“…As regards the spatial discretization there are much more options possible. Galerkin finite elements were used in [2,3,9,22,24,32], often together with mass lumping to ensure a maximum principle [8]. Locally mass conservative schemes for Richards' equation were proposed and analysed in [10,11] (finite volumes), in [16] (multipoint flux approximation) or [4,5,26,29,34,35] (mixed finite element method).…”