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DESIGN STANDARDDS-5 STORMWATER

TABLE OF CONTENTS

DS-5.1 General ..............................................................................................................1

DS-5.2 Minimum Requirements ......................................................................................1

DS-5.3 Regional Council Requirements .........................................................................1

DS-5.4 Design ................................................................................................................2

DS-5.5 Conveyance - Primary and Secondary Systems .................................................5

DS-5.6 Stormwater Treatment / Detention ....................................................................15

DS-5.7 Stormwater Discharge ......................................................................................19

DS-5.8 Collection .........................................................................................................22

DS-5.9 Further Considerations .....................................................................................27

DS-5 STORMWATER

Updated 01/07/2014 Page 1

DS-5.1 General

Many developments will change the natural existing drainage pattern so stormwater systemsare typically designed and constructed to manage this change and any potential adverseeffects which may include flood damage, erosion, sedimentation, water pollution and damageto ecosystems.

The primary goals of a stormwater drainage system are to collect, convey and treat surfacerunoff to minimise flood damage and adverse effects on the environment. There are severalways this can be done. Low Impact Design features such as planted swales, rain gardens,larger grass verges and detention ponds can allow groundwater recharge, slow the movementof water and reduce the amount of pollutants in receiving water bodies. These areas may alsobe used to enhance a development, contributing to the wider environmental quality of an area.

Understanding the impact of site development, such as the extent of site coverage (includingpaved surfaces), is important and options such as narrower carriageways andsemi-permeable paving for on-road parking can help to reduce runoff.

Stormwater systems may also integrate with the natural drainage system and this can helpmitigate environmental effects, as well as enhance amenity and ecological values.

DS-5.2 Minimum Requirements

Designs shall provide for a stormwater management system that:

a) Complies with the operative City Plan and Infrastructure Development Code (IDC).

b) Is designed to acceptable urban design, landscaping and engineering methods.

c) Minimises, isolates or eliminates health and safety hazards during both its constructionand its use.

d) Minimises, isolates or eliminates any adverse ecological and environmental effects.e) The stormwater management system shall be located in areas that are geotechnically

suitable for the system proposed.

Note: Where confirmation of this requirement is not clear a certification statement from aCategory 1 Geo-Professional may be required.

DS-5.3 Regional Council Requirements

The discharge of stormwater, the diversion of natural water during construction, thepermanent diversion of natural water as a consequence of development, activities in the bedor on the banks of a natural waterway and damming of waterways generally require ResourceConsents from Bay of Plenty Regional Council unless authorised as a permitted activity in theRegional Water and Land Plan.

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Page 2 Updated 01/07/2014

DS-5.3.1 Vesting of Assets and Transferring of Consents

If it is the intention of the developer to transfer any Stormwater Resource Consent fromBay of Plenty Regional Council to Council, a copy of the draft conditions shall beforwarded to Council for comment on receipt by the Consent Holder.

Council will not accept a transfer of a Bay of Plenty Regional Council issued ResourceConsent unless the assets pertaining to that Resource Consent have been constructed inaccordance with the Resource Consent conditions and comply with the IDC. Intention tovest ownership of any asset and/or transfer of any Resource Consent shall be discussedwith Council at an early stage of planning. Council reserves the right not to accept anyasset and/or accept a transfer of any Resource Consent.

DS-5.4 Design

The following shall apply:

a) Unless otherwise approved by Council, the design of the stormwater system shall be inaccordance with the IDC and may be supplemented by the documents noted in DS-5 ApxA.1 General.

b) For catchment areas less than 50ha, surface water run-off using the Rational Method willgenerally be accepted. For larger catchments or where significant storage elements e.g.Ponds are incorporated, surface water run-off shall be determined using an appropriatehydrological or hydraulic model.

c) Low Impact Design for stormwater management is the preferred approach whereappropriate. Well-designed and well-maintained systems which replicate the naturalpre-development hydrological regime can not only mitigate adverse environmental effectsbut can also enhance local amenity and ecological values. Low Impact Design methodstypically include swales, ponds, rain gardens, rain tanks, a reduction in impermeablesurfaces, permeable paving, filter strips, green roofs and constructed wetlands. The use ofLow Impact Design methods shall be discussed with Council at an early stage.

Detailed design is required at the time of Infrastructure Development Works Approval.Where no Infrastructure Development Works Approval is required, Council approval shallbe obtained at a time required by Council and before construction of the system.

DS-5.4.1 Alternative Design

Refer to DS-1.3 Alternative Design.

DS-5.4.2 Stormwater Management Systems


a) The stormwater management system is an overall system that manages thecollection, conveyance, treatment and discharge of stormwater. The overallstormwater management system shall provide a minimum standard of flood protectionfor the community and mitigate any adverse environmental effects.

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b) The overall system shall accommodate flows from a 50 year return period storm event(2% AEP) unless otherwise stated in a comprehensive stormwater discharge consent.The post development run off rates shall be no greater than pre development run offrates. Ponding areas shall be provided for only on public roads and public land.

c) Stormwater designs shall consider the system as a whole, ensure the upstreamcatchment is provided for, ensure the downstream receiving network has the capacityto cater for the design condition and be appropriately engineered to suit thesite-specific requirements. An appropriate mix of solutions comprising Low ImpactDesign and conventional solutions shall be considered as well as short and long termmaintenance responsibilities/requirements and the whole of life cost implications (i.e.cost of construction, maintenance, renewal or replacement). The overall system alsoneeds to provide for a range of storm events.

d) A subset of the overall system is the primary system. The primary system shallaccommodate flows from a 10 year return period storm event (10%AEP). When theprimary system overloads by either blockage, malfunction or rainfall events in excessof the design capacity then the part of the overall system that compliments the primarysystem is known as the secondary system.

e) Water Quality considerations are required to control potential for damagingenvironmental effects to our waterways, habour and aquatic life. Water quality shall beincluded in design where required by:

i) Bay of Plenty Regional Council Water and Land Plan requirements.

ii) Bay of Plenty Regional Council resource consent conditions.

iii) Councils Comprehensive Catchment Consent Conditions and associatedManagement Plans as approved by Bay of Plenty Regional Council.

The 90% rainfall storm shall be used as this is the maximised point of runoff volumecapture. The 90% rainfall for Tauranga is 33mm for a 2 year / 1 hour storm.

DS-5.4.3 Hydraulic Design


a) The hydraulic design of stormwater pipelines shall be based on tables for the hydraulicdesign of stormwater drains and pipelines or on graphs or other representation of thesame methods based on the Colebrook White or Manning's Formula.

b) The pipe roughness coefficient Ks used in the design shall be as shown in NZS4404Table 4.2.

