4-Modelling Soil Water Dynamics in Unsaturated-Saturated Zone.

Abstract

Richards equation with a sink (source) term adequately describes the dynamics of water in unsaturated-saturated soil-aquifer system. Galerkin's finite element method in conjunction with the iterative predictor-corrector finite difference analogue has been used to solve the one dimensional equation. At each time iterations continued till the criteria of preassigned tolerance value (TOL) or maximum number of iterations (MNIT) to stop the iterative process were satisfied. In the present study, MNIT and TOL were assigned the values of 10 and 1. E-06, respectively. A FORTRAN 77 computer program named RICHI has been developed for IBM compatible personal computers. The program has options for Brooks and Corey, and Van Genuchten's soil properties models as well as prescribed pressure head and flux type boundary conditions. The model is capable of computing nodal values of pressure head, volumetric moisture content and Darcy's specific discharge, and depth of water table from the land surface, capillary rise from the water table and depth of ground water recharge. Example computations have been made to stedy pressure head and moisture distribution in a soil-aquifer system subject to flux controlled infiltration at the land surface and evaporation .from shallow water table.