There are two main categories of drainage systems built today:

Taken from Technical Design Guide - Section 1.1 Hydraulic Design. Chart A1. Relative Velocity and Discharge in a Circular Pipe for any Depth of Flow.

1. Surface (or storm) water which generally is discharged untreated into rivers or water courses.
2. Foul water that feeds into sewage treatment plants.

Surface (storm) water includes agricultural, roof or paved areas and highway drainage.

Foul water can be from either domestic or industrial sources.

‘Sewerage’ is the entire system of pipes, manholes, gullies and channels.
‘Sewage’ is the foul water effluent that flows within the sewerage system.
A ‘sewer’ is the pipeline itself, for either surface or foul water.
A ‘drain’ is typically the length of pipe serving a single property before it joins another pipeline where it then becomes a sewer.

In the design of a storm sewer or foul sewer, similar criteria must be considered. These include:-

• average and peak flows and their duration gradient
• the ranking of the sewer and whether flooding can be tolerated
• the depth of the sewer
• any topographical or structural feature such as a valley, building or embankment
• surface characteristics e.g. road, field or paved area
• outfall/connection to existing systems
• access to the sewer for maintenance e.g. frequency, size and depth of manholes

Full details relating to the hydraulic design of pipelines are explained in the Technical Design Guide – Section 1.1 Hydraulic Design.

Download TECHNICAL DESIGN GUIDE Section 1: System Design