SWASH is a free-surface, terrain-following, multi-dimensional hydrodynamic simulation model to describe unsteady, rotational flow
and transport phenomena in coastal waters as driven by e.g., waves, tides, buoyancy and wind forces.
It solves the continuity and momentum equations, and optionally the equations for conservative transport of salinity,
temperature and suspended load for both noncohesive sediment (e.g. sand) and cohesive sediment (mud, clay, etc.).
In addition, the vertical turbulent dispersion of momentum and diffusion of
salt, heat and suspended sediment are calculated by means of the standard
k - turbulence model.
The transport equations are coupled with the momentum equations through the baroclinic forcing term, whereas the equation of
state is employed that relates density to salinity, temperature and suspended sediment.
SWASH accounts for the following physical phenomena:
The model has been validated with a series of analytical, laboratory and field test cases.
Overall, the level of agreement between predictions and observations is quite favourable, particularly in view of
the fact that a wide range of wave conditions and topographies were modelled.
SWASH is proved to reproduce the main features of surf zone dynamics, such as nonlinear shoaling, wave breaking, wave runup and wave-driven currents. For instance, considering a typical surf zone where the dominant processes of triad interaction and depth-induced breaking can be isolated, it was found that the model yields a realistic representation of the observed frequency spectra, including the overall spectral shape at frequencies above the spectral peak, and the inclusion of subharmonics. This is followed by a transformation toward a broadband spectral shape as the waves approach the shoreline. Such phenomena appear to be rooted in the ability of the momentum-conservative scheme to mimic the dynamics within travelling bores associated with wave breaking across the surf zone.