- We consider development of sand ripples in shallow water flows which do not reach an equilibrium height but have a time-varying ripple height that slowly reaches a maximum value and then is quickly destroyed by the fluid. A simple scenario to explain the time periodic behavior of the sand ripples is proposed and applied to data observed here. Our data for the wavelengths agree reasonably with previous observations of steady-state, deep ripples. The ripples we observed never became as tall as those previously reported for deep flows. This suggests that once the ripples coalesce into a pattern, the ripple height increases as more sand is deposited until the flow becomes turbulent and the pattern is destroyed before the deep-water steady state is achieved, The cycle then repeats as the newly flattened surface again faces instability and ripples grow at a determined wavelength.