Wave-current interactions in a tide dominated estuary

There is a need to understand the interactions of waves and currents in the nearshore and estuarine areas. By using observational data and an advanced model an assessment of the wave-current interactions was performed in a hypertidal estuary. The circulation model includes both barotropic and baroclinic processes arising from tides, rivers and atmospheric forcing. It is coupled to a spectral wave model and a turbulence model. Waves within the estuary are strongly modulated by the tide. Significant wave height and period are mainly controlled by time-varying water depth, but wave periods are also affected by a Doppler shift produced by the current. The major-axis depth-averaged current component is tidally dominated and wave-induced processes do not have a significant effect on it. However, the inclusion of wave effects, in particular 3D radiation stress, improves the depth-averaged minor-axis (transverse) current component. The residual currents show a clear two-layer system, indicating that the baroclinic river influence is the dominant process. The wave effects are second order, but their consideration improves the long-term modelled residual circulation profile, specially the along estuary component. The main improvement appears when a 3-dimensional radiation stress coupling is considered. The 3D version of radiation stress produced better results than the 2D version. Within the estuary, wave setup has little effect on the storm surge, while 2-way wave-current interaction improved the wave simulation. Using a 3D Doppler shift further improved the model compared with using a 2D version.