ABSTRACT
The explicit numerical method for saturated-unsaturated flow developed for FLAG in 1989 is implemented in the three-dimensional code FLAC3D. The method assumes a constant air phase pressure, negligible capillary pressure and a cubic relation between relative permeability and saturation. The algorithm, based on variable substitution and upstream weighting techniques, conserves fluid volume. The paper describes the method and compares the results of numerical simulations with analytic sharp front solutions in one, two and three dimensions.
