Improving the River Torrens from the foothills to the sea
The lower River Torrens crosses through the highly urbanised Adelaide Plains from Athelstone to the sea. It is vulnerable to the impacts of this built environment with contaminants entering the river with stormwater runoff, which pollutes the water.
Leaf drop from exotic trees increases nutrients in the water and lowers oxygen levels necessary for aquatic animals to survive. This can result in poor health and even death of aquatic animals that live in and rely on these waterways.
The roots of some exotic tree species can also cause a loss of habitat, and river bed and bank stabilisation is impacted by exotic tree roots leading to erosion.
This River Torrens Recovery (2014-16) project targets priority sites to improve water quality and biodiversity in the river and the coastal waters where it enters the sea. It will do this through:
- weed control
- revegetation with native plants
- stabilising river banks
- reducing litter and pollutants from entering the river.
In particular, non-native vegetation will be removed across 20 hectares and replaced with local native species, including 0.5 hectares of aquatic plants.
A section of the river bank which is eroding will be repaired in the City of Norwood Payneham and St Peters and European Carp will be significantly reduced from the Torrens Lake.
A gross pollutant trap will be installed at the Halsey Road Pump Station and water sensitive urban design structures will be constructed within the City of West Torrens.
Want to know more about a site?
Flinders Park (north side of the River Torrens), Henley Beach and Kidman Park - Kelly Mader City of Charles Sturt on 8408 1208
Felixstow - Martin Woodrow City of Norwood Payneham & St Peters on 8360 9008
Windsor Gardens (west of Sudholz Rd) - Andy Walker City of Port Adelaide Enfield on 8405 6600
Dernancourt, Highbury and Windsor Gardens (east of Sudholz Rd) - Brad Mann or Mick Medic, City of Tea Tree Gully on 8397 7444
Vale Park - Team Leader Assets and Infrastructure Town of Walkerville on 8342 7100
Athelstone and Paradise - Henry Haavisto Campbelltown City Council on 8366 9285
The project in detail
Why remove exotic trees
Most exotic trees along the River Torrens come from Europe, are deciduous and lose their leaves in autumn.
Whilst this can be visually spectacular, autumn leaf drop smothers aquatic habitat, creates barriers to flow, produces localised flooding and increases nutrients in the water as a result of the breakdown of organic matter. This results in unsuitable water quality for our native aquatic plants and animals.
When these nutrients flow out to sea they can impact on the coastal and marine environment, especially Adelaide’s coastal seagrass meadows. These meadows stabilise the near shore sands and provide habitat for many of our commercial and recreational fishing species.
Increased nutrient levels also promote algal growth which smothers seagrass leaf blades, reducing the amount of light available for these grasses to photosynthesise and grow.
Exotic trees that sucker and produce dense growth can block and divert the flow of water which sometimes leads to erosion and localised flooding. Poplars, ash and willows all exhibit this behaviour.
Willows produce a dense root mat which can build up the watercourse bed and reduce flow capacity. These dense roots stop native water plants from establishing. The increased shade of exotic trees also makes it hard for native water plants to grow.
So removing exotic trees reduces blockages and increases flow capacity. This helps reduce flood risks by increasing the volume of water held in the watercourse and decreasing the time it takes to reach the sea.
Local native vegetation
Our native trees also drop leaves, but they drop and replace their leaves in a more even pattern throughout the year, rather than contributing a large quantity of organic matter to watercourses over a short period.
Native trees do not sucker or produce dense growth to the same extent as some exotic trees.
Native trees produce hollows which provide a home for many of our local birds, bats and possums to nest. They also provide the best food resource for our native animals.
How do gross pollutant traps and water sensitive urban design help?
Gross pollutant traps and water sensitive urban design structures, such as roadside rain-gardens, improve water quality by capturing leaf-litter, urban rubbish and sediments before they enter watercourses.
Rain gardens also filter pollutants from water as it percolates through the soil profile before it then enters drains and watercourses.
Why remove European Carp?
The destructive feeding habits of European Carp lead to reduced water quality which in turn has negative impacts on native aquatic plants, animals and general river health.
European Carp uproot vegetation and stir up sediments, leading to increased turbidity. They also destroy aquatic plants by direct grazing and uprooting them, which leads to the undermining and erosion of watercourse banks.
This project is funded through the Australian Government's National Landcare Programme with support from the following organisations: