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Catchment Information

The Torrens Basin extends from Mount Pleasant in the Mount Lofty Ranges to West Beach on the Adelaide Plains and contains the River Torrens and Little Para River. Much of metropolitan Adelaide and the central Adelaide Hills lies within the Torrens Basin, an area of just over 620 square kilometres.  The Torrens Basin is home for close to 500,000 people living in more than 150,000 residences. Approximately 18,000 commercial and industrial premises (including most of Adelaide's CBD) are also located in the catchment, which represents a major proportion of Adelaide's economic and business activity.

The Rural Torrens Basin contains the Torrens Catchment, with its 13 sub-catchments including the Main Channel and the Little Para Catchment. It is located approximately 30 km east of Adelaide, and extends from Kersbrook in the north, Summertown in the south, and beyond Mount Pleasant to the east.

The average annual rainfall in the basin is 770 mm, varying between 700 mm in Mt Pleasant and 1000 mm near Summertown. Parts of the River Torrens Catchment supply the Millbrook and Kangaroo Creek Reservoirs, which have a total capacity of 16,500 ML and 19,160 ML, respectively. The River flows south-west past Gumeracha, down to the Gorge Weir, before entering the Adelaide Plains.

The headwaters of the catchment are characterised by a landscape of low relief related to the high summit plan.  Towards the middle of the catchment, the landscape grades to rolling hills, whilst in the west, the topography is dominated by the steep-sided rocky valley of the Torrens Gorge.

The hydrology of the Torrens catchment is influenced by the operation of the Metropolitan Adelaide Water Supply System.  There are two sources of water; natural catchment inflows and transfers from the River Murray.  River Murray water is transferred via the Mannum-Adelaide pipeline and discharged into the Upper Torrens catchment at Mt Pleasant, Angus Creek or Millbrook Reservoir.

The Torrens Catchment contains the townships of Mount Pleasant, Mt Torrens, Birdwood, Gumeracha, Forreston, and Kersbrook. A wastewater treatment plant (WWTP) which is owned and operated by SA Water, is located at Gumeracha. Treated effluent is pumped to a nearby 15 hectare pine plantation. Septic tank effluent disposal schemes (STEDS) are located at Birdwood (which also accepts effluent from Mt Torrens) and Mt Pleasant. Re-use schemes are operated at both STEDS sites with full re-use occurring either onsite or at local recreational facilities.  The other towns in the catchment and rural houses have onsite septic systems (approximately 1100 rural residences).

The Torrens Catchment is an open catchment where agricultural land use is largely unrestricted. The majority of land is held in private ownership (83%) with crown lands managed by Forestry SA, National Parks and Wildlife Service and SA Water. Major land uses in the catchment include; animal husbandry (broad-scale cattle, horse and sheep grazing and intensive grazing on dairying and horse studs), native vegetation (including forestry), recreation and protected areas, exotic vegetation (including forestry), vines and orchards. Landuse has change quite significantly over the last 10 years with grazing being replaced with viticulture or to a less extent other forms of annual or perennial horticulture.These land uses and associated management practices can conflict with source water protection goals. Such management practices include; grazing in watercourses, and the inappropriate use of pesticides or fertilisers.

The recent and continuing shift from broad based agricultural activities to more water intense industries such as horticulture, viticulture and vegetables in the Torrens catchment has seen an increase in farm dams of about 7% in 6 years (in 1999) to around 1,470 dams in 2005. 

Water quality is influenced by many factors, both natural and human-induced, including soil and vegetation types, climate, land use and management practices. Water quality may be particularly threatened by land uses operating in close proximity to watercourses and reservoirs, where there is little opportunity to buffer potential contaminants entering the system by overland flow or groundwater baseflow.

Total nitrogen and total phosphorus concentrations generally exceed guideline values for aquatic ecosystems and are sufficient to promote algae growth within reservoirs, with trends in concentration appearing to increase broadly across the area.  Nutrient and sediment loads are higher where land uses are intensive (such as market gardening, orchards, and urban development).

Land uses may generate point or diffuse source pollution. Point source pollution is generally associated with industrial activity or specific facilities such as wastewater treatment plants. Diffuse source pollution is a major contributor to poor water quality in the Region and is created when many small sources of water pollution across a catchment combine to create a significant water pollution impact. Urban development, agriculture and forestry can all create significant diffuse source pollution. Work in the Torrens and Onkaparinga catchments indicates that nutrients in surface water generally arise from catchments (diffuse sources). For example, 55% and 90% of the total phosphorus at Millbrook Reservoir and Kangaroo Creek respectively is from catchment sources. Diffuse catchment sources also supply significant amounts of suspended particulate matter, although bed and bank erosion also contributes a significant proportion of the suspended particulate matter.

