Part 4 – Stormwater Drainage
4.15 Manholes
4.15.1 General
Manholes shall normally be designed at each change of direction or gradient, and at each branching line and at a spacing of not more than 100 m.
On stormwater pipelines equal to or greater than 900 mm diameter, the spacing of manholes may be extended up to 200 m, and uniform curvature on the pipeline may be permitted providing that joint deflections are within the limits of the manufacturer’s recommendations.
On stormwater pipelines equal to or greater than 1.8 m, the spacing of manholes may be extended up to 300 m between manholes.
4.15.2 Shallow Manholes
Shallow manholes less than 1 m deep shall be a minimum of 750 mm diameter.
Note: The MPDC Infrastructure Code of Practice provides acceptable details.
4.15.3 Stormwater Manholes on Larger Pipelines
Manholes on stormwater pipelines more than 600 mm diameter and on smaller pipelines where the use of standard manholes are not suitable should be specifically designed. The minimum diameter of the manhole shall be equal to the largest pipe size plus 450 mm.
4.15.4 Hydraulic Flows in Manholes
In addition to the normal pipeline gradient, all manholes for pipelines less than 1 m in diameter shall have a minimum drop of 20 mm plus 5 mm per 10 degrees of the angle of change of flow within the manhole.
In addition to the normal pipeline gradient, all manholes on pipelines greater than 1 m in diameter shall have the drop through the manhole designed to a minimum of 20 mm plus compensation for the energy lost due to the flow through the manhole at the deviation angle (see Figure 4.4 of this Part).
4.15.5 Junctions
Catchpit leads not more than 300 mm diameter and not more than 20 m in length may be saddled on to pipes 600 mm diameter and larger, with manholes not required.
Branch lines should normally be connected into a manhole. However branch lines 300 mm diameter and smaller may be saddled on to pipelines 600 mm diameter or larger, providing a manhole is supplied on the branching line within 40 m of the main line. Proprietary “Y” connections shall be used where possible.
4.15.6 Step Irons and Steps
All manholes other than shallow manholes shall be provided with approved manhole steps in order to give reasonable access.
Steps to be included and located on the downstream side of the manhole.
Note: The MPDC Infrastructure Code of Practice provides acceptable details.
4.15.7 Manhole Covers and Frames
Manhole covers and frames shall be designed to be fit for purpose at their location.
Note: The MPDC Infrastructure Code of Practice provides acceptable details.
4.15.8 Drop Connections
Drop connections on stormwater manholes may be avoided by allowing pipes up to and including 300 mm diameter to have an open “cascade” inside the manhole, providing the steps are clear of any cascade. Otherwise a short ramped section must be provided on the connecting line.
