DEVELOPMENT OF AN APPROXIMATE MODEL FOR UNSATURATED FLOW WITH ROOT WATER-UPTAKE UNDER RECTANGULAR WATER-CONTENT PROFILES ASSUMPTION

The rectangular profiles assumption (as in the model of Green and Ampt) is utilized for developing an approximate model for one-dimensional, vertical, unsaturated flow with root water uptake. The simplified model reduces the non-linear partial differential equation (Richard's equation) for water movement to non-linear algebraic equations whose solutions require less computer effort. The basic hydraulic principles (continuity and Darcy's law) are retained in the approximate model. Soil surface boundary conditions of infiltration and redistribution are considered. Analytical solutions are available for the depth to the wetting front when the soil surface is held at saturation. Comparisons between the numerical solutions and approximate solutions are made for two distinct soil types. The approximate model predicts root water uptake quite accurately when compared with predictions from the numerical solution of Richard's equation. It is concluded that such simplified models hold promise in a variety of practical applications.