A GRAPHICAL SOLUTION TO ESTIMATE POTENTIAL RUNOFF IN CENTER-PIVOT IRRIGATION

This article describes a mathematical model for computing the potential runoff (RUNp) in center-pivot irrigation based on curvilinear regression analysis. The RUNp is related to the water depth application (WDP) and to the maximum water depth (WDPmx) that can be applied to the soil before runoff occurs. Furthermore, using a simple three-axis graphical tool, the RUNp-WDP-WDPmx relationship was also attained. The WDPmx was determined by solving an equation incorporating the peak water application rate (a center-pivot design parameter) and two physical parameters associated with the Green-Ampt infiltration model: the effective matric potential and the saturated hydraulic conductivity. From this study, using field data from irrigation events of several center pivots, selected with different lengths and sprinkler configurations, it was concluded that the proposed graphical solution is a reasonable and easy way to estimate potential runoff The model reliability in predicting runoff was confirmed by calculating the basic model performance statistics.