The results of an experimental study on the motion of heavy particles (heavierthan water) in an open channel flow over a smooth bed are presented in the paper. Some aspects of the diffusion and dispersion of the particles are analysed and especially the effects of lift force and the quadratic nature of drag forces when present. The results show that for a given fall velocity in still water, the vertical dispersion increases with increase in particle diameter. Measured mean particle downward velocities are lower than the settling velocities in still water.