NW Iberia Shelf Dynamics. Study of the Douro River Plume.
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1
Centro Interdisciplinar de Investigação Marinha e Ambiental, Portugal
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2
Instituto de Hidráulica e Recursos Hídricos, Portugal
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3
Centro de Ciências Matemáticas, Portugal
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4
Faculdade de Engenharia, Portugal
River plumes are one of the most important mechanisms that transport the terrestrial materials to the coast and the ocean. Some examples of those materials are pollutants, essential nutrients, which enhance the phytoplankton productivity or sediments, which settle on the seabed producing modifications on the bathymetry affecting the navigation channels. The mixing between the riverine and the oceanic waters can induce instabilities, which might generate bulges, filaments, and buoyant currents over the continental shelf. Offshore, the buoyant riverine water could form a front with the oceanic waters often related with the occurrence of current-jets, eddies and strong mixing. The study and modelling of the river plumes is a key factor for the complete understanding of sediment transport mechanisms and patterns, and of coastal physics and dynamic processes. On this study the Douro River plume will be simulated. The Douro River is located on the north-west Iberian coast and its daily averaged freshwater discharge can range values from 0 to 13000 m3/s. This variability impacts the formation of the river plumes and its dispersion along the continental shelf. This study builds on the long-term objective of generate a Douro River plume forecasting system as part of the RAIA and RAIA.co projects. Satellite imagery was analyzed showing that the river Douro is one of the main sources of suspended particles, dissolved material and chlorophyll in the NW Iberian Shelf. The Regional Oceanic Modeling System (ROMS) model was selected to reproduce scenarios of plume generation, retention and dispersion. Whit this model, three types of simulations were performed: (i) schematic winds simulations with prescribed river flow, wind speed and direction; (ii) multi-year climatological simulation, with river flow and temperature change for each month; (iii) extreme case simulation, based on the Entre-os-Rios accident situation. The schematic wind case-studies suggest that the Douro River plume is wind-driven. The simulations show important differences in the plume structure and dispersion pathways depending on the wind strength and direction that was simulated. When southerly winds are implemented, it can be seen that those winds push the river water to the north. With this scenario, the water associated with the Douro River can be found in the Galician Rías. The upwelling favorable winds (northerly winds) induce plumes with a narrow coastal current. The high surface salinity on the plume regions during strong wind events suggests that the wind enhances the vertical mixing. Several analysis shows that the plume is affected by Coriolis effect but its influence is mitigated by a strong wind forcing. The multi-year climatological study showed a variation of the plume structure with the climatological conditions in the area. During the first months of the simulation, a southwest protruding jet-like plume can be seem, meanwhile, during winter months the bulge and the coastal current seem to evolve to the north, according with the climatic wind conditions. On this simulation it was observed a plume response with the behavior of the offshore geostrophic current system. Offshore eddies and filaments are also responsible for the cross-shore transport, through the horizontal advection of plume waters. Extreme river discharges, associated with southerly winds, can transport debris to the Galician coast in about 60 h, helping to explain the tragic events of the Entre-os-Rios accident of March 2001. Analysis of the Rossby deformation radius and the Kelvin number confirm that the Douro supercritical plumes are strongly affected by the planetary rotation. The supercritical plumes coincided with the coastal current maximum widths. The values obtained for the densimetric Richardson number showed that the supercritical plumes are less mixed than the subcritical ones.
Acknowledgements
RAIA (0313-RAIA-1-E) and RAIA.co (0520-RAIA-CO-1-E) projects provided postdoctoral funds for Isabel Iglesias. The RAIA Coastal Observatory has been funded by the Programa Operativo de Cooperación Transfronteriza España–Portugal (POCTEP 2007–2013). Numerical model solutions were calculated at CIIMAR’s HPC unit, acquired and maintained by FCT pluriannual funds (PesTC/Mar/LA0015/2013). Rui Caldeira was supported by funds from the ECORISK project (NORTE-07-0124-FEDER-000054).
Keywords:
cross-shore transport,
advection,
alongshore currents,
buoyant plumes,
NW Iberian Peninsula
Conference:
IMMR | International Meeting on Marine Research 2014, Peniche, Portugal, 10 Jul - 11 Jul, 2014.
Presentation Type:
Poster Presentation
Topic:
OCEANOGRAPHY AND MARITIME TECHNOLOGY
Citation:
Iglesias
I,
Couvelard
X,
Avilez-Valente
P and
Caldeira
RM
(2014). NW Iberia Shelf Dynamics. Study of the Douro River Plume..
Front. Mar. Sci.
Conference Abstract:
IMMR | International Meeting on Marine Research 2014.
doi: 10.3389/conf.fmars.2014.02.00183
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Received:
30 May 2014;
Published Online:
18 Jul 2014.
*
Correspondence:
Dr. Isabel Iglesias, Centro Interdisciplinar de Investigação Marinha e Ambiental, Porto, 4050-123, Portugal, isabel.iglesias.fdz@gmail.com