Lake Eyre basin

The Lake Eyre basin ( ) is a drainage basin that covers just under one-sixth of all Australia. It is the largest endorheic basin in Australia and amongst the largest in the world, covering about , including much of inland Queensland, large portions of South Australia and the Northern Territory, and a part of western New South Wales. The basin is also one of the largest, least-developed arid-zone basins with a high degree of variability anywhere. It supports only about 60,000 people and has no major irrigation, diversions, or flood-plain developments. Low-density grazing that sustains a large amount of wildlife is the major land use, occupying 82% of the total land within the basin. The Lake Eyre basin of precipitation (rain water) to a great extent geographically overlaps the Great Artesian Basin underneath.

The basin began as a sinking landmass mostly covered by forest and contained many more lakes than now. The climate has changed from wet to arid over the last 60 million years. Most of the rivers in the Lake Eyre basin are now slow flowing, flat, and completely dry for lengthy periods. When the country north of the basin floods, floodwaters drain via the main rivers of the basin—Cooper Creek, Georgina River, and Diamantina River—southwards towards Kati Thanda–Lake Eyre, the country's lowest point at below sea level. The water overflows the river banks, across the floodplains, filling waterholes and wetlands and carving new channels, giving rise to the name Channel Country. Most of the rain which falls in the north never reaches the lake 1,000 km away, which only fills occasionally.

Management of the area has been problematic as it is covered by four different states' jurisdictions. As the ecological significance of the basin has become known and mismanagement of another Australian basin, the Murray-Darling Basin, became apparent during several drought cycles, it became clear that ongoing management issues had to be resolved. In 2001 the Lake Eyre Basin Intergovernmental Agreement was signed, which was set up to ensure the sustainability of the Lake Eyre Basin river systems.

In 2014, the Queensland Government changed the laws protecting the rivers and floodplains. there are fears that mining for coal seam gas could be very detrimental to the fragile environment of the floodplains.

Geology

thumb|right|220px|Lake Eyre in 1990, as seen by [[STS-35]]

The basin began to form in the early Paleogene (about 60 million years ago) when south-eastern South Australia started to sink and rivers began to deposit sediment into the large, shallow basin. A remnant of an old oceanic plate is currently sinking in the mantle beneath the basin. The suction effect of this sinking likely caused both the Lake Eyre Basin as well as the Murray-Darling basin to form. The basin is still gradually sinking, and still gradually accumulating sediment. For many millions of years, the Lake Eyre Basin was well-supplied with water and largely forested. About 20 million years ago, large, shallow lakes formed, covering much of the area for about 10 million years. From that time on, as Australia drifted further north and the climate became gradually more arid, the lakes and floodplains started to dry. Only in the last 2.6 million years did the onset of the ice ages bring about the present climatic regime and the consequent fairly rapid desertification of the area.

The basin covers just under one-sixth of all Australia and is the largest endorheic basin in Australia and amongst the largest in the world, covering about , including much of inland Queensland, large portions of South Australia and the Northern Territory, and a part of western New South Wales.

Geography

thumb|right|Strzelecki Desert, South Australia

During years of especially high rainfall, all the riverbeds in this vast, mostly flat, arid and semi-arid area lead inland (not towards the sea) towards Lake Eyre in central South Australia.

Lake Eyre itself lies approximately below sea level, and usually contains only salt. In flood years, it fills and, for a short time, undergoes a period of rapid growth and fertility: long-dormant marine creatures multiply and large flocks of waterfowl arrive to feed and raise their young before the waters evaporate once more. The annual mean runoff in the Lake Eyre Basin is the lowest of any of the world's major drainage basins.

None of the creeks and rivers in the Lake Eyre Basin are permanent: they flow only after heavy rain, a rare to very rare event in the arid interior of Australia. Average annual rainfall in the area surrounding Lake Eyre is , and the pan evaporation rate is . Annualised average figures are misleading: since 1885, annual rainfall over the of the Lake Eyre Basin has ranged from about in 1928 to over in 1974. Most of the water reaching Lake Eyre comes from the river systems of semi-arid inland Queensland, roughly to the north.

To provide a sense of scale, the Lake Eyre Basin is about the size of France, Germany, and Italy combined. It is slightly larger than the Murray-Darling basin (which drains inland eastern Australia and is responsible for a large proportion of the continent's agricultural productivity) but has vastly less water. Nevertheless, the entire flow of the Murray-Darling would be insufficient to fill Lake Eyre, merely keeping pace with evaporation. (In contrast, the flow of the Mississippi could fill Lake Eyre in 22 days, that of the Amazon in just three days.)

Other lakes in the basin include Lake Frome, Lake Yamma Yamma, and Lake Hart.

The basin is also one of the largest, least-developed arid-zone basins with a high degree of variability anywhere.

Rivers

The Cooper Creek, Finke River, Georgina River, and Diamantina River are the four main rivers of the basin. Other desert rivers include the Hale River, Plenty River, and Todd River that flow from the southeast of the Northern Territory, south. In the western parts of the basin, the Neales River and Macumba River flow into Lake Eyre.

Rivers within the basin have a low gradient, slow flow rate, and a naturally turbid water quality.

Deserts

The deserts that have formed in the basin, including Sturt Stony Desert, Tirari Desert, and the Strzelecki Desert, are most probably the southern hemisphere's largest source of airborne dust.

Fauna

A total of 27 individual species of fish are found in Lake Eyre basin, with 13 of them being endemic. The largest fish species is the Macquaria, reaching a maximum weight of about .

Traditional owners

Wangkangurru (also known as Arabana/Wangkangurru, Wangganguru, Wanggangurru, Wongkangurru) is an Australian Aboriginal language spoken on Wangkangurru country. It is closely related to Arabana language of South Australia. The Wangkangurru language region was traditionally in the South Australia–Queensland border region taking in Birdsville and extending south towards Innamincka and Lake Eyre, including the local government areas of the Shire of Diamantina as well as the Outback Communities Authority of South Australia.

Management

Indigenous Australians have lived with the cycles of the land for thousands of years and traditional owners are protective of its natural systems. The Ministerial Forum created a Community Advisory Committee to provide advice and facilitate community participation and a Scientific Advisory Panel to advise on scientific and technical issues.

Land use and mining

Low-density grazing is the major land use, occupying 82% of the total land within the basin. Significant minerals deposits such as oil and natural gas, including Australia's most significant onshore petroleum reserves, are found within the basin. The mining and petroleum industries account for the greatest economic activity in the Lake Eyre Basin. Opals, coal, phosphate, gypsum, and uranium are also mined from the basin. The spill has the potential to contaminate parts of the basin as far south as Lake Eyre.

In 2014, the Queensland Government changed the laws protecting the rivers and floodplains, which, according to environmentalists, could lead to shale gas mining or fracking in the area.

Protected areas

The Kati Thanda–Lake Eyre National Park, Strzelecki Regional Reserve, Witjira National Park, Sturt National Park, Diamantina National Park, and Simpson Desert National Park are among a number of protected areas established within the Lake Eyre Basin.

River diversion schemes

The Bradfield Scheme was an ambitious proposal by Dr John Bradfield in 1938. It would use large pipes, tunnels, pumps, and dams to divert water from the monsoon-fed Tully, Herbert, and Burdekin rivers into the Thomson River, Queensland. After a critical review in 1947, support for the scheme fell through. However, in the 2010s, interest in various updated or amended Bradfield schemes have increased among various politicians.

Other less-developed diversion schemes have been proposed to divert river or sea water into the Lake Eyre Basin from time to time.