Airborne observations of frontal systems in the inlet channel of the Ria de Aveiro, Portugal

Flow from the Atlantic Ocean into the inlet channel of the Ria de Aveiro, P ortugal, delimited by two west-converging breakwaters, moves a tidal prism of up to 110Mm(3). The associated velocity field controls the formation and movement of foam lines and turbid water masses, Observation by airborne 35 mm. photography and direct measurements of surface water temperature, salin ity and suspended solids concentration give a view of the circulation in th e littoral. zone, which is important as this area is soon to receive efflue nt from an outfall located c.3 kin to the north. On the flood tide turbid w ater, is diverted from the north-south direction of the littoral. drift int o the channel. On the ebb this turbid water is pushed offshore by a jet flo wing west and south-west from the channel. The surface water temperature in side the channel mouth is lower on the north side where the salinity is les s reduced by dilution with lagoon water. During the flood tide the water fl owing from the north rotates to the east forced by flow from the south-west along the axis of the channel. This motion holds the less dense water on t he south side and causes intense vertical mixing on the N side. The frontal convergence of these two water masses is usually marked at the surface by a clear foam line. (C) 2001 Elsevier Science Ltd. All rights reserved.