Sand ripples under water with complex wave motion.

Experiments studying ripple formation under water have usually used sinusoidal driving force. Here an experiment is presented where the driving force can be an arbitrary wave form, thus trying to mimic the realistic wave motion in shallow water coastal zones. We study a simple modulated sine wave and more complicated wave forms with several superposed harmonics. In particular we demonstrate how a small higher order harmonic can have a dramatic effect on the wavelength of the ripple pattern.