ANNUAL REPORT 2009–10

Agreed water shares delivered to states

Low water availability

As a result of near-average rainfall across the upper Murray region during the winter and spring of 2009–10, inflows to headwater storages and from the Ovens and Kiewa rivers were significantly higher than during the past four years. Good inflows were also received from the Darling River; however, inflows to the River Murray from other tributaries, including the Murrumbidgee and Goulburn rivers, remained extremely low.

Overall, inflows continued to be well below average, despite near-average rainfall over most of the Murray–Darling Basin in 2009–10 (see Figure 3.1). Inflows to the River Murray system, excluding releases from the Snowy Mountains Scheme, totalled about 5,600 gigalitres (GL) (a little over half of the long-term average). Such an inflow volume has been exceeded 77 years out of a 100 since records began, making 2009–10 inflows in the driest 23% (or driest quarter) of years on record.

Figure 3.1 River Murray system annual inflows from July 1891 to June 2010

While dry conditions continue, the focus of River Murray operations has been on water security. Flows along the River Murray have often been close to minimum requirements with as much water as possible being stored in Dartmouth and Hume reservoirs. 

The riverine environment along the Murray continues to decline; it is now 14 years since extensive overbank flooding occurred downstream of Echuca. 

In summary, the drought for many water users and the riverine environment, particularly in the southern Basin, is not over. Recovery from this severe period of water scarcity is expected to take multiple years of above-average inflow.

Rainfall and inflows

Rainfall was average to above average across most of the Murray–Darling Basin during 2009–10. February and March were wetter than average across most of the Basin, with parts of Queensland and New South Wales recording the highest monthly totals on record. However, the higher-yielding months of July to October 2009 and June 2010 were generally drier than average.

The Christmas–New Year period brought significant rainfall to the northern Basin, with good streamflow responses in the Castlereagh, Culgoa and Namoi rivers. Good rain across most of the Basin in early February was useful in wetting up the catchment and maintaining streamflows.

Confluence of the Paroo and Darling rivers, May 2010

Heavy rains fell in Queensland in late February–early March, resulting in record floods at St George and high flows in the northern tributaries of the Darling River. These rains contributed about 2,180 GL of inflow to the Menindee Lakes, with the Paroo River still contributing flows in June.

Murray system inflows (excluding Snowy Scheme releases and Menindee Lakes) were still well below average in 2009–10, despite the near-average rainfall in the catchment. The total inflow for the year was 3,380 GL, only 38% of the long-term average of 8,790 GL. Factors contributing to these low inflows include the dry antecedent conditions and the extremely low inflows to the River Murray from the Murrumbidgee and Goulburn rivers as storages in those catchments also gradually recover.

However, if inflows to Menindee Lakes are included, the total annual inflow was 5,560 GL, about half the long-term average of 10,900 GL (see Figure 3.2).

Figure 3.2  River Murray system monthly inflows, 2009–10

River Murray system inflows have been below average for 12 of the past 13 years. It will take a sustained period of above-average rainfall for river system inflows to recover to levels approaching the long-term average.

Active storage

Active storage under MDBA control at the beginning of July 2009 was 1,200 GL, or 14% of capacity. By 30 June 2010, active storage had increased to 3,285 GL, or 38% of capacity. Although this volume was significantly more than the historic minimum of 990 GL set at 30 June 2007, active storage was still well below the long-term average for June of 5,530 GL. Storage levels have now been below average since early 2002 (Figure 3.3).

Figure 3.3  MDBA active storage, June 2000 to June 2010

Water shares for New South Wales and Victoria in MDBA storages at the beginning and end of 2009–10 are shown in Table 3.1.

Table 3.1 Water shares for New South Wales and Victoria, June 2009 and June 2010

Notes:

Data relates to total storage.

Menindee Lakes came under MDBA control in April 2010. This resource ceases to be available to MDBA when the volume in Menindee Lakes is less than 480 GL and NSW resumes control of the storage.

Accounts are based on the best available data, which may contain some unverified operational data that could change in the future. Figures are rounded to the nearest GL.

Improving environmental outcomes

During 2009–10, MDBA delivered environmental water to a number of sites by managing weir-pool levels and river-flow rates. These sites included Werai Forest and Reed Beds Swamp in New South Wales, and Lake Walla Walla and Mulcra Island in Victoria, as well as delivering environmental water traded for environmental use in South Australia.  

