Georgina River
Encyclopedia
The Georgina River is the north-westernmost of the three major rivers of the Channel Country
Channel Country
The Channel Country is region of outback Australia located mostly in the state of Queensland but also in portions of South Australia, Northern Territory and New South Wales. The name comes from the numerous intertwined rivulets that cross the region, which cover 150,000 km²...

 in western Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...

 that flow in extremely wet years into Lake Eyre
Lake Eyre
Lake Eyre is the lowest point in Australia, at approximately below sea level, and, on the rare occasions that it fills, it is the largest lake in Australia and 18th largest in the world...

.

Geography

The river rise from several smaller streams over a wide area of northwestern Queensland and the eastern Northern Territory
Northern Territory
The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...

. These include the Burke River
Burke River (Queensland)
The Burke River is an ephemeral river in southwest Queensland, Australia. The river was named in memory of Robert O'Hara Burke of the Burke and Wills expedition....

, flowing through the basin's major town of Boulia
Boulia, Queensland
Boulia is a town in Central West Queensland, Australia. It is located approximately by road south of Mount Isa, and lies on the Burke River, which was named after the explorer Robert O'Hara Burke who passed through the area with the Burke and Wills expedition in 1860. The township was gazetted in...

, the upper Georgina River itself rising in the Barkly Tableland north of Camooweal
Camooweal, Queensland
Camooweal is a small town in north-western Queensland, Australia, located 188 km north-west of the city of Mount Isa and 12 km east of the Northern Territory border. Local government is provided by the Mount Isa City Council. The town lies on the Barkly Highway, and is adjacent to the Georgina River...

, the Ranken River rising in the extreme east of the Northern Territory beyond Tennant Creek, and the Sandover River
Sandover River
The Sandover River is a river in northeast Central Australia. It is the only major tributary of the Georgina River that does not rise in western Queensland. Instead it flows from the eastern Macdonnell Ranges in the Northern Territory northward to enter the Georgina near Urandangi...

. The Sandover, unlike all other tributaries of Lake Eyre, flows northwards from the Macdonnell Ranges
MacDonnell Ranges
The MacDonnell Ranges of the Northern Territory, are a long series of mountain ranges located in the centre of Australia , and consist of parallel ridges running to the east and west of Alice Springs...

 to enter the Georgina in very wet years near Urandangi
Urandangi
Urandangi is a town in north-western Queensland, Australia. The town is located on the banks of the Georgina River and in the Shire of Boulia local government area, north west of the state capital, Brisbane and south west of the regional centre of Mount Isa....

.

The basin of the Georgina totals around 232,000 km², or about the same size as the Australia state of Victoria
Victoria (Australia)
Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....

, but because it is so arid, its mean annual flow is only about 0.7 cubic kilometre. 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 cubic kilometre or more.

Although a small part of the rugged Macdonnell Ranges drains into the Georgina, most of the catchment is a flat as the Diamantina
Diamantina River
The Diamantina River is a river in south west Queensland and the far north of South Australia. Rising north-west of Longreach in the Swords Range, it flows in a south-westerly direction through central Queensland and the Channel Country to form the Warburton River at its confluence with the...

, though low ranges are very prominent in the north-west of the basin. This western part of the basin has soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

s that are too infertile to provide nutritious fodder for cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...

 or sheep and a large proportion is an Aboriginal reserve. 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
Vertisol
In both the FAO and USA soil taxonomy, a vertisol is a soil in which there is a high content of expansive clay known as montmorillonite that forms deep cracks in drier seasons or years. Alternate shrinking and swelling causes self-mulching, where the soil material consistently mixes itself, causing...

 that are quite fertile and provide very good feed in wet years for livestock. The Lake Machattie Area
Lake Machattie Area
The Lake Machattie Area is a 909 km2 tract of land comprising Lakes Machattie, Mipia and Koolivoo, with the surrounding Georgina River and Eyre Creek floodplains, in the arid Channel Country of western Queensland, Australia...

 is an important breeding site for waterbirds.

Climate

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
Bedourie, Queensland
Bedourie is a small town located in the Channel Country of western Queensland, Australia, lying on Eyre Creek. It is located 1600 kilometres west of the state capital, Brisbane, and 200 kilometres north of Birdsville. At the 2006 census, Bedourie and the surrounding area had a population of 142...

. 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. Frost
Frost
Frost is the solid deposition of water vapor from saturated air. It is formed when solid surfaces are cooled to below the dew point of the adjacent air as well as below the freezing point of water. Frost crystals' size differ depending on time and water vapour available. Frost is also usually...

s 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).

Flooding

During severe floods the river can be as wide as 15 to 20 km in the upper reaches and in the lower reaches from 25 to 30 km wide. Inundation can last for months at a time, which can disrupt road and rail transport in the area. The highest recorded flood occurred in January 1974.

Although it is the driest of the three main rivers of the Lake Eyre Basin
Lake Eyre Basin
The Lake Eyre basin is a drainage basin that covers just under one-sixth of all Australia. The Lake Eyre Basin is the largest endorheic basin in Australia and amongst the largest in the world, covering about 1,200,000 square kilometres, including much of inland Queensland, large portions of South...

, 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
Medieval Warm Period
The Medieval Warm Period , Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region, that may also have been related to other climate events around the world during that time, including in China, New Zealand, and other countries lasting from...

 Lake Eyre held permanent water. Large increases since the late 1960s in rainfall over the Northern Territory and pastoral areas of South
South Australia
South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...

 and Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

 that have not been duplicated over Queensland do suggest an enhanced greenhouse effect
Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...

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.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK