  We consider $N$ identical inertialess rigid spherical particles in a Stokes
flow in a domain $\Omega \subset \mathbb R^3$. We study the average
sedimentation velocity of the particles when an identical force acts on each
particle. If the particles are homogeneously distributed in directions
orthogonal to this force, then they hinder each other leading to a mean
sedimentation velocity which is smaller than the sedimentation velocity of a
single particle in an infinite fluid. Under suitable convergence assumptions of
the particle density and a strong separation assumption, we identify the order
of this hindering as well as effects of small scale inhomogeneities and
boundary effects. For certain configurations we explicitly compute the leading
order corrections.
