The sedimentation process of solid particles in a two-dimensional channel with an initially homogeneous, square configuration is numerically investigated at Reynolds numbers up to 10. The Lattice Boltzmann method is used to simulate the hydrodynamic interactions between fluid and particles. During the process the dispersion of particles in the horizontal direction fluctuates around zero, while the dispersion in the vertical direction (along the gravity direction) increases almost linearly. The increasing rate heavily depends on the initial symmetry of the suspension. The simulations show that the process of sedimentation encompasses three stages. In the first stage, the initial particle configuration plays a major role on the average velocity of the particles. A V-shape or W-shape front may be formed by the particles. During the second stage, the concentration is lower, strong particles interactions occur and the formation and destruction of particle clusters play a major role in the process. The sedimentation velocity depends to a large extent on the number of clusters formed and the velocity field developed. During the third stage, the concentration becomes low and the particle clusters are stable. The wakes generated by particle and clusters, especially of the leading cluster becomes important in the process. Average and fluctuation velocity have been obtained in the simulations and are reported in this paper. (C) 2003 Elsevier Science Ltd. All rights reserved.