The Great Artesian Basin

The Great Artesian Basin

Great Artesian Basin(1)

The Great Artesian Basin

Two million years ago water rained down on the Great Dividing Range in Queensland – today that same water can be found bubbling up in South Australia. Two hundred and fifty million years ago Australia was joined to Antarctica, South America, Africa and New Zealand. This land mass was called Gondwana.

One hundred and forty million years ago the ice age in Europe and the movement of tectonic plates caused the sea levels to rise. This water flowed into a basin in Australia and formed a sea and when the sea levels dropped a body of water remained trapped. When the water receded it left behind rivers covering the whole of Australia and these brought sand and gravel together making sandstone. The sandstone became hard and impermeable but a layer of permeable sandstone lay above. Today when the country floods the water flows into the basin but only through the permeable layer and this collection of water is called an “aquifer”.

The Artesian Basin covers one-quarter of Australia (1.7 million square kilometers beneath the arid and semi-arid parts of Queensland, New South Wales, South Australia and the Northern Territory). It is estimated that it contains 65 thousand million mega litres of water. One mega litres is one million litres. Sixty five thousand million mega litres is enough water to cover the entire earth in ½ mitre of water. It stretches from Cape York in the north, down to Dubbo and across to Coober Pedy. To clarify this even more it is equivalent to 130,000 Sydney Harbours.

Traditionally, artesian water that came to the surface under natural pressure was allowed to flow uncontrolled into open drains and creeks for distribution to stock. However, even in well-maintained drains, up to 95 per cent of this water can be wasted through evaporation. It was recognised by the early 1900’s that control over the Great Artesian Basin groundwater was inadequate and there was a reduction in water pressure and volume due to the increasing number of free-flowing bores drilled. Uncontrolled flow from bores and open earth bore drains in the Great Artesian Basin threatens the health of important groundwater- dependent ecosystems and continued access to artesian water by pastoralists. In addition, it has become difficult for new water users in or near the Great Artesian Basin to obtain access to groundwater resources.

The waste of water is causing environmental damage through:

• reduced pressure in some naturally occurring artesian springs;
• encouragement of the spread of pests, plants and animals;
• land and water salinization

To assist in improving pressure in the Basin, the Australian, state and territory governments are funding the Great Artesian Basin Sustainability Initiative (GABSI). The program is aimed at addressing pressure decline in the Basin through the replacement of inefficient bore drains with pipeline reticulation systems. It is a 15 year program jointly funded by the Australian, New South Wales, South Australian and Queensland governments. The first five-year phase of the GABSI program began in 1999 to assist landholders to accelerate work on capping uncontrolled artesian bores and replacing wasteful open earthen bore drains with pipes. A second five-year phase of GABSI began in 2004, with GABSI Phase 3 in 2009. Phase 3 was the establishment of a Basin-wide monitoring network to improve the quality of information about the Basin and to enable better management of the whole of the basin issues. The Northern Territory government is engaged in this latter part of GABSI.

The CSIRO in conjunction with the Geo science Australia has completed a two and a half-year $A 6.25 million assessment which involved a basin-scale investigation of water resources and the potential impacts of climate change and groundwater development to 2070.

CSIRO’s Doctor Brian Smerdon said that they had mapped out all the faults and ridges that impact on the groundwater flow conditions. Also the maps show not only the Great Artesian Basin (GAB) but also the older basins that are underneath the GAB. The older basins in some places connect very well and you have water going upwards to the GAB and down to the older basins. There are some locations that do not have that movement of water back and forward.

It is not known how long this resource will last but hopefully for some time. It has been heavily used for the last century but it would have been used long before that. Doctor Paul Smerdon said that you will find a natural decrease in the pressure but that has nothing to do with our influence on it.

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