Swash-groundwater dynamics in a sandy beach laboratory experiment

Experiments are carried out in a wave basin in order to study the swash-groundwater interaction. A set of wave gages and pressure sensors are used to monitor the free surface and groundwater dynamics. The study is based on the comparison of two selected cases which differ by the gravity and infragravity forcing conditions, the features of wave breaking in the surf zone, the presence of a standing wave attached to the beach face and the wave setup at the shoreline. Significant differences are observed in the response of the swash-groundwater system. The water table overheight appears to be controlled by the amount of infragravity energy available at the shore. Cyclic beach drainage processes can be observed when the water table is low. Significant time-averaged and time-resolved flows are observed into the sand, depending on the swash hydrodynamics. The presence of a gravity standing wave modulation attached to the shore is shown to affect swash and groundwater dynamics. Most of the pressure gradients observed under the swash zone are related to infiltration flows and are thus related to moderate increase of the sediment relative weight.