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)
River systems and their catchments are the fundamental unit of management for surface waters. There are three recognised catchment scales in Australia: drainage divisions, regions and basins, of which there are 13, 77 and 245 in number, respectively (NLWRA 2001a). A map of drainage regions is presented in Figure 2.
Surface waters are the main source of water for human use in Australia. The volume of water extracted from surface waters for human uses in each drainage division is presented in Table 2 and in the four drainage divisions with the highest water use by drainage region in Table 3. Between 1985 and 1996/97, the volume of water extracted from surface waters for human uses increased by 59% (NLWRA 2001a). The increase in water use is likely to have been dampened in some areas by the introduction of water reforms and technological advancements. Eighty-three per cent of water extracted from surface waters was used for irrigation, rural stock or domestic supplies.
|Drainage division||1996/97 Total use(GL/yr)||1996/97 Percentage of water used for urban/industrial||1996/97 Percentage of water used for irrigation/rural|
|1 North-east Coast||2 144||35||65|
|2 South-east CoastA||1 784||74||26|
|4 Murray-DarlingA||11 149||5||95|
|5 South Australian Gulf||272||92||8|
|6 South-west Coast||362||49||51|
|7 Indian Ocean||12||83||17|
|8 Timor Sea||318||14||86|
|9 Gulf of Carpentaria||98||31||69|
|10 Lake Eyre||7||14||86|
|12 Western Plateau||14||93||7|
|13 Island Territories||NA||NA||NA|
A Does not include diversions from unregulated streams in New South Wales.
B Total of drainage divisions is based on state estimates of total water use and is not a summation of drainage division values, which are incomplete for New South Wales.
C NA not available.
Source: NLWRA 2000.
|Drainage division||Water region||1996/97 Total use(GL/yr)||1996/97 Percentage of water used for urban/industrial||1996/97 Percentage of water used for irrigation/rural|
|1 North-east Coast||1 Princess Charlotte Bay||3||33||67|
|5 Shoalwater Bay||52||23||77|
|6 Fitzroy (Qld)||289||27||73|
|11 Gold Coast||102||64||36|
|2 South-east Coast||1 Coffs HarbourA||<1||NAB||NA|
|3 Sydney||>477||probably >80||probably <20|
|9 Millicent Coast||3||100||0|
|4 Murray-Darling||1 Upper Murray||78||21||79|
|7 Menindee LakesA||147||22||78|
|8 Border RiversA||291||1||99|
|13 Lower Murray||470||3||97|
|99 Barwon Darling||192||0||100|
|6 South-west||1 Esperance||<1||NA||NA|
A Does not include diversions from unregulated streams in New South Wales.
B NA not available.
Source: NLWRA 2000a.
The highest water use is in the Murray-Darling drainage division, principally for irrigation. Water extraction is particularly high in the Goulburn-Lodden, Murrumbidgee and mid-Murray river systems. Diversions have been capped at 93/94 levels of development in Basin states, with the exception of Queensland which is in the process of implementing a cap on diversions. Water use is also relatively high along the east coast of Australia, primarily for drinking water supply in Brisbane, Sydney and Melbourne. In comparison, water use in northern and western Australia is relatively low as these areas are generally not suitable for irrigation and have low populations. Water use in the Timor Sea drainage division is currently increasing with the development of the Ord River irrigation scheme.
In the water use figures presented in Tables 2 and 3, water captured by off-stream farm dams for irrigation, stock watering and domestic use is not included. Regulation of farm dams varies between states (see Responses - management of surface water resources), but until recently, off-stream farm dams have not required licensing. As a result, the impact of off-stream farm dams has not been estimated at a state, territory or national level. Recent studies (e.g. ICAM/SKM 1999) have indicated that off-stream farm dams can have significant effects on streamflow such as increasing the length and frequency of periods of low or no flow in downstream streams. In some catchments in Victoria for example, unlicensed off-stream farm dams capture up to 15 times the volume of water extracted from rivers by licensed users (VFDIRC 2000). While this is an extreme example, the volume of water captured by off-stream farm dams in many agricultural catchments is likely to be significant. Further investigations are currently under way to assess these impacts on a regional scale.
Because of the highly seasonal nature of streamflows and the severity of droughts in Australia, a large number of major reservoirs have been built to ensure a reliable supply of water for human uses. The total number and volume of water of major storages in Australia are shown in Table 4. The storage capacity of major dams is greatest in Tasmania (drainage division 3) and includes Lake Gordon, which is the largest surface water storage in Australia with a capacity of 12 450 GL. Although Tasmania's water storage capacity is high, its consumptive use of water is low with most of the water being used for hydroelectric power generation.
|Drainage division||Area (km2)||Number of major storages||Average catchment area per storage
|Storage capacity (GL)||Storage capacity per unit catchment area (ML/km 2)|
|1 North-east Coast||451 000||173||2 606||16 728||37|
|2 South-east Coast||274 000||220||1 245||13 199||48|
|3 Tasmania||68 200||72||947||59 734||875|
|4 Murray-Darling||1 060 000||200||5 300||28 838||27|
|5 South Australian Gulf||82 300||23||3 578||304||4|
|6 South-west Coast||315 000||90||3 500||1 097||3|
|7 Indian Ocean||519 000||2||259 500||96||<1|
|8 Timor Sea||547 000||8||68 375||10 454||19|
|9 Gulf of Carpentaria||641 000||17||37 706||681||1|
|10 Lake Eyre||1 170 000||19||61 579||93||<1|
|11 Bulloo-Bancannia||101 000||NAC||NA||NA||NA|
|12 Western Plateau||2 450 000||1||2 450 000||<1||<1|
|13 Island Territories||717||NA||NA||NA||NA|
|Total||7 680 000||825||9 309||131 225||17|
A Storages typically above 1000 ML to 1500 ML, but the audit often reports on smaller dams.
