USE OF GREEN-AMPT MODEL FOR ANALYZING ONE-DIMENSIONAL CONVECTIVE-TRANSPORT IN UNSATURATED SOILS

A general analytical solution to the equation describing purely convec tive vertical transport of a conservative solute under transient water flow conditions is presented. Richards equation does not yield analyt ical solutions for the flow field, except under restrictive choices of hydraulic properties relating water content, hydraulic conductivity a nd the soil matric potential. The utility of the Green-Ampt model for homogeneous unsaturated soils is investigated as an alternative to Ric hards equation. This model, though approximate, provides analytical so lutions to the flow field. It is found that the flow quantities requir ed for the analytical solution of convective transport (specifically t he soil water storage) are predicted accurately by the Green-Ampt mode l. Comparisons of numerical and analytical solutions of solute concent ration profiles suggest that the Green-Ampt water flow model is adequa te for convective solute transport predictions, and that the how held need not be computed by the more numerically expensive Richards equati on for this problem.