2.10 Stormwater and Water Management

Design the site layout to minimise disruption or disturbance of land surfaces or natural drainage patterns. Ensure that actual or potential surface flows from uphill lands can flow through the property unimpeded, and without redirection. For this control, fences, walls, and minor structures on uphill lands are not taken into account.

Incorporate water sensitive urban design (WSUD) wherever possible by including landscaped areas incorporating vegetated stormwater systems, bioswales, rain gardens, and rainwater harvesting. Design the treatment system in accordance with C27-C30 and Council's Water Sensitive Urban Design Guidelines.

Drain site runoff to the lowest boundary in accordance with the site drainage controls C8 to C14. The site drainage is to include a piped system for more frequent rainfall events and an overland flow path to convey for overflows and flows from uphill lands.

Set back buildings from at least one side boundary to create an overland flow path from uphill land and allow for its management. Provide a minimum clear width of 500mm to ensure adequate access for ongoing works. Increase the setback where necessary to comply with the controls in Section 2.9 Flooding and Foreshore Risk Management.

Provide a step of at least 150mm between the finished ground level and the adjacent finished floor level. Increase the step where necessary to prevent surface waters from multiple uphill properties entering the site.

Allow floor areas partly below the ground level only when the application can:

• a)Demonstrate that surface runoff will not enter these areas
• b)Provide an overland flow path from all adjacent external finished surfaces
• c)Design boundary fences as lightweight or partially open construction where needed to maintain the natural stormwater flow path

Locate stormwater infrastructure such as stormwater pipes outside the Notional Root Zone of any tree to be retained unless the method of installation is certified by an AQF Level 5 qualified arborist as not affecting the longevity of the tree to be retained.

Collect stormwater from all roofs and impermeable areas and discharge via a free-flowing gravity system to the public drainage network at the lowest street frontage.

Where gravity drainage to the street is not possible, discharge by gravity to:

• a)Parramatta River, Cooks River, or Sydney Harbour frontage
• b)A trunk drainage pipe passing through the site
• c)A registered drainage easement benefitting the site

For single dwellings, without these options, drain by gravity to the public drainage system of the higher street frontage.

Where no gravity solution exists, design a charged system to on-site storage retention (OSR) storage, ensuring:

• a)Charged lines are located outside the building footprint
• b)A cleaning eye pit is installed at the lowest point
• c)Overflow from the OSR storage to the kerb occurs via gravity
• d)Minor surface areas that cannot drain to the street under gravity are not to concentrate flows or cause nuisance to downstream properties

Where retained buildings prevent establishing an overland flow path, increase pipe capacity to capture and convey the 100-year Average Recurrence Interval storm flow from the contributing catchment, assuming 80% inlet blockage and 50% pipe blockage.

Connect all site drainage systems to the public drainage network in accordance with Council's standard plans and specifications.

Design the site drainage system to convey any existing flows from uphill land that are blocked, diverted, or concentrated by the development to the lowest street frontage or to an inter-allotment drainage system with a registered drainage easement.

Any development that results in site disturbance is to provide appropriate erosion and sedimentation control measures to control runoff, mitigate soil erosion and trap pollutants before they can reach downslope lands and receive watercourses.

Design erosion and sediment control measures in accordance with the document Managing Urban Stormwater–Soils & Construction Volume 1 (2004) by Landcom (the "Blue Book").

Include a landscaped area buffer along all common boundaries with public reserves, drainage corridors, or rail corridors, and new industrial, productivity support, and commercial developments. Buffers are to:

• a)Include continuous evergreen screen planting with shrubs and trees.
• b)Screen tall or bulky structures, assist with visual privacy, and provide an environmental buffer.

Provide on-site detention (OSD) for all developments except where:

Alterations or additions increase the total site impervious area by less than 40m² or

The site discharges directly to the Cooks River, Parramatta River, Sydney Harbour or

On-site retention (OSR) replaces OSD in accordance with C20 or

• a)The site connects directly to a Sydney Water asset and complies with the discharge controls imposed by Sydney Water

All On-Site Detention (OSD) systems are to be designed to control the rate of stormwater discharge from the site in accordance with the following requirements.

• a)Alterations and Additions:
• i.Storage: Provide a minimum Site Storage Requirement (SSR) of 3m³ for every 100m² increase in impervious area.
• ii.Discharge: Limit the Maximum Permitted Site Discharge (PSD) to 3 litres per second.
• b)All Other Developments (New builds and redevelopments):
• i.Storage: Provide a minimum SSR of 3m³ for every 100m² of total site impervious area.
• ii.Discharge: Limit the Maximum PSD to 3 litres per second for every 100m² of total site impervious area

For the purpose of OSD calculations, swimming pools and spas are counted as 100% impervious area.

Provide separate OSD and/or OSR systems, for each Torrens Title property, clear of all boundaries.

On site retention of stormwater (OSR) may be used in lieu of OSD in accordance with the following:

• a)For single dwellings, OSR storage may replace OSD in accordance with Table 2.10.1
• b)For all other developments, OSR may offset the calculated OSD storage volume at a rate of 1m³ for every 2.5m³ of OSR storage provided, up to a maximum OSD offset of 10m³
• c)The OSR is to supply water to at least all new and/or upgraded toilet cisterns, laundry washing machine connections, external taps, and irrigation systems. The standard labelling is to be displayed at such outlets

Design and locate water storage structures to be visually unobtrusive and sympathetic to the development, while still being evident to any future owner of the property.

Locate at ground/below ground storages away from overland flow paths that convey upstream catchment flows through the site.

For strata and community title developments, locate storages in common areas (rather than privately controlled areas such as courtyards).

