Hydrodynamic modelling of short-term dispersion in a macro-tidal sea, validation by high-resolution radionuclide tracer measurements

¹ Institut de Radioprotection et de Sûreté Nucléaire, Laboratoire de Radioécologie de Cherbourg-Octeville (IRSN/DEI/SECRE/LRC), rue Max Pol Fouchet, BP. 10, 50130 Cherbourg-Octeville, France
² IFREMER/DEL Applications Opérationnelles, Centre de Brest, Z.I. de la Pointe du Diable, BP. 70, 29280 Plouzané, France

Abstract

This work aims to validate the dispersion parameters of hydrodynamic models for the short term (hour to week), and short distances (100 m - 30 km), by using high precision and high frequency measurements of tritium obtained in the release plume. An instantaneous 2D hydrodynamic model has been developed with a mesh size of 110m and an area of 50×50 km. More than 7,000 samples have been collected and measured for tritium concentrations in 2002 and 2003. Currents and bathymetric measurements, as well as drifters observations complete these measurements. Results confirm the efficiency of the hydrodynamic model, main differences being attributable to bathymetry incertitudes. After calibration, the model gives accurate results during six hours following a release. The obtained field database represents an exceptional tool for hydrodynamic models validation in realistic conditions of releases, tide and wind, in an area where the current dynamic is particularly strong (more than 5 m/s during high tides). The dispersion parameters obtained will be applied for other hydrodynamic models covering continental macro-tidal seas. Such models will be used to simulate soluble pollutants dispersion, with known uncertainties, in realistic chronic or accidental release conditions.