page_title: River Torrens
section_title: Flood mitigation
hierarchical_section_title: River Torrens / Changes after 1836 / Flood mitigation
caption_attribution_description: "Breakout creek". The constructed outlet for Adelaide's River Torrens Photo from the bank of the river about 150m from the sea at Henley Beach
context_page_description: 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 85 kilometres 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.
context_section_description: A flood mitigation bill was passed in 1917 to not only combat the damage caused by floods but also the public health risk due to the lack of mains sewerage in the western suburbs. Popular opinion favoured diverting the flood waters into their "natural" outlets of the Port and Patawalonga Rivers. The chief engineer of the department of works favoured a cutting through sand dunes near Henley Beach, allowing the river an outlet, mitigating floods and preventing silting of the Port River. He also advocated the construction of a reservoir where the Kangaroo Creek Reservoir is now, to both mitigate floods and provide summer irrigation water for market gardens. Unfortunately the bill lapsed with no action as the government and local councils were unwilling to fund the works. The Millbrook Reservoir opened in 1918 as a summer water source, and flood mitigator if required. A bill was passed in 1923 to enact the earlier plan of cutting through the dunes and adding an upstream regulating weir. Again the bill lapsed due to a lack of commitment from parties on payment.
  A major flood in 1931 and another in 1933 led to the latest in a series of government enquiries. In 1934 the "Parliamentary Standing Committee on Public Works" recommended that an outlet for the river be created to accommodate flows of up to 370 m³/s (13,000 cu ft/s), covering a 1 in 60-year flood. The work was partly financed by a Commonwealth Government grant with the State Government arranging for the balance. The State Government, western and eastern local councils and the Municipal Tramways Trust shared interest costs. The scheme was enacted in 1935 and largely completed by 1939 with the creation of the "Breakout Creek" channel. The scheme involved diversion of the river at Lockleys (near Adelaide Airport), with the original channel blocked and a new channel created to the sea. The reedbeds and swamps were subsequently drained and some of their area is now the site for the suburb of West Lakes.
  Based on recommendations in a 1925 report on flood mitigation, work began in the 1960s on the building of the Kangaroo Creek Reservoir, opened in 1969 with a capacity of 24.4 megalitres (860×10³ cu ft). It remains the only reservoir damming the river rather than being fed from weirs. The "River Torrens Committee" was formed in 1964 to advise the minister of works on preserving and enhancing the river's natural beauty, and developing it for recreational uses. The "River Torrens Acquisition Act 1970–72" was passed, authorising the purchase of land, in some cases 60 metres (200 ft) back from the top of the river's banks.
  By 1980, further development along the riverbanks and removal of levées had reduced the outlet's capacity to a 1 in 35-year flood. A study showed that a 1 in 200-year flood would inundate 13,000 properties; so the Kangaroo Creek dam's level was raised, its spillway modified, the breakout creek channel capacity increased and some bridges reinforced. A development plan was approved in 1981 to purchase land along the length of the river, create a flood mitigating linear park and also to modify the Kangaroo Creek dam further. The sea outlet was enlarged to a capacity of 410 m³/s (14,000 cu ft/s) which now covered a 1 in 200-year flood. When the O-Bahn Busway was opened, the bridges were designed to cope with this scale of flood, although the two bridges in St Peters would likely be awash.
caption: The Torrens's sea outlet, "Breakout creek channel"
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