Calibration of free-flow radial gates with refined energy relations

Authors: CLEMMENS, ALBERT; WAHL, TONY - U.S. BUREAU OF RECLAMATION

Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2022
Publication Date: 8/11/2022
Citation: Clemmens, A.J., Wahl, T.L. 2022. Calibration of free-flow radial gates with refined energy relations. Journal of Irrigation and Drainage Engineering. 148(10). Article 04022036. https://doi.org/10.1061/(ASCE)IR.1943-4774.0001708.
DOI: https://doi.org/10.1061/(ASCE)IR.1943-4774.0001708

Interpretive Summary: Radial gate are control structures commonly used in irrigation canal networks because they require less lifting force than vertical sluice gates. These gates are commonly used to distribute water to farms and thus are used also to measure flow rate. Procedures for measuring flow rate through radial gates have been around for over a century but can be very inaccurate. This paper describes new procedures for the calibration of laboratory data for free-flowing radial gates, based on energy and momentum equations. The paper examines various gate conditions that influence the rate of water flow. Under the range of conditions tested, the new procedures produced accurate flow rate measurements. The new procedures are of interest to hydraulic engineers and to operators of water delivery systems equipped with radial gates.

Technical Abstract: Laboratory experiments were conducted on a radial gate to evaluate the energy equation for free-flow calibration. The experiments were used to develop new equations for the radial gate contraction coefficient for free flow. These were compared to equations for the contraction coefficient of radial and vertical sluice gates developed from prior studies and potential flow theory. The new radial gate free-flow contraction coefficient was related to both the gate lip angle and the gate opening relative to energy head on the gate. The pressure distribution and velocity distribution coefficients were also evaluated. The energy loss through the gate was expressed as a function of the velocity head in the vena contracta, with a gate energy loss coefficient that varies with the relative gate opening. With the revised energy equations, the free-flow discharge predictions were computed for three data sets: 1) experiments presented here conducted at the USWCL laboratory in 2004-2005, 2) experiments performed by Jan Tel in 2000 and earlier using the same USWCL facility operated over a narrower range of conditions, and 3) experiments performed in the early 1980s by Clark Buyalski in the Bureau of Reclamation’s hydraulics laboratory. The coefficients were developed based on the USWCL later data only. The average discharge computation error for the combined data sets was 0.37%, and the standard deviation was 1.03%. Submerged flow predictions are the subject of future work.