CHAPTER 13 - SPECIAL MEASUREMENT METHODS IN OPEN CHANNELS
4. Measuring Controls for Canals
Irrigation canal systems frequently include drops to adjust canal grades to the landscape. If the drop is great enough to make the flow pass through critical depth, a gage set in the canal a short distance upstream from the drop may be used to measure heads that, with calibration, can be related to discharge. Measured flow must pass through critical depth for the entire needed discharge measurement range. Chapter 2 has a section on critical depth. Discharge ratings are developed by current metering at various depths to produce tables and curves. In some channels where sufficient freeboard exists, side or bottom constrictions can be added, and a gage can be calibrated similarly. Measuring controls operate with the same principles as flumes and weirs but need special calibrations.