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Title: A STATISTICAL APPROACH TO ESTIMATING RUNOFF IN CENTER PIVOT IRRIGATION WITH CRUST CONDITIONS

Author
item LUZ, P - INIA
item Heermann, Dale

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2004
Publication Date: 3/2/2005
Citation: Luz, P.B., Heermann, D.F. 2005. A statistical approach to estimating runoff in center pivot irrigation with crust conditions. Agricultural Water Management.

Interpretive Summary: An important factor in designing center pivot sprinkler systems is the prevention of runoff which can significantly reduce the uniformity of application. We were able to develop a simple set of equations that can be used for estimating potential runoff as a function of the soil and system design and operation characteristics. The equations will allow estimates of the runoff where new center pivot systems are being considered for improving the irrigation. The simplified approach will allow estimates to be made with hand held calculators and included in center pivot design programs by the irrigation industry, action agencies and consultants.

Technical Abstract: There have been several proposals to evaluate potential runoff in center pivot irrigation, through the integration of time varying infiltration-precipitation rate curves, involving complex iterative procedures. Some methods use empirical infiltration functions, such as the Kostiakov equation. Others use physically based infiltration functions, such as the Green-Ampt equation. Another option is to use the Richards equation, describing the one-dimensional vertical infiltration of water into the soil for a specified irrigation event. This equation is generally accepted to provide a basis for comparison between other runoff estimation methods. Luz et al.(1998), developed a conceptual method of statistical nature, to estimate potential runoff in center pivot irrigation, comprising regression equations built with runoff results from a simulation computer model using the Richards equation. The procedure to simulate runoff involved a wide set of data related to water retention parameters and soil texture, reported by Rawls & Brakensiek, (1989), and water application. Such regression equations present a dependent variable, defined as an index of four parameters, related to the center pivot irrigation and to the soil-water system evaluation. The method had unacceptable results when a crust developed on the soil surface. Therefore, the objective of this study was to redefine the index, establishing new parameter coefficients with a trial and error approach. The model efficiency (similar to the coefficient of determination, r2) ranged from 90 to 98 %, showing the results are in good agreement to those computed by Richards equation, exhibiting a strong predictive value.