  We study the monotone energy stability of ``Poiseuille flow" in a
plane-parallel channel with a saturated porous medium modeled by the Brinkman
equation, on the basis of an analogy with a magneto-hydrodynamic problem
(Hartmann flow) (cf. \cite{Hill.Straughan.2010}, \cite{Nield.2003}).
  We prove that the least stabilizing perturbations, in the energy norm, are
the two-dimensional spanwise perturbations. This result implies a Squire
theorem for monotone nonlinear energy stability. Moreover, for Reynolds numbers
less than the critical Reynolds number $R_E $ there can be no transient energy
growth.
