Infrastructure Development Code

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City Plan Performance Standard: Appendix 12C
  1. Each wastewater management system shall be designed and constructed to ensure:
    1.  All wastewater reticulation pipelines and structures are to be sealed to contain design flows and prevent ground water infiltration. 
    2. They are ventilated to minimise the accumulation of foul gases.

The wastewater system shall be a piped reticulation system.

DS-6.5.1   Piped Reticulation

City Plan Performance Standard: Appendix 12C
  1. The following minimum pipe diameters apply:

Function                                                                                                                                               Minimum Diameter
Trunk mains                                                                                                                                                          225mm
Reticulation mains or high level pipelines receiving property connections only                                      150mm
Laterals < 25m in length & located clear of carriageways                                                                             100mm
Laterals > 25m in length or located under carriageways                                                                               150mm
Connections                                                                                                                                                           100mm

The piped reticulation system shall be designed to the following minimum requirements:

  1. It must comply with DS-1 - Appendix A.1 General.
  2. Reticulation mains shall be no smaller than 150mmØ.
  3. Trunk mains shall be > 225mmØ. 
  4. The minimum pipe size for connections or laterals shall be as follows:

1 or 2 independent dwelling units: 100mmØ
More than 2 independent dwelling units: 150mmØ
Commercial and industrial lots: 150mmØ
Reticulation servicing residential lots: 150mmØ
Carriageway crossings: 150mmØ

  1. Under no circumstances shall the pipe size be reduced on any downstream section.
  2. Manholes are required at each:
    1. Intersection of pipes (except for junctions between mains and laterals).
    2. Change of grade (except where vertical curves are used).
    3. Change of direction (except where horizontal curves are used).
    4. Combination of changes of pipe direction and grade (except where compound curves are used).
    5. Change of pipe size.
    6. Change of invert level.
    7. Change of material (except for repair/maintenance locations).
    8. Discharge of a pressure main into a gravity system.
    9. Permanent or temporary end of a pipe system.
  3. Each branch line (excluding connections) shall join the main line at a manhole junction.
  4. In potentially unstable ground or where special protection is required, the pipeline shall be specifically designed including the choice of materials.

DS-6.5.2   Reticulation Layout

City Plan Performance Standard: Appendix 12C
  1. Pipelines shall be located within the road zone and separated from any other infrastructure services laid parallel to it.  Where this is not practicable the pipeline can be provided on private property provided it is located within 1.5m of the property boundary and laid parallel to that boundary.
  2. Safe, reasonable and practical access shall be provided to the wastewater management system for its maintenance.

The following shall apply:

  1. The alignment of wastewater reticulation shall be laid out to follow the road pattern and either:
    1. Be located clear of the carriageway.
    2. Be located clear of wheel tracks if within the carriageway.
  2. Where this is not possible or practical, the main may be located:
    1. On public land with approval from Council.
    2. Within private property parallel to and located between 1m and 1.5m from the front, rear and/or side boundaries provided it avoids affecting future development options available within the lot.
    3. On the low side of lots that have a cross-fall of more than 1.5m.
    4. Drainage reserves outside the 50 year return period storm event (2%AEP) area.
  3. Where the only option for location of reticulation is within the carriageway, the reticulation shall be located in the centre of the driving lane & designed to support an 8.2 tonne design axle load.
  4. Horizontal curved pipes shall only be used only where approved by Council. Design standards for curved pipes can be found in Water Services Association of Australia : Sewerage Code of Australia : WSA 02 - 2002.
  5. Vertical curves may be specified where circumstances provide a significant saving or where maintenance structures would be unsuitable or inconvenient. The curvature limitations for vertical curves can be found in the Water Services Association of Australia : Sewerage Code of Australia : WSA 02 - 2002.
  6. Where an existing reticulation system exists, provision must be made for connection into this.
  7. Where the reticulation is within a private way, right-of-way, or joint-owned access lot the reticulation shall be located outside the logical wheel track alignment.

