Dynamics of wave-supported gravity currents in intermediate water

The dynamics of gravity currents propagating beneath intermediate water waves is investigated in the present study. Laboratory experiments were carried out in a wave flume, in which saltwater was released into freshwater by means of a point-release setup in the presence of a fully developed wave field. Results revealed a series of interesting features of the gravity current advancement and density distribution under the influence of the wave field. The advancing fronts oscillate with the same period of the wave, although front velocity appears not to be affected by increasing wave nonlinearity. The analysis of the density field highlighted the existence of an enhanced mixing process between ambient and gravity current fluid induced by the orbital motion, alongside a loss of symmetry between onshore and offshore fronts, in terms of front shape and density spatial distribution. Such an effect intensifies as wave height increases and wavelength decreases. Moreover, variations of the salinity concentration profiles during the wave phase revealed a ‘‘piston-type’’ oscillatory behavior of the gravity current concentration induced by the wave field, which oscillates accordingly to the wave phase.