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Accumulation and dispersion dynamics of mud and sand particles in a continental shelf under estuarine influence: a numerical modelling analysis (Gironde, France) ArchiMer
Diaz, Melanie; Grasso, Florent; Le Hir, Pierre; Caillaud, Matthieu; Thouvenin, Benedicte.
Coastal environments are directly influenced by terrigenous inputs coming from rivers through estuaries. Quantifying the amount of nutrients and contaminants brought by sediments from continental areas to the sea is of major interest for marine resource protection. The complexity of the intra-estuarine dynamics, associated with the strong variability of meteorological forcing makes it difficult to quantify the residence time of particles within the estuary and the accumulation and dispersion areas offshore the mouth. Moreover, the dynamics of fine sediment trapping areas in the adjacent continental shelf (e.g. temporary or permanent storage such as the “West-Gironde Mud Patch” (WGMP) ) remains extremely challenging to address. Based on a realistic...
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Ano: 2019 URL: https://archimer.ifremer.fr/doc/00514/62559/66913.pdf
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Analysis of mixed-sediment consolidation experiments ArchiMer
Grasso, Florent; Le Hir, Pierre; Bassoullet, Philippe.
Estuarine sediment transport models require that a time variation of erodibility due to consolidation be taken into account. If numerical modelling of mud sedimentation and consolidation is currently satisfactory, simulation of mud-sand mixture consolidation is more problematical. This is partly due to mixed-sediment processes, as hindered settling and segregation, not well understood yet. Hence, based on extensive settling columns experiments, the aim of this study is to improve our understanding of mud-sand mixture consolidation for varying concentrations (54 to 600 kg/m3) and large sand contents (15 to 80%). Firstly, we observed that for a given initial mass concentration and sand content the final consolidation appeared independent from the initial...
Tipo: Text Palavras-chave: Settling column experiments; Consolidation; Sedimentation; Mud/sand mixtures; Sand segregation; Gelling concentration..
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00206/31727/30129.pdf
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Influence des conditions hydrométéorologiques sur les flux et bilans sédimentaires en estuaire de Seine ArchiMer
Grasso, Florent; Schulz, Elisabeth; Le Hir, Pierre; Verney, Romaric; Thouvenin, Benedicte.
La dynamique sédimentaire à l’embouchure de l’estuaire de Seine est principalement contrôlée par les forçages hydrométéorologiques (débit, vent, vagues, marée) et les fortes pressions anthropiques (endiguement, dragage, clapage). La compréhension et la quantification de la dynamique des flux sédimentaires en suspension (sable/vase) est un enjeu majeur, autant d’un point vu écologique (ex. turbidité, envasement) que financier (ex. gestion des chenaux de navigation). La mise en place de réseaux de mesure in situ permet une meilleure compréhension de la dynamique sédimentaire de l’estuaire, mais leur caractère local rend difficile toute estimation des flux et bilans sédimentaires. Pour répondre à ces questions, cette étude s’appuie sur la modélisation...
Tipo: Text Palavras-chave: Dynamique hydro-sédimentaire; Sable/vase; Estuaire de Seine; Modélisation numérique; Mesures in situ; Dragage; Flux résiduels et bilans; Année/trimestres.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00348/45928/45621.pdf
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Influence of morphological changes on suspended sediment dynamics in a macrotidal estuary: diachronic analysis in the Seine Estuary (France) from 1960 to 2010 ArchiMer
Grasso, Florent; Le Hir, Pierre.
Estuaries are subject to extensive morphological changes through human activities, such as deepening and narrowing via dredging and channelization. The estuary sediment load, characterised by the estuarine turbidity maximum (ETM), can severely increase in response to channel deepening, shifting the estuary from a natural to hyperturbid state. The main processes driving the estuarine circulation, hydrology and sediment dynamics are relatively well known. However, their relative influence on suspended sediment concentration (SSC), as well as their role in the transition toward hyperturbid estuaries, is still a subject of debate. Therefore, this study aims at investigating the relative contribution of key estuarine drivers (gravitational circulation and tidal...
Tipo: Text Palavras-chave: Estuary deepening and narrowing; Sediment dynamics; Turbidity maximum; Tidal asymmetry; Stratification; Numerical modelling; Morphological changes.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00479/59046/65965.pdf
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Modélisation du fonctionnement HYdro-MOrpho-SEDimentaire de l’estuaire de la Seine [HYMOSED] - Volet « Mesures» ArchiMer
Grasso, Florent; Verney, Romaric.