DS-6.5.2.1  Close Proximity Rules

Drawing Ref: T653, T654

The following shall apply:

  1. Buildings or structures to be constructed close to a main or lateral/connection shall comply with the requirements of T653 and T654. Where dispensation has been granted for a building or structure to be built over a main or lateral/connection, foundations shall be designed by a Chartered Professional Engineer.
  2. No enclosed building or structure shall be sited over a manhole or closer than 500mm from the outside wall of the manhole structure.
  3. No building or concrete slab shall be constructed over a connection point to a main.
  4. No buildings shall be constructed over a main if there is a connection closer than 1.0m to the building unless the connection is relocated to the satisfaction of Council.
  5. Encroachment of removable, non-permanent structures e.g. carports, decks, fences may be approved by Council when the structure is designed and built such that it can be dismantled easily in sections. The removal and re-erection of these structures shall be at no cost to Council. Council approval is required in all instances. Council will assess each application on a case by case basis as the variables at each site will not always be the same e.g. pipe size, trench details etc. Council may add a record to the property file of any such approval to ensure that future property owners are aware of the approval and Council’s right to have the structure removed at any time for the purposes of maintenance work, emergency work or upgrade work.

DS-6.5.3   Minimum Grades for Self-Cleaning

City Plan Performance Standard: Appendix 12C
  1. Each wastewater management system shall be designed and constructed to ensure:
    1. The following pipe flow velocities are met:
  2. Maximum velocity: 3.0 metres / second for peak wet weather flow;
  3. Minimum velocity: 0.75 metres / second.
    1. The following minimum gradients for reticulation or trunk mains are met for self cleansing:
  4. 150mm internal diameter: 0.55%;
  5. 225mm internal diameter: 0.33%;
  6. 300mm internal diameter: 0.25%;

The following shall apply:

  1. The reticulation pipes within the wastewater management system shall be designed and constructed to:
    1. Achieve the velocity range required by the City Plan Performance Standards
    2. Meet or exceed the minimum grades required by the City Plan Performance Standards to achieve self-cleansing. 
  2. Where the normal velocity and gradient limits cannot possibly be met, Council may require certain additional works to ensure satisfactory operation of the system.
  3. Ideal grades as shown in Table 2: Reticulation Grades shall be met at the extremities of the wastewater network i.e. 150m from the terminal node of any branch.
  4. Grades for lateral connections as shown on Table 6.2: Reticulation Grades shall be met.

Table 6.2: Reticulation Grades for Self-Cleaning

Trunk or Reticulation Main
Pipe Size (Ø) Ideal Grade (%) Minimum Grade (%)
150mm 0.67 0.55
225mm 0.40 0.33
300mm 0.33 0.25
Lateral Connection
Pipe Size (Ø) Minimum Grade (%)
100mm 1.65
150mm 1.2
>150mm 1.0

DS-6.5.4   Steep Grades

Scour blocks and trench stop configuration shall be detailed on the design drawings and shall be in accordance with the Standard Drawings. Spacing of scour blocks shall be in accordance with Table 6.3: Spacing of Scour Blocks.

Table 6.3: Spacing of Scour Blocks

Grade % Requirement Spacing (S) (m)
15-35 Concrete bulkhead S=100/Grade (%)
>35 Special design Refer to Council

 

Explanatory Note:
On flat grades where scour is a problem, sand bags are often used to stabilise the trench backfill.
Where the natural transfer of water from the trench into the surrounding ground will not provide sufficient drainage, trench drainage shall be provided to divert the water.

DS-6.5.5   Cover Over Pipelines

The following shall apply:

  1. In private property:
    1. The minimum cover shall be 600mm. 
    2. If the cover exceed 3m, specific design and approval is required. 
    3. The design of cover shall avoid affecting the future development options available within the lot.
    4. Where the reticulation lines are located in the front yards of lots, the invert level shall be deep enough so as not to interfere with any future driveway construction.
  2. In Road Zones:
    1. Pipelines shall achieve 900mm of cover and be designed to support an 8.2 tonne design axle load.
  3. Where minimum cover cannot be achieved, specific design of pipe and cover is required.

