(This post originally appeared in Bobby Dazzler Newsletter #60, December 2013.)
Australia would be a very different place without the gift of the Great Artesian Basin, and several other smaller artesian basins. Many Outback towns, villages and properties depend for their water supply on bores and springs which bring the vital fluid to the surface. For example, the towns of Coober Pedy (SA) and Winton (Qld) depend on water from the GAB. Alice Springs water comes from the nearby Amadeus Basin (not shown on map).
The Great Artesian Basin (1,700,000 sq kms), which covers more than one fifth of the country, is the largest and deepest artesian basin in the world. It occupies substantial parts of Queensland, Northern Territory, South Australia and New South Wales. It is 3000 metres deep in places, and is estimated to contain 64,900 cubic kms (yes, kilometres!) of water, held inside porous sandstone. It was formed about 100 million years ago when much of inland Australia was below sea level, and the water-saturated sandstone was covered by a layer of sedimentary rock, thus trapping the water under pressure.
In due course, fault lines in the rock led to the formation of natural springs in many areas, such as Dalhousie Springs in the far north of South Australia, and the mound springs near the Oodnadatta Track. In the 1870s, the first bore was sunk into the GAB, and since then, many hundreds of bores have been drilled, some as deep as 2000 metres. The artesian water normally flows freely without the need for pumping, and at a temperature between 30 and 100°C. It often contains mineral salts and/or (smelly!) sulphur compounds, and needs to be treated before it can be used, even for irrigation. The big demineralisation towers can still be seen along the old Ghan railway line, where artesian water was treated before it could be used in the steam locomotives.
Replenishment of the GAB occurs mostly from rainfall on the relatively high ground on the western side of the Great Dividing Range, which runs down the East Coast. The water soaks into the ground until it reaches the sandstone stratum, and then percolates slowly westward at the rate of 1 to 5 metres per year. Carbon dating has shown that some water emerging from Outback springs has been under the ground for about two million years! Which of course makes the point that if we use up all the artesian water, we may have to wait two million years for the GAB to fill up again. That’s a long time between drinks!
Concerns have been expressed in many quarters about the rate at which artesian water is being used. Until recent times, many remote-area bores were left running continuously over many years, but there are now requirements for capping bores so that they can be used more efficiently. The Olympic Dam and mining complex in South Australia uses 35 million litres of water drawn from the GAB every day.
It’s obviously not an easy matter to measure the rate of depletion of water in the GAB, but some scientific studies have concluded that in certain areas, the amount of water remaining in the Basin has been measurably reduced.
Another concern is that “fracking” associated with coal seam gas extraction will contaminate subterranean water, including artesian basins, with toxic chemicals. One thing we can be certain about: loss of access to usable water from our artesian basins would have a massive impact on Australia.
Footnote: Back in 1896, Banjo Paterson wrote a poem about artesian water, and the first stanza goes like this:
Now the stock have started dying, for the Lord has sent a drought,
But we’re sick of prayers and Providence – we’re going to do without,
With the derricks up above us and the solid earth below,
We are waiting at the lever for the word to let her go.
Sinking down, deeper down,
Oh, we’ll sink it deeper down:
As the drill is plugging downward at a thousand feet of level,
If the Lord won’t send us water, oh, we’ll get it from the devil;
Yes, we’ll get it from the devil deeper down.
The full text of the poem, an account of the circumstances in which Paterson wrote the poem, and some interesting background on artesian water can be found at http://www.qhatlas.com.au/great-artesian-basin-water-deeper-down .
Please give us your thoughts on the use of artesian water, or on fracking, and maybe where you’ve seen bores running. Just click on “Add a comment” or “Comments” below. (You don’t have to give your name – just use a nom-de-plume.)