Farmers Learn To Conserve Ancient Aquifers
BURIED 3,000 feet under the soil is a huge underwater aquifer that stretches from Queensland to South Australia. The water in this vast underwater reservoir is up to 1 million years old by the time it comes to the surface in the deserts of South Australia. The aquifer is the result of rainfall percolating through porous sandstones in the Great Dividing Range, which follows Australia's east coast.
Tapping into these ancient water supplies, ranchers in arid regions of three states can provide water for their livestock even during the hot Australian summer. For centuries, aborigines have drunk the water that comes naturally from springs.
Drilling for water is essential because most of the outback is arid. The average rainfall in the Longreach region, for example, is 18 inches a year. It can be less. Over the past 10 years, the outback has had a series of droughts. This year it may be starting a wet cycle. There were floods in March and April and in one night, Longreach received 15 inches of rain.
The water coming from deep in the ground is not like surface water. Because the water is closer to the earth's core, it comes out of the wellhead at 150 degrees F. To cool the water, ranchers build long cement canals, leading into ponds. The water can have an unusual taste as well. Although it is generally safe for livestock to drink, it is usually not used for irrigation because of its sodium content.
Bob Cottam, division veterinary officer at the Arid Research Institute, shows a visitor a photo of a 6 1/2-year-old sheep. It has lost almost all of its back teeth from drinking water with a high fluoride content. ``Sometimes the bore water is even distasteful to stock,'' he says.
In Longreach the bore water has too much fluoride for human consumption and the town gets its water from the Thomson River.
When the artesian basin was first discovered 100 years ago, too many wells were drilled and it lost more water than it gained. However, today the recharge rate is about equal to the discharge rate, says Rien Habermehl, a senior research scientist with the Bureau of Mineral Resources, Geology, and Geophysics in Canberra.
Ranchers are now starting to find ways to conserve water. For example, instead of cooling the water on long concrete races where evaporation sucks up a large portion of it, they are funneling the water through plastic tubing, says A.E. Moloney, manager of Southern Cross, an irrigation supply company. The plastic tubing cuts evaporation, which can be as much as 50 percent of the water pumped from the well.
Some wells no longer can produce water without mechanical help because of a loss of pressure. ``It's now reached the stage where farmers are putting in windmills,'' says Mr. Moloney.