Ria–ocean exchange driven by tides in the Ria of Ferrol (NW Spain)

The hydrography of the Ria of Ferrol (situated North of Cape Finisterre, NW Spain) was analyzed during a year as a function of the two main forcing factors: river discharge and tide. Salinity, temperature and tidal currents were measured at a fixed station in the middle part of the estuary during a tidal cycle (12 h). In addition, thermohaline variables were also measured bihourly at six stations along the main channel of the estuary. The stratification and water column stability were found to vary in different sections of the estuary as a function of the estuarine Richardson number and the Brunt-Va¨ isa¨ la¨ frequency. Well-mixed conditions were found at the mouth where large tidal velocities enhance the turbulent mixing. In contrast, the middle and inner parts of the Ria of Ferrol were observed to be partially stratified during the wet season. This behavior is different to the one observed in the Galician Rias Baixas (situated further south) that are everywhere partially stratified despite the fact that the ratio of freshwater input to the water content is similar to that in Ria of Ferrol.