Le volet Mesures du projet SA5 HYMOSED se décompose en deux axes distincts : le suivi des évolutions morphodynamiques des vasières latérales intertidales et la quantification des matières en suspension (MES) de surface par télédétection couleur de l’eau. L’objectif du premier axe est d’évaluer notre capacité à observer les modifications morphodynamiques des vasières en comparant et combinant trois approches complémentaires (altimétrie ponctuelle ALTUS, topographie TLS (scanner laser terrestre), topographie par drone). Un suivi ALTUS sur 2 ans de trois vasières intertidales à l’aval de Tancarville (Tancarville, Pointe de la Roque, Vasière Nord) a été réalisé, permettant de quantifier l’influence des forçages hydrodynamiques et hydrologiques sur les phases...
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Ano: 2017 URL: http://archimer.ifremer.fr/doc/00414/52523/53292.pdf
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Modélisation du fonctionnement HYdro-MOrpho-SEDimentaire de l’estuaire de la Seine [HYMOSED]. Volet « Modélisation » ArchiMer
Grasso, Florent; Le Hir, Pierre.
Le projet HYMOSED (« Modélisation du fonctionnement HYdro-MOrpho-SEDimentaire de l’estuaire de la Seine ») du programme de recherche Seine-Aval 5 (déc. 2013 – mar. 2017) a eu pour objectif d’apporter une meilleure compréhension du fonctionnement hydro-morpho-sédimentaire de l’estuaire de la Seine des échelles de temps événementielle à annuelle. Cela s’est traduit par : (1) une analyse fine de la dynamique du bouchon vaseux, (2) la quantification des flux et bilans sédimentaires (sables/vase) pour différents scénarios hydrométéorologiques caractéristiques et (3) l'analyse de l’évolution morpho-sédimentaire à l'embouchure. Afin de répondre de manière pertinente à ces questions, ce projet s’est appuyé sur un important travail de validation du modèle...
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Ano: 2017 URL: http://archimer.ifremer.fr/doc/00412/52381/53170.pdf
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Modélisation environnementale de l'estuaire de la Seine ArchiMer
Bacq, Nicolas; Cugier, Philippe; Grasso, Florent; Le Gendre, Romain; Le Hir, Pierre; Lemoine, Jean-philippe; Riou, Philippe; Schulz, Elisabeth; Thouvenin, Benedicte; Verney, Romaric.
Dans le cadre du programme de recherche Seine-Aval 5, différentes stratégies de modélisation numérique sont mises en place pour aider à répondre aux questionnements scientifiques et sociétaux associés au fonctionnement physique, biologique, chimique et écologique de l'estuaire de la Seine (ex. projets RESET et HYMOSED). Les forçages météo-marins (vent, vague, marée) et hydrologique (débit) contrôlent le fonctionnement hydro-morpho-sédimentaire et biogéochimique de l'estuaire, modifiant ainsi les paramètres environnementaux de l’estuaire amont jusqu’à la baie de Seine (ex. nature des fonds, courant, turbidité, salinité, température, oxygène dissous, chlorophylle-a). La modélisation de ces paramètres, ainsi que leur évolution face à différents scénarios...
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Ano: 2015 URL: http://archimer.ifremer.fr/doc/00284/39480/37966.pdf
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Numerical modelling of equilibrium and evolving lightweight sediment laboratory beach profiles. ArchiMer
Dubarbier, Benjamin; Castelle, Bruno; Marieu, Vincent; Michallet, Hervé; Grasso, Florent; Ruessink, Gerben.
The recent advances of numerical beach profile models allowed the simulation of on/offshore sandbar migrations on timescales of weeks to months with fair success. These models were systematically applied to natural, persistently evolving, beaches. In this contribution, we apply our model to small-scale laboratory experiments for which coarse and lightweight sediment is used to satisfy the laws of similitude in the flume. Such experiments can result in equilibrium beach profiles and provide detailed information on the respective role of undertow and wave nonlinearities on sediment transport and the resulting cross-shore sandbar migration. Here we first apply the coupled, wave-averaged, cross-shore waves-currents-bathymetric evolution model 1DBeach to an...
Tipo: Text Palavras-chave: Beach profile; Numerical model; Physical modelling; Equilibrium profile; Sandbar migration.
