The Great Artesian Basin—What Is It?

BY AWAKE! WRITER IN AUSTRALIA

AS WE fly west over the last spreading fingers of Australia’s great coastal mountain range, the view unfolding before us is mesmerizing. Overhead a seamless blue sky arches forward to touch the horizon. The ground stretches out flat and featureless as far as the eye can see. The patchwork quilt of green crops and gold savannas soon gives way to a threadbare-looking landscape of red earth smeared with blotches of brown grass.

Believe it or not, below the ground is a body of water two thirds the size of the Mediterranean Sea. This massive underground reservoir is known as the Great Artesian Basin.

The existence of this underground ocean is vital to those who make a living in the remote, hot interior of the country. To appreciate why this buried treasure is so important and how it was formed, we need to understand how Australia is constructed.

Dry on Top

Australia is rightly called a sunburned country. This smallest of the world’s five continents is home to the world’s second-largest desert. It also has one of the world’s longest rivers, the Darling River. Yet, Australia’s rivers carry little water. In the United States, the Mississippi River alone empties almost 60 percent more water into the sea each year than all the rivers and streams in Australia combined. Why does rain avoid this land?

Because of the continent’s position on the globe—stretching along 30 degrees south latitude—its weather is dominated by large high-pressure patterns. These cells of fine weather sweep the country’s center with warm air. Wafting across the flat expanse, these winds meet no lofty mountain ranges to coax the  moisture from the air. The only substantial mountain range hugs the east coast of the continent. Its tallest peak rises only 7,310 feet [2,228 m], a baby by world standards. Any rain-bearing winds heading inland from the Pacific Ocean in the east meet these mountains and drop their life-giving cargo along a narrow coastal strip. The lack of elevation, the high average temperatures, and the location of its mountains conspire to make Australia the driest continent on earth—at least on its surface.

Wet Underneath

Beneath Australia’s parched crust lie 19 major groundwater basins. The largest, the Great Artesian Basin, underlies one fifth of the continent. This basin is 660,000 square miles [1.7 million sq km] in area, stretching from the tip of Cape York in the north down to Lake Eyre in South Australia. It contains some 2,000 cubic miles [8,700 km³] of water, enough to fill lakes Michigan and Huron in North America to overflowing.

Unlike the Great Lakes of North America, though, water in the Great Artesian Basin is not readily accessible. It enters the basin when rain soaks down through the soil and saturates water-bearing layers of sandstone. About  80 million gallons [300 million L.] of water a day enters the basin this way. What happens to all this water?

Soaking a Massive Sponge

The Great Artesian Basin is like a sponge, only on a gigantic scale. Spongelike layers of sandstone, ranging from 300 feet [100 m] to almost two miles [three km] in thickness, are sandwiched between layers of water-resistant rock. These curved plates are tilted downward to the west, with their eastern rim exposed along the Great Dividing Range. Rain soaking in along this rim seeps slowly westward, traveling just 16 feet [5 m] a year.

If a bore is drilled downhill from the mountain range through the top layer of water-resistant rock and into the sandstone, gravity forces the trapped water to the surface. Because the water rises under pressure, it is called an artesian bore, an expression derived from the former French province of Artois, where the first well of this type was drilled. When Australia’s artesian treasure was discovered, bores by the thousands were sunk into the ancient watercourse.

Draining the Reservoir

In the late 1800’s, settlers keen to exploit the wide-open plains of Queensland and New South Wales eagerly tapped what they thought was an unlimited supply of water. By 1915, some 1,500 bores were disgorging 500 million gallons [2 billion L.] (1,000 Olympic-size swimming pools) of water a day from the Great Artesian Basin. This drained the reservoir faster than it was filling; thus many of the bores stopped flowing.

Today, of the 4,700 artesian bores that have been drilled, only 3,000 still flow naturally. A further 20,000 bores tap this great sponge, water being drawn to the surface by the windmill pumps you see dotting the landscape beneath us. Concerned governments are working to safeguard this reservoir because at present, 95 percent of all artesian water brought to the surface is wasted, lost to evaporation.

The value of conserving this resource is obvious, as groundwater is the only reliable source of water across 60 percent of Australia. Many inland towns and industries rely totally on this supply. What does the water taste like? Jason, who was brought up on a Queensland farm reliant on artesian water, says: “It tastes a bit salty, and I prefer rainwater when it’s available; but the cattle love it.” The taste comes from dissolved minerals accumulating in the water as it seeps through the rock layers. On the edge of the basin, the water is almost pure, but toward the middle it can be unbearably salty—only fit for sheep and cattle to drink. Water not trapped and used by man continues its journey westward to the dry interior.

A Fragile Giant

As we fly toward the setting sun, far beneath us we see tiny shining disks of water, scattered like buttons in the desert. After traveling hundreds of miles underground, a journey taking thousands of years, rainwater finally reaches the southwestern edge of the Great Artesian Basin and oozes to the surface, creating these natural mound springs below us. Water evaporating from the springs leaves behind a buildup of mineral deposits. These deposits capture windblown sand, slowly raising the spring above the surrounding landscape.

Even these isolated havens for plant and bird life suffer damage by man. The book Discover Australia notes: “The introduction of cattle, rabbits and more recently, tourists, has brought about the destruction of many of the fragile mound-springs. . . . Perhaps most damaging of all, the amount of water being drawn from bores for stock has markedly reduced the flow rate of many springs, in some cases to no more than a trickle.”

This ancient watercourse is a fragile giant—massive in scale yet vulnerable to human influence. As is true of all the world’s resources, careful management is needed to preserve the enormous underground plumbing system that is the Great Artesian Basin.

[Map on page 25]

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GREAT ARTESIAN BASIN

[Credit Line]

Mountain High Maps® Copyright © 1997 Digital Wisdom, Inc.

[Picture on page 25]

A symbol of outback Australia, the windmill pump brings life to the desert

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Like the inhabitants of this isolated farm, 60 percent of Australia is totally dependent on groundwater

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Natural mound springs bubble up water thousands of years old

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Courtesy of National Parks and Wildlife South Australia

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A salt lake on the southwestern edge of the Great Artesian Basin

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The slow buildup of mineral deposits around the springs has elevated them as much as 45 feet [15 m]

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Courtesy of National Parks and Wildlife South Australia