Turbulent measurements in the surf zone suspension

International audienceAn irregular wave field experiment over a mobile bed is performed in a laboratory channel. The surf zone measurements are collected at the average breaking point after the formation of a stable, non-progressing beach profile (Michallet et al. 2007). The use of a wave averaging technique allows the decomposition of the velocity into mean, orbital and turbulent components for the representation of all ensemble averaged quantities as a function of wave period normalised time. As a result, we present fields of wave velocity, TKE, TKE production, TKE dissipation rate and sediment concentration (only two points in the outer region), below the trough of the waves. Nearbed and outer region processes are both seen in the TKE production and dissipation fields. In particular, the cross-shore velocity lead due to bed friction effects shown in Shin and Cox (2006) is observed in the wave velocity and TKE fields. Although the phase lead zone is seen in the velocity and TKE fields, no corresponding production or dissipation zones could be observed. Furthermore, the zone of high TKE is much more uniformly distributed over the water column than the zones of TKE production and dissipation that are clearly separated between the nearbed and the outer regions. In the outer region, the sediment concentration (orbital component) is seen to be well correlated to the TKE and TKE dissipation zones. Finally, we detect a low frequency correlation at 0.025Hz between the velocity and sediment concentration. This frequency corresponds well to the first mode of the infra-gravity wave released at the average breaking point (Michallet et al. 2007)