The water down underYou might not think it, but in a country as dry as Australia many people are literally walking on water.
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Key textMost people think of rain water, rivers and dams as the major sources of water that quench Australia's thirst. But the reality is that groundwater provides more than 20 per cent of the water used in Australia each year and is set to become even more important due to overallocation of surface water and the recent drought. Groundwater is the water that exists underground. While it can be present as underground lakes beneath the Earth's surface, it's more commonly the water that lies in the tiny spaces between grains of sand or bits of fractured rock. It's a bit like the effect you'd get if you poured water into a jar of sand or pebbles – the water wouldn't float to the top, but instead would settle in the spaces between grains, filling the spaces between sand or stones. Use of groundwater resources Across Australia, groundwater plays a critical role as a source of water for drinking, irrigation and industrial purposes. It some cases, it is also the source for spring water and mineral water companies, and provides the water for making soft drinks and beer. Bores utilise groundwater to water suburban gardens and to irrigate parks, golf courses and crops. It is also a vital part of the ecosystems that support wetlands and some unique plant and animal species. Groundwater also keeps many of our rivers flowing even when there are long periods without rain. Out of sight, out of mind Groundwater is a major resource, but one that has been taken for granted for decades. In the past, groundwater supplies were treated as an infinite resource, and subject to an 'out of sight, out of mind' attitude. But that's changing. There's now an enormous interest in the way our groundwater resources are measured, managed and utilised. There are also concerns over issues such as over-extraction of water, pollution, wastage, allocation and licensing issues, water pricing and groundwater salinisation. The water source beneath one-fifth of Australia The most well-known and important groundwater source in Australia is the Great Artesian Basin, or GAB. This is a vast groundwater source that underlies 22 per cent of Australia – extending beneath the arid and semi-arid regions of Queensland, the Northern Territory, South Australia and New South Wales. It covers about 1.7 million square kilometres, and contains an estimated 8700 million megalitres of water. Not surprisingly, it's one of the largest artesian water basins in the world.
Its other statistics are equally amazing. The water-bearing aquifers of the GAB extend down to a depth of three kilometres, and some of the water is believed to be up to two million years old (Box 1: Using science to measure and manage groundwater). The average water temperature is between 30 and 50 degrees, but it can be as hot as 100 degrees Celsius. History of the GAB The GAB has always been an important source of water for many outback communities, especially during drought. Indigenous people relied on its natural springs for thousands of years and the waters form part of their culture. More recently, the springs helped the development of the pastoral industry, with the drovers watering their stock as they pushed further across the outback (Box 2: Our outback oases – groundwater dependent ecosystems). The waters of the GAB are stored under natural pressure. Across much of the basin you can dig a bore and the water will come to the surface without the need for a pump. Such bores are called artesian bores. Troubled waters Hundreds of bores have been sunk into the GAB since the first in 1878 near Bourke in New South Wales. By 1915, there were 1500 bores and a peak flow of 2000 megalitres a day. Over the decades as more and more bores were sunk, water pressure and flow rates dropped across much of the GAB. Much of the water that is extracted is wasted. It is estimated that up to 80 per cent of the total outflow from the GAB is wasted because of inefficient water delivery systems. Thousands of kilometres of open drains dug across properties to water animals lose water to evaporation and seepage. Bore owners, as well as State and Australian Governments have undertaken the Great Artesian Basin Sustainability Initiative to counter waste and help restore pressure throughout the basin.
The GAB plan – capping the bores The Great Artesian Basin Consultative Council released a 15-year strategic management plan to cap bores so there is no further decrease in pressure and to reduce wastage. Part of the plan involves rehabilitating 880 bores and replacing 34,000 kilometres of bore drains with poly piping and troughs. In another attempt to maintain pressure in the basin, in 2005 the Queensland Government declared a moratorium on the issuing of new licences to extract water from most GAB aquifers. Sustainable use of groundwater or water mining?