DS-5.4.4 Rainfall Intensity


a) Designers shall use the Design Rainfall Tables located in DS-5 - Appendix B.1General.

b) These tables have been developed from the rainfall records from the rain gaugestations in the sub region and have been adjusted to allow for climate change to theyear 2055.

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c) The Rainfall Intensity Curves are included in DS-5 - Appendix C.1 General.

d) It shall be noted that several large streams have their headwaters in higher altitudeareas beyond the Tauranga City boundary. For the design of stormwater systems inthese areas, it may be necessary to use higher rainfall intensities than those requiredby a) and c) above.

DS-5.4.5 Freeboard Above Design Flood Level

The minimum freeboard height applied to the calculated top water level shall be asoutlined in DS-5.4.5 Table 2: Freeboard Heights.

The minimum freeboard shall be measured from the top water level to the underside of thefloor slab or the underside of the floor joists, whichever is appropriate.

Table 2: Freeboard Heights

Type of Structure Freeboard to Applied Design StormNon-habitable residential buildings,detached garages and carports

200mm

Commercial and industrial buildings 300mmHabitable dwellings/structures andattached garages

500mm

DS-5.4.6 High Levels of Groundwater

If there is a need to lower groundwater levels then designers shall provide a method ofallowing the groundwater into the stormwater system in a controlled manner. Such asolution may incorporate perforated inlet pipes together with drainage rock and geotextile.

DS-5.4.7 Calculating Water Quality Volumes

Calculating the water quality volume can be done by the following calculation:

2 year / 1hour storm event for Tauranga = 33mm.

Awq = 0.9(imp. %/100) x total site area + 0.15(pervious %/100) x total site area.

Where total site area = m2

The water quality volume Vwq = 0.033Awq

Where 0.033 = 90% storm depth (m)

Examples of this method can be found via case studies provided within the StormwaterManagement Guidelines.

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DS-5.5 Conveyance - Primary and Secondary Systems

A primary stormwater system may typically include:

a) Pipe reticulation.

b) Ground soakage systems.

c) Channels and open water courses.

d) 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 areasdesigned to safely convey and/or store stormwater that exceeds the capacity of the primarysystem.

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, location and areaconstraints.

DS-5.5.2 Piped Reticulation

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

a) The minimum pipe size other than for connections shall be:

Main receiving property connections only: 200mmØ internal diameterAll other mains and sump leads: 300mmØ internal diameter

b) Manholes are required at each:

i) Intersection of pipes (except for junctions between mains and laterals).

ii) Change of grade.

iii) Change of direction.

iv) Change of pipe size.

v) Change of material (except for repair/maintenance locations).

vi) Permanent or temporary end of a pipe system.

c) Shall provide for the design flow without surcharge.

d) Shall provide for a minimum full bore velocity of 0.6m/s at a flow of half the 50% AEPdesign flow.

e) Where the pipe full velocity is less than 1.3m/s the reticulation design shall allow for siltcollection.

f) Each branch line (excluding connections) shall join the main line at a manhole junctionexcept for mains ≤50% of the size of the main being connected to may be saddled onto600mmØ pipes or larger provided that:

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i) A manhole is supplied on the branch line within 50m of the saddle.

ii) The saddle is created using a 300mm pipe stub epoxied onto the 600mmØ orlarger main and is inspected prior to laying the first pipe from the stub.

iii) Council approval has been obtained.

g) Pipes shall be designed so that the pipes are laid soffit to soffit. Where this is notpossible or in potentially unstable ground or where special protection is required, thepipeline shall be specifically designed including the choice of materials.

DS-5.5.3 Reticulation Layout


a) The alignment of stormwater reticulation shall be laid out to follow the road pattern andeither:

i) Be located clear of the carriageway.

ii) Be located clear of wheel tracks if within the carriageway.

b) Where a) above is not possible or practical the main may be located:

i) On public land with approval from Council.

ii) Within private property parallel to and located between 1m and 1.5m from thefront, rear and/or side boundaries provided it avoids affecting futuredevelopment options available within the lot.

iii) On the low side of lots that have a cross-fall of more than 1.5m.

DS-5.5.3.1 Close Proximity Rules

T553 T554


a) Buildings or structures to be constructed close to a main or lateral/connectionshall comply with the requirements of T553 and T554. Where dispensation hasbeen granted for a building or structure to be built over a main orlateral/connection, foundations shall be designed by a Chartered ProfessionalEngineer.

b) No enclosed building or structure shall be sited over a manhole or closer than500mm from the outside wall of the manhole structure.

c) No building or concrete slab shall be constructed over a connection point to amain.

d) No buildings shall be constructed over a main if there is a connection closer than1.0m to the building unless the connection is relocated to the satisfaction ofCouncil.

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e) Encroachment of removable, non-permanent structures e.g. carports, decks,fences may be approved by Council when the structure is designed and built suchthat it can be dismantled easily in sections. The removal and re-erection of thesestructures shall be at no cost to Council. Council approval is required in allinstances. Council will assess each application on a case by case basis as thevariables 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 thatfuture property owners are aware of the approval and Council’s right to have thestructure removed at any time for the purposes of maintenance work, emergencywork or upgrade work.

DS-5.5.4 Steep Grades

Anti-scour blocks and trench stop configuration shall be detailed on the design drawingsand shall be in accordance with the Standard Drawings. Spacing of anti-scour blocks shallbe in accordance with DS-5.5.4. Table 3: Anti-Scour Block Spacing.

Table 3: Anti-Scour Block Spacing

Grade(%)

Requirement Spacing (S)(m)

15–35 Concrete bulkhead S = 100/Grade (%)

>35 Special design Refer to Council

Note: Where scour is a problem on grades flatter than the above, sandbags are often used to stabilise the trench backfill.

Where the natural transfer of water from the trench into the surroundingground will not provide sufficient drainage, trench drainage shall beprovided to divert the water.

DS-5.5.5 Cover Over Pipelines


a) In private property:

i) The minimum cover shall be 600mm.

ii) If the cover exceed 3m, specific design and approval is required.

iii) The design of cover shall avoid affecting the future development optionsavailable within the lot.

iv) Where the reticulation lines are located in the front yards of lots, the invert levelshall be deep enough so as not to interfere with any future drivewayconstruction.

b) In Road Zones:

i) The minimum cover shall be 900mm.

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ii) Sump leads shall achieve 700mm of cover and be a class 4 (Z) rubber ringjointed concrete pipe or equivalent.

c) Where minimum cover cannot be achieved, specific design of pipe and cover isrequired.

DS-5.5.6 Loads on Pipes


a) All pipelines shall be designed to withstand all the likely loads to which they will besubject to.

b) In the first instance, load parameters shall be designed to support an 8.2 tonne designaxle load. Following this:i) AS/NZS 3725 and AS2566 shall be used as design guides as applicable.

ii) Any loads relating to backfill techniques, construction traffic, temporary storageof materials and the like shall be incorporated into design parameters andconstruction methodology.

