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ARS Home » Research » Publications at this Location » Publication #67572
Title: PROPAGATION OF UPSTREAM CONTROL MEASURES ALONG A CANAL POOL

Author
item STRELKOFF, THEODOR - UNIVERSITY OF AZ, TUCSON
item DELTOUR, JEAN - GERSAR, FRANCE
item BAUME, JEAN - CEMAGREF, MONTPELLIER, FR

Submitted to: International Conference on Water Resources Engineering Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/18/1995
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 econsistent with crop and field irrigation system needs. Yet, open canals are not always easy to control, depending upon their hydraulic properties. For a needed change in flow rate downstream, flow changes must be made upstream. In this paper, we describe methods for examining the speed at which changes in flow rate propagate through a canal. A sudden change made upstream also spreads out or dampens as it moves downstream, affecting the users' ability to take the water suddenly, when it arrives gradually. We also show that the type of canal structure (e.g., weir, gate, etc.) influences the speed of wave travel. These results are useful for irrigation district engineers, consulting engineers and others who are interested in determining what types of hydraulic structures and operating procedures to use on a particular canal or in the design of new canals and their associated structures.

Technical Abstract: A step increase in inflow to a canal pool is routed to its downstream boundary by numerically solving the Saint Venant equations. The wave front deforms as it propagates down the pool, evolving to an ever more gradually rising form in response to the canal-pool characteristics: length, slope, roughness, cross section, initial flow rate, downstream boundary condition, ,and degree of checkup. Propagation times of different wave components are obtained for a wide range of pool conditions. The study is performed in dimensionless terms to get the maximum amount of information with minimum effort of calculation and display. The downstream boundary conditions investigated comprised fixed reservoir elevation; long-crested (essentially constant-head) weirs; and submerged, undershot gates with normal depth downstream; as well as a wide-open gate, such that the downstream boundary condition in the pool was simply normal depth at the local discharge. The stage-discharge relation defining the downstream boundary condition is seen to have a major influence on the delay in arrival of the bulk of the wave.