Murray–Darling Basin
Physical information

General description

This section provides details about the Murray–Darling Basin (MDB) region, its water resources, land use, and water-related infrastructure.

General description

Area: 1,055,600 km2 (Australian Bureau of Agricultural and Resource Economics and Sciences 2010)

Population: 2,190,000 (Australian Bureau of Statistics 2012)

The MDB is defined by the catchment areas of the Murray and Darling rivers and their many tributaries. The MDB covers 75% of New South Wales, more than 50% of Victoria, significant portions of Queensland and South Australia, and all of the Australian Capital Territory (shown in figures P1 and P2). It contains:

  • around 440,000 km of rivers, of which 40,000 km are major
  • some 30,000 wetlands, covering an area of around 25,000 km²
  • about 60,000 km² of floodplain area, which represents approximately 6% of the MDB.
Figure P1 Location map of the MDB within Australia
Figure P1 Location map of the MDB within Australia

Source for the boundaries of the MDB: Australian Government Department of Sustainability, Environment, Water, Population and Communities.

As shown in Figure P2, major rivers in the MDB include:

  • Murray River, which forms the border of Victoria and New South Wales, and flows east to west for 2,510 km
  • Darling River, which begins in northern New South Wales and flows 2,740 km (including its major tributaries—the Culgoa, Balonne and Condamine rivers) southwest to its junction with the Murray River at Wentworth
  • Murrumbidgee River, which flows 1,485 km from southern New South Wales, through the Australian Capital Territory and then westwards to the Murray River
  • Lachlan River, which starts in the central highlands of New South Wales and flows 1,339 km southwest to the Murrumbidgee River
  • Goulburn River, which flows 654 km from central northern Victoria northwards into the Murray River (Geoscience Australia 2010).

The MDB is a complex, interconnected river system rather than a series of separate catchments; however, its diverse climate and landscape and the presence of artificial structures means not all parts of the system are connected to the same extent. For example, rivers such as the Paroo, Lachlan, and Wimmera only rarely contribute flows further downstream.

Figure P2 Contextual map of the MDB showing the major rivers
Figure P2 Contextual map of the MDB showing the major rivers

Sources: Australian Government Department of Sustainability, Environment, Water, Population and Communities, and Geoscience Australia (2010).

Scope of the MDB region water account

The MDB is defined in Section 18A of the Australian Government Water Act 2007 (the Act). It includes all water resources within or beneath the MDB, but does not include groundwater that forms part of the Great Artesian Basin (GAB).

For the 2013 Account, the MDB region (see Figure P2) is defined as all the surface water connected to the channel network and all the groundwater (excluding any water in the GAB) located within the geographical boundaries of the MDB specified by the Act, except:

  • the areas drained by the Snowy Mountains Hydroelectric Scheme storages that are located inside the legal MDB's boundaries
  • the towns of Port Elliot and Middleton in South Australia.

Further, the following elements are not included in the MDB region water account:

  • off-channel water storages, such as landscape catchment storages (also known as farm dams) used to harvest runoff and floodwaters (these constitute water abstracted before it reaches the rivers or water owned by the users)
  • urban water systems at utility level, irrigation systems and private water supply systems.

The MDB region presents a varied landscape, from semi-arid ephemeral river systems in the north to highly regulated river systems in the south fed from the Australian Alps. To the east and south, the highlands of the Great Dividing Range form the limit of the MDB region, while in the north, west, and southwest the boundaries are much less distinct. The greater proportion of the MDB region is made up of extensive plains and low undulating areas; most of them are less than 200 m above sea level.

Geographical representation of the MDB region in the 2013 Account

The 2013 Account information is provided for the whole MDB region and in two segments: Northern Basin and the Southern Basin (see Figure P3). Boundaries for the Northern Basin and Southern Basin are largely determined by the physical geography of the Murray–Darling Basin, previous water management boundaries, and the level of hydrological connectivity. The hydrological boundary between the Northern Basin and the Southern Basin is located where the Darling River meets the upstream end of the Menindee Lakes.

The Northern Basin typically has less rainfall, less regulation, less development, and less water use than the Southern Basin. Furthermore, water management is characterised in the Northern Basin by a different rules framework, fewer water storages, and highly variable hydrological connectivity when compared with water management in the Southern Basin.

