in terms of run-up is evaluated through direct computations in specific areas or using theoretical formulas. Although the wave source appears reduced due to the rheology used compared to former works, the wave impact is still significant for the maximum slide volume considered on surrounding islands and coasts, as well as on remote most exposed coasts such as Guadeloupe. In Europe and in France, the wave impact is moderate (for specific areas in Spain and Portugal) to weak (Atlantic French coast). The comparison between the different wave models in overlapping computational regions shows an overall agreement in terms of first wave amplitude and time of arrival, but differences appear in the trailing waves.

Wave impact has been identified as the main source of failure for coastal breakwater. While wave transformation over low to mild sloping beaches have been widely studied, shoaling, breaking, reflection and dissipation over steep and very rough slopes are much less documented, especially in situ. The Artha breakwater, south-west of France, is a composite breakwater sitting on top of a complex, steep bathymetry. The results of in-situ measurement of wave transformation in the block armor of this structure are presented here.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/T8IINpfcPUM

In the framework of the French research project TANDEM dedicated to tsunami modelling, a series of benchmarks has been set up, addressing the various stages of a tsunami event: generation, propagation, run-up and inundation. We present here the results of five codes, involving both depth-averaged Boussinesq and fully 3D Navier-Stokes equations, aimed at being applicable to tsunami modelling. The codes are evaluated on a flow involving propagation, run-up, overtopping and reflection of the waves on two-dimensional reefs, and compared with the experimental data produced from a set of laboratory experiments carried out at the O.H. Hinsdale Wave Research Laboratory, Oregon State University (OSU, see Roeber et al., 2010 and Roeber and Chung, 2012).

Appartenant a un ordre religieux meconnu, les chanoines premontres ou norbertins ont connu une implantation importante dans le sud de la France et le nord de l’Espagne, avec une trentaine de monasteres et prieures des les annees 1135. Outre l’etablissement de ces maisons, dont certaines suivent les chemins de Saint-Jacques, on peut observer les mouvements de ces religieux a partir de sources originales : les necrologes de trois monasteres permettent d’apprehender le va-et-vient des chanoines et de leurs rouleaux des morts aux XIIe et XIIIe siecles ; la mise en place d’une circonscription religieuse, la circarie de Gascogne, imposa des visites regulieres de tous les membres ; enfin une reconstitution de la carriere de quelques ecclesiastiques eclaire egalement sur les deplacements de ces chanoines bien peu cloitres.

International audience; Port of Bayonne, located in SW France, is a channel harbor situated near the river mouth of the Adour. Long-period oscillations have repeatedly caused snapping of mooring lines of berthed ships and have led to wave resonances in an adjacent marina (seiche). To investigate mechanisms for generation of theses oscillations, a field campaign was carried out during a one-year return-period storm (Hs = 6 m and Tp = 15 s): four pressure sensors were deployed inside the port. To complement the data and to better understand the governing processes that lead to the wave transformations in Port of Bayonne, the storm event was computed with the Boussinesq-type model, BOSZ. The data confirm the model results, which show generation of long infragravity (IG) waves by the incident swell around the harbor entrance and free propagation of these waves without amplification over far distances inside Port of Bayonne. Excited by these long waves, resonance oscillations are only noticeable in a small enclosed marina. Though the IG-waves are not causing substantial changes to the water level along the harbor channel, they are suspected to excite the ships' eigen modes, which consequently results in mooring problems.

International audience; Cet article propose une étude du déplacement d'un caisson soumis des impacts de type flip-through plus ou moins verticaux. A cet effet, on considère les résultats de simulations numériques réalisées récemment auxquels on applique un modèle simplifié de mouvement. Les résultats montrent un déplacement de caisson assez peu sensible aux variations d'angles associées aux différents impacts considérés. La discussion de l'article propose des pistes d'explication de ce phénomène.

International audience; Tsunamis are among the most deadliest threat of coastal areas and a large number of tropical island are exposed because of their proximity to potential tsunami sources. However, far field sources may represent a threat and thus can not totally be eluded. In the framework of the project C3AF which studies the consequences of climate changes over the French West Indies, we used the numerical model SCHISM (ZHANG et al., 2016) to simulate several potential tsunamis propagation as well as their impacts over the Guadeloupe Island (French West Indies). In this study, we present the simulation of a potential tsunami scenario based on the collapse of the Cumbre Viera volcano, in the Canary Islands (ABADIE et al., 2012) to assess the potential threat of the Guadeloupe archipelago. Several scenario have been simulated and time arrival, wave heights and potential inundation are investigated.

