Part 3 – Road Works

3.9    Road Drainage

3.9.1    Subsoil Drains

Where topography dictates or soils are not free draining, subsoil drains will be required behind the kerb as follows:

Minimum subsoil pipe size – 110 mm Nexus
Minimum depth to pipe invert  –  700 mm
Minimum width  –  300mm

3.9.2    Batter Drains

Batter drains behind the boundary may be required to prevent water entering into or onto the berm.  They must be constructed as for 3.9.1 above.

3.9.3    Drain Outlet Inverts

Subsoil and batter drain outlets shall be to catchpits or manholes.

3.9.4    Kerb and Channel, Vertical Kerb and Island Kerb

1. All profiles are to be founded on subgrade with CBR of 7.  Where pavement depth (refer Table 3.1) is greater than 150 mm, profile shall be laid on a minimum of 75 mm of compacted GAP20 or WHAP 20; or:
2. The construction shall be in accordance with a specific design approved by the Council’s Asset Manager – Strategy and Policy.

For kerbs with radii tighter than the minimum specified in Table 3.1, or carriageway narrower than standard, “Heavy Duty Kerb and Channel” shall be used.
    
Note:  Suitable kerb profiles are detailed in the MPDC Infrastructure Code of Practice.

3.9.5    Catchpits

1. For developments where the stormwater connection is direct from each lot to stormwater drainage pipes, the area drained per catchpit:
   -    Gross area drained (carriageway, berm and footpath) - Maximum 900m²
   -    Area of carriageway  -   Maximum 450m²
   -    Maximum spacing of catchpits  - 100 m
   -    Maximum spacing of catchpits where private houses connect stormwater to kerb and channel - 60 m

2. Preferred location of catchpits:
   -    At intersections, at the kerbline tangent point
   -    Upstream of pram crossings
   -    At changes of gradient on steep roads
   -    Cul-de-sac heads

3. A double catchpit will be required:
   -    At the lowest point in a sag vertical curve
   -    At the ends of a cul-de-sac where water falls to the end
   -    On all channels where the gradient is steeper than 5%
   -    Grates shall be the alternative type with bars parallel or perpendicular to the kerb

    

3.9.6    Dish Channels

For dish channels with footpaths or accessways, concrete is to be on subgrade with CBR not less than 7.

Where possible, the design should avoid a requirement for dish channels.

Note:  Suitable dish channel profiles are provided in the MPDC Infrastructure Code of Practice.

3.9.7    Road Drainage in Rural and Rural Residential Areas

Channels shall generally be provided for the efficient drainage of surface water and shall be graded to outlets at regular intervals not exceeding 150 m.  On steep grades where channels are subject to scouring protection work and outlets at more frequent intervals may be required.

Traversable culvert ends should be installed at suitable locations, particularly on arterial and collector roads.

Swale drains may be allowed in suitable locations.

Culverts, where required, shall be designed in accordance with approved engineering standards.  Notwithstanding the outcome of any design calculations, no culvert traversing a road or vehicle entrance shall be smaller than 300 mm in diameter.

In non-urban subdivisions where stormwater from the road formation and adjoining properties cannot be discharged via either open channels or a piped system to an approved outlet, the construction of drilled and lined soakholes and/or roadside berm drainage beds is an option.  Any application for this type of disposal system must be accompanied by results of soil percolation tests, specifications and design calculations for Council’s approval.  The design and testing of these drainage systems shall be carried out by an approved geotechnical engineer. 

Note:  The MPDC Soakage Guidelines provide a useful guide.