supporting document 1: sustainable stormwater technical ... · • all water quality devices must...

Shoalhaven Development Control Plan 2014

Chapter G2: Sustainable Stormwater Management and Erosion/Sediment Control Supporting Document 1: Sustainable Stormwater Technical Guidelines

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Supporting Document 1: Sustainable Stormwater Technical Guidelines

Contents

1 Introduction ................................................................................................................... 3

2 Stormwater ................................................................................................................... 3

2.1 Minor and Major Systems Design ........................................................................... 3

2.1.1 Concrete channels............................................................................................... 3

2.1.2 Low flow concrete channel or pipe in a grassed/vegetated flowpath ................... 3

2.1.3 Constructed earthen/rocked low flow channel in vegetated flowpath .................. 3

2.1.4 Inter-allotment drainage easements .................................................................... 3

2.1.5 Drainage easements (in-gross) ........................................................................... 4

2.1.6 Pipe size and materials ....................................................................................... 4

2.1.7 Surcharge pits ..................................................................................................... 4

2.1.8 Building near drains and drainage easements. ................................................... 4

2.2 Water Sensitive Urban Design ................................................................................ 5

2.2.1 MUSIC Modelling................................................................................................. 5

2.2.2 Vegetated Swale/buffer strip beside roads .......................................................... 6

2.2.3 Constructed wetlands/ponds/lakes ...................................................................... 6

2.2.4 Bioretention Devices ............................................................................................ 7

2.2.5 Constructed basins (normally dry) ....................................................................... 8

2.2.6 Gross Pollutant Traps .......................................................................................... 8

2.2.7 In-pit litter baskets ............................................................................................... 9

2.3 Handover of WSUD Assets to Council .................................................................... 9

2.4 Disposal of Stormwater from Development Sites.................................................. 10

2.4.1 Absorption Disposal System .............................................................................. 10

2.4.2 Porous or permeable paving ............................................................................. 14

2.5 Climate Change Controls ...................................................................................... 14

2.6 Onsite Stormwater Detention ................................................................................ 14

3 Stormwater Quality and Waterway Protection ............................................................ 15

3.1 Erosion and Sediment Control .............................................................................. 15

3.2 Stormwater Retention and Reuse ......................................................................... 15

3.2.1 Volume of Retention Storage ............................................................................ 15



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3.2.2 Rainwater tanks ................................................................................................. 15

3.3 Small/medium scale development – Site Discharge Index ................................... 33

3.4 Large scale development ...................................................................................... 35

3.4.1 Discharging to a natural stream ......................................................................... 35

3.5 Design and maintenance of stormwater treatment measures ............................... 35

4 Waterfront Land .......................................................................................................... 35

4.1 Development on waterfront land ........................................................................... 35

4.2 Coastal Areas ....................................................................................................... 35

5 References ................................................................................................................. 35

Figures Figure 1: Infiltration trench plan (source: Melbourne Water) .............................................. 12 Figure 2: Infiltration trench cross section (source: Melbourne Water) ................................ 13 Figure 3: Infiltration system inlet (source: Melbourne Water) ............................................. 13 Figure 4: Infiltration system outlet (source: Melbourne Water) ........................................... 13 Figure 5: Typical paving detail ........................................................................................... 14 Figure 6: Typical Tank Setup ............................................................................................. 18 Figure 7: Typical Top Up Systems for Above and Below Ground Tanks ........................... 19 Figure 8: Above Ground Tank Typical Arrangement .......................................................... 24 Figure 9: Below Ground Tank Typical Arrangement .......................................................... 24 Figure 10: First Flush Device and Absorption Pit Details ................................................... 25 Figure 11: Suggested Plumbing Configuration for Rainwater Tanks in Urban Areas with Reticulated Mains Supply with Indirect Connection Only Via Mains Water Top Up ........... 26 Figure 12: Suggested Plumbing Configurations for Rainwater Tanks with a Direct Connection to the Mains Water Supply (Examples A and B) ............................................. 28 Figure 13: Suggested Plumbing Configurations for Rainwater Tanks with an Air Gap and Direct Connection to the Mains Water Supply via a Pump Bypass (Examples C and D) ... 30 Tables Table 1: Monthly Evapotranspiration Data for Nowra .......................................................... 5



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1 Introduction

This document is a technical reference to provide:

• Background information on the purpose of the provisions in Chapter G2: Stormwater Management and Erosion/Sediment Control.

• Useful references to assist in compliance with the relevant provisions. • Example calculations and drawings.

Refer to the DCP Dictionary for definition of terms where available.

2 Stormwater

2.1 Minor and Major Systems Design

The following design requirements for minor and major drainage systems are considered appropriate to mitigate against an increased risk to life or safety of persons during a storm event.

2.1.1 Concrete channels

• The use of concrete channels is generally discouraged with grassed/vegetated channels being preferred.

• No walkways or open grassed areas should be provided adjacent to the channel. • Maximum velocity x depth product = 0.3m2/s. • Egress points to be provided where side slopes 1 in 6 or steeper. • Fencing required where access possible to channels with side slopes 1 in 4 or

steeper. Warning signs to be provided regarding potential inundation and flowing water.

2.1.2 Low flow concrete channel or pipe in a grassed/vegetated flowpath

• Maximum velocity x depth product = 0.3m2/s. • Maximum side slopes 1 in 5. • Warning signs to be provided regarding potential inundation and flowing water.

2.1.3 Constructed earthen/rocked low flow channel in vegetated flowpath

• Maximum velocity x depth product = 0.3m2/s. • Maximum side slopes 1 in 5. • Warning signs to be provided regarding potential inundation and flowing water. • Regular maintenance required to ensure performance of channel to transmit flows.

2.1.4 Inter-allotment drainage easements

• Inter-allotment drainage easement shall not be less than 1.0m wide.



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• Inter-allotment drainage easement shall be at least 1.5x (trench depth) + pipe diameter.

• All pipes shall be located at least 0.5m from the property boundaries. • Inter-allotment drainage easement must be arranged such that runoff from public

land, reserves, parks, roads, or any other public drainage is NOT drained via the easement.

• Inter-allotment drains and easements must NOT be extended into, nor discharge onto, public land, reserves, parks, etc, unless that land is classified as a ‘Drainage Reserve’ or Operational Land, where approved by Council.

• Council shall not be a benefited authority or party in the section 88B instrument. • Benefitted lots as prescribed in the 88B instrument shall undertake all installation,

maintenance and repair works.