The region is divided into 20 surface water planning areas and 22 groundwater planning areas (both numbers include six combined surface water and groundwater water resource plan areas) to provide information in the 2013 Account. Detailed information has been provided where data are available at sustainable diversion limit areas. Details of water planning areas and sustainable diversion limit areas are included under Surface water and Groundwater.

Land use

Major towns and cities within the region

The major population centres of the MDB region and their population (as at 28 March 2013) include:

  • Canberra–Queanbeyan: 391,645

  • Albury–Wodonga: 82,083

  • Bathurst: 31,294

  • Dubbo: 32,327

  • Orange: 34,992

  • Tamworth: 36,131

  • Wagga Wagga: 46,913

  • Bendigo: 82,794

  • Mildura–Buronga: 33,432

  • Shepparton: 42,741

  • Toowoomba: 96,567 (Australian Bureau of Statistics 2013).

Note: The numbers are related to urban centre / locality.

There are also a number of smaller urban centres throughout the MDB region such as Griffith, Echuca, Moree, Horsham, Wangaratta, Warwick, and Murray Bridge.

Land use activities

The MDB is one of the most productive food and fibre regions in Australia. It contains approximately 40% of all Australian farms (by number), which produce wool, cotton, wheat, sheep, cattle, dairy products, rice, oilseeds, wine, fruit, and vegetables for domestic and overseas markets (Murray–Darling Basin Authority 2011).

The major land use activities in the MDB region are shown in Table P1. Figure P3 shows the distribution of these land uses within the region. Land use activities that are major water users in the MDB region are urban supply and irrigated agriculture.


Table P1  Major land use activities in the MDB region

Land use activity

Area (km2)

Total area of the region (%)

conservation and natural environments

107,600

10

dryland agriculture

133,300

13

forestry

34,000

3

grazing

727,800

69

irrigated agriculture

24,700

2

mining

300

<1

other intensive uses

1,200

<1

urban

14,300

1

water

12,400

1

Total

1,055,600

 

Source: Australian Bureau of Agricultural and Resource Economics and Sciences (2010)

 

Figure P3 Map of land use in the MDB region
Figure P3 Map of land use in the MDB region


Source: Australian Bureau of Agricultural and Resource Economics and Sciences (2010); source for boundaries of the MDB region: Australian Government Department of Sustainability, Environment, Water, Population and Communities.

 

Significant aquatic ecosystems

The MDB region contains 16 Ramsar-listed wetlands (Department of Sustainability, Environment, Water, Population and Communities 2010) of international importance:

  • Banrock Station wetland complex (South Australia)
  • Barmah Forest (Victoria)
  • Coorong and Lakes Alexandrina and Albert (South Australia)
  • Currawinya Lakes National Park (Queensland)
  • Fivebough and Tuckerbil swamps (New South Wales)
  • Ginini Flats (Australian Capital Territory)
  • Gunbower Forest (Victoria)
  • Gwydir Wetlands (New South Wales)
  • Hattah–Kulkyne Lakes (Victoria)
  • Kerang Lakes (Victoria)
  • Lake Albacutya (Victoria)
  • Macquarie Marshes Nature Reserve (New South Wales)
  • Narran Lake Nature Reserve (New South Wales)
  • New South Wales Central Murray State forests
  • Paroo River wetlands (New South Wales)
  • Riverland (South Australia).

The MDB region also contains nationally important wetlands, listed in the Directory of Important Wetlands in Australia (Department of Sustainability, Environment, Water, Population and Communities 2011).

Significant Indigenous cultural places and practices

The Murray–Darling river system has been of extreme importance to Aboriginal people and their history in the Basin extends over at least 45,000 years to the present day. There are at least 10,000 known Aboriginal sites in the Basin, indicating the deep physical, economic, and spiritual dependence of Aboriginal people on the Basin's rivers, creeks, lakes, and wetlands and other resources. The rivers and flood plains are of particular importance to the traditional cultural beliefs and practices of Aboriginal Nations. Today there are over 40 Aboriginal Nations in the  Murray–Darling Basin (Murray–Darling Basin Authority 2014 c).