Groundwater already plays a big part in irrigating many of Australia's crops, and water managers have plans for future domestic schemes to tap into groundwater supplies. In most areas, human use is currently in excess of the sustainable yield (Box 3: Research into sustainable groundwater use). Getting the balance right The sustainable yield of a groundwater source depends on balancing the use or discharge against recharge rates. Normally discharge of groundwater occurs through vegetation, into streams and lakes, or through evaporation into the atmosphere. Sustainable yield cannot simply be determined by a measure of the recharge rate. If water is extracted for human use at the recharge rate, discharge to other areas can be affected. 'Drought-proofing' urban areas Groundwater is also being used to provide more flexibility in water planning, particularly in times of drought. In New South Wales, for instance, a controversial desalination plant has been put on hold, and instead two aquifers to the west and south of Sydney are being investigated as potential sources of water for Sydney. The plan is to provide 30 gigalitres of water a year from the aquifers for several years during drought, and then allow the aquifers to replenish. However, the proposed scheme has some difficulties. Extraction of water from the Hawkesbury sandstone is proving a problem due to low flow rates. One estimate suggests that Sydney’s aquifers can supply about 10 gigalitres a year of the 630 gigalitres a year consumed by Sydneysiders. Repeat use of the aquifers depends on how quickly they are replenished. In the Sydney Basin, the apparent (uncorrected) age of the water can be thousands of years old. Corrections need to be applied to get a true measure of the age of the water, due to the presence of siderite on the water. Extraction of groundwater can also lead to salinity problems and have a negative impact on native vegetation with roots that tap into groundwater, as well as wetlands, rivers and streams. The full impact of using these aquifers as planned is not known, but is likely to reduce the rate of water flowing to support rivers and wetlands and other groundwater dependent ecosystems. In Western Australia, there is a plan to draw 45 gigalitres a year from the Yarragadee aquifer in the State's south-west. The aquifer is a large source of good quality groundwater, but it will only be developed as a source if proven to be sustainable. Changing land use in the area of Gnangara Mound north of Perth – which provides up to 60 per cent of Perth's water supplies – is also being investigated in an attempt to conserve water and increase recharge rates to the aquifer. Pollution problems Some residents of Sydney have another alarming groundwater to deal with: pollution. In August 2006, thousands of Sydney residents in several suburbs were banned from using groundwater bores due to industrial contamination of the Botany Sands aquifer. The residents can't use bore water for garden use, swimming pools or even washing their cars due to the presence of contaminants from eight industrial sites. For the residents involved, the precautionary groundwater ban is a very down-to-earth reminder of the importance of the water beneath our feet. Boxes 1. Using science to measure and manage groundwater 2. Our outback oases – groundwater dependent ecosystems 3. Research into sustainable groundwater use Related Nova topics: Salinity – awakening the monster from the deep
Box 1: Using science to measure and manage groundwaterWorld wide, groundwater is a huge source of water, with some estimates saying underground freshwater supplies total as much as eight million cubic kilometres – or 97 per cent of all freshwater (not frozen) found on the planet. In a dry country such as Australia, the challenge is to understand how groundwater systems and groundwater dependent ecosystems operate, how big they are, and how best to manage them in a sustainable and innovative way. It's not always easy: the science can be complicated, and there can be differing theories and unknown variables. The general view is that aquifers in Australia are topped up by rainfall, with the water slowly percolating through the aquifers and rock structures. In the case of the Great Artesian Basin, it's commonly believed that it is an open system which is fed by the rains falling on the eastern boundary of the GAB, along the western slopes of the Great Dividing Range. Dating of groundwater Radioactive isotopes such as tritium, carbon-14 and chlorine-36 can be used to date groundwater by estimating the time it has been in the aquifer. One study involving chlorine-36 dated water in the GAB to be 1.5 million years old, possibly some of the oldest flowing water on the planet. Isotope testing indicates the oldest water is in the centre of the basin, and the youngest waters come from the eastern side of the basin. Other types of tests identify the waters of the GAB as originating from rainwater. Using chlorine-36 dating, researchers discovered that there are some shallow aquifers in arid areas that appear to have recharged entirely during wetter periods in Australia's geological history. Because they are not currently being recharged, the use of such groundwater sources depletes the aquifer. This has important implications for communities who rely on old groundwater sources, including allowing sufficient time for infrequent, very large storms to recharge these aquifers. More recently, Australian researchers have used the isotope S35 to date groundwater. The shorter half-life of S35 – 87 days – means that it can be used to measure recent aquifer recharge, and to compare current recharge rates from, for example, heavy versus light rainfall events. Groundwater and surface water are connected There is a growing awareness of the interconnections between groundwater and surface water resources. Other isotopes can be used to measure evaporation and the extent of mixing of