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    1. CS-1 General
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    5. CS-5 Excavation in Trench
    6. CS-6 Fill
    7. CS-7 Bedding & Backfill
    8. CS-8 Subsoil Drainage for Earthworks & Roads
    9. CS-9 Pipework
    10. CS-10 Pipe Fittings
    11. CS-11 Manholes & Rodding Eyes
    12. CS-12 Sumps
    13. CS-13 Trenchless Technology
    14. CS-14 Road Ripping
    15. CS-15 Road Pavement Layers
    16. CS-16 Kerb & Channel
    17. CS-17 Concrete Work
    18. CS-18 Carriageway Surfacing
    19. CS-19 Roadmarking
    20. CS-20 Berm Features
    21. CS-21 Street Structures
    22. CS-22 Road Maintenance
    23. CS-23 Grassing & Turfing
    24. CS-24 Vegetation Planting & Gardens
    25. CS-25 Reinstatement
  9. Inspection & Testing Requirements
    1. IT-1 General Provision
    2. IT-2 Streetscape
    3. IT-3 Reserves
    4. IT-4 Transportation Network
    5. IT-5 Stormwater
    6. IT-6 Wastewater
    7. IT-7 Water Supply
    8. IT-8 Public Lighting
    9. IT-9 Network Utilities
Infrastructure Development Code

DS-5.5 Conveyance Primary and Secondary Systems

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A primary stormwater system may typically include:

  1. Pipe reticulation.
  2. Ground soakage systems.
  3. Channels and open water courses.
  4. Swales and rain gardens.

Mechanical systems such as pumping systems are generally not permitted.

The secondary system comprises a network of overland flowpaths and storage areas designed to safely convey and/or store stormwater that exceeds the capacity of the primary system. 

DS-5.5.1   Selection of a Primary Stormwater System

The type of primary system installed will be dependent on factors such as water quantity, water quality, aquatic resource protection, topography, soil type, groundwater level, location and area constraints.

DS-5.5.2   Piped Reticulation

City Plan Performance Standard: Appendix 12B 
  1. All pipelines shall be sealed to contain the design flows within the pipe and prevent un-designed sub- soil infiltration from entering the pipeline;
  2. The following minimum pipe diameters apply:

Function Minimum Diameter
Trunk mains and sump leads 300mm
Reticulation mains or high level pipelines receiving property connections only 200mm
Laterals < 25m in length & located clear of carriageways 100mm
Laterals > 25m in length or located under carriageways 150mm
Residential Connections 100mm
Commercial/Industrial 100mm

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

  1. The minimum pipe size other than for connections shall be:
    1. Main receiving property connections only: 200mmØ internal diameter
    2. All other mains and sump leads: 300mmØ internal diameter
  2. Manholes are required at each:
    1. Intersection of pipes (except for junctions between mains and laterals).
    2. Change of grade.
    3. Change of direction.
    4. Change of pipe size.
    5. Change of material (except for repair/maintenance locations).
    6. Permanent or temporary end of a pipe system.
  3. Shall provide for the design flow without surcharge.
  4. Shall provide for a minimum full bore velocity of 0.6m/s at a flow of half the 50% AEP design flow.
  5. Where the pipe full velocity is less than 1.3m/s the reticulation design shall allow for silt collection.
  6. Each branch line (excluding connections) shall join the main line at a manhole junction except for mains ≤50% of the size of the main being connected to may be saddled onto 600mmØ pipes or larger provided that:
    1. A manhole is supplied on the branch line within 50m of the saddle.
    2. The saddle is created using a 300mm pipe stub epoxied onto the 600mmØ or larger main and is inspected prior to laying the first pipe from the stub.
    3. Council approval has been obtained.
  7. Pipes shall be designed so that the pipes are laid soffit to soffit. Where this is not possible or in potentially unstable ground or where special protection is required, the pipeline shall be specifically designed including the choice of materials.

DS-5.5.3   Reticulation Layout

City Plan Performance Standard: Appendix 12B 
  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.

The following shall apply:

  1. The alignment of stormwater 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 a) above 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.

DS-5.5.3.1  Close Proximity Rules

Drawing Ref: T553, T554

The following shall apply:

  1. Buildings or structures to be constructed close to a main or lateral/connection shall comply with the requirements of T553 and T554. 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-5.5.4   Steep Grades

Anti-scour blocks and trench stop configuration shall be detailed on the design drawings and shall be in accordance with the Standard Drawings. Spacing of anti-scour blocks shall be in accordance with Table 3: Anti-Scour Block Spacing.