2.1.5 Drainage easements (in-gross)

• Drainage easements shall not be less than 3.0m wide • Drainage easement width shall provide sufficient space to safely excavate and

replace the pipeline. • Width must contain 1% AEP flow plus 0.5m freeboard. • The burdened property owner shall undertake day-to-day maintenance of the

easement, including vegetation management.

2.1.6 Pipe size and materials

• Council stormwater drains & road drains: - Pipes must be min. 375mm diameter. - Pipes under roads or areas subject to vehicular traffic shall be RCP class 4 or

above. • Private Inter-allotment drains:

- Pipes in inter-allotment drain must be min. 150mm diameter. - UPVC, HDPE, Polypropylene and RCP (class 2 or above) pipes are acceptable.

2.1.7 Surcharge pits

• Surcharge arrangements must be avoided. • Positive drainage must be provided into WSUD devices, SQIDs, Swales, Ponds or

Basins. • Surcharge pits with low-flow outlets is not an acceptable alternative.

2.1.8 Building near drains and drainage easements.

• Council will not permit building within/over/through a drainage easement. • No structure (above or below ground) is permitted within 1200mm of the outside

face of pipe. • Footing any structure is not to be founded within the ‘zone of influence’ of pipe



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• Pile footings to be socketed at least 150mm below bottom of trench/zone of influence

• The building and its foundations are to be designed in such a way that no building loads are transmitted to pipe and where possible, and that the pipe can be repaired or replaced at any time without affecting the stability of the building.

• Displacement piles or shoring will not be permitted within 5 metres of pipe • Screw piles will be permitted no closer than 2.0m to a pipe.

2.2 Water Sensitive Urban Design

2.2.1 MUSIC Modelling

• MUSIC modelling shall be undertaken in accordance with the latest version of the NSW MUSIC Modelling Guidelines (prepared for the Sydney Metropolitan CMA). Rainfall-runoff parameters and pollutant generation parameters shall be obtained from the NSW MUSIC Modelling Guidelines.

• The rainfall data from Station 068076 Nowra RAN AWS shall be utilised for MUSIC modelling in the Shoalhaven LGA outside of the Sydney drinking water catchment area at a 6 min timestep. Data for the 1965 to 1975 period shall be adopted for MUSIC modelling. The data for this period is relatively complete and has a mean annual rainfall that is representative of the long term mean annual rainfall record at this rainfall station. Depending on the location of the development within the Shoalhaven LGA, an alternative rainfall data set may be used if approved by Council. The monthly potential evapotranspiration (PET) values for the Shoalhaven LGA are shown in Table 1. Table 1: Monthly Evapotranspiration Data for Nowra

Month J F M A M J J A S O N D

PET (mm)

151.7 112.6 103.9 85.4 79.5 54.8 74.8 87.1 115.1 141.0 141.3 154.4

• All MUSIC simulations shall be run with a Stochastically generated pollutant export estimation method.

• All water quality devices must be positioned outside the 1% Annual Exceedance Probability (AEP) flood inundation extent unless a lower flood extent level of service is approved by Council.

• The TSS, TP and TN removal efficiency of trash racks must be assumed to be zero. The removal efficiency for CDS-type GPT devices shall be obtained from the manufacturer and be independently tested. The maximum TP and TN removal efficiency for CDS-type GPT devices must be 30% and 0% respectively.

• For large scale development that discharges into an area of significant biodiversity value, the post-development residual pollutant concentrations must not exceed the



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ecological trigger values listed in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality. This requirement is in addition to complying with the pollutant load reduction targets.

2.2.2 Vegetated Swale/buffer strip beside roads

• Not suitable for roadside areas where car parking is anticipated. • Roadside swales are not supported in developments with lot areas less than

4,000m2. • Side slopes 1 in 8 preferred, 1 in 5 maximum. • Minimum longitudinal grade of 1% and maximum longitudinal grade of 5% typically. • Maximum velocity x depth product 0.3m2/s. • Where grass swales are provided beside roadways property access must traverse

the swale, with means of crossing the flowpath (e.g. culvert, bridge or dish crossing (depending on depth of swale)) needing to be maintained. If responsibility for maintenance rests with property owner, this must clearly be defined in property records (e.g. s10.7 Planning Certificates, s88B instruments).

• Regular maintenance required to ensure performance of swale to transmit flows.

2.2.3 Constructed wetlands/ponds/lakes

• Constructed wetlands/ponds/lakes must be located in a treatment train approach immediately downstream of a sediment basin/forebay that is offline from the stormwater network to allow flows exceeding an approximately 1 Exceedances per Year (EY) event to bypass the treatment devices. The treatment train approach is required to remove gross pollutants/litter and coarse sediment within a primary stormwater treatment device prior to stormwater flows entering the secondary constructed wetland/ponds/lake secondary stormwater treatment device.

• The allowable extended detention depth for constructed wetlands varies between 0.25m to 0.5m.

• Water quality ponds shall have a permanent pool depth of 1m to 2m and an extended detention depth between 0.25m to 1m.

• Constructed wetlands shall be designed with a notional detention time of 72 hours unless a lower value is approved by Council. The absolute minimum notional detention time shall be 48 hours.

• Constructed wetlands and ponds/lakes shall have a minimum length to width ratio of approximately 10L:1W and 3L:1W respectively. All inflows must enter at the upstream end of the device to ensure flows pass through the full length of the treatment device.

• Land must be retained around the pond to allow Council to conduct maintenance activities (e.g. remove silt and unwanted vegetation). A minimum 5m average width buffer around these treatment devices are required for access and landscaping.



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• Edges of the wetland/pond should be planted with plants at a density to discourage entry into the water. All surfaces with a grade of 1 in 3 or steeper must be planted and fenced off.

• Constructed wetlands must be designed in accordance with the latest version of the Melbourne Water Wetland Design Manual or a demonstrated and approved equivalent.

• Batter slopes at side of wetlands/ponds are to be a maximum of 1 in 8. Where this is not possible the areas where the slope is steeper than 1 in 8 should be fenced off with a childproof fence or other suitable barrier.

• A concrete maintenance access pad must be provided into the pond/basin. Gate must be provided if the pond is fenced.

• The access pad must be connected to the nearest serviceable road via a concrete driveway.

• Pathways should not be provided immediately adjacent to pond edges.

