Ph.D. Thesis, 2010. Paper abstract bibtex
The Sado estuary is located in the surrounding area of an important Portuguese natural park (Arrábida Natural Park) near the city of Setúbal. The low freshwater discharge from Sado River, the mesotidal tide along the estuary and the strong currents observed turn the estuary a well‐mixed system, controlling the estuarine residence time, and therefore determining the patterns of conservative and non‐ conservative tracers. The salt dynamics inside this kind of system is very important, since salinity may be considered a natural tracer, allowing the comprehension of the dynamics of other conservative tracers. In such a system is also important to analyze the water quality determining the coliforms propagation from selected discharge stations and analyzing its relation with the estuarine hydrographic features. In this study, a two‐dimensional hydrodynamic model is implemented for the Sado estuary in order to study the horizontal patterns of salinity, as well as the propagation of fecal coliforms from sewage stations, both under different tidal and freshwater forcing conditions. The model used in this study is Mohid‐2D (www.mohid.com), a marine model that uses the shallow water approximation to study vertically homogeneous systems like the Sado estuary. The model domain includes the whole area of the estuary, using a realistic coastline and bottom topography The model results are explored in order to evaluate salinity differences between flood and ebb, spring and neap tide, and low (2m3s‐1), medium (50m3s‐1) and high (200m3s‐1) river inflow. Moreover, the propagation of fecal coliforms from sewage stations is also studied in light of different tidal and freshwater inflow conditions. Sea surface height and velocity model outputs are compared to in‐situ data, revealing the model skill in reproducing the tidal propagation along the Sado estuary. When the river inflow is weak (2m³/s), the hydrography of the estuary is clearly tidal dominated but when the river inflow is high (200m³/s), the horizontal patterns of salinity inside the estuary are determined by a balance between tide and river inflow effects. In this case is found a classic division of the estuary in three distinct regions: marine, mixing and freshwater. In this last region the estuary dynamics is mainly modulated by the freshwater discharge. Despite the significant estuarine dynamics, the concentration of fecal coliforms was found confined to small areas close to the discharge points. These organisms were found to affect only a restricted area near the sewage stations, with low concentrations found far the discharge points along the estuary.