Tidal and subtidal propagation in two Atlantic estuaries: Patos Lagoon (Brazil) and Ria de Aveiro (Portugal)

Abstract

Processes affecting the exchanges between lagoons and the adjacent inner continental shelf are controlled by tidal and subtidal oscillations. Patos and Ria de Aveiro are coastal lagoons located on the southeast coast of Brazil and northwest coast of Portugal, respectively. In the Patos Lagoon the tidal regime is micro-tidal and the local and nonlocal wind forcing dominate the hydrodynamics, while in the Ria deAveiro lagoon tides are meso-tidal and represent the main forcing. The main purpose of this study is to compare the propagation of tidal and subtidal oscillations throughout the access channel of the Patos Lagoon and the main channels of Ria deAveiro Lagoon. Predicted time series of sea surface elevation (SSE) were obtained through modelling experiments for Patos Lagoon, while measurements of SSE were carried out in several stations distributed along the main channels of the Ria deAveiro Lagoon, providing the data for this comparative study. The SSE time series were high-pass/low-pass filtered and the propagation of tidal and subtidal oscillations was estimated for both lagoons by shifting from the time domain into the frequency domain and applying spectral and cross-spectral analysis to the filtered SSE time series. Results indicate that tidal and subtidal oscillations are differently attenuated in these lagoons due to the different local and non-local forcing and to the morphology of the lagoons. This study also indicates that the proposed method is an efficient and alternative way of estimating tidal and subtidal attenuation in both micro- and meso-tidal coastal lagoons.