Tide-induced flow signature in rip currents on a meso-macrotidal beach

• Signature of tidal currents developing over the rip channel morphology.
• Observations and modelling of tide-induced asymmetry in a meso-macrotidal beach.
• Asymmetry increasing roughly linearly with increasing tidal range.
• Asymmetry varies from 20 to 45% (dependent on the morphologies and the waves).

On rip-channelled beaches, intense rip currents are driven by waves due to alongshore variations in breaking-induced wave energy dissipation. This study addresses for the first time the potential development of tidal currents superimposed onto the wave-driven circulation. This phenomenon is observed on a rip-channelled meso-macrotidal beach (Biscarrosse, SW France). Field measurements show 20 to 45% stronger mean rip velocities during ebb than during flood. Numerical experiments reveal that this asymmetry is the signature of tidal currents developing over the rip channel morphology. This asymmetry is found to increase roughly linearly with increasing tidal range. These results are significant to beach safety and lifeguarding and stimulate further numerical exercises.