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A model of fluff layer erosion and subsequent bed erosion in the presence of the bioturbator, Hydrobia ulvae ArchiMer
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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Accounting for Rough Bed Friction Factors of Mud Beds as a Result of Biological Activity in Erosion Experiments ArchiMer
Guizien, Katell; Orvain, Francis; Duchene, Jean-claude; Le Hir, Pierre.
The average bed shear stress and bed friction factor of samples with any roughness was derived from the head loss between upstream and downstream of a test section in an erosion tunnel. The method was validated in both hydraulically smooth (plexiglass; Reynolds number less than 25,000) and rough regimes (calibrated particles with known roughness). As a first step toward using this method on natural sediment, this method was tested with experimental mesocosms assembled from field collected materials (sieved sediments; diatoms). Bed shear stress measurement precision was high enough in the experiments to detect a positive significant relationship between bed friction factor and core roughness. The observed bed friction factor increase could be related to...
Tipo: Text Palavras-chave: Bed roughness; Friction factor; Mud beds; Biological activity; Erosion experiments.
Ano: 2012 URL: http://archimer.ifremer.fr/doc/00117/22807/20617.pdf
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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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Aide mémoire de dynamique sédimentaire. 7ème édition ArchiMer
Le Hir, Pierre.
This aide-mémoire is not a lesson on sedimentary dynamics but more of a calculation form. Its use implies a good knowledge of the involved processes. This report presents the basic formulations used for the calculation of the hydrodynamic forcings as well as the main sediment behavioural laws, in order to help the reader conduct a basic sediment transportation calculation.
Tipo: Text Palavras-chave: Bottom shear stress; Boundary layer; Mathematical modelling; Transport rate; Cohesive sediments; Non cohesive sediments; Sediment dynamics; Contrainte de cisaillement au fond; Couche limite; Modélisation mathématique; Fonctions de transport; Sédiments cohésifs; Sédiments non cohésifs; Dynamique sédimentaire.
Ano: 2008 URL: http://archimer.ifremer.fr/doc/2008/rapport-6273.pdf
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Amélioration de la salubrité des eaux conchylicoles de l'estuaire de l'Elorn et du Nord de la Rade de Brest - Etude du milieu marin ArchiMer
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.
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Ano: 1987 URL: http://archimer.ifremer.fr/doc/00103/21460/19041.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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Behaviour of a floc population during a tidal cycle: laboratory experiments and numerical modelling ArchiMer
Verney, Romaric; Lafite, Robert; Brun-cottan, Jean Claude; Le Hir, Pierre.
An approach combining laboratory experiments and numerical modelling was used to investigate the behaviour of a floc population during an idealized tidal cycle. The experiment was conducted on suspended sediments at a concentration of 93 mg l−1 collected in the field. It was based on a jar test device to reproduce tidal-induced turbulence and coupled with a CCD camera system and image post-processing software to monitor floc size distribution. At the same time, a 0D size-class based aggregation/fragmentation model (FLOCMOD) was developed to simulate changes in the floc population over the tidal cycle. Experimental results revealed strong variability of the behaviour of microfloc and macrofloc populations with respect to the varying shear rates observed in...
Tipo: Text Palavras-chave: Flocculation; Tidal cycle; Laboratory experiment; FLOCMOD; OD model; Sensitivity analysis; Optimization.
Ano: 2011 URL: http://archimer.ifremer.fr/doc/00027/13846/11020.pdf
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Circulation and suspended sediment transport in a coral reef lagoon: The south-west lagoon of New Caledonia ArchiMer
Ouillon, S.; Douillet, Pascal; Lefebvre, J. P.; Le Gendre, Romain; Jouon, Aymeric; Bonneton, P.; Fernandez,; Chevillon, C.; Magand, O.; Lefevre, J.; Le Hir, Pierre; Laganier, R.; Dumas, Franck; Marchesiello, P.; Madani, A. Bel; Andrefouet, S.; Panche, J. Y.; Fichez, R..
The south-west lagoon of New Caledonia is a wide semi-open coral reef lagoon bounded by an intertidal barrier reef and bisected by numerous deep inlets. This paper synthesizes findings from the 2000-2008 French National Program EC2CO-PNEC relative to the circulation and the transport of suspended particles in this lagoon. Numerical model development (hydrodynamic, fine suspended sediment transport, wind-wave, small-scale atmospheric circulation) allowed the determination of circulation patterns in the lagoon and the charting of residence time, the later of which has been recently used in a series of ecological studies. Topical studies based on field measurements permitted the parameterisation of wave set-up induced by the swell breaking on the reef barrier...
Tipo: Text Palavras-chave: Hydrodynamics; Suspended sediment; New Caledonia; Coral reef lagoon; Sediment; Turbidity; Resuspension.
Ano: 2010 URL: http://archimer.ifremer.fr/doc/00014/12526/9401.pdf
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Contraintes de fond dans le Golfe du Lion générées par les houles et les courants ArchiMer
Dufois, Francois; Garreau, Pierre; Le Hir, Pierre.
