Water sensitive urban design
What is water sensitive urban design?
Urban development impacts the natural water cycle by creating impervious surfaces that affect the quantity and quality of stormwater. This places a greater demand on potable water resources and creates artificial stormwater drains and by discharging wastewater.
In Moreland, stormwater runoff is discharged to the Port Phillip Bay via Merri Creek, Edgars Creek and Moonee Ponds Creek. Stormwater runoff and pollutants are detrimental to these waterways.
Water sensitive urban design mitigates these impacts while reducing water bills and creating greener urban areas.
Clause 22.08 Environmentally Sustainable Development of the Moreland Planning Scheme requires new development to satisfy best practice stormwater management objectives. This is done via adopting water sensitive urban design principles.
Benefits of water sensitive urban design
Water sensitive urban design also provides many social, economic and environmental benefits including:
Minimising impact on receiving waters
Reducing potable water use
Recharging local groundwater through the infiltration of stormwater
Creating greener urban environments with high visual amenity, and
Passive cooling through increased vegetation cover.
The Victorian Urban Stormwater Best Practice Environmental Management Guidelines (Victorian Stormwater Committee, 1999) mentioned in Clause 22.08-6 define best practice stormwater pollutant removal as:
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% retention of typical urban load of litter.
The Victorian Government 2016 Water for Victoria Water Plan notes that “increasing stormwater flows will degrade urban waterways unless we improve the way we manage stormwater”.
Water sensitive urban design treatments
A range of water sensitive urban design treatments can be used to demonstrate best practice stormwater management.
Moreland has created a hierarchy to demonstrate which treatments are considered to have the best co-benefits and should be explored as the first options.
See further detail of water sensitive urban design treatments (PDF 258Kb).
The benefits of the treatments are explained in the table below
How to develop a response
A water sensitive urban design (WSUD) response must clearly demonstrate how stormwater runoff will managed in accordance with the Clause 22.08-2 Stormwater Management objectives.
Step 1: When should you develop a WSUD response?
WSUD responses should be developed as early as possible in the development process to allow WSUD to be fully integrated with the site design, such as roof shape and the site levels. This will result in a better WSUD response and easier assessment process.
Step 2: 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, pergolas, concreted and paved areas. (Note that permeable paving does not count as a hard surface with respect to generating stormwater runoff).
Depending upon 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. Sub-roof areas may be combined where the roof runoff will be diverted to a common WSUD treatment, i.e. rainwater tank.
The legal point of discharge for the property should also be identified. Discharges from WSUD treatments will need to be conveyed to this point.
Step 3: Choosing WSUD infrastructure
Select which WSUD treatment will be used to treat runoff from each hard surface using the above hierarchy, such as a rainwater tank or a raingarden. Take into account any constraints on available space and site levels relative to the legal point of discharge.
Step 4: Size rainwater tank and/or treatment system
Two assessment tools are available to assist applicants to size WSUD infrastructure to meet the stormwater quality standards:
- STORM Calculator
Option 1: STORM Calculator
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 on using the calculator or designing stormwater treatment systems.
STORM Calculator inputs include the total development area and all impervious areas (including impervious areas where no treatment will be provided for stormwater runoff). The calculator enables users to select from a range of WSUD treatment types.
An overall STORM score of at least 100% is required to demonstrate that best practice Stormwater Management has been achieved.
Option 2: MUSIC
The Model for Urban Stormwater Improvement Conceptualisation (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 Moreland must be developed in accordance with Melbourne Water MUSIC Guidelines.
MUSIC users must have a software licence and a minimum level of training and competency to develop a MUSIC model. MUSIC training is provided by eWater. MUSIC is generally used by professionals with stormwater treatment expertise. MUSIC is generally the most suitable assessment tool for complex and/or large developments (e.g. large multi-lot subdivisions) and any proposal that involves stormwater harvesting.