By knowing the total amount of water flowing onto a measured border or field area, the irrigator can easily calculate the depth of water applied to the field. The best suited device depends on accuracy desired, ease of use, durability, availability, maintenance required, hydraulic characteristics, ease of construction, and installation cost. The devices measure the rate of flow in an open channel. Knowing the rate of flow and the time over which this rate is maintained, the total water volume used can be calculated. When properly constructed, installed, and maintained, it provides a simple and accurate means of measuring water.
Weirs are easy to construct and accurate if dimensions are followed carefully.
They will handle floating trash and not clog easily. By installing a simple concrete weir or bump in the bottom of an existing concrete ditch, the height of the water flowing over the bump or weir is measured. Automated, solid-state data recording devices can be added to any measuring weir. These devices automatically measure and constantly record the amount of water flow passing through the measuring weir. The digital data can be either read manually or downloaded to a portable computer which will produce a permanent graph or record of the measured flow.