DS-5.5.7 Concrete Capping of Pipelines

Where minimum cover cannot be achieved, concrete capping may be used taking intoaccount pipe protection and road integrity requirements. Approval from Council is requiredfor 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 appropriateunless otherwise approved by Council.

DS-5.5.10 Pipe Bedding and Backfill

T551


a) Pipe bedding and backfill shall be specifically designed, shown on the detailed designdrawings and submitted to Council for approval.

b) The design shall also include the compaction criteria to be used to certify the backfillhas been compacted to the required compaction standard.

c) All trench backfill under carriageways shall be designed and constructed to achieve forthe required pavement layers strengths for the class of road it is beneath.

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DS-5.5.11 Piped Reticulation Structures

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

a) Manholes.

b) Rodding Eyes.

c) 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 anystructure that may allow entry for maintenance and rescue equipment. Council maydetermine other specific requirements subject to the individual site characteristics.

DS-5.5.11.1 Manholes

T501, T502, T503, T504, T505, T506, T507


a) Manhole spacings shall not exceed 100m for pipe lines up to 900mmØ withoutspecific approval from Council. Greater spacing may be approved for largerdiameter pipes.

b) The entire manhole structure shall be located clear of all boundaries.

c) Manholes shall be located within Council property or Road Zones whereverpossible.

d) Manholes deeper than 5.0m to the pipe invert and shallow manholes may be usedin certain circumstances subject to the approval of Council. Where a manhole ismore than 5.0m deep it shall:

i) Be specifically designed.

ii) Have access steps installed.

iii) Incorporate clear warning that it is deep.

iv) Have a secure entrance.

v) Require larger diameter chambers and covers.

e) Standard 1050mmØ manhole risers are not suitable where the pipes are eitherlarger than 675mmØ or where multiple pipes enter a manhole causing loss of themanhole wall. Manholes shall be designed to maintain wall integrity in thesecircumstances.

f) Manholes shall not be located within the road carriageway unless approved by theCouncil. Where approved for installation within the road carriageway they shall belocated clear of vehicle wheel tracks.

g) All manholes shall have an entry safety grill fitted.

h) All standard manholes shall be constructed as detailed on the StandardDrawings.

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DS-5.5.11.2 Manhole Sizing


a) The standard internal diameter of circular manholes shall be 1050mmØ. Othernominal internal diameters that may be used for larger pipe sizes or situations are1200mmØ, 1500mmØ and 1800mmØ.

b) When considering the appropriate manhole diameter consideration shall be givenby the designer to the base layout to ensure hydraulic efficiency and adequateworking space in the chamber.

c) Where there are several inlets, consultation with Council on the layout of thechamber is recommended.

DS-5.5.11.3 Benching


a) Benching shall be provided in the base of each manhole that provides a safeplace to stand for maintenance purposes.

b) Benching shall be close to flat with a cross fall (6H:1V) into the manhole pipesystem for drainage purposes.

c) 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:

a) The invert of the outlet pipe from a manhole shall be 20mm lower plus 0.5mm perdegree of horizontal angle change between the two lines lower than the lowestincoming pipeline invert.

b) The soffit of the outlet pipe shall be level with or below the soffit of the lowestincoming pipeline.

c) 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 safetyagainst flotation of 1.25.

DS-5.5.11.6 Access Steps

T503

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.

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DS-5.5.11.7 Covers

T504, T505, T506, T507


a) Manhole covers with a minimum clear opening of 600mm in diameter shall beused.

b) Non-Rock covers shall be used on all Level 2 (or primary arterial) roads.

c) Refer to AM-5 Stormwater for manhole cover type.

d) All covers shall be painted with New Zealand Transport Agency (NZTA) Standardapproved "blue" road marking paint.

DS-5.5.12 Rodding Eyes

T520, T521


a) A rodding eye is required to be constructed at the ends of some lateral pipes that areinstalled between a property connection point and the stormwater main.

b) PVC-U bends up to 45° are acceptable.

c) A standard manhole frame and cover shall be installed over the entry point when notlocated in a hardstand area. A fire hydrant base and rodding eye cover shall be used inhardstand areas.

d) All covers must be painted with New Zealand Transport Agency (NZTA) Standardapproved "blue" road marking paint.

e) 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 thestormwater drainage system they shall generally be located within a drainage reserve ofsufficient width to contain the overall system design storm flow. The following shall apply:

a) It must be demonstrated that the open drain system:

i) Can be used where it is in keeping with the existing drainage network.

ii) Provides adequate capacity.

iii) Has a maximum velocity in an unlined open drain of 0.5m/sec where ash or claysoils are present. Where this can not occur, an appropriate channel lining will berequired.

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b) Drainage reserves shall have maximum and minimum slopes of 1:5 and 1:50respectively and when access for maintenance is required, shall also include:

i) A 4m wide access that is accessible by a 8.2 tonne axle weight vehicle for itsentire length as per NZ On-Road Tracking Curves RTS 18.

ii) Access from public carriageways.

c) 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 offroad pedestrian and cycle access. Access points for public use and maintenance shallbe provided at regular intervals along the system together with footpath andpedestrian bridges as may be defined in the Resource Consent.

d) The flow characteristics of natural open stream systems shall:

i) Be based on the likely long term stream condition in terms of density ofvegetation.

ii) Be cleared of all unsuitable plant growth and replanted to a landscape designapproved by Council.

iii) Take account of the possibility of blockage under all peak flood conditions.

iv) Include protection of the low flow channel against scour and erosion of thestream bed where necessary.

v) Not be adversely affected by the discharge of stormwater resulting fromdevelopment or a new discharge to the stream.

vi) Be designed to avoid erosion of the stream banks.

e) Catchment or detention factors that may lead to an increase in the temperature of thestormwater (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 inreserves. While their primary function is conveyance, filtration through the vegetation canreduce peak flows and provide water quality treatment. They can be used in place ofkerbs, gutters or piped networks to treat and transport stormwater runoff and can beaesthetically pleasing and contribute to the overall urban design of an area.

