This article treats of the flow motion over the so-called vortex ripples which are generated by water oscillations above a sand bed. We focus mainly our experimental works on the morphology and the dynamics of transient flow patterns above real vortex ripples. With the help of flow visualizations and Particle Image Velocimetry measurements with a high-speed video CCD camera, we test numerical simulations, which predict the existence of a secondary vortex with a streamlines representation. However, our experimental findings show only one vortical structure and validate the observations of Bagnold in 1946 (using real ripples but with no visualization and measurement) and Sand Andersen & al. in 2004 (using model ripples) with respect to the existence of a transient jet. 德國LaVision PIV/PLIF粒子成像測速場儀 HighSpeedStar PIV相機 用于粒子成像測速(PIV)的熒光示蹤粒子