Experimental Observations of the Morphodynamic Evolution of a Tidal Channel Flanked Laterally by Tidal Flats
Abstract
Recent works, both theoretical (Schuttelaars and de Swart, Eur. J. Mech., B/Fluids, 1996; Schuttelaars and de Swart, J. Geophys. Res., 2000; Lanzoni and Seminara, J. Geophys. Res., 2002; Seminara et al., J. Fluid Mech., 2010) and experimental (Tambroni et al., J. Geophys. Res 2005; Garotta et al., Proc. 5th IAHR RCEM Symposium, 2007) 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 emergence of the bed in the landward part of the channel. The above works have ignored the role of tidal flats, permanently submerged areas bordering laterally the main channel. More recently, Canestrelli et al. (5th IAHR RCEM Symposium 2007) and Tambroni and Seminara (Scientific Research and Safeguarding of Venice, 2008) have investigated numerically the morphodynamic evolution of tidal channels flanked by tidal flats making use of two dimensional numerical models. Moreover, Seminara et al. (J. Fluid Mech., 2010) have developed a fully analytical treatment, appropriate for short tidal channels, which shows that tidal flats tend to shorten the equilibrium length of the channels significantly. Here, we report on results of an experimental investigation of the latter problem, performed under controlled laboratory conditions. The experimental setup consists of a convergent, straight channel bounded laterally and symmetrically by shoals. Both channel and tidal flats have rectangular cross sections. The system is closed at one end and forced by free surface oscillations at the other end. As a first step, experiments have been conducted with non erodible tidal flats in order to analyze in which way, independently of the presence of intense sediment exchanges between channel and lateral flats, the presence of the latter, modifying the characteristics of tide propagation along the channel, affects the long term equilibrium profile of the tidal channel. Preliminary results do confirm some of the theoretical expectations, namely, starting from an initial flat bottom, the average bed profile evolves towards a configuration characterised by a deep scour at the channel inlet and the eventual formation of shores at the landward end of both channel and tidal flats. Both experimental observations, and comparison with the theoretical results of Seminara et al. (J. Fluid Mech., 2010) suggest that after 12000 tidal cycles the bottom of the channel is not jet at equilibrium. The development of a coupled theoretical model, able to take into account of the hydrodynamic and morphodynamic evolution of both tidal channels and tidal flats, is in progress and will allow further interpretation of the experimental results.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMEP24A..02D
- Keywords:
-
- 1824 HYDROLOGY / Geomorphology: general;
- 3022 MARINE GEOLOGY AND GEOPHYSICS / Marine sediments: processes and transport;
- 4217 OCEANOGRAPHY: GENERAL / Coastal processes;
- 4560 OCEANOGRAPHY: PHYSICAL / Surface waves and tides