MDBA continued to trial 'pulsed releases' from Dartmouth Reservoir to provide environmental outcomes along the Mitta Mitta River. During November and December 2009, two pulses of up to 4,600 megalitres per day (ML/d) that simulated natural variability were released. 

At Yarrawonga Weir (Lake Mulwala), a full drawdown of the lake took place in June–July 2009 to control the spread of the invasive aquatic weed leafy elodea (Egeria densa). This drawdown was reported as being very successful; however, further drawdowns will be required to minimise recolonisation by the weed. 

Refilling of Euston Lakes commenced when the temporary weir disconnecting the lakes was removed in December. Dry Lake filled relatively quickly; Lake Benanee initially filled at a very slow rate, but is now expected to fill by December 2010, following the clearing of cumbungi (Typha species) from Benanee Creek.  

No over-bank flows occurred along the River Murray in 2009–10; however, the release of water from Menindee Lakes by New South Wales provided significant flooding along the lower Darling River, some of which flowed into the Darling Anabranch. 

As in previous years, algal blooms developed to red alert levels along the River Murray, initially between Hume Dam and Cobram, but later in the year as far downstream the river as Wentworth. All red alerts had been lifted by early April. Public water supplies were treated by the local authorities to maintain water quality. Factors contributing to the algal blooms included low flows and high water temperatures. It was recognised that no feasible operational actions could have reduced such a large bloom given the water scarcity at the time.

Special arrangements for water sharing and contingencies

In response to the continued low water resource availability, partner governments agreed to special arrangements for sharing water resources between the states at the beginning of 2009–10. The initial water available for use in the River Murray system on 1 June 2009, whether from shared resources or from tributary inflow, was provided in the following priority order:

• conveyance water (including South Australia's 696 GL dilution and loss entitlement)
• critical human water needs within each state 
• private carryover within each state 
• 25 GL for each state. 

Initially, contingency measures were used to underpin these water requirements.  

By early August 2009, water availability had improved beyond the minimum adopted for planning purposes sufficient to meet conveyance water, critical human water needs, private carryover and an initial allocation of 25 GL for each state without the need for any contingency measures. 

These initial (Tier 2) sharing arrangements resulted in advances arising between the states. South Australia repaid its advance from the upper Basin states at a rate of 50% of its share of improvements (based on the normal Tier 1 arrangements of the Murray–Darling Basin Agreement). New South Wales repaid Victoria its advance at a rate of 100% of its share of improvements (based on Tier 1 arrangements). All advances were repaid by mid-October 2009 and further improvements were distributed in accordance with Tier 1 arrangements. 

The Lindsay River allocation was 30 ML/d plus 220 ML/d multiplied by the percentage allocation for Victorian high reliability water shares as at the end of the month, applied for that month less diversions, the same arrangement as in 2008–09.  

Most wetlands disconnected during 2007–08 to achieve water savings were reconnected during 2009–10; however, Euston Lakes was still filling as at 30 June 2010. 

Flooding during the Christmas–New Year period in mid-western New South Wales resulted in about 1,000 GL reaching Menindee Lakes while it was under New South Wales control. Of this, about 500 GL was delivered to the River Murray and shared between the states according to a special arrangement that ensured a significant portion was provided to the Lower Lakes with no adverse effect on Victoria. 

State water allocations and diversions

The 2009–10 water allocations for the Murray Valley started at minimal levels, with only South Australia making an allocation (2% of entitlement to its high security licence holders). Allocations increased slowly as River Murray system inflows improved. By 31 December 2009, New South Wales general and high security licence holders had been allocated 10% and 97%, respectively. Victorian high reliability water shareholders had a 60% allocation, and South Australian licence holders had a  45% allocation.

Inflows from the Darling River in early 2010 provided a welcome boost to the water resources of the River Murray system. By early April, water allocations had increased to 100% for high reliability water shareholders in Victoria; 27% and 97% for general and high security licence holders in New South Wales, respectively; and 62% for licence holders in South Australia.