2.2.4 Bioretention Devices

• Bioretention devices must be located in a treatment train approach immediately downstream of a sediment basin/forebay that is offline from the stormwater network to allow flows exceeding an approximately 4 EY to 1 EY event to bypass the treatment devices. The treatment train approach is required to remove gross pollutants / litter and coarse sediment within a primary stormwater treatment device prior to stormwater flows entering the secondary bioretention stormwater treatment device.

• An extended detention depth up to 0.3m is permitted for bioretention devices. • Some limited stormwater detention of up to 0.3m provided above the water quality

extended detention depth is permitted provided the inflow to the basin has been configured to ensure that the filter media and plantings are not damaged from scour. The maximum duration of ponding within a bioretention device must be 24 hours.

• Bioretention devices must be designed in accordance with the latest version of the Adoption Guidelines for Biofiltration Systems (CRC for Water Sensitive Cities) and Facility for Advancing Water Biofiltration (FAWB) Guidelines. Where there is an inconsistency between these documents, the ‘Adoption Guidelines for Stormwater Biofiltration Systems’ guidelines will prevail. The filter media depth and saturated hydraulic conductivity must be in accordance with these guidelines. The saturated hydraulic conductivity must be between 100 and 300mm/hour, with a 100mm/hour value adopted for design in MUSIC.

• Street-scale bioretention devices (rain gardens) are not supported in public road reserves.

• Water sensitive urban design (WSUD) measures located on private property are typically required to have a positive covenant and restriction on the use of land under Section 88B of the Conveyancing Act 1919 to ensure the ongoing future maintenance of privately owned water quality devices. The positive covenant and



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Restriction on use the land under Section 88B shall reference the Council approved operations and maintenance manual for bioretention or alternative devices.

2.2.5 Constructed basins (normally dry)

• Outlet structure must incorporate measures to prevent persons being trapped at the outlet by water pressure.

• Side slopes steeper than 1 in 6 should be fenced off with a childproof fence or other suitable barrier. All surfaces with a grade of 1 in 3 or steeper must be planted and fenced off.

• Water depth indicators should be provided. • Signage should be provided at spillway to identify specific hazards. • Maximum depth of water when operating at design capacity:

- Car park: 150mm - Other paved area: 200mm - Landscaped area: 600mm - Sporting field: 600mm - Area enclosed by a childproof fence or otherwise not accessible: no limit. - Refuge mounds are to be provide when design water depths exceed these

values. • A concrete access pad must be provided in order to allow for maintenance vehicle

to access the basin.

2.2.6 Gross Pollutant Traps

• A means to capture gross pollutants/litter must be provided within a treatment train immediately upstream of all stormwater treatment devices.

• Trash racks are preferred over proprietary GPT devices. Trash racks shall have a graduated offline design to prevent captured gross pollutants/litter overtopping trash rack screens.

• Unless approved otherwise, non-proprietary GPTs and sedimentation ponds/basins must be used in lieu of proprietary GPTs where possible. Where proprietary GPTs are approved, it must be demonstrated that the device can achieve the desired treatment performance, where the maintenance costs are less than that of an equivalent conventional device, where no specialist equipment is required to carry out maintenance activities and where major consumable parts e.g. filters and cartridges are not required to be purchased by Council on a regular basis. Where a proprietary GPT is supported by Council, the developer must provide documentation from the supplier providing evidence that the proposed device has been appropriately sized for the contributing catchment.

• Proprietary GPTs should have removable baskets. Captured gross pollutants should be removable by a Hiab or similar equipment.



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• A trash rack can be incorporated into the sediment basin inlet structure provided the invert of the trash rack is above the permanent water level of the pond.

• The structure should incorporate means to fend persons away from the outlet and out of the water flow area (inclined screens / racks).

• The structure should incorporate means for access sufficient for maintenance requirements. This may include access for mechanical equipment for large facilities or lifting equipment for smaller facilities incorporating bags or baskets. A maintenance plan shall be provided to Council by the developer detailing regular inspection and maintenance requirements.

• A concrete access pad must be provided in order to allow maintenance access with connection to the nearest serviceable road via a concrete driveway suitable for the required service vehicle.

• A sufficient area for drying of wet sediments must be provided. • Where proprietary GPTs are approved, a single large GPT is desirable over multiple

smaller GPTs. Where proposed, it must be demonstrated that the use of multiple GPTs cannot be avoided.

• Trash racks are required on outlets at sufficient spacing to prevent public access. • Flowrate and hydraulic loss must be calculated for GPTs based on a ‘full’ sediment

storage zone. • Access lids must be lockable ‘heel proof’ grates. Class of lid must suit location and

traffic loading.

2.2.7 In-pit litter baskets

• In-pit type litter baskets are not permitted in Council’s stormwater network or road drainage.

• Litter baskets may be used within a site drainage network in a private property where a maintenance plan is provided and approved by Council. The adopted removal efficiency of litter baskets to be used in MUSIC shall be assumed to be zero for Total Suspended Solids, Total Phosphorus and Total Nitrogen.

2.3 Handover of WSUD Assets to Council

The following conditions are required to be met for WSUD devices to be handed over to Council:

• A pre-lodgement meeting to be arranged with Council Development Advisory Unit to discuss the proposed water quality strategy.

• An operations and maintenance manual has been provided to Council, which includes the estimated annual maintenance costs for all water quality devices.



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2.4 Disposal of Stormwater from Development Sites

To assist smaller developments, information on a range of stormwater management measures that can be implemented at a residential scale to retain stormwater on site is provided below.

2.4.1 Absorption Disposal System

Where site gradients do not allow for street gutter disposal or disposal via an inter- allotment easement (i.e. older residential subdivisions), generally all roof stormwater must be conveyed to a minimum 5000-litre capacity rainwater tank to restrict the flow of sediment to the absorption disposal system and retard flow. Alternative methods may be considered on a case by case basis. The tank overflow must then be connected to an absorption disposal system. The area downstream must be grassed and vegetated in a manner that will ensure a reduction in subsurface flows into the adjoining properties. For subdivisions, proposals to use onsite absorption shall be submitted with the Development Application and must be accompanied with supporting geotechnical advice regarding the suitability of the soil conditions for the proposal. A rainwater tank may not be applicable for minor structures in consultation with Council. Situations where absorption disposal systems cannot be used without further engineering advice Absorption disposal systems must not be used on land where the following conditions exist:

• Slope instability.

• Loose sand.