Archaeological evidence can be found including such things as; shell middens, quarries, rock shelters with archaeological deposits (e.g., stone artefacts), open camp sites, rock paintings and engravings, axe grinding rocks with their grooves, burial grounds, and the sacred and ceremonial sites. The sites are dated from a range of ages:

  • 9,000–13,000 years old: The Kow Swamp burial site in northern Victoria
  • At least 20,000 years old: Excavations indicating Aboriginal presence at Keniff Cave, at the headwaters of the Darling
  • Around 40,000 years old: Evidence of Aboriginal populations from Lake Mungo and other lakes of the Willandra system
  • Of more recent origin are the many carved and scarred trees from which bark canoes, shields, boomerangs and carrying dishes were cut. These trees can be found along most of the Basin's waterways

Aboriginal people view themselves as an integral part of the land and river systems and feel a strong responsibility for the health of rivers and wetlands.The rivers have always been of great importance to the Aboriginal people, especially as sources of food. As an example, the fish traps of the Ngemba in the Barwon River at Brewarrina illustrate how the river serves as a critical source of food. Brewarrina is well known for the 40,000 year old aboriginal fishtraps which are located just below the weir in the Brewarrina Township. These traps are constructed from carefully placed rocks in a circular arrangement and are still used today.

Water resources

The water resources in the MDB region are highly developed, as illustrated by the following statistics:

  • As a long-term average 42% of the total surface water runoff to the MDB region is diverted for consumption or environmental management, while 58% currently remains in the environment (Murray–Darling Basin Authority 2013b).
  • The majority of the surface water consumed in the MDB region, 10.9 million ML/year, is diverted from the watercourse and used for irrigation and urban supply (the 2013 Account reports diversion of 10.7 million ML). In addition 2.7 million ML/year is intercepted by local catchment storages and forestry plantations that intercept runoff before it reaches the watercourse (Murray–Darling Basin Authority 2011).

Around 1.8 million ML of groundwater is consumed each year from the MDB region's water resources (Murray–Darling Basin Authority 2014d); however, due to abundance of surface water resources, the consumption has been below this volume during recent years. The majority of groundwater use is centred on a small number of large alluvial aquifers in New South Wales, Queensland, Victoria, and South Australia where the groundwater is used for agricultural purposes. Elsewhere there are areas in the Basin where groundwater is the only reliable source of water for stock and domestic uses.

A Murray–Darling Basin Cap (the Cap) was established in 1995 to limit the volume of surface water that could be diverted in the MDB region in any year to that based on the 1993–1994 levels of development (Murray–Darling Basin Authority 2012h). The Cap does not place a restriction on groundwater extraction; however, the Basin Plan 2012 (Murray–Darling Basin Authority 2013b) assessed sustainable diversion limits for both groundwater and surface water within the MDB region. See Operating rules and constraints within the 'Water rights' section for further information on the Cap.

Surface water

The southern part of the MDB region is mostly a regulated system with major storages in many rivers. The storages in the three major southern rivers—the Murrumbidgee, Murray, and Goulburn—are used to provide regulated flows downstream as far as the lower lakes in South Australia.

Although there are major storages in the rivers including Border, Gwydir, Namoi and Macquarie, the northern part of the MDB region consists mostly of unregulated systems. Many of the rivers and streams in the northern MDB region are ephemeral and fed by seasonal rainfall. Generally, water users in much of the northern MDB region rely on collecting water during floods and storing it on-farm for later use.

The 2013 Account presents information on the surface water volumes for the 20 water resource planning areas for the MDB region as shown in Figure P4 (Murray–Darling Basin Authority 2011). Table 2 lists both water resource planning areas and sustainable diversion limit areas.

