murray-darling basin

The Murray-Darling Basin drains one-seventh of Australia and is by far the most significant agricultural area on that continent. Most of the 1,072,000 square kilometre basin is flat, low-lying and far inland, and receives little rainfall. The many rivers it contains tend to be long and slow-flowing, and carry a volume of water that is large only by Australian standards. Although the Murray-Darling Basin receives only 6% of Australia's rainfall, it is the scene of 70% of Australia's irrigation. It contains 42% of the nation's farmland and produces 40% of the nation's food. The basin drains roughly three-quarters of New South Wales (including all of the A.C.T.), half of Victoria, a substantial portion of southern Queensland, and a small part of eastern South Australia. In general, the climate is hot and dry in summer, mild in winter. Much of the terrain is semi-arid and nearly all of it is only a few tens of metres above sea level. Typically, tree-lined watercourses meander slowly through mulga or mallee scrub, grasslands or chenopod shrublands. Rainfall is unpredictable and varies from place to place as well as year to year, but is typically around 250 or 300 mm a year (10 to 12 inches) on average. In the south-east, average temperatures are lower, elevations a little higher, and rainfall more frequent: 500 mm (20 inches) a year is representative, most of it falling in winter and spring. Along the southern and eastern borders of the basin are the inland slopes of the Great Dividing Range. It is here that most of the water in the rivers of the basin originates either as rainfall or, in the case of the Australian Alps which straddle the New South Wales-Victoria border, as winter snowfall. Total water flow in the Murray-Darling basin averages 14,000 gigalitres per year, of which 11,500 gigalitres is removed for irrigation, industrial use, and domestic supply. Agricultural irrigation accounts for about 95% of the water removed.

Major streams

The Murray is the largest of the basin's many rivers, the Darling the longest. It is 3370 kilometres from the Queensland headwaters of the Darling to the Coorong where the Murray flows into the sea.