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Be like the beaver: build more dams

By Viv Forbes - posted Wednesday, 2 March 2016


Water is essential for all life, and happily it is abundant on our blue watery planet.

However, salty oceans cover 70% of Earth's surface and contain 97% of Earth's water. Salt water is great for ocean dwellers but not directly useful for most life on land. Another 2% of Earth's water is tied up in ice caps, glaciers and permanent snow, leaving just 1% as land-based fresh water.

To sustain life on land, we need to conserve and make good use of this rare and elusive resource.

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Luckily, our sun is a powerful nuclear-powered desalinisation plant. Every day, solar energy evaporates huge quantities of fresh water from the oceans. After a stop-off in the atmosphere, most of this water vapour is soon returned to earth as dew, rain, hail and snow – this is the great water cycle. Unfortunately about 70% of this precipitation falls directly back into the oceans and some is captured in frozen wastelands.

Much of the water that falls on land is collected in gullies, creeks and rivers and driven relentlessly by gravity back to the sea by the shortest possible route. Allowing this loss to happen is poor water management. The oceans are not short of water.

Some animals and plants have evolved techniques to maximise conservation of precious fresh water.

Some Australian frogs, on finding their water holes evaporating, will inflate their stomachs with water then bury themselves in a moist mud-walled cocoon to wait for the drought to break. Water buffalo and wild pigs make mud wallows to retain water in their private mud-baths, camels carry their own water supply and beavers build lots of dams.

Some plants have also evolved water saving techniques – bottle trees and desert cacti are filled with water, thirsty humans can even get a drink from the roots and trunks of some eucalypts and many plants produce drought/fire resistant seeds.

Every such natural water conservation or drought-proofing behaviour brings benefits for all surrounding plants and animals.

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People have long recognised the importance of conserving fresh water – early Australian settlers built their homes near the best waterholes on the creek and every homestead and shed had its corrugated iron tanks. Graziers built dams and weirs to retain surface water for stock (and fence-crashing wildlife), used contour ripping and good pasture management to retain moisture in soils, and drilled bores to get underground water. And sensible rules have evolved to protect the water rights of down-stream residents.

In some snow-fed rivers like the Nile, floods are generally a reliable and predictable annual event. For millennia the Nile delivered water and silt fertiliser to the farmers on the flood plains in Lower Egypt. The massive High Aswan Dam may have done more harm than good – it certainly did great harm to the farmers and land down-stream by stealing the silt and the water that supported the productivity of farms that have fed millions since Roman times. The value of the electricity generated by the dam probably does not compensate for these losses.

But in Australia, rainfall is usually a boom and bust affair. Much fresh water is delivered to the land surface suddenly in cyclones, storms and rain depressions. But "The Wet" is always followed by "The Dry", and droughts and floods are normal climatic events. People who fail to store some of the flood must put up with the drought.

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About the Author

Viv Forbes is a geologist and farmer who lives on a farm on the Bremer River.

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