• Clay soils that collapse in contact with water.

• Soils with hydraulic conductivity of less than 0.36mm/hr.

• Contaminated soil and/or groundwater. In relation to medium and reactive clay soils, the following parameters are required:

• Medium clay 36-3.6 mm/hr.

• Reactive clay 3.6-0.036 mm/hr. Concessions with acceptable engineering advice Council may permit absorption disposal systems in soils with a hydraulic conductivity of less than 0.36 mm/hr, slopes greater than 15% or extensively paved areas provided that the design of the absorption disposal system is prepared by a suitably qualified and experienced engineers and submitted with a development application and include an assessment of the



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infiltration of the soil profile, consideration of antecedent moisture conditions and performance over a variety of rainfall events. The design must also be supported by a report from a practicing geotechnical engineer with local knowledge attesting to the suitability of the site for the system, absorption capacity of the system demonstrating that there will be no adverse impacts on the subject land/buildings, adjoining and/or downstream properties by the redirection or concentration of stormwater.

Design Absorption disposal systems may be one of two types:

• Absorption trenches: - Trenches must be fully lined with geotextile fabric - A 30mm diameter course gravel is to be used. Gravel is typically used to fill

the trench and is to be clean and washed prior to use and free of fines. Use of recycled concrete or bricks is not permitted. All gravel must be inert and be of high compressive strength.

- Gravel is to be topped with a 300mm soil and grass layer for aesthetics that restrict the entry of silt to the system via a geotextile underlay.

- The connection into the absorption trench from the rainwater tank must be via a 90mm diameter inflow pipe passing through a 250mm diameter covered PVC inspection trap to a 90mm perforated distribution pipe allowing stormwater to percolate to the gravel.

- The base of the trench must not exceed a slope of 3%. - A covenant or restriction as to use notice must be placed over the trench so

that it shall remain in place and in use.

• Infiltration cells - These are modular plastic systems that can be used in an absorption trench instead of gravel fill:

- Infiltration cells must be fully lined with geotextile fabric. - A 300mm diameter of sand or loam is to be used. - These systems must be installed in accordance with the manufacturers

recommendations. This particularly relates to the required volume which is dependent on-site soil conditions.

- Details must be submitted to Council with a development application. - The connection into the infiltration cells from the rainwater tank must be via a

90mm diameter distribution pipe allowing stormwater to fill the cells. - The base of the trench must not exceed a slope of 3%. - A covenant or restriction as to use notice must be placed over the trench so

that it shall remain in place and in use.



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Notes:

• All plumbing within the site must be carried out in accordance with Australian Standard AS/NZS3500.3.2015 Plumbing and Drainage – Stormwater Drainage.

• All stormwater disposals must not result in diversion of surface water being concentrated onto adjoining property above or below ground.

Storage Capacity Guide

Absorption disposal systems must be designed with sufficient capacity to store the inflow of a one in three-month average recurrence interval design storm, with an emptying time of less than 24 hours. Location and siting

Absorption disposal systems must:

• Be sited across the gradient of the site and may be used in series i.e. 2 x 3m2 in place of 1 x 6m2

• Be located a minimum three metres from the allotment boundaries and at least five metres away from all buildings.

• Not be placed under any paved surfaces and must be at least one metre away from pavements subject to vehicle traffic.

• Not to require excavation beneath the drip-line of any trees to be retained unless approved by a qualified arborist certifying that such excavation will not affect the longevity of the subject tree(s). Any trees proposed to be removed must be shown on the construction certificate plans and include signed documentation from an arborist certifying the tree(s) would not survive.

Figure 1: Infiltration trench plan (source: Melbourne Water)



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Figure 2: Infiltration trench cross section (source: Melbourne Water)

Figure 3: Infiltration system inlet (source: Melbourne Water)

Figure 4: Infiltration system outlet (source: Melbourne Water)



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2.4.2 Porous or permeable paving

Permeable paving may be used to reduce the impervious area of the proposed development in certain circumstances. For example, low use visitor/overflow parking spaces which are constructed from permeable paving will not fully contribute to the total impervious area on a site. It can be assumed that 50% of porous or permeable paving surfaces are pervious and therefore only 50% of these surfaces will contribute to the total impervious area on a site. All pavers are to be laid in accordance with manufacturers recommendations. A typical paving detail is provided at Figure 5; however, advice may be required from a builder or engineer. Porous or permeable pavements on public roads will not be permitted.

Figure 5: Typical paving detail

2.5 Climate Change Controls

• No supporting guidelines.

2.6 Onsite Stormwater Detention

• No supporting guidelines.



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3 Stormwater Quality and Waterway Protection

3.1 Erosion and Sediment Control

Refer to the “Blue Book” as follows or as amended: • Managing Urban Stormwater: Soils and Construction Volume 1 (Landcom 2004) (Blue

Book Vol. 1) • Managing Urban Stormwater: Soils and Construction Volume 2 (DECCW, 2008) (Blue

Book Vol. 2) • Supporting Document 2: Planning for Erosion and Sediment Control on Single

Residential Allotments Guideline (Landcom 2004).

3.2 Stormwater Retention and Reuse

In order to encourage water conservation in non-residential buildings and other areas where BASIX does not apply, a range of additional measures may be considered including (but not exclusively):

• Water efficient fittings and appliances.

• Rainwater tanks for non-residential developments.

• Reduction in water use in public open space.

3.2.1 Volume of Retention Storage

Scenario: A new single residential dwelling is proposed consisting of a 250m2 roof and 100m2 of paved landscape area. A total of 350m2 of impervious surface is added. The development is a single dwelling, therefore the storage depth (refer to Table 2 in Chapter G2) is 10mm (0.01m).

Retention storage = impervious surface x storage depth Retention storage = 350m2 x 0.01m = 3.5m3

Therefore, a minimum of 3.5m3 of retention storage must be provided for impervious surfaces on the site, either as a rainwater tank, or as volume in an infiltration trench, or combination.

3.2.2 Rainwater tanks

Rainwater tanks can be used as retention volume. If you do decide to use a tank, then you need to decide what you want to use the rainwater for. Rainwater is often softer and



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less salty than potable water and a range of filters easily available today can ensure that rainwater will not stain your toilet or laundry. If you do decide to use a tank, then you also need to decide how large to make it. Use of Non-Potable Water From Rainwater Tanks The NSW State Government, through the Committee on Uniformity of Plumbing and Drainage Regulations in NSW has issued the following advice regarding rainwater use in areas with a reticulated water supply, and should be considered when installing a rainwater tank:

“A rainwater collection system can provide water for a number of uses including the following:

• Toilet/urinal flushing; • Clothes washing machines; • Hot water systems; • Garden irrigation; • Car washing and similar outdoor use; • Filling ornamental ponds; • Filling of swimming pools and spas; • Fire fighting (subject to the requirements of AS 2419.1, 2118 and 2441).

