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| Registros recuperados: 58 | |
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| Le Hir, Pierre; Bassoullet, Philippe; Erard, E.; Blanchard, Michel; Hamon, Dominique; Jegou, Anne-marie. |
| Ce rapport en 6 volumes est le résultat d'une étude pluridisciplinaire (6 thèmes correspondant aux volumes du rapport), réalisée sur un secteur géographique bien délimité, présentant des caractéristiques physiques et biologiques particulières (très fort marnage, grande hétérogénéité des fonds, forte production biologique à base de mollusques filtreurs…), et siège d'activités humaines importantes et diversifiées (essentiellement basées sur l'exploitation des ressources du milieu). L'étude fait suite à un Livre Blanc établi en 1982, synthétise les données existantes, et les complète par des travaux originaux sur la connaissance des mécanismes naturels, en particulier de ceux qui ont une relation directe ou indirecte avec les activités humaines (processus... |
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| Ano: 1986 |
URL: http://archimer.ifremer.fr/doc/00047/15837/13240.pdf |
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| Mengual, Baptiste; Le Hir, Pierre; Cayocca, Florence; Garlan, Thierry. |
| This study describes the building of a common erosion law for fine sand and mud, mixed or not, in the case of a typical continental shelf environment, the Bay of Biscay shelf, characterized by slightly energetic conditions and a seabed mainly composed of fine sand and muddy sediments. A 3D realistic hydro-sedimentary model was used to assess the influence of the erosion law setting on sediment dynamics (turbidity, seabed evolution). A pure sand erosion law was applied when the mud fraction in the surficial sediment was lower than a first critical value, and a pure mud erosion law above a second critical value. Both sand and mud erosion laws are formulated similarly, with different parameters (erodibility parameter, critical shear stress and power of the... |
| Tipo: Text |
Palavras-chave: Sand-mud mixture erosion; Numerical modelling; Non-cohesive to cohesive transition. |
| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00394/50588/51280.pdf |
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| 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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| Le Hir, Pierre; Breton, M; L'Yavanc, J.. |
| Afin de préciser les rejets où il est préférable d'intervenir pour réduire les contaminations des secteurs conchylicoles de l'Elorn et du Nord de la rade de Brest, un calcul de dilution de chacun des rejets a été mené à l'aide d'un modèle mathématique. Après une description des courants de marée calculés dans tout le secteur d'étude, des figures de dilution sont présentées. L'impact de chaque rejet se déduit facilement. |
| Tipo: Text |
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| Ano: 1987 |
URL: http://archimer.ifremer.fr/doc/00103/21460/19041.pdf |
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| Le Hir, Pierre; Kervella, Stephane; Walker, Patrice; Brenon, Isabelle. |
| Managing sediments in the bate de Marennes-Oleron (Atlantic coast of France) can be achieved providing particulate fluxes at the scale of the basin are available as well as tidal and meteorological conditions during which major transports occur A sediment dynamics model accounting for tide- and wave-induced sand and mud transport has been applied to the Pertuis Charentais area Consolidation of pure mud and mixtures of sand and mud is accounted for The model validation is achieved by current and turbidity measurements, local altimetric surveys during one year and pressure measurements for waves on the tidal flat An asymmetry between eastern and western halves of the bay is observed on turbidity signals in agreement with a residual circulation from north to... |
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| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00019/13034/10302.pdf |
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| Grasso, Florent; Mengual, Baptiste; Le Hir, Pierre; Walther, Régis; Verney, Romaric. |
| L'embouchure de l’estuaire de la Seine a subi de fortes altérations morphosédimentaires au cours du dernier siècle et son évolution se poursuit encore actuellement. La question du devenir du système et des habitats associés est donc posée, en tenant compte d'éventuels changements environnementaux ou climatiques. La modélisation morphosédimentaire a pour ambition de simuler le devenir de la morpho-bathymétrie, en rendant compte des couplages entre processus hydrodynamiques, transports de sédiment et évolution de la morphologie. Le projet MORPHOSEINE vise à exploiter l'outil de modélisation MARS3D CurviSeine mis en place par l’Ifremer dans le cadre des programmes Seine-Aval (SA) 4 et 5, afin de répondre à l'attente concernant l'évolution possible de... |
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| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00684/79630/82353.pdf |
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| Orvain, Francis; Sauriau, Pierre-guy; Le Hir, Pierre; Guillou, Gael; Cann, Philippe; Paillard, Michel. |
