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A methodology is proposed for estimating furrow infiltration under time-variable ponding depth. The methodology approximates the solution to the two-dimensional Richards equation, and is a modification of a procedure that was originally proposed for computing infiltration under constant ponding depth. Two computational approaches were developed and tested using several combinations of soil hydraulic properties, furrow geometry, and flow depth variations. Both methods yielded solutions of reasonable and similar accuracy relative to numerical solutions of the two-dimensional Richards equation. The analysis also showed that the accuracy of the approximate model varies mostly as a function of soil hydraulic properties. The accuracy of the approximate solution can be improved with calibration. Two calibration methods were examined, one assuming that the calibration parameter varies with depth, and the other assuming a constant value. The analysis showed that latter approach, in combination with one of the proposed computational methods, reproduced the Richards equation solution more accurately. This means that a unique calibration parameter can be developed for the particular soil and geometric configuration conditions, and applied to different patterns of ponding depth variation.

Abstract. Characterizing the infiltration and hydraulic resistance process is critical to the use of modeling tools for the hydraulic analysis of surface irrigation systems. Because those processes are still not well understood, various formulations are currently used to represent them. A software component has been developed for estimation of the parameters of infiltration and hydraulic resistance models. Infiltration computations rely on volume balance analysis. The software provides flexibility for defining the estimation problem with various data configurations. The procedure works with various infiltration and resistance formulations. Given the inherent inaccuracies of volume balance analysis, the software provides tools for identifying and correcting some of those inaccuracies. Computational tests are provided to illustrate the capabilities and limitations of the proposed procedures. Keywords: Basin irrigation, Border irrigation, Computer model, Computer software, Furrow irrigation, Model calibration, Surface irrigation, Water management, WinSRFR.

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