International audience; Le port de Bayonne, situé proche de l'embouchure de l'Adour, rencontre fréquemment des problèmes de tenu à quai des navires en période de tempête. Afin de comprendre l'origine de l'agitation du port, une campagne de mesures, composée d'un houlographe mouillé à 50 m de fond et de trois capteurs de pression déployés dans le port, est réalisée durant un épisode de tempête de période de retour de 1 an (Hs=5 m et Tp=16 s). Cet événement est également simulé avec un modèle numérique basé sur la résolution des équations de Boussinesq (BOSZ) afin de comprendre l'origine du forçage des oscillations mesurées dans le port. L'étude montre que les deux digues situées à l'embouchure de l'Adour assurent efficacement la protection du port contre la houle incidente en provoquant un amortissement de Hs de 85 % dans la bande de périodes des vagues courtes (5-25 s). L'agitation du plan d'eau est majoritairement contrôlée par les ondes infra-gravitaires (IG). En période de tempête des valeurs de Hs de 0,70 m dont 0,65 m dans les IG (30- 300 s) ont été mesurées à 1,4 km en amont du fleuve. Un dépôt sous-marin de dragage, situé entre 2,5 et 3,5 km des plages, provoque la levée des vagues et une augmentation de Hs de l'ordre de 20 %. Ce phénomène semble favoriser la génération d'ondes IG par interaction non linéaire entre les vagues courtes. En pénétrant dans le port, les ondes IG se propagent librement dans le fleuve et se dissipent progressivement par frottement. Cependant, elles conservent suffisamment d'énergie pour, d'une part, provoquer la résonance d'un port de plaisance situé à 1,4 km en amont de l'embouchure, et d'autre part probablement exciter les navires amarrés dont les périodes propres sont dans la bande IG.

Arnoux, F.,; Abadie, S.; Bertin, X.; Kojadinovic, I. 2018. A database to study storm impact statistics along the Basque Coast. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 806–810. Coconut Creek (Florida), ISSN 0749-0208. A database aiming at studying storm impact on the French Basque coast and covering the period 1949–2015 is presented in this paper Wave and water level data originate from synthetic or numerical hindcast complemented by buoys or tide gauge measurements. A statistical validation of each variable and, when needed, a distribution correction of biased variables was carried out. The constructed database will be used in confrontation with an historical review of past storm damages to try to find a statistical link between the two though a damage function.

ACT; International audience

International audience; Une base de données de niveau de dommages consécutif à la submersion couvrant les 60 dernières années et focalisée sur la Grande Plage de Biarritz a été récemment élaborée. Cette base repose sur l'analyse d'archives et de documents de presse locaux. Parallèlement, une base de données de variables d'aléas couvrant la même période a également été constituée. Elle utilise des simulations numériques pour les vagues et une analyse harmonique pour les niveaux d'eau, validées par les observations disponibles sur site. Dans le présent article, nous détaillons l'analyse du lien statistique existant entre les deux bases de données. L'objectif est de trouver quelles variables d'aléa ou combinaison de variables expliquent le mieux l'occurrence de la submersion de la Grande Plage et la survenue de dommage. Les résultats préliminaires montrent que le couple flux maximum d'énergie des vagues et niveau d'eau maximum durant l'événement expliquent très bien les dommages répertoriés sur cette plage spécifique.

International audience; This paper focuses on the analysis of the flow field and pressures generated by flip-through impacts on a vertical breakwater. A multiphase Navier\textendashStokes model is used as a numerical wave tank to analyse the influence of interface steepness on pressures and forces generated in the real configuration of a breakwater caisson. The numerical simulations consist in a solitary wave propagating over a reef and impacting a caisson breakwater placed over a porous rubble mound. After careful validation, the model allows us to make an in-depth investigation of three flip-through impacts with different incidence angles at impact (least steep, medium steep and steepest flip-through impact). The main characteristics of flip-through impacts are identified for the three cases: no air entrapped, presence of an ascending jet with large accelerations and large pressures. The focusing phase before impact introduced by Lugni et al. [30] is only observed for the steepest case. The understanding of the process of this extreme impact is improved by analysing velocities and accelerations for the three cases. Pressures and forces are shown to be directly linked to the flip-through impact inclination at impact. The flow field and pressure variations inside the porous rubble mound are also analysed in this study.