Types of swale include:

a) Dry Swale (including an underdrain) – generally grassed

b) Infiltration Swale (No underdrain) – generally grassed

c) Bioretention Swale (Planted with low lying native wetland plants and permanently wet)

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

DS-5.5.15.1 Minimum Requirements

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

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a) A maximum catchment area not greater than 4 hectares.

b) Appropriate functionality and adequate capacity.

c) Capacity for a 10% AEP storm event.

d) A longitudinal slope of between 1 and 5%. For longitudinal slopes that are greaterthan 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.

e) Minimum hydraulic residence time of 9 minutes.

f) Maximum side slope of 5H:1V for maintenance access.

g) Level spreaders shall be provided where piped flows enter the swale in order forflows to be dispersed.

h) Planted with grass or other low lying plants in a permeable soil with the purpose ofreducing flow velocities and protecting against erosion. Grass shall have a designvegetation height between 50-150mm. A planting plan shall be submitted toCouncil for approval.

i) Achieves all other relevant performance standards for the primary system

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

DS-5.5.16 Vegetated filter Strips

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

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


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

a) A maximum catchment area not greater than 2 hectares.


c) Capacity for a 10% AEP storm event.

d) A slope less than 5% unless terracing or level spreaders are provided mid slope.

e) Minimum hydraulic residence time of 9 minutes.

f) Velocity no greater than 1.5 m/s in a 10% AEP storm event unless erosionprotection is provided.

g) Grass shall have a design vegetation height 50-150mm.

h) Achieves all other relevant performance standards for the primary system.


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DS-5.5.17 Rain Gardens

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


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

a) Capacity for a 10% AEP storm event without significant scour or erosion.


c) Size is calculated to achieve water quality volume.

d) Entry and overflow positions to restrict short circuiting.

e) Appropriately planted (for wet and dry conditions) with native plant species(preferred) and incorporating a mulch, pebble or rock surface layer. A plantingplan shall be submitted to Council for approval.

f) Ponding area with a maximum ponded water depth of 300mm.

g) An overflow bypass system shall be provided for when the Rain Garden pond isfull.

h) Filtration layers shall comprise of the following:

i) Filtration soil media layer: 400-600mm deep.

j) Transition coarse sand layer: 100mm deep.

k) Final drainage layer of 2-5mm washed gravel: 50mm deep (minimum).

l) Filtration soil media shall be sandy loam or loamy sand, free of rubbish, plants andweeds.

m) An underdrain shall be provided if piping to the downstream network. This shallhave a minimum 50mm gravel cover.

n) Includes geotextile on the side walls.

o) Achieves all other relevant performance standards for the primary system.

p) Provides access for maintenance.q) 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. Anoperation and maintenance plan shall be submitted to Council for approval.


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DS-5.5.18 Other Alternative Design Methods

Refer to DS-1.3 Alternative Design.

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:

a) Preferred Options:

i) Temporary ponding on local and collector roads.

ii) Temporary flow along local and collector roads.

iii) Temporary flow on public land such as accessways, parks and reserves.

b) Least Preferred Options:

i) Flow across private land (the least desirable option). Such flows must be ina defined channel or swale, clear of existing or future building sites andprotected by an easement in favour of Council as well as a ResourceConsent notice which prohibits ground reshaping and the erection of anybarriers to the secondary flows.

ii) Stormwater pumping systems are not permitted.

iii) Piped secondary systems are not permitted.

DS-5.6 Stormwater Treatment / Detention

Stormwater ponds are an accepted method of improving stormwater quality, reducingdownstream flood potential and peak downstream flow rates. Council is not in favour ofencouraging a proliferation of small stormwater ponds but prefers a total catchment/treatmenttrain approach.

DS-5.6.1 Permanent Pond Type

Council accepts the use of dry and wet ponds as a part of an engineered solution and/ortreatment train. However, the selection and design criteria (short term as well as long termfunctionality, maintenance, ownership) must be approved by Council before construction.Access from public carriageways shall be provided for maintenance.

DS-5.6.1.1 Regional Council Resource Consent


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a) Permanent ponds may require Resource Consent from Bay of Plenty RegionalCouncil as part of an earthworks and/or stormwater discharge Resource Consent.Refer to DS-5.3 Regional Council Requirements and contact Bay of PlentyRegional Council for more information.

b) Temporary ponds may require Resource Consent from Bay of Plenty RegionalCouncil as part of the earthworks Consent and/or discharge Resource Consent.Refer to DS-5.3 Regional Council Requirements and contact Bay of PlentyRegional Council for more information.

c) Pollutants and contamination issues shall be identified and managed to thesatisfaction of Council and any Resource Consent conditions related to the pond.

DS-5.6.1.2 Permanent Pond Ownership and Location

a) If acceptance of ownership of a pond is agreed by Council all stormwater pondsshall be located on land either:i) Owned by Council.

ii) Proposed to be vested in Council at completion of the development.

iii) Covered by appropriate easements approved by Council relating to access,serviceability, storage and replacement or repair of the pond.

b) Ponds that are not proposed to be vested in Council shall be discussed withCouncil prior to application for Resource Consent or, if no Resource Consent isrequired, prior to construction of the pond to ensure the pond construction hasminimal or no impact on Council’s existing stormwater system.

DS-5.6.1.3 Detention Pond Design


a) Detention Ponds shall be designed to the following minimum requirements:

i) Compliance with DS-1 - Apx A.1 General.

ii) Stormwater ponds shall be designed to ensure that retention and treatmentto achieves removal of 75% of total suspended sediment smaller than120µm diameter on a long term average basis.

iii) Any pond shall be designed to ensure any discharge has a suspendedsolids concentration no higher than 150 g/m³.

b) Specific matters to consider in pond design:

i) Side slopes with safety considerations - maximum 1:5 slope above andbelow water level.

ii) Ease of access for and of maintenance including mowing and silt removaland disposal and access to public roads.

iii) Shape and contour for amenity value.

iv) Effectiveness of inlet and outlet structure/s.

v) Overflow design and scour protection.

vi) Pest control (rats, mosquitoes etc.) and wind blown debris.

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vii) Sustainability of aquatic life.

viii) Depth of water.

ix) Use in treatment of stormwater.

x) Minimise dead zones and short-circuiting to improve the treatmentperformance of the pond.

Note: Dependent on catchment water quality, local ground conditions and soil properties,Council may require, (in exceptional cases), that ponds shall be lined.


DS-5.6.1.4 Pond Location


a) If acceptance of ownership of a pond is agreed by Council all stormwater pondsshall be located on land either:

i) Owned by Council.

ii) Proposed to be vested in Council at completion of the development.

iii) Covered by appropriate easements approved by Council relating to access,serviceability, storage and replacement or repair of the pond.

b) Ponds that are not proposed to be vested in Council shall be discussed withCouncil prior to application for Resource Consent or, if no Resource Consent isrequired, prior to construction of the pond to ensure the pond construction hasminimal or no impact on Council’s existing stormwater management network.

DS-5.6.2 Constructed Wetlands

Constructed wetlands are large shallow planted ponds which are designed to providestormwater quality improvement, reduce downstream flood potential and peakdownstream flow.

They differ from Detention Ponds in that they can be shallower, provide greatercontaminant removal (including nutrients) and support a wider variety of aquatic plantsand wildlife. They can also be more attractive and designed to provide greater amenity,ecological and safety benefits.