Simulated data of both currents and waves for the entire year 2001 are used in order to assess their statistical contribution to the erodability power over the shelf of the Gulf of Lion. Bottom circulation patterns are also analysed in response to wind forcing. A method to compute the skin friction component of the total bottom shear stress is then proposed and compared with a classical method.
Tipo: Text Palavras-chave: MARS 3D; Golfe du Lion; Contraintes de peau; Contraintes de fond; Courants; Houles.
Ano: 2006 URL: http://archimer.ifremer.fr/doc/2006/publication-6306.pdf
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Development and validation of a sediment dynamics model within a coastal operational oceanographic system ArchiMer
Cayocca, Florence; Verney, Romaric; Petton, Sebastien; Caillaud, Matthieu; Dussauze, Morgan; Dumas, Franck; Le Roux, Jean-francois; Pineau-guillou, Lucia; Le Hir, Pierre.
The rising interest in environmental and ecosystem dynamics have lead coastal oceanographers to not only investigate the “traditional” physical parameters describing the ocean state and its dynamics (e.g. temperature, salinity, currents, water levels in coastal areas), but to also account for the dynamics of parameters describing its biogeochemical components. To that end, MARS3D regional and coastal modelling system has been coupled to ecosystem modules (ECO-MARS3D, ECO3M) as well as sediment dynamics modules (MARS3D-SEDIM): sediment, nutrient and primary production contents can be considered as the lower level environment and ecosystem descriptors of the “biogeochemical” ocean. Early investments into physical and biological analysis at the regional scale...
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Ano: 2014 URL: http://archimer.ifremer.fr/doc/00194/30572/29015.pdf
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Dragages et environnement marin Etat des connaissances ArchiMer
Alzieu, Claude; Abarnou, Alain; Bassoullet, Philippe; Boutier, Bernard; Chiffoleau, Jean-francois; Crenn, Isabelle; Derrien, Annick; Erard-le Denn, Evelyne; Gourmelon, Michele; Guiliaud, Jean-françois; Silva Jacinto, Ricardo; Le Cann, Pierre; Le Guyader, Françoise; Le Hir, Pierre; L'Yavanc, Jacky; Mauvais, Jean-louis; Menard, Dominique; Michel, Pierre; Monbet, Yves; Pommepuy, Monique; Quiniou, Francoise.
Port activities require continuous or occasional dredging of considerable quantities of sediments : approximately 50 million m3 along the French coastline. A large proportion of the dredgings is authorized for dumping at sea in geographically delimited areas and following an impact evaluation of their potential harmfulness to the marine environment. The environmental risks assessment linked to dredging operations relies on knowledge related to several scientific disciplines contributing to changes in the regulations. This work, intended both for managers and for environmental scientists and engineers, is designed to take stock of the current state-of-the-art in the field of sediment contamination and related ecotoxicological hazards, along with a review of...
Tipo: Text Palavras-chave: Regulations; Management; Impact; Contaminants; Dredging; Réglementation; Gestion; Impact; Contaminants; Dragages.
Ano: 1999 URL: http://archimer.ifremer.fr/doc/1999/rapport-1040.pdf
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Dynamics of sand and mud mixtures: a multiprocess-based modelling strategy ArchiMer
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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Erosion threshold of sand-mud mixtures ArchiMer
Jacobs, Walter; Le Hir, Pierre; Van Kesteren, Walther; Cann, Philippe.
Results of a large number of erosion tests on artificially generated and relatively dense sand-mud mixtures are presented. Soil sample compositions are varied concerning clay-silt and sand-silt ratio, and clay mineralogy. The experimental set-up consists of a re-circulating small-scale rectangular erosion flume with unidirectional flow conditions. The erosion threshold and erosion rate are studied through step by step increasing the flow rate during a test. Results clearly indicate time-decreasing erosion during which individual flocs are randomly eroded, and time-independent (steady) erosion during which both sand and mud particles are continuously and uniformly eroded. These two erosion types appear to be floc and surface erosion, respectively...
Tipo: Text Palavras-chave: Erosion; Sand-mud mixtures; Clay; Sediment structure; Critical shear stress; Strength.
Ano: 2011 URL: http://archimer.ifremer.fr/doc/00041/15252/12678.pdf
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Erosions, dépots et transits sédimentaires associés dans le bassin de Marennes-Oléron ArchiMer
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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Etude de l'estuaire de la Seine - Modélisation numérique des phénomènes physiques ArchiMer
Salomon, Jean-claude; Le Hir, Pierre.
Les zones côtières, et les estuaires en particulier, fournissent au bien-être de l'homme et à son activité économique une aide très appréciable. Contrairement au milieu terrestre pauvre en eau, et au milieu marin pauvre en éléments nutritifs, les estuaires riches de ces deux constituants sont un lieu de vie privilégié. On connait le rôle de frayère et de nurserie qu'ils jouent pour de très nombreuses espèces. Ces estuaires sont actuellement utilisés comme collecteurs des rejets industriels et domestiques. Bien que ces rejets lorsqu'ils sont convenablement traités et dilués ne soient pas obligatoirement néfastes, il est de première utilité de pouvoir juger de leurs effets selon leur nature, leur localisation et leur importance, pour ne pas mettre en danger...