International audience; Two validation cases of the Navier-Stokes VOF (Volume-Of-Fluid) model THETIS are presented in this study: uplift pressures on a rubble mound due to wave impacts and flip-through impacts on a vertical wall. The first validation case demonstrates the ability of the model to reproduce uplift pressure overall variations due to wave impacts inside a porous rubble mound. The presence of a marked pressure peak in the porous medium is also stressed. Then, the flip-through phenomenon is modeled using the THETIS model. These results are compared with other numerical data computed with a potential model. The Navier-Stokes simulations which take into account water and air, underestimate pressures along the wall. The wave interface is modified by the presence of air, which is not considered in the potential model, and this seems to be enough to generate such pressure differences. A better agreement between the two models is obtained while lowering the surrounding gas density to almost zero. \textcopyright Société Hydrotechnique de France, 2017.

International audience; This work presents an original numerical model for a free surface flow interacting with a spring-block system. The formulation is based on the fictitious domain approach and a penalty method on viscosity to describe the rigid solid motion. The incompressible Navier\textendashStokes equations are solved in the whole domain and the free surface and the body contour are captured using a volume of fluid method. To describe the rigid body motion, a single degree of freedom model, able to represent translation or rotation, is embedded in the code. The discrete equations are written in a well-known finite volume framework over Cartesian grids. In such a context, the external spring and damping forces are represented as body forces in the solid region. The proposed strategy is tested in a sloshing damping system. The numerical results are compared with experimental data obtained within the present study. Finally, the method is used to simulate a wave energy converter system as an illustration of a rotational case. \textcopyright 2017 International Association for Hydro-Environment Engineering and Research.

De Santiago, I., Morichon, D., Abadie, S., Castelle, B., Liria, P. and Epelde, I., 2013. Video observation of the morphodynamics of nearshore sandbars on a partially engineered embayed beach. Embayed beaches are prevalent environments along the northern Spanish coastline. The present work analyses the temporal and spatial variability of nearshore sandbars on the pocket beach of Zarautz using daily video observations over 2 years. This partially urbanized beach can be divided into two well defined distinct areas: a natural section backed by a sand dune system to the East and an engineered section with rigid seawalls to the West. The objective of the present work is to evaluate if the engineered and natural sections of the beach present different morphological behaviors. The video image analysis was performed in two steps: First, sand bars were characterized visually and classified following standard classification schemes. Then, the outer sand bar migration was measured using automatic bar detecti...

The collapse of a 2D bore propagating shoreward on a sloping beach and the subsequent run-up from the shoreline and run-down are simulated using a Reynolds Averaged Navier–Stokes (RANS) model based on a Volume of Fluid (VOF) method. The results are compared with experimental results. The bore collapse phenomenon is first studied and the transition between bore collapse and run-up is characterized. Numerical results indicate that the bore collapse phenomenon is not completed at the shoreline. The transition is further upslope and the energy at the transition includes a significant part of potential energy unlike that predicted by the classical theory of Whitham. The swash flow is investigated, showing the dissymmetry between run-up and run-down. Taking into account the modeling of turbulence slightly reduces the run-up height and allows recovering the value experimentally recorded. The bottom shear stress variations were computed from the results of numerical simulations. The maximum bottom shear stress is at any time found in the vicinity of the bore head. It is maximum at the transition between bore collapse and run-up flow and decreases while the run-up flow climbs on the beach.

This work reports on the application and experimental validation, for idealized geometries, of a multiple-fluid Navier–Stokes model of waves generated by rigid and deforming slides, with the purpose of improving predictive simulations of landslide tsunamis. In such simulations, the computational domain is divided into water, air, and slide regions, all treated as Newtonian fluids. For rigid slides, a penalty method allows for parts of the fluid domain to behave as a solid. With the latter method, the coupling between a rigid slide and water is implicitly computed (rather than specifying a known slide kinematics). Two different Volume of Fluid algorithms are tested for tracking interfaces between actual fluid regions. The simulated kinematics of a semi-elliptical block, moving down a water covered plane slope, is first compared to an earlier analytical solution. Results for the vertical fall of a rectangular block in water are then compared to earlier experimental results. Finally, more realistic simulations of two- and three-dimensional wedges sliding down an incline are compared to earlier experiments. Overall, in all cases, solid block velocities and free surface deformations are accurately reproduced in the model, provided that a sufficiently resolved discretization is used. The potential of the model is then illustrated on more complex scenarios involving waves caused by multi-block or deformable slides.