It must be demonstrated that a constructed wetland complies with the following:

a) A catchment area greater than 1 hectare.

b) Size is calculated to achieve water quality volume.

c) Includes a littoral and main wetland area at a depth not exceeding 1.0m.

d) Shall be appropriately planted.

e) Includes inlet pipework with appropriate erosion control.

f) Includes an emergency overflow.

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g) Designed for a controlled discharge rate that allows for continuous flow through awetland to prevent stagnation.

h) Provides access for maintenance.

Council approval shall be obtained prior to design and construction of any wetland. AllResource Consent, location, functionality, maintenance and ownership issues shall beconfirmed prior to any detailed design commencing.


DS-5.6.3 Permeable Pavements

Permeable Pavements are hard surface paving systems that reduce stormwater runoffflows and improve runoff water quality. Their porous surface allows stormwater to soakthrough them before slowly draining away.

The 3 main types that exist are:

a) Open cell grid of concrete or plastic with sand/gravel or grass cover.

b) Solid interlocking blocks with drainage gaps.

c) Porous interlocking blocks.Permeable Pavements shall only be used in low traffic areas such as carparks, drivewaysand footpaths.

Council approval shall be obtained prior to design and construction of PermeablePavement.

The designer shall refer to Council's Stormwater Management Guidelines for moreinformation regarding designs of this type.

DS-5.6.4 Bio-Retention Tree Pits

Bio-Retention Tree Pits collect stormwater from small car park areas or roads. They canreduce stormwater runoff flow velocity, improve runoff water quality and contribute to theoverall urban design and aesthetics of an area.

It must be demonstrated that a Tree Pit complies with the following:

a) Appropriate functionality and adequate capacity.

b) Has a ponding area at a level which sits below surrounding land and a maximumponded water depth of 300mm deep.

c) Filtration layers shall comprise of the following:

i) Filtration soil media layer: 400-600mm deep.

ii) Final drainage layer of 2-5mm washed gravel: 300mm deep.

d) Filtration soil media shall be sandy loam or loamy sand, free of rubbish, plants andweeds with a minimum permeability of 0.3m/day.

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e) Ponding area should drain completely within 24 hours.

f) An underdrain shall be provided in the final drainage layer with a minimum cover of50mm.

g) An overflow bypass system shall be provided which sits below the surrounding groundsurface.

h) Achieves all other relevant performance standards for the primary system.

i) Provides access for maintenance.Council approval shall be obtained prior to construction of Bio-Retention Tree Pits.


DS-5.7 Stormwater Discharge

This section describes the requirements for structures or methods for discharge of stormwaterrunoff. These are categorised as:

a) Discharge structures.

b) Ground soakage discharge.

c) Open watercourses.

d) Public roadside kerb and channel connection.

e) Road or bubble-up sumps.

f) Discharge Quality.

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 anystructure that may allow entry for maintenance and rescue equipment. Council may determineother specific requirements subject to individual site characteristics.

DS-5.7.1 Discharge Structures


a) Discharge structures shall be installed at the outlets of pipelines to the detail shown onStandard Drawings.

b) There shall be a single point of discharge from any one structure.

c) Shall be designed to minimise the effect of erosion on the receiving environment andinclude an energy dissipation device where required. (Submitted designs must clearlyillustrate this requirement).

d) No grill shall be constructed on outlet structures. A hazard warning sign shall beplaced on all outlet structures 500mmØ or larger as defined on the StandardDrawings.

e) Where a pipe is to be installed in a swale or open drain to allow for access over thedrain, an outlet structure may be required to be installed to prevent erosion around thepipe exit.

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DS-5.7.2 Ground Soakage Discharge

Disposal of stormwater by ground soakage or ground water recharge is only suitable insome areas of Tauranga (i.e. parts not located near relic slips or plateau edges) and mostareas of the Mount Maunganui and Papamoa portions of Tauranga City. The followingapplies to ground water soakage methods:

a) Concept approval is required from Council before undertaking detailed design for anyuse of Ground Soakage. The detailed design is then subject to InfrastructureDevelopment Plan Approval.

b) Where no Development Works Approval is required as part of a Resource Consent,then Council approval shall be obtained at either application for Resource Consent oranother time specified by Council and before construction of the system

c) All soakage systems shall be specifically designed to meet the performance criteriarequired by the New Zealand Building Code Handbook and Approved Documentssection E1 - Surface Water and include the design parameters outlined in this sectionof the IDC.

d) Testing determines that the soil, geotechnical and groundwater characteristics aresuitable.

e) The rate of soakage is determined by an assessment conducted by an appropriatelyqualified and experienced Chartered Professional Engineer. (In some cases aCategory 1 or 2 Geo-Professional will be required.

f) A soakage rate reduction factor of 0.5 is applied to ensure that the system is designedfor what can be expected in its operating environment.

g) Confirmation that use of the soakage system will not have an adverse effect on otherland, property and structures including land stability, seepage or overland flowperspectives. i.e. that adjoining slopes, basements, retained and unretained battersare identified and the possible effects on these features quantified.

h) Confirmation of the expected overland flowpath/s where the soakage systemoverflows and how this will be managed.

i) Confirmation that the specifically designed soakage system can service the "maximumpotential impermeable area" of the site to cater for future development.

j) It includes areas clear of a flood event up to the 50 year return period storm event(2%AEP).

k) The system contains the volume of storage required where the rate of inflow exceedsthe rate of soakage for the design storm.

l) The method of storage is approved.

m) Details of how the soakage system will be constructed, accessed and what the longterm maintenance regime for the system is.

n) All stormwater entering the storage/soakage portion of the system enters does so via asilt entrapment device to ensure the long term serviceability of the system.

o) Soakholes, soakpits or entry points shall be located to allow for adequate and safeaccess for maintenance.

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p) Each soakhole, soakpit or entry point pit shall be fitted with a removable lid for ease ofaccess and maintenance.

q) Location of soakholes, soakpits or entry points shall be submitted for Council recordsbefore issue of building Code of Compliance certificates.

r) Stormwater entry to soakholes, soakpits or other soakage mechanism from externalhardstand areas shall be through a yard sump (as shown on the Standard Drawings)or other such similar structure so minimal sediment enters the soakage environment,ensuring the long term serviceability of the system.

s) The entire soakhole, soakpit or soakage mechanism shall be located above the staticgroundwater level in heavy rain conditions.

t) Areas of soakage suitability, specific design and soakhole decommissioning areas aredisplayed in Council’s GIS system. This is available for viewing at the CustomerService Centre at the main Council offices. Also refer to DS-5 - Apx D – Appendix D:Disposal of Stormwater by Ground Soakage.