Table 3: Anti-Scour Block Spacing

Grade
(%)

 

Requirements Spacing (S)
(m)
15-35 Concrete bulkhead S = 100/Grade (%)
>35 Specific Design.

Refer to council.

Where scour is a problem on grades flatter than the above, 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-5.5.5   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. The minimum cover shall be 900mm.
    2. Sump leads shall achieve 700mm of cover and be a class 4 (Z) rubber ring jointed concrete pipe or equivalent.
  3. Where minimum cover cannot be achieved, specific design of pipe and cover is required.

DS-5.5.6   Loads on Pipes

The following shall apply:

  1. All pipelines shall be designed to withstand all the likely loads to which they will 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 AS2566 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-5.5.7   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-5.5.8   Pipe Materials

Refer to AM-5 Stormwater.

DS-5.5.9   Pipe Joints

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

DS-5.5.10   Pipe Bedding and Backfill

Drawing Ref: T551

City Plan Performance Standard: Appendix 12B 
  1. All stormwater 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-5.5.11   Piped Reticulation Structures

This section describes the requirements for structures that may be present in conveying stormwater through a reticulated system. Theses are categorised as: 

  1. Manholes.
  2. Rodding Eyes.
  3. Alternative structures as specifically designed.

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 and rescue equipment. Council may determine other specific requirements subject to the individual site characteristics.

DS-5.5.11.1   Manholes

Drawing Ref: T500, T501, T502, T503, T504, T505, T506, T507, T508

City Plan Performance Standard: Appendix 12B 
  1. Manhole structures shall have a minimum internal diameter of 1050mm and be provided on all pipelines for inspection and maintenance purposes at:
    1. All intersections of pipelines; (except for junctions between mains and laterals).
    2. Changes of gradient;
    3. Changes of direction;
    4. Changes in pipe size; or
    5. Changes in materials.

The following shall apply:

  1. Manhole spacing shall not exceed 100m for pipe lines up to 900mmØ. 

Where the designer can clearly demonstrate that larger spacing is appropriate without negatively affecting the design outcome, operations and maintenance requirements, an alternative design may be submitted to Council for consideration.

  1. The entire manhole structure shall be located clear of all boundaries.
  2. Manholes shall be located within Council property or Road Zones wherever possible.
  3. 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.
  4. 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. 
  5. Manholes shall not be located within the road carriageway unless approved by the Council. Where approved for installation within the road carriageway they shall be located clear of vehicle wheel tracks.
  6. All manholes shall have an entry safety grill fitted.
  7. 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-5.5.11.2   Manhole Sizing

Drawing Ref: T501

The following shall apply:

  1. The standard internal diameter of circular manholes shall be 1050mmØ. Other nominal internal diameters that may be used for larger pipe sizes or situations are 1200mmØ, 1500mmØ and 1800mmØ. 
  2. When considering the appropriate manhole diameter, designers shall ensure it is appropriate to the design needs for the manhole. Consideration shall also be given by the designer to the base layout to ensure hydraulic efficiency and adequate working space in the chamber. 
  3. Where there are several inlets, consultation with Council on the layout of the chamber is recommended.

DS-5.5.11.3   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 (6H:1V) into the manhole pipe system for drainage purposes.
  3. Channels shall have a minimum inside radius of 300mm.

DS-5.5.11.4   Internal Falls Through Manholes

The fall through a manhole shall be the greater of either of the following:

  1. The invert of the outlet pipe from a manhole shall be 20mm lower plus 0.5mm per degree of horizontal angle change between the two lines lower than the lowest incoming pipeline invert.
  2. The soffit of the outlet pipe shall be level with or below the soffit of the lowest incoming pipeline.
  3. The extension of the grade of the steepest pipe across the width of the manhole.

DS-5.5.11.5   Flotation

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

DS-5.5.11.6   Access Steps

Drawing Ref: T505

Manhole steps shall comply with the Standard Drawings and AM-5 Stormwater. Stormwater manhole steps shall not be located above any inlet or outlet pipes.

DS-5.5.11.7   Covers

Drawing Ref: T506, T507, T508, T509 

The following shall apply:

  1. Manhole covers with a minimum clear opening of 600mm in diameter shall be used.
  2. Non-Rock covers shall be used on all Level 2 (or primary arterial) roads.
  3. Refer to AM-5 Stormwater for manhole cover type.
  4. All covers shall be painted with New Zealand Transport Agency (NZTA) Standard approved "blue" road marking paint.

