On the effect of tidal flats on the hydrodynamics of the Tagus estuary

Abstract

The effects of tidal flats on the hydrodynamics of the Tagus estuary are analysed using an accurate highresolution shallow water model, supported by field data. Tidal flats act mainly as energy filters, rather than sinks, transferring energy from astronomic to non-linear frequencies. They also play a major role in determining the strong resonance mode that amplifies semi-diurnal constituents. We show that the upper estuary, with extensive tidal flats, has an increasing accretion rate. This "filling-up" results from a positive feedback between sediment deposition and the hydrodynamics: accretion in the upper estuary lengthens the duration of ebbs, decreasing sediment flushing and further increasing accretion. 0 Elsevier, Paris / Ifremer / Cnrs / Ird tidal flats / tidal propagation / numerical model / Tagus estuary RCsumC-Sur l'effet des estrans sur l'hydrodynamique de l'estuaire du Tage. Les effets des estrans sur l'hydrodynamique de l'estuaire du Tage sont analysCs B travers un modtile d'Ccoulement de haute r&olution, et des donnCes de terrain. Les estrans fonctionnent surtout comme des filtres d'Cnergie, et non pas comme des dissipateurs, transfkrant 1'Cnergie des frkquences astronomiques 5 des frkquences non-lintaires. Les estrans ont aussi un rale t&s important dans la ddtermination du mode de rCsonance qui amplifie les constituantes semi-diumes. Nous montrons que la partie sup&ieure de l'estuaire, dominCe par des estrans, a un taux de stdimentation croissant. Ceci est d0 B une r&o-action positive entre le dtp6t de stdiments et l'hydrodynamique : le dkp& dans la partie supt%ieure de l'estuaire augmente la dun% des reflux de marCe, rkduisant le transport de sCdiments vers l'extkrieur, et contribuant ainsi ti leur accumulation dans l'estuaire.

Tidal, Riverine, and Wind Influences on the Circulation of a Macrotidal Estuary

“…Although convenient, these assumptions can only describe essential features and can be very restrictive in dynamical macrotidal environments. Extensive areas of wetting and drying modify an estuary's cross channel profile, causing tidal variation in stratification and turbulence, and changes in residual circulation (e.g., Fortunato et al 1999), which requires three-dimensional modeling. Therefore, a better strategy is to compare different physical influences, captured through modeling, with observations as suggested by Burchard and Hetland (2010).…”

Stratification on the Skagit Bay tidal flats

“…Although tidal flats form a relatively small portion of the total coastal and estuarine area, they can affect the circulation patterns throughout larger basins by increasing heating (Kim et al, 2010;Kim and Cho, 2011), bed friction (Nicolle and Karpytchev, 2007), and tidal volume storage (Friedrichs and Aubrey, 1988), and by altering basin resonance characteristics (Fortunato et al, 1997(Fortunato et al, , 1999 and nonlinear tidal interactions (Speer and Aubrey, 1985;Fortunato et al, 1999;Blanton et al, 2002). Tidal flats also can provide a coastal buffer (Kirby, 2000;Kim, 2003) and important habitat for fish and game (Grossman et al, 2007).…”

“…Chen et al, 2010;Talke and Stacey 2008;Lee et al, 2004), or the effects of the flats on their surroundings (e.g. Kim et al, 2010;Nicolle and Karpytchev, 2007;Fortunato et al, 1999). However, understanding the complicated circulation and salinity characteristics resulting from the shallow depths, periodic inundation, tidal flows, and river discharge on the shoals is vital to managing these natural resources.…”

Internal tide modelling and the influence of wind effects

“…In such fine grid models in regions of large tidal amplitude, wetting and drying occurred during the tidal cycle and finite difference and finite element codes were modified to take account of this (e.g. Flather and Hubbert (1989); Fortunato et al (1997Fortunato et al ( , 1999; Heniche et al (2000); Ip et al (1998)). This gave rise to a significant increase in accuracy of both the fundamental and higher harmonics of the tide.…”