Numerical modelling of two-dimensional wave transformation processes from nearshore to a shallow foreshore: comparison between the MIKE21, SWASH and XBeach models.

Sieglien De Roo, Tomohiro Suzuki, Gerasimos Kolokythas, Gensheng Zhao, Toon Verwaest

Monday 29 june 2015

15:20 - 15:35h at Amazon (level 1)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 2C. Coastal engineering

Coastal protection measures against extreme storm surges and sea level rise (e.g. beach nourishments, storm return walls) are based on the estimated extreme wave characteristics at the foreshore or at the toe of a dike since they determine the amount of wave overtopping over the dike during a storm event. To obtain these wave characteristics, wave transformation from nearshore to foreshore needs to be calculated accurately. Wave transformation processes are characterized by, amongst others, shoaling, wave energy dissipation by bottom friction and depth-induced wave breaking but also depend on two-dimensional effects such as wave shortcrestedness and wave refraction. In addition, wave-wave interactions and wave breaking result in the release of the bounded long waves that travel with an irregular wave group. It is important to take into account this frequency shift since these free long waves will influence wave run-up and wave overtopping. Given time and resources constraints, physical model tests are frequently complemented with numerical modelling to increase the number of investigated cases. These numerical models however do have limitations as well; for example, in their representation of wave transformation processes from nearshore to a shallow foreshore. For this particular condition, a comparison between the MIKE21, SWASH and XBeach models will be presented in this paper. Their results will be mutually compared in terms of accuracy (against the in situ measurements carried out in Petten (NL)) and calculation cost.