river waters and groundwater. This can be helpful in determining what's called 'conjunctive water management' – basically developing integrated water management plans which combine groundwater and above ground supplies in modelling and planning. The individual characteristics of each aquifer, determined by the rainfall, evaporation, river flow, rock types, vegetation cover, extraction and recharge rates can all impact on the sustainability of aquifer use. Because of these variables, extraction of water from each aquifer should be considered on a case-by-case basis. With increasing knowledge about groundwater systems, sustainable yields are being revised. With changing rainfall patterns being experienced across Australia due to global warming, re-evaluation of existing information is required. For example, a 10 per cent decrease in rainfall due to climate change does not simply mean a 10 percent decrease in surface runoff or aquifer recharge. In times of drought much of the water wets the parched soil, providing little runoff or recharge. Related sites:
Box 2: Our outback oases – groundwater dependent ecosystemsThe Great Artesian Basin is not just important for people to survive in the outback. The natural surface or mound springs of the GAB support many distinctive communities of plants and animals. Mound springs are places where the groundwater has naturally flowed to the surface, with a small mound or hill created due to the build-up of sediments or salts from evaporating water. They vary from a few centimetres to 100 metres in diameter. These springs have been dubbed the 'oases of the outback' and there are hundreds stretched across the Basin, mainly in the south-west. The mound springs support a variety of plants, aquatic invertebrates and fish – some of which occur nowhere else in the world – that are in danger of becoming extinct because water flows are declining as the pressure in the GAB falls due to over-extraction. Mound springs support a variety of grasses, such as the salt-tolerant samphire and button grass, reeds, green algae and Cyanobacteria. They are also home to more than 40 species of freshwater snails found nowhere else, some of which are only found in a single spring. Because the springs are on pastoral land, the tiny animals are in danger of being trampled by stock that drink from the spring. It's probable that some species have already been driven to extinction. Many springs have dried up over the past century due to pastoral bores being drilled and over-extraction of water. Of the springs that remain, it's estimated that some now flow at only 10 to 30 per cent of their former discharge rate. Apart from these unique species, the mound springs are also an important habitat and source of water for birds and land animals which have few alternative water sources in such arid landscapes. While some native – and introduced – species benefit from introduced bores in arid areas, others adapted to the dry conditions are decreasing in number. Related sites:
Box 3: Research into sustainable groundwater use The aim of groundwater management is to ensure that there is water for all who need it, that the resource is not exhausted, and that the local environment is protected. The Centre for Groundwater Studies has a series of projects underway looking at these issues. Although groundwater provides the drinking water supply for many towns across Australia, there is no single definition of what is sustainable yield, with most being guided by recharge rates. The sustainable use of groundwater resources depends on measuring the balance between the current rate of extraction and the rate of recharge. Recharge rates depend on a number of variables such as the origin of the water, the site of recharge and rainfall. Also of interest is the question of how the recharge rate will be affected by altered rainfall patterns due to climate change. At present major groundwater resources in Australia such as the Great Artesian Basin and the Murray-Darling Basin, are not being used sustainably, because the rate at which water is extracted is greater than the rate of recharge. If an aquifer is from an ancient sea or lake, a so-called formation aquifer, then the water can only be withdrawn once, leaving a depleted aquifer. The same applies to aquifers that were charged during much wetter times in Australia's geological past. While water in these aquifers can be used, it cannot be sustained because they are not being recharged. In addition to measuring recharge rates, water researchers also need to keep an eye on water quality issues – such as pollution from industrial discharges or seawater discharging into an aquifer – and monitoring and licensing of users to assist in assigning water allocations and entitlements. Prize-wining Australian research Australian researchers are leading the way in developing better ways of managing groundwater resources. In 2001, researchers from the CSIRO Land and Water and South Australia's Department of Water Resources won the UNESCO Great Man-Made River International Water Prize for their work on managing groundwater in arid areas. Since 1993, the group has been researching better ways of utilising groundwater, such as topping up aquifers with recycled stormwater or wastewater for storage and improving its quality so it can be used for irrigation. Called aquifer storage and recovery, or water banking, the technology has since been adopted elsewhere in Australia and overseas. Similar projects are now underway in other states, including Western Australia, which is working with CSIRO researchers on a managed aquifer recharge project in Perth and Mandurah which tops up aquifers with treated wastewater for either irrigation or possible use in Perth's water supply. Related sites:
Activities
Further readingAustralasian Science April 2007, pages 32-34 Groundwater dreaming (by Brad Moggridge) Explores the management of groundwater by the Australian Aborigines.
