A NUMERICAL STUDY OF EXTREME WAVE RUNUP BEHAVIOR: SPECTRAL AND STATISTICAL ANALYSIS

International audienceA numerical study using SWASH model is realized on a multi-barred beach in order to explore spectral and statistical behavior of wave runup caused by moderate to extreme offshore wave conditions. Numerical experiments based on bathymetric characteristics, wave climate and tidal level of the Aquitanian coast, are compared to collected field data from the bibliography and derivate parametric models. Correlations between runup and several environmental parameters are estimated and discussed and a hybrid model (based on observations and simulated results) is proposed. We analyse the longshore spatial variability of incident and infragravity swash heights and R2%, in order to identify hot spot of runup related to the near shore morphology. Depending on wave conditions and tidal level, local positive anomaly of R2% varies between 10 to 36 % and are in average 22% higher than longshore mean values at high tide

Approche intégrée et opérationnelle du risque de submersion marine sur une commune littorale

International audienceDans un contexte de remontée du niveau de la mer liée au réchauffement climatique, la problématique du risque de submersion est amenée à devenir centrale pour la gestion des côtes basses dans les décennies à venir. Le programme de recherche CRISSIS lancé début 2015 pour deux ans et financé par le CSFRS a pour objectif de proposer, à travers une démarche pluridisciplinaire associant géographes, modélisateurs, géomaticiens et spécialistes de la gestion des risques et des crises, une approche intégrée et opérationnelle du risque submersion.La démarche suivie intègre les quatre dimensions du risque, depuis l'analyse de l'aléa, des enjeux et de leur vulnérabilité, à celle dela perception et de la représentation du risque par les populations, jusqu'à la gestion de la crise

The Application of X-Band Radar for Characterisation of Nearshore Dynamics on a Mixed Sand and Gravel Beach

Remote sensing using X-band radar allows the estimation of wave parameters, near surface currents and the underlying bathymetry. This paper explores the use of radar to derive nearshore bathymetry at a complex site, at Thorpeness in Suffolk, UK. The site has a history of sporadic and focused erosion events along the beach frontage and as part of the X-Com project (X-band Radar and Evidence-Based Coastal Management Decisions) a radar system was deployed with the aim of further understanding the complex nearshore sediment processes influencing erosion. Initially, the bathymetric variation at the site is quantified through analysis of current and historic multibeam surveys. These indicate depth changes approaching 3 m. Subsequently, validation of the radar data against concurrent multibeam survey data has been undertaken. Results show that the radar derived bathymetry has a precision of ±1m at the site, with the largest errors being associated with areas of more complex bathymetry and where wave data quality was less suitable for analysis by the X-band radar bathymetry algorithms. It is concluded that although the accuracy of radar-derived bathymetry is lower than traditional multibeam survey, the low cost for high temporal coverage can be utilised for long-term monitoring of coastal sites where a cost-effective means of quantifying large-scale bathymetric changes is required

FOREDUNE GUIDED REMOBILIZATION EXPERIMENTS ALONG THE SOUTHWEST COAST OF FRANCE

This contribution presents the response of experimental management methods implemented along 2 km stretch of the southwest coast of France with the objective to restore aeolian dynamics and foredune mobility to promote quasi alongshore-uniform landward foredune migration. The analysis based on eight airborne LiDAR campaigns and several morphometric indicators shows that the alongshore and temporal variability of foredune evolution depends on natural dynamics and contrasted managed strategies. These experiments offer new perspectives and guidelines for coastal dune managers in areas where chronic erosion threatens fixed dune systems

Observations in situ des états de mer depuis l'embouchure jusqu'à l'intérieur du Bassin d'Arcachon : mers de vent, houles et ondes infragravitaires

