River Torrens
The River Torrens is the most significant river of the Adelaide Plains. It was one of the main reasons for the siting of the city of Adelaide, capital of South Australia. It flows from its source in the Adelaide Hills near Mount Pleasant, across the Adelaide Plains, past the city centre and empties into Gulf St Vincent between Henley Beach South and West Beach. The upper stretches of the river and the reservoirs in its watershed supply a significant part of the city's water supply.
The river is also known by the native Kaurna name for the river—Karrawirra Parri or Karrawirraparri, having been officially dual-named in 2001. Another Kaurna name for the river was Tarndaparri. The river was thought to be a reflection of the Milky Way, and was the heartland of the Kaurna people, who lived along its length and around the tributary creeks.
At its 1836 exploration by William Light, an inland bend was chosen as the site of the Adelaide city centre and North Adelaide. The river was first named the Yatala by the initial exploration party, but later renamed to honour Robert Torrens senior, chairman of the board of Colonisation Commissioners for South Australia from 1834 to 1841.
From March 1837 settlers camped in tents and makeshift huts along the west end of the River Torrens and freely used the river's resources. A Native Location was created on the north banks of the Torrens and indigenous labour was often used by the settlers for tasks such as hewing wood or delivering water. During the early years of settlement, the river acted as both the city's primary water source and main sewer, leading to outbreaks of typhoid.
Since European settlement the river has been a frequently touted tourist attraction. The river's long linear parks and a constructed lake in the lower stretch are an icon of the city. The river's flora and fauna have been both deliberately and accidentally impacted since settlement. In the 19th century, native forests were cleared, gravel removed for construction and many foreign species introduced. With construction of the linear parks, many species native to the river have been replanted, and introduced species have been controlled as weeds.
The river and its tributaries are highly variable in flow, and together drain an area of. They range from sometimes raging torrents, damaging bridges and flooding city areas, to trickles and completely dry in summer. Winter and spring flooding has prompted the construction of flood reduction works. A constructed sea outlet, landscaped linear parks and three holding reservoirs contain peak flow.
Physiography
The River Torrens runs largely westward from the Adelaide Hills, through the centre of Adelaide to the Gulf St Vincent. It originates close to the eastern fault scarp of the Mount Lofty Ranges, near Mount Pleasant, approximately above sea level. It runs predominantly along faulted north-south ground structures, which were formed over 250 million years ago during the Paleozoic era then further dislocated during the Cretaceous and earliest Tertiary. There is a subsidence along the Para Fault which also affects the rivers flow. This subsidence was formed in the last two million years, after the Pliocene era.From its origin to Birdwood the river follows rolling, relatively level country before entering a hilly section that continues to Gumeracha. The river then follows sedimentary rock strata before entering a gorge after Cudlee Creek. It flows through the gorge to Athelstone, passing over the Eden Fault Zone of the Adelaide Hills face and associated escarpment. After the scarp it flows over sedimentary rocks of varying resistance to erosion, which has led to interspersed narrows and broad basins. From the base of the Adelaide Hills to the Adelaide central business district it runs in a shallow valley with a terraced floor, then down the slope of its own alluvial fan. The structure of this fan shows that the river formerly entered Gulf St Vincent via the Port River. Over time the Torrens deposited sediment, choking its own outflow; becoming locked behind coastal sand dunes and forming the swampy areas of the Cowandilla Plains and The Reedbeds.
Tributaries
The Torrens is fed by numerous seasonal creeks, which are dry for most of the year in their lower reaches, but prone to occasional flooding during the winter and spring. There are five main creeks that join it from the southern side as it crosses the Adelaide Plains east of Adelaide, and at least five more in its path through the Adelaide Hills.The plains tributaries, known as First to Fifth Creeks, lie to the east of the city, with First being the most southerly and the rest numbered consecutively northward. They were once named Greenhill, Hallett, Todd, Anstey and Ormsby rivulets respectively, and had Kaurna names before European settlement.
First, Second and Third Creeks have been particularly heavily modified. Some sections have been converted to concrete channels; others run through landscaped private gardens and some run in underground pipes. Much of the original vegetation has disappeared from the creeks, particularly those closest to the city. Introduced species including olives, bamboo, boxthorn, watsonia and blackberries have displaced native flora. There is some risk of flooding from all of these eastern suburbs creeks, as shown by the Floodplain Study, which includes plans and maps drawn up by the City of Burnside and neighbouring councils.
