Author
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Clemmens, Albert |
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Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/1/2009 Publication Date: 10/1/2009 Citation: Clemmens, A.J. 2009. Errors in surface irrigation evaluation from incorrect model assumptions. Journal of Irrigation and Drainage Engineering. 135(5):556-565. Interpretive Summary: Surface irrigation has a reputation for poor performance, yet it represents roughly half the irrigated acreage in the U.S. and 90% worldwide. It is possible to improve the performance of surface irrigation through improvements in design and operation. The process for making improvements includes evaluating an irrigation event, determining infiltration and roughness conditions, conducting analysis to provide recommendations for improvement, and implementing the recommendation. This paper discusses difficulties in properly describing infiltration and roughness conditions. Examples show how this can lead to improper recommendations for improvement. Suggested strategies for properly describing infiltration and roughness are left for a companion paper. This information should be useful to irrigation farmers, the Natural Resources Conservation Service, extension specialists, and agricultural consultants. Technical Abstract: Some two-dozen methods have been proposed in the literature for estimating an infiltration function from field measurements. These methods vary in their data requirements and analytical rigor, however most assume some functional form of the infiltration equations. The assumptions regarding the influence of wetted perimeter on furrow infiltration can also result in inappropriate infiltration equations and parameters. Also, the Manning n has also been shown to vary with time during an irrigation event as the soil is smoothed by the flowing water. Thus estimates of Manning n based on the advance curve may vary substantially from those based on measured water depths. Inappropriate selection of equations or parameter values for one (infiltration or roughness) can lead to unrealistic parameter values for the other. This leads to a great deal of uncertainty when such parameters are then used in simulation and design software in order to deduce system behaviour, with the intent of improvement. In this paper, we provide examples that demonstrate the difficulty in the estimation of parameters. |
