30km east of Adelaide. It flows in a south westerly direction and enters the Gulf of St Vincent at Port Noarlunga. There are two major water storages on the Onkaparinga River. The largest is the Mt Bold Reservoir, used to supply water to the Adelaide metropolitan area. The water from the reservoir is not directly extracted, but is released downstream to the second storage, Clarendon Weir, where it is then diverted to the Happy Valley Reservoir.The total area of the Onkaparinga Catchment is 557 km2. The main tributaries of the Onkaparinga River to Mt Bold Reservoir are Inverbrackie, Lobethal, Lenswood, Cox, Aldgate and Echunga Creeks. Downstream of the reservoir are the Scott Creek and Baker Gully.
The major towns in the catchment to Mt Bold Reservoir are Lobethal, Balhannah, Hahndorf, Stirling, Aldgate and Bridgewater. Downstream the Onkaparinga River passes through Clarendon and through the southern Adelaide suburbs of Old Noarlunga and Port Noarlunga.
The population within the Onkaparinga Catchment is estimated at 130,000 residents.
Land Use:
The Onkaparinga Catchment is used for many different activities. Part of the catchment is urbanised, while large portions are used for farming. The most common land use type is grazing, both dairy and non-dairy. The dominant crop in the northern catchment is rotational potatoes, while the north-western section is perennial horticulture. Along the western side of the catchment, and particularly surrounding Mt Bold Reservoir, there exist large areas of native vegetation. The urbanised region lies in the Aldgate Creek Catchment, which is located on the western side, stretching from Crafers to Bridgewater. Below the Mt Bold Reservoir, and in the Baker Gully Catchment, the land use is vineyards and grazing. The Onkaparinga Gorge is used for recreational purposes.
Port Noarlunga Reef:
Port Noarlunga Reef is a narrow reef, formed from a consolidated Pleistocene Epoch sand dune, about 29km south of Adelaide and on the eastern seaboard of the Gulf of St Vincent. The reef is 1.6km long and lies 400m offshore. The reef has been protected from spearfishing since 1965 and fully protected as an Aquatic Reserve since 1971. A jetty runs from the shore to the reef and, prior to a severe storm in the late 70's, a ladder provided access to the reef-top during low tide. Presently the end of the jetty is about 20m from the reef.
The reef has several distinct features:
An algal-mussel community forms a mat on the reef-top, kelp, Ecklonia radiata, dominates the outer reef slope and supports a diverse community a rich sponge, hydroid and ascidian community is found on the southern end of the reef numerous fish species live around the reef parts of the reef are cavernous, with overhangs and undercut areas that support ascidians and hydroids.
Onkaparinga Estuary:
The estuary is the floodplain into which the Onkaparinga River discharges. The estuary is a 10.5km system, from its mouth near Port Noarlunga to the ford at Old Noarlunga. It is the third largest in South Australia.
The estuary has four distinct areas:
The coastal dunes and bar, the river, which is under tidal influence, revealing narrow mudflats upstream to Old Noarlunga, floodplains, the salt-tolerant samphire community on the estuarine mudflats, which is the only example of this plant community type south of Adelaide, along the shores of the Gulf of St Vincent.
Water Resource Management:
Pollutants in the catchment include bacteria, nitrogen and suspended solids.
There also exists the threat of pollution from stormwater run-off, heavy metals, oil spills, bridge construction, effluent discharge, road run-off, housing development, and general human activity.
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