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Title: SIMPLE OPTIMAL DOWNSTREAM FEEDBACK CANAL CONTROLLERS: THEORY

Author
item Clemmens, Albert
item SCHUURMANS, J - UNIV OF TWENTE, THE NETH

Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2003
Publication Date: 8/1/2003
Citation: Clemmens, A.J., Schuurmans, J. 2003. Simple optimal downstream feedback canal controllers: theory. Journal of Irrigation and Drainage Engineering. 130(1):26-34.

Interpretive Summary: Demand for water is the western United States now significantly exceeds available supplies, especially when considering water needed for environmental purposes. Agriculture's share of available water is likely to decrease in the future. Agricultural water purveyors are being pressured 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 determining control actions. One such tool is computerized automatic control of canal gates. This technology, however, is not routinely available to irrigation district personnel and consultants. This paper presents a new method for the automation of irrigation canals that can be adapted to a wide variety of canals and operational situations for improving water delivery operations and service. These results should be of use to irrigation districts, consultants, and the Bureau of Reclamation. Ultimately better management of irrigation water supplies will conserve water and benefit the environment.

Technical Abstract: A new class of downstream water-level feedback controllers is proposed that can vary from a series of individual proportional-integral (PI) controllers (each gate adjusted based on one water level) to fully-centralized controllers (each gate adjusted based on all water levels) that include the effects of lag time. The controller design method uses discrete-time state- -feedback control with a quadratic penalty function, physically-based states, and no state estimation. A simple, linear model of canal pool response, the integrator-delay (ID) model, is used to define the state- transitions. All controllers within this class are tuned for the entire canal using optimization techniques. This avoids the tedious task of manually tuning simple controllers. The relative performance of the various controllers within this class can be directly compared without simulation, since the same objective function is used to tune each controller. An example is provided which suggests that the fully-centralized controller will perform better than a series of local controllers. However, reasonably good performance can be obtained for some intermediate PI controllers that pass information to one additional check structure upstream and downstream. This should limit some of the difficulties reported for full optimal controllers where all check structures respond to water-level errors in all pools (e.g., saturation of inputs). The results of simulation studies of these controllers are provided in a companion paper (Clemmens and Wahlin 2001).