Numerical modeling of Tagus estuary tidal dynamics

Abstract

A basic knowledge of tidal dynamics is a condition to understand different processes occurring in coastal zones, and in this particular study, in the Tagus estuary. The main goal of this study is to characterize Tagus estuary tidal dynamics through an analysis of the amplitude, phase and tidal ellipses parameters of the main semi-diurnal and diurnal tidal constituents. A two-dimensional vertically integrated hydrodynamic model was considered to be adequate to simulate Tagus estuary hydrodynamics and a model developed from the SIMSYS2D model was applied. Harmonic analysis of the model results was carried out to identify the main constituents of the tide as well as the tidal ellipses along the entire estuary. This work proved to be important because until the present there were few studies about the specific analysis of these parameters in Tagus estuary, and therefore the estuarine tidal dynamics was barely known. Results showed that the most important semi-diurnal and diurnal constituents in this system are M2 and K1, respectively. It was observed that the variations in amplitude occur where changes in the estuary morphology and depth are larger. The ellipses orientation reveals the importance of the bottom topography and of the bay geometry on the tidal fluxes, with the main flux being through the deeper zones. In fact, model results show that the tidal dynamics of this system is extremely dependent on the estuarine topography and coastline features, resulting essentially from a balance between convergence/divergence and friction effects and from an estuarine resonance mode with a period close to twelve hours.