Depth-Averaged Idealized Modelling of Morphodynamic Equilibria in Short Semi-Enclosed Meso-Tidal Basins

The bed shape of many tidal basins in coastal regions is characterized by complex patterns of channels and shoals, which exhibit cyclic behaviour, resulting from the interplay among water motion, sediment transport and bottom changes. A depth-averaged (2DH) idealized model is developed to directly identify morphodynamic equilibria in short semi-enclosed meso-tidal inlet systems with arbitrary planform geometries using a continuation approach. By means of this model, the morphodynamic equilibria in short tidal basins are systematically studied, with a specific focus on their sensitivity to the Coriolis effect and variations in planform geometry.
The model results show that in the case of a sufficient degree of widening in the landward direction, the equilibrium bed profile exhibits significant lateral structures, characterized by a central shallow ridge flanked by two deeper channels. The first channel bifurcation, as observed in many short tidal inlet systems, is forced by the planform geometry of the basin and is sensitive to the exact planform geometry considered. The associated physical mechanisms are explained. Furthermore, two mechanisms inducing asymmetric morphodynamic equilibria are investigated, of which the effect of an asymmetric basin planform seems to be dominant over that of the Coriolis force.