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wetlands - nature's filter

What is a wetland?

Edithvale Seaford wetlands

Wetlands are areas of land that contain pools of shallow water. Wetlands include lakes, swamps, damplands, mangroves and seagrass meadows. They can be large or small, natural or constructed, permanent or temporary, and the water in them can be static or flowing, fresh or salty.

Wetlands only cover about 3 percent of the Earth's surface. However, they are important ecosystems for many reasons.

Wetlands:

• support a wide variety of plants and provide a home for native wildlife such as birds, fish, frogs, tortoises and invertebrates.
• help reduce the severity of floods by acting as sponges, storing and soaking up excess water.
• act as filters, cleaning and filtering out any nasty pollutants caught in the water as it flows through.
• are great locations for recreation and sporting activities, such as camping, swimming, boating, fishing, bushwalking and birdwatching.

Wetlands slow down the flow of water and help reduce the amount of sediment in stormwater runoff. They also allow natural processes, the sunlight and time to help clean the water.

Melbourne has many wetlands - both natural and constructed.

How do constructed wetlands work?

Wetlands slow the flow of water, as water is forced to travel through a series of small ponds. It also holds water like a sponge, and slowly releases water to a river or creek. These characteristics are the basic principles behind constructed wetlands.

Constructed wetlands are normally built on land set aside for flood protection, usually next to rivers or creeks that are moderate or poor in condition. Shallow ponds are dug out on these lands.

There are many types of wetland designs. However, most constructed wetlands will have:

• Sedimentation ponds - to remove rubbish and large sediments
• Carbon filters - to remove organic material such as leaf litter and grass clippings
• Marshes - to remove nutrients and to allow sunlight to help purify the water

Wetlands are planted with thousands of hardy indigenous aquatic and semi-aquatic plants, including sedges and rushes. Some plants are planted in shallow areas, others in deeper areas. All the plants, however, have a role - they remove nitrogen and other pollutants from the water.

Sedimentation ponds are generally placed before the wetland, to allow allows sediment to settle out of the water.

A carbon filter trap is placed at the beginning of the wetland to trap leaves and grass clippings, and organic matter.

When water enters the marshes, more particles slowly settle on the bottom of the pond. Very fine particles are absorbed by plant stems. Nitrogen in the water is removed by the plants and through natural processes.

What is Melbourne Water’s role?

Stormwater is often polluted by litter and other contaminants washed from roads, gardens, nature strips and gutters.

We build and manage wetlands to treat stormwater - these remove nutrients and other pollutants before they reach our rivers, creeks and bays. We manage 117 constructed wetlands. More wetlands are being designed or constructed to treat stormwater run-off.

We are also working with developers and local councils to include wetlands into new housing estates to help treat stormwater before it reaches a local river and creek.

Bio-retention median at Lynbrook Estate

Case study: Lynbrook Estate Lynbrook Estate, a housing estate in Melbourne's south-east, has one of the earliest examples of Water sensitive urban design in Melbourne. At the estate, the stormwater system has been specially designed and built to treat stormwater before it reaches the Eumemmerring Creek. Stormwater flows down roads designed especially to funnel water to shallow grassed swales. The water seeps through the swales into an underground system of gravel trenches and perforated pipes. The pipes carry the water to a set of constructed wetlands. The wetlands filter and clean the stormwater naturally, before it reaches Eumemmerring Creek.

Follow the stormwater in a water sensitive urban design housing estate