Ano: 2013 URL: http://archimer.ifremer.fr/doc/00180/29089/27503.pdf
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Numerical modelling of mixed-sediment consolidation ArchiMer
Grasso, Florent; Le Hir, Pierre; Bassoullet, Philippe.
Sediment transport modelling in estuarine environments, characterised by cohesive and non-cohesive sediment mixtures, has to consider a time variation of erodibility due to consolidation. Generally, validated by settling column experiments, mud consolidation is now fairly well simulated; however, numerical models still have difficulty to simulate accurately the sedimentation and consolidation of mixed sediments for a wide range of initial conditions. This is partly due to the difficulty to formulate the contribution of sand in the hindered settling regime when segregation does not clearly occur. Based on extensive settling experiments with mud-sand mixtures, the objective of this study was to improve the numerical modelling of mixed-sediment consolidation...
Tipo: Text Palavras-chave: Mud-sand mixtures; Hindered settling; Consolidation; Experiments; Numerical modelling; Segregation.
Ano: 2015 URL: https://archimer.ifremer.fr/doc/00254/36539/35168.pdf
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Observations of turbulence within the surf and swash zone of a field-scale sandy laboratory beach ArchiMer
Brinkkemper, J. A.; Lanckriet, T.; Grasso, Florent; Puleo, J. A.; Ruessink, B. G..
Current coastal-evolution models generally lack the ability to accurately predict bed level change in shallow (<~2 m) water, which is, at least partly, due to the preclusion of the effect of surface-induced turbulence on sand suspension and transport. As a first step to remedy this situation, we investigated the vertical structure of turbulence in the surf and swash zone using measurements collected under random shoaling and plunging waves on a steep (initially 1:15) field-scale sandy laboratory beach. Seaward of the swash zone, turbulence was measured with a vertical array of three Acoustic Doppler Velocimeters (ADVs), while in the swash zone two vertically spaced acoustic doppler velocimeter profilers (Vectrino profilers) were applied. The vertical...
Tipo: Text Palavras-chave: Turbulence; Plunging breakers; Swash; Laboratory experiment.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00277/38812/37538.pdf
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Physical modeling of intermediate cross-shore beach morphology: Transients and equilibrium states ArchiMer
Grasso, Florent; Michallet, H.; Barthelemy, E.; Certain, R..
Laboratory experiments on cross-shore beach morphodynamics are presented. A lightweight sediment (density rho(s) = 1.19 g cm(-3)) model is used in order to fulfill a Shields number and Rouse number scaling. This choice aims at correctly reproducing bed load transport as well as suspension dynamics. Terraces and barred beach profiles obtained in the experiments also present close similarities with profiles observed in the field. In order to question the concept of equilibrium beach profile, wave forcings conforming to a JONSWAP spectrum were imposed over long periods (up to more than a hundred hours). An average bottom evolution velocity is defined and used to determine when the profile reaches equilibrium. Usually, beach profiles are characterized...
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Ano: 2009 URL: http://archimer.ifremer.fr/doc/00092/20345/17988.pdf
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Potential of UAVs for Monitoring Mudflat Morphodynamics (Application to the Seine Estuary, France) ArchiMer
Jaud, Marion; Grasso, Florent; Le Dantec, Nicolas; Verney, Romaric; Delacourt, Christophe; Ammann, Jerome; Deloffre, Julien; Grandjean, Philippe.
Intertidal mudflats play a critical role in estuarine exchange, connecting marine and continental supplies of nutrients and sediments. However, their complex morphodynamics, associated with a wide range of physical and biological processes, are still poorly understood and require further field investigation. In addition, mudflats are challenging areas for Structure-from-Motion (SfM) photogrammetric surveys. Indeed, the mudflats generally hold back residual tidal water, which can make stereo restitution particularly difficult because of poor correlations or sun-glint effects. This study aims to show the potential of light UAVs (Unmanned Aerial Vehicles) for monitoring sedimentary hydrodynamics at different spatial scales in a silty estuary. For each UAV...
Tipo: Text Palavras-chave: Coastal monitoring; Unmanned Aerial Vehicle; Photogrammetry; Estuary; Mudflat areas; Morphological features.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00326/43721/43167.pdf
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Sediment transport associated with morphological beach changes forced by irregular asymmetric, skewed waves ArchiMer
Grasso, Florent; Michallet, H.; Barthelemy, E..
