Wavenumber selection, hysteresis, and other phenomena were also discussed. Modern experiments make use of an annular cell to minimize end effects, and had novel ways of imaging two dimensions in the frame of the sand. Resonance between ripple size, amplitude of oscillations, and distance scale of vortices creates ripples. On the Origin and Growth of Ripple-mark. M. Scherer, F. Melo, M. Marder.
Sand ripples in an oscillating annular sand-water cell.
A. Stegner, J. E. Wesfreid. Dynamical evolution of sand ripples under water. Some images from the talk.