Orbital Wave Velocity

Orbital velocity is the speed of water particles moving in closed orbits as a surface gravity wave passes, distinct from the wave celerity, which is the speed of the form, not the water. In deep water the orbits are circles that shrink exponentially with depth, the diameter halving about every L/9 and becoming negligible below half a wavelength. In shallow water the orbits flatten to horizontal ellipses, and at the bed the vertical motion vanishes, leaving an oscillating horizontal flow that stirs sediment. Particle speed peaks at the crest in the direction of travel; breaking starts when that crest orbital speed reaches the wave celerity, the kinematic breaking limit.