Automatic calculation of bathymetry for coastal hydrodynamic models

International audienceA methodology is proposed to facilitate the construction of gridded bathymetry data for the use of hydrodynamic models on the continental shelf. It relies on the carrying out of three successive tasks: (1) automatic selection of records of better quality among multiple sets of overlapping data; (2) elimination of data points located on land; and (3) taking into account the shoreline as bathymetric data. Algorithms are proposed to perform sorting of the records according to their quality as well as masking by the coastline. The suggested method facilitates the updating of bathymetry data and optimizes their use. It enables automatic execution of all the tasks and building of new digital bathymetry models in a few hours, without action from the operator. The method has been tested many times on the continental shelf of NorthWest Europe. The bathymetric data so generated do not require corrections, and the hydrodynamic models on which these data are based could be very precise

Quantitative assessment of dissolved radiotracers in the English Channel: Sources, average impact of la Hague reprocessing plant and conservative behaviour (1983, 1986, 1988, 1994)

International audienceKnowledge of long-term movements of water-masses in the English Channel has been substantially improved using hydrodynamic modelling coupled with radio-tracers studies; nevertheless, the precision of results so obtained is still largely dependent on measurement precision. New tools are now available to make more accurate determinations of radio-tracer distribution: (1) Repositioning of station locations at the same tide reference-time, giving a homogeneous spatial data set, coupled with the possibility of interpolating and quantifying the amounts of dissolved radioactivity #owing through the English Channel; (2) the "rst measurements of tritium (H) in seawater on a large scale in the English Channel demonstrate that this fully conservative radionuclide is a clearly identi"able marker of industrial releases; (3) recent campaigns carried out during the FLUXMANCHE II CCE (1994) programme show the general distribution of dissolved radionuclides Cs, Cs, Co, Sb, Ru and H in the English Channel and the Irish Sea; and (4) the re-utilisation of data from previous campaigns (1983, 1986, 1988) provides indications, at any given location in the English Channel, about the average dilution and distribution of releases derived from the La Hague reprocessing plant. Excesses and losses of radionuclides are now quanti"ed with respect to known source terms; estimates of losses are provided for non-conservative radionuclides, while an excess of Cs was observed in the English Channel during the period 1983}1994. This excess, which has the same order of magnitude as the quantities released from La Hague plant in the English (P. Bailly du Bois) 0278-4343/99/$-see front matter 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 8-4 3 4 3 (9 9) 0 0 0 4 9-7 Channel, could be explained by about 1% of the Sella"eld reprocessing plant releases entering the Channel. These results con"rm and give a more detailed picture of the previously known distribution of water masses in the English Channel. They lead to clear information about transit times and dilution at this scale, and provide directly comparable data for the validation of hydrodynamic models

TRANSMER, hydrodynamic model for medium-and long-term simulation of radionuclides transfers in the English Channel and southern North Sea

International audienceTRANSMER hydrodynamic model simulates dispersion of dissolved substances in seawater at the scale of the English Channel and the south of the North Sea with a mesh size of one kilometre and a time step of 30 minutes. This model evaluates the medium-and long-term consequences of releases of soluble pollutants in the marine ecosystem under normal or accidental conditions, at a very low computation cost (it takes less than one hour to simulate one year). It has been qualitatively and quantitatively validated by 1400 measurements of 125 Sb in seawater in the English Channel and the North Sea. Budgets of measured and simulated radionuclide quantities are balanced for theses seas. The correlation factor between individual measurements in seawater and calculation results is 0.88 with an average error of ± 54%, the error attributable to the measurement process being 15% on average. TRANSMER appears as a robust tool for modelling medium-and long-term consequences of releases of soluble pollutants in the marine ecosystem under normal or accidental conditions

Fast hydrodynamic model for medium-and long-term dispersion in seawater in the English Channel and southern North Sea, qualitative and quantitative validation by radionuclide tracers

