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SYDNEY (Reuters) - An ancient underground water basin the size of Libya holds the key to Australia avoiding a water crisis as climate change bites the drought-hit nation.
Australia's Great Artesian Basin is one of the largest artesian groundwater basins in the world, covering 1.7 million sq kms (656,370 sq miles) and lying beneath one-fifth of Australia.
The basin holds 65 million gigaliters of water, about 820 times the amount of surface water in Australia, and enough to cover the Earth's land mass under half a meter of water, says the Great Artesian Basin Coordinating Committee.
And it is slowly topped up with 1 million megaliters a year as rain filters through porous sandstone rock, becoming trapped in the underground basin.
"There is probably enough water in there to last Australia's needs for 1,500 years, if we wanted to use it all," says John Hillier, a hydrogeologist who has just completed the Great Artesian Basin Resource Study.
But he and other experts warn that access to the basin's water supply is under threat from declining artesian pressure, which forces the water to the surface via bores and springs.
If artesian pressure falls too far, due to excessive extraction of water, the ancient water source will be unreachable, except through costly pumping.
Lying as much as two kms (1.2 miles) below ground, some parts of the basin are 3 km deep (1.8 miles) from top to bottom.
The basin was formed between 100 and 250 million years ago and consists of alternating layers of waterbearing sandstone aquifers and non-waterbearing siltstones and mudstones.
Basin water is extracted through bores and is the only source of water for mining, tourism and grazing in Queensland, New South Wales and South Australia states, and the Northern Territory.
The underground water spawns A$3.5 billion (US$2.4 billion) worth of production a year from farming, mining and tourism, says the Great Artesian Basin Coordinating Committee.
The mining and petroleum industry extracts 31,000 megaliters of basin water a year, which is used in production or pumped out as a by-product of mining, and is vital for future expansion.
Mining giant BHP-Billiton draws about 11,680 megaliters a year from the basin to operate its Olympic Dam gold, copper and uranium mine in South Australia. It would treble water usage under a plan to double production, with the extra water drawn from the basin and a new desalination plant.
Swiss-based miner Xstrata Plc is looking at the basin as a water source for what would be Australia's biggest open cut thermal coal mine, at Wandoan in Queensland, which would supply 20 million tons a year, with a mine life of 30 years.
But the pastoral industry is by far the biggest user, taking 500,000 megaliters a year to water some of Australia's most productive farmlands.
Angus Emmott runs a cattle property called Moonbah in central Queensland and relies on basin water in times of drought.
"The bores underpin the social and economic value of this huge inland area of Australia where there wasn't permanent fresh water," said Emmott.
"With climate change, we will be more reliant on the Great Artesian Basin, so we're morally obliged to make the best use of that water...so we don't waste it."
Since it was first tapped in 1878, an estimated 87 million megaliters has been extracted and up to 90 percent of it wasted.
As a result of falling water pressure, more than 1,000 natural springs have been lost and one-third of the original artesian bores have ceased flowing.
The extraction of ancient basin water into the atmosphere also contributes to Australia's greenhouse gas emissions, releasing 330,000 tons of CO2 annually.
A 15-year Great Artesian Basin Sustainability project started in 1990 aims to protect the water supply and the hydraulic pressure necessary to access it.
Today, there are still some 3,000 bores which pour water into 34,000 kms (21,130 miles) of open bore drains, with 90 percent of the water evaporating in the outback heat.
But more than 1,052 bores have now been controlled and tens of thousands of kilometers (miles) of open drains removed and pipelines laid, saving 272 gigaliters of water a year.
Farmers are now fencing off bores and using mobile telephone, satellite and computer imaging technology to control livestock access to bores and control bore flows.
"Bores and springs that had previously ceased to flow have begun to flow again. It's a huge change to land management and has allowed better pasture and stock management," said Emmott.
"With the capping and piping program you don't get the bogging of domestic animals, you don't get the maintenance cost of drains and you don't get soil salination," he said.
Farmers and scientists say it is crucial that more work is done to avoid a water crisis in the Great Artesian Basin as there will be greater demand on basin water in the future.
"It is absolutely crucial for the existence of communities that it is looked after," said Emmott.
"We realize there is a lot there, but we need to look after it very carefully because it needs such a huge time for recharge that if we lose it now it will not recharge in human lifetimes."
A A$17 million long-term sustainability report on the Great Artesian Basin announced this month will look at how to ensure water for future mining, pastoral and environmental development.
The global commodities boom in recent years has seen mining activity over the basin increase dramatically and authorities expect the mining industry's extraction will continue to rise.
"An expansion in exploration and mining activities in the area will place increased demands on securing groundwater allocations for economic development," said Andy Love, from Flinders University in Adelaide, who will lead the study.
"Clearly a balance between development and environmental protection needs to be achieved. However, this is not possible without increased knowledge about the amount of groundwater that can be safely extracted," said Love.
Editing by Megan Goldin