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
The key findings in relation to water resources are as follows.
Surface water use has traditionally been high and continues to increase. At the same time, scientific knowledge about sustainable yields has improved, placing limits on the availability of surface water for consumptive use. The current estimates of water use relative to sustainable yield indicate that approximately one-quarter of Australia's river basins are either close to sustainable yields or are being over-used. These river basins account for around 70% of total surface water use. It is clear from this assessment that any growth in water use in these basins must be serviced either from other river basins or from other sources of water such as groundwater, improvements in water-use efficiency, or re-use of wastewater. In river basins where sustainable yields have already been exceeded, other regulatory and/or economic mechanisms may need to be triggered. These include embargoes on further extraction and structural readjustment.
In response to pressures on the availability of surface water resources, a number of reforms have progressively been introduced as part of the National Water Reform Framework. These reforms include changes to legislation, water industry structure, water policy, water trading, water pricing and the increasing incorporation of environmental flow provisions into water resources planning. States and territories have progressed well in implementing these reforms, with the exception of environmental flows. Environmental flow provisions have been developed or are being developed in many river basins, but as yet have largely not been implemented. Only 13% of Australia's river basins had a formal environmental flow allocation in place as of June 2000 (NLWRA 2001). Caps on water diversion have been put in place in a number of river basins in the interim until adequate environmental flows are established. Groundwater reforms are lagging behind surface water reforms.
Groundwater available for allocation has reduced substantially in the last decade, and is now over-used and over-allocated in many Groundwater Management Units (GMUs). Use has increased not only because of increasing demand on groundwater, but also because of caps placed on the extraction of surface water resources. Unsustainable use of groundwater has significant impacts on both users and the environment, including:
- reduced water levels which can leave bores dry and impact on dependent ecosystems
- inducing seawater intrusion which results in reduction in beneficial use of groundwater
- land subsidence due to compaction of aquitards that have dried up due to pumping
- reduced access to water, not only for current users but also future users, due to substantially reduced groundwater levels.
The primary difference in accounting for water resources in the current SoE Report is the inclusion of updated figures on water use and water availability for the year 1996/97, which were extracted from data compiled as part of the National Land and Water Resources Audit. Importantly, these latest data include consideration of sustainable yields. Prior to this, the most recent figures on water use and water availability at the river basin scale were for the year 1983/84, which formed the basis of the assessment of surface water availability in Australia: State of the Environment 1996 (State of the Environment Advisory Council 1996). Yields from this report were only available as divertible yields and did not take into account any environmental considerations.
Mean annual water use in Australia has increased by 65% from 14 600 GL to 24 100 GL. Most of this change was attributable to a 70% increase over the same period in average annual irrigation water use from 10 200 GL to 17 400 GL. Mean annual surface water use was estimated to have increased by 59% from 12 000 GL in 1983/84 to 19 100 GL in 1996/97.
The current estimated volume of nationwide mean run-off (392 000 GL/yr) is essentially the same as the 1983/84 estimate. However, where available, estimates of sustainable yield are considerably lower than 1983/84 estimates of divertible yield. For instance, in the Timor Sea Drainage Division, the current annual sustainable yield is approximately 10 000 GL compared with a divertible yield in 1983/84 of 22 000 GL.
Groundwater extraction has increased considerably over the last two decades. Australia: State of the Environment 1996 (State of the Environment Advisory Council 1996) did not discuss groundwater in detail and hence no comparison can be made. However, a comparison of the status of groundwater from the AWRC review (1987) and recent NLWRA assessments (NLWRA 2001b) has been made. Nationally groundwater extraction has increased by 90% from 2634 GL in 1983/84 to 5000 GL in 1996/97. This increase in use has occurred predominantly in discrete areas, which are now encapsulated within GMUs.
From a state and territory perspective the changes in groundwater use are as follows:
- Western Australia, New South Wales and Victoria increased their use of groundwater by over 200% between 1983/84 and 1996/97.
- In Western Australia, groundwater use increased by nearly 800 GL/year, and in New South Wales by 690 GL/year between 1983/84 and 1996/97.
