  Hydrodynamic simulations suggest that galactic gas disks form when coplanar
gas spirals into the inner regions of the disk. We recently presented a simple
"modified accretion disk" model of viscous galactic disks in which
star-formation is fed by a radial flow of gas. However, little observational
evidence has been presented for such inflows, which are expected to be only a
few km s$^{-1}$ in the central regions of the disk, i.e. within three disk
scale-lengths, but could reach of order 50-100 km s$^{-1}$ in the very outer
disk. The effects of systematic inflow on the 2-d velocity field are examined
and it is shown that these are quite similar to those produced by geometric
warps of the disks, with twist distortions of both the kinematic major and
minor axes. This makes it potentially difficult to distinguish between these in
practice. By comparing the handedness of the observed twisting of the kinematic
axes and of the spiral arms for a sample of nearby galaxies, we find (assuming
that the spiral arms are generally trailing) that the effects of warps are in
fact likely to dominate over the effects of radial inflows. However, the common
practice of treating these twist distortions of the kinematic major and minor
axes as being due only to warps can lead, for galaxies of low-to-intermediate
inclinations, to substantial underestimates of any systematic inflow.
