Overview and Uncertainty Analysis for an Irrigation Flow Measurement Facility

Accurate flow measurement is critical for modern water resource management. At the irrigation district level, instantaneous flow rates must be well-measured at key bifurcation points to reliably meet downstream demand in open channel systems while also minimizing diversions. Furthermore, good flow measurement at each delivery point is a pre-requisite for successful volumetric water billing. Accuracy and repeatability are important characteristics of good flow measurement. Maximizing these traits requires periodic calibration to a common standard. This paper presents an overview of calibration efforts and the engineering background behind an active flow measurement facility at the Irrigation Training and Research Center at California Polytechnic State University, San Luis Obispo (Cal Poly). The facility is fitted with two major flow measurement devices, a gravimetric weighing tank and a volumetric tank. Although both are used for comparison, verification, and calibration of closed pipe and open channel flow measurement devices, this report will focus on an uncertainty analysis for the gravimetric weighing tank.