The current work describes the development of a new, non-intrusive optical method for the evaluation of water heights along a gravity wave in shooting water flows in an experimental water table facility. The technique involves superimposing alternating dark and clear mechanical fringes on the water flow. Images of the fringe deviation patterns formed due to the gravity waves are obtained. The images are analyzed to determine the angles and the lengths of fringe deviations, which are related to the local flow heights. It is proposed that the deviations can be simulated using flat-topped optical prisms oriented along the direction of the gravity wave. The height of such a prism corresponds to the local water height. In the present work, shooting flows past a wedge profile for a zero angle of attack have been studied. The variation of flow field heights along a gravity wave has been obtained by the optical technique and by a conventional intrusive depth-gauge technique. The results are in good agreement.