Les embouchures tidales sont des environnements très dynamiques soumises à la fois aux forçages associés aux vagues, aux courants de marée et à l'hydrologie continentale. L'association de ces dynamiques rend la compréhension fine des processus hydrosédimentaires et l'expression des aléas érosion ou submersion particulièrement complexes. Or, et de surcroît en conditions énergétiques lors de la période hivernale, il existe peu de données hydrodynamiques in situ du fait des complexités logistiques liées à l'étendue, à l'accessibilité, à la rapidité et l'ampleur des évolutions morphosédimentaires. Cette contribution détaille les données acquises dans le cadre du projet ARCADE, lors de deux campagnes de mesures long terme réalisées pendant les hivers 2021 et 2022. Les données de vagues, de courants et de marée ont été acquises de manière simultanée depuis le large jusqu'à l'intérieur du Bassin d'Arcachon. Ces jeux de données permettent d'améliorer les connaissances sur la complexité des processus associés à la propagation des vagues et leurs transformations du large vers l'intérieur de la lagune. Un effort particulier est mis ici sur la caractérisation des ondes infragravitaires (ondes longues allant de plusieurs dizaines de secondes à plusieurs minutes) depuis l'embouchure jusqu'au fond du Bassin et du clapot (ondes courtes générées localement dont les longueurs d'ondes sont inférieures à 4 s) dans le bassin lors de différentes conditions de forçage de vent, de marée et de houle au large

Wave Set-up and Run-up Variability on a Complex Barred Beach During Highly Dissipative Storm Conditions

International audienceThis study assessed the ability of the SWASH model to reproduce wave set-up and run-up on complex realistic 3D morphology during highly dissipative stormy conditions, based on the most energetic field data set reported in the bibliography (ECORS-Truc Vert’08 beach experiment). Several approaches (1D and 2D) and forcing methods (spectral and parametric) were applied. For the three days of high-energy conditions caused by the Johanna storm, wave set-up was accurately reproduced, with simulation performance in 1D and 2D at R² = 0.66, 0.81 respectively for all data considered; RMSE = 0.13 m, 0.08 m; bias = 0.06, -0.02. Run-up in the 1D configuration is significantly overestimated while in 2D, the reproduction of run-up using spectral forcing was very accurate with R² = 0.73; RMSE = 0.19; bias = 0.04, underlining the role of spectral frequency and directional spread to precisely reproduce the surf zone processes during a storm on a complex barred beach. The maximum estimated values for set-up, run-up and spatial variability of run-up are comparable with results from previous studies, even though significantly higher offshore wave conditions. These results support the hypothesis of a run-up saturation signature in dissipative contexts, mainly influenced by extreme offshore wave conditions

Coastal Flooding and Storm Surges: How to Improve the Operational Response of the Risk Management Authorities: An Example of the CRISSIS Research Program on the French Coast of Languedoc

International audienceThis chapter presents an example of the CRISSIS research programme launched to study the French Mediterranean coast in Languedoc in spring 2015 over a two-year period. The first component of the CRISSIS project focuses on characterizing the coastal flood risk and its likely evolution in a context of climate change and sea level rise. The second stage in the programme was characterizing and mapping human and material vulnerability relative to the coastal flooding risk in Leucate. The third component of the programme focuses on socio-cultural vulnerability appraised using a geo-sociological study to characterize the level of risk culture in Leucate. The operational component of the CRISSIS programme was designed to test the crisis management approach applied in Leucate by organizing two drills that were devised, run, and assessed by students on a vocational master's course specialized in crisis management, supervised by crisis management professionals

Varaibilidad del nivel del mare desde 1950 hasta el 2000 y riesgos asociados a episodios del mar de leva en las peninsulas de Bocagrande y Castillogrande, Cartagena de Indias, Colombia

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Performance and Uncertainty of Satellite-Derived Bathymetry Empirical Approaches in an Energetic Coastal Environment

International audienceObjectives of this study are to evaluate the performance of different satellite-derived bathymetry (SDB) empirical models developed for multispectral satellite mission applications and to propose an uncertainty model based on inferential statistics. The study site is the Arcachon Bay inlet (France). A dataset composed of 450,837 echosounder data points and 89 Sentinel-2 A/B and Landsat-8 images acquired from 2013 to 2020, is generated to test and validate SDB and uncertainty models for various contrasting optical conditions. Results show that water column optical properties are characterized by a high spatio-temporal variability controlled by hydrodynamics and seasonal conditions. The best performance and highest robustness are found for the cluster-based approach using a green band log-linear regression model. A total of 80 satellite images can be exploited to calibrate SDB models, providing average values of root mean square error and maximum bathymetry of 0.53 m and 7.3 m, respectively. The uncertainty model, developed to extrapolate information beyond the calibration dataset, is based on a multi-scene approach. The sensitivity of the model to the optical variability not explained by the calibration dataset is demonstrated but represents a risk of error of less than 5%. Finally, the uncertainty model applied to a diachronic analysis definitively demonstrates the interest in SDB maps for a better understanding of morphodynamic evolutions of large-scale and complex coastal system