Sensitivity analysis of unsaturated infiltration flow using head based finite element solution of Richards' equation

Abstract

Sensitivity analysis is one of the tools available for analyzing the effects of soil parameter on the variably unsaturated flows in porous media, that may easily be implemented into existing conventional Galerkin finite element solution of Richards’ equation based computational fluid dynamics codes. The sensitivity of the model is evaluated on the basis vertical infiltration problem with time dependent boundary condition, sharp gradient in the infiltration front, and discontinuous derivatives in the soil hydraulic properties. Simulation results demonstrate the complicated nature of unsaturated porous media during redistribution water flow.  The sample case presented highlight different aspects of the performance of the algorithm and the different factors that can affect their convergence and efficiency, including temporal discretization, convergence error norm, conductivity and moisture content characteristics, boundary conditions, and the extent of fully unsaturated zones in the soil. From the preliminary assessment performed herein, consideration of the number of degrees of freedom used when performing a sensitivity analysis is shown to demand enormous concern, if predicted sensitivities are to have significant physical interpretations. The proposed model is capable of simulating preferential flow situations using parameters which can be related to soil hydraulic properties.