Introduction
Large artesian aquifer in Australia
Great Artesian BasinAquiferInteractive map of Great Artesian BasinLocationAustraliaArea • Total1,700,000 km2 (660,000 sq mi)
Lightning Ridge bathing thermes supplied by artesian bore water Hot water bore hole into the Great Artesian Basin in Thargomindah
Beel's Bore, Hariman Park near Cunnamulla.
The Great Artesian Basin (GAB) of Australia is the largest and deepest artesian basin in the world, extending over 1,700,000 square kilometres (660,000 sq mi). Measured water temperatures range from 30 to 100 °C (86 to 212 °F). The basin provides the only source of fresh water through much of inland Australia.
The basin underlies 22% of the Australian continent, including most of Queensland, the south-east corner of the Northern Territory, north-eastern South Australia, and northern New South Wales. It is 3000 metres (9800 feet) deep in places and is estimated to contain 64,900 cubic kilometres (15,600 cubic miles) of groundwater. The Great Artesian Basin Coordinating Committee (GABCC) coordinates activity between federal, state/territory, and local levels of government and community organisations.
Physiography
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This area is one of the distinct physiographic provinces of the larger East Australian Basins division, and includes the smaller Wilcannia Threshold physiographic section.
Geology[edit]
The water of the Great Artesian Basin is held in a sandstone layer laid down by continental erosion of higher ground during the Triassic, Jurassic, and early Cretaceous periods. During a time when much of what is now inland Australia was below sea level, the sandstone was covered by a layer of marine sedimentary rock, which formed a confining layer that trapped water in the sandstone aquifer. The eastern edge of the basin was uplifted when the Great Dividing Range formed. The other side was created from the landforms of the Central Eastern Lowlands and the Great Western Plateau to the west.
Most recharge water enters the rock formations from relatively high ground near the eastern edge of the basin (in Queensland and New South Wales) and very gradually flows toward the south and west. A much smaller amount enters along the western margin in arid central Australia, flowing to the south and east through the permeable sandstone, at a rate of one to five metres per year.
Discharge water eventually exits through a number of springs and seeps, mostly in the southern part of the basin. The age of the groundwater, determined by carbon-14 and chlorine-36 measurements combined with hydraulic modelling, ranges from several thousand years for the recharge areas in the north to nearly 2 million years in the south-western discharge zones.
Water source[edit]
Prior to the arrival of Europeans, waters of the Great Artesian Basin (GAB) discharged through mound springs, many in arid South Australia, such as Witjira-Dalhousie Springs. These springs sustained a variety of endemic invertebrates, such as molluscs, and supported extensive Aboriginal communities and trade routes. After the arrival of Europeans, the springs facilitated exploration, and allowed the provision of faster communications between south-eastern Australia and Europe, via the Australian Overland Telegraph Line. The Great Artesian Basin became an important water supply for cattle stations, irrigation, and livestock and domestic purposes, and is a vital lifeline for rural Australia. To tap it, boreholes are drilled down to a suitable rock layer, and the pressure of the water often forces it up without the need for pumps.
The discovery and use of the water in the Great Artesian Basin allowed the settlement of thousands of square kilometres of country away from rivers in inland New South Wales, Queensland, and South Australia, that would otherwise have been unavailable for pastoral activities. European discovery of the basin dates from 1878 when a shallow bore near Bourke produced flowing water. There were similar discoveries in 1886 at Back Creek east of Barcaldine, and in 1887 near Cunnamulla.
In essence, water extraction from the GAB is a mining operation, with recharge much less than current extraction rates. In 1915, there were 1,500 bores providing 2,000 megalitres (1,600 acre⋅ft) of water per day, but today the total output has dropped to 1,500 megalitres (1,200 acre⋅ft) per day. This included just under 2,000 freely-flowing bores and more than 9,000 that required mechanical power to bring water to the surface. Many bores are unregulated or abandoned, resulting in considerable water wastage. These problems have existed for many decades, and in January 2007 the Australian Commonwealth Government announced additional funding in an attempt to bring them under control. However, many of the mound springs referred to above have dried up due to a drop in water pressure, probably resulting in extinction of several invertebrate species.
The Olympic Dam mine in South Australia is permitted to extract up to 42 megalitres (1.5×10^6 cu ft) of water daily from the Great Artesian Basin under the Roxby Downs (Indenture Ratification) Act 1982. The underground copper and uranium mine commenced operations in 1988 and is expected to continue operating until approximately 2060.[citation needed]
In addition, the Basin provides water, via a 1.2-kilometre-deep (3⁄4 mi) bore, for a geothermal power station at Birdsville. Water emerges from the bore at 98 °C (208 °F) and provides 25% of the town's electricity needs. After being cooled, the water is also the source of the town's drinking water.