Our Stormwater Quality Wetlands
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.
Generally, we construct our wetlands on land set aside for flood protection, using the following steps:
- A (usually shallow) depression is dug into the floodplain.
- Structures are built to allow water flow into and out of the wetland.
- Suitable vegetation is planted.
Location
Wetland sites are generally next to rivers and creeks that require water quality treatment, and also involve other measures such as litter traps.
Function
The wetlands are designed to filter stormwater. Thousands of aquatic and semi-aquatic plants remove nitrogen and other pollutants. The wetlands also:
- slow the flow of water
- reduce the amount of sediment being carried
- enable biological processes, sunlight and time to help purify the water.
Design
The design of the wetlands revolves around several methods of treatment, including:
- sedimentation ponds
- carbon filters
- marshes.
Flow control structures are used to:
- direct the required amount of water into the wetland
- ensure that the water is held in the wetland and treated for a specific amount of time.
We select tough and healthy indigenous plants, including sedges and rushes, which adapt well in wetlands, rivers and creeks. The plants vary in size, 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 is vegetation that 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.
For a more in depth look at this process, visit the Areas within a wetland.
Water quality wetlands (Huntingdale Retarding Basin)
Protecting Port Phillip Bay
Our wetlands will help reduce the amount of nitrogen entering Port Phillip Bay by 100 tonnes a year by 2010. We are managing various 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 Port Phillip Bay.
Our investment in the future
We invest about $6 million a year building wetlands to act as nature's filter by removing nitrogen and other pollutants from stormwater.
We manage 117 constructed wetlands, and more are being designed or constructed to treat run-off. We are continuing to investigate other potential sites for wetlands.
We work 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.
Guidelines for constructing wetlands
Constructed wetlands play a vital role in reducing the impacts of urban development. To provide design professionals, developers and councils with increased clarity around the requirements for designing and constructing wetlands in new urban areas, Melbourne Water has published Constructed Wetlands Guidelines. These guidelines are the first in a series of documents to be revised and the information provided will supersede that of a similar nature in other documents.
A wetland case study
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.