Residual circulation in the Ría de Muros (NW Spain): A 3D numerical model study R. Carballo ⁎, G. Iglesias, A. Castro University of Santiago de Compostela, Escuela Politécnica Superior, Campus Universitario s/n, 27002 Lugo, Spain article info abstract Article history: Received 29 April 2008 Received in revised form 30 July 2008 Accepted 1 August 2008 Available online 17 August 2008 The residual circulation of the Ría de Muros, a large coastal embayment in NW Spain, are studied using a three-dimensional baroclinic finite-difference model. The driving forces considered by the model include the tide, winds, river inflows and density forcing at the open boundary. In situ data of current velocity and direction, water level, wind velocity and direction, river discharge, and temperature and salinity are used for model validation. Simulated and observed time series of water level and current velocity are in good agreement. Once validated, the model is applied to compute the residual circulation induced by the relevant agents of the ría hydrodynamics—the tide, an upwelling-favourable wind characteristic of spring and summer, a downwelling-favourable wind typical of winter, and freshwater inflows associated with high river runoff. The resulting residual circulation differ notably. The tide does not generate significant residual flows except in the inner ría. By contrast, winds and river discharges induce important residual flows throughout; in the middle and outer ría they generate a 3D residual circulation pattern which renders the conventional two-layer scheme of estuarine circulation too simplistic in this case. Thus, this first application of a 3D numerical model to the Ría de Muros sheds new light on its fundamental hydrodynamics. © 2008 Elsevier B.V. All rights reserved. Keywords: Hydrodynamics Numerical models Finite-difference method Residual circulation Ría de Muros Rías Baixas 1. Introduction The Ría de Muros is the northernmost of the Rías Baixas, four large embayments jutting into the NW Atlantic coast- line of the Iberian Peninsula between 42° and 43° N. From a geographical and geomorphological standpoint, the Rías Baixas are characterised as rías (Cotton, 1956) or as ‘young estuaries’ (Vidal-Romaní, 1983). From a thermohaline and dynamical standpoint, they are classified as partially mixed estuaries with a positive circulation (Souto et al., 2003). The Ría de Muros covers an area of 90 km 2 , with a mean volume of 2060 hm 3 ; its main axis extends 13 km in a general NE–SW direction (Fig. 1). The inner part of the ría, east of Pt. Testal, consists of two narrow branches oriented towards the north and the south-east. The northern branch in turn divides into two branches, into which the rivers Tambre and Tines, the main tributaries to the ría, empty. West of Pt. Testal the north bank forms a succession of bays with a general ENE–WSW orientation, whereas the south bank, less indented, has a NE–SW direction. As a result, the ría broadens from a width of 850 m at Pt. Testal to over 6000 m at its mouth. The bathymetry (Fig. 2) presents roughly triangular transverse sections in the outer and middle ría, with depths along the axis decreasing steadily from ~45 m at the mouth to less than 10 m in Freixo Bay. Upstream water depths are also below 10 m, with tidal flats constituting a significant part of the inner ría surface. The largest freshwater inflow is provided by the River Tambre, with an annual mean flux of 54 m 3 s - 1 . The contribution of the River Tines, 0.61 m 3 s - 1 (annual mean flux), is relevant only in the vicinity of its mouth. The average tidal range is 2.5 m (mesotidal). The amplitudes and phases of the seven major tidal con- stituents, obtained from the LeProvost global data base Journal of Marine Systems 75 (2009) 116–130 ⁎ Corresponding author. Fax: +34 982285926. E-mail address: rcarba@usc.es (R. Carballo). 0924-7963/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jmarsys.2008.08.004 Contents lists available at ScienceDirect Journal of Marine Systems journal homepage: www.elsevier.com/locate/jmarsys