DESIGN STANDARD TABLE OF CONTENTS

Transcription

1 DESIGN STANDARD DS-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

2 DS-5.1 General Many developments will change the natural existing drainage pattern so stormwater systems are typically designed and constructed to manage this change and any potential adverse effects which may include flood damage, erosion, sedimentation, water pollution and damage to ecosystems. The primary goals of a stormwater drainage system are to collect, convey and treat surface runoff to minimise flood damage and adverse effects on the environment. There are several ways 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 movement of water and reduce the amount of pollutants in receiving water bodies. These areas may also be 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 (including paved surfaces), is important and options such as narrower carriageways and semi-permeable paving for on-road parking can help to reduce runoff. Stormwater systems may also integrate with the natural drainage system and this can help mitigate 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 construction and 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 a Category 1 Geo-Professional may be required. DS-5.3 Regional Council Requirements The discharge of stormwater, the diversion of natural water during construction, the permanent diversion of natural water as a consequence of development, activities in the bed or on the banks of a natural waterway and damming of waterways generally require Resource Consents from Bay of Plenty Regional Council unless authorised as a permitted activity in the Regional Water and Land Plan. Updated 01/07/2014 Page 1

3 DS Vesting of Assets and Transferring of Consents If it is the intention of the developer to transfer any Stormwater Resource Consent from Bay of Plenty Regional Council to Council, a copy of the draft conditions shall be forwarded to Council for comment on receipt by the Consent Holder. Council will not accept a transfer of a Bay of Plenty Regional Council issued Resource Consent unless the assets pertaining to that Resource Consent have been constructed in accordance with the Resource Consent conditions and comply with the IDC. Intention to vest ownership of any asset and/or transfer of any Resource Consent shall be discussed with Council at an early stage of planning. Council reserves the right not to accept any asset and/or accept a transfer of any Resource Consent. DS-5.4 Design a) Unless otherwise approved by Council, the design of the stormwater system shall be in accordance with the IDC and may be supplemented by the documents noted in DS-5 Apx A.1 General. b) For catchment areas less than 50ha, surface water run-off using the Rational Method will generally be accepted. For larger catchments or where significant storage elements e.g. Ponds are incorporated, surface water run-off shall be determined using an appropriate hydrological or hydraulic model. c) Low Impact Design for stormwater management is the preferred approach where appropriate. Well-designed and well-maintained systems which replicate the natural pre-development hydrological regime can not only mitigate adverse environmental effects but can also enhance local amenity and ecological values. Low Impact Design methods typically include swales, ponds, rain gardens, rain tanks, a reduction in impermeable surfaces, permeable paving, filter strips, green roofs and constructed wetlands. The use of Low 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 shall be obtained at a time required by Council and before construction of the system. DS Alternative Design Refer to DS-1.3 Alternative Design. DS Stormwater Management Systems a) The stormwater management system is an overall system that manages the collection, conveyance, treatment and discharge of stormwater. The overall stormwater management system shall provide a minimum standard of flood protection for the community and mitigate any adverse environmental effects. Page 2 Updated 01/07/2014

4 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 off rates. 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 upstream catchment is provided for, ensure the downstream receiving network has the capacity to cater for the design condition and be appropriately engineered to suit the site-specific requirements. An appropriate mix of solutions comprising Low Impact Design and conventional solutions shall be considered as well as short and long term maintenance responsibilities/requirements and the whole of life cost implications (i.e. cost of construction, maintenance, renewal or replacement). The overall system also needs to provide for a range of storm events. d) A subset of the overall system is the primary system. The primary system shall accommodate flows from a 10 year return period storm event (10%AEP). When the primary system overloads by either blockage, malfunction or rainfall events in excess of the design capacity then the part of the overall system that compliments the primary system is known as the secondary system. e) Water Quality considerations are required to control potential for damaging environmental effects to our waterways, habour and aquatic life. Water quality shall be included in design where required by: i) Bay of Plenty Regional Council Water and Land Plan requirements. i Bay of Plenty Regional Council resource consent conditions. Councils Comprehensive Catchment Consent Conditions and associated Management Plans as approved by Bay of Plenty Regional Council. The 90% rainfall storm shall be used as this is the maximised point of runoff volume capture. The 90% rainfall for Tauranga is 33mm for a 2 year / 1 hour storm. DS Hydraulic Design a) The hydraulic design of stormwater pipelines shall be based on tables for the hydraulic design of stormwater drains and pipelines or on graphs or other representation of the same 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 NZS4404 Table 4.2. DS Rainfall Intensity a) Designers shall use the Design Rainfall Tables located in DS-5 - Appendix B.1 General. b) These tables have been developed from the rainfall records from the rain gauge stations in the sub region and have been adjusted to allow for climate change to the year Updated 01/07/2014 Page 3

