The other is to use power records and information about the system to calculate the amount of water pumped through the system. For purposes of measuring flow rates for derivation of power consumption coefficients and calibrating installed flow meters, the Department will accept any standard measuring device that will measure water flow within plus or minus 2 percent of rate readings. A device which meets this requirement for closed conduits and which is recommended by IDWR is the ultrasonic, transit time type flow meter. This instrument is portable and non-invasive, which means it does not intrude the pipe, and measures flow from outside the pipe wall. The instrument transducers can be mounted on the pipe in a short period of time and flow measurements made without stopping the flow or contacting the water in any way.
Many units are portable and can easily be moved from one pipe to another.
In order to maintain the integrity and confidence level of the ultrasonic instrument, the Department requires each instrument used in district water measurement activities be checked for accuracy and reliability at the USDA Agriculture Research Service's water laboratory at Kimberly Idaho at least once each year under the supervision of Department staff or other qualified laboratory staff. This will insure the accuracy of the instrument and when used properly in the field, accurate measurements. In some cases the ultrasonic measuring device may not work accurately due to entrained air or other flow irregularity. If the ultrasonic device cannot be used, an impact pitot tube measuring device such as a Collins, Hall or annubar meter can be used with good accuracy. This meter is an invasive type device and requires the water flow to be stopped in order to install the equipment.