Pipelines and culverts Print

Design Outcome

​4.3.9.1. Alignment of Pipelines​
​The expectation is that the pipe will be located within the overland flow path. 

Stormwater pipes shall be located, where practicable, within the road reserve (preferably in the berm) or other public land. Only where this is not possible shall the location of stormwater pipes within private property be considered. In such cases the pipe shall be located so as not to reduce the building area available on the lot (i.e. located as close as possible to a boundary) or where it can be shown that a satisfactory house location site is available clear of the pipe, and that access points have been allowed for, suitably placed so that access will be available post-development. Where stormwater pipes are installed adjacent to wastewater pipes within the berm or under the footpath, they shall preferably be installed on the carriageway side of the wastewater pipe.

The order of preference for the location of stormwater pipes is summarised as follows:

1. Within overland flow path

2. Road reserve and other public land

3. Shared accessway

4. As close to the property boundary as is practicable, and parallel to the boundary.

Pipelines adjacent to boundaries, structures and foundations shall be located at least a distance equal to the depth to invert away from such boundaries and the edge of such structures and foundations with an absolute minimum clearance of 1m in all cases (Refer to drawing SW22 in Appendix B).

The stormwater network layout shall ensure the following:

a) Access to all parts of the reticulation shall remain available for inspection and maintenance. Adequate spacing of manholes, access points and access chambers shall be provided for regular maintenance and inspections including CCTV inspection, water jetting, root cutting and grouting.

b) The proposed pipe system shall comply with the design, construction and maintenance aspects of AS/NZS 2865:2001 (Safe Working in a Confined Space).

c) The potential for infiltration and exfiltration shall be minimised, for example by optimising the number of manholes and access points.

d) Siphons and inverted siphons are generally not permitted, however the council will exercise its discretion on a case by case basis. These will require specific design and approval.

e) In general, pipelines between access points shall be straight with manholes at a change in​ direction or grade. Horizontally or vertically curved pipelines will require specific design and approval by the council. Pipelines with both horizontal and vertical curvature will not be permitted.​

4.3.9.2. Other Services

For normal trenching and trenchless technology installation, clearance from other service utility assets shall generally be in accordance with those established in Watercare’s Chapter 5 – Water and Wastewater CoP.

Service crossings of open stormwater channels or watercourses shall be installed beneath the channel or watercourse. In the event that it is impractical to install the service beneath the channel, specific design approval is required from the council.​​

4.3.9.3. Design for Installation

All pipes shall be designed to support all existing and any predicted future dead loads. Design live loads shall be HN-HO-72 for motorways and arterial roads, HN for local streets and driveways, and 20kN wheel load for non-trafficable areas. Reinforced concrete pipe installation design shall be in accordance with AS/NZS 3725:2007 and CPAA Engineering Guideline Selecting Materials for Bedding Steel Reinforced Concrete Pipe. The minimum acceptable support type shall be H2 as shown in drawing SW03 in Appendix B. The use of higher support types to reduce pipe class shall be subject to specific design and council approval.

All reinforced concrete pipes shall be designed to AS/NZS 4058 and AS/NZS 3725.

All flexible pipes shall be designed and constructed to AS/NZS 2566 parts 1 and 2.

Installation of reinforced concrete pipe in road reserve shall require specific design to demonstrate that any possible heavy compaction of trench fill to achieve road subgrade and pavement stability requirements will not cause excessive cracking of pipes. The use of free flowing granular materials for pipe embedment as shown in drawings SW02 and SW03 in Appendix B is recommended to reduce compaction stresses on pipes.

In areas with a high water table, it shall be demonstrated to the council’s satisfaction that all pipelines are designed against flotation.​

4.3.9.4. Materials

The pipe types listed in Table 4.6 below may be used for stormwater drainage work when appropriate, provided they are designed, manufactured and installed to the current New Zealand or Australian standards.​

Wherever it may be reasonably anticipated that concentrations of chlorides, sulphates and acids may be elevated, and in industrial areas, the pipe material and grade shall be selected to resist attack from any chemicals that are identified through a suitable testing regime. In all cases where elevated chemical concentrations may exist, including in peat soils and the marine environment, the soil, groundwater, and stormwater shall be tested and results provided with the design report.

Table 4.6: Pipe Materials​​

Pipe Type

Standard

Conditions of Use*

Reinforced concrete (RC)

AS/NZS 4058 and AS/NZS 3725

All stormwater applications

Polyvinyl chloride (PVC)

AS/NZS 1254 or AS/NZS 1260 – Minimum SN16

Generally for up to 375mm diameter

Polyethylene (PE)

AS/NZS 4130 and 5065 – Minimum PE100 or base resin from which PE100 is compounded, with Standard Dimension Ratio (SDR) of 17 or superior including for thrust and drilled lines that are grouted

Generally confined to trenchless applications or trenched applications where required by specific site conditions. Will be approved for use following demonstration of satisfactory specific design.

