Design Best Practices
Practical habits that make a sewer easier to build and maintain.
Design guidancePractice guidance, not a compliance requirement.
Most problems in gravity sewers are not hydraulic. They come from difficult access, poor construction tolerances, uncoordinated services and details that cannot be built as drawn.
The habits below are inexpensive at design stage and expensive to fix later. They complement, but do not replace, the requirements of the code and the authority.
Key design considerations
- Keep straight alignments between maintenance holes; minimise bends and avoid acute-angle junctions.
- Avoid grades close to the minimum where tolerance and settlement could take the pipe below it.
- Site maintenance holes on public land with permanent, safe access where possible.
- Coordinate with other services early, using potholed information rather than desk study alone.
- Minimise the depth of the network by following the surface fall, but keep cover requirements.
- Design for the maintenance method: jetting reach, machine access, and safe confined space entry.
- Provide spare capacity at the head of the system, where future connection requests arrive.
- Detail transitions, crossovers and connections rather than leaving them to site.
- Avoid siphons and pumped sections in a gravity network unless there is no alternative.
- Document departures and assumptions as they are made, not after review.
Design checks
- Alignment and access reviewed with the maintenance team's requirements in mind.
- Grades and cover checked against construction tolerance, not just the nominal value.
- Drawings buildable: every junction, transition and crossing detailed.
Standards and authority references
- WSA 02 (current edition)
- Authority standard details
- Authority maintenance practice
Confirm the current edition, amendment and any local supplement before applying any of the above.
Limitations and assumptions
- Best practice does not override a requirement; where they conflict, the requirement governs.
This reference is general engineering information. Confirm requirements against WSA 02, the current Australian Standards and the local water authority's supplement before use in design, and obtain project-specific advice for the conditions at hand.