A assimetria da onda de maré na Baía de Guanabara - RJ

Abstract

The Guanabara Bay, located in Rio de Janeiro, is considered the most prominent coastal bay in the country. Measurements by tidal gauges allowed to characterize it as a flood dominant estuary, which concerns the asymmetric character of the tidal wave. A finite volume hydrodynamic model (MOHID) was used to verify and characterize the asymmetric tidal field in all grid points and to evaluate the importance of nonlinear mechanisms, nonlinear terms of the continuity equation, horizontal advection and vertical diffusion. The model, forced with tide, reproduced the observed tidal elevations and currents successfully. For all analyzed constituents from both, data and the numerical experiments, it was observed that, at the entrance of the BG, the phase lines reach first the eastern margin, being the M4 constituent the main harmonic of shallow water indicator of this asymmetry. The tidal wave propagates with preferential orientation of the navigation channel, whose larger amplitudes are observed in the eastern portion of the BG for all semidiurnal, diurnal and M4 constituents. The asymmetry degree increases inside the BG varying from approximately 0.1 to 0.3 as observed through the data and, satisfactorily, reproduced in the numerical simulation (control experiment). The asymmetry is verified of spring and neap tides conditions in both margins, but when spring tides occur, the difference between the flood and ebb times is greater. The results indicate, therefore, the dominance of the nonlinear terms of the continuity, at the entrance station, and the vertical friction, in the other stations.