Initial formation and long-term evolution of channel–shoal patterns

A complex process-based model (Delft3D) is used to simulate the formation of channels and shoals in a schematised estuary. The model set-up enables a comparison with results obtained from other studies using idealised models. Initial (one tidal cycle) as well as long-term (up to 300 years) simulations are made. Dominant wavelengths of channel–shoal patterns are investigated together with their dependency on width and depth of the basin and the local maximum velocity. Prevalent wavelengths range between 5 and 10 km and increase with increasing width and flow velocity. Initial model results are compared with those of idealised models. The dominant wavelengths are of the same order of magnitude as those found in idealised models and their dependency on width and velocity agrees qualitatively. (Exponential) growth of the perturbations during long-term simulations provides information on the limits of validity of the idealised models. Subsequent pattern formation and changes of dominant wavelengths are attributed to non-linear interactions. Morphological developments during long-term simulations suggest that channel–shoal patterns evolve into a unique morphodynamic equilibrium state, independent of the initial perturbation.