5 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 altitude areas beyond the Tauranga City boundary. For the design of stormwater systems in these areas, it may be necessary to use higher rainfall intensities than those required by a) and c) above. DS Freeboard Above Design Flood Level The minimum freeboard height applied to the calculated top water level shall be as outlined in DS Table 2: Freeboard Heights. The minimum freeboard shall be measured from the top water level to the underside of the floor slab or the underside of the floor joists, whichever is appropriate. Table 2: Freeboard Heights Type of Structure Non-habitable residential buildings, detached garages and carports Commercial and industrial buildings Habitable dwellings/structures and attached garages Freeboard to Applied Design Storm 200mm 300mm 500mm DS High Levels of Groundwater If there is a need to lower groundwater levels then designers shall provide a method of allowing the groundwater into the stormwater system in a controlled manner. Such a solution may incorporate perforated inlet pipes together with drainage rock and geotextile. DS 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 (pervious %/100) x total site area. Where total site area = m 2 The water quality volume Vwq = 0.033Awq Where = 90% storm depth (m) Examples of this method can be found via case studies provided within the Stormwater Management Guidelines. Page 4 Updated 01/07/2014

6 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 areas designed to safely convey and/or store stormwater that exceeds the capacity of the primary system. DS 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 area constraints. DS 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: All other mains and sump leads: 200mmØ internal diameter 300mmØ internal diameter b) Manholes are required at each: i) Intersection of pipes (except for junctions between mains and laterals). i iv) Change of grade. Change of direction. 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% AEP design flow. e) Where the pipe full velocity is less than 1.3m/s the reticulation design shall allow for silt collection. f) 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: Updated 01/07/2014 Page 5

7 i) A manhole is supplied on the branch line within 50m of the saddle. i 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. Council approval has been obtained. g) 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 Reticulation Layout a) The alignment of stormwater reticulation shall be laid out to follow the road pattern and either: i) Be located clear of the carriageway. 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. i 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. On the low side of lots that have a cross-fall of more than 1.5m. DS Close Proximity Rules T553 T554 a) 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. b) No enclosed building or structure shall be sited over a manhole or closer than 500mm from the outside wall of the manhole structure. c) No building or concrete slab shall be constructed over a connection point to a main. d) 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. Page 6 Updated 01/07/2014

8 e) 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 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 DS Table 3: Anti-Scour Block Spacing. Table 3: Anti-Scour Block Spacing Grade (%) Requirement Spacing (S) (m) Concrete bulkhead S = 100/Grade (%) >35 Special design Refer to Council Note: 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 Cover Over Pipelines a) In private property: i) The minimum cover shall be 600mm. i iv) b) In Road Zones: If the cover exceed 3m, specific design and approval is required. The design of cover shall avoid affecting the future development options available within the lot. 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. i) The minimum cover shall be 900mm. Updated 01/07/2014 Page 7

9 Sump leads shall achieve 700mm of cover and be a class 4 (Z) rubber ring jointed concrete pipe or equivalent. c) Where minimum cover cannot be achieved, specific design of pipe and cover is required. DS Loads on Pipes a) All pipelines shall be designed to withstand all the likely loads to which they will be subject to. b) In the first instance, load parameters shall be designed to support an 8.2 tonne design axle load. Following this: i) AS/NZS 3725 and AS2566 shall be used as design guides as applicable. 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 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 Pipe Materials Refer to AM-5 Stormwater. DS Pipe Joints All pipelines shall be fully sealed by use of rubber joint rings or welding as appropriate unless otherwise approved by Council. DS Pipe Bedding and Backfill T551 a) Pipe bedding and backfill shall be specifically designed, shown on the detailed design drawings and submitted to Council for approval. b) The design shall also include the compaction criteria to be used to certify the backfill has been compacted to the required compaction standard. c) 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. Page 8 Updated 01/07/2014

