Water in the desert. Imagine what that meant
to the early inhabitants of inland Australia in one of the harshest and most arid places
on the planet for them to know that they had permanent access to fresh water and wetlands.
No wonder Australia’s natural spring systems became so sacred for so many.
But when the lakes turn to salt pans and the rivers are sucked dry where does the water
come from? Okay, get your head around this. About two million years ago it rained on the
Great Dividing Range in Queensland. Today that same water bubbles up in South Australia.
Think about it. The last time this water saw the light of day giant hippopotamus-sized
diprotodonts were grazing on the coast, the Tasmanian Tiger was alive and hunting and
Australia was the home of a lion called the Thylacoleo that had the strongest bite of
any mammal in history, living or extinct. So, this water has been travelling at a painfully
slow pace through porous rocks deep underground. Sometimes it bubbles and soaks its way to
the surface through natural springs. At other times we’ve found ways to dig down and find
it. Either way, it is the key to life to about a quarter of the continent. We call it the
Great Artesian Basin. To explain how the Great Artesian Basin works
you need to know how it came to exist in the first place. So here it is, the past 250 million
years in a nutshell. Back in the Triassic Age Australia was joined
together with the other southern continents including Antarctica, South America, Africa
and New Zealand in a land mass called Gondwana. Now have a look at the top right quarter of
Australia. Can you see how it kind of forms a natural dip? That’s the area that will eventually
become the Great Artesian Basin. Over the next 140�million years huge events like
ice ages in Europe and tectonic plate movements cause the ocean level to rise and fall. When
the ocean levels rose water became trapped in that natural dip and formed a sea. But
when the ocean levels fell the whole area became land again.
When the seas drained away they left clay and silt deposits behind which hardened into
impermeable stone. Remember this. So now we’re back to dry land again but it’s
not desert yet and there are rivers crossing it. The rivers carried sand and gravel with
them which later joined together to form sandstone and that sandstone is the key to how the basin
works. Silt stones and mud stones are what scientists call impermeable. There’s no way
water can get through them. They’re like plugs. Check this out.
Okay. We’ve got our impermeable rock and we’ve got our sandstone. Okay.
It ain’t going through. Soaking it up. Now we wait.
Okay. Imagine our layers of impermeable and permeable stone deep underground. I’ll demonstrate.
This sponge is our sandstone, our permeable layer and if you see the water, it goes straight
through it. But if we put an impermeable layer – this frisbee � underneath, the water has
nowhere to go except forward or to the sides. When that happens the layer of sandstone is
called an aquifer. It’s a massive area. It stretches from Cape
York to Dubbo and Coober Pedy to the south-east corner of the Northern Territory. That’s almost
a quarter of Australia. When it rains on what we call the recharge bed areas of the basin
the water seeps down and collects in the aquifers. Scientists estimate that there’s around 65,000
million megalitres of water in the basin right now. A megalitre is a million litres. 65,000
million of them would be enough to cover all the land on the planet in almost half a metre
of water. So that whole basin area we saw earlier now
has aquifers running all the way through it and has become the Great Artesian Basin.