Dynamics of vortices on a uniformly shelving beach

Abstract

Laboratory experiments are described which investigate the dynamics of a vortex dipole moving in water towards a planar sloping beach inclined at an angle α to the horizontal. Results are compared with those of a vortex ring model first developed by Peregrine (1996). The vortices separate as they travel up the beach, eventually moving in opposite directions and nearly parallel to the shoreline. The ranges of conditions examined are 3°[les ]α[les ]45°, 1×103[les ]Re[les ]6×103 and 0.05[les ]Fr[les ]0.14, where Re and Fr are the on-slope Reynolds number and the Froude number of the vortices, respectively. The minimum distance from the shoreline reached by the vortices and their along-shore speed are in general agreement with the predictions when, respectively, R*i<3 (where R*i is the non-dimensional initial distance of the vortices from the shore-line) and Re[gsim ]1500. The vortex ring model is likely to have useful applications to the study of the dynamics of the near-shore zone.