Polypropylene (PP) twin-walled pipe

AS/NZS 5065 – Minimum SN16

Will be approved for specific applications following demonstration of satisfactory specific design 

* Refer also to Section 4.3.9.4.​

All other pipe materials are excluded from use without specific approval from the council.

4.3.9.5. Minimum Pipe Sizes​

​​​Public Mains

All public mains shall have a minimum internal diameter of 225mm. The upstream point of a public main shall start at a manhole, non-access chamber or catchpit, and shall terminate at a manhole or outlet. The pipe shall be sized in accordance with Section 4.3.5. In this context, a public main is a pipeline which meets all of the following criteria:
  • Has been vested or is in the process of being vested in the council
  • Is designed to convey at least the Maximum Probable Development (see Section 4.2.8) 10% AEP storm for the sub-catchment it services
  • Is (or could be in the future) connected to a public catchpit.​
Branch Lines

All branch lines shall have a nominal diameter of minimum 150mm (or minimum 100mm if serving up to two lots) and maximum 225mm. If a capacity assessment indicates that 225mm is too small, the pipeline shall be a public main instead of a branch line. Branch lines shall be sized in accordance with Section 4.3.5. In this context, a branch line is a pipeline which meets all of the following criteria:
  • ​Has been vested or is in the process of being vested in the council
  • Is generally the connection between the lot or lots that it serves and the public main
  • Shall be no greater than 25m in length
  • Connects to the public main via a manhole when connecting more than three dwellings to the public system, or where more than three dwellings may be connected in the future

Where the point of connection to the public system is not at a chamber, appropriate access for CCTV inspection shall be provided on the private section of the line (as per drawing SW04 in Appendix B).

Refer to drawing SW24 in Appendix B for examples of public/private boundaries for stormwater connections.

For further information regarding connections to the public system refer to Section 4.3.11, and for information regarding connection to public mains refer to Section 4.3.12.​

4.3.9.6. Minimum Cover

All pipelines shall be specifically designed to support all likely loadings, in relation to the minimum cover to the top of pipe to be provided in accordance with the relevant standards. The cover shall be not less than 600mm (including during the development of the site).

In the road reserve the cover shall be not less than 1000mm.

Where the reticulation pipelines are laid in the front yard of lots and the lots are elevated above the carriageway, the minimum cover on the pipelines within the lot area shall be 600mm below the adjacent road level. This is to avoid damage when the lot is subsequently levelled out to make way for building platforms and/or driveways are subsequently excavated.​

The requirements for minimum cover on pipelines are summarised in Table 4.7.​

Table 4.7 Minimum Cover on Pipelines Pipeline Location

Min. Cover (mm)

Location where specific design shows no additional cover is required

600

Front yard of lot where the lot is elevated above the carriageway

600 below finished surface level of carriageway

Road reserve

1000 


For special cases and with agreement from Auckland Council, cover can be reduced by using higher class pipe, special bedding, concrete protection or a combination of these. Reference shall be made as noted in the clause above to AS/NZS 3725:2007 (Design for Installation of Buried Concrete Pipes) or similar standards for pipes of other materials.

Reference shall also be made to AS/NZS 3725:2007, AS/NZS 2566.2:2002 (Buried Flexible Pipelines Part 2: Installation), or to similar standards for pipes of other materials. The key issue is that pipes shall not be installed in situations where their design load capability is exceeded during construction or subsequent operation.​

4.3.9.7. Minimum Gradients and Flow Velocities

Pipe Velocity Limits

The velocity of stormwater in pipes and box sections shall be maintained within acceptable limits to both ensure self-cleaning of the pipe or box section and to avoid scouring and erosion of the conduit.

The acceptable minimum flow velocities for all pipes of all materials for the 50% Annual Exceedance Probability (AEP) design storm are an absolute minimum of 0.6m/s and desired minimum of 1.0m/s.

The acceptable maximum flow velocity for all pipes for the 10% AEP design storm is 4.0m/s.

Notwithstanding the above velocity limits, hydraulic considerations may well require the velocity to be controlled to well below the stated maximum velocity and/or the pipe size increased to minimise structure losses and the slope of the hydraulic grade line.​

Pipe Grade Limits

Pipeline gradients shall be designed to allow for the maximum and minimum velocities stated​​ 
above. Within these limits, the maximum gradient shall not exceed 25% (1 in 4), and the minimum gradient shall not be less than 0.1% (1 in 1000) for all pipes. Gradients outside these limits shall be at the council’s discretion.

