  We present modeling of the incompressible viscous flows in the domain
containing an unconfined fluid and a porous medium. For such setting a rigorous
derivation of the Beavers-Joseph-Saffman interface condition was undertaken by
J\"ager and Mikeli\'c [SIAM J. Appl. Math. \rm 60 (2000), p. 1111-1127] using
the homogenization method. So far the interface law for the pressure was
conceived and confirmed only numerically. In this article we justify rigorously
the pressure jump condition using the corresponding boundary layer.
