Depth-Induced Breaking and Wave Set-up Representation by Coupling Spectral Wave and Coastal Hydrodynamics Models

A parallelised coupled two-dimensional model is developed to capture wave-current interactions at regional scales. The framework comprises of a spectral wave model, Simulating WAves Nearshore (SWAN), and a coastal hydrodynamics shallow-water equation model, Thetis. The two models are coupled through the Basic Model Interface (BMI) structure. They run iteratively and exchange information at prescribed time-intervals. SWAN provides the necessary parameters for the calculation of radiation stress, introduced in Thetis, upon solving the action density equation in a manner encompassing source terms accounting for deep- and shallow-water phenomena. In turn, Thetis returns water elevation and current velocity fields by considering the 2-D depth-averaged formulation of the shallow water equations. The coupled model's capability to account for depth-induced breaking, wave set-up and bed friction is tested using the physical modelling experiment of Boers (1997) on the behaviour of waves acting on a barred beach. The model’s results exhibit good correlation with experimental data, which consists of derived wave characteristics and water elevation measurements. Additionally, the model’s performance is compared against other coupled models with 3-D ocean model. The proposed model’s results showcase the same level of accuracy as other coupled models and could be extensible to 3-D modelling applications and complex geometries.