Rip Currents in the Directional Wave Basin

In this picture, the beach is at the left. At the far right is the directional wavemaker, creating waves propagating directly to the beach. Towards the middle of the picture are the "sand bars" with two rip channels. In each rip channel, the rip current flowing offshore causes the incident waves to refract, curving the wave crests around the outgoing rip current.

The rip currents in this experiment, funded by the Office of Naval Research, are created by waves breaking over the sand bar, creating a piling up of water at the beach. This water must flow seaward and the most efficient way is through the rip channels.

The interesting part of this experiment is that the rip currents become unstable as they flow seaward, oscillating side-to-side within the rip channel.

References:

Haller, M. C., Dalrymple, R. A., and I. A. Svendsen, Rip Channels and Nearshore Circulation, Coastal Dynamics '97, 594-603, 1997.
Haller, M. C., Dalrymple, R. A., and I. A. Svendsen, Rip Channels and Nearshore Circulation, Waves '97, ASCE, 1997.
Haas, K., I.A. Svendsen and M.C. Haller, ``Numerical Modeling of Nearshore Circulation on a Barred Beach with Rip Channels,'' Proc. 26th Intl. Conf. Coastal Engineering, ASCE, Copenhagen, 1998.
Haller, M.C., Ph.D. disseration, 1999.
Haller, M.C. and R.A. Dalrymple, Rip Current Dynamics and Nearshore Circulation, CACR-99-05, 1999.