Some consumers in single domestic premises may also wish to use rainwater for all domestic purposes including drinking, cooking and bathing. Should consumers wish to use rainwater for all domestic purposes, it is particularly important to consider the advice in NSW Health Guideline GL2007_009 of June 2007, which in part states:

“A properly maintained rainwater tank can provide good quality drinking water. NSW Health strongly advises householders, councils and developers to ensure that an adequate system of cleaning and maintenance is in place where rainwater is used for drinking. People who choose to use rainwater for drinking and cooking should be aware of potential risks associated with microbiological and chemical contamination. Rainwater tanks in urban areas can be contaminated with air borne contaminants from heavy traffic, smelters and heavy industry. Rainwater tanks can also be contaminated from roof or plumbing materials or with bacteria from bird or animal droppings. In urban areas, NSW Health recommends that people use the public water supply for drinking and cooking because it is filtered, disinfected and generally fluoridated. The quality of public water supplies is regularly monitored. Premises that serve the public or employees and use rainwater for drinking and/or cooking should comply with NSW Health’s Private Water Supply Guidelines.”



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Requirements of Design

• All tank construction is required to comply with relevant Australian/New Zealand Standards that apply to tanks and their associated fixtures and fittings:

- AS 2070 - 1999, "Plastics materials for food container use". - AS/NZS 2179-1994, "Specifications for rainwater goods, accessories and

fasteners". AS 3500.1-2003, "National plumbing and drainage - Water Supply".

- AS 3500.3-1998, ―National plumbing and drainage – Stormwater drainage - AS 3855-1994, "Suitability of plumbing and water distribution systems

products for contact with potable water". - AS 4020 - 2005, "Testing of products for use in contact with drinking water".

HB 230 – 2006, ―Rainwater Tank Design and Installation Handbook‖. - NSW Code of Practice for Plumbing and Drainage 3rd Edition 2006

• Rainwater tanks are available in a range of suitable materials including galvanised, aquaplate or zincalume steel; fibreglass; plastic; and concrete.

• For new developments, tank capacity is to be as determined by BASIX or any other water conservation/stormwater management policy that applies to the development. For relocatable homes that are to be installed on land other than a caravan park, given BASIX does not apply to these dwellings, a minimum 10kL tank is required to be installed and connected to, at a minimum, all toilets, washing machines and external taps.

- For retrofitting of tanks on existing buildings, the property owner should select the most appropriate tank size based on the anticipated use of the tank, roof area and space available.

- Advice on appropriate tank sizes can be found in HB 230-2006 – Rainwater Tank Design and Installation Handbook.

• All tanks and associated structures, including stands, shall be installed in accordance with manufacturers/designer’s specifications and are required to act independently of all other structures. Tanks and associated structures shall not rest on footings of buildings or rely on walls (including retaining walls) for support unless integrated with the building design and approved by a structural engineer. Council may require certification from a structural engineer of the stability of a tank.

Tank set-up

• The tank is to be enclosed and inlets screened, so as to prevent the entry of foreign matter and to prevent mosquito breeding.

• Tanks being used to provide internal supply must ensure a reliable back up supply for the connected fixtures is available from the mains water system. This should be done by one of the following ways:



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- With an indirect connection via an automatic mains water top up. - With a direct connection via an automatic mains water/rain water diversion

valve. - With a dual feed system to toilets and/or washing machines.

• The tank capacity is to include: - A minimum storage volume; - A rainwater storage volume; and - An airspace for additional stormwater management (See Figure 6).

Figure 6: Typical Tank Setup

• For a mains water top up system, the minimum storage volume is to be supplied by mains water. Mains top up should not occur until the tank is at least 80% empty. The minimum storage volume to be provided should consider the intended use of the tank water and maximum anticipated tank demand and the top up rate (refer Clause 3.6) to ensure reliability of supply and pump protection.

• The mains top up is to be restricted to an indirect connection. The indirect connection shall be by means of a visible "Air Gap", in accordance with the provisions of the National Plumbing Code, AS/NZS 3500 Part 1 2003 - Minimum Air Gap Requirements (see Figure 7).



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Figure 7: Typical Top Up Systems for Above and Below Ground Tanks

• The maximum size of a potable water supply pipe used for "topping up" shall be 20mm diameter and requires a flow restrictor. For single residential developments, the flow rate should be restricted to, if possible, 2 litres per minute. If this is not possible, flow rates of 4 or 6 litres per minute will be permitted.

• For new dual occupancy or multi occupancy developments where the tank services more than one dwelling, the flow rate should be restricted to a maximum of 2 litres/minute times the total number of dwellings connected to the development.

- Ensuring reliability of supply and pump protection through selection of appropriate minimum storage volume, top up rate and use of water from the



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tank if choosing to install tanks smaller than 10kL or for uses greater than those recommended in Clause 1 of this document are the responsibility of the owner. Guidance on the selection of appropriate minimum storage volumes, tank sizes and top up rates in these instances is provided below.

• Automatic three-way diversion valves/bypass systems shall have WaterMark certification in accordance with the Standards listed in AS 5200.000 or authorisation under the Plumbing Code of Australia.

Calculating appropriate minimum storage volumes (and tank sizes) and top-up rates for tank retrofits or tanks with high water demand The following table and example calculation are provided to be used as a guide only to assist in determining household rainwater demand and therefore appropriate tank sizes and minimum storage volumes and top up rates required in small rainwater tanks and/or tanks with high water demand during dry periods. Note that it is a guide only, and excessive use of water or faulty/leaky fixtures and appliances can still lead to a tank running dry, therefore causing pump damage. It is the responsibility of the tank/property owner to ensure the reliability of supply and pump protection at all times.

