-The hydrologkal features of Ria de Aveiro, a coastal lagoon on the northwest Atlantic coast of Portugal, were investigated in two sampling surveys carried out between 316 and 2416197 and between 2916 and 717197, respectively. There was a significant freshwater inflow into the lagoon during the first survey, especially in the first days, due to the recent rainfalls. Records concerning water level, salinity, temperature and current velocity were performed at several stations located along the four main channels of the lagoon. The type of tide at the mouth was determined and was observed that astronomical tide is the main fiorcing agent driving water circulation in Ria de Aveiro. The tide at the mouth is semidiurnal and the tidal wave propagation in the lagoon has the characteristics of a damped progressive wave. Typical estuarine longitudinal salinity and temperature gradients connected with the distance to the mouth were identified, whereas vertical and transverse gradients were found unimportant, except in the frontal zone between oceanic and fresh water masses. According to the results, even though Ria de Aveiro should be considered as vertically homogeneous, some channels may reveal characteristics of a partially mixed estuary, depending on the freshwater input. 0 1999 Ifremer / CNRS / IRD / Editions scientifiques et medicales Elsevier SAS water level I salinity I temperature I current velocity I Ria de Aveiro RCsumC -CaractCrisation hydrologique de la Ria de Aveiro, Portugal, au dCbut de I'&& Les caracteristiques hydrologiques de la Ria de Aveiro, lagune c&i&e situ&e au nord-ouest du Portugal, ont Cte 6tudiCes au tours de deux campagnes effectuees entre le 38 et le 24 juin 1997 et entre le 29 juin et le 7 juillet 1997. Ces periodes suivent d'importants apports d'eau deuce dus a des pluies survenues au debut de la premiere campagne. Le niveau de l'eau, la salinite, la temperature ainsi que l'intensitt et la direction du courant ont CtC enregistres en plusieurs stations situees le long des quatre branches principales de la Ria de Aveiro. Les caracteristiques de la maree a l'embouchure de la Ria ont ttt mises en evidence. La circulation a l'interieur de la lagune est principalement for&e par la make astronomique de type semi-diurne.

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This work presents results from numerical modelling studies on the hydrodynamics and sediments and passive particles transport properties in Ria de Aveiro, a shallow lagoon located on the Portuguese Northwest Atlantic coast. The hydrodynamic of the lagoon was systematically studied, from both the Eulerian and Lagragian point of view, in order to understand the overall circulation in the lagoon, characterize the dynamics of its different channels and assess the transport of suspended cohesive sediments.The two complementary approaches, Lagrangian and Eulerian (general and residual transport), were found to be useful tools in order to assess the overall and longterm transport of suspended particles in the lagoon.Tidal, wind-and river-induced residual currents contribute to the net exportation of water and particles towards the ocean. Residual currents at the far end of the channels are small, indicating areas of deposition and bed consolidation.Tidal currents are the main forcing processes in transport of suspended sediments and the concentration of sediments follows the tidal cycle. The effect of Vouga river inputs on the suspended concentration in the lagoon is enhanced during spring tides, high river runoff and periods of strong wind. In most parts of Ria de Aveiro, deposition is the dominant process, indicating that the lagoon has a very consolidated bed.

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Abstract.A two-dimensional vertically integrated hydrodynamic model coupled to a particle tracking model is applied to study the dispersion processes and residThe only dispersion process that is considered in this study is the advection, according to the main characterence time in Ria de Aveiro lagoon (Portugal).istics of the local hydrodynamic.The particle tracking model computes the particles position at each time step, using a fourth-order Runge-Kutta integration method. The dispersion of passive particles released along the lagoon and in critical areas are studied in this work. The residence time is also determined for the entire lagoon. The results show that the mixture between particles coming from different channels of the lagoon is negligible in a time scale higher than 2 tidal cycles. The residence time for the lagoon central area is about 2 days, revealing a strong marine influence in this area. At the upper reaches of the channels were found values higher than 2 weeks. Q