Improvement to the Treatment of the Wave Setup Along Open Boundaries in the Swan Wave Model

Abstract

The calculation of the increase of mean sea level during hurricanes is a major issue in ocean modeling. Consequently, the wave setup is an important aspect of research which can reach significantly high values. Storm events in particular, when wave setups generated by wind storms are able to increase the mean sea level, enhance the risks of damage to coastal infrastructure. SWAN is a third-generation wave model, developed at the Delft University of Technology that computes random, short-crested wind-generated waves in coastal regions and inland waters. The optional command SETUP in the SWAN configuration activates the wave-induced set-up computation, modifying the water level taken into account by the model. Concerning SWAN-SWAN nesting, SWAN reads the wave boundary conditions in the relevant output file of the parent grid that are then transferred to the child grid. By default, the wave setup information is not contained in this file. When the wave setup is involved, the user can impose only one value of wave setup in the child grid. This imposed value will not cover the open boundaries, but will be applied at the deepest point in the computational grid. The latest SWAN version 40.91 was improved to facilitate the transfer of wave setup simulated on the parent grid into the child grid without the intervention of the user, and as a consequence of increasing the accuracy of wave setup simulations. This new version was validated through a particular violent wind storm that impacted on the French coast on the 28th of February 2010 (Xynthia). This specific event generated significant wave setup, accumulating offshore throughout the period in question and propagating toward the Pertuis coast.