Improving Flow Measurement Accuracy Using a Portable Irrigation Turnout Calibration Unit

Relatively accurate flow measurement at irrigation district water delivery points is an important component of volumetric billing and equitable service. In California, this has often occurred with conversions to pressurized irrigation systems which commonly include the installation of pipeline flow meters as part of the on-farm system. However, a large portion of irrigation turnouts in the western US continue to operate via gravity and fall into one of the following categories: (a) a metergate, or similar structure was installed without adherence to standard construction requirements, or (b) the structure was never intended for flow measurement. For these and other scenarios, there is a need to efficiently calibrate turnouts in the field. While some in-situ calibration methods exist for open channel turnouts, they are rarely applied in the field for a variety of practical reasons. After identifying this gap in field-practice, a special pump, or portable irrigation turnout calibration unit (calibration unit) was designed and constructed at the Cal Poly Irrigation Training and Research Center (ITRC). Within six weeks, thirty-two field turnout calibrations were performed using the Calibration Unit throughout seven California irrigation districts. Field testing protocol followed new guidelines developed by the USBR Mid Pacific Region and the California Department of Water Resources (DWR). The results and analyses of these calibrations are presented in this paper. Practical applications, such as compliance with California regulations developed out of The Water Conservation Act of 2009 (SB X7-7) and constraints of this new calibration method are also discussed.