“…To discretize, we use the lowest order Raviart-Thomas finite element space (RTO), in which the discrete scalar unknown p h is approximated as a constant over each cell, and the components of the discrete vector u h are approximated by functions that are piecewise linear in one spatial dimension and constant in the other (Bernardi et al, 2005;Estep et al, 2009a). The discrete interface unknown, £ ) h , is represented by piecewise discontinuous linears on the interface grid cells (Arbogast et al, 2000(Arbogast et al, , 2007.…”