The Great Artesian Basin

John Waechter

Introduction to Hydrogeology, Spring 2007



Figure 1: The extent of the Great Artesian Aquifer.

Picture from Queensland Government

Introduction

The Great Artesian Basin is one of the largest aquifers in the world. The extent of this aquifer lies beneath approximately one fifth of the total continent of Austrailia. The total area that the aquifer covers is 1,711,000 square km, or 660,620 square miles or 422,797,307 acres. There is about 64,900 million megaliters worth of water storage within the aquifer which also equates to about 52,615,285,518 acre feet. With this much water a person could fill the Sydney harbor 130,000 times. This aquifer suppossedly formed about 100 to 250 million years ago. The aquifer has alternating layers of permeable and impermeable layers of sandstones, siltstones, and mudstones.

Hydrologic Setting Hydrologic and Geologic Properties Water Resource Ground Water Contamination

Hydrologic Setting

The groundwater flow rate for this aquifer varies from year to year. Usually there is a total difference between one to five meters per year. Along the eastern edge of the aquifer most of the recharge comes from rainwater infiltration that travels down into the sandstone within this area. The most recharge happens in the area that is just west of the Great Dividing Range. There is a line of springs that has formed from faulting along the southwestern edge of the basin. This causes for a natural form of discharge from the aquifer. The climate around the aquifer is a temperate and tropical climate. This provides a great chance for there to be a large amount of precipitation in order to recharge the aquifer. The amount of rainfall and snowmelt from the mountains of the Great Dividing Range are what recharge this aquifer. The recharge enters the aquifer on the eastern side through areas of the aquifer that have risen up to the surface in order to provide an opening that will allow for the precipitation to enter the aquifer and recharge the aquifer(NRW About the Basin, 2005). This can be seen in Figure 2 below.


Figure 2: The recharge process of the aquifer.

Picture from Recharge Process

Hydrologic and Geologic Properties

The Great Artesian Basin consists of many different alternating layers. These layers are both permeable and impermeable. Both types of layers can be seen at the surface as I explained a little bit before with how the aquifer is recharged. The layers that make up the permeable aquifer are made up of sandstones and the impermeable layers are composed of siltstones and mudstones. These layers formed from three major depressions that now form the GAB aquifer. Back in the Triassic period that was uplifting that was eventually eroded away and eventually formed the alternating layers that are there today. With all of the layers combined the aquifer ranges from anywhere around 100 meters thick in the shallowest spots to being as deep as 3,000 meters or just a bit more in the deepest parts of the aquifer(NRW GAB pdf, 2006).This aquifer is referred to as an artesian aquifer because its waters are confined within its permeable layers by its impermeable layers. These impermeable layers cause pressure to build within the aquifer which will cause the water to flow outward to the surface if there are any bores that are tapped into the aquifer. This aquifers hydraulic conductivity ranges from anywhere of 0.1 to 10m per day(GABCC). The water quality is variable within the aquifer. With the amount of total dissolved solids only being around 500 milligrams to a liter the water is pretty safe. However, the pH level of the aquifer is rather high in comparisson to other sources of water from aquifers. The waters within the aquifer are also high in sodium levels which takes the possiblity of using this water for irrigation out of the equation(NRW About the Basin, 2005).

Water Resource

As I said just a bit ago in the Hydrologic and Geologic Properties section this water is not suitable to be used for irrigation because of its high sodium content. Throughout the aquifer the temperatures range a great deal at the well heads. The waters here range anywhere from 30 degrees Celsius to p to 100 degrees Celsius. See Figure 3 for temperatures. With these temperatures being this high the water is not suitable for consumption for the public and livestock. In order for there to be consumption of this water there have been cooling towers put around in order to cool the water down for consumption to be able to take place. When the temperatures are this high there are a few things that can be done in order to be able to use this water as a resource. Water from this aquifer is used for many things like space heating, geothermal bathing, air conditioning, and power generation(Geoheat, 2002). The water within the aquifer is under no immediate danger. There are new bores being installed into the aquifer because of better conservatin techniques. Uncontrolled bores are being capped off or piped over to new areas in order to conserve as much water as possible. This allows for many bores that have gone dry to once again start flowing. These wells will then flow from a natural state and the aquifer will be closer to the state of equilibrium that it had when the aquifer was first formed(NRW Management, 2005). The largest problem that this aquifer is that it wastes (or losses) 95% of the discharged water to evaporation and seepage. There are other small problems that cause a little concern. These problems range anywhere from salinity problems within the soil, erosional problems, to having problems with bores being eaten away from corrosive waters(NRW Wastage, 2004).


Figure 3: Water temperatures of the aquifer.

Picture from Water Temperatures

Ground Water Contamination

This aquifer is not really known to have any sort of contamination. A lot of the area is used for cattle grazing which helps reduce the possibility of contamination from any type of agricultural use. If there was any type of contaminations it would probably only get to the first permeable layer. Once the contamination got to the first impermeable it would be stopped from entering the rest of the aquifer and contaminating the rest of the water. Since there really is no type of contamination there is not anyone agency that can be specified for the cleanup. However, companies like the Great Artesian Basin Sustainability Iniative (GABSI) looks after the aquifer and how the water and land resources are being affected by the aquifer(NRW GAB pdf, 2006). This gives State and Federal agencies along with landowners the opportunity to get subsidies in order to cap and pipe the bores that are on their land(NRW GAB pdf, 2006). Over 31.8 million dollars have been put into the GABSI in order to monitor and manage the wells from 2000 to 2005. Any wells that are not in proper working condition are rehabilitated from the money that has been put into the system(GABSI, 2006).

References:

GHC Bulletin. Geothermal Resources of the Great Artesian Basin, Australia. June 2002. http://geoheat.oit.edu/bulletin/bull23-2/art5.pdf Accessed 22 Apr. 2007

Great Artesian Basin Conservation Committee. Overview of the Great Artesian Basin. http://www.gabcc.org.au/public/content/ViewItem.aspx?id=96 Accessed 23 Apr. 2007

Image. 23 Apr. 2007 http://www.soil.pir.sa.gov.au/images/mar_rep_fig7_pg31.gif

Natural Resources and Water. The Great Artesian Basin. 2006. http://www.nrw.qld.gov.au/factsheets/pdf/water/w68.pdf Accessed 22 Apr. 2007

The Great Artesian Basin. About the Basin. 01 Aug. 2005http://www.nrw.qld.gov.au/water/gab/ Accessed 22 Apr. 2007

The Great Artesian Basin. Management. 28 Feb. 2005. http://www.nrw.qld.gov.au/water/gab/management.html Accessed 22 Apr. 2007

The Great Artesian Basin. Wastage. 19 Nov. 2004. http://www.nrw.qld.gov.au/water/gab/wastage.html Accessed 22 Apr. 2007

Water Resources.Great Artesian Basin Sustainabiltiy Iniaitive. 30 June 2006. http://www.dwlbc.sa.gov.au/water/projects/gabsi.html Accessed 23 Apr. 2007