Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2004
Publication Date: 11/20/2005
Citation: Bautista, E., Clemmens, A.J. 2005. Volume compensation method for routing irrigation canal demand changes. Journal of Irrigation and Drainage Engineering. 131(6):494-503
Interpretive Summary: In many irrigated areas of the world, farmers receive water through networks of canals. Controlling deliveries through canal networks is difficult, in part because unsteady effects persist for long periods of time after flow changes are made. This leads to inaccurate deliveries and canal spills. Since most of these canal systems are currently operated based on experience, physical and mathematical principles need to be applied to the development of improved canal operational strategies. This paper compares two methods for scheduling the operation of a canal for known changes in canal demand ' the canal open-loop control problem. One method is based on a solution of the full equations of unsteady open-channel flow, the other is a simpler approach that only accounts for canal volume changes and travel time estimates. While the former method controls deliveries more accurately, the simpler method was found to be nearly as effective for the range of conditions tested. The simple approach can be easily applied to complex canal systems consisting of multiple pools, gates, and delivery structures. Comparison of the two scheduling methods shows that when subjected to realistic canal operational constraints, such as limitations on how frequently canal gates can be operated and uncertain knowledge of canal hydraulic properties, there is no advantage in using the more sophisticated method. Thus, the simpler method can serve as the foundation for a practical open-loop control system. These results are of interest to researchers and canal operators interested in developing simple yet reliable canal control procedures.
Technical Abstract: This paper examines the problem of routing known or predicted water demands through gate-controlled open-channel irrigation delivery systems. Two scheduling methods are compared, one based on the inverse solution of the unsteady flow equations and the other based on volume compensation. Both methods can be applied to complex scheduling problems, consisting of multiple demand changes in a multiple-pool canal. The volume-compensation method schedules each individual demand change separately, under the assumption of a series of steady-states, and develops a global solution by superimposing the individual results. The test cases proposed by the ASCE Task Committee on Canal Automation were used in the analysis. Under ideal flow control conditions the volume-compensation method can control water levels nearly as effectively as gate-stroking. When considering realistic operational conditions, such as constraints on the regulation interval and imprecise knowledge of the canal's hydraulic roughness, there is no advantage in using the gate-stroking routing approach over the volume-compensation method.