Catchment runoff has a strong seasonal pattern, with most occurring between May and October after periods of significant rainfall and following adequate catchment wetting. The natural annual stream flow in the Torrens catchment is highly variable with volumes varying by more than an order of magnitude. Annual gauged flows at Sixth Creek had a range of 21,550 ML/year (4.88 ML/ha) to 2,600 ML/year (0.59 ML/ha) over a 21-year period. Similarly, at Mt Pleasant Creek, at the lower rainfall end of the catchment, the range was 8,800 ML/year (0.34 ML/ha) to 30 ML/year (0.01 ML/ha) over a 29-year period. An indication of the intra-annual variation in flow is provided by gauged data from Sixth Creek, where the average monthly runoff is highly seasonal with 59 ML/month in February and 1803 ML/month in August.  When rainfall occurs, producing catchment run-off, the water quality of rivers and streams can be reduced significantly. During two weeks of intense runoff in 1996, 81% of the annual suspended sediment load and 67% of the total phosphorus load were exported from the Sixth Creek sub-catchment. During this period, the suspended sediment concentration went from 62 mg/L to 2,010 mg/L (AWQC 2001).

Pathogen levels in the upper River Torrens catchment are variable but have been recorded above desirable levels (for drinking water supplies) in winter at Gumeracha Weir. The presence of these pathogens is reduced through detention in reservoirs, treatment processes and management actions within the catchment. The loads of human-infectious parasitic pathogens and bacterial indicators, have been assessed in the Torrens Catchment.  Cattle were considered to be the most significant source, closely followed by sheep. For both cattle and sheep, juvenile stock was considered the most significant source.  The Board has a Watercourse Restoration Program, which improves water quality (including reducing pathogen loads) and improves biodiversity within the region.

There is over 840km of watercourse (third order or greater) in the catchment. Watercourses in the upper subcatchments are less stable, particularly where land clearance has allowed the mobilisation of soil onto floodplains. This sediment is currently being eroded from these floodplains, creating incised watercourses in many locations. Further down the catchment, watercourse beds and banks become rockier and more resistant to erosion; generally the bench deposits that occur in these areas can be stripped off during high flow or heavy rain. Catchment managers have made significant investments to fence sensitive areas from grazing animals and provide a buffer to the transport of pollutants. By 2004, a total of 161km of watercourse had been, or was being, fenced or revegetated through the activities of the Torrens Catchment Water Management Board.  A more recent watercourse fencing survey (conducted in 2009) in the Upper Torrens Catchment (upstream of Gumeracha) estimates that 66 km, equivalent to 34% of watercourses have been fully fenced, with an additional 22.7km or 11% partially fenced.

The Board also provides a Land and Biodiversity Services which is directed at protecting biodiversity, native vegetation, habitats (including inland waters) and primary production, and managing interactions between primary production, and cleared rural land and ecosystems.   These services contribute to improving water quality within the region. 

A draft Water Allocation Plan for the Western Mount Lofty Ranges has been developed. This Plan will guide the management of the water resources of the Western Mount Lofty Ranges, to achieve a sustainable long-term productive future for our region.

The EPA has assessed River Health in the Mt Lofty Ranges, stating that region is biologically diverse, with more than 500 types of aquatic macroinvertebrates being recorded from 1994–1999. The most common members include oligochaetes (worms), hydrobiid snails, amphipod crustaceans (Austrochiltonia australis), chironomid midge larvae (Cricotopus and Chironomus species), blackfly larvae (Simulium ornatipes) and hypogastrurid springtails. A number of rare types of macroinvertebrates are found in the region.  Streams in good condition were generally from catchments with large proportions of native vegetation or sites located in the mid to upper reaches of region, characterised by high rainfall and minimal human disturbance (e.g. Torrens River at Gumeracha and Angas Creek). The waterways that rated poorly were generally from streams that flowed through urban areas or received considerable runoff from agricultural lands. The urban stormwater impacts were noted from part of the North Para River, the lower reaches of the Little Para and Torrens rivers. Transfers of River Murray water impact on the Torrens River from Mt Pleasant to the junction with Sixth Creek.

 

Select a site below to view Water Quality Summary Information
Catchment Sites
First Creek @ Waterfall Gully A5040517
Sixth Creek @ Castambul A5040523
Torrens River @ Gorge Weir A5040501
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