The wetland consists of three large connected basins, covering a total of 16.9 hectares, 10.7 of which is underwater. The overall design of the wetland is to filter water slowly through the basins, which is being progressively planted with species of water plants to remove phosphorus and nitrogen from the water. Each basin is divided into individual cells, with concrete spreader bars, which slow down the movement of water across the basin. The water will take approximately 150 days to flow from the effluent ponds through the entire system. All basins are connected, and can also be isolated, so that any basin can be dried or flooded when necessary to mimic a natural system. This sets Laratinga apart from other constructed wetlands. An important function of the wetland system is that water does not enter the Mt Barker Creek, except perhaps during winter. The wetland-cleansed water is used for local irrigators, and the creek will return to a more natural state of drying in summer and running in winter and spring. This will benefit the ecology of the creek tremendously.
This basin is where 80-90% of the nutrients will be removed from the water. This shallow, serpentine shaped basin is designed to slow water down and spread it out, as well as allowing for the survival of existing River Red Gums (Eucalyptus camaldulensis). Several concrete spreader bars will slow the movement of water further. This basin will be planted with Phragmites australis (Common Reed) which is widely known for its effectiveness at removing nutrients from water.
The ground to the west of basin one has been planted with Drooping Sheoak (Allocasuarina verticillata) with an understorey of Hakeas to form a food forest for Cockatoos and in particular the Yellow Tail Black Cockatoo.
This basin is approximately 3.6 hectares in size, connected to basin one by a concrete pipe to combat slope problems between basins one and two. The water entering this basin has improved considerably in clarity due to the filtering of basin one. This gently sloping basin is designed to support a variety of plant species. Deep pools provide habitat for aquatic organisms such as fish when the basin dries out in summer. This basin will be stocked with indigenous fish species, including Mountain Galaxias Galaxias olidus. Eastern Snake-necked turtles and invertebrates such as Yabbies, Shrimp and aquatic insects colonise the basin at present.
An island in the centre of the basin, planted with River Red Gums (Eucalyptus camaldulensis) with a Wattle and shrubby understorey with native grasses and Common Buttercup (Ranunculus lappaceus) is designed to provide a safe refuge for birds.
Stormwater from the nearby Martindale Estate runs past the basin and enters the Mt Barker Creek, and has been planted with species including Bolboshoenus and Juncus to filter the water and prevent erosion.
Between basin two and three, a shallow rock pool area has been created for the use of schools as part of the Environmental Education Program. This area will provide an opportunity that is easily visible for children to view aquatic flora and fauna.
This is the final basin in the system which also has a large island in its centre, as a bird roosting area. This island has been planted with River Red Gums and Silver Banksias (Banksia marginata) with an understorey of tussocky grasses A bird hide has been constructed on the island for research purposes of managers and university students. When the basin is full, the island will only be accessible by boat.
This large basin (approximately 5.9 hectares) varies in depth from a few metres to shallower ponds between 300 and 750mm deep. Dead branches introduced to the water to provide habitat for aquatic organisms. As with basin two the area has been planted with a variety of indigenous aquatic, semi aquatic and terrestrial plants, with prickly species to provide nesting habitat for smaller bird species. The water can be pumped from this basin to local irrigators, parks and gardens.
The wetting and drying cycle
Many natural wetlands in Australia are recharged by seasonal rainfall/runoff inflows (or springs) and under normal conditions dry out in low rainfall/runoff periods. For many native plants and animals in southern Australia, these wet and dry periods are a necessary part of life.
Periodic drying of constructed wetlands imitates this natural cycle, which has a range of benefits to the wetland itself and its ecosystem components. Dry periods help to ensure the wetland soils maintain their ability to absorb nutrients, particularly phosphorus. They also allow oxygen into the soil that aids the decomposition of plant material, increasing soil fertility. (Water resource requirements for Laratinga Wetland by Natural logic, 2011)