The waveshape effects on sediment transport are investigated for cross-shore beach profile changes. This study is based on experiments performed in the Laboratoire des Ecoulements Geophysiques et Industriels wave flume for irregular waves. The interest of such experiments resides in presenting complex combinations of wave skewness and asymmetry in bed load, ripple, and sheet flow regimes. Net sediment transport rates on typical beach morphodynamics are analyzed in regard to wave skewness and asymmetry, undertow, and ripple occurrence. Onshore bar migration is mainly associated with onshore-directed sediment transport, whereas terrace profile and offshore bar formation correspond to offshore sediment transport. As for natural beaches, energetic (moderate)...
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Ano: 2011 URL: http://archimer.ifremer.fr/doc/00092/20341/17991.pdf
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Suspended Sediment Dynamics in the Macrotidal Seine Estuary (France) - Part 1: Numerical Modeling of Turbidity Maximum Dynamics ArchiMer
Grasso, Florent; Verney, Romaric; Le Hir, Pierre; Thouvenin, Benedicte; Schulz, Elisabeth; Kervella, Youenn; Fard, I. Khojasteh Pour; Lemoine, J. -p.; Dumas, Franck; Garnier, Valerie.
Tidal pumping, baroclinic circulation and vertical mixing are known to be the main mechanisms responsible for the estuarine turbidity maximum (ETM) formation. However, the influence of hydro-meteorological conditions on ETM dynamics is still not properly grasped and requires further investigation to be quantified. Based on a realistic 3-dimensional numerical model of the macrotidal Seine Estuary (France) that accounts for mud and sand transport processes, the objective of this study is to quantify the influence of the main forcing (river flow, tides, waves) on the ETM location and mass changes. As expected, the ETM location is strongly modulated by semidiurnal tidal cycles and fortnightly timescales with a high sensitivity to river flow variations. The ETM...
Tipo: Text Palavras-chave: Estuary; Mud; Sand; Hydrodynamics; Turbidity maximum; Waves; Measurement; Modeling.
Ano: 2018 URL: http://archimer.ifremer.fr/doc/00416/52770/53638.pdf
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Suspended Sediment Dynamics in the Macrotidal Seine Estuary (France) - Part 2: Numerical Modeling of Sediment Fluxes and Budgets Under Typical Hydrological and Meteorological Conditions ArchiMer
Schulz, Elisabeth; Grasso, Florent; Le Hir, Pierre; Verney, Romaric; Thouvenin, Benedicte.
Understanding the sediment dynamics in an estuary is important for its morphodynamic and ecological assessment as well as, in case of an anthropogenically controlled system, for its maintenance. However, the quantification of sediment fluxes and budgets is extremely difficult from in-situ data and requires thoroughly validated numerical models. In the study presented here, sediment fluxes and budgets in the lower Seine Estuary were quantified and investigated from seasonal to annual time scales with respect to realistic hydro- and meteorological conditions. A realistic three-dimensional process-based hydro- and sediment-dynamic model was used to quantify mud and sand fluxes through characteristic estuarine cross-sections. In addition to a reference...
Tipo: Text Palavras-chave: Macrotidal estuary; Sediment fluxes; Numerical modelling; Mud/sand; Wind/waves; River discharge.
Ano: 2018 URL: http://archimer.ifremer.fr/doc/00416/52772/53640.pdf
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Turbulent viscosity in natural surf zones ArchiMer
Grasso, Florent; Ruessink, B. G..
Waves breaking in the shallow surf zone near the shoreline inject turbulence into the water column that may reach the bed to suspend sediment. Breaking-wave turbulence in the surf zone is, however, poorly understood, which is one of the reasons why many process-based coastal-evolution models predict coastal change during severe storms inadequately. Here, we use data collected in two natural surf zones to derive a new parameterization for the stability function C-mu that determines the magnitude of the eddy viscosity nu(t) in two-equation turbulent-viscosity models, nu(t) = C(mu)k(2)/epsilon, where k is turbulent kinetic energy and epsilon is the turbulence dissipation rate. In both data sets, the ratio of turbulence production to dissipation is small...
Tipo: Text Palavras-chave: Eddy viscosity; Field measurements; Parameterization; Production; Surf zone; Turbulence.
Ano: 2012 URL: https://archimer.ifremer.fr/doc/00114/22512/20204.pdf
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