Surf-zone dynamics

The surf zone of sandy beaches is the region where incoming waves break while propagating towards the shore and release most of their energy and momentum. It is characterized by highly turbulent flows and intense sediment transport so that is a highly dynamic region and significant morphological changes at horizontal length scales of tens of meters may occur within a few hours.  The surf zone is important because it dissipates the wave energy thereby protecting the dry beach (and human settlements on the nearshore). In addition, it is a sand buffer that exchanges sand with the beach. During storms the beach tends to lose sand which is stored in the surf zone while during fair weather this sand tends to return to the beach.  Finally, the surf zone is the place where many beach recreational activities (swimming, surfing) take place and knowing the currents there (e.g. rip currents) is important for safety and efficient use.

A scientific challenge is the dynamics of the cross-shore bed profile and the advance/retreat of shoreline position. This is coupled to the generation and displacement of breaker bars, i.e., sand deposits at certain distance offshore. Sand bars can be more or less rectilinear and parallel to the shore or can adopt  morphologies called rhythmic bars (crescentic, transverse). Rhythmic bars are associated to megacusps (undulations of the planform shoreline shape) and, more importantly, to rip channels. The latter are bed depressions in between the shoals of the bars that focus strong offshore directed currents that are dangerous to the beach users.  The intricate dynamics of shoreline position, bed topography in the surf zone and the associated currents and wave breaking distribution is the aim of our research.