Velocity measurements close to a smooth bed have been made downstream of a range of rearwardfacing steps. When the step height is greater than the thickness of the viscous sublayer, the effect of the step on velocities close to the bed is large and is apparent for 30 step heights and more in the downstream direction. The ratiotends toward a constant value, however, within about 10 step heights. Large fluctuations in the instantaneous length of the separation bubble occur. The extent to which the instantaneous shear stress would exceed the critical shear stress for initial movement of a given sand is relevant to the formation and propagation of ripples.