Numerical modelling of residual flow and salinity in the Río de la Plata

The Río de la Plata discharges into the Atlantic Ocean. The particular characteristics of the study area, the variable width and shallowness of the river, the high fluvial discharges and the dynamic processes involving interactions between river discharges, tidal currents and wind, generate complex velocity and salinity fields. We applied the hydrodynamic model RMA-10 to examine the effects of various forcing (tides, flow discharge and winds) on residual currents and salinity fields in the Río de la Plata, focusing on the outer zone of the river. The RMA-10 code, developed by Ian King, is a multiparameter finite element model representing estuarine flow in three dimensions. In this study the model has been applied in a depth-averaged-baroclinic mode and a series of observed data is used for model calibration and verification. The model result shows that it is able to simulate velocity and the salinity fields with a reasonable accuracy. The analysis of residual currents in the river, when forced by freshwater discharge and astronomical tide, shows that the flow discharge takes place mainly over the shallower areas of the river and that the saline water is advected up-river through the deeper channels. The numerical simulations show that the winds from the South-West and North-East quadrants have a great influence over the salinity and velocity fields.