 


P4 Map of Murray–Darling Basin surface water resource plan areas
P4 Map of Murray–Darling Basin surface water resource plan areas

Source: Murray–Darling Basin Authority

 

Table P2  Surface water resource planning areas and sustainable diversion limit areas in the 2013 Account for the MDB region
Segment

Jurisdiction

Water resource plan area

Sustainable diversion limit area

River system

Code

Name

Code

Name

Southern Basin ACT SW1 ACT (surface water) SS1 ACT (surface water) Murrumbidgee ACT
Vic. SW2 Victorian Murray SS2 Victorian Murray  Victorian Murray 
SS3 Kiewa Kiewa
Vic. SW3 Northern Victoria SS4 Ovens  Ovens 
SS5 Broken  Broken 
SS6 Goulburn Goulburn
SS7 Campaspe  Campaspe 
SS8 Loddon Loddon
Vic. SW4 Wimmera–Mallee (surface water) SS9 Wimmera–Mallee (surface water)  Wimmera–Mallee 
SA SW5 South Australian Murray Region* SS10 SA Non-Prescribed Areas  SA Non-Prescribed Areas 
SA SW6 South Australian River Murray  SS11 SA Murray SA Murray
SA SW7 Eastern Mount Lofty Ranges* SS12 Marne–Saunders  Marne–Saunders 
SS13 Eastern Mount Lofty Ranges Eastern Mount Lofty Ranges
NSW SW 8 NSW Murray and Lower Darling SS14 NSW Murray NSW Murray
SS18 Lower Darling Lower Darling
NSW SW9 Murrumbidgee  SS15 Murrumbidgee  NSW Murrumbidgee  NSW
NSW SW10 Lachlan SS16 Lachlan  Lachlan 
Northern Basin NSW SW11 Macquarie–Castlereagh SS20 Macquarie–Castlereagh  Macquarie–Castlereagh 
NSW SW12 Barwon–Darling Watercourse SS19 Barwon–Darling Watercourse  Barwon–Darling 
NSW SW13 NSW Intersecting Streams SS17 NSW Intersecting Streams Paroo, Warrego, Culgoa, Bokhara, Narran, and Moonie
NSW SW14 Namoi SS21 Namoi  Namoi 
NSW SW15 Gwydir SS22 Gwydir Gwydir
NSW SW16 NSW Border Rivers SS23 NSW Border Rivers  NSW Border Rivers 
Qld SW17 Queensland Border Rivers* SS24 Queensland Border Rivers  Queensland Border Rivers 
Qld SW18 Moonie* SS25 Moonie  Moonie 
Qld SW19 Condamine–Balonne* SS26 Condamine–Balonne  Condamine–Balonne 
Qld SW20 Warrego–Paroo–Nebine* SS27 Nebine  Nebine  
SS28 Warrego  Warrego 
SS29 Paroo Paroo 

 * Combined surface water and groundwater resource plan areas
Major storages

The total storage capacity (including dead storage) for the 54 major storages (excluding weirs not considered as storages) within the MDB region for which data are available for the 2013 Account is 23,193,359 ML. A full list of these storages and their individual total storage capacities can be found in line item 1.1 Storages.

Streamflow summary

The 2013 Account includes streamflow summary at the following gauging stations within the region:

  • River Murray at Doctors Point (Albury) (Station 409017)
  • Darling River at Bourke (Station 425003)
  • Ovens River at Peechelba (Station 403241).

The River Murray at Doctors Point (Albury) represents a regulated reach of the Murray downstream of major regulating storages (within the Southern Basin).

The Darling River at Bourke represents the unregulated Northern Basin.

The Ovens River at Peechelba represents a largely unregulated major river in the Southern Basin.

Figure P5 shows mean monthly rainfall and flow volumes for these three gauging stations. The locations of the gauging stations are shown in Figure P6.

 


Figure P5 Graph of mean monthly flows at selected gauging stations in the Murray, Darling and Ovens rivers; mean monthly rainfall for the region is also shown
Figure P5 Graph of mean monthly flows at selected gauging stations in the Murray, Darling and Ovens rivers; mean monthly rainfall for the region is also shown


Figure P6 Map of the streamflow gauging station locations used to develop flow charts
Figure P6 Map of the streamflow gauging station locations used to develop flow charts

 Sources: Bureau of Meteorology and Murray–Darling Basin Authority

 

Information on streamflow patterns, monthly flow volumes and variations for the flows at the stations are available in Streamflow in the 2013 Account 'Water overview' for MDB.

 

Water transfers

In a number of locations, water is transferred into or out of the region, as well as from one catchment to another within the region (see Figure P7). 

