A simple model based on numerical simulations in bulk is used to exami
ne the pinning characteristics of vortices in helium films adsorbed in
the vicinity of substrate defects. The film profile in the absence of
a vortex is first calculated including both the Van der Waals potenti
al of a bump defect and surface tension. The displacement and ultimate
de-pinning of a vortex line constrained within the profile is then fo
llowed as a function of an imposed superfluid flow. The behavior of th
e vortices lends insight into recent experimental results sensitive to
the presence of pinned vortices and indicates that the relevant pinni
ng sites are atomic in dimension.