Typical water use of various household fixtures and appliances

Household Fixture/Appliance Average Typical Water Use

Single flush toilet 11 litres/flush

Dual flush toilet 4 litres/flush

Old top loading or inefficient 1 to 2 star rated washing machine

180 litres/load

4 star or higher rated washing machine

70 litres/load

Garden tap 17 litres/minute (1000 litres/hour)

Shower – non-efficient 20 litres/minute

Shower – 3 star rated water efficient 9 litres/minute

Internal taps (kitchen and bathroom) 17 litres/minute

Dishwasher – old 50 litres/load

Dishwasher – new 1 to 3 star rated water efficient

18 litres/load

Dishwasher – new 4 to 5 star rated water efficient

11 litres/load



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There are two ways to calculate appropriate minimum storage volumes (and tank sizes) and top-up rates to ensure reliability of supply during dry periods.

1. The first is to determine the maximum anticipated possible demand over a short period (ie if all internal uses from the tank were to be used while maximum external use was occurring) and ensuring the tank supply from the minimum storage volume and the top-up system during this period is adequate.

2. The second (and safest) is to determine the total anticipated maximum daily water demand from the tank and ensure that the minimum storage volume is equal or greater to the demand, thereby making the top-up rate inconsequential. Example calculations are provided below.

Scenario 1: A 3,000 litre tank is intended to be connected for garden watering and toilet use only. A 20% minimum storage volume is desired, giving a minimum storage volume of 600 litres (0.2 * 3,000). The highest anticipated water demand from the tank over a short period is as follows:

• The property only has a small lawn and vegetable garden and requires no more than 30 minutes watering a day during dry periods from one tap = water use of 500 litres.

• Three people live in the house, and it has two single flush toilets, with a maximum expected flush rate of 6 flushes per hour = water use of 66 litres.

Therefore, assuming these were both to occur at the same time, the total worst-case water demand from the tank for any period would be 566 litres over that particular hour that garden watering and toilet flushing were both occurring, which is less than the 600 litre minimum storage volume. Therefore, even during dry periods, the minimum storage volume (and tank size) chosen would easily be adequate to ensure reliability of supply from the tank during peak demand, regardless of the top-up rate. This is provided the minimum storage volume was full at the start of this period and no extensive demand was placed on the tank (by garden watering or leaks) until the tank had completed the top-up process.



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Scenario 2: For the same size tank and house, the tank is also connected to a top loading washing machine, and it is also anticipated a higher external use of 2 taps at 20 minutes each. The highest anticipated water demand from the tank over the same short period is as follows:

• 680 litres for garden watering. • 66 litres for toilet flushing. • 2 loads of washing over an hour = 360 litres.

Therefore, assuming these were all to occur at the same time, the total worst-case water demand from the tank would be 1,106 litres over that particular hour. During dry periods with the minimum storage volume full, in one hour, the tank has the capacity to provide the minimum storage volume plus the top-up water provided during that period i.e. 600 litres + (2 litres/minute * 60 minutes) = 720 litres. Therefore, unless household habits were changed, and washing was not done whilst watering the garden, the tank is likely to run dry. Therefore, a higher top-up rate or minimum storage volume (and therefore tank size) should be used. For example, to provide 1,200 litres in an hour, the same tank would need a top-up rate of 10 litres/minute i.e. 600 litres + (10 litres/minute * 60 minutes) = 1,200 litres. Alternatively, a 5,000 litre tank could be used, with a minimum storage volume of 1,000 litres, and a top-up rate of 3 litres/minute, would give 1000 litres + (3 litres/minutes * 60 minutes) = 1,180 litres. Therefore, even during dry periods, the 2nd two options would be adequate to ensure reliability of supply from the tank. This is provided the minimum storage volume was full at the start of this period and no extensive demand was placed on the tank (by garden watering, clothes washing or leaks) until the tank had completed the top-up process. A summary of the results of this calculation is as follows:

Maximum Anticipated Tank Demand

Maximum Tank Supply During Dry Periods 3,000 litre tank with 2 L/min top up rate

3,000 litre tank with 10 L/min top up rate

5,000 litre tank with 3 L/min top up rate

1,106 litre/hour 720 litres 1,200 litres

1,180 litres



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Alternatively, the safest way to ensure complete reliability is to ensure that the minimum storage volume is equal to or greater than the total anticipated daily demand from the tank. The total daily demand could be calculated as follows:

• 680 litres for garden watering. • Assume 6 flushes per person per day = 198 litres. • 2 loads of washing = 360 litres.

Therefore, the total water demand from the tank would be 1,238 litres/day. Therefore, a minimum storage volume of approximately 1,300 litres would be adequate to ensure reliability of supply, regardless of the top-up rate. Therefore, a minimum tank size of 6,500 litres would be needed.

Inlet Pipes

• Water from roof areas only is to be directed to the system. The proportion of roof area directed into tanks for new buildings is to be in accordance with BASIX requirements or any other planning or building control that applies to the development. For relocatable homes that are to be installed on land other than a caravan park, given BASIX does not apply to these dwellings, then a minimum of 90% of the roof area of the home and all associated structures is to be captured and directed into the tank. For retrofitting of tanks on existing buildings, as much of the roof area as possible should be captured. Wherever possible all sections of inlet pipe should flow into the top of the tank. If it is necessary to include rising sections, the design will require a method of bleeding off trapped water (see item B figure 3) to prevent the formation of stagnant water in pipes between storm events. In systems with rising sections, pipework from downpipe to tank is to be a minimum of 100mm diameter class 12 and be capable of resisting pressure heads imposed by the system. Where one or more downpipes enter a main line, the main line is to be increased to a minimum 100mm diameter, unless otherwise specified by a hydraulic engineer as resisting pressure heads imposed by the system. An approved proprietary screened downpipe rainhead device (e.g. Leaf Eater or similar) shall be installed on each downpipe. Recommended screen mesh to be 4 to 6mm and designed to be self-cleaning. Figures 8 and 9 show typical arrangements and requirements of inlet piping for above and below ground tanks.



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Figure 8: Above Ground Tank Typical Arrangement

Figure 9: Below Ground Tank Typical Arrangement

• Inflow to the rainwater reuse tanks is to include the provision of a first flush device with a capacity of 0.2 litres per square meter (20L/100m2) of roof area. The outlet of the first flush device is to be directed to a landscaped area via an irrigator hose and drip irrigator or an absorption pit, which are to be located a minimum of 2 metres from any buildings, tanks or property boundaries. The first flush device must be accessible for routine maintenance and cleaning purposes.



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The basic design features and required sizes of a floating ball first flush system and absorption pit are shown in Figure 10.

