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Water is pumped up from Whites Creek into the ‘sedimentation basin’ of the wetland. In this basin, mud and dirt particles settle to the bottom. The water is then moved through the other ponds of the wetland one by one. In the last pond, some water returns to the creek and some is ‘reticulated’ (sent back around the wetland).

Only a portion of the creek water enters the wetland. The wetland is designed to deal with “low flows”, taking most of the water from the creek in dry weather, but not much of the water in very wet weather. If the wetland had been much bigger it would have been able to treat much more water.

Cleaning stormwater

Wetlands use natural processes to help clean water. Water in the city carries pollution from roads, pavements, and gutters into the Bay and Harbour. This can damage marine life and create unhealthy water for people using our waterways. Constructed wetlands are one way to reduce the amount of pollution that enters these waterways.

This wetland is designed to treat stormwater in low flow conditions, using natural physical processes (e.g. settling of particles, filtration through reeds) and biological processes (plants removing nutrients from the water, small organisms breaking down organic matter).

Design features

  • The Whites Creek Wetland system consists of 5 ponds and a sedimentation basin. Each pond has a surface area of approximately 130m2 with gradual slopes and a maximum water depth of 0.5m.
  • The total wetland area is approximately 1,200m2.
  • Contaminated water and sediments from the channel are pumped up to the wetland by a pump-out system.
  • Water and sediment first enters the wetland system at the sediment basin located at the southern end of the wetland. Here the sediment in the water is allowed to settle out and the water continues to travel slowly through the remaining five ponds in a clockwise direction.
  • Each time the water passes through a pond the water quality is improved since the nutrients and chemicals contained within the water are absorbed by the plants and soil’s structure within each pond. As the water is slowed down, a natural process of settling also takes place.
  • Treated water returns to the channel after passing through the fifth pond.

Sedimentation

Snake-necked TortleIn August 2009, 60 tonnes of sediment were removed from the Whites Creek wetland. The sediment had been building up in the wetland in the seven years since the wetland was completed in 2002.

This is a great result for the health of Rozelle Bay, as the sediment contains nutrients, heavy metals and other contaminants that would have a negative effect on the marine ecosystem if they were allowed to find their way into the harbour. The wetland was purpose-built to remove these contaminants from stormwater in the Whites Creek canal, while at the same time providing a freshwater habitat for long-necked tortoises, frogs, native fish and many other aquatic life-forms. 

The periodic removal of large amounts of sediment is a normal and necessary part of wetland maintenance, and has only a temporary effect on the biodiversity value of the wetland. The wetland recovered quickly from the disturbance - frogs, native fish, dragonflies and other animals  returned to the wetland.