DS-6.5.6   Loads on Pipes

The following shall apply:

  1. All pipelines shall be designed to withstand all the likely loads that they may be subject to.
  2. In the first instance, load parameters shall be designed to support an 8.2 tonne design axle load. Following this:
    1. AS/NZS 3725 and AS 2566 shall be used as design guides as applicable.
    2. Any loads relating to backfill techniques, construction traffic, temporary storage of materials and the like shall be incorporated into design parameters and construction methodology.

DS-6.5.7   Concrete Capping of Pipelines

Where minimum cover cannot be achieved, concrete capping may be used taking into account pipe protection and road integrity requirements. Approval from Council is required for the use of concrete capping.

DS-6.5.8   Pipe Materials

Refer to AM-6 Wastewater.

DS-6.5.9   Pipe Joints

All pipelines shall be fully sealed by use of rubber joint rings or welding as appropriate unless otherwise approved by Council.

DS-6.5.10   Pipe Bedding and Backfill

Drawing Ref: T651

City Plan Performance Standard: Appendix 12C
  1. All wastewater pipelines shall be bedded, backfilled and reinstated to ensure that their structural integrity and life will not be compromised through existing ground conditions and/or anticipated loading;

The following shall apply:

  1. Pipe bedding and backfill shall be specifically designed, shown on the detailed design drawings and submitted to Council for approval.
  2. The design shall also include the compaction criteria to be used to certify the backfill has been compacted to the required compaction standard.
  3. All trench backfill under carriageways shall be designed and constructed to achieve for the required pavement layers strengths for the class of road it is beneath.

DS-6.5.11   Venting

City Plan Performance Standard: Appendix 12C
  1. Each wastewater management system shall be designed and constructed to ensure:
    1. They are ventilated to minimise the accumulation of foul gases.

The following shall apply:

  1. The wastewater management system shall be ventilated to minimise the likelihood of foul gases accumulating in the drainage system.
  2. In urban developments pipes will normally be adequately ventilated within private property drainage via terminal vent stacks. However there are some situations where additional vent stacks may be required. These are:
    1. Pumping stations.
    2. Manholes where pumping station rising mains discharge to a gravity pipe.
  3. Vents and pump stations shall be located to avoid being a noise or odour nuisance to occupants of buildings or likely building sites.

DS-6.5.12   Piped Reticulation Structures

City Plan Performance Standard: Appendix 12C
  1. Each wastewater management system shall be designed and constructed to ensure:
    1. Pump stations or network structures (e.g. manholes) located within the stormwater management system’s secondary flowpath (excluding Road Zone and vehicle and pedestrian accessways) shall have a finished lid level of 500mm above the design flow of the flowpath or the level of ponding.

The following shall apply:

  1. This section describes the requirements for structures that may be needed in conveying wastewater through a reticulated system. These are:
    1. Manholes.
    2. Rodding Eyes.
    3. Alternative structures as specifically designed.
  2. The selection of a suitable location for these structures may influence the pipe alignment. Generally a minimum clearance of 1.0m shall be provided clear of the opening around any structure that may allow entry for maintenance or rescue equipment. Council may determine other specific requirements subject to the individual site’s characteristics.

DS-6.5.12.1   Manholes

Drawing Ref: T601, T602, T603, T604, T605, T606, T607, T608, T609, T610, T611, T612, T613, T614, T615

City Plan Performance Standard: Appendix 12C
  1. Each wastewater management system shall be designed and constructed to ensure:
    1. Pump stations or network structures (e.g. manholes) located within the stormwater management system’s secondary flowpath (excluding Road Zone and vehicle and pedestrian accessways) shall have a finished lid level of 500mm above the design flow of the flowpath or the level of ponding. 
  2. Manhole structures shall have a minimum internal diameter of 1050mm and be provided for inspection and maintenance purposes at:
    1. All intersections of pipes (except junctions between pipelines and laterals);
    2. Changes of grade (except where vertical curves are used);
    3. Change in direction (except where horizontal curves are used);
    4. Change of pipe size;
    5. Change of invert level;
    6. Change of material; 
    7. Discharge of a pressure main into a gravity system;

The following shall apply:

