An increasing number of local authorities are requiring project developers to incorporate Water Sensitive Urban Design (WSUD) principles into their developments.

Although we are still in the early adoption phase, many design companies are still considering the changes WSUD may have to their drainage design philosophy, system styles, and material selection. The biggest change for some traditionalists is that local and regional stormwater infrastructure has moved towards minimum impact, not minimum maintenance.

The following low cost environmental tools may be a good starting point for designers new to WSUD:

• Grassed verges to provide a zone for the deposit of heavy metals and silts.
• Vegetated swales to transport stormwater more slowly, remove gross pollutants and silts, allow percolation, evaporation and cooling.
• Ponding to reduce high run-off in small storm events, remove suspended solids, allow percolation, evaporation and cooling.
• Bio-retention trenches (BRTs), to strip nitrogen and phosphorus contaminants.
• Wetlands to strip nitrogen and phosphorus contaminants, trap fine suspended solids, transform organic components.

Details of these and similar tools are extensively available, however an excellent source of further information is the ‘Urban Stormwater Best Practice Environmental Management Guidelines’ published by the CSIRO. Computer programs are also available to help in designing appropriate combinations of these tools for effective land use, the most popular at present being ‘MUSIC’ (Model for Urban Stormwater Improvement Conceptualisation) which is available from CRC Publications at www.catchment.crc.org.au

Projects incorporating WSUD design principals are slowly emerging in most States; and the Lynbrook Residential Estate in Victoria is one popular example. For those interested in visiting Lynbrook, you will find a combination of WSUD tools specifically chosen to satisfy the developer’s requirements. The requirements were in concise terms:

• To exist and function within public land.
• To place treatment as close as possible to the source.
• To avoid any reduction in useable, developable land.
• To appear as close as practical to a typical urban development.
• To fit into standard road reserve widths.
• To retain barrier kerb profiles.
• To integrate any large land consuming treatments into public open space and the proposed open water body.

The resulting design is one that is not outrageously obvious, as meeting normal expectations of the south east suburb house and land purchaser was paramount.

Stormwater quality and quantity treatment was taken up to the property line, with grassed swales and BRT’s within the standard nature strip zone. As very few pits were included, opportunities for rubbish to enter piped drains are highly reduced. The BRT’s did not use the more common sand filter material, but fine granite aggregate to substantially increase their operative life. This has reduced their effectiveness per meter of trench, but as many meters have been installed, overall effectiveness has been sustained. More importantly, council’s maintenance and life expediency requirements were satisfied. Property drainage points have a creative tri-option operation that allows for percolation, and pipe and swale disposal paths, depending on the rainfall event.

The integration of simple WSUD principles met the client’s requirements, and to the surprise of many, it did not cost more. What is amazing is that it has taken so long to realize that using nature to control rainwater is the best method available to us all.

For further information please contact Rudd Lindley, KLM Development Consultants
on 03 9794 9438.

Swale Drain Pit