Abstract:
A laboratory study of the flow over a bar with a single rip channel has been performed. First, the well-known pattern of a bar
circulation cell with a strong offshore-directed current out through the rip channel and a weaker onshore-directed return flow over
the bar is documented. Then measurements of the three-dimensional structure of the flow in the area where the rip channel, the
bar and the trough meet and well inside the rip channel are presented. These measurements reveal that 3D effects play an
important role, and that a depth-integrated viewpoint may not always be sufficient for predicting the flow in the near bed region.
Particle-tracking experiments illustrate the near bed flow pattern over the entire area. These demonstrate how the overall
trajectory pattern changes as a function of the distance of wave breaking from the bar crest: For some conditions, the rip current is
fed from the trough and for other conditions it is fed directly from the bar. Both the 3D measurements and the trajectory tests show
the existence of a weaker onshore-directed near-bed drift in the area where the rip current ceases. Finally, in a series of sensitivity
tests, measurements of the rip current intensity for different wave climate and water level conditions reveal a strong correlation
between the rip current intensity and the wave height (both normalized).
