Australians irrigate about 885,000 acres of crop land, of which twothirds are in Victoria and one-sixth is in New South Wales. The acreage varies considerably from year to year, depending upon rainfall and the amount of stored water. The larger irrigation projects are associated with the Murray River and its principal tributaries. Smaller projects are in the Inkerman and Dawson Valley districts of Queensland and at Harvey and Davesbrook in Western Australia.
The Murray River and its principal southern tributaries, the Goulburn, Lodon, and Mita, provide most of the water for irrigation in Victoria. The Murrumbidgee and Lachlan rivers are the most important sources of water for irrigation in New South Wales. Burrinjuck, Hume, Waranga, Eildon, and smaller reservoirs on these rivers provide a combined storage capacity of about 2 ½ million acrefeet of water. The capacity of several of these storages is being increased.
The catchment area of the Murray River and its tributaries includes over 400,000 square miles, but only the higher lands adjacent to the headwaters (158,000 square miles) contribute runoff. The contributing watershed has 20 to 40 inches of rainfall; most of the non-contributing area has 10 to 20 inches, and a small part has less than 10 inches. In its original condition, the Murray spread its muddy waters over hundreds of square miles of lowland during times of flood, and during times of drought it was little more than a succession of water holes stretching through its semi-arid middle and lower basin.
Irrigation was begun as early as 1882, when the Echuca and Waranga shires joined forces in the establishment of the GoulburnWaranga irrigation system in Victoria. In 1886 the passage of an irrigation act in Victoria, which vested in the Crown the right to use water from any stream, lake, or swamp for irrigation, marked the beginning of several important projects along the Murray. The important irrigation communities of Mildura and Renmark were established by the Chaffey brothers from Southern California during the late 1880's.
In 1906 the Victoria State Rivers and Water Supply Commission was established to control and direct the use of Murray River water for irrigation. Storage reservoirs have been constructed, and irrigated land has been steadily expanded through the efforts of that group. In 1915 the Commonwealth and the three states involved in the flow of the Murray agreed on a program of future development. A system of locks and weirs was designed to improve the navigation of the river without interfering with irrigation interests. Continued decline of navigation in competition with railroad and highway transport gradually brought about a shift in emphasis to irrigation, flood control, and power development. The Murray River Agreement also led to the construction of several large storage reservoirs to regularize the flow of the river.
Hume Reservoir, near Albury, New South Wales, comprises the largest artificial fresh-water storage on the continent with its 50 square miles of water surface and 1,250,000 acre-feet of storage. Plans are being made to increase its capacity to 2,000,000 acre-feet. Water is backed up the Murray for 40 miles and up the Mitta for 20 miles.
The total flow of the Murray River at Euston (below the junction with the Murrumbidgee) was 5,330,000 acre-feet in the year 19461947. In 1945-1946, the amount of water passing into South Australia amounted to 5,500,000 acre-feet after New South Wales and Victoria had extracted 2,600,000 acre-feet for irrigation. These facts indicate that the effective use of Murray River water has only begun.
The Darling River, principal tributary of the Murray, has been little developed. It drains an area of about 250,000 square miles in New South Wales and southern Queensland. It has failed to flow only occasionally, as during periods in 1902 and 1919, despite the fact that most of its drainage basin has less than 10 inches of rainfall. The flow at Menindee has ranged from none to 11,000,000 acre-feet per annum since measurements began in 1885. The average flow is about 1,250,000 acre-feet yearly.