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| Registros recuperados: 58 | |
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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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| 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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| 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... |
| Tipo: Text |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00514/62559/66913.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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| Mengual, Baptiste; Le Hir, Pierre; Cayocca, Florence; Garlan, T.. |
| Based on experiments, a trawling-induced erosion dynamics was included in a 3D realistic and pre-validated hydro-sedimentary model so as to assess its contribution to the overall regional sediment dynamics in the specific case of the Bay of Biscay continental shelf. The effect of trawling was investigated throughout a 5-year period in terms of horizontal/vertical fluxes and changes in seabed mud content, and compared to the natural variability of sediment fluxes at different spatio-temporal scales. Trawling is shown in the model to significantly contribute to sediment re-suspension, and changes in the seabed at the scale of the shelf. The contribution of trawling to re-suspension is >80% during the high fishing season at many locations on the outer... |
| Tipo: Text |
Palavras-chave: Sediment fluxes; Bottom trawling; Numerical modelling; Bay of Biscay; Continental shelf. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00500/61146/64574.pdf |
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| 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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| 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... |
| Tipo: Text |
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| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00194/30572/29015.pdf |
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| 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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| 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... |
| Tipo: Text |
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| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00213/32427/30896.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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| 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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| 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... |
| Tipo: Text |
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| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00019/13034/10302.pdf |
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| 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... |
| Tipo: Text |
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| Ano: 1981 |
URL: http://archimer.ifremer.fr/doc/00105/21638/19219.pdf |
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| 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. |
| Tipo: Text |
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| Ano: 1987 |
URL: http://archimer.ifremer.fr/doc/00080/19124/16719.pdf |
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| 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. |
| Tipo: Text |
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| Ano: 1987 |
URL: http://archimer.ifremer.fr/doc/00103/21458/19039.pdf |
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| Registros recuperados: 58 | |
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