DS-5.7.3 Open Watercourse

This is generally permitted but only where an existing open public watercourse isavailable. This method may require a Resource Consent for discharge from Bay of PlentyRegional Council.

DS-5.7.4 Public Roadside Kerb and Channel Connection

T535

Kerb connections can be made only to vertical kerb and channel and service 1independent dwelling unit per connection. This option will be approved by Council onlyproviding the kerb connection can be shown not to cause or increase flooding in thedownstream catchment for the street and no other reasonable options are available.

DS-5.7.5 Road or Bubble-up Sumps

T425, T426, T427, T525

This option is not a preferred solution. A connection to a road sump or construction of abubble up sump shall occur only with approval from Council. Subsoil drainage reticulatinggroundwater seepage or under channel drains may be connected to road sumps.

DS-5.7.6 Discharge Quality

If the discharge is a permitted activity the quality shall meet the discharge standard asspecified in the Bay of Plenty Regional Council Regional Water & Land Plan.

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DS-5.8 Collection

This section describes the requirements for structures or methods for collection of stormwaterrun off. These are categorised as:

a) Inlet structures (e.g. wingwalls).b) Sumps.

c) Property service connections.

d) Alternative collection methods.

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 anystructure that may allow entry for maintenance and rescue equipment. Council may determineother specific requirements subject to individual site characteristics.

DS-5.8.1 Inlet Structures

T523, T524


a) Inlet structures (such as wingwalls) shall be provided at the inlets of pipelines to thedetail shown on Standard Drawings.

b) A grill shall be installed on all inlet structures of 500mmØ or larger. This grate shall bespecifically designed and submitted to Council for approval.

c) Where the consequences of a grating blockage are likely to be severe, a backupoverflow system that allows runoff to enter the pipe or a clearly defined secondaryflowpath shall be provided.

d) Where a pipe is to be installed in a swale or open drain to allow for access over thedrain, an inlet structure may be required to prevent erosion around the pipe entry.

DS-5.8.2 Sumps

T425, T426, T427, T525


a) Yard sumps shall be provided as a means of capturing run-off from private land,swales and any other grassed areas where applicable. These shall be constructed asper the Standard Drawings.

b) For road and right-of-way sumps refer to DS-4 Transportation Network.

DS-5.8.3 Property Service Connections

The point of connection is the junction between a property’s private drain and the publicstormwater network. Private drainage generally extends through to the property boundaryat which point Council accepts responsibility for the downstream pipelines.

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DS-5.8.4 Minimum Requirements

Property service connections shall be designed to the following minimum requirements:

a) Each lot shall have one service connection (except where internal ground soakage isprovided and appropriate).

b) All lots shall be connected to a piped reticulation system or a specifically designedstormwater mechanism (including soakage devices if appropriate).

c) Specific Council approval is required to connect to the following:

i) An open drain.

ii) A public roadside kerb & channel connection.

iii) A road or bubble up sump.

d) Any individual lot/property connection shall be designed and located to suit theexisting and future development scenarios and where possible sized, located anddesigned to service the whole property (land parcel), but as a minimum, to service thebuilding platform and impermeable area.

e) Any connections shall be located to service the lowest practical building platform onthe property.

f) The design shall specify the requirements for the property connections including planlocation, lot contours and invert level at property boundary or junction with the main asapplicable.

DS-5.8.5 Private Drainage

Generally all stormwater pipes installed between a building and the point of connection toCouncil’s stormwater network are private assets. The Building Act requires that a BuildingConsent shall be obtained for their installation or alteration and that this work must becarried out only by a registered drainlayer.


a) Further approval must also be obtained from Council before these drains may beconnected to the stormwater network. Application for this shall be on Council's WaterSupply / Drainage / Vehicle Crossing Connection Application Form.

b) All connections to Council infrastructure can be carried out only by a Council LicensedContractor.

DS-5.8.6 Connection Locations

Connections shall be:

a) Clear of obstructions, e.g. tree, tree roots, paved areas.

b) Easily accessible for future maintenance.

c) Clear of any known future developments e.g. swimming pools or driveways.

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DS-5.8.7 Connection Depth

T530, T531


a) Connection depths shall be set to drain the whole serviced area recognising thefollowing factors:

i) Any connection points shall have a minimum cover of 600mm and be no deeperthan 1.5m. (Deeper connections may be installed in some circumstances butonly with the prior approval of Council).

ii) Surface level at plumbing fixtures of buildings (existing or proposed).

iii) Depth to the invert of pipe at plumbing fixture or intermediate points.

iv) Invert of the public main at junction point.

v) Allowance for crossing other services.

vi) Allowance for minimum gradients of laterals and private drainage.

vii) Lateral junctions installed at minimum of 45° (vertical) to main.

b) The designed invert level at the connection shall be no higher than the lowestcalculated level consistent with these factors.

DS-5.8.8 Installation of Connections

T530, T531, T532, T533, T534, T535, T536


a) The end of each connection pipe shall be sealed with a solvent welded cap paintedblue if the connection does not occur immediately.

b) Where the inspection is to a property servicing multiple residential units then a surfaceaccessible inspection chamber such as a manhole, rodding eye or other Councilapproved structure shall be installed.

c) Each connection point shall be marked with a 50mm x 50mm timber stake painted bluewhich shall extend from the invert to a minimum of 300mm above finished groundlevel. A blue PVC marker tape shall be attached to the connection pipe, brought upand tied to the top of the stake.

d) Where larger sized capping is required or a factory supplied cap is not available,specific design of these shall be required for approval.

DS-5.8.9 Connection Destinations

Where practicable and where connection is to be within 5m of a manhole, the connectionshall be to the manhole.

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DS-5.8.10 Lateral Configurations

T537, T538, T539, T540, T541,T542

To provide a service connection to each lot, a minimum 100mmØ line shall be extendedfrom the main reticulation system to terminate within the property boundary at a minimumdistance of 1.0m from the front and side boundaries whether created by cross-lease, unittitle or fee-simple subdivision.

These connections shall also form part of the public system to the site boundary and bebrought up to within 1.2m of the final ground surface level.

