  We study capillary-gravity and capillary surface waves for fluid flows
governed by Darcy's law. This includes flows in vertical Hele-Shaw cells and in
porous media (the one-phase Muskat problem) with finite or infinite depth. The
free boundary is acted upon by an external pressure posited to be in traveling
wave form with an arbitrary periodic profile and an amplitude parameter. For
any given wave speed, we first prove that there exists a unique local curve of
small periodic traveling waves corresponding to small values of the parameter.
Then we prove that as the parameter increases but could possibly be bounded,
the curve belongs to a connected set $\mathcal{C}$ of traveling waves. The set
$\mathcal{C}$ contains traveling waves that either have arbitrarily large
gradients or are arbitrarily close to the rigid bottom in the finite depth
case. To the best of our knowledge, this is the first construction of large
traveling surface waves for a viscous free boundary problem.
