Wetlands
Wetland management
Melbourne Water builds and manages wetlands to treat stormwater before it reaches our rivers, creeks and bays. Stormwater is often polluted by litter and other contaminants washed from roads, gardens, nature strips and gutters.
Melbourne Water is undertaking a significant number of projects to reduce the level of nitrogen that reaches Port Phillip Bay from stormwater and other sources. These projects, including the construction of wetlands, will help protect the long-term health of the bay.
We invest about $5.6 million a year building wetlands to act as nature's filter by removing nitrogen and other pollutants from stormwater. Our wetlands will help to reduce the amount of nitrogen entering Port Phillip Bay by 100 tonnes a year by 2010.
We manage 99 wetlands, and more are being designed or constructed to treat run-off. We are continuing to investigate other potential sites for wetlands.
We are working with developers and local councils to incorporate wetlands into new subdivisions to minimise the environmental impact of these developments. Water sensitive urban design (WSUD) techniques, including wetlands, can be used at these subdivisions to treat stormwater.
For example, at Lynbrook Estate in Melbourne's south-east, stormwater pipes have been replaced by shallow grassed swales and an underground system of gravel trenches and perforated pipes. Stormwater then flows slowly to wetlands for further treatment before it is discharged to a local waterway and then into Port Phillip Bay.
What are wetlands?
A wetland is an area of land covered at least sometimes by usually quite shallow water. Wetlands can be natural or artificial, permanent or temporary, and the water in them can be static or flowing, fresh, brackish or salty.
Minerals and nutrients carried by regular flows of water enrich wetlands, and coastal wetlands such as mangroves and seagrass meadows are among the most productive ecosystems on Earth.
Although wetlands cover about 3% of the Earth's surface, they are vital to our environment. They act as sponges, storing and soaking up excess water; and filters, cleaning water as it flows through.
How do wetlands work?
We generally construct wetlands on land set aside for flood protection. Wetlands are constructed by excavating (usually to a shallow depth) into the floodplain, where inlet and outlet structures are built, and vegetation is later planted.
Wetland sites are generally chosen next to rivers and creeks that require water quality treatment, and in conjunction with other measures such as litter traps.
The wetlands are designed to filter stormwater, with thousands of aquatic and semi-aquatic plants in various water depths removing nitrogen and other pollutants.
The wetlands also slow the flow of water, reduce the amount of sediment being carried and enable biological processes, sunlight and time to help purify the water.
The design of the wetlands revolves around several methods of treatment, including sedimentation ponds, carbon filters and marshes. Flow control structures are used to direct the required amount of water into the wetland, and to ensure that the water is retained and treated for a specified period of time.
We select robust indigenous plants, including sedges and rushes, which adapt well to conditions in wetlands and urban rivers and creeks. The plants are of varying sizes, with the largest growing up to 1.2 metres out of the water.
The ephemeral carbon filter trap is located at the beginning of the wetland. This vegetation traps plant material, such as leaves and grass clippings, and organic matter before it enters the wetland. The largest particles in the stormwater settle on the bottom of the wetland ponds, and fine particles are absorbed by the plant stems. Nitrogen from stormwater is removed by plant uptake and other biological processes occurring naturally in the water.
A refuge for wildlife
Each wetland has its own unique ecosystem that provides food, water, critical habitat and breeding grounds for an array of plants and animals.
The wetlands at Melbourne Water's Western Treatment Plant at Werribee attract an amazing array of birdlife and some 270 species have been recorded.
Downloads
- Design Guidelines for Shallow Lake Systems (PDF, 538kb)
- Wetlands - Nature's Filter (PDF, 182kb)
You will need Adobe Acrobat to access the above PDF documents. 