10 DS 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: 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 any structure that may allow entry for maintenance and rescue equipment. Council may determine other specific requirements subject to the individual site characteristics. DS Manholes T501, T502, T503, T504, T505, T506, T507 a) Manhole spacings shall not exceed 100m for pipe lines up to 900mmØ without specific approval from Council. Greater spacing may be approved for larger diameter pipes. b) The entire manhole structure shall be located clear of all boundaries. c) Manholes shall be located within Council property or Road Zones wherever possible. d) 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 it shall: i) Be specifically designed. i iv) Have access steps installed. Incorporate clear warning that it is deep. Have a secure entrance. v) Require larger diameter chambers and covers. e) 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. f) 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. g) All manholes shall have an entry safety grill fitted. h) All standard manholes shall be constructed as detailed on the Standard Drawings. Updated 01/07/2014 Page 9

11 DS Manhole Sizing a) 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. b) When considering the appropriate manhole diameter consideration shall be given by the designer to the base layout to ensure hydraulic efficiency and adequate working space in the chamber. c) Where there are several inlets, consultation with Council on the layout of the chamber is recommended. DS Benching a) Benching shall be provided in the base of each manhole that provides a safe place to stand for maintenance purposes. b) Benching shall be close to flat with a cross fall (6H:1V) into the manhole pipe system for drainage purposes. c) Channels shall have a minimum inside radius of 300mm. DS 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 per degree of horizontal angle change between the two lines lower than the lowest incoming pipeline invert. b) The soffit of the outlet pipe shall be level with or below the soffit of the lowest incoming pipeline. c) The extension of the grade of the steepest pipe across the width of the manhole. DS Flotation In areas of high water table all manholes shall be designed to provide a factor of safety against flotation of DS 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. Page 10 Updated 01/07/2014

12 DS Covers T504, T505, T506, T507 a) Manhole covers with a minimum clear opening of 600mm in diameter shall be used. 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) Standard approved "blue" road marking paint. DS Rodding Eyes T520, T521 a) 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. b) PVC-U bends up to 45 are acceptable. c) 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. d) All covers must be painted with New Zealand Transport Agency (NZTA) Standard approved "blue" road marking paint. e) All standard rodding eyes shall be constructed as detailed on the Standard Drawings. DS Ground Soakage Systems Refer to DS Ground Soakage Discharge. DS 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. a) It must be demonstrated that the open drain system: i) Can be used where it is in keeping with the existing drainage network. i Provides adequate capacity. 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. Updated 01/07/2014 Page 11

13 b) 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: i) 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. 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 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. d) The flow characteristics of natural open stream systems shall: i) Be based on the likely long term stream condition in terms of density of vegetation. i iv) Be cleared of all unsuitable plant growth and replanted to a landscape design approved by Council. Take account of the possibility of blockage under all peak flood conditions. Include protection of the low flow channel against scour and erosion of the stream bed where necessary. v) Not be adversely affected by the discharge of stormwater resulting from development 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 the stormwater (e.g. large sealed areas) shall be mitigated. DS 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: 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 treatment requirements. DS Minimum Requirements It must be demonstrated that a swale system complies with the following: Page 12 Updated 01/07/2014

14 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 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. 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 for flows to be dispersed. h) 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 mm. A planting plan shall be submitted to Council for approval. i) 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 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 Minimum Requirements It must be demonstrated that a filter strip system complies with the following: a) A maximum catchment area not greater than 2 hectares. b) Appropriate functionality and adequate capacity. 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 erosion protection is provided. g) Grass shall have a design vegetation height mm. h) 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. Updated 01/07/2014 Page 13

15 DS 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 Minimum Requirements 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. b) Appropriate functionality and adequate capacity. 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 planting plan 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 is full. h) Filtration layers shall comprise of the following: i) Filtration soil media layer: mm 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 and weeds. m) An underdrain shall be provided if piping to the downstream network. This shall have 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. 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. Page 14 Updated 01/07/2014

