Effects of Wave-Current Interactions on Bay-Shelf Exchange

Bay-shelf exchange is critical to coastal systems because it promotes self-purification or pollution dilution of the systems. In this study, the effects of wave-current interactions on bay-shelf exchange are explored in a micromesotidal system-Daya Bay in southern China. Waves can enlarge the shear-induced seaward transport and reduce the residual-current-induced landward transport, which benefits the bay-shelf exchange; however, tides work oppositely and slow the wave-induced bay-shelf exchange through vertical mixing and reduced shear-induced exchange. Five wave-current interactions are compared, and it is found that the depth-dependent wave radiation stress (WRS) contributes most to the bay-shelf exchange, followed by the wave dissipation as a source term in the turbulence kinetic energy equation, and the mean current advection and refraction of wave energy (CARWE). The vertical transfer of wave-generated pressure to the mean momentum equation (also known as the form drag) and the combined wave-current bottom stress (CWCBS) play minor roles in the bay-shelf exchange. The bay-shelf exchange is faster under southerly wind than under northerly wind because the bay is facing southeast; synoptic events such as storms enhance the bay-shelf exchange. The CARWE terms are dominant in both seasonal and synoptic variations of the bay-shelf exchange because they can considerably change the distribution of significant wave height. The WRS changes the bay-shelf exchange mainly through altering the flow velocity, whereas the wave dissipation on turbulence alters the vertical mixing. The form drag and the CWCBS have little impact on the bay-shelf exchange or its seasonal and synoptic variations.

Automated summary

Bay-shelf exchange is crucial for coastal systems, as it facilitates self-purification and pollution dilution. This study examines the impacts of wave-current interactions on bay-shelf exchange in Daya Bay, Southern China. Waves enhance seaward transport while tides slow exchange; wind direction and synoptic events like storms affect the exchange. CARWE and WRS are key factors in the exchange process.