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Highlights

This article provides an overview of operations and benefits of using a variable frequency drive to operate agricultural subsurface drainage system sump pumps.

Abstract. Subsurface drainage plays a crucial role in excess water removal through perforated pipes buried in the soil. The Red River Valley of eastern North Dakota and west central Minnesota often requires pumped drainage outlets due to its flat topography, with many modern systems incorporating variable frequency drives (VFD) for improved efficiency. VFDs adjust pump speeds to match drainage needs, but this dynamic operation complicates accurate flow rate estimation for edge-of-field monitoring. This project aimed to devise an automated method for calculating flow rate estimates from VFD pumping systems involving tank geometry, operational water levels, and pump duty cycling. Linear regressions with calibration data from a transit-time ultrasonic flowmeter produced mixed outcomes. Some linear regressions revealed errors in calculated versus measured flow rate of ≤14%, while other regressions showed errors nearing 40%. To address this, future efforts should explore methods incorporating the pump‘s electrical characteristics. This approach would provide a more accurate representation of the unstable and intricate pumping operations during transient conditions.