By Lance Endersbee Posted Sunday, 15 August 1999. ON LINE opinion - Australia's e-journal of social and political debate
Australia’s Artesian Basin – $14 Billion down the drain each year
The traditional view of the Great Artesian Basin, which is the basis of government policies and which is taught in schools, is that the aquifer is a porous rock where the water content is continuously replenished by slow seepage from the strata outcrops in the uplands to the east. This concept is incorrect and the resulting mis-management of the Basin is causing irrecoverable damage to this valuable asset.
As a result the assessment of potential life of the groundwater resource is wrong and hopelessly optimistic with a volume of water equal to 80% of Sydney Harbour wasted each year, equivalent to annual economic output of $14 billion.
Substantial and permanent damage is being done to the aquifer by the present uncontrolled usage. The economic cost is so great that the costs of immediate correction are trivial by comparison.
This is a matter of such vital importance to the national economy that there can be no question of insufficient funds.
The present conceptual model of the characteristic behaviour of the Great Artesian Basin is that of an open system. This conceptual model is shown in the Queensland government web page – www.dnr.qld.gov.au/resourcenet/water/artesian_basin/flow.html.
The accompanying illustrations are taken from that webpage.
The concept of an open system assumes that as water is withdrawn from the aquifer it can be replaced by lateral transfer from recharge areas or from elsewhere in the basin. The concept looks plausible in the diagram, which has been drawn to a grossly exaggerated vertical scale.
However, the depth to the aquifers is some 500 to 1000 metres, and the lateral extent of the Basin is some 1000 by 1500 kilometres. If the above diagram were to be drawn to a natural scale, it would show only as a single line across the page.
Because of the huge lateral extent of the Great Artesian Basin, that covers 1.7 million square kilometres, there are virtually no prospects whatsoever for lateral transfer from recharge areas.
It is also assumed that the withdrawal of water causes no change in the physical dimensions or characteristics of the aquifer.
The present interpretation is based on the assumption that the Jurassic sandstones are porous, and that the porosity is unchanged by the discharge of water from the basin, or by the drop in water pressure. The flow of groundwater through the aquifer is considered to correspond to that of flow through porous media. This interpretation suits some of the open fluvioglacial aquifers in North America, which are radically different to our Jurassic sandstones.
These related assumptions are implicit in the descriptions of the operation of the Great Artesian Basin which are given in various government reports on the management of the Basin.
The above diagrams present a false concept of the operation of the Basin, and are repeated in many reports and publicity documents. They create false expectations about the potential and sustainability of the Basin.
This information is also included in material for Education Departments and schools, and via the Internet. It is not acceptable as an explanation to young children in schools, and is certainly not acceptable as a basis for government decisions on the management of the Basin.
The water that is now in the basin is all that will ever be available. It is a closed system. That has several implications.
When the Great Artesian Basin was first penetrated by bores, the water gushed out at high pressures and high discharges, the fountains extending 100 feet and more into the air.
That is certainly not the result of seepage through porous sandstones into a borehole, but the release of high pressure water stored in open fissures in the rock. The porosity of the sandstone rock is not a factor.
The proper understanding of the operation of the aquifer is that of an open jointed rock mass.
The water pressures in the aquifer a century ago, prior to exploitation of the Great Artesian Basin, were almost comparable to the overburden pressure of the rocks.
The original formation of the aquifer should be seen as the consequence of the effects of high hydraulic pressures in rock fissures, effectively jacking the rock apart. In this case, the extra-ordinary continuity of the sedimentary basin enabled these water pressures to open up fissures in the sandstone over great distances.
Let us first state the overall physical conditions. We are dealing with saturated, incompressible rocks, and incompressible water in fissures and bedding planes. It is a closed system.
In physical terms, the effect of withdrawal of water is a reduction of the overall volume of the aquifer by an amount equal to the volume of water removed. The ground surface subsides by an amount equal to the volume of water removed.
Because it is a closed system, the removal of water is accompanied by a reduction in the water space in the fissure openings in the rock. The fissures close. The water pressure is reduced, the pressure on the rocks is less, and the rocks expand into the fissure openings. There is a reduction in discharge capacity of the aquifer.
