Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2012
Publication Date: 8/1/2012
Citation: Bautista, E., Strelkoff, T., Clemmens, A.J. 2012. Errors in infiltration volume calculations in volume balance models. Journal of Irrigation and Drainage Engineering. 138(8):727-735.
Interpretive Summary: Nearly half of the irrigated surface in the U.S. uses surface irrigation methods for water application. Surface systems, also known as flood systems, are often associated with poor levels of irrigation efficiency and uniformity. However, if properly designed and managed, surface systems can attain high levels of performance. The advent of personal computers has promoted the development of simulation models and hydraulic analysis tools for surface irrigation. Tools developed by the Agricultural Research Service are being used by the Natural Resources Conservation Service to analyze current system operation and propose improvements to the operation and alternative designs. These tools are still evolving and new features are being contemplated for future development. This article reviews a particular type of procedures that have been in use in surface irrigation analysis for many years. The study shows that those procedures produce systematic errors that can undermine the accuracy of results. Importantly, the magnitude of errors can be substantial under particular sets of conditions. Users need to be aware of conditions where those procedures are prone to errors. A methodology for correcting those errors is suggested. The results of this study should be of interest to users of surface irrigation analysis tools, including NRCS personnel, consultants and researchers.
Technical Abstract: Volume balance models of surface irrigation calculate the infiltrated volume at a given time as a product of the stream length, upstream infiltration, and shape factors. The best known expression of this type was derived by combining the Lewis-Milne equation with empirical power-law expressions for infiltration and advance as functions of time. This expression results in systematic errors that are not well understood by users of volume balance methods. This article examines those errors in furrow irrigation by comparison with infiltrated volumes computed with zero-inertia simulation. The potential for errors is greatest with light soils and where the bottom slope is large enough to produce kinematic flow conditions. An example is presented to show how these errors in a parameter estimation problem based on a volume balance can be corrected iteratively with the help of zero-inertia simulation.