DS-5.5.12   Rodding Eyes

Drawing Ref: T520, T521 

The following shall apply:

  1. A rodding eye is required to be constructed at the ends of some lateral pipes that are installed between a property connection point and the stormwater 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 "blue" road marking paint.
  5. All standard rodding eyes shall be constructed as detailed on the Standard Drawings.

DS-5.5.13   Ground Soakage Systems

Refer to DS-5.7.2 Ground Soakage Discharge.

DS-5.5.14   Channels and Open Watercourses

Where natural open stream systems or formed channels are to be incorporated in the stormwater drainage system they shall generally be located within a drainage reserve of sufficient width to contain the overall system design storm flow. The following shall apply:

  1. It must be demonstrated that the open drain system:
    1. Can be used where it is in keeping with the existing drainage network. 
    2. Provides adequate capacity.
    3. Has a maximum velocity in an unlined open drain of 0.5m/sec where ash or clay soils are present. Where this can not occur, an appropriate channel lining will be required. 
  2. Drainage reserves shall have maximum and minimum slopes of 1:5 and 1:50 respectively and when access for maintenance is required, shall also include:
    1. A 4m wide access that is accessible by a 8.2 tonne axle weight vehicle for its entire length as per NZ On-Road Tracking Curves RTS 18.
    2. Access from public carriageways.
  3. To encourage the best use of the open stream systems the drainage reserve shall, where possible, be linked with other reserves and open spaces to accommodate off road pedestrian and cycle access. Access points for public use and maintenance shall be provided at regular intervals along the system together with footpath and pedestrian bridges as may be defined in the Resource Consent.
  4. The flow characteristics of natural open stream systems shall:
    1. Be based on the likely long term stream condition in terms of density of vegetation.
    2. Be cleared of all unsuitable plant growth and replanted to a landscape design approved by Council.
    3. Take account of the possibility of blockage under all peak flood conditions.
    4. Include protection of the low flow channel against scour and erosion of the stream bed where necessary. 
    5. Not be adversely affected by the discharge of stormwater resulting from development or a new discharge to the stream. 
    6. Be designed to avoid erosion of the stream banks. 
    7. Catchment or detention factors that may lead to an increase in the temperature of the stormwater (e.g. large sealed areas) shall be mitigated.

DS-5.5.15   Vegetated Swales

Vegetated swales are stormwater channels that are often located alongside roads or in reserves. While their primary function is conveyance, filtration through the vegetation can reduce peak flows and provide water quality treatment. They can be used in place of kerbs, gutters or piped networks to treat and transport stormwater runoff and can be aesthetically pleasing and contribute to the overall urban design of an area. Types of swale include:

  1. Dry Swale (including an underdrain) – generally grassed
  2. Infiltration Swale (No underdrain) – generally grassed
  3. Bioretention Swale (Planted with low lying native wetland plants and permanently wet)

The type of swale chosen depends on physical site conditions and quality treatment requirements. 

DS-5.5.15.1  Minimum Requirements

It must be demonstrated that a swale system complies with the following:

  1. A maximum catchment area not greater than 4 hectares.
  2. Appropriate functionality and adequate capacity.
  3. Capacity for a 10% AEP storm event.
  4. A longitudinal slope of between 1 and 5%. For longitudinal slopes that are greater than 5% or where velocity is greater than 1.5m/s in a 10% AEP storm event, erosion protection or check dams to reduce effective gradient may be required.
  5. Minimum hydraulic residence time of 9 minutes.
  6. Maximum side slope of 5H:1V for maintenance access. 
  7. Level spreaders shall be provided where piped flows enter the swale in order for flows to be dispersed. 
  8. Planted with grass or other low lying plants in a permeable soil with the purpose of reducing flow velocities and protecting against erosion. Grass shall have a design vegetation height between 50-150mm. A planting plan shall be submitted to Council for approval. 
  9. Achieves all other relevant performance standards for the primary system

The designer shall refer to Councils Stormwater Management Guidelines for more information regarding designs of this type. 

DS-5.5.16   Vegetated filter Strips

Vegetated Filter Strips are used to manage stormwater runoff from impervious surfaces by slowing runoff velocities, providing treatment and promoting infiltration. They often act as pre-treatment for other stormwater devices or receiving systems. 