  1. Manhole spacings shall not exceed 100m. Where the designer can clearly demonstrate that larger spacing is appropriate without negatively affecting the design outcome, operations and maintenance requirements, an IDC Departure may be submitted to Council for consideration.
  2. The entire manhole structure shall be located clear of all boundaries and at the end of all public reticulation mains.
  3. Manholes shall be located within Council property or Road Zones as often as possible. They shall be clear of floodways, stormwater detention areas, stormwater secondary flowpaths and inter-tidal regions.
  4. Manholes deeper than 5.0m to the pipe invert and shallow manholes may be used in certain circumstances subject to the approval of Council. Where a manhole is more than 5.0m deep:
    1. It shall be specifically designed with an emphasis on safety during installation, operation and maintenance.
    2. The designer shall provide the proposed construction method with the design documentation.
    3. Comment on how the renewal, upgrade or improvement of the manhole can be safely undertaken in the future shall be provided. 
    4. Have access steps installed.
    5. Incorporate clear warning that it is deep.
    6. Have a secure entrance.
    7. Require larger diameter chambers and covers.
  5. Standard 1050mmØ manhole risers are not suitable where the pipes are either larger than 675mmØ or where multiple pipes enter a manhole causing loss of the manhole wall. Manholes shall be designed to maintain wall integrity in these circumstances.
  6. Manholes shall not be located within the road carriageway unless approved by Council.
  7. All manholes shall have an entry safety grill fitted.
  8. All standard manholes shall be constructed as detailed on the Standard Drawings.    

Designers shall also refer to the Concrete Pipe Association of Australasia Guidance Note, Loads on Circular Precast Concrete Manholes and Access Chambers for technical guidance.  

DS-6.5.12.2   Manhole Sizing

Drawing Ref: T601

The following shall apply:

  1. The standard internal diameter of circular manholes is 1050mmØ and the preferred nominal internal diameters are 1050mmØ, 1200mmØ and 1500mmØ. 
  2. When considering the appropriate manhole diameter consideration shall be given by the Designer to the base layout to ensure hydraulic efficiency and adequate working space in the chamber. 
  3. Where the effective working space is reduced by internal drop pipes, a larger diameter may be required. 
  4. Where there are several inlets, consultation with Council on the layout of the chamber is recommended.

DS-6.5.12.3   Benching

The following shall apply:

  1. Benching shall be provided in the base of each manhole that provides a safe place to stand for maintenance purposes.
  2. Benching shall be close to flat with a cross fall (3H:1V upslope failure zone) into the manhole pipe system for drainage purposes.
  3. Channels shall have a minimum inside radius of 300mm.

DS-6.5.12.4   Internal Falls through Manholes

The following shall apply:

  1. Reticulation pipes:
    1. The minimum internal fall through a reticulation channel in a manhole shall be as outlined in Table 6.4: Minimum Internal Fall Through a Manhole.
    2. The maximum benched fall through a manhole shall be 600mm.
    3. Where the outlet diameter at a manhole is greater than the inlet diameter, the minimum fall through the manhole shall be not less than the difference in diameter of two pipes, in which case the pipes shall be aligned soffit to soffit.
    4. For manholes where the maximum internal fall of 600mm across the base of the manhole is exceeded due to a large difference between the levels of incoming and outgoing pipes then internal or external drops shall be provided as shown in the Standard Drawings.
  2. Lateral connections to manholes:
    1. The invert of a lateral must connect to the manhole at a level no lower than the average of the soffit levels of the main inlet and outlet pipes.
    2. The maximum angle of deflection of lateral into the manhole main channel shall be 90 degrees.

Table 6.4: Minimum Internal Fall Through a Manhole

Deflection angle at manhole Degrees (º)

Minimum additional fall (mm)

0 to 30

>30 to 60

> 60 to 120

30

50

80

DS-6.5.12.5   Allowable Deflection Through Manholes

The maximum allowable deflection through a manhole shall be as outlined in Table 6.5: Allowable Deflection Through Manholes.