November–December 2006, page 10 Sponge offers arsenic solution Reports on a method to remove arsenic from groundwater using iron-coated sponges.
June 2006, pages 39-41 Groundwater isn't a get out of jail free card (by Derek Eamus) Argues that plans to extract groundwater to 'drought proof' Sydney will have widespread ecological and economic consequences.
March 2006, pages 38-41 Stormwater pollution: Is it damaging urban waterways? (by Michael Barry) Suggests that stormwater run-off from roads could be damaging urban waterways.
August 2005, pages 22-24 New life for urban streams (by Chris Walsh) Looks at engineering approaches to stormwater drainage and how they may benefit urban streams.
Cosmos June 2006, pages 66-73 Unquenchable (by Sara Philips) Looks at the 'water crisis' across Australia.
Ecos No. 137, 2007, pages 28-30 A call for tougher groundwater management (by Max Berry) Looks at the need for strong policy action for groundwater management.
No. 134, 2007 page 34 Seaweed trial promises inland aquaculture (by Max Berry) Looks at the use of saline groundwater to grow seaweed.
No. 130, 2006, page 15 Rain gardens buffer Melbourne's waterways Reports on research on 'rain gardens' that filter stormwater before it is collected for re-use.
No. 117, 2003, page 35 Enticing mat cleans up – fast (by Steve Davidson) Describes a polymer-mat system which can be used to remove fertilisers, pesticides, industrial waste and other pollutants from groundwater.
No. 110, 2002, pages 28-30 Water alchemy (by Steve Davidson) Discusses the use of aquifers to store and recover urban stormwater and treated sewage effluent.
No. 107, 2001, pages 12-15 Taking water out of range (by Steve Davidson) Looks at the benefits and problems for native plants and animals caused by the availability of water from bores.
No. 106, 2001, pages 28-31 Bubble, bubble... (by Wendy Pyper and Steve Davidson) Discusses the threats of acid sulphate soils and soil acidification in Australia as a result of rising groundwater.
New Scientist 17 January 2008, page 24 ‘Pac-man’ molecule chews up uranium contamination (by Paul Marks) Investigates a molecule which could clean up groundwater contaminated with uranium.
5 August 2006, page 23 Electro-map spies salty aquifers Looks at the use of electric currents passing through the Earth to map salt contamination in groundwater supplies.
1 July 2006, pages 30-31 Water, water everywhere, but not a drop to drink (by Julie Rehmeyer) Looks at the use of desalination of seawater to provide freshwater.
12 May 2006, page 5 Tsunami still pollutes Sri Lankan wells Reports that the drinking water in Sri Lanka is still contaminated with seawater, long after the tsunami.
17 December 2005, page 5 Bangladesh's arsenic woes are here to stay Suggests that the arsenic in the wells of Bangladesh will be topped-up every rainy season.
6 August 2005, pages 28-33 Life underground, down under (by Stephanie Pain) Reveals the creatures that live in underground water in the Australian outback.
16 April 2005, page 9 Cities may be abandoned as salt water invades (by Fred Pearce) Describes the threat to the groundwater supplies of major cities by rising sea levels due to global warming.
5 March 2005, page 26 Gold cure for heavy industry's hangover (by Kurt Kleiner) Reports on a cheap method to clean up a persistent pollutant in groundwater.
18 December 2004, page 17 Bug 'batteries' send out pollution alert (by Anna Gosline) Bacterial films growing in polluted aquifers generate signals that can be used to pinpoint the source of pollution.
28 August 2004 Asian farmers sucking the continent dry (by Fred Pearce) Warns of the potentially disastrous consequences of farmers using electric pumps to draw ever more water from underground sources.
13 March 2004, page 16 World's oldest fresh water flows beneath the Sahara's sands Reports that the aquifer under the Sahara contains water between 200,000 and 1 million years old.
PhysicsWeb 29 October 2004 Optical trap dates Egyptian water Describes a method to date samples of water up to 1 million years old using isotopes of krypton.
Scientific American 9 November 2006 Rust could be the key to arsenic-free water Reports on a method to remove arsenic from groundwater using nanoparticles and magnets.
