1301.0 - Year Book Australia, 2001  
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 25/01/2001   
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Fifty per cent of Australia receives an annual rainfall of less then 300 mm and is categorised as arid or semi-arid (see Geography and climate). A dominant characteristic of semi-arid environments is variable rainfall patterns, within and between years. Low annual rainfall, coupled with high temperatures, produces high evaporation rates and low annual runoff by world standards (Davies et al. 1994). In the late 1800s dams were constructed to modify the highly variable flow regime of semi-arid river systems. The construction of dams and weirs ensured that Australians had a reliable water resource for both domestic and economic purposes.

The Murray River was the lifeblood of many early settlements and was one of the first major river systems to become regulated. Irrigation of agricultural land with Murray River waters in Victoria commenced in the 1870s. As the demand for water increased, disputes arose between States over the distribution of the variable resource, leading to the commencement of the Murray River water agreement in the early 1900s. This agreement saw the construction of dams on the Upper Murray and at Lake Victoria, as well as 26 weirs and locks from Echuca in Victoria to Blanchetown in South Australia. These developments on the Murray and the nine weirs built on the Darling and Murrumbidgee Rivers as part of the Murray River agreement ensured a reliable water resource in this region (MDBC 1990).

As Australia's population increased, not only in the Murray region but nationwide, so did the number of dams. Graph 14.20 shows the growth in the number of dams greater than 100 Gigalitres from 1910 to 1994. In 1939 there were 10 large dams of over 100 gigalitres, which increased substantially to 90 large dams by 1994 (ANCOLD 1990).

Together with increases in the number of large dams throughout Australia in the last century there were continual and substantial increases in water diversions (MDBC 1995). For example, in the Murray-Darling Basin annual diversions continually increased from 1920 to 1994 (graph 14.21). The basin has grown to support 42% of Australia's farm land, which includes 90% of Australia's irrigated crops (MDBC 2000).