Vegetated Filter Strips receive stormwater runoff as sheet flow whereas swales accept more concentrated flow. Filter strip performance relies on even distribution of flow  across vegetated areas as well as residence time.  

DS-5.5.16.1  Minimum Requirements

It must be demonstrated that a filter strip system complies with the following:

  1. A maximum catchment area not greater than 2 hectares. 
  2. Appropriate functionality and adequate capacity.
  3. Capacity for a 10% AEP storm event. 
  4. A slope less than 5% unless terracing or level spreaders are provided mid slope. 
  5. Minimum hydraulic residence time of 9 minutes.
  6. Velocity no greater than 1.5 m/s in a 10% AEP storm event unless erosion protection is provided.
  7. Grass shall have a design vegetation height 50-150mm. 
  8. Achieves all other relevant performance standards for the primary system. 

The designer shall refer to Councils Stormwater Management Guidelines for more information regarding designs of this type. 

DS-5.5.17   Rain Gardens

Rain Gardens are engineered bioretention systems designed to use the natural ability of flora and fauna to reduce stormwater volumes, peak flows and contaminant loads. They can be designed for either infiltration to groundwater or discharge to the downstream network. Rain Gardens can be used in place of conventional landscape areas and contribute an attractive urban design feature as well as having an ecological value. 

DS-5.5.17.1   Minimum Requirements

It must be demonstrated that a Rain Garden complies with the following:

  1. Capacity for a 10% AEP storm event without significant scour or erosion.
  2. Appropriate functionality and adequate capacity.
  3. Size is calculated to achieve water quality volume.
  4. Entry and overflow positions to restrict short circuiting.
  5. Appropriately planted (for wet and dry conditions) with native plant species (preferred) and incorporating a mulch, pebble or rock surface layer. A planting plan shall be submitted to Council for approval.
  6. Ponding area with a maximum ponded water depth of 300mm. 
  7. An overflow bypass system shall be provided for when the Rain Garden pond is full. 
  8.  Filtration layers shall comprise of the following:
  9. Filtration soil media layer: 400-600mm deep.
  10. Transition coarse sand layer: 100mm deep.
  11. Final drainage layer of 2-5mm washed gravel: 50mm deep (minimum).
  12. Filtration soil media shall be sandy loam or loamy sand, free of rubbish, plants and weeds. 
  13. An underdrain shall be provided if piping to the downstream network. This shall have a minimum 50mm gravel cover. 
  14. Includes geotextile on the side walls.
  15. Achieves all other relevant performance standards for the primary system.
  16. Provides access for maintenance. 
  17. Where Rain Gardens are to be provided on individual lots, covenants on each lot title are to be created to require owners to maintain the Rain Gardens. An operation and maintenance plan shall be submitted to Council for approval.

The designer shall refer to Councils Stormwater Management Guidelines for more information regarding designs of this type. 

DS-5.5.18   Other Alternative Design Methods

The designer shall refer to Councils Stormwater Management Guidelines for more information regarding designs of this type and refer to DS-1.3 Alternative Design for how to propose an alternative method.

DS-5.5.19   Secondary System

No buildings or structures shall be located within secondary overland flow paths.

DS-5.5.19.1  Secondary System Options

Secondary system options may include: 

  1. Preferred Options:
    1. Temporary ponding on local and collector roads. (refer to DS-4.5.2.12)
    2. Temporary flow along local and collector roads. (refer to DS-4.5.2.12)
    3. Temporary flow on public land such as accessways, parks and reserves.
  2. Least Preferred Options:
    1. Flow across private land (the least desirable option). Such flows must be in a defined channel or swale, clear of existing or future building sites and protected by an easement in favour of Council as well as a Resource Consent notice which prohibits ground reshaping and the erection of any barriers to the secondary flows.
    2. Flow from secondary systems on public land (e.g. along local and collector roads) can only discharge onto private land in Infill Subdivision if agreed with Council and with an easement.
  3.  Not permitted
    1. Stormwater pumping systems are not permitted.
    2. Piped secondary systems are not permitted.
    3. Flow from secondary systems on public land (e.g. along local and collector roads) are not permitted to discharge onto private land in Greenfield Development unless during staged subdivisions and this is a temporary arrangement until the development is completed or where the secondary flow path is not part of the subdivision development and it has been agreed with Council.

Definitions in this section

AEP

Chartered professional engineer

Council

Design

Drainage system

Ground

Lot

New zealand transport agency

NZTA

Owner

Pavement

Road

Stormwater

Sump

Swale

 

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