Tide distortion and attenuation in an Amazonian tidal river

Abstract

A B S T R A C TThe present study seeks to evaluate tidal propagation in the Guamá-Capim river system, in the Amazonian region, considering hydrodynamic and geomorphological aspects. Available data sets on fluvial discharge and water level variations were considered, besides several methods of measuring the tides (currents, water levels and discharges) recorded at different stations and in different periods. The main point argued is that fluvial discharge is the key-factor in tidal distortion and tidal bore formation in the system investigated, whereas the low relief of the area would be the main factor contributing to landward tidal incursion. The results show an impressive upward tidal incursion of more than 200 km, including substantial distortion -increasing upstream -of the tidal wave, of which the ebb phase lasts up to 5 hours longer than the flood, including higher flood current velocities as far as 161 km upstream. Generally, only hyposynchronous tidal response was observed. Seasonally, the fluvial discharge varies about 10 times in the Guamá and 4 times in the Capim River. The increase of the fluvial discharge results in an increasing distortion of the tide, besides a weak increase of the attenuation. During high fluvial discharge periods in conjunction with equinoctial tides (e.g. MarchApril), a tidal bore occurs in the system, also increased by the generally low relief. Therefore, the conclusions include: low relief and the distortion related to high fluvial discharges are the main factors controlling tidal propagation along the system and tidal bore formation. Furthermore, the system could be classified as a tidal river, in which massive regional fresh water input results in virtually non-existent salinity throughout the Guamá-Capim system. R E S U M OO presente estudo teve como objetivo investigar a propagação da maré no sistema fluvial Guamá-Capim, na região amazônica, considerando aspectos hidrológicos e geomorfológicos. Os métodos empregados incluem dados históricos de vazões fluviais e níveis d'água, além de medições próprias de maré em diferentes locais e períodos ao longo do sistema. Os principais pontos defendidos no presente trabalho incluem a vazão fluvial como principal fator para a distorção da maré e consequente formação de pororoca no sistema, assim como o baixo relevo da área seria responsável por incremento na incursão da maré para o continente. Os resultados revelam uma penetração da maré de mais de 200 km, ocorrendo também uma forte deformação da maré, se intensificando gradualmente a montante, resultando em uma vazante até 5 horas mais longa que a enchente 161 km a montante, apresentando também velocidades de enchente levemente superiores, incluindo o decaimento contínuo da altura da maré, intensificado a partir desse ponto. Sazonalmente, a vazão fluvial aumenta 10 vezes no rio Guamá e 4 vezes no rio Capim. Durante períodos de alta descarga, combinados com marés equinociais (e.g. março-abril), o fenômeno da pororoca ocorre no sistema, em associação ao baixo relevo da área. Desta for...

Seasonal, tidal, and geomorphic controls on sediment export to Amazon River tidal floodplains

“…Tides on the Amazon shelf and within the river are principally semidiurnal, with the M 2 and other semidiurnal constituents comprising 85% or more of the variance (Beardsley et al, 1995). Tides approach 5 m at the river mouth (Ponta do Céu), deform and decrease with distance upstream due to frictional effects and overtides (Gallo and Vinzon, 2005;Freitas et al, 2012;Hoitink and Jay, 2016), and reach zero near Óbidos, more than 800 km from the mouth (Figure 1). The Amazon's immense freshwater discharge forces salinity and associated estuarine processes onto the shelf (Gibbs, 1970;Geyer et al, 1996).…”

The Influence of Tides on Coastal Plain Channel Geomorphology: Altamaha River, Georgia, USA

“…Tidal river processes and dynamics have been presented in a conceptual framework depicting along‐channel sediment transport, particle size distribution, and relative energy status (Dalrymple & Choi, 2007; Lawrence et al., 2015). Further, the fluvial‐tidal interactions give rise to a transitional river reach linking terrestrial and marine dominant sections, typically referred to as the fluvial‐tidal transition zone (FTTZ) (Dalrymple et al., 2012; Freitas et al., 2012). The FTTZ may be located in single‐thread rivers (e.g., Torres, 2017) or at several locations within deltaic distributary systems (e.g., Kastner et al., 2017; Hoitink et al., 2017; Sassi et al., 2012).…”

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“…Tidal bores occur when the tide overcomes the resistance of the river flow, and once past the sandbanks that form at the mouth of the river, they run into the estuary, forming a single wave of 1997). Tidal bores are seen in many estuaries in Amapá (rivers Amazon, Gurijuba, Araguari, Amapá Grande, Calçoene, Cunani, Cassiporé), Pará (Capim River), and Maranhão (rivers Arari and Mearim) (Kjerfve and Ferreira, 1993;Costa and Torres, 2000;Freitas et al, 2012).…”