16 DS Other Alternative Design Methods Refer to DS-1.3 Alternative Design. DS Secondary System No buildings or structures shall be located within secondary overland flow paths. DS Secondary System Options Secondary system options may include: a) Preferred Options: i) Temporary ponding on local and collector roads. i Temporary flow along local and collector roads. 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 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. i Stormwater pumping systems are not permitted. Piped secondary systems are not permitted. DS-5.6 Stormwater Treatment / Detention Stormwater ponds are an accepted method of improving stormwater quality, reducing downstream flood potential and peak downstream flow rates. Council is not in favour of encouraging a proliferation of small stormwater ponds but prefers a total catchment/treatment train approach. DS Permanent Pond Type Council accepts the use of dry and wet ponds as a part of an engineered solution and/or treatment train. However, the selection and design criteria (short term as well as long term functionality, maintenance, ownership) must be approved by Council before construction. Access from public carriageways shall be provided for maintenance. DS Regional Council Resource Consent Updated 01/07/2014 Page 15

17 a) Permanent ponds may require Resource Consent from Bay of Plenty Regional Council as part of an earthworks and/or stormwater discharge Resource Consent. Refer to DS-5.3 Regional Council Requirements and contact Bay of Plenty Regional Council for more information. b) Temporary ponds may require Resource Consent from Bay of Plenty Regional Council as part of the earthworks Consent and/or discharge Resource Consent. Refer to DS-5.3 Regional Council Requirements and contact Bay of Plenty Regional Council for more information. c) Pollutants and contamination issues shall be identified and managed to the satisfaction of Council and any Resource Consent conditions related to the pond. DS Permanent Pond Ownership and Location a) If acceptance of ownership of a pond is agreed by Council all stormwater ponds shall be located on land either: i) Owned by Council. i Proposed to be vested in Council at completion of the development. 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 with Council prior to application for Resource Consent or, if no Resource Consent is required, prior to construction of the pond to ensure the pond construction has minimal or no impact on Council s existing stormwater system. DS Detention Pond Design a) Detention Ponds shall be designed to the following minimum requirements: i) Compliance with DS-1 - Apx A.1 General. i Stormwater ponds shall be designed to ensure that retention and treatment to achieves removal of 75% of total suspended sediment smaller than 120µm diameter on a long term average basis. Any pond shall be designed to ensure any discharge has a suspended solids concentration no higher than 150 g/m ³. b) Specific matters to consider in pond design: i) Side slopes with safety considerations - maximum 1:5 slope above and below water level. i iv) Ease of access for and of maintenance including mowing and silt removal and disposal and access to public roads. Shape and contour for amenity value. Effectiveness of inlet and outlet structure/s. v) Overflow design and scour protection. vi) Pest control (rats, mosquitoes etc.) and wind blown debris. Page 16 Updated 01/07/2014

18 v Sustainability of aquatic life. vi Depth of water. ix) Use in treatment of stormwater. x) Minimise dead zones and short-circuiting to improve the treatment performance 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. The designer shall refer to Councils Stormwater Management Guidelines for more information regarding designs of this type. DS Pond Location a) If acceptance of ownership of a pond is agreed by Council all stormwater ponds shall be located on land either: i) Owned by Council. i Proposed to be vested in Council at completion of the development. 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 with Council prior to application for Resource Consent or, if no Resource Consent is required, prior to construction of the pond to ensure the pond construction has minimal or no impact on Council s existing stormwater management network. DS Constructed Wetlands Constructed wetlands are large shallow planted ponds which are designed to provide stormwater quality improvement, reduce downstream flood potential and peak downstream flow. They differ from Detention Ponds in that they can be shallower, provide greater contaminant removal (including nutrients) and support a wider variety of aquatic plants and 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. Updated 01/07/2014 Page 17

