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)

Pressures on groundwater resources

  • Groundwater use
  • People, stocks and crops supported by groundwater
  • Changing groundwater levels
  • Messages about pressures on groundwater resources
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    Groundwater use [IW Indicator 1.5]

    In some regions, groundwater provides for the majority of water needs, while other regions have no access to viable groundwater resources. Demand for groundwater is influenced by the quality of the resource, with some groundwater being of higher quality than surface waters and other resources unable to be used without treatment. Most of the groundwater extracted is used for irrigation, and the annual volume extracted for irrigation has doubled between 1985 and 1996/97. There is considerable variation in groundwater usage between states and territories (see Table 7). South Australia, New South Wales and Victoria use more than 60% of extracted groundwater for irrigation, while Western Australia uses 72% for urban and industrial purposes. Interestingly, Queensland uses a third of groundwater for rural stock and domestic uses. It must be noted that the accuracy of rural groundwater use in all states and territories is low, as most rural bores are not metered.

    Table 7: Groundwater use type proportions in Australia
    State Urban/industrialA (%) RuralB (%) IrrigationC (%)
    Australian Capital Territory 0 67 33
    New South Wales 16 20 64
    Northern Territory 38 25 37
    Queensland 17 33 50
    South Australia 5 10 85
    Tasmania 36 18 46
    Victoria 22 9 69
    Western Australia 72 3 25

    A Urban/industrial use includes: mine dewatering; salinity dewatering; fire fighting; national parks; agri-industries (e.g. dairy); commercial, along with urban and industrial uses.
    B Rural use is predominantly stock watering and some domestic use on rural properties.
    C Irrigation covers all irrigated areas such as irrigated pasture, horticulture, viticulture, and crops.

    Irrigation use varies from as little as 1.5 GL/year in the Australian Capital Territory to 643 GL/year in New South Wales. South Australia, Queensland, Western Australia, New South Wales and Victoria all use over 200 GL/year for irrigation. Despite Western Australia only using 25% of groundwater extracted for irrigation, the volume is still significant.

    The highest rates of groundwater extraction are from the Tasman Basin, the Great Artesian Basin and the Perth Basin. Rural enterprises and agriculture are the largest users in the Great Artesian Basin and Tasman Basin while drinking water supply and industrial use is dominant in the Perth Basin. It is generally smaller GMUs within the province that have the high use. The intensity of use in the Perth Basin is higher than in other provinces.

    Eight of the ten provinces with the highest groundwater use are in eastern Australia (see Table 8). As with the Perth and Great Artesian Basins, these provinces have highly developed GMUs (see Figure 4). In terms of economic return, water from the Basins underpins significant mining activity in New South Wales, Queensland and South Australia that could otherwise not proceed. Groundwater resources in eastern Australia are more developed than in the western regions, despite extensive resources in the Northern Territory and Western Australia. Fifty per cent of groundwater is used in small GMUs lying outside the Great Artesian Basin and Western Australia. This reflects the high demand for water in eastern Australia due to higher population and greater industrial and agricultural development.

    Table 8: Provinces with the highest groundwater use
    Province Province no. Groundwater use
    (GL/yr)
    Allocation(GL/yr) Sustainable yield
    (GL/yr)
    Tasman 3F 890 (1)A 433 (5) 1 979 (3)
    GABB 55S 825 (2) 835 (3) 731 (15)
    Perth 26S 744 (3) 744 (4) 1 869 (6)
    Lachlan 7F 619 (4) 1 678 (1) 2 026 (2)
    Murray 14S 480 (5) 1 080 (2) 1 969 (4)
    Otways 12S 217 (6) 368 (6) 1 816 (7)
    Gippsland 8S 186 (7) 204 (7) 628 (17)
    Clarence Moreton 4S 147 (8) 85 (11) 806 (13)
    Yilgarn - Gold Fields 29F 135 (9) 135 (9) 368 (20)
    Sydney 6S 86 (10) 169 (8) 1 315 (9)

    A Ranking of provinces by use, allocation and sustainable yield volumes.
    B The GAB Province includes unconfined alluvial aquifers, along with the Great Artesian Basin.

    Source: NLWRA 2001a.

    The term 'use' refers to the volume of water extracted from the aquifer, not the final volume of water used. Water losses may occur through leaks in bores and from evaporation or seepage from channels. In the Great Artesian Basin there are many unlined channels transporting extracted groundwater and it has been estimated that 90% of groundwater extracted is lost before it can be used (GABCC 1998).

    Groundwater use poses a significant threat to the sustainability of groundwater-dependent ecosystems and groundwater resources, along with possible impacts on surface water. The MDBC is currently assessing likely impacts of groundwater use and transferred demands from groundwater to surface water on the integrity of the cap. This will also have significant implications for groundwater-dependent ecosystems and with river baseflows in some areas.

    People, stocks and crops supported by groundwater [IW Indicator 1.6]

    The number of people and crops supported by groundwater is difficult to estimate as some people are only partly dependent on groundwater, with other water needs supplied from surface waters, dams and rain tanks. Similarly, groundwater used for irrigation is sometimes mixed with other water supplies to meet quantity or quality requirements.

