National Water Commission

The Murray-Darling Basin is Australia’s largest river system covering about 20% of the continent. The Murray-Darling Basin extends approximately 1450 kilometres from north to south and 750 kilometres from east to west covering a total area of 1,086,853 km2.

In addition to the River Murray and the Darling River, the Murray-Darling Basin consists of a number of smaller but important rivers including the Murrumbidgee River, Lachlan River, Goulburn River, Campaspe River and the Namoi River.

Since the arrival of Europeans, flow volumes and regimes in the Murray-Darling Basin have become a highly altered, resulting in a number of problems such as overuse of water resources and salinity.

The Murray-Darling Basin provides 41% of Australia’s gross value of agricultural production. Crops include dryland crops such as cattle, sheep and wheat as well as irrigated agriculture such as rice, cotton dairy and horticulture. Total agricultural value exceeds $10 billion of which $3 billion is derived from irrigation. Water use is high in the basin with 9,979,000 ML of water used in 2004-05 primarily for irrigated agriculture.

The Murray-Darling Basin interjurisdictional area is managed by four states Queensland, Victoria, South Australia and New South Wales. In addition, the basin is also administered by the Murray-Darling Basin Commission.

The major control on the development of water resources in the Murray-Darling Basin is known as the Cap. The Cap was imposed in 1995 following a review of water use and water equity in the basin. For New South Wales and Victoria, the cap is defined as “The volume of water that would have been diverted under 1993/94 levels of development.” In South Australia, the Cap is set at “…the level that enables the development of its existing high security entitlements … and is equal to the long term average of 90% of the amount of very high security licences that existed in 1993/94.” For Queensland, a moratorium on further development was set from September 2000, while the ACT is yet to enter the Cap.

The Living Murray Initiative was established in 2002 by the Murray-Darling Basin Ministerial Council. The program will invest $500 million from 2004-05 to improve the health of the River Murray by returning 500 GL/yr of water to the system. In particular, the program is focussed on improving the environmental outcomes of six icon sites:

• Barmah Millewa Forest
• Gunbower Koondrook-Perricoota Forest
• Hattah Lakes
• Chowilla Floodplain
• Lower Lakes, Cooring and Murray Mouth
• River Murray Channel

 


Figure 1 Murray-Darling Basin interjurisdictional area locality map

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Murray-Darling Basin interjurisdictional area locality map (2.2 Meg)

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Because of the size of the Murray-Darling Basin, it is not appropriate to make a blanket description of rainfall patterns. The Murray-Darling Basin Commission Water Audit Monitoring Report (2006) states:

“Average rainfall was observed throughout most of the Basin in 2004-05. … Above average rainfall was recorded in a large area in north east NSW and the border regions between NSW and Queensland encompassing several towns e.g. Gunnedah, Narrabri, Mungindi and Hebel, in the irrigation areas of NSW and Victoria on the either side of the River Murray downstream of Albury, and along the Murray river corridor downstream of Morgan covering some of the irrigation areas of SA and its major off-takes for town water supply.

Below average rainfall was recorded in a very large area in NSW and Qld in the western part of the Basin, in two large areas in central NSW around the Yellow Mountain and south west NSW including the north west Victorian town of Mildura and in some isolated pockets in central and western NSW. Very much below average rainfall was recorded in the western part of the Basin in NSW and Qld in the catchments of the Warrego and Paroo rivers.”

Figure 2 illustrates the total rainfall and Figure 3 illustrates the percentage of mean annual rainfall for July 2004 – June 2005.




Figure 2 Total rainfall for July 2004 – June 2005 (Source: BOM, 2006)




Figure 3 Percentage of mean annual rainfall for July 2004 – June 2005 (Source: BOM, 2006)

Table 1 Opening and closing volume of dams in excess of 1000 GL. (Source: MDBC, 2006)

Dam Name	Opening Volume (GL)	Closing Volume (GL)	Change (GL)
Blowering Reservoir	88	286	+198
Burrinjuck Reservoir	403	249	-159
Eildon Reservoir	677	940	+263
Burrendong Reservoir	147	182	+35
Wyangala Reservoir	108	86	-22
Menindee Lakes	332	330	-2
Dartmouth Reservoir	1889	1748	-141
Hume Reservoir	307	913	+606
Copeton Reservoir	340	324	-16
Total for all dams (including < 1000 GL capacity)	6720	7562	+842

Large volumes of water are transferred into the Murray-Darling Basin from the Snowy Mountains Scheme. In 2004-05, 481 GL was transferred to the River Murray and 81 GL was transferred to the Murrumbidgee River (MDBC, 2006).

