Map of the Murray-Darling Basin

The Murray-Darling Basin is a geographical area in the interior of southeastern Australia, which spans parts of the states of Queensland, New South Wales, Victoria, and South Australia, and the Australian Capital Territory. It is 3,375 km in length (the Murray River is 2589 km long), drains one-seventh of the Australian land mass, and is currently by far the most significant agricultural area in Australia. The name of the basin is derived from its two major rivers, the Murray River and the Darling River.

Most of the 1,061,469 km² 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.

[edit] Native fauna

The Murray Darling Basin is home for many native animal species. The true numbers are not known, but a fairly accurate estimate has been made of these animals and the current status of their population. Among the indigenous fauna in the region, the study found^{[citation needed]} that there were:

• 85 species of mammals, with 20 extinct and 16 endangered.
• 53 species of frogs, with none endangered.
• 46 species of snakes, with 5 endangered.
• 5 tortoises, with none endangered
• 34 species of fish, with none endangered.

[edit] Introduced species

The carp, introduced in 1850, is now a nuisance species in the Murray-Darling river system

The Basin has also played host to a variety of introduced species. One of the most well known is the Carp.

Introduced in around 1851, the four varieties of Carp were used to stock up fish dams. Since then they have made their way into the river systems, where they spread quite quickly. These fish are very mobile, as they can travel easily on flood waters and their eggs can be transported by birds.

These fish are a problem because they feed by sucking gravel from the river bed and taking all the edible material off it, before returning the rest to the water. This stirs up all the sediment, reducing the quality of the water. If you catch one you legally must kill it.

[edit] Physiography

This area is one of the physiographic provinces of the larger East Australian Basins division, and encompasses the smaller Naracoorte Platform and Encounter Shelf physiographic sections.

[edit] Hydrology

Total water flow in the Murray-Darling basin in the period since 1885 has averaged around 24,000 gigalitres per year, although in most years only half of it reaches the sea and in dry years much less. Estimated total annual flows for the basin range from 5,000 gigalitres in 1902 to 57,000 gigalitres in 1956. The hydrology of the streams within the basin is quite varied even considering its size. There are three main types^[1]:

• The Darling and Lachlan basins. These have extremely variable flows from year to year, with the smallest annual flow being typically as little as 1 percent of the long-term mean and the largest often more than ten times the mean. Periods of zero flow in most rivers can extend to months and in the drier parts (Warrego, Paroo and Lower Darling basins) to years^[2]. Flows in these rivers are not strongly seasonal. Though in the north most floods occur in the summer from monsoonal penetration, in most of the Darling and Lachlan catchments it is typical to see high or low flows begin in winter and extend to the following autumn (see El Niño). High water extraction rates for irrigation and mining have heavily compromised these rivers.

• The south-western basins (Campaspe, Loddon, Avoca, Wimmera). These have a marked winter rainfall maximum and relatively lower precipitation variability than the Lachlan or Darling. However, the age and infertility of the soils means that run-off ratios are exceedingly low (for comparison, around a tenth that of a European or North American catchment with a similar climate^[3]). Thus, variability of runoff is very high and most of the terminal lakes found in these basins very frequently dry up. Almost all runoff occurs in the winter and spring and, in the absence of large dams for regulation, these rivers are often or usually seasonally dry during summer and autumn.
  • A number of small catchments in South Australia, of which the largest are the Angas River flowing through Strathalbyn and the Finniss River further west, are part of the Murray-Darling Basin because they flow into Lake Alexandrina, one of the lakes at the end of the Murray system. The Angas River is often dry in summer because of high levels of water extraction. The Finniss River has permanent flow which previously went into Lake Alexandrina but know has been cut off by a weir. The Finniss now fills the Goolwa Channel for recreational boating.

• The Murrumbidgee, Murray and Goulburn basins (except the Broken River which resembles the south-western basins). Because these catchments have headwaters in alpine country with relatively young peaty soils, the runoff ratios are much higher than in other parts of the basin. Consequently, although gross precipitation variability is no lower than in the Lachlan or Darling basins, runoff variability is markedly lower than in other parts of the basin. Typically these rivers never cease to flow and the smallest annual flow is typically around 30 percent of the long-term mean and the largest around three times the mean. In most cases the flow peaks very strongly with the spring snow melt and troughs in mid-autumn.

Of the approximately 13,000 gigalitres of flow in the basin which studies have shown to be divertible, 11,500 gigalitres is removed for irrigation, industrial use, and domestic supply. Agricultural irrigation accounts for about 95% of the water removed, with the growing of rice and cotton being highly controversial among scientists in Australia, owing to their high water use in a region extremely short of water (as much due to exceptionally low run-off coefficients as to low rainfall).

• • • Namoi River
    • Gwydir River
    • Macquarie River
  • Murrumbidgee River
    • Numeralla River
    • Naas River
    • Cotter River
    • Molonglo River
      • Queanbeyan River
    • Yass River
    • Goodradigbee River
    • Tumut River
    • Lachlan River
    • Abercrombie River
  • Edward River (anabranch)
  • Avoca River
  • Loddon River
  • Campaspe River
  • Goulburn River
    • Broken River
    • Jamieson River
    • Howqua River
  • Ovens River
    • King River
    • Buffalo River
    • Buckland River
  • Kiewa River
  • Mitta Mitta River

[edit] See also

• Australian south-west coast drainage division
• Indian Ocean drainage division: see Pilbara region of Western Australia
• Timor Sea drainage division: see Top End and Kimberley region of Western Australia
• Gulf of Carpentaria
• Australian north-east coast drainage division
• Australian south-east coast drainage division
• South Australian gulf drainage division
• Lake Eyre Basin
• Western Plateau
• Salinity in Australia
• Climate change in Australia
• Murray-Darling Cap

[edit] References

[edit] External links

• The Murray Darling Crisis - ABC TV Catalyst
• Murray-Darling Basin Authority
• Murray-Darling Basin Water Budget Project
• Murray Darling Freshwater Research Centre
• River Murray Water Restrictions
• Murray Outback - Guide to the major towns on the Murray and Murray Outback Region.
• [1]
• Murray Darling Basin Resources

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