 

Figure P7 Map of water transfers into, out of, or between catchments within the MDB region
Figure P7 Map of water transfers into, out of, or between catchments within the MDB region

 Sources: Bureau of Meteorology and Murray–Darling Basin Authority

 

Major transfers into the MDB region are from:

  • the Snowy Mountains Hydro-Electric Scheme into the Murrumbidgee and Murray rivers (see line item 1.5 Inter-region claim on water for more details)

  • the Glenelg catchment to the Wimmera system

  • Perseverance, Cressbrook, and Wivenhoe reservoirs (through Cressbrook reservoir, which started in 2010) in the Brisbane valley to Toowoomba in the Condamine–Balonne region.

Major transfers out of the MDB region include diversion of water from:

  • the South Australian River Murray to supply metropolitan Adelaide and country towns

  • the Macquarie River water sources (Fish River scheme) to the Blue Mountains area in Sydney

  • the Goulburn River system via the north–south pipeline for distribution to Melbourne

  • water transfers from the Goulburn–Broken region to Ballarat (in the Barwon River basin) via the Goldfields superpipe since May 2008

  • water transfers from the Goulburn–Broken region (from Silver and Wallaby creeks, which are tributaries of the Goulburn River, not shown in Figure P7) to the Melbourne urban supply system.

Channels and pipelines in the river system of the Southern Basin allow water to be moved and traded from one catchment to another. For example, the Waranga Western Channel delivers water from the Goulburn River to the Campaspe, Loddon, and Wimmera–Avoca catchments.

Groundwater

The groundwater systems of the MDB region can be categorised into four distinct hydrogeological types:

  • the aquifers in sedimentary deposits of the Murray basin and the Great Artesian Basin (GAB) within the low topography landscapes (including the Lower Murrumbidgee and the South Australian Murray)
  • the shallow aquifers of the Darling River basin overlying the GAB ( including the Lower Namoi and Gwydir)
  • valley-fill alluvium (including the Mid-Murrumbidgee, Upper Namoi and Upper Lachlan) in the highlands bordering the region
  • the local fractured rock aquifers of the Great Dividing Range and other areas where the basement rock outcrops.

While the Great Artesian Basin is a major groundwater resource under the Basin, its management is not included in the Basin Plan 2012.

The boundaries of the groundwater systems do not coincide with those of the Murray–Darling Basin, which is defined on the basis of its surface water resources. The different groundwater systems behave somewhat independently of each other, with only relatively small volumes of groundwater directly flowing from one system to another; however, water from different aquifer systems is transferred across boundaries as surface water base flow.Through this process, a substantial volume of groundwater enters the surface streams in the upper and middle catchments as base flow and then re-enters the groundwater systems further down through seepage from stream beds (Murray–Darling Basin Commission 1998).

In the 2013 Account, groundwater information has been reported where data is available at the data collection stage for the 22 groundwater resource planning areas (Murray–Darling Basin Authority 2013b). Detailed information has been provided where data is available at the level of sustainable diversion limit areas. It is likely that any subsequent changes to groundwater information in the water resource planning areas after data collection occurred are not included in the 2013 Account. Figure P8 and tables P3 and P4 include details of groundwater water resource planning areas and sustainable diversion limit areas.

  


Figure P8 Map of groundwater resource plan areas within the Murray–Darling Basin
Figure P8 Map of groundwater resource plan areas within the Murray–Darling Basin

Source: Murray–Darling Basin Authority


Table P3  Groundwater resource planning areas and sustainable diversion limit areas in the Northern Basin of the MDB region for the 2013 Account

