Built in 1894–96 as a solution to Adelaide's sewer problems, the weir supplied water to the Adelaide plains to flush the sewers as there simply was not enough water to keep the population healthy. A tunnel was built with ponies and carts through the hills to Happy Valley where a reservoir was built. The water flowed by gravity from the Weir through the tunnel to Happy Valley Reservoir. There is no other catchment for this reservoir. Mt Bold Reservoir was added in the 1940s to again supplement Adelaide's water supply with the Clarendon Weir acting as a holding dam down stream. The water is used to supply about half of the Adelaide region's water needs.[citation needed]
In the mid-1960s, the wall of the Clarendon Weir, originally constructed with large blocks of Macclesfield marble, was raised from 14 metres (46 ft) to its current height of 14.6 metres (48 ft) .[2]
^"Clarendon Weir, Onkaparinga River". South Australian Heritage Places Database. South Australian Government. 8 November 1984. Retrieved 26 April 2018.