Les glissements de terrain induits par des instabilites de pente sont frequents dans les reservoirs d’eau mais peuvent egalement se produire en zones cotieres. Cet article presente les resultats d’une etude portant sur l’influence de la forme et de la deformation de ce type de glissement sur les caracteristiques des vagues generees et les hauteurs d’inondation associees. L’approche repose sur un canal numerique base sur un solveur Navier-Stokes VOF. Le glissement est simule par un fluide newtonien. Les resultats montrent que la forme initiale du glissement a peu d’effet sur les caracteristiques finales des vagues mais influence l’inondation. En revanche, dans la gamme de glissements simules, l’effet de la deformabilite est determinant sur l’ensemble des parametres de risque.

Resume : Les leves bathymetriques a haute frequence en zone de surf sont delicats et dangereux a cause du deferlement des vagues. C'est pourtant dans ces zones energetiques intenses que les evolutions morphologiques sont particulierement utiles a connaitre. Une technique de mesure locale de l’evolution du niveau du fond utilisable dans la zone de deferlement a ete developpee. Il s’agit d’une methode basee sur des mesures de resistivite et nous presentons ici les resultats preliminaires d’une campagne de mesure in situ de 30 jours. Les champs d’application auxiliaires de cette methode sont multiples. Nous presentons comment ils peuvent etre etendu au suivi du niveau de la surface libre dans la zone de deferlement et dans certaines conditions, donner des informations sur les variations de resistivite dans le sol sous l’action des vagues.

Significant river discharges are usually associated with episodic rainstorms, leading to turbid storm water plumes clearly visible in the vicinity of river mouths. The composition of the suspended particulate matter transported by these plumes can alter the quality of coastal waters. The survey of marine coastal zones has thus become a major issue for water managers. For several decades, satellite imagery has allowed the daily monitoring of river plumes behavior over large distances. Nevertheless, it fails to provide data on their hourly evolution, which is important to operationally manage coastal waters in tourist areas. This study investigates the possibility of using the Argus video system to continuously survey the evolution of a storm water plume impact region. The system was installed in Anglet, at the Adour River mouth (southwest of France), in February 2005. An image-processing technique, based on pixel intensity clustering, is proposed to delineate river plume fronts along beaches from ...

La generation de vagues par des glissements de terrain est etudiee a l'aide d'un modele base sur les equations de Navier-Stokes et un suivi d'interface VOF. L'originalite de l'etude repose sur la prise en compte implicite du couplage glissement/fluide. Le modele est valide dans un premier temps, dans le cas de generation d'un soliton par la chute d'un bloc rigide a l'extremite d'un canal. Une etude numerique de l'influence du caractere deformable du glissement est ensuite proposee. Ce travail met en evidence l'importance et la complexite du role de cette deformation sur les caracteristiques des vagues generees. Il convient donc de prendre en compte de maniere plus fine la rheologie du glissement dans le processus de prediction des tsunamis.

Anglet beach, located in the south of the French Atlantic coast, has been experiencing severe erosion for several decades, whereas recurrent dredging has been necessary to fight against the shoaling of the mouth of the Adour River. The channel entrance is protected from the very energetic wave climate by a main jetty, the effect of which on the system appears to be crucial. In this paper, we study the relationship between the two systems in terms of sedimentary exchanges. First, we determine the time history of volume of subtidal beach sand with a bathymetry dataset spanning 24 years. This analysis highlights continuous and large erosion affecting the subtidal part of Anglet beach. This phenomenon had been masked until 1990 thanks to dredged sand releases. However, after that date, the drastic reduction of artificial sediment intakes led to a drop in the sand volume. Numerical modeling is used to study the flow pattern around the mouth of the river. Different wave scenarios are simulated with the...

