RESUMO.O estuário do rio Pará representa um sistema complexo e peculiar, com processos físicos de micro e mesoescala gerados por forçantes de diferentes fontes (por exemplo, as marés astronômicas e a descarga fluvial). No presente estudo, as principais componentes semidiurna (M2) e de água-rasa (M4) são analisadas para quantificar graus de distorção e identificar assimetrias no estuário do rio Pará. Dois medidores de maré foram fundeados. Um na margem direita (ponto #RG) e outro na margem esquerda (#LF), durante 6 meses (Setembro de 2014 à Março de 2015). Além disso, foram utilizadas cartas harmônicas da Fundação de Estudos do Mar (FEMAR). Variações laterais foram identificadas entre #RG e #LF de acordo com as cartas cotidais de amplitude e fase, com defasagem de aproximadamente 10 minutos e variação de 2 cm na amplitude. Verificamos que a onda de maré entra pelo sistema pela margem direita (#RG). Os resultados indicaram graus de distorção maiores que 10% e assimetria positiva da onda de maré, sendo que a atenuação da maré no estuário pode ser maior que 400 km estuário acima ao longo da bacia de drenagem. ABSTRACT. The Pará River estuary is a complex and special system in amazon continental shelf, with micro and mesoscale physical processes generated by forces of different sources (e.g., astronomical tides and river discharge). In this study, the main semidiurnal (M2) and the overtide (M4) components were analyzed by quantifying distortions degrees and identifying tidal asymmetries in the Pará River estuary. Two submersible tidal gauges were moored to measure the water level. One on the right margin (point #RG) and another on the left margin (#LF) recorded measurements 6 months (from September 2014 to March 2015). Furthermore, we used harmonic charts from Marine Studies Foundation (FEMAR, Fundação de Estudos do Mar). Lateral variations were also identified between #RG and #LF points from the amplitude and phase cotidal charts, with about 10 minutes delay and variation of 2 cm in tidal amplitude. We verified that the tidal wave enters in system by the right margin (#RF). The results show distortion degrees higher than 10% and positive asymmetry of the tidal wave in the Pará River, and the tidal attenuation in the estuary may be greater than 400 km upstream along the drainage basin.
This paper describes the influence of tidal currents on sediment transport on Amazonian equatorial beaches during extreme events. The study area (Salinópolis city) was divided into two sectors: western (Sampaio tidal channel) and eastern (Atalaia Island). Field surveys were conducted in 2013 during two periods of highest tides: April (the rainy season) and October (the less rainy season and Spring Equinox). The optical backscatter sensors (tide, turbidity, and wave data) and current meter sensors (velocity field data) were programmed to collect data every 0.1 and 60 seconds, respectively. They operated together for 24/12 hours on the upper shoreface (surf zone). Wave heights were higher in the Atalaia Island (up to 1 meter during the less rainy season). The currents were stronger, reaching 1.2 m.s-1, during ebb tide in the rainy season (Sampaio tidal channel). Higher turbidity values (maximum 1,200 FTU) occurred at the Atalaia Island during the less rainy season. The coastal dynamics in the area derives mostly from the Amazonian continental shelf, where intense tidal currents interact with a high volume of particulate debris, especially fine sand in Salinópolis. Nevertheless, estuaries and tidal channels are also largely responsible for sediment supply and play a key role in shoreline stability and coastal transport, especially during extreme tide events.
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