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Title: RESPONSE OF IDEALLY CONTROLLED CANALS TO DOWNSTREAM WITHDRAWALS

Author
item BURT, CHARLES - CAL POLY, SLO, CA
item GOOCH, ROBERT - SALT RIVER PROJ, PHX, AZ
item STRELKOFF, THEODOR - UNIVERSITY OF AZ, TUCSON
item DELTOUR, JEAN - GERSAR, FRANCE

Submitted to: International Conference on Water Resources Engineering Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/1/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Much of the water supplied to irrigated farms is delivered through networks of canals. Competition for water and the desire to reduce negative environmental effects from irrigated agriculture are prompting the need for better control of canal operations, which in turn is expected to improve the potential efficiency of farm irrigation systems by providing water more consistent with crop and field irrigation system needs. However, open canals are not always easy to control, depending upon their hydraulic properties. In this paper, we describe a method we developed to test the ability of a canal pool to respond to changes in downstream demand (that is, downstream control). We also show that these results can be generalized based on some standard hydraulic properties (for example, the Froude number which is the ratio of inertial to gravitational forces). These results are useful for irrigation district engineers, consulting engineers and others who are interested in the feasibility of applying downstream control to existing canals or in the design of new canals.

Technical Abstract: In recognition of the different degrees of success achieved by a given downstream controller in different canals, the effect of pool characteristics on controllability of water levels is investigated. To eliminate the properties of the controller algorithm from consideration, control is assumed ideal, i.e., simultaneous, exact upstream replacement of fwithdrawals from a downstream turnout. The maximum drawdown at the turnou is then, for any given withdrawal fraction, a function primarily of pool geometry and dynamics. This is viewed, first, for a pool of specified dimensions in terms of consecutive steady states. Then, the transitory depth variations of unsteady flow are considered through an example from a general nondimensional study. When complete, the results will allow prediction of maximum drawdown at the turnout and, so, indicate circumstances in which even ideal control is insufficient and anticipatory control measures become necessary.