Table 6.5: Allowable Deflection Through Manholes

Pipe Size (Ø) Maximum deflection (º)

150-300mm

150-300mm

Up to 120° for internal fall along manhole channel
Up to 150° when using an internal or external drop structure 

DS-6.5.12.6   Effect of Steep Grades on Manholes

Where a pipe of grade >7 % drains to a manhole, the following precautions shall be taken:

  1. Steep grades shall be continuous through the manhole at the same grade.
  2. Depth of a manhole to exceed 1.5m to invert for 150mmØ and 225mmØ pipes.
  3. Depth of a manhole is to exceed 2.0m deep for 300mmØ pipes.
  4. Change of direction at the manhole is not to exceed 45º.
  5. No drop junctions or verticals shall be incorporated in a manhole.
  6. Inside radius of channel inside a manhole is to be greater than 6 times the pipe diameter and benching is to extend 150mm above the top of the inlet pipe.
  7. To avoid excessively deep channels within manholes, steep grades (>7 %) shall be "graded-out" at the design phase where practicable. The design of pipelines on gradients over 7% must be agreed with Council.
  8. Benching of channels to ensure that the final platform is parallel with the main channel so maintenance workers are able to stand comfortably on a flat surface. The benching shall be sloped towards the channel.

DS-6.5.12.7   Flotation

In areas of high water table, all manholes shall be designed to provide a factor of safety against flotation of 1.25.

DS-6.5.12.8   Access Steps

Drawing Ref: T605

Manhole steps shall comply with the Standard Drawings and AM-6 Wastewater. Wastewater manhole steps shall be located above the downstream outlet pipe.

DS-6.5.12.9   Covers

Drawing Ref: T606, T607, T608, T609

The following shall apply:

  1. Manhole covers with a minimum clear opening of 600mm in diameter shall be used.
  2. Non-Rock covers must be used on all Level 2 (or primary arterial) roads.
  3. Refer to AM-6 Wastewater for manhole cover type.
  4. All covers shall be painted with New Zealand Transport Agency (NZTA) Standard approved "white" road marking paint.

DS-6.5.12.10   Areas Subject to Flooding

City Plan Performance Standard: Appendix 12C
  1. Each wastewater management system shall be designed and constructed to ensure:
    1. Pump stations or network structures (e.g. manholes) located within the stormwater management system’s secondary flowpath (excluding Road Zone and vehicle and pedestrian accessways) shall have a finished lid level of 500mm above the design flow of the flowpath or the level of ponding.

The following shall apply:

  1. The top of manholes in areas subject to flooding or located in a stormwater secondary flowpath shall be raised at least 500mm above the 50 year return period storm event (2%AEP) where practicable. This may require local ground recontouring to suit. 
  2. Sealed/watertight access covers may be required where the possibility of surcharge exists or the manhole is located:
    1. In a hardstand area (e.g. in a carriageway or walkway).
    2. Along a watercourse that is subject to flooding above the level of the cover
    3. In tidal areas or in any location where surface waters could inundate the top of a manhole.

DS-6.5.12.11   Internal and External Drop Manholes

Drawing Ref: T608, T609

The following shall apply:

  1. All drop connections to new wastewater manholes shall be constructed as detailed in the Standard Drawings.
  2. Internal drop connections will be permitted only by written approval and may require the installation of a 1200mmØ manhole. Internal drop connections may be allowed when working in sand country with potentially high groundwater and a resultant danger to the carriageway exists.
  3. The minimum height for drop connections shall be 600mm.

DS-6.5.12.12   Rodding Eyes

Drawing Ref: T620, T621

The following shall apply:

  1. A rodding eye shall be required at the ends of some lateral pipes installed between a property connection point and the wastewater main.
  2. PVC-U bends up to 45° are acceptable.
  3. A standard manhole frame and cover shall be installed over the entry point when not located in a hardstand area. A fire hydrant base and rodding eye cover shall be used in hardstand areas.
  4. All covers must be painted with New Zealand Transport Agency (NZTA) Standard approved "white" road marking paint.

Definitions in this section

AEP

Chartered professional engineer

City plan

Council

Design

Designer

Drainage system

Ground

Lot

New zealand transport agency

NZTA

Owner

Pavement

Private way

Road

Secondary flowpath

Stormwater

Wastewater