International audience; This work addresses the problem of numerical simulation of the dynamic loads generated during a dry dam break flow impact on a wall. The numerical model used is the multi-fluid Navier-Stokes Volume Of Fluid (VOF) model THETIS. The results are compared with two experiments allowing pressure evolution validation at two relative positions on the wall. A first analysis of the results shows the large spatial and temporal variability of the pressure field after impact, highlighting the need for extreme care when performing measurements. When using first a free-slip boundary conditions on the bottom, the computed pressure peaks are found to behave differently depending on the distance to the stagnation point. Above a certain position, which is determined in the paper, computed peak pressures are stable with resolution while under this position, a divergent behavior is observed. This divergence is attributed to the shape of the bore tip which is poorly resolved with our model when a free-slip condition is used. This is confirmed by showing that starting from an identical free surface profile right before impact, the pressure peaks are convergent. The pressure peak instability problem can be solved by resolving the boundary layer structure with a suitable model (in our paper a v2-f RANS model) but this requires much more CPU resources. \textcopyright 2016 Elsevier Ltd.

International audience; La maison des abbés de La Casedieu (commune de Marciac, Gers) est à la fois un exemple de maison de seigneur parier dans une bastide et un exemple de maison d'abbaye dans une petite ville. L'étude croisée des données archéologiques et historiques permet de reconstituer en partie l'architecture et l'histoire de ce type inédit d'habitat urbain dans le sud-ouest de la France. Article publié dans le Bulletin monument 174-2 (2016).

COM; International audience

Le concept de dependance ne peut pas se reduire aux seules conduites toxicomaniaques. En effet l’etat de dependance doit etre considere comme pathologique, des lors que l’utilisation de cette conduite, repetitive et compulsive, apparait quasi systematique dans la gestion des excitations de l’appareil psychique. Dans le cas de la dependance sportive ou bigorexie, nous verrons, au moins, deux geneses distinctes de tels comportements : le remplissage d’un vide affectif et l’utilisation de la pratique physique en tant que voie comportementale de l’economie psychique du sujet, recours particuliers aux procedes autocalmants.

The Aquitaine coast, the southern part of the French Atlantic coast, is exposed to very energetic waves, inducing large sediment transport rates and shoreline changes. Local wave characteristics are, however, not accurately defined. Neither is the longshore drift along the shore. In this paper, statistical parameters of directional waves are determined by using outputs over 8 years from numerical model WAVEWATCH III. Wave statistics obtained point out a very weak variability of peak directions, almost all events coming from the same 300° direction, highly energetic extreme events and a predominance of swells over wind sea states. Representative sea states are calculated using a classification process. They are set as boundary conditions for the numerical model SWAN to compute the wave parameters along the breaking line and the corresponding longshore drift with the Kamphuis formula. The net annual longshore drift is assessed by taking into account the occurrence of the wave classes. Results show a reversal of the longshore current at the town of Capbreton. To the north, the current is directed southwards while it is northwards but very weak to the south. Locally, the pattern is reversed due to the influence of the submarine canyon of Capbreton. This new result is supported by in situ current measurements carried out along the shore. The annual average amount of sediment transported longshore is about 40,000 m3/year to the north of Capbreton and only 1000 m3/year to the south. However, along this latter area, the drift shows larger variations than in the north. Energetic swells account for more than two-thirds of the net annual longshore drift while they only occur 25% of the year. Moderately energetic swells and sea states with higher steepness, though more frequent, contribute less to the total drift. Around the town of Capbreton, results are dependent on the frequency spectrum set at the boundary of the numerical model, highlighting the complex role played by the submarine canyon and suggesting the need for further investigations in that area.

International audience; The scope of this work is to present and discuss the results obtained from simulating three-dimensional plunging breaking waves by solving the Navier-Stokes equations, in air and water, coupled with a dynamic subgrid scale turbulence model (Large Eddy Simulation, LES). An original numerical tool is used for the complete description of the plunging breaking processes including overturning, splash-up and the occurrence of air entrainment. The first part of the paper is devoted to the presentation and the validation of the numerical models and methods. Initial 3D conditions corresponding to unstable periodic sinusoidal waves of large amplitudes in periodic domains are then used to study further the ability of the numerical model to describe accurately the air entrainment occurring when waves break. The numerical results highlight the major role of this phenomenon in the energy dissipation process, through a high level of turbulence generation. The numerical model represents a substantial improvement in the numerical modelling of breaking waves since it includes the air entrainment process neglected in most previous existing models.

