Melbourne Water : Publications : Fact Sheets : Drainage : Wetlands

Wetlands - Nature's Filter

Protecting our rivers, creeks and bays

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.

We are 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.

Melbourne Water invests 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.

Our wetlands also provide flood protection, and are often areas of natural beauty. Some include boardwalks to provide recreational and educational amenity, and increase environmental awareness in local communities. We also manage major internationally-recognised wetlands that are a haven for native wildlife.

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.

Water-sensitive techniques

Melbourne Water is constructing wetlands at many sites as part of a long-term plan to protect the health of Port Phillip Bay.

We manage a number of wetlands, and more are being designed or constructed to treat run-off. We are continuing to investigate other potential sites for wetlands across greater Melbourne.

We are also working with developers and local councils to incorporate wetlands into new subdivisions to minimise the environmental impact of these developments. Water-sensitive urban design 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 Port Phillip Bay.

Cleaning up - by design

We generally construct wetlands on land set aside for flood protection. The 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.

Stormwater often carries litter and sediment into rivers, creeks and bays. Contaminants and nutrients are attached to the sediment particles. The wetlands are designed to act as a filter, 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 inner workings

Research has shown that the vegetation used in these wetlands maximises treatment efficiency.

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. These plants, propagated in specialist nurseries, range from low groundcovers to macrophytes and from those suited to the wetland edge to others at home in shallow, deep or ephemeral marshes. 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 and critical habitat and breeding grounds for an array of plants and animals.

The wetlands at Melbourne Water's Western Treatment Plant at Werribee (right) attract an amazing array of birdlife. Some 270 species have been recorded, with waterfowl including the Pink-Eared, Blue-Billed and Black ducks, Chestnut Teal, Australian Shoveler, Australian Shelduck, and grebes favouring the treatment lagoons. Up to 50,000 Pink-Eared Ducks have been recorded at one time at the plant.

Coots and Eastern Swamphens use pond fringes, while swans and pelicans tend to roost on small, muddy islands among the dead trees, and Straw-Necked and White Ibis roost on the trees in Lake Borrie at the plant.

Every year, thousands of migratory waders fly 12,000 kilometres south from Siberia to the Western Treatment Plant wetlands to avoid the harsh northern Winter.

Species that make the six to eight-week journey from Siberia include the Sharp-Tailed and Curlew sandpipers and the tiny Red-Necked Stint. The birds fly non-stop for two to three days at a time, in stretches of up to 5000 kilometres.

Edithvale and Seaford Wetlands in Melbourne's south-east are estimated to be home to as many as 7000 birds at a time. Among the star attractions are migratory waders including Latham's Snipe from the northern islands of Japan.

The wetlands feature a bird hide and educational display, as well as an extensive walking and bicycle track and a mob of Eastern Grey kangaroos.

Home for frogs

Several frog species identified in the Melbourne Water Frog Census, a community-based monitoring program, are commonly found in wetlands in greater Melbourne. These frogs favour the slow-moving water of wetlands, reeds and other vegetation for breeding.

The endangered Growling Grass Frog, which was once commonly found in and around Melbourne wetlands, was discovered in a wetland near Pakenham in the first census during 2001. (Census results can be found at melbournewater.com.au/frogs). Frogs are an important indicator of waterway and wetland health.

Other aquatic life found in some of Melbourne's wetlands includes a native fish species, Dwarf Galaxias (right), which favours the ephemeral nature of wetlands and hides in low-lying muddy water in Summer.

Shellfish including mussels and snails, water beetles and other aquatic insects are also at home in Melbourne's wetlands. Leaves from large aquatic plants are a source of food for macroinvertebrates such as insect larvae.

Well-designed and managed wetlands create a healthy aquatic ecosystem that can prevent mosquitoes breeding. Melbourne Water designs wetlands with a lack of shade and smooth sloping surfaces to avoid pockets of water, minimising the prevalence of mosquitoes.

Our world-class wetlands

To help protect wetlands, an international treaty was signed on 2 February 1971 in the Iranian town of Ramsar. This date is commemorated each year with World Wetlands Day. This Convention on Wetlands provides a framework for national action and international co-operation for the conservation and wise use of wetlands.

Some 130 countries have signed the convention, and more than 1100 wetlands totalling almost 90 million hectares are designated as wetlands of international importance. These sites are selected because of their unique qualities, diverse or threatened habitat, or their importance to shorebirds or fish.

Australia has 63 of these internationally-recognised wetlands, which cover more than seven million hectares. Eleven of these are in Victoria, most of which are public reserves or Crown land. Melbourne Water's Edithvale and Seaford Wetlands (below) was declared a Ramsar site in 2001, and the western shores of Port Phillip Bay, including the Bellarine Peninsula and the Western Treatment Plant, was declared a Ramsar site in 1982.

Glossary

Aquatic: Living in, growing in or frequenting water.

Brackish: Between saltwater and freshwater.

Ecosystem: A term used to describe a specific environment including all the biological, chemical and physical resources and the relationships between those resources.

Ephemeral: Short-lived, transitory. Ephemeral wetlands are wet for only short periods.

Habitat: The native environment or kind of place where a given plant or animal naturally lives or grows.

Macrophyte: Large plant.

Nutrients: Substances such as nitrogen and phosphorus in various forms required for the growth of plants.

Organic matter: Naturally-occurring material derived from plants and animals.

Sediment: Sand, clay, silt, pebbles and organic material carried and deposited by water or wind.

Stormwater: Rainfall that runs off roofs, roads and other surfaces and flows into gutters, rivers, creeks and eventually bays. This water can carry contaminants such as plastic, detergents, nutrients and heavy metals.

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Wetlands - Nature's Filter (PDF, 182kb)

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