DESIGN STANDARD - Tauranga

1 DESIGN STANDARDDS-5 STORMWATERTABLE OF General .. Minimum Requirements .. Regional Council Requirements .. DESIGN .. Conveyance - Primary and Secondary Systems .. Stormwater Treatment / Detention .. Stormwater Discharge .. Collection .. Further Considerations ..27DS-5 STORMWATERU pdated 01/07/2014 Page GeneralMany developments will change the natural existing drainage pattern sostormwatersystemsare typically designed and constructed to manage this change and any potential adverseeffects which may include flood damage, erosion, sedimentation, water pollution and damageto primary goals of astormwater drainage systemare to collect, convey and treat surfacerunoff to minimise flood damage and adverse effects on the environment. There are severalways this can be Impact DESIGN features such as plantedswales, rain gardens,larger grass verges and detention ponds can allow groundwater recharge, slow the movementof water and reduce the amount of pollutants inreceiving water bodies.

2 These areas may alsobe used to enhance a development, contributing to the wider environmental quality of an 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-roadparking can help to reduce may also integrate with the naturaldrainage system and this can helpmitigate environmental effects, as well as enhance amenity and ecological Minimum RequirementsDesigns shall provide for astormwatermanagement system that:a) Complies with the operative City Plan andInfrastructureDevelopment Code (IDC).b) Is designed to acceptable urbandesign, landscaping and engineering ) Minimises, isolates or eliminates health and safety hazards during both its constructionand its ) Minimises, isolates or eliminates any adverse ecological and environmental ) Thestormwatermanagement system shall be located in areas that are geotechnicallysuitable for the system.

3 Where confirmation of this requirement is not clear a certification statement from aCategory 1 Geo-Professional may be Regional Council RequirementsThe discharge ofstormwater, 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 requireResourceConsents fromBay of Plenty Regional Council unless authorised as a permitted activity in theRegional water and Land STORMWATER Page 2 Updated 01/07 Vesting of Assets and Transferring of ConsentsIf it is the intention of thedeveloperto transfer anyStormwater Resource Consent fromBay of Plenty Regional CounciltoCouncil, a copy of the draft conditions shall beforwarded toCouncilfor comment on receipt by theConsent not accept a transfer of aBay of Plenty Regional Council issuedResourceConsent unless theassets pertaining to thatResource Consenthave been constructed inaccordance with theResource Consent conditions and comply with theIDC.

4 Intention tovest ownership of anyassetand/or transfer of anyResource Consentshall be discussedwithCouncilat an early stage of the right not to accept anyassetand/or accept a transfer of anyResource DesignThe following shall apply:a) Unless otherwise approved byCouncil, thedesignof thestormwatersystem shall be inaccordance with theIDC and may be supplemented by the documents noted inDS-5 ) 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 are incorporated,surface water run-off shall be determined using an appropriatehydrological or hydraulic )Low Impact DESIGN forstormwatermanagement 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.

5 Low Impact DESIGN methodstypically includeswales, ponds, rain gardens, rain tanks, a reduction in impermeablesurfaces, permeable paving, filter strips, green roofs and constructed wetlands. The use ofLow Impact Designmethods shall be discussed withCouncilat an early required at the time ofInfrastructure Development Works noInfrastructure Development Works Approval is required,Councilapproval shallbe obtained at a time required byCounciland before construction of the Alternative DesignRefer to Alternative Stormwater Management SystemsThe following shall apply:a) Thestormwatermanagement system is an overall system that manages thecollection, conveyance, treatment and discharge ofstormwater. The overallstormwatermanagement system shall provide a minimum STANDARD of flood protectionfor the community and mitigate any adverse environmental STORMWATERU pdated 01/07/2014 Page 3b) The overall system shall accommodate flows from a 50 year return period storm event(2%AEP) unless otherwise stated in a comprehensivestormwaterdischarge post development run off rates shall be no greater than pre development run offrates.

