An improved Green-Ampt soil infiltration and redistribution method and its application to 1-dimensional and quasi 3-dimensional (point source) flow domains

Unsaturated flow can best be described by Richards' equation. Numerical solutions of Richards' equation are generally computationally intensive and require extensive soil property data; therefore, simplified physically-based approaches have often been used. The purpose of this research was to develop and validate a physically-based approximate model for simulating infiltration and soil water redistribution in 1-D and quasi 3-D flow domains. The first step was to improve an existing 1-D infiltration and redistribution model, GAR, by increasing the number of redistributing wetting fronts and adding a correction factor, Gamma (a function of redistribution number - NR, redistribution time - T R, and saturated hydraulic conductivity - KS). A comparison of a numerical solution of Richards' equation against the GAR and the modified GAR (MGAR) methods showed that the modified method predicts better the surface water content and is also able to predict the average water content for a desired observation layer. Next, the 3-D form of the Green-Ampt (3DGA) infiltration method was compared to several established point source models and published data. The results of the comparison showed that the 3DGA method is a viable model for simulating quasi 3-D flow domains. An equation for the 3DGA supply radius parameter was developed based on a simplified form of Philip's point source radius equation which is a function of emitter flow rate, saturated hydraulic conductivity and suction at the wetting front. Testing of the proposed equation showed good results for a wide variety of soils. Lastly, 3DGA was extended based on the MGAR method to calculate the change in water content during the 3-D redistribution phase. Comparison with 2-D Richards' numerical solution (Hydrus 2D) showed the model to provide good point-source simulations for a wide variety of soils.