19 g) Designed for a controlled discharge rate that allows for continuous flow through a wetland to prevent stagnation. h) Provides access for maintenance. Council approval shall be obtained prior to design and construction of any wetland. All Resource Consent, location, functionality, maintenance and ownership issues shall be confirmed prior to any detailed design commencing. The designer shall refer to Councils Stormwater Management Guidelines for more information regarding designs of this type. DS Permeable Pavements Permeable Pavements are hard surface paving systems that reduce stormwater runoff flows and improve runoff water quality. Their porous surface allows stormwater to soak through 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, driveways and footpaths. Council approval shall be obtained prior to design and construction of Permeable Pavement. The designer shall refer to Council's Stormwater Management Guidelines for more information regarding designs of this type. DS Bio-Retention Tree Pits Bio-Retention Tree Pits collect stormwater from small car park areas or roads. They can reduce stormwater runoff flow velocity, improve runoff water quality and contribute to the overall 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 maximum ponded water depth of 300mm deep. c) Filtration layers shall comprise of the following: i) Filtration soil media layer: mm deep. 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 and weeds with a minimum permeability of 0.3m/day. Page 18 Updated 01/07/2014

20 e) Ponding area should drain completely within 24 hours. f) An underdrain shall be provided in the final drainage layer with a minimum cover of 50mm. g) An overflow bypass system shall be provided which sits below the surrounding ground surface. 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. The designer shall refer to Councils Stormwater Management Guidelines for more information regarding designs of this type. DS-5.7 Stormwater Discharge This section describes the requirements for structures or methods for discharge of stormwater runoff. 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 any structure that may allow entry for maintenance and rescue equipment. Council may determine other specific requirements subject to individual site characteristics. DS Discharge Structures a) Discharge structures shall be installed at the outlets of pipelines to the detail shown on Standard 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 and include an energy dissipation device where required. (Submitted designs must clearly illustrate this requirement). d) No grill shall be constructed on outlet structures. A hazard warning sign shall be placed on all outlet structures 500mmØ or larger as defined on the Standard Drawings. e) Where a pipe is to be installed in a swale or open drain to allow for access over the drain, an outlet structure may be required to be installed to prevent erosion around the pipe exit. Updated 01/07/2014 Page 19

21 DS Ground Soakage Discharge Disposal of stormwater by ground soakage or ground water recharge is only suitable in some areas of Tauranga (i.e. parts not located near relic slips or plateau edges) and most areas of the Mount Maunganui and Papamoa portions of Tauranga City. The following applies to ground water soakage methods: a) Concept approval is required from Council before undertaking detailed design for any use of Ground Soakage. The detailed design is then subject to Infrastructure Development 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 or another time specified by Council and before construction of the system c) All soakage systems shall be specifically designed to meet the performance criteria required by the New Zealand Building Code Handbook and Approved Documents section E1 - Surface Water and include the design parameters outlined in this section of the IDC. d) Testing determines that the soil, geotechnical and groundwater characteristics are suitable. e) The rate of soakage is determined by an assessment conducted by an appropriately qualified and experienced Chartered Professional Engineer. (In some cases a Category 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 designed for what can be expected in its operating environment. g) Confirmation that use of the soakage system will not have an adverse effect on other land, property and structures including land stability, seepage or overland flow perspectives. i.e. that adjoining slopes, basements, retained and unretained batters are identified and the possible effects on these features quantified. h) Confirmation of the expected overland flowpath/s where the soakage system overflows and how this will be managed. i) Confirmation that the specifically designed soakage system can service the "maximum potential 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 exceeds the 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 long term maintenance regime for the system is. n) All stormwater entering the storage/soakage portion of the system enters does so via a silt 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 safe access for maintenance. Page 20 Updated 01/07/2014

22 p) Each soakhole, soakpit or entry point pit shall be fitted with a removable lid for ease of access and maintenance. q) Location of soakholes, soakpits or entry points shall be submitted for Council records before issue of building Code of Compliance certificates. r) Stormwater entry to soakholes, soakpits or other soakage mechanism from external hardstand 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 static groundwater level in heavy rain conditions. t) Areas of soakage suitability, specific design and soakhole decommissioning areas are displayed in Council s GIS system. This is available for viewing at the Customer Service Centre at the main Council offices. Also refer to DS-5 - Apx D Appendix D: Disposal of Stormwater by Ground Soakage. DS Open Watercourse This is generally permitted but only where an existing open public watercourse is available. This method may require a Resource Consent for discharge from Bay of Plenty Regional Council. DS Public Roadside Kerb and Channel Connection T535 Kerb connections can be made only to vertical kerb and channel and service 1 independent dwelling unit per connection. This option will be approved by Council only providing the kerb connection can be shown not to cause or increase flooding in the downstream catchment for the street and no other reasonable options are available. DS 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 a bubble up sump shall occur only with approval from Council. Subsoil drainage reticulating groundwater seepage or under channel drains may be connected to road sumps. DS Discharge Quality If the discharge is a permitted activity the quality shall meet the discharge standard as specified in the Bay of Plenty Regional Council Regional Water & Land Plan. Updated 01/07/2014 Page 21