Groundwater issues in 1996 were similar to 2000. The difference is that groundwater is now beginning to be managed at more discrete spatial scales through the GMUs, and that many policy and management initiatives are being developed or implemented at national and state levels.
Emerging issues in relation to surface water quantity include:
- Current estimates of sustainable yield are based on methods adopted by each state or territory. These methods vary widely, and the absence of a consistent method for estimating sustainable yield for surface waters makes it difficult to directly compare yield estimates across state borders. It also brings into question the validity of sustainable yield estimates when alternative assessment methods potentially produce different results.
- Surface water use is close to or exceeds estimates of sustainable yields in 26% of river basins across Australia. If surface water extraction is to be sustainable into the future, then it will need to be reduced, alternative sources found, or efficiencies in usage implemented in order to meet demands.
- There is evidence of a climatic shift that has reduced inflows in south-west Western Australia. Sustainable yields in this catchment have been adjusted accordingly. The enhanced greenhouse effect may result in lower average rainfalls across much of Australia and produce a corresponding decrease in river flows. In general, and in the context of climate change, the adjustment of sustainable yields may require a similar adjustment in allocation if environmental flows are to remain unchanged. This will be particularly important in river basins with water use close to or exceeding current estimates of sustainable yield.
- Water use and losses from farm dams have not been incorporated into current water-use estimates. A number of studies are emerging which more accurately quantify the hydrologic effects of farm dams and will form the technical basis for water resources planning on this issue.
- The hydrologic effects of farm forestry and tree clearing on sustainable yields are an emerging issue, but are unlikely to be resolved before the next SoE reporting cycle in anything other than isolated case studies.
- Similarly, the effects of groundwater use on surface water baseflows are currently being investigated. Increased groundwater use has the potential to reduce sustainable surface water yields.
Although our understanding of groundwater has not changed significantly in recent years, the management of the resource is currently undergoing much change, and will continue to evolve as the use of groundwater management units increases and data are collated at local scales. Water scarcity means that the pressures on groundwater will continue to increase over time. To ensure sustainable practices, water resources will have to be used more efficiently in the future. An important issue that needs urgent attention is how to reduce allocations and use to sustainable levels.
- New policy and management initiatives are required to manage the resource. Several policies have recently been developed on the issue of over-allocated and over-used systems. The solutions have considerable socioeconomic impacts. Each GMU will need to identify the most appropriate way to either 'buy back' or redistribute water resources within its area to ensure sustainability and fairness. Trading of water licences will play a part in ensuring that this occurs, although most states are still grappling with the issues and solutions are yet to emerge.
- Environmental water requirements of groundwater-dependent ecosystems need to be determined. Currently there is considerable information available, but it has not been included in the management and resource allocation processes currently in place. In the future, groundwater-dependent ecosystems will play a significant role in resource development, and if allocations are not determined soon, these ecosystems will be affected by over-development of resources that are the lifeline of these ecosystems.
- Reliable information on groundwater use is required. Without accurate data it will not be possible to determine areas which are over-developed or nearing full development. A way of determining impacts on the environment will be through monitoring. Groundwater information is scarce in many GMUs, and the cost of groundwater investigations and data collation is high. Minimum groundwater monitoring standards are required for GMUs to ensure that consistency in reporting and assessment occurs nationally, and within each state.
- Funding for bore capping and maintenance programs is not sufficient and the implications of not undertaking these works include loss of resources, pollution due to corrosion and cross-contamination of aquifers
The main threats to sustainability are:
- the continuing over-extraction of water from many river systems, especially in the Murray-Darling Basin
- the absence of sound estimates of sustainable surface water yields and total water use in areas of rapidly increasing demand for water
- the ability to reduce water use or find alternative sources of water in the context of:
- climate change
- increasing farm dam development
- changes in land use cover.
The sustainability of groundwater resources relate to four main issues:
- groundwater use in excess of sustainable yields
- aquifer salinisation from rising water tables, aquifer leakage and recycling of salts (irrigation and groundwater pumping)
- rising water tables causing dryland salinisation
- seawater intrusion.