Author(s): Garotta Valeria; Rummel Andreas Christof; Seminara Giovanni
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Keywords: Tide; Meanders; Scours; Deposition; Point bars; Shallow jets; Ebb-tidal delt
Abstract: This paper describes a controlled laboratory experiment on the long term morphodynamic evolution of a tidal meandering channel connected to a tidal basin. The channel consisted of five meandering reaches with a sine generated shape and constant width (0. 4 m). The channel was closed at one end and connected at the other end with a basin, representing the sea, where a prescribed tidal oscillation was generated. Two different experiments have been carried out, starting with different initial values of the mean flow depth. Observations have confirmed some of the theoretical expectations, namely the development of a quasi equilibrium pattern of the average bed profile, with deep scour at the inlet and the eventual formation of a shore landward. The interpretation of the observed characteristics of the bar-pool pattern, i. e. of the sequence of scour and deposition regions forced by channel curvature, is less straightforward. In fact, bars turned out to be in phase with curvature only in the inner portion of the channel, while the seaward pattern exhibited deposition at the outer bends and scour at the inner bends. The present experiments were also able to reproduce the formation of an ebb-tidal delta in the basin. We have performed detailed PIV measurements of the flow field over the ebb-tidal delta in the final stage of the experiment. Results show the highly asymmetric nature of the flow field, namely a quasi – irrotational character of the inflow during the flood phase and the formation of an ebb turbulent shallow jet, which is enhanced by two recirculation cells.
Year: 2007