Study of instantaneous flow behind a single fixed ripple

•Investigation of different hydrodynamic mechanisms process generated behind a single fixed ripple.•Two-component PIV measurements are performed to provide new experimental data references to contribute to the knowledge of unsteady flow downstream a ripple.•Quadrant decomposition from instantaneous Reynolds shear stress is used to analyse the contribution of the four events in the sediment transport process and bed form evolution in river or estuary.