A characteristic feature of these rocks is their plasticity and capacity to flow under shear stresses. At depth, these rocks do not normally have open joints or fissures, as the rock itself simply flows or changes shape to close the openings. The rocks may have fractures, but not open joints. Open joints and fissures may be evident in near surface rocks, but not normally at depth.
In the Great Artesian Basin there are fissures in the sandstones in the aquifer. These open fissures were originally formed as closed fractures during crustal movements, and then opened and sustained by the high water pressure in the aquifer. Over geological time there was a hydraulic jacking effect, which effectively opened up joints in the strata over vast distances.
The aquifer was made possible by these high water pressures.
The effect of a reduction in aquifer water pressure is quite catastrophic.
The open fissures close as the rocks respond to the effect of the lower water pressures and the driving force of the weight of the overlying sediments. There is a loss in potential energy as the overlying rock mass subsides.
It is definite and slow change. For all practical purposes it is quite irreversible, as the matter can only be corrected by applying water injection pressures sufficient to carry much of the weight of the overburden over a long period of time.
In effect, the depressurizing of the aquifer has resulted in a huge loss in potential energy, and that energy, and more, has to be re-applied to reverse the process.
The pressure drop since the first development of the Great Artesian Basin is assessed at up to 100 metres of water pressure head.
It is inevitable that the closure of fissures arising from that loss of pressure is still occurring, and that we may expect continuing closure for some time. It is much worse if boreholes are permitted to flow freely, as that accelerates the process. The immediate capping of all open bores is absolutely vital if we are to have any prospect of retaining the Great Artesian Basin at anywhere near present levels of useful output.
Even within a capped bore there is still the real possibility of leakage from a high-pressure aquifer into the various strata above. Many bores may have to be reconstructed to ensure that there is no internal leakage.
It should be recognised that the dry bores represent the end phase in the permanent destruction of the aquifer. There is little prospect of long term supply by using pumping to lift water from a dry bore, as the lowering of the water pressure at the pump intake would lead to final closure of the fissures.
The dry bores appear to be aggregated in certain areas. These areas now form a break in the continuity of the aquifer.
The aquifers have been penetrated by a very large number of waterbores, which complicates the task of long term protection of the resource. Some 4700 artesian bores have been drilled, and 3100 of these remain flowing.
There is a wide body of historical evidence showing the continued decline of the available yield from the aquifer.
In a paper in 1969, the declining yield in the NSW section of the Basin, up until that time, was reported. The data is transcribed in the table below.
Peak Aggregate Flow From Bores in NSW
Year Output in million gallons per day Total number of bores Number of flowing bores
1910 112 394 364
1920 86.5 510 420
1930 77 — 475
1940 68 — 550
1968 50 (restricted) 1167 692
From Journal IEAust.,March, 1969, page 37.
The table shows the way the annual output decreased markedly from 1910 while the number of bores increased. It is of interest to note the comments that accompanied the presentation of the above data in that 1969 paper. “The reduction of flows quoted above should not be construed, as it was in the early1900′s, as indicating a limited life to this resource. It is largely a function of the hydraulics of bores in confined aquifers, the theory of which was not adequate until 1935.”
With such reassurance, based on a fundamental misconception of the characteristics of the aquifers, and similar reassurances over the years, the disastrous waste of water has continued to this day.
It is stated in the web page, “Great Artesian Basin Facts”, that the estimated total water storage is 8,700 million megalitres. I am not aware how that figure was assessed, but it is clearly in error. It is equivalent to a uniform depth of water of 5 metres in thickness over the entire area of the Basin. It may be an estimate of all of the captive water in all of the saturated sandstones, which is something radically different to the potentially recoverable water in the joints and fissures in the aquifers.
The total volume of water taken from the Basin in the past 100 years is about 50 million megalitres. That is equivalent to 100 times the volume of Sydney Harbour (0.5 million megalitres). With waste of water at 80 percent and more, the waste of water to date has been equal to more than 80 times the volume of Sydney Harbour.
In the light of the evidence of declining pressures and declining yields, it is quite likely that the remaining volume of accessible water may be substantially less than the yield to date, certainly less than half, say 20 million megalitres or much lower.
