Inland Waters Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Jonas Ball, Sinclair Knight Merz Pty Limited, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06750 7
Water resources (continued)
This section reports on the following environmental indicators, which are defined in Fairweather and Napier (1998):
|IW 1.1||Depth to water table|
|IW 1.2||Groundwater salinity|
|IW 1.3||Bore capping|
|IW 1.4||Estimated resources of groundwater/basin|
|IW 1.5||Net amount abstracted/discharged|
|IW 1.6||People, stock and crops supported|
Groundwater can be found beneath most land in Australia; however, its quality and yield are extremely variable. In areas with viable resources, groundwater is used for urban water supply and as a key source of water for agricultural production. Use of groundwater has grown considerably in the last 50 years due to improvements in pump, drilling and materials technology and because many surface water resources are already over-allocated. As use has grown, so too has the need for management of groundwater.
For the purposes of this report, the definition of groundwater is 'water in the ground in a persistently saturated state'. A hydraulically connected group of saturated soils and rocks are referred to as an aquifer. Throughout Australia the number of aquifers in any one area varies. In most areas there are many aquifers overlying each other, separated by aquitards. These aquitards create a barrier to water flowing from one aquifer to the other, or at least restrict the hydraulic connection between the two aquifers. Aquifers have historically been split into two categories:
- porous (sands, silts, gravels, sandstones etc.)
- fractured rock aquifers (basalts, shales, granites etc.)
Porous aquifers in Australia are commonly developed for groundwater supply as they generally have a higher yield that makes extraction more economical. The quality of groundwater can be an impediment to development in some areas, with naturally occurring salts in the aquifer causing high salinity. Some states and territories assume that this water will not be developed and hence do not include it in their groundwater resource estimates. In fact, saline water can be used for industrial, mining, and agricultural purposes when 'shandied' with less saline water.
The states and territories determine sustainable yield volumes. In some instances they take into account leakage between aquifers and/or environmental water provisions for groundwater-dependent ecosystems. However, overall environmental water provisions have not been made for many groundwater-dependent ecosystems.
Over-extraction, and particularly over-extraction of surface aquifers, can have significant impacts on groundwater-dependent ecosystems such as wetlands, rivers and caves. Groundwater inflow provides the majority of the baseflow of many rivers, streams, wetlands and lakes and any reduction of inflow due to over-extraction is likely to threaten the health of dependent ecosystems. Groundwater-dependent ecosystems are further discussed in Aquatic ecosystems later in this report.
Historically, groundwater and surface water have been managed as separate resources, despite the often complex and intrinsic links between the two systems. Groundwater has also been viewed on a province 1 scale, such as the Great Artesian Basin, Gippsland Basin and Perth Basin, although, it has frequently been 'managed' at the scale of individual bores or by jurisdictional boundaries.
More recently, smaller groundwater management units (GMUs) have been used to manage high-value resources. Groundwater management units are defined by state governments and are based on areas where groundwater has a low salinity and high use or where groundwater is used in environmentally sensitive areas. Eighty seven per cent of total groundwater use occurs in the GMUs and 47% of the total sustainable yield of groundwater resources in Australia is contained within the GMUs (NLWRA 2001a). GMUs are defined by the following characteristics:
- a GMU includes one aquifer, unless multiple aquifers are hydraulically connected
- a GMU may lie below, or above, many other GMUs
- a GMU does not cross state boundaries, since groundwater management is undertaken by the states
- a GMU does not cross a province boundary.
Cooperative management arrangements are required across state borders to manage groundwater resources that are split by state boundaries and different management practices. The Great Artesian Basin (GAB) is an example where four states manage the resource.
There are 442 GMUs in Australia, of which a small percentage can be seen in Figure 4 as many GMUs overlay each other. Although Figure 4 is a poor representation of the GMUs in Australia it does indicate the development of groundwater across Australia, with two peculiarities. In Western Australia all of the state is included in GMUs due to the legal regime of groundwater management. The Great Artesian Basin is also treated as a series of GMUs. For this reason, the GMU map as shown in Figure 4 appears distorted, indicating a greater proportion of Australia managed on a GMU basis than in fact occurs. Areas outside of GMUs are referred to as 'unincorporated areas' (UAs).
Figure 4: Groundwater management units in Australia.
Source: National Land and Water Resources Audit 2001.
Information on groundwater is generally collected at a state and territory level, and is now being collated more commonly on a GMU or province level. The province scale has been used where information is available. There are 61 provinces in Australia, covering vast expanses of the continent such as the Great Artesian Basin, down to smaller areas such as the Eyre Peninsula in South Australia and the Leeuwin Province on the south-western tip of Western Australia (see Figure 5).
1. A province is an area having a broad uniformity of hydrogeological and geological conditions identified as either predominantly sedimentary or fractured rock; areas previously defined by the Australian Water Resources Council in the 1980s.