  In this note, the existing porousMultiphaseFoam toolbox, developed initially
for any two-phase flow in porous media is extended to the specific case of the
Richards' equation which neglect the pressure gradient of the non-wetting
phase. This model is typically used for saturated and unsaturated groundwater
flows. A Picard's algorithm is implemented to linearize and solve the Richards'
equation developed in the pressure head based form. This new solver of the
porousMultiphaseFoam toolbox is named groundwaterFoam. The validation of
thesolver is achieved by a comparison between numerical simulations and results
obtained from the literature. Finally, a parallel efficiency test is performed
on a large unstructured mesh and exhibits a super-linear behavior as observed
for the other solvers of the toolbox.