August 2004, pages 70-75 Arsenic crisis in Bangladesh (by A Mushtaque and R Chowdhury) Discusses strategies being tested in Bangladesh to prevent arsenic poisoning from contaminated groundwater supplies.
Velocity December 2005 Search for water goes underground Reports on the use of nuclear techniques to investigate groundwater trapped beneath the Sydney basin.
Useful sitesGroundwater resources (Natural Resource Management, Murray-Darling Basin Commission, Australia)
Describes the different types of aquifers, as well as groundwater in the Murray-Darling Basin, the Great Artesian Basin, and the Dumaresq river valley. Also supplies some definitions of terms and estimates of groundwater resources.
South Australian Department of Land Water and Biodiversity Conservation
Water access entitlements, allocations and trading, 2004-05 (Australian Bureau of Statistics)
Provides tables of each state and territory's surface and groundwater entitlement volumes.
Australian Government Department of the Environment and Water Resources
Water Recycling in Australia – 2004 (Australian Academy of Technological Sciences and Engineering)
Comprehensive analysis of water use in Australia. The summary highlights suggested areas for change.
Groundwater – our hidden treasure (CSIRO, Australia)
Provides some facts and figures about groundwater and a case study on groundwater use in South Australia.
Australian Broadcasting Corporation
Geothermal resources of the Great Artesian Basin, Australia (Geo-Heat Center, Oregon Institute of Technology, USA)
Provides an overview of the Great Artesian Basin as a geothermal resource.
Award-winning solar powered desalination unit aims to solve central Australian water problems (University of Wollongong, Australia)
Describes a solar powered desalination unit for use in remote areas of Australia.
Solar-powered reverse osmosis desalination (Remote Area Developments Group, Murdoch University, Australia)
Describes a solar-powered reverse osmosis desalination unit for remote areas.
Desalination of brackish water with wind-powered reverse osmosis (University of Hawaii, USA)
Describes a research project investigating the feasibility of using wind energy to power the desalination of brackish water.
Glossaryaquifer. A layer of rock or sand that contains water. For more information see Aquifers (Tasmanian Department of Primary Industries and Water, Australia). desalination. The removal of salts from water or soil. For more information see Desalination (Ask an Expert, Australian Broadcasting Corporation). ecosystem. A term used to encompass all the organisms in a community together with the associated physical environmental factors with which they interact (eg, a rockpool ecosystem, a forest ecosystem). gigalitre. A gigalitre is one thousand million (1,000,000,000 or 109) litres. groundwater dependent ecosystem (GDE). Ecosystems that require a supply of groundwater to maintain their current structure (special composition) and function (for example, rates of carbon fixation). Some GDEs need a continual supply of groundwater, others require intermittent supply. half-life. The time it takes for half the atoms in a sample of radioactive material to break down into a non-radioactive element. Half-lives vary significantly, from a few days for some elements to millions of years for others. Half-life measurement is important when considering the long-term storage or disposal of radioactive waste. invertebrates. Usually defined as animals without backbones, invertebrates make up the vast majority of all animal species. Only fish, amphibians, reptiles, birds and mammals are not invertebrates. Insects, spiders, worms, slaters and many marine creatures such as corals, sponges and jellyfish are examples of invertebrates. isotope. One of the different kinds of an atom of the same element. All atoms of an element have the same chemical properties, but the different isotopes have different weights. The different weights are because the isotopes have a different number of neutrons. For more information, see Isotopes (Carlton Comprehensive High School, Canada) megalitre. A megalitre is one million (1,000,000 or 106) litres. recharge or discharge. The recharge rate is the rate at which an aquifer is replenished or topped up with water (inflow). The other important variable for groundwater management is the discharge rate, or the rate at which water is taken out of the system (outflow). In some cases aquifers can discharge naturally to rivers and springs and so the water is not being removed from the system. The two variables determine the water balance, which is part of the larger water cycle involving the journey of water as it falls from the sky, onto land or sea or aquifer, and back again. siderite. Natural iron(II) carbonate, FeCO3.
External sites are not endorsed by the Australian Academy of Science. Posted February 2007. The Australian Foundation for Science is also a supporter of Nova. This topic is sponsored by the Australian Research Council Linkage Learned Academies Special Project Grant.
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