Geoscience Reference
In-Depth Information
Today, the Murray-Darling Basin is Australia's most important agricultural area, producing
over one-third of the nation's food supply. It contains 65% of the country's irrigated farm-
land and supports more than one-quarter of the national cattle herd and nearly half of its
sheep. It also provides water to major cities including Canberra and Adelaide. In its natural
state, however, the River Murray was a highly variable and unpredictable source of water.
During severe droughts, it ceased to be a river at all and was transformed into a chain of
salty waterholes, but flow has been regulated for many years to maintain a reliable sup-
ply. River regulation on the Murray has been achieved with an array of water engineering
structures and techniques. They include five main water storage points, including two large
dams - Dartmouth and Hume - and the major managed lakes of Mulwala, Victoria, and
Menindee. Since the Hume Dam was completed in 1936, a continuous flow has been main-
tained throughout the length of the river. The Murray and the Murrumbidgee Rivers also
receive additional water supplies diverted through a series of tunnels and pipes from the
Snowy River. A system of thirteen weirs and locks further aids flow regulation, and five
barrages have been constructed near the river mouth to prevent the intrusion of sea water.
Salt occurs naturally in the Murray-Darling Basin in large quantities, and is a water-qual-
ity issue for domestic and agricultural use. Hence, a series of salt-interception schemes has
been established to keep salt out of the river. These schemes involve large-scale groundwa-
ter pumping and drainage projects that intercept flows of saline water and dispose of them
by evaporation.
Natural barriers
There are many examples of rivers acting as natural barriers to interaction between groups,
and in some cases the separation has continued over periods long enough to be apparent in
genetic studies. Among primates in Central Africa, the Congo River forms a clear divide
between bonobos, or pygmy chimpanzees, which are found only on the south side of the
Congo, and common chimpanzees, which occur only to the north. Chimpanzees are not
known to swim, so the river has effectively isolated the two groups, for about 1.3 million
years according to genetic analysis, which also confirms that they have a common ancestry.
Similar river barriers to the flow of genes, cultures, and languages have been identified in
some human societies. A classic case has been documented by anthropologists in the High-
lands of New Guinea where the Lamari River marks a very sharp cultural and linguistic
divide between the Fore and the Anga. These two groups speak completely unrelated lan-
guages and have markedly different cultures. They are also mortal enemies. Although there
may be several reasons for their differences, the formidable natural barrier presented by the
