On the development and verification of a 2-D coupled wave-current model on unstructured meshes

In this paper, the numerical framework for a freely available fully coupled wave-current model, which solves the Shallow Water and the Wave Action Equation (WAE) on unstructured meshes in geographical space and some first applications are presented. It consists of the hydrodynamic model SHYFEM (Shallow Water Hydrodynamic Finite Elements Model), and the 3rd generation spectral wave model WWM (Wind Wave Model). The application of numerical schemes on unstructured meshes renders the coupled model more efficient in resolving the model domain, the bathymetry and the involved gradient fields of currents, water levels and wave action. The source codes of the models have been coupled using FIFO (First In First Out pipes) data files. This technique makes an effective model coupling possible without cumbersome merging of both codes. Furthermore, it gives both source codes a universal interface for coupling with other flow or wave models. The coupled model was applied to simulate extreme events occurring in the Gulf of Mexico and the Adriatic Sea. In particular the wind and wave-induced storm surge generated by Hurricane Ivan was investigated and the results have been compared to the tidal gauge at Dauphin Island with reasonable results. For the case of the Adriatic Sea, the model, validated for the year 2004, has been applied to simulate waves and water levels induced by the century storm in November 1966 that lead to catastrophic and widespread damages in the regions of the Venice Lagoon. The obtained results have been compared to in situ measurements with respect to the wave heights and water level elevations revealing good accuracy of the model in reproduction of the investigated events. Especially, the Hurricane Ivan simulations showed the importance of inclusion of the wave–current interactions for the hindcast of the water levels during the storm surge. In a comparison to water level measurements at Dauphin Island, inclusion of the wave induced water level setup reduced the root mean square error from 0.13 to 0.11 m and increased the correlation coefficient from 0.75 to 0.79. For the case of the Venice Lagoon, the comparison with the measurements showed that the model without wave–current interactions led to a good hindcast of water levels for the location Punta Salute, which is located in the inner part of the Lagoon. Nevertheless, the comparison of subsequent simulations with and without the influence of the waves clearly showed a simulated effect of intense wave setup-up in the coastal area in front of the lagoon, which is plausible given the intensity of flooding that occurred there.