The generally accepted procedure is to average velocity measurements at 0. 2D and 0. 8D, measured vertically from the water surface,or alternatively to measure velocity at a position equal to 0. 6D, where D is the total depth of flow. In some situations, one may wish to measure at depths other than 0. 2D and 0. 8D. For instance, a temporary stream gage may be continuously monitoring velocity with two probes located at fixed vertical positions. As the total depth changes, the relative measurement position changes. This paper presents a general two-point method that can be used to determine the depth-averaged velocity when measurements at two arbitrary but known depths are available.
Additional publication details
GENERAL TWO-POINT METHOD FOR DETERMINING VELOCITY IN OPEN CHANNEL.