The present rate of extraction from the Basin is about 0.5 million megalitres per year. That is an annual discharge equal to the volume of Sydney Harbour. It is really quite incredible that people have believed that a groundwater yield of that magnitude could continue forever.
At the present rate of extraction, the remaining supplies may only last a few decades. However, present wastage is over 80 percent. It is only by the complete elimination of such waste that the life of the resource can be extended beyond the next century.
There is a critical need for a major new assessment of safe extraction levels to ensure a much longer life for the resource. The available data on trends in pressures and flow rates should enable the development of predictive models of aquifer behaviour.
The present groundwater flow from the Great Artesian Basin supports a total level of production in the region of $3.5 billion per annum, according to a press release. Much of that production would not be possible, or would be different and much less, without the availability of groundwater.
The current artesian bore discharge is about 0.5 million megalitres per annum. It is estimated that 80 per cent of the current outflow is wasted because of inefficient delivery systems. Thus, the useful part of the outflow is 100,000 megalitres per annum.
It follows that the water that is used effectively enables and supports a level of total economic activity equal to $35,000 for each megalitre. That simply reflects the critical importance of these secure supplies of water to the regional economy.
But 80% of the water that is extracted from the Basin is wasted. With a level of wasted water of 80%, or 400,000 megalitres per annum, the annual loss in potential future production is 400,000 x $35,000.
This wastage equals a loss of $14 billion each year in total value of future national production, or $38 million each day! With these huge numbers, it really does not matter how we assess the present value of future lost production. It will be very big indeed. With 3100 flowing boreholes, the loss to the future national economy of the 80% waste is equal, on average, to $12,000 per day per borehole. That water is irreplaceable.
This waste is of truly enormous proportions and should be corrected immediately. In all these circumstances, the costs of immediate action are quite trivial in relation to the colossal damage that is occurring to the national economy as each day passes.
The Great Artesian Basin covers three states, Queensland, NSW and South Australia as well as the Northern Territory. The rapid decline of this national resource has very serious implications for the national economy, and that means that the Australian Government also carries responsibilities. In legislative terms, there are no legal provisions for the management of the Basin as a whole, and it is evidently out of control. There is a Great Artesian Basin Consultative Council with broad representation, but their role is advisory.
Concerted action is required, and that is a responsibility of all of the governments involved. It seems appropriate for the Commonwealth, Qld, NSW, SA, and NT to enact similar joint legislation restricting all extraction of groundwater from the Basin to consumptive use only, and defining how that will be assessed and controlled.
In view of the need for prompt action, one approach may be to put together a national action team, which could be created by seconding officers from the states involved, and the Commonwealth. Alternatively, the tasks could be assigned to the private sector.
A set of standard designs is required for rapid production of new wellheads with water control, video transmission and monitoring facilities. It is likely that a very large number of bores will need to be reconstructed to control waste to other strata within the borehole itself.
An achievable objective could be to correct all waste within 2 years. As a rough guide to probable costs, a total allocation of $200 million may be required. The Commonwealth could assume responsibility for all of the basic costs involved in stopping the waste of water, primarily to ensure high and uniform standards and immediate action. The Shire Engineers in the many Shires throughout the Basin are available. They know the region and the people involved, and can act quickly to assist with site works if they have authority and funds to do so. The Army could assist, especially the Army Engineers and the Helicopter units for deliveries to borehole sites. It is, after all, a national emergency.
Emeritus Professor Endersbee AO FTSE is a civil engineer of long experience in water resources development. His early professional career included service with the Snowy Mountains Hydro-Electric Authority, the Hydro-Electric Commission of Tasmania and the United Nations in South-East Asia as an expert on dam design and hydro power development. In 1976 he was appointed Dean of the Faculty of Engineering at Monash University. In 1988-89 he was Pro-Vice Chancellor of the University.
His fields of specialisation include the management of planning and design of major economic development projects, water resources, energy engineering and transport engineering. He has been associated with the design and construction of several large dams and underground power station projects and other major works in civil engineering and mining in Australia, Canada, Asia and Africa. He was President of the Institution of Engineers, Australia in 1980-81.
In 2005 he published, A Voyage of Discovery, a history of ideas about the earth, with a new understanding of the global resources of water and petroleum, and the problems of climate change.
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