Inlet and Outlet Arrangements
Benching, channel shape and the angles at which pipes enter.
The channel and benching control how flow passes through the structure. A well-formed channel carries flow smoothly from inlet to outlet with minimal turbulence; poor benching creates eddies, deposits and odour.
Inlet and outlet arrangements are constrained by the angles at which pipes enter, by the level differences between them, and by the number of connections. Large angle changes or high inlet falls usually require a drop.
Key design considerations
- Channel formed to match pipe diameters, with benching rising to the wall springline.
- Smooth transition between inlet and outlet, and alignment of obverts.
- Number of inlets and the included angle between them; acute angles are best avoided.
- Level difference between inlet and outlet, and whether a drop is needed.
- Sealing of penetrations against groundwater and root intrusion.
- Property connection junctions, and whether they enter the maintenance hole or the pipe.
- Access past the channel for maintenance without damaging benching.
Design checks
- Channel and benching detailed on the drawing, not left to the contractor.
- Inlet angles within the authority's permitted practice.
- Drop provided where the inlet fall exceeds the authority's limit.
Standards and authority references
- Authority standard maintenance hole details
- WSA 02 (current edition)
Confirm the current edition, amendment and any local supplement before applying any of the above.
Limitations and assumptions
- Acceptable angle and fall limits vary by authority and are not reproduced here.
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.