Georgina River
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The Georgina River is the north-westernmost of the three major rivers of the Channel Country in western Queensland that flow in extremely wet years into Lake Eyre.
The river rise from several smaller streams over a wide area of northwestern Queensland and the uppern Northern Territory. These include the Burke River, flowing through the basin's major town of Boulia, the upper Georgina River itself rising in the Barkly Tableland north of Camooweal, the Ranken River rising in the extreme east of the Northern Territory beyond Tennant Creek, and the Sandover River. The Sandover, unlike all other tributaries of Lake Eyre, flows northwards from the Macdonnell Ranges to enter the Georgina in very wet years near Urandangie.
The basin of the Georgina totals around 232,000 km², or about the same size as the Australia state of Victoria, but because it is so arid, its mean annual flow is only about 0.7 km³ (or 570,000 acre feet)[1]. However, there is such extreme variation that - although streamgauging records are too poor to prove it conclusively - meteorological records leave no doubt that there have been many years of zero runoff in the entire basin (1905, 1928 and 1961 would without doubt fit into this category, and several others are likely to as well were decent data available), whilst in very wet years such as 1974, 1977 and 2000, runoff can be as high as 6.28 km³ (5,100,000 acre feet) or more[2].
Although a small part of the rugged Macdonnell Ranges drains into the Georgina, most of the catchment is a flat as the Diamantina, though low ranges are very prominent in the north-west of the basin. This western part of the basin has soils that are too infertile to provide nutritious fodder for cattle or sheep and a large proportion is Aboriginal land. The eastern part of the Georgina catchment near Boulia is very similar to the Diamantina and Cooper basins, being flaw grassy plains with heavy cracking clay soils that are quite fertile and provide very good feed in wet years for livestock.
Climatically, the Georgina catchment tends to be somewhat drier than the Diamantina or Cooper, with average annual rainfall ranging from around 400mm (16 inches) north of Camooweal to around 225mm (9 inches) at Bedourie[3]. Extremely dry years can give the entire basin less than 100mm (4 inches) whilst in 1974, 1977 and 2000 many areas had over 800mm (32 inches) and some as much as 1,000mm (40 inches). Almost all of this rain falls in the summer, and it is quite normal for the period from May to September to not record any measurable falls at all. In extremely wet summer months such as January 1974 or March 1950, most of the catchment can receive as much as 350mm (14 inches) in a month or 150mm (6 inches) in a day or two. Temperatures are generally hot, with most areas having maxima of over 30°C (86°F) on over 225 days per year. Frosts are rare but have been reported on occasions in all areas of the basin - however even in June and July maxima are around 25°C (77°F).
Although it is the driest of the three main rivers of the Lake Eyre Basin, there is evidence that the Georgina has, in the past, actually reached the lake more frequently than either the Diamantina or Cooper. Some wave built shingle terraces suggest that during the Medieval Warm Period Lake Eyre held permanent water. Large increases since the late 1960s in rainfall over the Northern Territory and pastoral areas of South and Western Australia that have not been duplicated over Queensland do suggest an enhanced greenhouse effect in the Medieval Warm Period may have caused the Georgina to regularly fill Lake Eyre. However, far too little evidence exists for any certainty of this.
[edit] References
- ^ Brown, John Alexander Henstridge; Australia's Surface Water Resources; published 1983 by Australian Government Publication Service. ISBN 064402567X
- ^ Allen, Robert J.; The Australasian Summer Monsoon, Teleconnections, and Flooding in the Lake Eyre Basin; published 1985 by Royal Geographical Society of Australasia, S.A. Branch; ISBN 0909112096
- ^ Willcocks, Jacqui and Young, Phillip; Queensland's Rainfall History: Graphs of Rainfall Averages, 1880-1988; published 1991 by Queensland Department of Primary Industries. ISBN 0724239138