In addition, designers shall consider the peak velocity in the pipe against the maximum design velocity provided by manufacturers and suppliers.​

4.3.9.8. Culverts

For the purposes of this document, a culvert is defined as any conduit that transfers the flows of a watercourse or waterway across a road or embankment. The design of culverts shall comply with Auckland Transport Code of Practice (ATCOP) and the following criteria:

a) The culvert shall be designed to cater for the flows and water levels generated by the 1% AEP event without affecting upstream or downstream property.

b) The headwater pond created by the culvert during the 1% AEP event shall have a depth not exceeding 3.0m above the invert of the pipe and shall provide 500mm freeboard to the edge of the seal of the road (or similar feature) at the top of the embankment. For cases where the approach velocity is greater than 2m/s, the freeboard shall be at least 1.5 times the velocity head at the entrance. The headwater pond created by the 10% AEP event shall not be higher than the soffit of the pipe.

c) Culverts shall be designed such that the maximum velocity within the culvert generated by the 1% AEP event does not exceed 6.0m/s. Higher velocities in culverts require approval from the council. High outlet velocities are likely to cause scour and erosion of natural channels and reference shall be made to Auckland Council technical report TR2013/018 (Hydraulic Energy Management: Inlet and Outlet Design for Treatment Devices) for design guidance for energy dissipation. Note that energy dissipation will be required at far lower velocities than the maximum allowed within the conduit stated above.
d) Culverts shall be designed such that an absolute minimum velocity of 0.6m/s and desired minimum of 1.0m/s is achieved. Minimum flow velocities apply to the 50% AEP design storm.

e) Culverts shall have a minimum internal diameter of 375mm (for vehicle crossing standards refer to ATCOP).

f) A suitable transition structure is required at both the inlet and outlet to the proposed culvert which shall ensure that there is no scour or erosion in the watercourse, private property and/or the road formation. Refer to ATCOP for special requirements adjacent to roads.
g) A secondary flow path shall be kept unobstructed at all times. The secondary flow path 
design shall assume the total blockage of the culvert in cases where it is less than 1500mm in diameter, and 50% blockage of the culvert where it is greater than or equal to 1500mm in diameter.

h) Allowance for 100% blockage of pipes greater than 1500mm in diameter may be necessary in some circumstances. The risk of blockage resulting from the contributing catchment shall be assessed on a case-by-case basis (this includes situations where a safety grille or trash screen is used) to determine if specific culvert design (including consideration of a secondary inlet) is required.

i) No obtrusive brand names on proprietary devices and other visible components of the stormwater system shall be visible once constructed.

j) For culverts whose inlets may be difficult to locate if submerged, green retro reflective raised pavement markers shall be required to mark the presence of the culvert under the roadway. For all culverts to be maintained by Auckland Transport, markings shall be in accordance with ATCOP requirements.

k) Provision of safety measures may be required, for example a barrier along the culvert headwall. Refer to ATCOP for special requirements adjacent to roads.

l) Culverts under road fencing or barriers are to be designed to Auckland Transport approval.

m) Adequate provision shall be made for maintenance. This shall include, but not be limited to: access to inlet and outlet for inspection, debris removal and scour protection maintenance, and any other activities stated in the operation and maintenance manual.

n) Fish passage shall be provided in accordance with Section 4.2.8.

o) The need for debris screens will be subject to specific design, taking into account the likelihood of debris flowing from the upstream catchment and potential impact on the culvert.

p) Culverts will be single-barrelled unless specific design is approved by the council.​

Culverts of watercourses and roadside drains are owned and maintained by the property owner(s) served by that crossing, except all culverts transferring flow across the road reserve which are owned and maintained by Auckland Transport or NZ Transport Agency. Note that culverts for private vehicle crossings (i.e. serving a private property) within the road reserve will be owned and maintained by the property owner.

4.3.9.9. Inlets and Outlets

Where a pipeline discharges into a natural or constructed waterway, or vice versa, consideration shall be given to energy dissipation or losses, erosion control, and land instability. This is often​ with permission from Standards NZ.
achieved by an appropriately designed headwall structure and rock armour.

For outlets, the design shall ensure non-scouring velocities at the point of discharge. Acceptable outlet velocities will depend on soil conditions, and reference shall be made to Auckland Council technical report TR2013/018 (Hydraulic Energy Management: Inlet and Outlet Design for Treatment Devices) for the maximum velocities allowable prior to the requirement for specific provision for energy dissipation and velocity reduction.

