Modelling tidal currents on the coast of Portugal

Abstract

A tide circulation model of the Atlantic coast of the Iberian Peninsula has been constructed. This regional numerical model covers the whole continental shelf. The finite element computational grid is made of some 16,300 triangular elements with sizes ranging between 13 km (on the offshore boundary) and 1 km (near the coast), with local refinements on the continental shelf and in the area of Figueira da Foz. This site was selected as experimental site for the study of waves and currents in the frame of the MAST2/WAVEMOD research project. Boundary conditions along the three oceanic limits of this widely open domain are obtained from the North-Atlantic component of a World Ocean tidal numerical model known as FES94 [Le Provost, C., Genco, M.L., Lyard, F., Vincent, P. and Canceil, P. (1994) Spectroscopy of the world ocean tides from a finite element hydrodynamic model, Journal of Geophysical Research, Topex-Poseidon Special Issue]. A new radiation-like boundary condition has been introduced in the modelling system used (Telemac-2D), which solves the Shallow Water Equations (SWE), in order to interface the two models and to allow for the tidal wave to leave the northern limit without reflection. Model calibration has been performed on the dominating M 2 constituent. The introduction of the astral static potential generating the tide in the SWE improved this regional model. A long duration run (1 month) has been performed, the model being forced by the eight major tide constituents. Harmonic analysis of results has been performed on 17 tide constituents, due to non-linear interactions of constituents on the continental shelf. Comparisons with the FES94 model on one hand, and with a set of coastal tide gauges on the other hand, are good. A database of tidal harmonics is now available for forecasting sea levels and currents in this area. This work has shown that diurnal shelf trapped tide waves exist in some places along the Portuguese continental shelf, which induce diurnal dominant tidal currents in these places (North of Figueira da Foz).