Flow and sediment transport induced by tide propagation: 1. The flat bottom case

A fully three-dimensional model for the generation and evolution of sand waves and sand banks from bottom perturbations of a flat seabed subject to the action of tidal currents is proposed. A horizontally two-dimensional basic flow, comprehensive of Coriolis effects and forced by tide propagation, is considered. The basic flow is completely resolved also in the vertical direction from the sea bed up to the free surface. The flow regime is assumed to be turbulent and a Boussinesq's approach is adopted to model Reynolds stresses. The eddy viscosity depends on the distance from the bed and an accurate description of the flow close to the sea bed, where sediment motion is mainly confined, is obtained. Sediment transport is modelled in terms of both suspended and bed loads. Finally, the presence of wind waves is taken into account. The model is capable of predicting the conditions leading to the appearence of both sand waves and tidal sand banks and to determine their main characteristics (wavelength, orientation and migration speed). The predictions of the model are supported by comparing them with field data.