“…Over the past three decades, several numerical models including finitedifference models (FDMs), finite-element models (FEMs), mixed FEMs, finite-volume models (FVMs), and the Eulerian-Lagrangian model have been developed for simulating saturated-unsaturated flow (e.g. Abdollahi-Nasab et al, 2010;An et al, 2011;Bause et al, 2004Bause et al, , 1999Boufadel, 2000;Boufadel et al, 2011;Celia et al, 1990;Clement et al, 1994;Farthing et al, 2003;Forsyth et al, 1995;Guo et al, 2010;Huang et al, 1994;Jie et al, 2004;Jones and Woodward, 2001;Boufadel, 2010, 2011;Manzini and Ferraris, 2004;Simunek et al, 1999;Tocci et al, 1997;Xia et al, 2010). FDMs, in particular, have certain advantages over other numerical models with respect to the ease of coding and understanding, owing to its simplicity of discretization; FDMs have thus been widely used for simulating saturated-unsaturated flow in porous media.…”