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

The effects of tidal flats on the hydrodynamics of the Tagus estuary are an alysed using an accurate high-resolution shallow water model, supported by field data. Tidal flats act mainly as energy filters, rather than sinks, tr ansferring 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 p ositive feedback between sediment deposition and the hydrodynamics: accreti on in the upper estuary lengthens the duration of ebbs, decreasing sediment flushing and further increasing accretion. (C) Elsevier, Paris / Ifremer / Cnrs / Ird.