The total amount of water diverted by the states was about 2,060 GL, including water traded in from the Murrumbidgee and Goulburn regions (see Figure 3.4). About 1,200 GL of allocated water in 2009–10 was carried over by individual water licence holders in preparation for the 2010–11 water year. This volume of carryover water was more than double the amount carried over during the previous year (approximately 580 GL) and was more than one-third of the MDBA active storage on 30 June 2010.

Figure 3.4 State diversions, 1991–92 to 2009–10: River Murray system 

Notes: 2009–10 figures are indicative only and will change.

Diversions include the Lower Darling and any inter-valley trade received by a state. 

Flow to South Australia

The 2009–10 flow to South Australia was 1,175 GL, including 341 GL trade and 834 GL entitlement. This was the highest total flow since 2006–07, but was about a third of the long-term median of 4,880 GL and below the normal annual entitlement of 1,850 GL.  

South Australia elected to receive low flows during the first six months of the year to build reserves to carry over to 2010–11. With improved water availability, full normal monthly entitlement volumes (plus trade) were delivered from January 2009 onwards. Higher flows from January 2010, including 194 GL from the Darling River floods, assisted in reducing the salinity downstream of Lock 1 and raising the water level in Lake Alexandrina.

The Murray component of the Snowy Mountains Scheme 

The required annual release from the Murray 1 Power Station was gradually increased during the year from 334 GL at 1 July 2009 to 1,067 GL at 30 June 2010, including 200 GL of transfer from the Murrumbidgee system. An additional 14 GL was released by Snowy Hydro as a partial repayment of the dry inflow sequence volume, resulting in a total release of 1,081 GL.

Operation of the River Murray system

Low storage levels and inflows saw 2009–10 begin with New South Wales, Victoria and South Australia on zero or near-zero water allocations. System operations were aimed at maximising water availability by storing as much water as possible in Dartmouth Reservoir, where evaporation losses are lower, and minimising losses along the river. As in recent years, river levels and flows were generally well below historical averages. 

Upper Murray system

At the start of 2009–10, storage was low in both the Dartmouth (837 GL, 21% of capacity) and Hume reservoirs (333 GL, 11% of capacity).

Releases from Dartmouth Reservoir were close to minimum for most of the year. However, two pulsed releases, totalling about 48 GL, were made to Hume Reservoir in late 2009. High inflows to the River Murray system from the Darling River in early 2010 meant that further releases from Dartmouth to Hume Reservoir were not required. Dartmouth Reservoir therefore increased in volume over the year by 444 GL to 1,281 GL (33% of capacity).

Releases from Hume Reservoir peaked at 16,000 ML/d in December 2009, but did not exceed 13,000 ML/d after early February 2010. These lower releases were possible because water from Menindee Lakes was used to deliver the entitlement to South Australia. The volume stored in Hume Reservoir at the end of the year was 814 GL (27% of capacity), about 481 GL more than in the previous year.

Mid-Murray

Lake Mulwala was refilled in mid-July 2010 by inflows from the Ovens and Kiewa rivers, after last year's drawdown to control leafy elodea. The lake was then maintained close to its normal operating target of 124.7 metres Australian height datum (AHD), or 0.2 m below full supply level. Other weir pools along the mid-Murray remained close to full supply level, with the exception of a short period in May when the pool at Torrumbarry Weir was lowered to assist with supply of irrigation water through the National Channel.

Flows along the River Murray between Yarrawonga and Wentworth weirs were lower than usual in autumn 2010 because the Menindee Lakes were supplying downstream water requirements. Flow at Swan Hill in April 2010 averaged 2,530 ML/d, compared with the 50-year average of 4,570 ML/d for April.

Lake Victoria

In 2009–10, the volume stored in Lake Victoria varied between a low of 242 GL in July and a high of 550 GL in April. Water released from Menindee Lakes in January–February, in anticipation of high Darling River inflows, was stored in Lake Victoria. Storage of this Darling River water in Lake Victoria also assisted in improving the quality of the water supplied to South Australia through mixing and dilution.

Lake Victoria was also used to store and dilute further releases from Menindee Lakes made during March. At the end of the year, storage in Lake Victoria was 358 GL (53% of capacity).

