Submitted to: Water Management Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/25/2000
Publication Date: N/A
Interpretive Summary: Surface irrigation is used on about half of the irrigated lands in the U.S.; in other parts of the world this figure approaches 100%. In terms of performance indicators such as application efficiency and uniformity of distribution, most of these systems are not achieving their potential, which in some cases can rival that of pressurized systems. Field properties ssuch as topography, soil infiltration, and flow resistance have a profound effect on the performance of surface irrigation systems, and reasonable estimation of these parameters is crucial to good management and design. Sophisticated computer models provide performance predictions based on these parameters, but the predictions are only as accurate as their input data. This paper constitutes an introduction to the process of estimating field properties. It describes characteristics of field properties that are often overlooked and provides caveats regarding common estimation practices. It introduces a new Environmental and Water Resources Institute (ASCE)Task Committee formed to develop a consensus report of recommended practices. The ultimate beneficiaries of this information would be the growers, who with advice on proper design and operation can conserve water and protect the environment from excessive contamination by agricultural and soil chemicals in excess irrigation water running off into surface water supplies or percolating into the groundwater.
Technical Abstract: Field properties topography, hydraulic resistance, infiltration, and erodibility have a profound effect on the performance of surface irrigation systems. Good management and design are totally dependent on reasonable estimates of these parameters. Yet, quantitative evaluation to the required accuracy is elusive. There can be substantial spatial and temporal variations, giving rise to techniques that use instrumented test irrigations to deduce likely average values of extant field parameters. The tests can be as crude as pressing a metal rod into the soil after an irrigation to determine the depth of penetration, or as complicated as measuring water-surface profiles during the irrigation along with the inflow and outflow hydrographs. What is lacking in all of the methods is an appreciation of the likely error with each approach and the extent to which that error affects predicted performance. A brief overview of descriptive formulas and approaches to determining their parameters is presented. Direct measurements are contrasted with indirect approaches deducing extant parameters from system behavior. A new ASCE Task Committee is noted, formed to sort through the different approaches, strike a balance between theory and practical needs, and make recommendations in a manual of practice.