Surface water and groundwater are stored in a number of ways to supply agriculture, industry and urban users. Some of these storages include:
- large dams (generally constructed by a government water authority or large industry)
- farm dams
- aquifer storage (use of an underground aquifer as a storage mechanism for water).
The most visible of these storages are large dams and farm dams. Data on the storage capacity of large dams has been sourced from the Water Account, Australia 2004–05, which assessed data from the Australian National Committee on Large Dams (ANCOLD). They define large dams as dams with a crest or wall height of greater than 15 metres, or as dams with a dam wall height of greater than 10 metres but meeting other size criteria as follows:
- having a crest more than 500 metres in length
- creating a reservoir capacity of no less than 1000 megalitres
- the ability to deal with a flood discharge of no less than 2000 cubic metres per second
- being of unusual design.
Location of large dams across Australia as registered by ANCOLD
Data on farm dams and minor storages are more difficult to source. In 2003, it was estimated farm dams that supply water for irrigation stored 3257 gigalitres. And the Australian Water Resources Assessment 2000 estimated that farm dams accounted for approximately 9 per cent of water stored in Australia.
Farm dams appear to be a significant interceptor of runoff. Investigations have shown that for every megalitre stored in farm dams, streamflow is reduced by 0.84 megalitres. Furthermore, estimates from Victoria suggest that up to 70 per cent of the stored water is lost to evaporation. Studies of the Murray-Darling Basin, suggest that 2200 gigalitres can be stored in hillslope farm dams, and that this reduces average annual streamflow by 1900 gigalitres. The increase in storage over the last ten years in the Murray-Darling Basin is estimated to have reduced streamflow by 450 gigalitres.
The total storage capacity of large dams across Australia in 2004–05 was 83,853 gigalitres. Large dam storage levels have steadily declined since 2001. They dropped from 44,164 gigalitres at 1 July 2004 to 39,959 gigalitres at 30 June 2005, because of reduced dam inflows and continued water extractions from these storages during the year. The greatest decline in storage levels between 2002 and 2005, in percentage terms, occurred in New South Wales (33 per cent) and Victoria (22 per cent), with an overall decline of 18 per cent across Australia.
In June 2005, the combined capacity of large dams with the highest storage levels, in percentage terms, was Western Australia (at 83 per cent) and Northern Territory (at 70 per cent). The states with lowest levels were New South Wales (at 33 per cent) and Victoria (at 39 per cent).
The map below shows the spatial distribution of water stored in large dams. It shows the higher water storage levels as a proportion of total storage capacity in the northern drainage divisions, with low storage levels in the Murray-Darling Basin and South West drainage divisions.
Large dam storage by jurisdiction in Australia for 2002 to 2005 summary table.
| Volume (GL)
| 2002 (GL)
| 2003 (GL)
| 2004 (GL)
| 2005 (GL)
| Volume (GL)
Data sourced from ABS Water Account, Australia 2004-05 and ANCOLD
*South Australia: large dam storages are maintained by transfers from the Murray River.
Water stored in large dams for each drainage division as at June 2005 (Sourced from Geoscience Australia and the Bureau of Rural Sciences)
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More detailed discussion of water storage is provided in the Water Availability Level 2 Report – National Perspective, available from the