Menindee Lakes

Menindee Lakes received high inflows from the Darling River in January–February 2010 as a result of flooding rainfall during the Christmas–New Year period in the Castlereagh, Culgoa and Namoi river catchments. At that time, insufficient flows were forecast to warrant filling lakes Menindee and Cawndilla because these lakes had been dry since 2002 and high seepage losses would have been incurred. Therefore, about 630 GL of water was released into the lower Darling River, while lakes Wetherell and Pamamaroo were surcharged.

A second flood occurred in the Darling River catchment in late February–early March, with major flooding in south-western Queensland. Inflows from these floods reached Menindee Lakes in late March and were still continuing, albeit slowly, at the end of June. These inflows were sufficient to justify filling lakes Menindee and Cawndilla, which, at the end of June 2010, were at 81% capacity. At this time, lakes Wetherell and Pamamaroo were close to surcharge levels and the total volume stored in the Menindee Lakes was 1,522 GL (88% capacity).

MDBA resumed control of Menindee Lakes in mid-April 2010, when the stored volume exceeded 640 GL. The lakes will return to New South Wales' control when the volume in storage drops below 480 GL.

Lower Lakes

The levels in the Lower Lakes in South Australia have improved over the past year, from a low of –0.93 m AHD in January to –0.20 m AHD at 30 June 2010 (see Figure 3.5). However, this level still poses an environmental risk and emergency response measures, including pumping water into Lake Albert and maintaining a blocking bank at Clayton to isolate the Goolwa Channel, remain in place. There has been no release to the sea since October 2006 and consequently salt continues to accumulate in excess of normal entitlement flow in the Lower Lakes. It will take a year with substantial flow to South Australia to return the lakes to their full supply level of +0.75 m AHD.

Figure 3.5 Lake Alexandrina water levels, January 1962 to June 2010

Operations Review

The River Murray System Operations Review continued into its second year with the program responding to a number of key requirements of the Murray–Darling Basin Agreement and continuing to progress projects related to River Murray System Operations. 

During the year, a large focus of the Operations Review was helping prepare drafts of two new schedules to the Murray–Darling Basin Agreement — the schedule to account for South Australia's storage right and the schedule for water sharing. 

This work has involved considerable modelling and legal drafting. It is expected that these schedules will come into effect in 2010–11. 

Apart from the schedules, Operations Review has also contributed to:

• preparation of guidelines for the operation of River Murray system storages to examine and take into account possible environmental effects
• oversight and development of phase 3 of the Barmah Choke Study (the individual options modelling and assessment phase).

Water monitoring data for the River Murray

MDBA is responsible for streamlining and managing the collection and delivery of reliable and timely water information for day-to-day river operations and other business activities. During 2009–10, an automated data acquisition system was implemented to deliver near-to-real-time river information for flood operations and day-to-day river operations. This system continues to expand as more data is gathered through the automated data acquisition system. 

Water resource modelling

MDBA develops, operates and maintains river models and hydrographic data management systems for use in river management, water sharing and salinity management, and for other water resource issues and projects.

During 2009–10, some members of the modelling team were seconded to work on modelling for the proposed Basin Plan. This work has included significant development of the MDBA's MSM-Bigmod model (see Glossary for description) of the River Murray system and the development of a framework to allow the models of the Basin to be run in conjunction with each other.

A major modelling task undertaken in 2009–10 was the investigation of water delivery options for The Living Murray program. This included adding proposed physical works to the model to determine volumes required to meet environmental targets with the proposed works and measures in place. Improvements to the MSM-Bigmod modelling suite in 2009–10 included the addition of detailed models of Gunbower–Koondrook–Perricoota Forest and Mulcra and Lindsay islands.

Operations Review program work included extensive modelling of state water-sharing options in times of drought, the provision of critical human water needs, the holding by South Australia of a storage right in major Murray storages, and alternative reserve policies to address potential water shortages. 

The modelling group continues to support the development of eWater's River Manager software, including writing specifications for additional functionality, undertaking a River Murray test case and developing a water resource assessment module. The group was also involved in specifying and managing a major consultancy to investigate using freshwater flows from upstream to maintain water quality at South Australia's urban offtakes below Lock 1.

During 2009–10, longstanding modelling programs continued, including modelling and data services for the Basin Salinity Management Strategy, the Cap on water diversions, state water sharing in accordance with the Murray–Darling Basin Agreement and supporting river operations. 

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