To ensure that stormwater infrastructure remains functional for the life of the development, the following legal requirements apply:

• a)Requirement for Title Registration: A Positive Covenant and Restriction as to User is to be registered on the Title (under Section 88B of the Conveyancing Act 1919) for all OSD and WSUD systems. This ensures ongoing maintenance and formally notifies future owners of their legal obligations.

Exemption for Single *Dwelling Houses: This requirement does not apply to dwelling houses (including secondary dwellings*). For these properties, ongoing management obligations will be managed through standard Conditions of Consent rather than a formal covenant on the Title.

For alterations and additions resulting in 25m² or more of additional impervious area, install a stormwater pit inside the property adjacent to the boundary with sediment device with RH3030 screen or similar.

For building works other than single dwellings, design and construct the stormwater pit/s with a water quality filtration basket or similar primary treatment device

Design surface and subsurface drainage systems to exclude sources of pollutants and treat water to minimise likelihood of water pollution by expected activities and sources within the development site.

Applicants are to demonstrate compliance with Council's water quality targets through one of the following two pathways, based on the scale and type of development as defined in Table 2.10.2.

For developments falling within the "Small-scale" GFA thresholds in Table 1, the water quality requirements are satisfied by implementing one of the following options:

• a)Option 1: Rainwater Harvesting
• i.Drain at least 80% of the roof area to a rainwater tank
• ii.The tank is to have a minimum capacity of 3,000 litres per 100m² of roof area
• iii.The tank is to be plumbed to all toilets, laundry, and outdoor irrigation at a minimum
• b)Option 2: Bio-retention (Rain Gardens)
• i.Provide a bio-retention system (rain garden) with a surface area equal to at least 1.5% of the total site impervious area
• ii.Ensure at least 80% of all impervious areas on the site drain directly to the system

The system is to be designed in accordance with the Water Sensitive Urban Design (WSUD) Guidelines

For all developments exceeding 2,000m² GFA, or where Pathway A is not practicable, a MUSIC (Model for Urban Stormwater Improvement Conceptualisation) report is to be submitted. The model is to demonstrate the following minimum pollutant load reductions:

• a)85% Total Suspended Solids (TSS)
• b)65% Total Phosphorus (TP)
• c)45% Total Nitrogen (TN)
• d)90% Gross Pollutants (>5mm)

Vegetated Treatment: Systems are to incorporate vegetated treatment (e.g., swales, bio-retention) unless it is demonstrated to be technically impracticable on the site

Hydrocarbon Management: For car parks with 10 or more uncovered spaces, or basement car parks with pump-out systems, an additional proprietary device (e.g., oil/water separator) is to be installed to remove oils and grease

Design non-residential development which proposes new or additional floor space, or involves a change of use to a commercial laundry or car washing facility, to incorporate the following:

• a)Meet minimum standards defined by the Water Efficiency Labelling and Standards (WELS) Scheme for any new water use fittings
• b)Install rainwater tanks to meet all non-potable demands, including outdoor use, servicing vehicle washing facilities, toilets, laundry, with the exception of centre-based childcare, where this water is to be used for irrigation and toilet flushing only
• c)Incorporate passive cooling methods that rely on improved natural ventilation to supplement or preclude mechanical cooling
• d)For cooling towers:
• i.Use locally harvested rainwater or recycled water
• ii.Connect to a conductivity meter to ensure optimum circulation before discharge
• iii.Include a water meter connected to a building energy and water metering system to monitor water usage

Design and install any proposed on-site sewage treatment to meet all relevant statutory requirements and relevant Australian Standards.

Connect all developments to the centralised sewerage waste disposal system operated by Sydney Water, including any overflow and surcharge from any on-site wastewater treatment system.

Detailed geotechnical investigation provided with the application is to demonstrate that any structure partially or fully below ground does not result in any adverse hydrogeological impacts, either during or after construction.

Basements must be fully tanked. Pump-out systems for groundwater are prohibited unless it is demonstrated that no other engineering solution exists and hydrogeological impacts are zero.

Where it is not practicable, Council will only consider a pumped system where the application demonstrates that:

• a)Surface stormwater will not enter the subfloor space
• b)Groundwater flows are minimal or intermittent
• c)The pump system does not impact the surrounding groundwater table
• d)The pumped water causes no adverse hydrogeological impacts on any surrounding properties or infrastructure, both during and after construction
• e)The water quality is suitable for discharge from the site to the public drainage system
• f)The pumped system connects directly to the public underground drainage system
• g)The sump and pump facilities are housed and accessed to allow upkeep from an area external to the building above.

Protect access to basements associated with car parking facilities from the weather to minimise the entry of stormwater runoff to the basement. A pump out system may be used only for minor surface areas that drain to the basement.

To ensure the long-term integrity and accessibility of the public drainage network, development is to comply with the following restrictions regarding existing infrastructure:

• a)Permanent structures or fill must not be placed over Council's piped drainage systems. Permanent structures include, but are not limited to buildings, eaves, balconies, garages, impervious fences, swimming pools, and retaining walls.
• b)Where an easement exists, these restrictions apply to the full width of the easement.
• c)Where no easement exists, a minimum clearance of 1.5m must be maintained from both sides of the centreline of the drainage structure.
• d)These distances may be increased by Council where necessary to manage specific flood risks.
• e)Council may permit open, lightweight structures (such as carports, pergolas or open parking spaces) over drainage systems, provided the applicant demonstrates that the structure will not increase flood risk or impede future management access.
• f)A registered easement in favour of Council is required for any site containing a Council pipeline that is not currently protected. The easement width must be the width of the pipe/channel plus 1.5 metres, with a total minimum width of 2.5 metres.
• g)Where structures are proposed over or adjacent to Sydney Water piped stormwater assets, separate approval from Sydney Water is required. Compliance with Sydney Water requirements does not exempt a development from the additional conditions or setbacks imposed by this DCP.