Techniques for long-term morphological simulation under tidal action

Abstract

Long-term morphological simulation using real time models—i.e. models designed to reproduce short-term processes and run on the long-term—leads to prohibitively time consuming computation. This paper deals with very pragmatic techniques aiming at the reduction of this computational cost in the case of tidal current situations. In the first part, the reduction in the number of distinct events to be simulated is investigated, by selecting a limited set of natural situations which affect the bed like the whole actual set of tidal situations would do. Then methods for computation, at a reasonable cost, of the flow perturbations induced by the bed changes are presented: they make it possible to avoid too frequent complete re-computation of the hydrodynamics during long-term simulations. Finally, four methods aiming at the increase of the effective morphological time step are described and tested; as a matter of fact, they lead to quite cheaper computations, while the error specifically linked to this time schematization remains quite small.