B This is not the catchment area of the storages, but the average density of dams within the drainage division.
C NA not available.
Source: NLWRA 2000.
The number of major storages in a drainage division area is an indicator of significant barriers to the movement of fish and other species up and down river systems. It is also an indicator of the potential for cold water pollution from releases of cold water. These are further discussed in the Aquatic ecosystems section.
While figures were not readily available on the construction of major storages since 1990, the growth in total water storage has declined significantly since the mid-1980s. This is partly because the most economically efficient sites for water storage have already been developed and because attitudes have changed towards major storages and their potential effects on river flows and floodplain habitats.
- Between 1985 and 1996/97 the volume of water extracted from surface waters for human use has increased by 59% to 19 100 GL/year. Eighty-three per cent of water extracted was used for irrigation and agricultural purposes, while 17% was used for drinking water supply and by industry.
- The highest water use is in the Murray-Darling drainage division, particularly for irrigation in the Goulburn-Lodden, Murrumbidgee and mid-Murray catchments. Water extraction is also relatively high from the river systems providing drinking water for major cities on Australia's east coast. Water use in the Murray-Darling drainage division is not expected to increase significantly, as allocations are capped at the 1993/94 levels of water resource development.
- The volume of water captured by farm dams is likely to be significant, but it has not been estimated on a national or regional scale.
- Future increases in water use are likely to occur in the relatively undeveloped northern regions such as the Timor Sea.
Case study 1: The conflicts between water supply and Indigenous cultural heritage — Lake Victoria
Lake Victoria is located in south-western New South Wales immediately upstream of South Australia and is one of the four major water storages on the Murray-Darling River system. The Lake Victoria storage was constructed in the late 1920s by the Murray River Commission to provide a reliable water supply for the development of the Lower Murray region in South Australia and to mitigate flood peaks. It has a storage capacity of 680 GL of water and its strategic position in the Murray-Darling River system means the Murray-Darling Basin Commission (MDBC) can deliver between 3000 and 7000 ML of water a day to South Australia, in accordance with its water entitlements. Lake Victoria is also downstream of all the major tributaries to the Murray River and can store water originating from any of these tributaries. This enables the lake to store surplus water to be used for entitlement flows to South Australia, thereby securing water supply to irrigators in New South Wales and Victoria, particularly during drought.
The Lake Victoria region has significant Aboriginal and European cultural heritage values that are threatened by the operation of Lake Victoria as a water storage. Prior to European occupation, the Lake Victoria region was the traditional country of the Maraura, a subgroup of the Barkindji people. Radiocarbon dating of shell material and charcoal has revealed the Aboriginal association with the region can be traced back at least 5500 years. The lake and surrounding region contain relatively intact Aboriginal campsites with shell middens, fireplaces, stone artefacts and burial grounds. Initial archaeological investigations estimated that there were between 6000 and 16 000 burial sites in the major burial grounds. A reassessment of burial numbers indicates that there are likely to be fewer than 6000.
As the lake has been operated as a water storage with consistent water levels over long periods of time, many important Aboriginal sites have been submersed. Shoreline sites have also been affected by the long-term erosional and accretional activities of waves and wind.
In 1994, while the lake's water level was lowered to undertake maintenance on weirs and barrages, the MDBC undertook archaeological investigations of the normally submersed lands. These investigations confirmed and enhanced the high cultural significance of the lake and consequently the New South Wales National Parks and Wildlife Service required MDBC to prepare an environmental impact statement (EIS) on the operation of Lake Victoria as a water storage. The EIS concluded that Lake Victoria plays a key role in water supply, flood control and salinity mitigation especially for South Australia. It predicted that any modification to the operation of the Lake Victoria (i.e. lowering the operating water level or decommissioning) would result in a decrease in security of water supply to South Australia, increased inflow of saline groundwater into the Murray River and Lake Victoria, and increased flooding downstream.
Because of the water-sharing agreement between New South Wales, Victoria and South Australia, the reduction in capacity at Lake Victoria would result in a reduction of allocation for the entire Murray-Darling Basin. It was estimated that a lower storage level would cost Victoria and New South Wales on average $10 million every year and up to $90 million in a drought year. Decommissioning the storage completely would cost the two states on average of $25 million every year and up to $109 million in a drought year. The saline inflow of groundwater associated with any decommissioning of the dam would result in damage to the archaeological sites. The EIS also identified some engineering works that could be undertaken to protect cultural sites such as the construction of burial mounds that would reduce the impact of wind and water erosion. Approximately $2.5m of mitigation works have already been undertaken after consultation with Barkindji people.
The New South Wales National Parks and Wildlife Service determined that there was insufficient information in the EIS about the cultural heritage and environmental impacts associated with the operation of Lake Victoria at its full storage capacity and has only granted approval for operation of the lake at 60% storage capacity pending further investigations. They have also specified that all future management plans and committees are to include the Barkindji people.
Because of the key role of Lake Victoria for water supply and salinity mitigation, and its undeniably high cultural significance to the Barkindji people, a federal commissioner has been appointed to mediate and facilitate the process of preparing a final management plan.