Submitted to: Proceedings of the World Water and Resources Congress
Publication Type: Proceedings
Publication Acceptance Date: 5/30/2004
Publication Date: 7/1/2004
Citation: Clemmens, A.J. 2004. Avoiding submergence transition zone for radial gates in parallel. In: Proceedings of the World Water and Environmental Resources Congress, June 27-July 1, 2004, Salt Lake City, Utah. 2004 CDROM.
Interpretive Summary: Agriculture's share of available water is likely to decrease in the future because of the competition for water supplies, particularly in the arid west where large irrigation projects are common. Agricultural water purveyors are being pressed by other water users to improve water measurement, control, and accounting, while their water users are demanding more flexible water deliveries so they can compete in the marketplace and implement water conservation measures on farm. Operation of irrigation-water delivery systems can be improved by providing canal operators with better tools for measuring flow rates. Radial gates are commonly used to control and measure flow rates within irrigation canals. Unfortunately, calibration of these gates has been problematic, particularly when the downstream water level is high (that is, the gate is submerged on the downstream side). A new procedure has been developed to provide reliable calibrations for radial gates regardless of flow conditions. This paper provides an evaluation of how these procedures can be applied to several gates in parallel. These results should be of use to irrigation districts, consultants, and the U.S. Bureau of Reclamation. Ultimately better management of irrigation water supplies will conserve water and benefit the environment.
Technical Abstract: The calibration of partially submerged radial and vertical-sluice gates has proven difficult to determine under field conditions. In a recent paper, the author and colleagues developed a method for determining the calibration of radial gates from free flow to submerged flow, continuously through the transition. The method uses the energy equation on the upstream side of the vena contracta and the momentum equation on the downstream side, and thus has been named the energy-momentum or EM method. Because of the nature of the partially submerged jet, an empirical energy correction is needed during partial submergence. One advantage of the method is the ability to account for a wide variety of downstream conditions, including channels that are significantly wider than the gates. It was anticipated that the method would allow estimation of discharge based only on gate openings and upstream and downstream water levels, even for multiple gates with different openings. However, if one gate is free-flowing and another in the transition zone, estimation of discharge is complicated by lateral flow, and may become intractable. One solution is to measure the downstream pressure in the vena contracta. With the energy correction term, this measurement avoids the need for use of the momentum equation downstream. However, such measurements are difficult in the field. Another solution is to move all gates to the same position, so that the EM-method can be used in the transition. This option is not suitable where operators prefer to move only one of several gates to obtain finer resolution. An alternative is to determine the position of the gates such that each is either free-flowing or fully submerged. The purpose of this paper is to explore the feasibility of options for avoiding the transition zone for multiple radial gates in parallel while still allowing the operator to adjust one gate to vary discharge. The approach is demonstrated on the Salt River Project's Arizona Canal.