Investigation of Coastal Effects of Current-Wave Coupling during a Typhoon Event using Delft3D-FM

In this study, the effects of current-wave coupling on coastal hydrodynamics during a typhoon event were investigated using the Delft3D-FM (Flexible Mesh) model. This model is advantageous for simulating flows and waves without the need for nesting, transitioning from the deep seas of the far offshore area, which have coarse resolution, to the shallow waters of the coastal area, which require high resolution. As a result, its computational time is relatively shorter compared to other unstructured grid-based numerical models. This study focused on Typhoon Maysak, which caused significant damage along the coast of Busan, a metropolitan city located on the southeastern coast of Korea. The flow module of the model was forced at the offshore boundaries with the main 13 tidal constituents extracted from the TPXO 8.0 Global Tidal Model database. Boundary conditions and wind forcing for the wave simulations were provided by the ERA5 reanalysis wave data. The flow and wave modules were coupled to simulate the storm surge during the typhoon event. The simulation results showed good agreement with the measured water level and wave data. The results also indicated that the coupling effects tend to increase the storm surge in the inner parts of the bays and raise current speeds in the nearshore.