Glossary of terms

Sewer slope

Sewer slope is the inclination of the channel invert in the direction of flow, usually expressed in per mille (‰) or as a ratio such as 1:200. It is calculated as the difference between invert elevations at the ends of a section divided by its length. The slope determines wastewater velocity: too small may cause sedimentation, too large may cause excessive velocity and abrasion. In a longitudinal profile the slope is visible from the invert line and the section label. It is worth recalculating it from elevations and length and checking that the invert falls with the flow.