Useful links and previous articles
alternative water (pdf)
harvesting smaller rains
community action on water
Watropy- shifting the water paradigm.pdf
Reaping the benefits.doc
The Waterright philosophy
Chapter 4 Local water harvesting
Myths and realties of water
We are continuously being told of the severe water shortages facing Australia. Yet the total amount of water available in Australia would appear to be far in excess of our needs, approaching half a mega litre per person per day. Not many countries exceed that Iceland seems to top the score at 2.8 megalitres per person per day and poor Kuwait only gets about 30 litres per person per day.
The proportion of the rain that we harvest though is only 1 in 2,000. Why is that so low and what can we do about it?
There are many reasons;- rain does not fall where we want it, much of the rain falls in the Northern tropics while there is still significant rain in the the mountains of Tasmania where it is not viable to harvest. The actual catchments area are only a small proportion of the total land area, largely limited by the availability of suitable dam site. It is where rainwater tanks such as of Rainwater Tanks Direct are very helpful which can be installed on roof gutters to catch the rain water.
Not all rain is equally useful. The first 10mm or so of rain simply wet the surface layer and rapidly evaporate. Rain over 10mm but under 50mm will typically wet the root zone and it therefore useful, but will not cause run off.
Typically at least 50mm is required for run off.
Evaporation is not always lost water. In high rainfall high humidity conditions water will evaporate and fall again as rainfall. In area such as the Amazon jungle some 60 to 70% of the rain fall is simply recycled rain that has evaporated. In dry arid conditions or after a long dry period most of the evaporation will be blown away without doing nay useful work.
Not lack of rainfall but excessive evaporationAustralia's problem is not so much lack of rainfall but excessive evaporation, so much of the rain that does fall cannot be readily captured. In much of Australia evaporation exceeds rainfall, You do not have to travel far inland evaporation for evaporation to be double rainfall, while nearer the centre it can be ten times.
Do we just have to accept this excessive evaporation or can we do something about it?
If we look at those areas with extreme evaporation, multiples of rainfall we se that they are not empty deserts but there is extensive vegetation. At first we may think that this is because of the specialist nature of the vegetation with many inbuilt methods of saving water. But all of these would be useless if there were not some underlying mechanism.
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|Updated 7 nov 2015|