A RESEARCHER from the UNSW Australia is calling for a multi-generational approach to aquifer regeneration in irrigated cotton country.
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Associate Professor Bryce Kelly, a research finalist at last week’s biennial cotton conference on the Gold Coast, has joined forces with isotope hydrologist Dr Dioni Cendon, from the Australian Nuclear Science and Technology Organisation, to prove an interesting point.
The research team has dated the age of the groundwater used by western irrigators by measuring the physical properties of Tritium and Carbon-14 within the groundwater.
Tritium is used to map where the groundwater is less than 70 years old, and Carbon-14 is used to map the age of groundwater up to 50,000 years old.
Their measurements indicate that the groundwater used by many irrigators, particularly those who are located away from river beds, is ancient groundwater that first entered the earth’s aquifers between 5000 and 30,000 years ago.
It doesn’t take an Einstein to realise that aquifer recharge is necessary if groundwater is to remain a viable irrigation water supply down the track. It will take decades of skimming water from floods to recharge groundwater up to pre-1960 levels, when cotton was first grown in the far west.
New earthworks in the form of channels and concrete structures would first need to be built in key locations to redirect the floodwater.
Just don’t expect the return on building recharge structures anytime soon.
Dr Kelly points out that the majority of family owned farming operations throughout the Murray Darling Basin have been doing their work for generations and as a result the concept of future-proofing water supply should not come as an unattainable goal.
“All over the world countries are actively working to recharge aquifers but it is not happening enough in rural Australia,” he said.
“Underground water levels have fallen in just 50 years of extracting groundwater for irrigated agriculture.”
To start the process, Dr Kelly suggests scraping topsoil to let floodwaters enter porous sands and gravels.
In some places three to six metres of soil will need to be cleared and channel banks will need to be sculpted to guide the broadly flowing flood waters typical of inland events towards aquifer entry points.
In the US,a different technique has been adopted, with large diameter holes drilled into the earth’s surface to access aquifer sands.
These giant sinkholes allow floodwaters to enter the aquifer during massive rain events.
