Analytical and numerical modelling of unsaturated flow

Abstract

It is shown that the solution of the Richards' equation by full linearisation provides a reasonably good approximation for infiltration when rainfall is of relatively high intensity, but results in too fast surface drainage during evaporation. In numerical schemes for solving the complete non-linear Richards' equation, on the other hand, small times steps have to be used to guarantee stability when surface flux is large, but relatively large time steps can be used when surface flux is small. A hybrid scheme for solving the Richards' equation would consist of a superposition of the redistribution solution for the complete non-linear equation under zero surface flux and the linear perturbation..