New Results for an Approximate Method for Calculating Two-Dimensional Furrow Infiltration

This study expands the analysis of a proposed furrow infiltration formulation based on an approximate solution to the two-dimensional Richards equation. The approach calculates two-dimensional infiltration flux as the sumof one-dimensional infiltration and a second term labeled the edge effect. The edge effect varies linearly with time when the applied water pressure is constant. It is a function of sorptivity, soil water content, and the empirical parameters gamma and W* that require calibration for the specific soil and furrow geometry. The primary objectives of the analysis were to better understand how furrow geometry affects the edge effect and the resulting empirical parameter values and to provide additional guidance for calibration. For a given flow depth, furrow geometry defines the wetted perimeter and the water pressure applied along that wetted perimeter. A subobjective was to evaluate the effect of the assumed soil water retention model on the calibration results. The results show that the range of variation of. depends on the pressure value used for one-dimensional infiltration and edge effect calculations. This range can be reduced by using the wetted-perimeter averaged flow depth, h(avg), instead of the centroid depth, h(c), as in the original formulation. The use of havg also eliminates the need to calibrate W*, which is simply equal to the furrow wetted. For the range of soils and geometry examined,. varied in the range of 0.6-1.0, but the range was narrower with soils described with Brooks-Corey soil hydraulic models than with soils described with the van Genuchten model (VG model). This is explained by the larger values of wetting front suction associated with water retention data fitted to the Brooks-Corey model. With careful calibration, the approximate infiltration model can produce results of high accuracy in relation to the Richards equation solution. Calibration is especially needed with heavier soils for which the contribution of the edge effect relative to total infiltration is substantial. (C) 2014 American Society of Civil Engineers.