Resume Une analyse des parametres statistiques de la houle pour la zone cotiere sud-aquitaine a ete realisee par comparaison de deux jeux de donnees : une mesure locale sur une periode courte et des resultats de simulation du modele Wavewatch III sur 6 ans et 9 mois. On montre qu'il existe une tres bonne correlation entre les hauteurs significatives ( H s ) issues respectivement de la mesure et des simulations. La correlation pour les periodes pic ( T p ) et les directions de pic ( D p ) est moins bonne, du fait respectivement du caractere intrinsequement instable du parametre T p et de la distribution particulierement etroite de D p . Le traitement statistique des sorties du modele ajuste sur la mesure permet de donner une evaluation des parametres statistiques de la houle dans cette zone. Le lien entre les trois parametres ( H s , T p , D p ) est enfin analyse sous la forme d'une classification des etats de mer. Cette derniere classification montre la predominance des houles, en grande majorite d'une direction avoisinant les 300°, sur les mers du vent. Pour citer cet article : S. Abadie et al., C. R. Geoscience 337 (2005).

In their pioneering work, Ward and Day suggested that a large scale flank collapse of the Cumbre Vieja Volcano (CVV) on La Palma (Canary Islands) could trigger a mega-tsunami throughout the North Atlantic Ocean basin, causing major coastal impact in the far-field. While more recent studies indicate that near-field waves from such a collapse would be more moderate than originally predicted by Ward and Day [Lovholt et al. (J Geophy Res 113:C09026, 2008); Abadie et al. (J Geophy Res 117:C05030, 2012)], these would still be formidable and devastate the Canary Island, while causing major impact in the far-field at many locations along the western European, African, and the US east coasts. Abadie et al. (J Geophy Res 117:C05030, 2012) simulated tsunami generation and near-field tsunami impact from a few CVV subaerial slide scenarios, with volumes ranging from 20 to 450 km $$^3$$ ; the latter representing the most extreme scenario proposed by Ward and Day. They modeled tsunami generation, i.e., the tsunami source, using THETIS, a 3D Navier-Stokes (NS) multi-fluid VOF model, in which slide material was considered as a nearly inviscid heavy fluid. Near-field tsunami impact was then simulated for each source using FUNWAVE-TVD, a dispersive and fully nonlinear long wave Boussinesq model [Shi et al. (Ocean Modell 43–44:36–51, 2012); Kirby et al. (Ocean Modeling, 62:39–55, 2013)]. Here, using FUNWAVE-TVD for a series of nested grids of increasingly fine resolution, we model and analyze far-field tsunami impact from two of Abadie et al.’s extreme CVV flank collapse scenarios: (i) that deemed the most “credible worst case scenario” based on a slope stability analysis, with a 80 km $$^3$$ volume; and (ii) the most extreme scenario, similar to Ward and Day’s, with a 450 km $$^3$$ volume. Simulations are performed using a one-way coupling scheme in between two given levels of nested grids. Based on the simulation results, the overall tsunami impact is first assessed in terms of maximum surface elevation computed along the western European and African, and US east coasts (USEC). Strong wave elevation decay is predicted over the wide USEC shelf, which is shown to be essentially due to bottom friction effects. We then show more detailed results for the USEC, which is the object of high-resolution tsunami inundation mapping under the auspices of the US National Tsunami Hazard Mitigation Program. In this context, we compare the maximum surface elevation predicted along the coastline for each CVV scenario and show that, besides the initial directionality of the sources, coastal impact is mostly controlled by focusing/defocusing effects resulting from the shelf bathymetric features. A simplified ray-tracing analysis confirms this controlling effect of the wide USEC shelf for incident long waves. Finally, we perform high-resolution (10 m) inundation mapping for the most extreme CVV scenario and show results at one of the most vulnerable and exposed communities in the mid-Atlantic US states, in and around Ocean City, Maryland. Such maps are being generated for all exposed areas of the USEC, to be used in tsunami hazard assessment and mitigation work.

International audience; Ce travail présente une méthode numérique originale pour l'interaction fluide/structure basée uniquement sur la simulation numérique des équations de Navier-Stokes avec un suivi d'interface de type VOF. À l'aide d'une phase fluide de viscosité infinie, on cherche à simuler une structure solide indéformable à un seul degré de liberté en translation ou en rotation, et ce, de manière totalement implicite. Une force de rappel (proportionnelle au déplacement) ainsi qu'un amortissement (proportionnel à la vitesse de déplacement) peuvent être ajoutés sous la forme d'une force volumique dans la phase "solide". Des résultats préliminaires obtenus à l'aide de cette méthode sont présentés dans cet article.