  We study the driven collective dynamics of a colloidal monolayer
sedimentating down an inclined plane. The action of the gravity force parallel
to the bottom wall creates a flow around each colloid, and the hydrodynamic
interactions among the colloids accelerate the sedimentation as the local
density increases. This leads to the creation of a universal "triangular"
inhomogeneous density profile, with a traveling density shock at the leading
front moving in the downhill direction. Unlike density shocks in a colloidal
monolayer driven by applied torques rather than forces [Phys. Rev. Fluids,
2(9):092301, 2017], the density front during sedimentation remains stable over
long periods of time even though it develops a roughness on the order of tens
of particle diameters. Through experimental measurements and particle-based
computer simulations, we find that the Burgers equation can model the density
profile along the sedimentation direction as a function of time remarkably
well, with a modest improvement if the nonlinear conservation law accounts for
the sub-linear dependence of the collective sedimentation velocity on density.
