Quantification of wave–current interactions in a tide-dominated harbour: A fully coupled modelling study of Darwin Harbour, Australia

The present work investigates the effects of wave-current interactions in a tidally dominant harbour, using Darwin Harbour in Australia as a case study. Numerical experiments were performed using a two-way coupled FVCOM modelling system across five distinct configurations: a hydrodynamic model, a fully coupled wave-current interaction model, a wave model, a fully coupled model excluding wind forcing, and a fully coupled model without swell input. The findings indicate that the fully coupled model produces stronger, spatially diverse velocity fields during both flood and ebb tides. Directional patterns of surface and bottom current fields indicate wave-induced modification of flow vectors near wave-exposed boundaries and shallow zones, resulting in spatial variation in current direction and intensity in different regions of the harbour during flood and ebb phases. The spatial autocorrelation analysis of wavelength reveals a sharp contrast between the dynamics of the outer and inner harbours, with swells ensuring coherent long-period wave behaviour offshore, while local wind forcing leads to shorter wavelengths and higher variability inland. The study found that wave refraction due to depth has a stronger impact than refraction due to current, influencing wave direction and height at different tidal phases. The results analyse radiation stress gradients, refraction, and swell and wind-induced waves, identifying tidal depth modulation as the primary control on wave transformation and radiation stress gradient feedback as the primary wave effect on current circulation. These findings emphasise the importance of two-way coupling for accurately depicting wave transformations, flow patterns, and directional energy redistribution in morphodynamically complex, tide-dominated harbours.