Where inlets or outlets are located on or near natural waterways, their appearance in the riparian landscape and likely effect on in-stream values shall be considered. Methods to reduce such impacts may include:​
  • Cutting off the pipe end at an oblique angle to match soil slope
  • Constructing a headwall from local materials such as rock or boulders
  • Planting close to the structure
  • Locating outlets well back from the water’s edge.
Design of inlet and outlet structures in high-amenity open space areas requires additional consideration to achieve a sympathetic and unobtrusive design. Auckland Council Community Services Department is to be consulted when the outlet is located in public reserve land.

Direct discharge to a waterway or the sea may require a discharge permit from the council unless authorised by a Network Discharge Consent held by the council, or a permitted activity under the relevant plan(s).

An example standard design drawing for an inlet/outlet headwall is provided in drawing SW19 in Appendix B. Energy dissipation and erosion control is likely to be required in addition to the headwall structure, and shall be specifically designed using guidance from Auckland Regional Council technical publications TP10 (Stormwater Management Devices: Design Guidelines Manual), and TP131 (Fish Passage Guidelines for the Auckland Region) if fish passage is required. For further technical guidance on the design of stormwater device outlets, see TR2013/018.

Inlet/outlet structures for pipe culverts shall be either a standard precast wingwall supplied by a certified precast manufacturer, or a specifically designed structure as approved by Auckland Council. Inlet/outlet structures require specific design and will be subject to Auckland Council approval in the following situations:
  • Pipe culverts larger than 600mm
  • Duplicate pipe culverts
  • Culverts at complicated natural soil locations
  • Where special appearance and/or energy dissipaters are required
Inlets and outlets adjacent to roads may require additional road user safety considerations. Refer to Auckland Transport Code of Practice (ATCOP).

With respect to health and safety, all inlets to the stormwater network greater than 375mm diameter shall be fitted with a safety grille. The inlet grille shall be specifically designed and requires Auckland Council approval. The grille shall have a clear opening of 100mm between bars. Note that grilles are not required on manholes or, generally, at the inlet to a culvert.

Culvert inlets are not generally screened for safety reasons. When designing inlets to culverts, debris screening may be required as discussed in Section 4.3.9.8 above. However, a risk assessment shall be undertaken on each culvert (and the surrounding catchment) to ascertain if a grille is required to prevent accidental entry to the culvert. If a grille is required, provision shall be made for the effects of debris build-up against that grille. There shall also be suitable access for maintenance personnel and for any mechanical plant required to remove debris build-up from the grille.

Fencing around inlet/outlet structures is required unless it can be demonstrated that human access to the inlet/outlet structure is unlikely and/or the height of the structure is less than 1.2m. A standard detail for a safety fence for inlet/outlet structures is provided in drawing SW20 in Appendix B.

4.3.9.10. Outfall Water Levels

Backwater profiles shall be considered such that the design is fully informed with respect to any likely adverse effects.

Similarly, for tidal outfalls, peak flow may or may not coincide with extreme high tide levels. A full dynamic analysis and probability assessment may be required. In circumstances where a flap valve or flood gate is necessary, specific design and approval from the council is required.

Sea level rise shall be taken into account in design (see Section 4.3.5.8).

4.3.9.11. Subsoil Drains

All subsoil drains to provide land stability are considered to be private and should be self-contained within the individual lot.

Where private subsoil drains are installed behind a retaining wall, subsoil drains shall discharge into a silt trap before connecting into the public drainage system via the private connection pipe. Retaining walls shall be positioned to ensure that subsoil drainage will be capable of connecting into the drainage system at the public connection point.

All other subsoil drains shall also be connected to a settling chamber or catchpit before ​connecting to the public line via the private connection pipe.​

4.3.9.12. Anchor Blocks and Waterstops

Steep Gradients and Anchor Blocks

Where gradients of pipes are between 10% and 20%, pipelines shall be laid from downstream to upstream with sockets facing upstream and shall be bedded in low strength concrete (7MPa). Where gradients of pipes are in excess of 20%, anchoring will be required to prevent movement. Anchor blocks also help to prevent:
  • Bedding scour
  • Migration of fine granular particles
  • Separation of joints
  • Transfer of groundwater through the backfill material surrounding the pipe.
In situations where anchor blocks are to be implemented, pipelines shall be laid from downstream to upstream with sockets facing upstream. A protective/compressible membrane shall be wrapped around the pipeline for the length of the anchor block at the concrete interface. Spacings between anchor blocks shall not exceed 6m, measured centre to centre. See drawing SW23 in Appendix B.

Manholes with flanged bases adequately installed against a trimmed excavation may be considered as an anchor block.