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Ano: 1981 URL: http://archimer.ifremer.fr/doc/00105/21638/19219.pdf
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Etude d'impact du rejet des eaux d'exaure du tunnel sur l'environnement marin ArchiMer
Monbet, Yves; Delpech, Jean-paul; Le Hir, Pierre.
En 1983, plus de 20 millions de voyageurs et près de 20 millions de tonnes de marchandises ont traversé la Manche ou la Mer du Nord entre la Grande-Bretagne et le continent. Ces échanges sont trois fois supérieurs à ceux enregistrés en 1970, ce qui représente une augmentation annuelle de l'ordre de 10 %. Les prévisions les plus réalistes tablent actuellement sur une augmentation moyenne légeretnent supérieure à 4 % par an d'ici l'an 2000, ce qui équivaut à plus que doubler à cette date le trafic actuel. Pour répondre à une telle demande, il a été nécessaire d'envisager différentes solutions permettant de faire face à l'augmentation prévue.
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Ano: 1987 URL: http://archimer.ifremer.fr/doc/00080/19124/16719.pdf
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Etude d'impact du rejet des eaux d'exhaure du tunnel sur l'environnement marin ArchiMer
Monbet, Yves; Delpech, Jean-paul; Le Hir, Pierre.
En 1983, plus de 20 millions de voyageurs et près de 20 millions de tonnes de marchandises ont traversé la Manche ou la Mer du Nord entre la Grande-Bretagne et le continent. Ces échanges sont trois fois supérieurs à ceux enregistrés en 1970, ce qui représente une augmentation annuelle de l'ordre de 10 %. Les prévisions les plus réalistes tablent actuellement sur une augmentation moyenne légèrement supérieure à 4 % par an d'ici l'an 2000, ce qui équivaut à plus que doubler à cette date le trafic actuel. Pour répondre à une telle demande, il a été nécessaire d'envisager différentes solutions permettant de faire face à l'augmentation prévue.
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Ano: 1987 URL: http://archimer.ifremer.fr/doc/00103/21458/19039.pdf
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Evolution morphodynamique cross-shore d’un estran vaseux ArchiMer
Monbet, Valerie; Maisondieu, Christophe; Le Hir, Pierre.
The main goal of this study consists in evaluating the combined effect of cross-shore waves and current on the long term evolution of a mud flat profile. An original method is used to create a database of realistic wind fields and sea states. These data are applied to a numerical model of sediment transport and morphological changes. A description of long term simulations is proposed.
Tipo: Text Palavras-chave: Morphodynamique; Estran vaseux; Courant de marée; États de mer; Mer du vent.
Ano: 2006 URL: http://archimer.ifremer.fr/doc/00203/31429/29824.pdf
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Formulating Fine to Medium Sand Erosion for Suspended Sediment Transport Models ArchiMer
Dufois, Francois; Le Hir, Pierre.
The capacity of an advection/diffusion model to predict sand transport under varying wave and current conditions is evaluated. The horizontal sand transport rate is computed by vertical integration of the suspended sediment flux. A correction procedure for the near-bed concentration is proposed so that model results are independent of the vertical resolution. The method can thus be implemented in regional models with operational applications. Simulating equilibrium sand transport rates, when erosion and deposition are balanced, requires a new empirical erosion law that involves the non-dimensional excess shear stress and a parameter that depends on the size of the sand grain. Comparison with several datasets and sediment transport formulae demonstrated the...
Tipo: Text Palavras-chave: Sand; 1DV model; Erosion rate; Suspended sediment transport.
Ano: 2015 URL: http://archimer.ifremer.fr/doc/00276/38763/37304.pdf
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Golfe Normano-Breton. Bilan des connaissances ArchiMer
Blanchard, Michel; Chardy, Pierre; Chaussepied, Marcel; Dao, Jean-claude; Le Hir, Pierre; Jegou, Anne-marie; Larsonneur, C.; Loarer, Ronan; Manaud, Francois.
Ce document a été élaboré dans le cadre de la préparation d'un programme d' "étude régionale intégrée" du golfe normano-breton. Réalisé dans des délais très courts, il ne constitue pas un inventaire exhaustif des travaux effectués dans le golfe mais une illustration par grands secteurs disciplinaires de l'état actuel des connaissances. Son objectif est de cerner les domaines à développer dans le cadre d'une programmation poly-disciplinaire orientée vers la gestion de l'espace littoral. La présentation par disciplines fondamentales de l'océanographie (physique, sédimentologie, biologie) est associée à un bilan de l'utilisation du milieu, faisant apparaître la diversité et la complexité des problèmes à résoudre. En effet, point privilégié entre la Manche...
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Ano: 1982 URL: http://archimer.ifremer.fr/doc/00450/56186/57739.pdf
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