On energy coupling between waves and rip currents

The theory of rip currents has been extended to include energy exchange between the waves and the rip currents that they produce. This added coupling does not modify the flow field appreciably but changes the wave energy distribution across the surf zone. It is also found that for the same flow field the longshore varying energy density at the breaker line (which causes the currents) is now increased: the energy interaction resists the flow, and larger wave perturbations are needed to induce rip currents. A criterion for rip spacing is advanced, based on a minimization of the relative rate of energy dissipation. The results obtained with this criterion do not compare well with observations and indicate that lateral friction, neglected in this model, should play a significant role in the dynamics of rip currents.