    To estimate the number of people supported by groundwater a usage of 300 L/day/person was assumed. The area of irrigated crops supported was estimated by assuming a usage rate of 6 ML/ha/yr 1. Information on stock usage was not available and has not been estimated.

    ARMCANZ (1996) estimated two million people are supported by groundwater and the results in Table 9 are similar. This estimate excludes any remote rural areas that are wholly or partially dependent on groundwater. If it is assumed that 25% of the rural groundwater use was for domestic purposes, another two million people could rely on groundwater.

    Table 9: People and crops supported by groundwater
      Groundwater use
    (GL/yr)
    Number supported by groundwater
    Urban areas 245 2 236 000 people
    Rural areas 197A 1 795 000 people
    Crop irrigation 2 581 430 303 hectares

    A This is assuming 25% of rural use is for domestic purposes.

    Source: NLWRA 2001a

    In 1985, groundwater supplied 12% of the irrigation water requirements (1275 GL/year), which equates to an irrigated crop area of 212 084 hectares (AWRC 1987). Groundwater use has increased by 102% since then to 2581 GL/year, providing water for 430 000 hectares of irrigated crops.

    Changing groundwater levels [IW Indicator 1.1]

    Depth to a groundwater resource is an important factor in determining the feasibility of developing the resource. It does not, however, indicate the current status of the resource and any changes that may have occurred through development, climatic influences (especially drought) or other impacts. A more representative indicator is the trend in level or pressure in the aquifer. This variation over time can indicate whether the groundwater is responding to extractions, increased recharge from irrigation, and other impacts from land uses. It can also warn of other potential impacts such as loss of baseflow to rivers and land salinisation. Land and water salinisation from rising groundwater is further discussed in the Land Theme Report and in Water quality and pollutant sources.

    Groundwater levels fluctuate naturally with the seasons and in some aquifers fluctuate up to 15 m a year due to the high recharge rates or low storativity 2 of the aquifer. Levels are also influenced by extractions, and so falling groundwater levels can indicate where the resource is being over-used.

    Trends in level or pressure in an aquifer are determined from the analysis of monitoring data from the aquifer. This information has been collated for the NLWRA for each GMU and UA. In each GMU or UA, representative bores 3 were used to determine the aquifer trend. It should be noted that where only one or two monitoring bores were available, the trend analysis is not accurate. In some areas, conflicting trends have been measured due to extreme local effects. (Further information can be found at http://www.nlwra.gov.au/ )

    There are many possible causes of rising and falling groundwater levels (see Table 10). Many of the good quality groundwater aquifers in Australia are highly developed, with some having falling levels due to over-extraction. In other areas with falling levels, drought conditions over the last few years are to blame. Groundwater levels do not respond immediately to recharge, and so the effects of drought or over-extraction may occur years after the stress on the system. Monitoring and management of over-stressed systems is required on an ongoing basis.

    Table 10: Possible causes for and effects of rising or falling groundwater levels or pressure
      Falling levels or pressure Rising levels or pressure
    Possible causes Mine dewatering
    Salinity dewatering
    Groundwater extractions for irrigation or stock
    Reduced recharge due to drought conditions
    Seepage to rivers in low flow times (known as baseflow in rivers)
    Seepage from dams, ponds and other storages
    Land clearance
    Increased recharge from irrigation
    Increased recharge from high rainfall
    Recharge from rivers due to flooding or high flows
    Possible effects of change in level Loss of ease of access to resource by existing users
    Reduction in baseflow to rivers.
    Seawater intrusion in coastal aquifers
    Groundwater salinity increase
    Ecosystem impacts - insufficient water to sustain dependent
    Increased discharge to rivers
    Increased discharge to land, possibly causing land salinisation and/or waterlogging
    Ecosystem impacts - increase in inundation of dependent ecosystems and impacts from the discharge of saline groundwater.
    Messages about pressures on groundwater resources
    • Between 1985 and 1996/97 the annual volume of groundwater extracted has increased from 2600 GL/year to 5000 GL/year, with irrigation use doubling to 2581 GL/year.
    • In western and northern Australia, groundwater is predominantly used for drinking water and industrial uses. Up to 4 million people may rely on groundwater for drinking water.
    • Queensland, Western Australia and New South Wales extract the most groundwater. The Tasman Basin, Perth Basin and Great Artesian Basin have the highest rates of groundwater extraction.
    • Groundwater levels are changing (i.e. rising and falling) in many areas. Falling groundwater levels can be indicative of over-extraction and could result in a decrease in baseflow in rivers, streams and wetlands.

    1. Statistics from Review 85 indicate that a volume of 10 22 000 ML was used on an area of 1 700 000 hectares, giving an application rate of 6 ML/ha/yr over the different crop types.

    2. The ability of an aquifer to store water as a percentage of the volume of the aquifer which is commonly between 0.01 and 0.0001 for a confined aquifer, and around 0.1 for an unconfined aquifer.

    3. Bores which monitor aquifer levels or quality which are not influenced by local impacts, such as pumping from a nearby irrigation bore, and illustrate the regional impact of land use on the aquifer.