Bill McCormick, Science, Technology, Environment and Resources
Australia’s climate and landscape, coupled with the demands of agriculture and a growing urban population, can make water supply a difficult matter. Northern Australia has significant water resources but these are not easy to capture and store.
In terms of rainfall, Australia is the driest inhabited continent, and the amount of rainwater that enters rivers is also very low. On average, only 12% of rainfall flows into rivers in Australia, compared to 39% for Europe and 52% for North America. In addition, our rainfall is often highly variable: ‘droughts and flooding rains’ is an apt description of the natural condition in much of the continent.
Water is a limited resource in most of the country, and a vital economic asset. In 2010–11, total water consumption was 13,337 Gigalitres (GL) of which agriculture used 54%, households 13%, manufacturing 5%, and mining 4%: 3% of total water used was recycled.
Under section 100 of the Constitution the Commonwealth cannot interfere with the right of states to make ‘reasonable use’ of river waters for irrigation purposes. The Commonwealth’s attempts to solve the problems associated with water use in the Murray-Darling Basin (MDB) have been affected by this fact. (See Murray-Darling brief.) Much of the Commonwealth’s involvement in water matters has occurred through financial assistance to the states.
Water supply and demand
The growth of urban centres puts pressure on existing water supplies both directly (more homes) and indirectly (more food consumption and industrial use). The major source for cities is surface water (that is, rivers, lakes or accumulated rainwater).
In order to combat the problem of our naturally variable rainfall, water storage dams in Australia are designed to store far more water than is the case for similar population demands in Europe. Many of the best dam sites are already utilised and future storage options are therefore limited.
Climate change is increasing the existing variability of rainfall and reducing the average rainfall in some areas. For example, there has been a long-term decline in rainfall in south-west Western Australia since the 1970s. Water utilities across the nation are looking at ways to save and to increase supply.
An option for increasing regular water supply even during droughts is seawater desalination, although this applies mainly to coastal settlements. Desalination plants remove salts and other dissolved substances from seawater, brackish water or waste water. The usual technology used in the desalination process is reverse osmosis (RO), which allows water to pass through a membrane, leaving behind salts and other impurities. Seawater desalination plants reduce reliance on rainfall but can be expensive compared to water conservation or recycling. Significant electrical power is required to drive the RO process.
During the recent drought, severe water restrictions were put into effect and several water authorities started construction of desalination plants. However, once the drought ended, water storages were replenished, thereby reducing the need for supplies from the RO plants. Some plants have subsequently closed.
Dams and northern development
Over the past hundred years there have been many calls to develop the substantial water resources in northern Australia. Several schemes were proposed to channel water from tropical Australia to supply farms and cities in drier areas, but the benefits were considered inadequate for the great economic and environmental cost.
The Bradfield Scheme, first discussed in 1936, proposed to divert rivers from coastal north Queensland westwards for use in the dry interior. Schemes to pipe water from the Kimberley to Perth were also proposed in the 1980s and 2000s.
In 2009, the Northern Australia Land and Water Taskforce reported on the potential for further water development in the north of the country. It found that the development of groundwater resources provides the best prospect. Unlike the MDB, most rain in the tropics falls near the coast (not in the river’s headwaters) and this therefore limits the potential for new dams. The few streams in northern Australia that maintain flow through the dry season do so through groundwater discharge to the stream.
The rainfall in northern Australia is equivalent to eight and a half times the annual runoff in the MDB, but only 20% enters the rivers and streams, and 15% recharges groundwater resources. The rest ultimately evaporates. The report concluded that, despite the huge volumes of water in the wet season, ‘the north can be described as being water limited’. This is because there may be little or no rain during the dry season; rainfall is highly variable between years; it mostly occurs near the coasts and on floodplains making it hard to capture; and the very high rates of evaporation require very large and deep storages.
The Coalition’s Dams and Water Management Taskforce identified some opportunities for new or enhanced surface water storages in northern Australia. Its 2013 election policy for developing northern Australia proposes a White Paper that will consider establishing a Water Project Development Fund to support the advancement of water infrastructure proposals across northern Australia, including dams and groundwater projects.
Depletion and pollution of aquifers
Groundwater is important for many remote settlements and properties in Australia, but is not a major source of water supply for the bulk of the population. However, it can be a significant source in some areas, for example in Perth. It may also be used to replace surface water during drought or when restrictions are placed on use of surface water.
There was a significant shift to groundwater extraction in the MDB when the cap on surface water use came into effect in the late 1990s. As a result, the Basin Plan will implement further caps, referred to as sustainable diversion limits (SDLs) on groundwater as well as surface water extraction. However, unlike the situation with surface water, only three out of the Basin’s 81 groundwater resource units are over-allocated; 34 of the resources units are under-allocated. A potential concern with groundwater use is that we have less immediate knowledge of how quickly the water is replenished and how sustainable its use is compared with that of surface water.
Sections of the community have concerns about the impacts of coal mining and coal seam gas (CSG) production on the quantity and quality of water in aquifers that are used for domestic and agricultural purposes. This is part of the reason that New South Wales has placed restrictions on CSG exploration in agricultural areas and is carrying out a review of CSG-related activities. The Commonwealth now requires assessment of the impact of coal mining and CSG proposals on aquifers.
State of the Environment 2011 Committee, Australia state of the environment 2011: an independent report presented to the Australian Government Minister for Sustainability, Environment, Water, Population and Communities, Department of Sustainability, Environment, Water, Population and Communities, Canberra, 2011.
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