Author(s): N. Tambroni; G. Seminara
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Keywords: Tidal Channels; Tide Propagation; Lagoons; Tidal Flats
Abstract: Recent theoretical works (Schuttelaars and de Swart, 1996, 2000; Lanzoni and Seminara, 2002; Bolla Pittaluga, 2003) have investigated the long term morphodynamic equilibrium of tidal channels. The main outcome of such works is the prediction of the existence of an equilibrium bed profile, which is established through the propagation of a sediment wave leading to the formation of a beach in the landward part of the channel. The above works have ignored the possible presence of tidal flats adjacent to the main channel. In the present work we attempt to overcome the above limit by analyzing the effect of tidal flats on the hydrodynamics of tidal channels, as a first step to proceed to analyse their morphodynamic role. We start by attempting to gain some general insight of the process on the basis of an analytical approach. The latter is necessarily based on a simplified scheme relying on classical assumptions, namely 1-D model, tidal forcing characterised by small relative amplitude, no channel convergence and linear dissipation. Results show that the resonance length decreases as the width of tidal flats increases, a behaviour which explains why, for a given channel length, as a result of the presence of tidal flats the flow velocity in the channel is typically increased. The above 1-D analytical findings have then be extended to cover non linear effects, by first relaxing the linear constraints still in the context of a l-D model. Finally we solve the full 2-D shallow water equations numerically for the case, often encountered in nature, of frictionally dominated channels with adjacent tidal flats. Numerical results do confirm the general behaviour emerged from the analytical results and suggest that addition of tidal flats to the channel modify the character of the flow field in the channel.
Year: 2007