“…For the case of saturated-unsaturated flow, we mention the contributions of Forsyth et al (1995), Pan and Wierenga (1995), Diersch and Perrochet (1999), Berganaschi and Putti (1999), Wiliams et al (2000), Lima-Vivancos and Voller (2004), Bause and Knabner (2004), Hao et al (2005), Marinoschi (2005), Basombrio et al (2006), McBride et al (2006), Pei et al (2006), Kees et al (2008), Bevilacqua et al (2009), Casulli and Zanolli (2010), Radu et al (2010), and Wu (2010). For 2D and 3D problems, the standard numerical approach consists of: -space discretization by finite volume, finite element (Galerkin), mixed finite element, finite differences; -method of lines for time discretization; -solution of the discrete nonlinear problems using Newton/Picard method; -solution of the linear problems by iterative linear solvers (preconditioned conjugated gradient, preconditioned Krylov subspace methods, algebraic multigrid, and so on).…”