Rob Banks Researches the GAB

Coonamble NSW

Anne Kennedy, an advocate and campaigner for the protection of the Great Artesian Basin, was introduced to soil scientist Rob Banks by Penny Blatchford. Anne employed Rob to do a similar report to Penny’s, on the Petroleum Exploration Licence (PEL 238) which covered her property near Coonamble in the West Pilliga district.

Part of Penny’s and Anne’s PELs were on the Great Artesian Basin’s (GAB) recharge areas. Anne’s PEL covered part of the Coonamble lobe area, where artesian water is the only reliable water source. After completing Anne’s study, the NSW Artesian Bore Water Users Association commissioned Rob to study the recharge and discharge areas of the GAB in NSW and the potential risks from CSG.

‘I suggested that it was probably more efficient to study the whole Basin rather than just a part of it,’ said Rob.

The Great Artesian Basin is poorly understood. A lot of bores have failed in Queensland, where gas mining has taken very large drawdowns of water from the coal underneath it. The potential risk of the same thing happening in NSW is highlighted in Rob’s study.

CSG extraction may significantly affect groundwater resources and groundwater resource access within the GAB if bores or springs begin to fail as a result of depressurisation caused by dewatering of recharge zones. (SoilFutures Report, p. 17)

Water flows very slowly into the GAB from the eastern recharge areas on the western slopes of NSW and Queensland. It then travels a few metres a year sideways towards the west and south, ultimately to Lake Eyre in South Australia.

‘Rainwater filters down to the GAB where there are underlying Jurassic-Cretaceous sandstones,’ said Rob. ‘These water holding beds are mostly sandy, and are a porous rock aquifer. It’s like a sponge with a few holes in it.’

‘The pressure from the higher eastern fringe makes the water flow. Water, ponding at the top of aquifers on the eastern side, awaits its turn to pass through the system. That little head of water, only between 18 and 100 metres deep, stands in the equivalent of a pipe above the rest of the basin and that’s what drives all the bores out west.  This is hydraulic pressure. If the pressure is taken off, it can stop quite quickly.’

Ref: Great Artesian BasinRecharge Systems and Extent of Petroleum and Gas Leases, 2011, SoilFutures Consulting Pty Ltd for the Artesian Bore Water Users Association.