Learn how managing stormwater helps to prevent flooding, improve water quality and protect our waterways.
Clause 56.07-4 of the Victorian Planning Provisions, commonly referred to as Clause 56, sets stormwater management objectives that residential subdivisions must meet. These objectives are designed to reduce the harm to our waterways, bays and ocean.
The traditional approach to stormwater quality treatment involves constructing a sediment pond and wetland at the bottom of a large catchment.
Although this single-site approach can reduce travel time between maintenance activities, it does not reduce stormwater volumes enough to protect waterway ecosystems from erosion and unnatural disturbances.
The distributed approach involves installing a number of smaller and potentially different treatments throughout a catchment. In the case of managing urban hydrology, stormwater treatment measures are best implemented at every scale.
This is why you can make a difference.
Stormwater is rainwater that has fallen onto roads or roofs and often contains chemicals or pollutants. Water sensitive urban design (WSUD) is an approach to planning and designing urban areas to make use of this valuable resource and reduce the harm it causes to our rivers and creeks.
Water sensitive urban design (WSUD) protects water quality from urban development impacts. It reduces peak flows, uses water in the landscape and maintains a more natural water system. Pollution is captured using litter traps, sediment traps, filtration and wetlands.
There are a range of options that may be used depending on your site.
For more information on options and requirements check the WSUD Resource Kit
Rainwater tanks can reduce the harm to our waterways caused by too much stormwater. Tank water can be used to flush toilets, wash clothes, water gardens and wash cars, significantly reducing demand on drinking water.
Rainwater tanks can only provide benefits when the tank water is used frequently, creating space to capture more water each time it rains. Try to connect as much of the roof area to the rainwater tank. A slow irrigation dripper line to a suitable garden area can ensure your tank can always capture water.
Porous paving is an alternative to conventional impermeable pavements, with many stormwater management benefits. These surfaces allow water to percolate through to a sub-surface course, from where it either infiltrates to the soil or is filtered back to the drainage system.
Porous paving can be used for a variety of water management objectives to:
reduce peak stormwater discharges from paved areas
increase groundwater recharge
improve stormwater quality
reduce the area of land dedicated solely to stormwater management
Swales are linear, depressed channels that collect and transfer stormwater. They can be lined with grass or more densely vegetated and landscaped.
Swales can convey stormwater and screen and remove gross pollutants, such as litter and coarse sediment.
Swales initially immobilise pollutants by binding them to organic matter and soil particles, then remove them by settling, filtration and infiltration into the subsoil.
Certain pollutants, such as hydrocarbons, may be digested and processed by soil microorganisms in the filter strip. To optimise pollutant removal, swales need adequate contact time between the run-off and the vegetation and soil surface.
Raingardens are specially-designed garden beds that filter stormwater runoff from surrounding areas or stormwater pipes. Raingardens are also called bioretention systems because they use soil, plants and microbes to biologically treat stormwater.
Although they may look similar to a normal garden, raingardens are designed to stop stormwater run-off from polluting our waterways with nutrients, rubbish and sediment:
Water collects and settles on the garden surface
Water soaks through the plants and filter media, trapping rubbish and sediment on the surface
Plants use the nutrients in the stormwater, and toxins stick to the soil
The soil and plant roots work together to naturally filter the water and remove pollutants
Raingardens need particular plants with roots that help keep the filter media absorbent, and break down the pollution.
Sediment basins are ponds with open water that capture coarse sediment and litter carried by stormwater. They intercept stormwater before it reaches the waterway, and slow it down to allow the coarse sediment to fall to the bottom.
A sediment basin needs to be cleaned out when the sediment builds up to 0.5 metres below the water level, which usually takes about two to five years.
Constructed wetlands are a series of shallow, densely-planted, man-made ponds that help filter water through physical and biological processes. They provide a natural way to treat and remove pollutants from stormwater before it enters our creeks, rivers and oceans.
Constructed wetlands typically have three parts that work together to help filter stormwater and protect it from flooding:
inlet zone – a sediment basin that removes coarse sediment
macrophyte zone – a shallow area densely planted with aquatic plants and the main part of the wetland, which removes fine particles and dissolved pollutants
high flow bypass channel – lets excess water flow around the wetland without damaging the plants
These work on three levels: physical, biological and chemical uptake, and pollutant transformation.
Wetlands are usually used close to a catchment outlet or within a reserve where there is plenty of space. They are best built in land subject to flooding, but outside the main waterway channel.
Wetlands may have open water ponds at the inlet and outlet, but should otherwise be planted so densely that the water is not easily visible. This avoids problems such as algal growth and sediment re-suspension through wind and waves.
For more information on Constructed Wetlands check here.
Gross pollutants traps are structures that use physical processes to trap solid waste such as litter and coarse sediment. They are commonly used as the primary treatment because they mostly remove large, non-biodegradable pollutants.
Most off-the-shelf gross pollutant traps are suited to pre-treatment of small to medium sized systems, so are not meant for treating large areas of catchment like wetlands. Sediment ponds are usually the preferred option for larger systems.
An infiltration trench is an excavation filled with porous material, which collects stormwater run-off. Stormwater infiltrates into the surrounding soil, while particulate and some dissolved pollutants are retained in the porous media.
Infiltration trenches can increase the soil water levels and groundwater flow rates, as well as reduce stormwater flow velocities. Their ability to remove particulate and dissolved pollutants depends on local soil geochemistry, treatment measure configuration and grading.
To reduce their visual impact, they can be covered with a layer of fibre fabric and finished with a shallow layer of topsoil and grass. The trench can be lined with a layer of geotextile fabric, to prevent soil migrating into the rock or gravel fill.