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The paper presents the results of an experimental study of mean fluid flow and turbulence over bed forms in a unidirectional flow with superimposed surface waves. Experiments were performed with only current and with combined wave‐current flows over a series of bed forms under different surface wave frequencies for two different Reynolds numbers. Three‐dimensional velocity was measured using a 3‐D micro acoustic Doppler velocimeter. The superposition of surface waves with increasing frequency leads to an increase in the apparent bottom roughness due to a vortex in the lee, which causes the resistance to the flow. The effect of surface waves is to increase the flow stability, consequently reducing flow separation and enhanced mixing in the lee side of the bed form. A stronger circulation pattern in the lee side of the bed forms is observed at a higher Reynolds number.