Often in nature and sometimes in flumes, asymmetrical sand ripples do not form when considerations of hydraulic variables and grainsize indicate that they should. This paper reports experimental inhibition of ripple formation by allowing small waves, generated from sources both at the surface and on the bed, to pass upstream along a flume. If ripples do not appear on a bed, form drag is greatly reduced and equilibria between flows and particles consequently differ from those existing if ripples are present.