Uniform Darcy-Brinkman flow over a surface with periodic rectangular grooves is studied by domain decomposition and matching. It is found that the effect of corrugations is equivalent to replacing the rough surface with a smooth surface with an apparent slip for the bulk flow. Such equivalence would greatly simplify the boundary conditions for porous flow bounded by a rough surface. The slip velocity is larger along the grooves than transverse to the grooves, and is increased by the porous media parameter k.