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.

This work presents the results of an investigation on how wave overtopping at a near-vertical seawall at the back of a sandy foreshore is influenced by sequences of erosive storms. The experiments were carried out in the Large Wave Flume (GWK) at Leibniz University, Hannover (Germany). The tested layout consisted of a near-vertical 10/1 seawall and a sandy foreshore with an initial 1/15 slope. Three sequences of idealised erosive storms were simulated. Within each storm both the incident wave conditions and still water level were varied in time to represent high and low tide conditions. Each sequence started from a 1/15 configuration and the beach was not restored in between storms. The measurements included waves, beach profile, wave overtopping volumes. The profile of the beach was measured after each sea state tested. Wave overtopping at each stage of the tested storms was significantly influenced by bed changes. This was linked to the measured evolution of the beach. Measurements showed that a barred profile developed quickly at the start of each sequence, and scour developed at the toe of the structure during high water level conditions, while accretion or partial backfilling developed during low water level conditions. Due to these processes, the position of a sea state in the tested sequence is shown to be an important factor in determining the wave overtopping volume. Remarkably, when a weaker idealised storm followed a more energetic one, nearly the same level of overtopping was recorded. This is explained by the foreshore erosion, leading to increased water depths and wave heights at the toe of the structure. This finding allows to quantify and to explain the variability of wave overtopping in storms following one another at intervals shorter than the recovery time of the foreshore.