SWAN

SWAN can be used for the simulation of wave generation, propagation and dissipation in coastal areas.

Data on wave conditions is often available offshore but not nearshore. Accurate on site wave data is crucial in studies into coastal development, harbour design or breakwater design. SWAN is a wave generation and propagation model which can be applied to derive the wave conditions in the nearshore area. SWAN is also suitable for use as a wave hindcast model in water of intermediate and shallow depth for situations where the wind field may be considered constant. Typical areas for the application of SWAN range between 10 X 5 km2 and 30 X 100 km2 (e.g. along a coastal strip).

The processes modeled by SWAN are:

• Wave generation by a spatially varying wind;
• Refraction over a bottom of variable depth;
• Refraction over a spatially varying ambient current;
• Dissipation by wave breaking;
• Dissipation by bottom friction;
• Wave blocking by current;
• Non-linear wave interactions.

SWAN explicitly includes the effects of non-linear four wave interactions (quadruplets) and three wave interactions (triads). The discrete representation of the frequency spectrum means that SWAN is more suitable than previous models for application in areas where strong growth due to wind action may occur where swell or the remains of old sea states is also present (e.g. behind island barriers or bank systems)

SWAN represents the wave field on a two dimensional horizontal rectangular grid covering the computational area. At each grid point, SWAN represents the complete 2D-action density spectrum discretely as a function of frequency and direction. (Action is equivalent to energy when there are no currents). SWAN represents wave propagation in all directions. It explicitly includes the effect of non-linear four wave interactions (quadruplets) and three wave interactions (triads). The solution technique marches forward row by row over the grid beginning at the incident wave boundary, where the incident wave characteristics can be defined. The results in each direction sector at each grid point are computed from the results for the grid points in the previous row. The propagation of energy is modeled using an energy balance equation adapted to include terms for wave growth by wind action or dissipation due to bottom friction or wave breaking.

SWAN was developed by the Delft University of Technology and has been verified using results from both field measurements and from physical model tests. The SWAN-model can be obtained from the internetsite of Delft University of Technology, see http://fluidmechanics.tudelft.nl/.

© 2001Alkyon Hydraulic Consultancy & Research, The Netherlands.