Figure 10: First Flush Device and Absorption Pit Details

Overflow Water

• Overflow pipes from tanks shall be 100mm minimum diameter and designed in accordance with AS3500.1 2003. Tanks with 90mm diameter outlets can be modified with uni seal rubber grommets. The outlet should divert excess water away from tank foundations, buildings or other structures. Provisions should be



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included for vector proofing. This can be done with a flap if 100mm gauze is not available. Wherever possible, the overflow is to be piped to the kerb and gutter by gravity feed. Where this is not possible, a plan prepared by a suitably qualified person, detailing an alternative treatment method, is to be submitted to Council for consideration.

• For below ground tanks, the tank overflow must discharge to a surcharge pit prior to the nominated discharge point. The top of this surcharge pit must be a minimum of 150mm below the invert of the tank overflow outlet pipe. If this cannot be achieved, a reflux valve is to be installed as close to the tank as possible, and a rainhead device or similar is to be installed on each downpipe to avoid surcharge into roof gutters.

• For retrofitting tanks on existing buildings, overflow from the tank is to be directed into the existing stormwater disposal system, unless otherwise approved by Council.

Reticulation

• The conceptual layout for the arrangement of pipework and ancillary devices from the water meter and the rainwater tank to the dwelling for rainwater tank systems with a mains water top-up or automatic diversion valve are depicted in Figures 11-13. For information on dual feed systems, see AS/NZS 3500.1:2003 Figure 14.1.

Figure 11: Suggested Plumbing Configuration for Rainwater Tanks in Urban Areas with Reticulated Mains

Supply with Indirect Connection Only Via Mains Water Top Up



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Figure 12: Suggested Plumbing Configurations for Rainwater Tanks with a Direct Connection to the Mains Water

Supply (Examples A and B)



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Figure 13: Suggested Plumbing Configurations for Rainwater Tanks with an Air Gap and Direct Connection to the Mains Water Supply via a Pump Bypass (Examples C and D)

Backflow Prevention

• Backflow prevention is required to prevent cross contamination and to protect the Council mains water supply. Details of required backflow prevention is to be in accordance with the NSW Code of Practice for Plumbing and Drainage.

• For systems that have an indirect connection with the mains supply via a mains water top-up only (Figure 11), a dual check valve and strainer are required at the property boundary (containment protection) for all tank installations. For above ground tanks, provided the water meter at the property boundary has a dual check valve, no further backflow prevention is required. For below ground tanks, a further



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dual check valve and strainer must be provided on the topup system (see Figure 7).

• Systems that have a direct connection with the mains water supply (Figures 12 - 13) require containment protection (at the property boundary water meter) and zone protection (at the connection point of rainwater and mains water supply). The level of protection required is dependent on whether the tank is above ground or below ground. All tanks require, at a minimum, a non-testable dual check valve for zone protection. For containment protection, above ground tanks require a dual check valve, whilst tanks that are either fully or partially buried require a non-testable vented dual check valve at the water meter.

• A dual check valve and strainer may already be fitted as part of the water meter. For properties with 20 or 25mm meters that don’t already have a dual check valve, where one is required, Council will replace the meter free of charge. Any backflow prevention required for containment protection beyond a dual check valve, including a vented dual check valve, must be installed on the property side of the meter at the cost of the property owner. Any backflow prevention required for containment protection for properties with water meters 32mm or above must be installed on the property side of the meter, at the cost of the property owner. All backflow prevention required for zone protection must be installed at the cost of the property owner.

• If testable backflow prevention devices are used, they shall be fitted, maintained and tested in accordance with AS/NZS 3500.1:2003 Section 4 at the cost of the property owner. All testable backflow prevention devices must be registered with Council.

Pumps

• Pumps must not create a noise problem and must be housed so that they cannot be heard in a habitable room of any other residence.

• A habitable room means any room other than a garage, storage area, bathroom, laundry, toilet or pantry in a dwelling, whether or not the windows or doors are open or closed. Approved systems are obligated to meet the requirements of the Protection of Environmental Operations (Noise Control) Regulation 2000.

New Dwellings

• Approval of a Development Application (DA) for a dwelling will require information to be lodged for the installation of a rainwater tank. In assessing the suitability of an installation, Council will take into account aesthetic considerations with regard to location, material of construction, and colour scheme. It is suggested that colour schemes should be compatible with that of the main dwelling or trim.

Existing Dwellings



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• For retrofitting rainwater tanks on existing dwellings, a development application is not required provided the proposed rainwater tank satisfies the criteria for Exempt Development as set out in State Environmental Planning Policy (Exempt and Complying Development Codes) 2008.

• For installations where the tank is connected to internal uses such as toilets or washing machines or requires an indirect or direct connection with the mains supply, a permit application for plumbing and drainage works for the tank installation, and a schematic plan showing all the details of the proposed tank installation, must be submitted to Council before installation can begin. A Works as Executed schematic plan and tank detail, are to be submitted on completion of the installation and must show the tank location, stormwater drainage and non-potable cold water reticulation to the building and tank

Construction standards

• All works are required to comply with the Building Code of Australia and relevant Australian Standards. It should be noted that installations in bushfire prone areas are required to comply with AS3959.

• All electrical work is to be carried out by a licensed electrician.

• All plumbing work is to be carried out by a licensed plumber.

• Installation and materials shall be in accordance with AS/NZS 3500.

• Marking and labelling of rainwater services shall be in accordance with the following: - Above ground distribution pipes shall be continuously marked

―RAINWATER‖ in accordance with AS1345. Alternatively, pipes can be clearly labelled ―RAINWATER‖ with adhesive pipe markers made in accordance with AS1345.

- Below ground rainwater pipes shall be continuously marked ―RAINWATER‖ in accordance with AS1345. Alternatively, identification tape/pipe sleeve continuously marked ―RAINWATER‖ made in accordance with AS2648 can be used.

- Every rainwater tank outlet and all taps, valves and rainwater tank apertures shall be identified as ―RAINWATER‖ with a sign complying with AS1319 or a green coloured indicator with the letters ―RW‖. Alternatively, a permanent sign, at the front of the premises and visible to all visitors, may be displayed advising that rainwater is in use.

- Identification tape marked ―RAINWATER‖ shall be at least 75mm wide. The identification tape shall be installed on top of the rainwater pipeline installed within the trench, running longitudinally, and fastened to the pipe at not more than three metre intervals.

- Separation between above ground rainwater services and any parallel potable water supply must be a minimum of 100mm.



