Articles | Volume 6, issue 6
Hydrol. Earth Syst. Sci., 6, 983–988, 2002
Hydrol. Earth Syst. Sci., 6, 983–988, 2002

  31 Dec 2002

31 Dec 2002

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

J. Figueiredo da Silva1, R. W. Duck2, T. S. Hopkins3, and J. M. Anderson4 J. Figueiredo da Silva et al.
  • 1Departamento de Ambiente e Ordenamento, Universidade de Aveiro, 3810-193 Aveiro, Portugal
  • 2Department of Geography, University of Dundee, Scotland
  • 3Department of Marine Earth and Atmospheric Sciences, North Carolina State University, Raleigh, USA
  • 4Division of Electronic Engineering and Physics, University of Dundee, Scotland
  • Email for corresponding author:

Abstract. The 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.

Keywords: water circulation, upwelling, ocean outfall, remote sensing, eutrophication, Ria de Aveiro