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The Bradfield Scheme, a proposed Australian water diversion scheme, is an inland irrigation project that was designed to irrigate and drought-proof much of the western Queensland interior, as well as large areas of South Australia. It was devised by Dr John Bradfield (1867–1943), a Queensland born civil engineer, who also designed the Sydney Harbour Bridge and Brisbane's Story Bridge.
The scheme that Bradfield proposed in 1938 required large pipes, tunnels, pumps and dams. It involved diverting water from the upper reaches of the Tully River, Herbert River and Burdekin River rivers. These Queensland rivers are fed by the monsoon, and flow east to the Coral Sea. It was proposed that the water would enter the Thomson River on the western side of the Great Dividing Range and eventually flow south west to Lake Eyre.
G. W. Leeper of the school of agricultural science at the University of Melbourne considered the plan to be lacking in scientific justification.
In 1981, a Queensland NPA subcommittee proposed a variation of the scheme. The Revised Bradfield Scheme, November 1981
It is claimed that extra water and vegetation in the interior may then produce changes to the climate of Australia, however various studies have concluded that this is unlikely. This may increase the rainfall in areas of southern Queensland and northern New South Wales. Extra rainfall may drought-proof Eastern Queensland, and thereby improve river inflows to the Murray-Darling River system. It is claimed that a full Lake Eyre would moderate the air temperature in the region by the absorption of sunlight by the water instead of heat radiation from dry land into the air. No evidence to support the theory that an inland sea would increase rainfall has ever been produced, nor have any of the other claims been supported.
Elevation measurements were taken with a barometer, leading to inaccuracies in land heights and mistakes in the proposal. In most cases no flow record of the rivers were available to Bradfield. He used an empirical formula which assumed 33% of the water flow would be lost to evaporation and seepage. The estimated water available for the scheme was .
The extreme evaporation rate in the interior is another negative determinant. No clear evidence has been provided that the amount of water supplied would exceed the evaporation rate. The reduction in river discharge to the Great Barrier Reef Lagoon may diminish coastal fisheries by reducing the supply of terrestrial organic matter to the coastal and estuarine environment.
In 1947, W.H.R. Nimmo conducted a critical review of the scheme. He proved that Bradfield's estimates of the amount of water available from the easterly flowing rivers were about two and half times greater than it actually was. The error was attributed to the methodology used to calculate flow estimates which was based on German rivers where the average temperature was much less than in northern Australia.
A 2022 CSIRO investigation found the scheme to be completely unviable due to a lack of reliable water.
In May 2019, former Nationals leader Barnaby Joyce and Pauline Hanson's One Nation party expressed support for the scheme.
In November 2019, the Liberal National Party of Queensland, through the opposition leader Deb Frecklington, provided support of the project as a long term investment.
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