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

Author
item LUZ, P. - ESTACAO ARGRONOMICA NACIO
item Heermann, Dale

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2004
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. Vol 72 (1) pp 33-46

Interpretive Summary: Runoff under center pivot irrigation systems is a major contributor to non-uniformity of irrigation water being stored in the soil profile. This study added the ability to estimate runoff when soil crust forms on the surface after rainfall and irrigation events. The model developed is a simple approach to estimate runoff under field conditions that includes both soils with and without soil crusts. The technology is important in the evaluation of design of center pivot systems and is of particular importance to the NRCS as they evaluate designs for cost sharing under the EQIP program.

Technical Abstract: There have been several proposals to evaluate potential runoff under center pivot irrigation systems as a function of time varying intake and water application rates. The Richards equation is used to describe one dimensional vertical infiltration of water into soil. A computer model was used to estimate runoff through the integration of infiltration-precipation rate curves. Luz et al., (1998) developed a conceptual statistical method to estimate potential runoff under center pivot irrigation systems. Regression equations of the runoff results from the simulation with the Richards' equation were developed. The procedure simulated runoff for a wide set of data for water application and the water retention parameters and soil texture, reported by Rawls and Brakensiek, (1989). An independent variable for estimating runoff is defined as an index of four parameters, related to the center pivot irrigation system characteristics and to the soil-water parameters. However, when soil surface crust conditions existed, the method produced unacceptable results. The indices were redefined and new parameter coefficients established to provide an estimate of runoff with soil surface crusts. The model efficiency ranged from 90 to 98% showing the results are in good agreement with those computed by the Richards' equation.