The Murray-Darling Basin consists of 104 GMUs or parts of GMUs. Because of the large variety of aquifer types, depth and usage amounts, it is not appropriate to make any generalised statement on groundwater in the Murray-Darling Basin. Depending on location, some areas will have rising groundwater levels, while in other areas the levels are falling. A lack of groundwater monitoring within the Murray-Darling Basin creates makes it difficult to fully understand the level of the resource. However, we do know that with the introduction of the Murray-Darling Basin cap in 1993-94 and the decrease of surface water allocations due to drought, the volume of groundwater use is gradually increasing (Figure 4).

The River Murray is a highly regulated river system (for irrigation, water quality and navigation) that receives input from both natural runoff within the catchment and the Snowy Mountain Scheme (~2000 GL/yr). The representative hydrograph (Figure 5) was chosen as it is upstream of the large water storage dams and therefore more accurately represents natural inflow into the River Murray. The hydrograph shows both the episodic nature of rainfall in the Murray Darling Basin and also the historically low flows in the river since 2001.



Figure 4 Showing the gradual increase in groundwater use in the Murray-Darling Basin since the introduction of the Cap (Source: MDBC, 2006)

Table 2 Summary of Murray-Darling Basin contextual information

Figure 5 Streamflow hydrograph for the Murray-Darling Basin for the Murray River at Biggara (gauge 401012)




Figure 6 Streamflow hydrograph for the Murray-Darling Basin for the Murray River at Corowa (gauge 409002)

Summary of the total water resources in the basin

The total volumes of water available and supplied from water resources in the Murray-Darling Basin are shown in Table 3.

Table 3 Summary of water balance in the Murray-Darling Basin

 

Figure 6 Water balance summary diagram for the Murray-Darling Basin

Outcomes from the water cycle report

The following information becomes apparent from the water balance.

• Water use is well known due to the co-operation of the various regulating agencies.
• Considering the number of unknown data, the error in the water balance was low at -5%.
• Recharge, extractions and diversions, evapotranspiration and surface water losses estimates dominated the water balance. The BRS Water 2010 estimates for runoff were generally slightly high with accuracy greater than ±25% (Category B).
• Groundwater / surface water interactions were thought to be primarily the transfer of surface water to the groundwater resource.
• Groundwater recharge estimates were approximately 60% of the long term average recharge rate due to rainfall being about half of average rainfall during 2004-05.
• Water use was from both surface water and groundwater sources although the amount of surface water use was about 6 times higher than groundwater.
• Data could not be obtained for the following items in the water balance:
• Groundwater storage volumes (renewable and non-renewable)
• Soil - unsaturated zone storage volumes
• River channels storage volumes
• Seepage from streams to groundwater
• Groundwater use
• Groundwater discharge to ET

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Murray-Darling Basin – Interjurisdictional area water cycle report (100 kb)

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Summary of data availability and reliability

The data for the Murray-Darling Basin water balance is highly variable with the majority of the surface water information obtained from models and estimates. Groundwater information is poorly understood at every scale within the Murray-Darling Basin.

The data for this water balance was predominantly category A (see Table 4), indicating that the majority of the data was of a high standard. However, 61% of the fields had no information for them either due to them being not applicable (e.g. no snow so no snow pack value), or not available. The overall reliability for the catchment was estimated as ±71% (between a C and D rating).

Table 4 Summary of data reliability for the Murray-Darling Basin

Reliability category Number of items in category Volume in each category (ML) Percentage of total volume (%) A (+/- 10%) 16 21225229 48.61 B (+/- 25%) 5 16966000 38.85 C (+/- 50%) 5 4875000 11.16 D (+/- 100%) 2 600000 1.37 E (no data) 42 - - F (no data currently available) 0 - - Not applicable 2 - - Total 72 43666229 WMA reliability index ±71% Water balance error (%) -5%