CHAPTER 13 - SPECIAL MEASUREMENT METHODS IN OPEN CHANNELS
Pitot tubes are sometimes used to measure relatively fast velocities such as at drops, chutes, and overfall crests. Velocity traversing and discharge computations may be done in the same manner as with current metering (described in chapter 5). Pitot tubes are difficult to use in slow canal flow because they produce small differentials in slow flow. For example, the velocity needed to produce 0.1 ft velocity head is 2.6 ft/s. Thus, pitot tubes have the problem of precision of head measurement relative to the size of head differential. Depending on needed accuracy, the secondary equipment could be costly and difficult to use in slow velocity. Pitot tubes and their use are more fully described in chapter 14.