The natural water cycle is impacted by buildings and sealed surfaces. As a result, natural water flows are altered and stormwater is created. This stormwater carries pollution into our waterways and can cause local flooding during heavy rainfall events.
Water Sensitive Urban Design (WSUD) is the design of buildings, subdivisions and works to minimise the impact of development on the surrounding environment and waterways. WSUD involves treating and reducing stormwater flows, increasing soil moisture, urban greening and providing an alternative water source.
Water Sensitive Urban Design planning requirements
The Melbourne Planning Scheme has various policies that require the treatment of stormwater on private land. These are:
- Clause 19.03-3S Integrated water managementOpens in new tab
- Clause 53.18 Stormwater Management in Urban DeveloOpens in new tabpment
- Clause 55.03-04 Site layout permeability and stormwater management objectivesOpens in new tab
- Clause 55.07-05 Apartment Developments - Integrated water and stormwater management objectivesOpens in new tab
- Clause 58.03-08 Site layout - Integrated water and stormwater management object Opens in new tab
Your planning application should demonstrate how you have achieved the best practice water quality performance objectives as set out in the Urban Stormwater Best Practice Management Guidelines, CSIRO 1999.
- 80% reduction in the typical urban load of total suspended solids
- 45% reduction in the typical urban load of total phosphorous
- 45% reduction in the typical urban load of total nitrogen
- 70% reduction of typical urban load of litter.
Addressing these requirements on your site will not only minimise negative impacts on waterways on local drainage but can also reduce the need for potable water on your development and create passive cooling through increased vegetation.
Developing your WSUD response
Step 1 – Determine catchment area and discharge point(s)
Identify and measure the area of all outdoor 'hard' surfaces on your site plan. Hard surfaces include roofs, balconies, verandas, concreted and paved areas (excluding permeable paving). Depending on the type of roof construction, sections of the roofed areas may drain to different points of the development, and therefore may need to be separated into sub-roof areas.
Finding out your legal point of discharge for your property will assist you in your WSUD design as all discharges will need to be conveyed to this point. See Stormwater for more information.
Note: Run-off from balconies and trafficable roof area is generally dirtier than other roof run-off so should not be diverted to rainwater tanks. Balcony runoff should be treated prior to discharge from site.
Step 2 – Choose WSUD treatment
A range of WSUD systems can be used to treat stormwater run-off from your development. Select which WSUD treatment will be used to treat runoff from each hard surface. Take into account:
- constraints on available space and site levels relative to the legal point of discharge.
- ease of maintenance and operability
- capital and lifecycle costs
- secondary benefits, such as alternative water supply.
Step 3 – Size your treatment system
The following tools are available to assist you to size your WSUD infrastructure to meet the stormwater quality standards.
The STORM Calculator is a user friendly, free online tool developed by Melbourne Water. It is designed to be suitable for applicants without any formal training. An overall STORM score of at least 100% is required to demonstrate that best practice stormwater management has been achieved.
View STORM CalculatorOpens in new tab
MUSIC is a modelling tool that uses historic rainfall data to estimate catchment runoff and predict the performance of WSUD infrastructure. It enables a significantly higher degree of modelling complexity and flexibility compared to the STORM calculator. The MUSIC model should only be used by those with appropriate expertise. MUSIC models used to prepare WSUD Responses for the City of Melbourne must be developed in accordance with Melbourne Water MUSIC GuidelinesOpens in new tab.
A complying MUSIC model needs to demonstrate a treatment train that achieves the best practice targets (80:45:45).
What to include in your application
All applications must include:
- A site layout plan and other relevant drawings, showing:
- location and type of all paved and sealed areas (notated as to porous/permeable or not)
- rainwater tank size and associated roof catchment area
- location and type of WSUD features.
- A report that demonstrates how the best practice stormwater quality performance objectives are achieved. Consisting of a complying STORM or MUSIC report (meeting a minimum of 100 per cent for STORM, or 80:45:45 for MUSIC).
Note: Civil drainage drawings and the stormwater management plan submitted as a requirement of planning permit conditions will be also checked to ensure compliance with best practice stormwater targets.
Water Sensitive Urban Design treatment options
Rainwater tanks
Rainwater tanksOpens in new tab collect run-off from roof areas. This water can be used where drinking quality water is not needed, like flushing toilets, washing clothes and watering gardens. By storing rainfall, rainwater tanks can reduce peak flow rates to the stormwater drainage network.
Diverting roof run-off to a rainwater tank and using rainwater for toilet flushing and other internal uses is one of the most effective options for achieving water quality treatment objectives.
Permeable Paving
Permeable or porous pavingOpens in new tab allows water to pass through it and infiltrate to the soil or filter back into the drainage system. There are a number of permeable pavement products available.
Raingardens
RaingardensOpens in new tab are specially designed garden beds that filter stormwater runoff from surrounding areas or stormwater pipes. Raingardens use soil, plants and microbes to biologically treat stormwater.
Raingarden tree pits
Raingarden tree pits are configured to support the growth of a tree rather than the understorey plants typically seen in standard raingardens. In addition to treating stormwater runoff, they provide passive irrigation for the tree, reducing the need for manual watering. Tree pits can be open or covered depending on your space requirements.
