Australia's Great Artesian Basin
The Great Artesian Basin (GAB) is one of the largest artesian
groundwater basins in the world. It underlies approximately one-fifth
of Australia and extends beneath arid and semi-arid regions of
Queensland, New South Wales, South Australia and the Northern
Territory, stretching from the Great Dividing Range to the Lake Eyre
depression. The Basin covers a total area of over 1 711 000 square km
and it has an estimated total water storage of 64 900 million
megalitres (a megalitre is one million litres and is equivalent to
about half the water in an Olympic swimming pool).
The Great Artesian Basin was formed between 100 and 250 million
years ago and consists of alternating layers of waterbearing
(permeable) sandstone aquifers and non-waterbearing (impermeable)
siltstones and mudstones. The thickness of this sequence varies from
less than 100 metres on the Basin extremities to over 3 000 metres in
the deeper parts of the Basin. Individual bore depths vary up to 2 000
metres with the average being 500 metres. Some of the sandstone
sequences contain oil and gas where conditions are suitable.
Groundwater in the Basin flows generally westward to the south-west
over most of the Basin but to the north-west and north in the northern
section. The rate at which water flows through the sandstones varies
between one and five metres per year. Recharge by infiltration of
rainfall into the outcropping sandstone aquifers occurs mainly along
the eastern margins of the Basin, more specifically along the western
slopes of the Great Dividing Range. Natural discharge occurs mainly
from mound springs in the south-western area. Mound springs are natural
outlets of the artesian aquifers from which groundwater flows to the
surface. Dating of the artesian waters has given ages of almost 2
million years for the oldest waters, which occur in the south-western
area of the Basin. Water quality in the main aquifers is generally good
with Total Dissolved Solids (TDS) varying between 500 to 1 500
milligrams/litre, although pH may be very high, and high sodium levels
make it generally unsuitable for irrigation. Water temperatures vary
from 30 degrees C in the shallower areas to over 100 degrees C in the
deeper areas.
The Importance of using Licensed Water Bore Drillers
Natural Resources and Water Minister Craig Wallace has urged
landholders to ensure that drillers are licensed before they do any
water bore work on properties in Queensland. Mr Wallace said a recent decision in the Goondiwindi Magistrates Court
earlier this month underlined the need for landholders to use licensed
drillers. "Standards have to be met to ensure that bores are constructed
soundly and efficiently and groundwater supplies are not contaminated,"
Mr Wallace said. "The contamination to our underground resources is too great a risk to think about," he said. "The department insists on licensed drillers meeting exacting
standards and these are in place to protect our underground water
resources."
A driller was fined $12487.50 and ordered to rectify a bore on a
property at South Kurumbil to comply with minimum standards under the Water Act, 2000. He was also ordered to pay $66.50 in court costs. The defendant was operating an unlicensed drilling business in 2004 when the offence occurred. Mr Wallace said the department was aware of a number of instances
where landholders had performed work themselves or had hired
unqualified drillers to do the work at a discount rate. "The siting, design, materials and construction method used in a
bore all influence the quantity and quality of water obtained and you
need someone with experience to help you decide on these factors before
starting work," Mr Wallace said. "The State Government has introduced legislation controlling the
construction of water bores to ensure the continued protection of
groundwater. The general community and many agricultural enterprises
rely on groundwater resources to continue," he said. About 40 per cent of South West Queensland's water is from
underground supplies with many towns and properties relying on this
resource for domestic use. "The licensing system provides a series of checks to ensure only
competent and qualified persons become licensed. Qualified contractors
are essential to protect not only the resource from contamination, but
to protect landholders from possible harm if the bore being drilled is
for domestic consumption. "Magistrate Andrew Cridland noted in his sentencing remarks that a
deterrent penalty had to be imposed due to the "value" that residents
placed on water resources, particularly during the drought.
For further information contact the Department of Natural Resources and Water by calling 13 13 04 or visit the NR&W web site.
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