In addition the following shall apply:

a) For a lateral providing a service connection for 1 lot connecting to a manhole refer toStandard Drawing T537.

b) For a lateral providing a service connection for 2-6 lots connecting to a manhole referto Standard Drawing T538.

c) For a lateral providing a service connection for 1 lot connecting to a main refer toStandard Drawing T539.

d) For a lateral providing a service connection for 2 lots connecting to a main refer toStandard Drawing T540.

e) Where lateral is over 50m long or the number of connections exceeds 6 lots, normalstormwater reticulation conditions apply.

f) Where practicable and where the connection is within 5m of a manhole the connectionshall be to the manhole.

g) Where the main is within the property boundary a separate connection shall beprovided to each lot.

h) The following connections can be connected directly to the main. These connectionsare all to be factory manufactured:

i) 100mmØ or 150mmØ connection can connect to 150mmØ line or greater.

ii) Above diameter and 200mmØ connection can connect to 600mmØ line orgreater.

iii) A factory made 300mmØ connection can connect to 900mm line or greater.

iv) Any combinations outside the following shall connect via a manhole.

i) For major land use development where significant privately owned reticulation works(i.e. not being vested with Council) are being constructed and are connecting intoCouncil infrastructure, any watercourse or the sea, all works shall be designed andconstructed in accordance with the IDC requirements, however the reticulation willremain private.

DS-5.8.11 Infill Subdivision – 3 Lots or Less (Excludes Existing Lot)

It is recognised that infill subdivisions require flexibility in their reticulation layout.However, normal trade practices and standards are needed to ensure that the desiredservice life is achieved.

DS-5 STORMWATER


a) Reticulation of infill subdivisions shall comply with the following criteria:

i) Stormwater drainage within the parent lot shall remain private and be protectedby an appropriate easement.

ii) Stormwater drainage lines shall be separated at the point of connection to theCouncil’s reticulation system and remain separate for each lot unless specificapproval is gained from Council.

iii) Infill subdivisions shall be reticulated on a site-by-site basis.

iv) For minor infill subdivision type works, all private Stormwater works shall beconstructed in accordance with the NZ Building Code regulations.

b) Infill subdivisions shall be reticulated on a site by site basis to the approval of Council.

c) Lateral connections shall be constructed or upgraded in accordance with the IDC. Thislateral can be vested in Council and provide each lot with the same standard ofindividual connection as new ‘greenfields’ lots.

d) Where this is considered impractical or unnecessary, the Consent Holder may makeapplication to Council for the lateral to remain private within an appropriate easement.However common private reticulation is not encouraged so as to alleviate the frictionthat sometimes occurs between neighbours when shared services are involved.

e) Lateral connections shall be separated at the point of connection to Council’sreticulation system and remain separate for each lot unless specific approval isgranted by Council. Where the main is within a neighbour's property, the new junctionmay be installed immediately within the property being subdivided.

DS-5.8.12 Multi-Unit Properties (Such as Apartment Buildings and BodyCorporate Developments)

For multiple occupancies (unit title, cross lease or company lease) service of the wholeproperty shall be achieved by providing a single point of connection to the stormwatersystem. Connection of the individual units is by joint service pipes owned and maintainedby the body corporate, tenants in common or the company as the case may be. In thisinstance the whole of the multiple occupancy shall be regarded as a single lot. All drainagewithin the development boundary would be private.

Alternatively, if authorised by Council, developers may have the option of providingdrainage facilities to individual titles or tenements in new developments by extending thepublic line into the lot and providing a separate lateral/connection to each unit. In suchcases all internal drainage shall be in accordance with the IDC. Easements shall becreated at Council's discretion and to Council standards.

DS-5.8.13 Commercial and Industrial Connections


a) All commercial and industrial lots shall be provided with a stormwater connection.

b) The connection and accepting reticulation mains shall be sized to cater for themaximum potential impermeable area of the site. All paved areas shall be reticulatedfor piped stormwater disposal.

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c) Pollutants and contamination issues shall be identified and managed to thesatisfaction of Council though the Building Consent Process.

DS-5.8.14 Connection to Existing Council Reticulation

Approval shall be obtained from Council before connection can be made to the stormwaternetwork. Application for this shall be on Council's Water Supply / Drainage / VehicleCrossing Connection Application Form.

All connections to Council infrastructure shall be carried out only by a Council LicensedContractor.

DS-5.9 Further Considerations

The following shall also be considered as part of the design process:

a) DS-5.9.1 Trenchless Technology.

b) DS-5.9.2 Access Requirement.

c) DS-5.9.3 Fencing.d) DS-5.9.4 Easements.

e) DS-5.9.5 Rural and Rural-Residential Zones.

DS-5.9.1 Trenchless Technology

Trenchless technology may be preferred or required for alignments passing through orunder:

a) Environmentally sensitive areas.

b) Built-up or congested areas to minimise disruption and reinstatement.

c) Railway and major road crossings.

d) Significant vegetation.

e) Vehicular crossings.

Refer to CS-5.8 Trenchless Technology for information on trenchless technologyinstallation.

DS-5.9.2 Access Requirement

Where any assets are being created as part of a stormwater management system that is tobe maintained by Council, legal and practical access shall be provided for maintenance.For the purpose of this standard provision legal and practical access shall be a minimum ofa 4.0m wide access path constructed to an all weather standard able to accommodate an8.2 tonne design axle load.

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DS-5.9.3 Fencing

T320, T321


a) The fencing of open watercourses and ponds is not required unless the watercoursehas vertical or near vertical sides. In this case the provisions of the Building Act apply.

b) Fencing may be a condition of easements for constructed waterways or drainagestructures. A permeable fence (i.e. that can be seen through, rather than a solidconstruction), is recommended.

c) Fences shall not significantly impede flood flows.

d) Fencing shall not be permitted across overland flowpaths unless approved by Council.

DS-5.9.4 Easements

Discussion with Council regarding easements is recommended early in the design phase.

An easement in gross will be required where a structure, pipe or other asset that forms partof the wastewater / stormwater / water supply system is to be vested in or maintained byCouncil and is located within land not vested in Council or a Reserve.

An easement in gross may not be required where the structure, pipe or other asset islocated within 1.5m of a property boundary.

All easements shall allow for right of access for practical maintenance.

DS-5.9.5 Rural and Rural-Residential Zones

Rural-residential zone stormwater systems shall be designed in accordance with the IDC.Flexibility may be considered where the risk factors are less significant for rural zonestormwater system design. These designs shall be subject to Council approval.

