OCEANOLOGICA ACTA - VOL. 22 - N” 2 / A two-dimensional particle tracking model for pollution dispersion in A Corufia and Vigo Rias (NW Spain) Moncho GOMEZ-GESTEIRA ‘, Pedro MONTERO a, Ricardo PREGO b, Juan Jose TABOADA a, Paulo LEITAO ‘, Manuel RUIZ-VILLARREAL ‘, Ramiro NEVES ‘,Vicente PEREZ-VILLAR a a Group of Nonlinear Physics, Faculty of Physics, 15706 Santiago de Compostela, Spain. uscfmrgg@cesga.es b Instituto de Investigaciones Marinas, CSIC, Vigo, Spain ’ Departamento de Engenharia Me&mica, Instituto Superio Tecnico (IST), Lisboa, Portugal (Received 21 January 1998, revised 24 March 1998, accepted 24 June 1998) Abstract - A two-dimensional hydrodynamic model coupled to a particle tracking model is applied to study the dispersion processes and residence time in two Galician rias (A Coruiia and Vigo, NW Spain) under summer conditions. In A Coruiia a long residence time was found in the harbour area due to the existence of a dock, and a short one in the river area. On the contrary, in Vigo, the residence time is smaller in the harbour area, due to the Rande Strait, beyond which the river effect is negligible. 0 Elsevier, Paris / Ifremer / Cnrs / Ird two-dimensional model / passive tracers / residual currents / pollution / Galician rias Resume - Modele bidimensionnel de suivi des particules et dispersion de la pollution dans les rias de La Corogne et de Vigo (Espagne). Un modele hydrodynamique bidimensionel couple a un modele de suivi des particules a Ctd applique a deux rias de Galice (La Corogne et Vigo) pour Ctudier la dispersion et les temps de residence dans les deux estuaires en ttt. Dans la ria de La Corogne, le temps de residence des eaux est important dans la zone portuaire et court a l’embouchure du fleuve. L’inverse est observe dans la ria de Vigo, oti le detroit de Rande limite l’effet du fleuve. 0 Elsevier, Paris / Ifremer / Cnrs / Ird modele bidimensionnel / traceur passif / circulation rt%iduelle / pollution / rias de Galice 1. INTRODUCTION According to the classic definition of F. von Richtofen [31], a ria is a transverse coast, resulting from a marine transgression, which interferes with a preexistent relief of fluvial origin [37]. Along the northwestern shoreline of the Iberian Peninsula [26], a great number of bays corre- spond to this general description. The vertically integrated two-dimensional (2D) models have been widely used over the last two decades [l, 11, 16, 24, 331. In spite of the improvement of three-dimen- sional (3D) models during the past decade, 2D models still remain valid to describe situations with a weak verti- cal stratification. They are very useful for wave phenom- ena such as tides and tidal currents, or transport of solutes for which effective dispersion coefficients can be deter- mined empirically. Thus, a 2D model can be used to describe the above-mentioned rias, during seasons with low river discharge or when the area under study is far enough from the river mouth, and stratification is weak. Finally, one of the main advantages of 2D models is their low computational cost. Some of the Galician rias have been studied by different authors using these kinds of models. Pascual [28, 291 modelled the circulation driven by tide and wind in the Ria de Arousa. Using a finite-ele- ment method, Bermudez et al. [5,61, carried out different numerical studies in the rias of Pontevedra and Vigo. Oceanologica Acta (1999) 22, 2, 167-177 0 Elsevier, Paris I lfremer I Cnrs / Ird 167