Hidden Water for a Thirsty Land
BY “AWAKE!” CORRESPONDENT IN AUSTRALIA
CAN you imagine a deposit of water larger in area than Lake Superior in North America, Lake Victoria in Africa and the Caspian Sea in Russia put together, in fact, larger than the world’s thirty-five principal lakes combined? There is such a reservoir of water in Australia.
“In Australia?” you may ask. “Is that not the world’s most arid continent?”
Yes, this is true, yet there is in Australia, hidden underground, such a large deposit of water. The water is in the Great Artesian Basin that covers an area of 670,000 square miles. In all, there are six artesian basins that lie under about a million square miles in Australia.
“But what is an artesian basin?” you may inquire.
It is essentially underground water confined under pressure within a porous bed of sedimentary rocks. The word “artesian” is derived from the Latin Artesium, a Roman name for the French province of Artois, near Calais. It was here, in the year 1126 C.E., that the first artesian well in Europe was sunk, hence the name artesian.
When an artesian basin is tapped by a bore, the water, under pressure, rises. When the pressure is great enough to cause the water to rise to the surface and overflow, it is called an artesian bore or an artesian well. Sometimes the underground water is under such great pressure that it shoots up many feet into the air. If the pressure is not sufficient for the water to reach the surface and overflow, then it is termed subartesian.
Significance of Discovery
The Great Artesian Basin extends from within one hundred miles of the Pacific coast to the center of the Australian continent, and stretches from the Gulf of Carpentaria down to northern New South Wales. Its maximum length and breadth is approximately 1,100 miles. The basin is located mostly in the state of Queensland.
In this hot, arid, sparsely populated land the life of a traveler frequently depends upon water. Recently, an inexperienced traveler died from heat exhaustion and thirst in this area. He recorded his last words on a portable tape recorder. Yet, unknown to him, an artesian bore was only a stone’s throw away. What a difference it would have made if he had known!
In the 1880’s the news that water had been struck in western Queensland was greeted enthusiastically. The plains were ideal for grazing, many persons realized, if only there were a water supply. Thus, discovery of underground water set the stage for rapid expansion by those who were willing to endure the heat, flies, dust and other difficulties.
Bore after bore was sunk until now there are in the Great Artesian Basin some 3,500 flowing bores and about 5,000 subartesian ones. Yields from some of these wells reached as high as two million gallons a day.
Watering Stock
Artesian water is not suitable for use in continuous irrigation on a large scale. This is because of its sodium carbonate content. However, it is valuable for watering stock. Indeed, some 20 percent of Australia’s sheep are reportedly wholly or partly dependent on artesian supplies.
The sodium carbonate content of the Great Artesian Basin is 20 to 120 grains per gallon. But since cattle thrive on water with 1,000 grains and sheep on water with 1,350 grains per gallon or even more, the mineral content presents no real problem for stock.
The water from the bores is channeled in open-earth drains to where it is desired. Some bores supply many stockmen. The greatest length of drain from a single bore is 117 miles from the Wild Horse bore near Bollon, Queensland. It has a flow of 891,000 gallons per day. Unlike in former years, the present-day bores are throttled down or shut off completely when the supply is not in use. In this way it is hoped to conserve water and maintain a degree of pressure.
How Long the Water Supply?
Interestingly, artesian bores continued to produce more and more water until 1914, at which time a peak of over 350 million gallons a day were pouring forth on the soil. From this time on, a gradual decrease in flow began. In spite of thousands of bores being sunk since that time, the total gallons have decreased to the present flow, which is estimated at approximately 200 million gallons daily in the Great Artesian Basin.
Why has there been this decrease in flow? Well, with all the bores being sunk, a great amount of water has been released and with it a great amount of pressure. And the water entering the intake beds is filtering down through the porous rocks slower than the water that is gushing up through the bores. Thus the flow has been diminishing gradually.
What has been happening over the past sixty years or so in the Great Artesian Basin might be compared with what happens when you use a garden hose. If you put your finger over the end of it, the pressure and the amount of water build up within the hose so that when you take your finger away the water spurts out suddenly, but then falls off to a steady flow. Although the falling off to a steady flow only takes a few seconds after you remove your finger from a hose, this reduction has been going on gradually for many years in the artesian basin. The flow of water is still falling off.
Some stockmen express concern as to whether the water from the bores will eventually cease. But it does not seem that it will. The intake areas for the subterranean basin receive water at an estimated rate of 130 million gallons per day, and so it is expected that the decrease in the flow of water will continue until the intake and output are equal.
Thus, it appears that for many years to come there will be adequate water for raisers of sheep and cattle. What a phenomenon a great artesian basin is! Here in Australia it is indeed hidden water for a thirsty land!
[Map on page 25]
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AUSTRALIA