First Creek begins in Cleland Wildlife Park on the western side of Mount Lofty and Crafers, flows north-west through the south-eastern suburbs, past a drop at the Waterfall Gully falls, through Hazelwood and Tusmore Parks, and Marryatville High School, before discharging into the Torrens near Adelaide Zoo. Much of its course through the suburbs has been canalised, some underground. About 7.5% of its flow is diverted as it flows through the Adelaide Botanic Garden to create the First Creek Wetland, a scheme set up to ensure water security and to encourage diversity of flora and fauna in the area, thus helping to maintain healthy urban environments. Botanic Creek runs through the eastern Adelaide parklands from south to north, into the Adelaide Botanic Garden before joining First Creek.
Second Creek arises in the Summertown area of the Adelaide Hills, north of First Creek, and flows through Greenhill, through Slape Gully, entering the more populated suburbs as it flows through the Michael Perry Reserve in Stonyfell and onwards through the eastern suburbs of Erindale, Marryatville, Kensington and Norwood, much of it canalised underground as far as St Peters. The St Peters section is an open canal shortly before it joins the Torrens. It was once called Hallet's Rivulet. Stonyfell Creek, arising on the eastern boundary of Stonyfell, flows through Kensington Gardens, including an open stretch in the Reserve before again being piped underground under West Terrace, passing under Kensington Park and Beulah Park. It joins Second Creek near the junction of Magill and Portrush Roads.
First and Second Creeks come within about of each other in Marryatville, with formerly only flat land between them.
Third Creek arises near Norton Summit and flows through the suburbs of Magill, Tranmere, Trinity Gardens and Payneham, much of the way underground, before discharging into the Torrens at Felixstow.
Fourth Creek, or Morialta Creek, arises on the other side of Norton Summit, with various tributaries flowing into it from Marble Hill and Lobethal. It is most well known for its falls in Morialta Conservation Park. "Moriatta", a Kaurna word meaning "ever flowing", is now the official name of Fourth Creek. This name has been adapted to Morialta, which is now the name of an electoral district, school and the park through which the creek flows.
Fifth Creek arises within the Morialta Conservation Park, runs alongside Montacute Road for some way and discharges into the Torrens at Athelstone.
The largest catchment of the Torrens is Sixth Creek in the Adelaide Hills, which joins the Torrens at Castambul on Gorge Road.
Water flow
At the time of European settlement the river was a summertime chain of waterholes bounded by large gum trees. Flowing through the area where the city of Adelaide is sited the river was sometimes invisible beneath its gravel stream bed. It frequently flooded in winter and did not reach the sea, instead ending at coastal dunes where its waters created a vast but shallow freshwater wetlands. These wetlands, known as The Reedbeds after the dominant vegetation, occupied a large area of the western Adelaide Plains and were also fed by other waterways.The river only flowed to the sea through the Port River, Barker Inlet, and Patawalonga River following heavy rain.
The river's catchment area of approximately is the largest of any waterway within the Adelaide region. The upper reaches are used to create a potable water supply for metropolitan Adelaide with the river supplying three of Adelaide's eight reservoirs. The upper catchment has an average annual rainfall of between at its eastern end to near Uraidla. The Torrens has a very variable flow leaving early settlers to use trial and error in determining bridge heights, with many bridges consequently being washed away. Due to the variability of Adelaide's climate, flow rates can change from a trickle to flood conditions quickly. On 5 June 1889, prior to major flooding, the flow rate before it entered the suburbs was, rising to, eight days later.
Since settlement it has repeatedly flooded, sometimes with disastrous consequences. Adelaide's western suburbs were especially prone to flooding due to their location on the river's alluvial fan. As development of Adelaide progressed the amount of rainfall required for flooding decreased and consequent damage increased. Increased stormwater runoff, modification of the river's banks and other changes all served to exacerbate the problem. Work done by various groups to minimise flooding was often counter productive with the creation of levees, moving and widening channels and other works simply shifting the flooding elsewhere.
Two early floods were, 18 September 1841 which resulted in two people drowning while trying to cross the river at Klemzig, and 22 September 1844, the largest recorded since settlement began, when "Shands' Brewery" was washed away after the river undermined its foundations. The 1899 flood was particularly widespread with extensive flooding of both the river and its tributaries, after a year with of rain compared to the Adelaide average of. The river flooded market gardens and farms throughout its hills course causing extensive damage. Norwood was inundated to The Parade, Adelaide to Pirie and Rundle Streets, and many areas west of the city were left in a shallow lake. The river ran deep over the weir near Thorndon Park Reservoir, over the Torrens Lake Weir and over the Morphett Street Bridge. The Underdale Bridge was destroyed, the Torrens Lake weir's bridge damaged, and the Felixstow Bridge over the Fourth Creek washed away.