Experimental investigation of vanes as a means of beach protection

Abstract

Vanes are essentially flat vertical flow guiding structures. In the beach protection application vanes are placed, inshore of the breaking zone, in the upper part of the vertical water column and with a predefined angle of attack to the design wave orthogonal. They are thus subjected to a generally inshore-directed flow, which induces a lift, and drag force on the vane. These forces, in turn, induce a flow that counteracts the wave-induced longshore current, thus decreasing the longshore current velocity, which facilitates sediment deposition. Two experiments were conducted in a small-scale wave basin with the purpose of investigating the vane function. Both experiments were conducted with a movable bed that formed a crenulate-shaped bay between two headland structures. The first experiment showed that the vanes created a salient upstream of the vanes. This result is also supported by initial prototype results. The second experiment showed that the longshore velocity was reduced upstream of the vane and that the bulk of the velocity reduction took place in the nearshore part of the breaking zone. The main flow feature is identified as a large horizontal vortex inshore of the vane.