International audienceThe database for medium-and long-term model validation using 125 Sb released by the La Hague reprocessing plant includes 1400 measurements performed between 1987 and 1994 in the English Channel and the North Sea and data for each release since 1982. Antimony-125 has a conservative behaviour in water masses over a period of several years. These data can be used qualitatively and quantitatively to compare the measured concentrations with the calculated ones and quantities of tracers. Tritium measurements are also available for model calibration. A two-dimensional hydrodynamic model has been developed to allow repetitive long-term simulations. This model uses a database of residual tidal currents calculated using the Lagrangian barycentric method [Salomon, J.C., Guéguéniat, P., Orbi, A., Baron, Y., 1988. A Lagrangian model for long-term tidally induced transport and mixing. Verification by artificial radionuclide concentrations. (P. Bailly du Bois). www.elsevier.com/locate/ocemod Ocean Modelling 9 (2005) 169-210 The main adjustment parameters of this model are the sources of wind data used and the calculation method for evaluating wind stress at the sea surface. With these parameters, the fluxes of radionuclides and water masses in the English Channel and the North Sea were balanced for the whole period of field measurements (1987-1994). The correlation factor between individual measurements in seawater and calculation results is 0.88 with an average error of ±54%, the error attributable to the measurement process being 15% on average. The mean flux through the Dover Strait is 126,000 m 3 s À1 , close from the one obtained from previous studies [Salomon, J.C., Breton, M., Guéguéniat, P. 1993. Computed residual flow through the Dover Strait. Oceanologica Acta 16 (5-6) 449-455; Bailly du Bois, P., Salomon, J.C., Gandon, R., Guégué-niat, P. 1995. A quantitative estimate of English Channel water fluxes into the North Sea from 1987 to 1992 based on radiotracer distribution. Combining modelling and monitoring to determine fluxes of water, dissolved and particulate metals through the Dover Strait. Continental Shelf Research 16 (2) 237-257]. This model appears as a robust tool for modelling long-term dispersion at a low computation cost (it takes less than 1 h to simulate one year on a personal computer). It could forecast consequences of controlled or accidental releases of soluble substances in seawater under realistic conditions or calculate water masses fluxes and transit times

Caractère conservatif de l'antimoine 125 dans les eaux marines soumises à l'influence des rejets de l'usine de retraitement des combustibles irradiés de La Hague

125Sb est représentatif de la fraction soluble des rejets liquides de l'usine COGEMA La Hague spécialisée dans le retraitement des combustibles irradiés. Son élimination des effluents a été entreprise à partir de 1976, d'abord par voie chimique d'extraction au moyen de l'hydroxyde de titane, depuis 1990, par évaporation et vitrification des concentrats. Par rapport à l'année 1975, l'efficacité du procédé a été multipliée par 1500. Le comportement de 125Sb dans le milieu marin s'interprète en fonction de l'hydrolyse de Sb à l'état d'oxydation V. Ses capacités de transfert à partir de l'eau de mer vers les constituants du milieu sont faibles ; les valeurs des facteurs de transfert évalués in situ (en L kg-1 référencées par rapport à la matière fraîche) ne dépassent pas 50 pour les espèces végétales et animales, elles varient de 60 à 900 pour les sédiments (en fonction de leur teneur en argiles fines). Ainsi, 125Sb constitue un excellent marqueur des masses d'eau qui a permis l'adaptation des modèles océanographiques de la Manche et de la mer du Nord aux conditions réelles du milieu naturel. Depuis la mise en service de l'usine en 1966 le maximum des rejets de 125Sb se situe entre 1983 et 1987 au niveau de 150 à 180 TBq an-1. Ensuite, une nette diminution des rejets est constatée. Ils ne dépassent pas 0,5 TBq en 1995 et 1996

Interactions hydrodynamiques dans le Raz Blanchard.

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Interactions hydrodynamiques dans le Raz Blanchard.

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New estimation of La Hague contribution to the artificial radioactivity of Norwegian waters (1992-1995) and Barents Sea

International audienceA release of 10000 GBq per month of a conservative radionuclide into the central part of the English Channel gives rise to activities (in Bq m-3) of 68-89 at Goury, 50-70 in Cherbourg (5 and 30 km from the waste outlet of La Hague), 25-40 in the Straits of Dover, 4-5 at the entrance of the Norwegian Channel and l-3 at the entrance of the Barents Sea. Taking account of La Hague releases and transit times of 17 and 36 months, a calculation of the contribution of La Hague to the artificial radioactivity of the entrance to the Norwegian Channel and the Barents Sea is given