Robust numerical methods for saturated-unsaturated flow with dry initial conditions in heterogeneous media

A robust numerical method for saturated-unsaturated flow is developed which uses a monotone discretization and variable substitution. This method is compared to a conventional formulation and to a two phase (active air phase) model. On some published test examples of infiltration into dry media, the variable substitution method shows an order of magnitude improvement (in terms of nonlinear iterations) compared to the conventional pressure based method. One, two and three dimensional computations using both finite element and finite volume discretizations are presented.

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