Nearshore circulation revealed by wastewater discharge from a submarine outfall, Aveiro Coast, Portugal

Abstract

Nearshore circulation revealed by wastewater discharge from a submarine outfall, Aveiro Coast, Portugal 983Hydrology and Earth System Sciences, 6(6), 983-989 (2002) AbstractThe morphological and climatic conditions of the Atlantic coast of northern Portugal result in a prevailing upwelling circulation over the continental shelf. A submarine outfall releases wastewater into the ocean c. 3 km directly offshore (at ~16 m water depth) from S. Jacinto, 5 km to the north of the inlet to the estuarine coastal lagoon system of the Ria de Aveiro. The buoyant plume has a distinctive reddish brown colour and is clearly visible at the water surface. The transport and dispersion of the plume was monitored by airborne photography and by in situ water sampling. Results revealed the surface currents present and water mass fronts in the nearshore zone of the Aveiro coast. During the spring and summer, the plume was not transported offshore in the manner expected by the upwelling shelf circulation. Instead, it was commonly observed to be transported alongshore with the prevailing southerly circulation or with an onshore component. The transport to the south caused the outfall plume to interact with the circulation associated with the tidal currents generated in the inlet channel to the Ria de Aveiro. The observations suggest that the trophic status of the Ria de Aveiro is unlikely to change because of the operation of the submarine outfall. Furthermore, this study demonstrates how simple observations of wastewater discharge from a submarine outfall can be used to improve understanding of nearshore circulation.

Occurrence and sources of selected phenolic endocrine disruptors in Ria de Aveiro, Portugal

“…The prevailing inshore water current along the Aveiro coast is to the south. In a study on the Ria de Aveiro wastewater outfall using aerial observations and in situ water sampling, Figueiredo da Silva et al (2002a, b) observed no offshore transport of the wastewater plume, but most commonly transport in the direction of the lagoon inlet channel. This suggests that impacts of pollutants discharged can be anticipated in nearshore waters and potentially within the estuarine system (Figueiredo da Silva et al 2002a).…”

“…The wastewater treatment facilities in the estuary were built relatively recently, and until 2000, the effluents were discharged directly into the lagoon. Presently, all legal sources of effluent discharge are directed towards the ocean via a submarine outfall, which discharges domestic (30%) and industrial (70%) effluents after secondary treatment into the coastal area at 3.3 km offshore, 5 km north of the lagoon inlet (Figueiredo da Silva et al 2002a ). The prevailing inshore water current along the Aveiro coast is to the south.…”

“…Some literature suggests that a considerable part of this effluent flows back into the lagoon with tidal currents and could therefore be a relevant source of contaminants to the lagoon area (Figueiredo da Silva et al 2002a). In the current study, the wastewater outfall was considered as one possible main source of EDCs for Ria de Aveiro.…”

“…Another interesting feature of Ria de Aveiro is the submarine wastewater outfall which was constructed several years ago and discharges all the treated wastewater of the area into the Atlantic Ocean, a few kilometres from the inlet of the estuary. Some literature suggests that a considerable part of this effluent flows back into the lagoon with tidal currents and could therefore be a relevant source of contaminants to the lagoon area (Figueiredo da Silva et al 2002a ). In the current study, the wastewater outfall was considered as one possible main source of EDCs for Ria de Aveiro.…”

Freshwater Dispersion Plume in the Sea: Dynamic Description and Case Study

“…Garvine (1987) classified plumes as supercritical or subcritical using the ratio of horizontal discharge velocity to internal wave phase speed and he later proposed (Garvine, 1995) a classification system based on bulk properties of the buoyant discharge. Referenced plume studies present numerical modelling of the case, in situ observations (Sherwin et al, 1997;Warrick & Stevens, 2011;Ogston et al, 2000), satellite observations (Di Giacomo et al, 2004;Nezlin and Di Giacomo, 2005;Molleri et al, 2010) or aerial photographs (Figueiredo da Silva et al, 2002;Burrage et al, 2008). In several cases two techniques are coupled (O'Donnell, 1990;Stumpf et al, 1993;Froidefond et al, 1998;Siegel et al, 1999).…”