Channelling, which occurs during the batch thickening of concentrated slurries, allows water to escape the settling slurry at a high rate, thus increasing the interface settling velocity. This research shows that the upper layers of the settling column are progressively diluted and that the channel zone occurs at the interface between the diluted slurry and the slurry in compression. As the solids in the lower sections of the column compress and expel water, this water escapes by means of the channels.