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- Below ground rainwater services must be separated by a minimum of 300mm from any parallel potable water supply pipe.

• Work as executed drawings are to be submitted to Council upon completion and will form part of Council’s documentation process for the registration of rainwater tank systems. The drawings and must show the tank location, stormwater drainage and non-potable cold water reticulation to the building and tank

Maintenance Requirements

• In order to ensure consistent water quality and reliability of supply, it is essential for regular maintenance to be carried out. Maintenance and operation of a rainwater tank and all associated infrastructure such as downpipes, roof and roof gutters, first flush devices, top-up systems and pumps, and the quality of the water supplied from a tank, are the responsibility of the owner, not Council. The primary focus of maintenance procedures should be to keep all components clean and to minimise the risk of contamination/rubbish either entering or remaining in rainwater tanks. A maintenance program should consider the rainwater catchment (roof area and gutters), downpipes, inlet screens and first flush/bypass devices, tank structure, tank desludging and tank cleaning. Particular care with monitoring and maintenance is needed if intending to drink water supplied from a rainwater tank.

• Recommended monitoring and maintenance procedures and schedules and preventative measures and corrective actions are attached in Appendix 4. Routine monitoring and maintenance should be undertaken by the property owner in accordance with this maintenance schedule and the documents referenced below.

3.3 Small/medium scale development – Site Discharge Index

The SDI is a relatively simple tool to allow assessment of small/medium scale developments of how they meet stormwater quality and quantity goals. The SDI is a value that relates the total area of a site with the impervious portion of the site draining directly to the stormwater network.

The SDI control overlaps with the stormwater retention control in that the retention control specifies the volume of stormwater to be retained on site, while the SDI encourages as much impervious surface as possible be connected to retention systems. This is also the case for OSD.

The SDI calculation is carried out as follows:

• Total site area (S)

• Total impervious area (I)= Roof area (R) + Paved area (P)

• Impervious surfaces draining to a control (not directly to the stormwater network) (M)

• Impervious surface directly to the stormwater network (DC) = I – M



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• Site Discharge Index (SDI) = DC / S

Scenario 1:

A new single residential dwelling on a 600m2 block is proposed consisting of a 250m2 roof and 100m2 of paved landscape area. A total of 350m2 of impervious surface is added. The entire roof (250m2) drains to a rainwater tank, and half of the paved area (50m2) drains to a landscaped depression in the front yard, with the remaining paved area draining directly to the street. Site area (S) = 600m2 Roof area (R) = 250m2 Paved area (P) = 100m2 Total impervious area (I) = 350m2 Area draining to a control (M) = 300m2 (all of roof and half of paved area) Area draining directly to stormwater network (DC) = 350m2 - 300m2 = 50m2 SDI = 50m2/600m2 = 0.083. Less than the required 0.1, so meets the required SDI. The development complies with the SDI.

Scenario 2:

A block of units on a 1,000m2 block is proposed consisting of a 700m2 roof and 200m2 of paved landscape area. The roof (700m2) drains to a rainwater tank, and the paved area drains directly to the street. Site area (S) = 1,000m2 Roof area (R) = 700m2 Paved area (P) = 200m2 Total impervious area (I) = 900m2 Area draining to a control (M) = 700m2 (all of roof) Area draining directly to stormwater network (DC) = 900m2 – 700m2 = 200m2 SDI = 200m2/1000m2 = 0.2. More than the required 0.1, so does not meet the required SDI.



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The development does not comply with the SDI. There are two options, reduce the impervious surface area proposed on the site (replace with permeable paving or landscape), or drain a larger area to some type of retention or infiltration system.

Refer to the following sections of this Supporting Document for information on systems that may assist in meeting the SDI for smaller developments:

• Infiltration trenches/absorption disposal system – Section 2.4.1.

• Porous or permeable paving – Section 2.4.2.

• Rainwater tanks – Section 3.2.2.

3.4 Large scale development

3.4.1 Discharging to a natural stream

For development discharging to a natural stream of 3rd order or lower that is not tidal, the post development duration of stream forming flows must be no greater than 2 times the pre-development duration of stream forming flows at the site discharge point, i.e. a stream erosion index of 2.

3.5 Design and maintenance of stormwater treatment measures

No supporting guidelines.

4 Waterfront Land

4.1 Development on waterfront land


4.2 Coastal Areas


5 References

• A guide to the use of MUSIC in Sydney’s Drinking Water Catchments (SCA, 2006)

• Adoption Guidelines for Stormwater Biofiltration Systems; Cities as Water Supply Catchments – Sustainable Technologies (CRC for Water Sensitive Cities)



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• Australian Rainfall and Runoff Guidelines (2019)

• Australian Runoff Quality (Engineers Australia, 2006)

• Council’s Engineering Design Specifications

• Developments in Sydney’s Drinking Water Catchment, Water Quality Information requirements (SCA, 2011)

• Flood Risk Management Guide: Incorporating sea level rise benchmarks in flood risk assessments (Department of Environment, Climate Change and Water, 2010)

• Guidelines for controlled activities, Riparian Corridors (Department of Water and Energy, 2008)

• Guidelines for filter media in biofiltration systems (version 3.01) (Facility for Advancing Water Filtration, 2009)

• HB 230-2006 – Rainwater Tank Design and Installation Handbook

• Impacts of Climate Change on Urban Stormwater Infrastructure in metropolitan Sydney (Sydney Metropolitan Catchment Management Authority, 2011)

• Managing Urban Stormwater: Soils and Construction Volume 1 (Landcom 2004) (Blue Book Vol. 1)

• Managing Urban Stormwater: Soils and Construction Volume 2 (DECCW, 2008) (Blue Book Vol. 2)

• Managing Urban Stormwater; Harvesting and Reuse (Department of Environment and Conservation, 2006)

• NSW Health Guideline GL2007_009 of June 2007

• NSW Sea Level Rise Policy Statement (Department of Environment, Climate Change and Water NSW, 2009)

• State Environmental Planning Policy (Exempt and Complying Development Codes) 2008

• WSUD Engineering Procedures: Stormwater (Melbourne Water, 2005)

• WSUD Technical Design Guidelines for South East Queensland (Healthy Waterways and Water by Design, 2009)

http://www.environment.nsw.gov.au/resources/stormwater/managestormwatera06137.pdf

supporting document 1: sustainable stormwater technical ... · • all water quality devices must...

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