NONDIMENSIONAL EXPRESSION OF UNSTEADY CANAL FLOW

Authors: STRELKOFF, THEODOR - UNIVERSITY OF AZ, TUCSON; Clemmens, Albert

Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/1997
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. These canal hydraulic properties are determined from the laws of physics. In this paper, we show that the equations describing the physics of water flow can be expressed in a form that allows us to define canal response in terms of a minimum number of parameters. This allows us to generalize the canals hydraulic properties in terms of only a few key properties. These results have been used in a series of general studies on canal properties, the results of which are useful for those who design or develop operating rules for irrigation distribution canals.

Technical Abstract: Through an appropriate choice of reference variables, the dimensionless governing equations and initial and boundary conditions of unsteady canal flow have fewer independent parameters than their dimensioned counterparts, and so the same information can be expressed with substantially less bulk. With the choice of design discharge and normal depth as reference variables, unsteady flow is governed by cross-section shape factors, the Froude number at normal depth, and the dimensionless length, as well as initial and boundary conditions. A particular dimensionless form of the Saint Venant equations was found having the same appearance as the dimensioned equations. This was achieved by a dimensionless g, the ratio of weight to mass in the dimensioned real-world equations, now related to the Froude number at normal depth in the dimensionless equations. The Manning unit's coefficient, normally used to express the Manning formula in nEnglish or metric systems, in the dimensionless system relates to the shap of the channel cross under normal flow conditions. It was also shown that dimensionless results can be interpreted in real world terms by specifying a normal flow depth and a Manning roughness. With the normal Froude number of the flow given, all pertinent dimensioned variables follow directly from any dimensionless results.