A statistical approach to estimating runoff in center pivot irrigation with crust conditions

[P.B. Luz, J.C. Martins, M.C. Gonçalves, Reliable estimate of runoff in center pivot irrigation: statistical approach, in: Proceedings of the 16 Congress Mondial de Science du Sol, Poster 2-658, ISSS, Montpellier, France, August 19-25, 1998, pp. 577-593], 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 [W.J. Rawls, D.L. Brakensiek, Estimation of soil water retention and hydraulic properties, in: H.J. Morel-Seytoux (Ed.), Unsaturated Flow in Hydrologic Modeling, Theory and Practice, Kluwer Academic Publishers, Dordrecht, 1989, pp. 275-300], 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.