Characteristics Of The Entrained Air Bubble Cloud In The Swash-Zone

The swash zone plays an important role in the erosion and deposition of a beach because of the interaction of the loose sediments with the highly turbulent incoming and retreating swash flow. Details of a new experimental investigation to further understand the hydrodynamics of this flow in the swash zone are presented in the current paper. The focus of the investigation is on the effect of the entrained air bubble cloud on the hydrodynamics. Flow in the swash zone was generated in the laboratory using a dam-break mechanism that yielded a single, large-scale and highly repeatable swash-event on a 1: 10 impermeable coarse-sand beach with a surface roughness based on 2.0 mm sand. Measurements of the hydrodynamics, the flow depth and flow velocity, were obtained simultaneously through a combined PIV, particle image velocimetry, and LIF, Laser induced fluorescence, system at five different locations along the beach. At those same locations the phase-signal of the flow was obtained through phase optical probes at several heights above the beach surface. Results are presented that show the time-dependent hydrodynamic properties of the flow, including the ensemble-averaged flow depths, depth-averaged ensemble-averaged bed-parallel velocities, and the corresponding properties of the entrained air bubble cloud, including the void fraction time-series and profiles, the mean air bubble size and mean air bubble velocity.