6 Ponding areas shall be provided for only on publicroads and public )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 thedesign condition and be appropriately engineered to suit thesite-specific requirements. An appropriate mix of solutions comprising Low ImpactDesignand conventional solutions shall be considered as well as short and long termmaintenance responsibilities/requirements and the whole of life cost implications ( of construction, maintenance, renewal or replacement). The overall system alsoneeds to provide for a range of storm ) 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 thedesigncapacity then the part of the overall system that compliments the primarysystem is known as the secondary ) water Quality considerations are required to control potential for damagingenvironmental effects to our waterways, habour and aquatic life.

7 water quality shall beincluded in DESIGN where required by:i)Bay of Plenty Regional Council water and Land Plan )Bay of Plenty Regional Council resource consent ) Councils Comprehensive Catchment Consent Conditions and associatedManagement Plans as approved by Bay of Plenty Regional 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 Hydraulic DesignThe following shall apply:a) The hydraulicdesignof stormwaterpipelines shall be based on tables for the hydraulicdesignof stormwaterdrains and pipelines or on graphs or other representation of thesame methods based on the Colebrook White or Manning's ) The pipe roughness coefficient Ks used in thedesignshall be as shown inNZS4404 Table Rainfall IntensityThe following shall apply:a)Designers shall use theDesignRainfall Tables located inDS-5 - Appendix ) 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 STORMWATER Page 4 Updated 01/07/2014c) The Rainfall Intensity Curves are included inDS-5 - Appendix ) It shall be noted that several large streams have their headwaters in higher altitudeareas beyond the Tauranga City boundary.

8 For thedesignofstormwatersystems inthese areas, it may be necessary to use higher rainfall intensities than those requiredby a) and c) Freeboard Above DESIGN Flood LevelThe minimumfreeboardheight applied to the calculated top water level shall be asoutlined in Table 2: Freeboard minimumfreeboardshall be measured from the top water level to the underside of thefloor slab or the underside of the floor joists, whichever is 2: Freeboard HeightsType of StructureFreeboardto AppliedDesignStormNon-habitable residential buildings,detached garages and carports200mmCommercial and industrial buildings300mmHabitable dwellings/structures andattached High Levels of GroundwaterIf there is a need to lower groundwater levels thendesigners shall provide a method ofallowing the groundwater into thestormwatersystem in a controlled manner. Such asolution may incorporate perforated inlet pipes together with drainage rock and Calculating water Quality VolumesCalculating the water quality volume can be done by the following calculation:2 year / 1hour storm event for Tauranga = = (imp.

9 %/100) x total site area + (pervious %/100) x total site total site area = m2 The water quality volume Vwq = = 90% storm depth (m)Examples of this method can be found via case studies provided within theStormwaterManagement STORMWATERU pdated 01/07/2014 Page Conveyance - Primary and Secondary SystemsA primarystormwatersystem may typically include:a) Pipe )Groundsoakage ) Channels and open water )Swales and rain systems such as pumping systems are generally not secondary system comprises a network of overland flowpaths and storage areasdesigned to safely convey and/or storestormwater that exceeds the capacity of the Selection of a Primary Stormwater SystemThe type of primary system installed will be dependent on factors such as water quantity, water quality, aquatic resource protection, topography, soil type, location and Piped ReticulationThe 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: 200mm internal diameterAll other mains andsumpleads:300mm internal diameterb) Manholes are required at each.

10 I)Intersection of pipes (except for junctions between mains and laterals).ii)Change of ) Change of ) Change of pipe ) Change of material (except for repair/maintenance locations).vi) Permanent or temporary end of a pipe ) Shall provide for thedesignflow without ) Shall provide for a minimum full bore velocity of at a flow of half the 50% ) Where the pipe full velocity is less than the reticulationdesignshall allow for ) 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 onto600mm pipes or larger provided that:DS-5 STORMWATER Page 6 Updated 01/07/2014i)A manhole is supplied on the branch line within 50m of the )The saddle is created using a 300mm pipe stub epoxied onto the 600mm orlarger main and is inspected prior to laying the first pipe from the )Councilapproval has been ) Pipes shall be designed so that the pipes are laid soffit to soffit.