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DS-5 - Appendix AAssociated Standards

DS-5 - Appendix A.1 General

The latest revision or operative version of the following standards shall be used inconjunction with the IDC:

a) Council documentation:

i) City Plan

ii) Stormwater Management Guidelines

b) New Zealand Standards:

i) AS/NZS 1252:1996 High-strength Steel Bolts with Associated Nuts andWashers for Structural Engineering)

ii) AS/NZS 1254:2002 PVC Pipes and Fittings for Stormwater and Surface WaterApplications

iii) AS/NZS 1260:2009 PVC-U Pipes and Fittings for Drain, Waste and VentApplication

iv) AS/NZS 1477:2006 PVC Pipes and Fittings for Pressure Applications

v) AS 1579:1993 Spiral Welded Steel

vi) AS 1646.1:2000 Seal Rings

vii) AS 1657:1992 Fixed Platforms, Walkways, Stairways and Ladders. Design,Construction and Installation

viii) AS/NZS 2280:2004 Ductile Iron Pipes and Fittings

ix) AS/NZS 2544:1995 Grey Iron Pressure Fittings

x) AS/NZS 2566 Buried Flexible Pipelines

xi) AS/NZS 2638.2:2002 Gate Valves for Waterworks Purposes – Resilient Seated

xii) NZS 3114:1987 Specification for Concrete Surface Finishes

xiii) AS/NZS 3725:2007 Design for Installation of Buried Concrete Pipes

xiv) AS 3996 Vehicle Loading (Covers)

xv) AS 4087 Facing and Drilling of Flanges

xvi) AS/NZS 4058:2007 Precast Concrete Pipes (Pressure and non-pressure)

xvii) AS/NZS 4130:2009 Polyethylene (PE) Pipes for Pressure Applications

xviii) AS/NZS 4131:2003 Polyethylene (PE) Compounds for Pressure Pipes andFittings

xix) AS/NZS 4158:2003 Thermal-bonded Polymeric Coatings on Valves and Fittingsfor Water Industry Purposes

xx) NZS 4402:1986 Methods of Testing Soils for Civil Engineering Purposes

xxi) NZS 4404:2010 Land Development and Subdivision Infrastructure

DS-5 STORMWATER


xxii) AS/NZS 4441:2008 Oriented PVC (PVC-O) Pipes for Pressure Applications

xxiii) NZS 4442:1988 Welded Steel Pipes and Fittings for water, sewage and mediumpressure gas

xxiv) AS/NZS 4765:2007 Modified PVC (PVC-M) Pipes for Pressure Applications

xxv) AS/NZS 5065:2005 Polyethylene and Polypropylene and Fittings for Drainageand Sewerage Applications

xxvi) NZS/BS 5163:1986 Specification for Predominantly Key-Operated Cast IronGate Valves for Waterworks Purposes

xxvii) BS EN 124 Vehicle Loading (Covers)

xxviii) NZTA M/7 Roadmarking Paints

c) Other reference material:

i) Resource Management Act 1991

ii) New Zealand Building Act

iii) New Zealand Health and Safety in Employment Act 1992

iv) IPENZ Procedure for Hydrological Design of Urban Stormwater Systems,December 1980

v) New Zealand Building Code Handbook and Approved Documents section E1 -Surface Water

vi) Auckland Regional Council - TP10 Stormwater Management Devices, DesignGuidelines Manual)

vii) Auckland Regional Council - TP124 Low Impact Design Manual

viii) Christchurch City Council - Waterways, Wetlands and Drainage Guide

ix) Part B, North Shore City Council – Bioretention Guidelines 2008.

x) New Zealand Ministry for the Environment Climate Change Effects and ImpactsAssessment Publication 2008.

xi) New Zealand Department of Labour Approved Code of Practice for Safety inExcavation and Shafts for Foundations – April 2000

DS-5 STORMWATER


DS-5 - Appendix BDesign Rainfall Tables

DS-5 - Appendix B.1 General

The Table A Climate-Adjusted Design Rainfall Depth Estimate and Table BClimate-Adjusted Design Rainfall Intensity Estimate are applicable to the Tauranga Cityarea.

Table A: Climate-Adjusted Design Rainfall Depth Estimate (2055) in mm

Return DURATION

Period(years)

10minutes

20minutes

30minutes 1 hour 2 hours 6 hours

12hours

24hours

48hours

X2.33 13 20 25 33 45 71 91 115 1305 18 26 35 49 69 102 128 150 172

10 21 33 44 65 90 131 158 183 21220 24 40 52 80 112 159 189 219 25550 30 48 64 100 141 197 230 273 320

100 33 56 72 115 163 225 259 320 377

Note: For 2.33 years read annual.

Table B: Climate-Adjusted Design Rainfall Intensity Estimates (2055) inmm/hour

Return DURATIONPeriod(Years)

10minutes

20minutes

30minutes 1 hour 2 hours 6 hours

X2.33 78 60 50 33 23 125 108 78 70 49 35 17

10 126 99 88 65 45 2220 144 120 104 80 56 2750 180 144 128 100 71 33

100 198 168 144 115 82 38

Note: For 2.33 years read annual. For intermediate durations refer to DS-5 Appendix C.1General.

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DS-5 - Appendix CRainfall Intensity Curves

DS-5 - Appendix C.1 General

The following rainfall data is applicable to the Tauranga City area.

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DS-5 - Appendix DDisposal Of Stormwater By Ground Soakage

DS-5 - Appendix D.1 General

The disposal of stormwater from roofs, parking access and manoeuvring areas hashistorically been successfully undertaken by discharging the stormwater to drilledsoakholes or soakpits on private property.

However, such disposal methods have contributed to land instability and the creation ofnuisance due to groundwater seepage in elevated urban areas on the edge of TaurangaHarbour.

The degree of success and long-term serviceability of such soakage systems is alsodependent on the presence of permeable sub-soils (and their permeability), theconstruction of the soakage system and the amount of maintenance undertaken.

The soils present in the Tauranga City area vary, with the more permeable soils likely toexist adjacent to Tauranga Harbour, on elevated ground at Te Puke, along the coastalmargins where sand-derivative soils are present, at Pukehina, and on most elevated ruralareas (generally east of Te Puke).

Some areas of Tauranga City are suitable for on-site disposal of stormwater by groundsoakage. Traditionally, building at Mount Maunganui and Papamoa has used soakpitsconstructed from porous concrete liners, while in elevated areas adjacent to TaurangaHarbour holes were augered down through the Rotoehu Ash (soakage) layer and into anunderlying marker bed, the Hamilton Ash (“chocolate”) layer, to achieve adequatesoakage.

For Mount Maunganui and Papamoa the stormwater disposed of by soakage helpsrecharge the groundwater and prevent salt-water intrusion into the water table. InTauranga the stormwater is disposed of into a porous ash layer within the soil profile. Asboth communities developed stormwater infrastructure was sized, in general, to cater forstormwater generated on roads and not from residential lots.

With the intensification of development, the ability of the land to deal with the increasingvolumes of stormwater generated has, in some cases, become compromised with theresults affecting both the subject property and adjacent properties.

In Mount Maunganui these off-site effects have mainly been overland flows into adjacentproperties and in some cases inundation of buildings during significant rainfall. InTauranga off-site effects have resulted in elevated groundwater levels with surface“breakout” in some areas, overland flows when the soakhole capacity has been exceededand, in some cases, slope failure due to erosion from overland flows and/or elevated porepressures within the soil profile.

Accordingly, the use of ground soakage for the disposal of stormwater is no longerappropriate in some areas.