23 DS-5.8 Collection This section describes the requirements for structures or methods for collection of stormwater run 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 any structure that may allow entry for maintenance and rescue equipment. Council may determine other specific requirements subject to individual site characteristics. DS Inlet Structures T523, T524 a) Inlet structures (such as wingwalls) shall be provided at the inlets of pipelines to the detail shown on Standard Drawings. b) A grill shall be installed on all inlet structures of 500mmØ or larger. This grate shall be specifically designed and submitted to Council for approval. c) Where the consequences of a grating blockage are likely to be severe, a backup overflow system that allows runoff to enter the pipe or a clearly defined secondary flowpath shall be provided. d) Where a pipe is to be installed in a swale or open drain to allow for access over the drain, an inlet structure may be required to prevent erosion around the pipe entry. DS 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 as per the Standard Drawings. b) For road and right-of-way sumps refer to DS-4 Transportation Network. DS Property Service Connections The point of connection is the junction between a property s private drain and the public stormwater network. Private drainage generally extends through to the property boundary at which point Council accepts responsibility for the downstream pipelines. Page 22 Updated 01/07/2014

24 DS 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 is provided and appropriate). b) All lots shall be connected to a piped reticulation system or a specifically designed stormwater mechanism (including soakage devices if appropriate). c) Specific Council approval is required to connect to the following: i) An open drain. i A public roadside kerb & channel connection. A road or bubble up sump. d) Any individual lot/property connection shall be designed and located to suit the existing and future development scenarios and where possible sized, located and designed to service the whole property (land parcel), but as a minimum, to service the building platform and impermeable area. e) Any connections shall be located to service the lowest practical building platform on the property. f) The design shall specify the requirements for the property connections including plan location, lot contours and invert level at property boundary or junction with the main as applicable. DS Private Drainage Generally all stormwater pipes installed between a building and the point of connection to Council s stormwater network are private assets. The Building Act requires that a Building Consent shall be obtained for their installation or alteration and that this work must be carried out only by a registered drainlayer. a) Further approval must also be obtained from Council before these drains may be connected to the stormwater network. Application for this shall be on Council's Water Supply / Drainage / Vehicle Crossing Connection Application Form. b) All connections to Council infrastructure can be carried out only by a Council Licensed Contractor. DS 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. Updated 01/07/2014 Page 23

25 DS Connection Depth T530, T531 a) Connection depths shall be set to drain the whole serviced area recognising the following factors: i) Any connection points shall have a minimum cover of 600mm and be no deeper than 1.5m. (Deeper connections may be installed in some circumstances but only with the prior approval of Council). i iv) Surface level at plumbing fixtures of buildings (existing or proposed). Depth to the invert of pipe at plumbing fixture or intermediate points. Invert of the public main at junction point. v) Allowance for crossing other services. vi) v Allowance for minimum gradients of laterals and private drainage. Lateral junctions installed at minimum of 45 (vertical) to main. b) The designed invert level at the connection shall be no higher than the lowest calculated level consistent with these factors. DS 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 painted blue if the connection does not occur immediately. b) Where the inspection is to a property servicing multiple residential units then a surface accessible inspection chamber such as a manhole, rodding eye or other Council approved structure shall be installed. c) Each connection point shall be marked with a 50mm x 50mm timber stake painted blue which shall extend from the invert to a minimum of 300mm above finished ground level. A blue PVC marker tape shall be attached to the connection pipe, brought up and 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 Connection Destinations Where practicable and where connection is to be within 5m of a manhole, the connection shall be to the manhole. Page 24 Updated 01/07/2014