Specific anchor block design and arrangement is required for pipelines where:
  • The gradient is greater than 30%, or
  • High groundwater table or unstable ground conditions are apparent.
Waterstops

Where a pipeline is to be installed between an area with a high water table and an area with a lower water table or in tidally affected areas, transfer of groundwater through the backfill material in the reinstated trench is likely to occur. Transfer of groundwater through backfill materials may also occur due to the gradient of the pipeline/trench and the geotechnical conditions of the native soil. A waterstop shall be used to prevent transfer of groundwater where required. For pipelines up to 750mm diameter, an anchor block as shown in drawing SW23 in Appendix B shall be used to provide a waterstop at a maximum spacing of 10m. Waterstops for pipelines in excess of 750mm diameter are subject to specific design and approval, including spacing.

4.3.9.13. Trenchless Technology

In general, open-cut trenching is the default stormwater pipe installation method. However trenchless technologies may be preferable or required by Auckland Council and should be assessed for practicality for deep installations or alignments passing through or under:
  • Environmentally sensitive areas
  • Built-up or congested areas
  • Railway and road crossings
  • Significant vegetation.
​Trenchless installation may include:
  • Horizontal directional drilling
  • Uncased auger boring/pilot bore microtunnelling/guided boring
  • Microtunnelling
  • Pipe jacking
  • Pipe ramming.
Trenchless pipe rehabilitation/renovation may include:
  • Slip lining/grouting
  • Closefit slip lining
  • Static pipe bursting
  • Reaming/pipe eating/inline removal
  • Soil displacement/impact moling
  • Cured in place pipe
  • Spiral wound pipe.
Any trenchless technology and installation methodology shall be chosen to be compatible with achieving the required gravity pipe gradients.

For trenchless solutions, the following details shall be submitted to Auckland Council for information/approval:
  • ​Clearances from services and obstructions
  • A plan and long section identifying surface levels, pipe invert levels, depths to invert and chainages
  • Proposed pipe support
  • Proposed pipe material and pipe class including supporting design calculations​
  • Factual and interpretative geotechnical reports
  • How pipes will be protected from damage during construction
  • Any assessed risk to services, surfaces and structures
  • Location of pipe welding and laydown area
  • Pipe pulling route
  • Location of access pits, shafts and working spaces
  • Specific proposals for risk mitigation when working close to or under watercourses
  • Identification of high risk areas for “frac-outs”
  • Methodology for controlling “frac-outs”
  • Anticipated settlement due to overcut, groundwater drawdown and excavation support deflection including supporting calculations.
Materials and Gradient

The two types of pipe approved for trenchless installation are polyethylene and reinforced concrete. Reinforced concrete pipes shall be specifically manufactured for jacking operations. Pipe classes for each type are subject to specific design. The joints for all pipes are subject to specific approval by the council. The methodology used shall ensure that the design gradients are met along with hydraulic efficiency of the pipeline. Microtunnelling is recommended where gradients are less than 1.5%. For fusion welded polyethylene pipe, removal of internal weld beads (de-beading) is generally not required.

Acceptance

Where trenchless methods of construction are used, the resulting pipeline will not be accepted if it contains sags or crests in the vertical plane which will retain flow and consequently lead to siltation in the pipeline. Horizontal deviation from alignment is acceptable without loss of vertical alignment provided that the maximum horizontal deviation is not more than one pipe diameter. Clear line or laser profiling shall be undertaken to meet the requirements of Table 5.6 of AS/NZS 2566. Profiling shall be undertaken 30 days after installation of the trenchless section. Note that where the annulus is grouted, this profiling shall be undertaken 30 days after grouting.

4.3.9.14. Pipeline and Culvert Ownership

The ownership rules in the SWCoP apply to assets vested after the publication date of the SWCoP. Assets vested prior to the first publication of the SWCoP (1 October 2013) will remain public or private in accordance with legacy rules (codes of practice or infrastructure design manuals).

​Where a pipe that is not on the council’s asset register is discovered on a property, the pipe shall be deemed to be private unless the land owner can provide documentation of a completed​ vesting process that proves beyond doubt that the asset belongs to the council. See Section 4.3.16 for information on cross-boundary ownership.

​Where approval has been gained for a watercourse in private land to be piped by private land owners, ownership and maintenance responsibility remains with the landowner. Where approval has been granted for a watercourse in private land to be piped and for the constructed pipe to be vested in the council, the pipe shall be deemed to be a public asset. In all other instances, whether the watercourse was piped through a consenting process or not, the pipe shall be considered to be private and is the responsibility of the owner(s) of the land through which it passes.​

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