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)
Groundwater resources (continued)
Condition: Groundwater availability and sustainable yields
Sustainable yield definitions, methodologies and accuracy
The availability of groundwater is based on the sustainable yield of an aquifer or group of connected aquifers. By definition, the sustainable yield is the volume and/or rate of water that can be extracted from an aquifer without impacting on 'higher value use' of groundwater. Compromises are made between social, environmental and cultural values in the determination of groundwater sustainable yields. By monitoring groundwater use and groundwater levels, the sustainability of extraction can be assessed and the sustainable yield estimates re-calculated. There is still debate on how to estimate a sustainable yield, and state and territory organisations use different methodologies.
Current sustainable yield volumes in Australia
Sustainable yield estimates for each groundwater province are shown in Figure 6. Within the GMUs there are still considerable resources available for use. However, many resources are located in undeveloped remote areas or they are saline with a limited potential for use. Some states and territories assume that highly saline groundwater is not likely to be extracted and have not included these resources in their estimates of sustainable yield. As well, estimates for unincorporated areas include highly fractured rock aquifers that have low yields and may not be economically viable to develop. The volume of saline and potable groundwater resources in each state and territory is presented in Table 11.
Figure 6: Sustainable yield of groundwater provinces.
Source: National Land and Water Resources Audit 2001.
| State or territory | 0-500 mg/L TDSA Potable |
501-1500 mg/L TDSPotable |
1501-5000 mg/L TDSIrrigationB | 5001-14 000 mg/L TDS Saline |
>14 000 mg/L TDS Highly saline |
State sustainable yield total |
|---|---|---|---|---|---|---|
| Australian Capital Territory | 103 | NAC | NA | NA | NA | 103 |
| New South Wales | 554 | 4 468 | 1 276 | NA | NA | 6 297 |
| Northern Territory | 5 797 | 510 | 147 | NA | NA | 6 455 |
| Queensland | 1 423 | 1 041 | 154 | 22 | NA | 2 641 |
| South Australia | 0 | 998 | 157 | 25 | NA | 1 181 |
| Tasmania | 1 585 | 767 | 178 | NA | NA | 2 530 |
| Victoria | 412 | 528 | 542 | 22 | 2 152 | 3 657 |
| Western Australia | 513 | 2 312 | 2 266 | 0 | 1 212 | 6 303 |
| Australia | 10 388 | 10 626 | 4 721 | 70 | 3 364 | 29 169 |
A TDS = total dissolved salts.
B Generally requires shandying before use. Water generally unsuitable for irrigation then TDS >5000 mg/L.
C NA = not available as not estimated.
Source: NLWRA - Theme 1: Water Availability, and includes total sustainable yields from GMUs and UAs.
A summary of the groundwater sustainable yield statistics [IW Indicator 1.4] is that :
- 29 169 GL is estimated as the sustainable groundwater yield volume for Australia
- 47% of groundwater resources are in GMUs which, outside of Western Australia and the Great Artesian Basin, cover less than 10% of Australia
- 43% of the total sustainable yield in the GMUs is licensed to users (i.e. allocated)
- 27% of the total sustainable yield in the GMUs is actually used
- 21 013 GL, or 72% of sustainable yield, is suitable for drinking water supply (<1500 mg/L TDS)
- 25 735 GL, or 88% of sustainable yield, is suitable for irrigation (<5000 mg/L TDS).
Groundwater extraction in UAs is very low in all states except South Australia, where use in the UAs is greater than 30% of the sustainable yield. The biggest impact on the environment from groundwater use will be in the GMUs, which cover 10% of Australia and include 50% of the total sustainable yield.
Victoria and Queensland have the highest rate of groundwater extraction with about 64% of the sustainable yield in GMUs extracted. New South Wales and South Australia also show relatively high development status with use in GMUs over 35% of the sustainable yield extracted.
| State or territory | Groundwater use in GMUs | Percentage of sustainable yield used in GMUs | Groundwater use in UAs | Percentage of sustainable yield used in UAs | Total Groundwater use in state | Percentage of sustainable yield used in state |
|---|---|---|---|---|---|---|
| Australian Capital Territory | 5 | 4 | NAA | NA | 5 | 4 |
| New South Wales | 928 | 46 | 80 | 8 | 1008 | 16 |
| Northern Territory | 69 | 1 | 109 | 2 | 178 | 3 |
| Queensland | 1337 | 65 | 285 | 48 | 1622 | 61 |
| South Australia | 394 | 36 | 33 | 33 | 427 | 36 |
| Tasmania | 7 | 2 | 13 | 0.5 | 20 | 1 |
| Victoria | 512 | 64 | 110 | 3 | 622 | 17 |
| Western Australia | 1137 | 18 | 0.6 | 1 | 1138 | 18 |
| Australia | 3872 | 31 | 631 | 4 | 4503 | 15 |
A NA not available
Source: NLWRA 2000a.
The current development status of groundwater (equivalent to use divided by sustainable yield) in each province is shown in Figure 7. The high use areas of the Perth Basin, Great Artesian Basin and Murray Basin are over-developed (i.e. groundwater extraction exceeds the sustainable yield). Many other smaller GMUs are also over-developed. It must be noted that many sustainable yield estimates are based on technical assessments rather than measurable environmental stress. Many sustainable yield estimates do not include an environmental water allocation for groundwater-dependent ecosystems and only consider maintaining human uses.
Figure 7: Groundwater development status.
Source: National Land and Water Resources Audit 2001.
The Great Artesian Basin is the largest available groundwater resource in Australia and has a sustainable yield of less than 500 GL/yr. This is split across four states and 23 GMUs, and covers 11 main aquifers (GABCC 1998). The current rate of extraction from the Great Artesian Basin is 570 GL/yr, which is greater than the current sustainable yield estimate. It should be noted that the area referred to as the Great Artesian Basin covers only the 'artesian' aquifers in the province, with the shallower alluvial aquifers excluded. The total sustainable yield of the province (including the shallower aquifers) is 1657 GL/yr and the total province use is estimated at 588 GL/yr.
Throughout Australia much of the high quality groundwater has been developed or is in the process of being developed. Low yielding aquifers or more saline resources have not been fully developed. As such, groundwater salinity is an indicator of groundwater availability for human uses. However, groundwater, regardless of its salinity, will always be important in supplying water to groundwater-dependent ecosystems.
Messages about groundwater availability and sustainable yields
- Sustainable yields have been estimated for many GMUs; however, the methods used to estimate sustainable yields vary between states and territories and often do not include an environmental water allocation for dependent ecosystems.
- 72% of total sustainable yield is suitable for drinking water supply (<1500 mg/L TDS)
- Victoria and Queensland have the highest rate of groundwater extraction with 64% of the sustainable yield in GMUs extracted.
- Groundwater extractions are exceeding sustainable yields in the Great Artesian Basin, Murray Basin and some small basins in the eastern states.