| A portable erosion device (ERIS) was deployed in November 2000 and May 2001 to investigate the spatio-temporal variation of fine-grained sediment erosion over a transect on the intertidal mudflats of Marennes-Oleron Bay, western France. The objective was to relate changes in bed erodability over diurnal emersion periods to bioturbation, rapid changes in sediment characteristics, and microphytobenthos biomass. Macrofaunal assemblages were dominated by the bivalve, Scrobicularia plana, on the upper mudflat, and by the gastropod, Hydrobia ulvae. on the middle mudflat. A power relationship was obtained where tau(cr) was plotted as a function of sediment density. Results from the upper part of the mudflat deviated from this relationship due to bioturbation by... |
| Tipo: Text |
Palavras-chave: EPS; Microphytobenthos; Erodability; Intertidal mudflat; Sediment; Scrobicularia plana; Hydrobia ulvae; Bioturbation; Resuspension; Eris. |
| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-3779.pdf |
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| Le Hir, Pierre; Bassoullet, Philippe; L'Yavanc, Jacky. |
| In order to determine the fate of the fine particles and adsorbed contaminants in a short macrotidal estuary, a mathematical modelling system for cohesive suspended mater transport and bottom evolution, including a new consolidation algorithm, is developed. An analysis of successive erosion, transport and deposition processes due to tidal forcing is given and comparisons with field data are provided. A description of mean-terrn bottom variations has been attempted and is partially validated by differential sounding. |
| Tipo: Text |
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| Ano: 1988 |
URL: http://archimer.ifremer.fr/doc/00080/19146/16741.pdf |
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| Orvain, Francis; Le Hir, Pierre; Sauriau, Pierre-guy. |
| Previous studies have shown that the gastropod Hydrobia ulvae destabilizes the top layers of fine-grained sediments. This process is mediated by the formation of a "biogenic" fluff layer that includes tracks, faecal pellets and mucus. This fluff layer has been shown to be easily resuspended before general bed erosion. In order to examine how fluff layer and bed. erosion interact, flume experiments were performed with fluid sediments of varying water contents. Ten thousand snails were placed and allowed to crawl for 5 h on the sediment surface, and then the resuspended sediment mass was measured in response to step-wise shear stress increases. Two distinct erosion phases were observed: (1) initial resuspension of the fluff layer and (2) the subsequent bed... |
| Tipo: Text |
Palavras-chave: Gastropoda; Erosion sediment; Bioturbation; Cohesive sediment; Marine sediment. |
| Ano: 2003 |
URL: http://archimer.ifremer.fr/doc/2003/publication-805.pdf |
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| Le Hir, Pierre; Cayocca, Florence; Waeles, Benoit. |
| Mixed sediments are constituted of cohesive and non-cohesive materials with distinct behaviours that numerical models traditionally manage separately. This paper first introduces a rapid state of the Art in sediment transport modelling in order to point out the specific requirements for process-based models applied to mixed sediments. Based on a preliminary study by Waeles et al. (2007), which showed the validity of the advection approach to compute fine sand transport, a complete modelling strategy is described: it is applied to the suspended transport of sand and mud mixtures, and accounts for consolidation of mixed sediments. Special care is paid to the realistic representation of the structure and density of sand and mud mixtures, and to the... |
| Tipo: Text |
Palavras-chave: Sediment transport modelling; Mixed sediment; Sand; Mud; Suspension; Consolidation. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00028/13952/12567.pdf |
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| 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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| Jourdin, Frederic; Tessier, Caroline; Le Hir, Pierre; Verney, Romaric; Lunven, Michel; Loyer, Sophie; Lusven, Andre; Filipot, Jean-francois; Lepesqueur, Jeremy. |
| A pair of self-contained acoustic Doppler current profilers (SC-ADCPs) operating with different frequencies were moored on a muddy sea bottom at about 20 m depth in the Bay of Vilaine off the French Atlantic coast. With their acoustic beams oriented upwards, the SC-ADCPs ensonified most of the water column. The results of several months of in situ recorded echo intensity data spanning 2 years (2003 to 2004) from the dual-frequency ADCPs are presented in this paper. The aim was to estimate suspended particle mass concentration and mean size. A concentration index CI is proposed for the estimation of particle concentration. Based on theory the CI-unlike the volume backscatter strength-does not depend on particle size. Compared with in situ optical data, the... |
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| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00213/32427/30896.pdf |
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| 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... |
| Tipo: Text |
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| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00412/52381/53170.pdf |
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| Registros recuperados: 58 | |
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