Abstract: The invention relates to a sedimentation basin for sewage treatment plants, the sedimentation basin separating materials such as sand, rocks or broken glass, from waste water, which materials settle by gravitational action. The waste water is introduced in the inlet region of the sewage treatment plant. The sedimentation basin is provided with flow guide walls having a wave or meander shape, a plurality thereof being disposed vertically adjacent to each other and parallel to the main flow direction of the sedimentation basin. The slowing of the flow caused by this arrangement results in improved sedimentation that occurs in an efficient and compact basin requiring less space.