Jurisdiction

Water resource plan area

Segment of the MDB region

Sustainable diversion limit area

Code

Name

Code

Name

NSW GW7 Darling Alluvium1  Northern Basin GS42 Upper Darling Alluvium
NSW GW11 Lachlan and South Western Fractured Rock2  Northern Basin GS19 Kanmantoo Fold Belt
GS20 Lachlan Fold Belt
NSW GW12 Macquarie–Castlereagh Alluvium  Northern Basin GS11 Bell Valley Alluvium
GS14 Castlereagh Alluvium
GS15 Collaburragundry–Talbragar Alluvium
GS16 Cudgegong Alluvium
GS26 Lower Macquarie Alluvium
GS45 Upper Macquarie Alluvium
NSW GW13 New South Wales Great Artesian Basin Shallow Northern Basin GS34 NSW Great Artesian Basin Surat Shallow
GS35 NSW Great Artesian Basin Warrego Shallow
GS36 NSW Great Artesian Basin Central Shallow
NSW GW14 Namoi Alluvium  Northern Basin GS29 Lower Namoi Alluvium
GS30 Manilla Alluvium
GS40 Peel Valley Alluvium
GS47 Upper Namoi Alluvium
GS48 Upper Namoi Tributary Alluvium
NSW GW15 Gwydir Alluvium Northern Basin GS24 Lower Gwydir Alluvium
GS43 Upper Gwydir Alluvium
NSW GW16 Eastern Porous Rock  Northern Basin GS17 Gunnedah-Oxley Basin
GS41 Sydney Basin
NSW GW17 New England Fractured Rock and Northern Basalts  Northern Basin GS18 Inverell Basalt
GS22 Liverpool Ranges Basalt
GS37 New England Fold Belt 
GS49 Warrumbungle Basalt
NSW GW18 New South Wales Border Rivers Alluvium  Northern Basin GS32 NSW Border Rivers Alluvium
GS33 NSW Border Rivers Tributary Alluvium
Qld GW19 Queensland Border Rivers3  Northern Basin GS54 Queensland Border Rivers Alluvium
GS55 Queensland Border Rivers Fractured Rock
GS57 Sediments above the Great Artesian Basin: Border Rivers
Qld GW20 Moonie4 Northern Basin GS59 Sediments above the Great Artesian Basin: Moonie
GS62 St George Alluvium: Moonie
Qld GW21 Condamine–Balonne5  Northern Basin GS53 Condamine Fractured Rock
GS56 Queensland MDB: deep
GS58 Sediments above the Great Artesian Basin: Condamine–Balonne
GS61 St George Alluvium (deep and shallow)
GS64 Upper Condamine Alluvium (Central Condamine Alluvium and  tributaries)
GS65 Upper Condamine Basalts
Qld GW22 Warrego–Paroo–Nebine6  Northern Basin GS60 Sediments above the Great Artesian Basin: Warrego–Paroo–Nebine
GS63 St George Alluvium: Warrego–Paroo–Nebine
GS66 Warrego Alluvium


1-2 Straddles in both the Northern Basin and the Southern Basin

3-6 Combined surface water and groundwater resource plan areas

 

Table P4  Groundwater resource planning areas and sustainable diversion limit areas in the Southern Basin of the MDB region for the 2013 Account

Jurisdiction

Water resource plan area

Segment of the MDB region

Sustainable diversion limit area

Code

Name

Code

Name

ACT GW1 Australian Capital Territory (groundwater)  Southern Basin GS52 Australian Capital Territory (groundwater) 
Vic. GW2 Goulburn–Murray  Southern Basin GS8 Goulburn–Murray (Shepparton Irrigation Region, sedimentary plain, highlands and deep)
Vic. GW3 Wimmera–Mallee (groundwater)  Southern Basin GS9 Wimmera–Mallee (sedimentary plain, highlands and deep)
SA GW4 South Australian Murray Region1  Southern Basin GS3 Mallee (pliocene sands, Murray limestone group and Renmark group)
GS5 Peake–Roby–Sherlock (confined and unconfined)
GS6 SA Murray
GS7 SA Murray salt interception schemes
SA GW5 Eastern Mount Lofty Ranges2  Southern Basin GS1 Angas Bremer (Quaternary sediments,and Murray limestone group)
GS2 Eastern Mount Lofty Ranges
GS4 Marne Saunders (Murray limestone group and Renmark group)
NSW GW6 Western Porous Rock  Southern Basin GS50 Western Porous Rock
NSW GW7 Darling Alluvium3  Southern Basin GS23 Lower Darling Alluvium
NSW GW8 Murray Alluvium  Southern Basin GS13 Billabong Creek Alluvium
GS27 Lower Murray Alluvium (deep[Renmark Group and Calivil formation]; and shallow[Shepparton formation])
GS46 Upper Murray Alluvium
GS38 Oaklands Basin
NSW GW9 Murrumbidgee Alluvium  Southern Basin GS21 Lake George Alluvium
GS28 Lower Murrumbidgee Alluvium (deep[Renmark Group and Calivil formation]; and shallow[Shepparton formation])
GS31 Mid-Murrumbidgee Alluvium
NSW GW10 Lachlan Alluvium  Southern Basin GS12 Belubula Alluvium
GS25 Lower Lachlan Alluvium
GS44 Upper Lachlan Alluvium
NSW GW11 Lachlan and South Western Fractured Rock4  Southern Basin GS10 Adelaide Fold Belt
GS20 Lachlan Fold Belt
GS39 Orange Basalt
GS51 Young Granite

1-2 Combined surface water and groundwater resource plan areas

3-4 Straddles in both the Northern Basin and the Southern Basin

 

The sedimentary aquifers within the region cover the main depositional areas of the Murray geological basin and the Darling River basin including upstream reaches of other major rivers such as the Murrumbidgee and Namoi rivers. The major aquifers within or at the margins of the Murray geological basin include the Shepparton, Calivil, Parilla-Loxton Sands, Murray limestone, and Renmark group aquifers, and the upland alluvium of the Cowra and Lachlan formations. The important alluvial sediments of the Darling River basin include the Gunnedah and Narrabri aquifers.

Sedimentary aquifers are the most important for groundwater extraction, with nearly all of the extracted groundwater (more than 95%) coming from these aquifers.  These groundwater aquifers have relatively high water holding capacity and hydraulic conductivity, and therefore are suited to extraction for use in irrigation and urban water supply. Most of the groundwater data used in the 2013 Account were for these aquifers. Groundwater quality is another significant consideration—water quality typically deteriorates down the groundwater flow path, constraining groundwater use to areas with acceptable water quality (primarily determined by low salinity).

The GAB is the largest groundwater basin in Australia. It underlies about one-third of the MDB (Figure P2) and extends beyond the MDB drainage basin boundary to the north and west. The GAB contains confined aquifers at depth, with confining layers that can be at or near the land surface.  The GAB provides vital water resources for domestic and town water supply, for stock use by the pastoral industry and water supplies for the operations of mining and petroleum industries and associated communities.

The GAB is recharged in small areas of the MDB (along the south-eastern edge of the GAB) where the aquifer layers are exposed at the land surface. The GAB is not considered to be part of the MDB water balance because the GAB aquifers are effectively hydraulically disconnected from near-surface systems in the MDB. Groundwater extraction and leakage from the GAB to the MDB are not represented in the 2013 Account, but may be represented in the future as an inter-basin transfer.

In the areas where the GAB confining layer is near or at the land surface, storage is limited to the near-surface soil zone and is lost from this zone almost entirely as evapotranspiration. Thus there is no need to evaluate change in groundwater storage in these areas to establish an annual regional water balance in the MDB. In the areas overlaying the GAB—where the confining layer does not outcrop—there are some shallow alluvial areas associated with drainage lines.

Fractured rock aquifers occur in the highland areas around the margins of the region (see Figure P8). In fractured rock aquifers, groundwater is stored in the fractures, joints, bedding planes and cavities of the rock mass and due to the difficulty of obtaining high yields from most fractured rocks, the volume of groundwater extracted from any one bore and in a given area is relatively low. In most fractured rock areas of the MDB, groundwater use is limited to stock and domestic supply. It is considered that the annual change in groundwater storage and annual groundwater flow out of fractured rock areas is much less significant to regional water balance. A groundwater balance in these areas is not explicitly estimated in the 2013 Account.

More details about the groundwater resources within the MDB region are available in the Groundwater note.

Other water resources and systems

Across the MDB region, many towns and urban centres abstract water and then return treated urban wastewater to the river for subsequent use downstream. For example, on the Murrumbidgee, average returns to surface water from Canberra are more than half of the Australian Capital Territory diversions from the river. Returns may also flow from irrigation channels and infrastructure back to the rivers. Line item 9.9 Discharge from urban water system includes information on urban return flows.