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Part 2: Deliver water efficiently and equitably for domestic consumption, sustainable economic use and environmental benefit

Strategy 2.1
Deliver agreed water shares in the Murray River

Water availability

Extreme drought was the overwhelming feature of Murray River operations in 2006– 07. Total inflow to the Murray River system, excluding Snowy Mountain Scheme releases, set a new record low of 1,040 GL. The nearest comparable drought period was in 1914–15, when a total of 2,000 GL flowed in (based on modelled data). Figure 7 shows how inflows in 2006–07 compare with those in 1914–15 and how they represent only 10 per cent of the long-term average of 11,100 GL.

Allocations across the Murray River system were also at record low levels, with system management and operations presenting a challenging year for state water agencies and the River Murray Water operations team alike. The volume of active storage under control of the Commission at the start of 2006–07 was 3,370 GL, which was 570 GL more than at the start of 2005–06 but still 1,750 GL below the long-term average of 5,100 GL.

Figure 7 Murray River system inflows 2006–07, 1914–15 and long-term average

2695 MDBC AR Fig 7 RM system inflows 0707.eps

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MDBC active storage at the end of 2006–07 fell to a new end-of-June record low of 990 GL, about 1,000 GL below that observed at the end of June 1983, which was the previous lowest level since Dartmouth Dam was commissioned in 1979.

The greatest deficits occurred in the Hume and Ovens catchments; however, new minimum inflows were recorded in every tributary of the Murray except for the Mitta Mitta River.

As the season progressed and inflows tracked below those used for assessment purposes, MDBC assessments of shares available to the states decreased. It was necessary for New South Wales and South Australia to reduce allocations and Victoria was unable to increase allocation to levels that had been anticipated early in the season.

The Barmah–Millewa environmental watering account remained ‘on loan’ to irrigators in New South Wales and Victoria throughout the season (see Table 8). Small volumes of environmental water available under The Living Murray were used for maintaining fish passage at the barrages, and for pumping to severely stressed wetlands such as Hattah Lakes. The volume of environmental water used in 2006–07 was less than 1 per cent of the total water consumed. The majority of the water held in environmental accounts was loaned to irrigators to supplement record low allocations.

Table 8 Water accounts for New South Wales and Victoria, 2006–07 (GL)
Storage Storage at 30 June 2006 Storage at 30 June 2007
  New South
Wales
Victoria Total Out of balance New South
Wales
Victoria Total Out of balance
Dartmouth Reservoir 864 1,661 2,525 797 154 362 516 208
Hume Reservoir 164 475 639 311 211 186 397 –25
Lake Victoria 226 186 412 –39 119 165 284 48
Menindee Lakesa
Total 1,254 2,322 3,576 1,069 482 713 1,197 231

a. Menindee Lakes has been in New South Wales control since March 2002, and the resource will not become available to the MDBC until the storage next exceeds 640 GL, hence no shares are available from the storage.

Notes

1. Accounts are based on the best available data, which may contain some unverified operational data. Figures are rounded to the nearest GL.

2. Data relate to gross storage.

3. The ‘out of balance’ figure reflects the volume of stored water accounted to Victoria, minus the volume of stored water accounted to New South Wales.

4. Figures may differ from those reported in the 2005–06 annual report due to the replacement of operational data with verified (quality assured) data.

State irrigation allocations

In response to the extreme dry conditions, the states initiated a number of actions, including adjustments to irrigation season lengths in the major gravity irrigation areas and the introduction of carryover for high-security allocations.

State irrigation diversions

State diversions from the Murray River and Lower Darling are summarised in Table 9.

Table 9 Summary of state diversions, 1991–92 to 2006–07 (GL)
Year Murray Rivera Darlingb
  New South Wales Victoria South Australia Total New South Wales
1991–92 2,431c 1,827 589 4,847 101
1992–93 1,633 1,147 482 3,262 77
1993–94 1,902 1,407 587 3,896 158
1994–95 2,254 1,970 663 4,887 54
1995–96 1,935 1,740 568 4,243 168
1996–97 2,231 1,745 600 4,576 136
1997–98 1,886 1,696 664 4,246 71
1998–99 2,000 1,766 690 4,456 192
1999–2000 1,234 1,522 642 3,398 85
2000–01 2,070 1,682 662 4,414 246
2001–02 2,113 1,884 621 4,618 126
2002–03 879 1,701 737 3,317 107
2003–04 1,312 1,442 612 3,366 23
2004–05 1,241 1,466 623 3,330 29
2005–06 1,670 1,670 625 3,965 39
2006–07d 610 1,510 640e 2,760 14

a. Data based upon the official MDBC record for the reporting requirements of implementation of the Cap on diversions, with the exception of data for 2006–07.

b. Includes data from Cawndilla Outlet to the Great Darling Anabranch.

c. Record high diversion.

d. Data presented for 2006–07 is estimated based on hydrographic and operational data for New South Wales and Victoria, and approximate data from the SA Department of Water, Land and Biodiversity Conservation.

e. Includes 60 GL metropolitan Adelaide.

Flow to South Australia

Low inflows to the Hume Dam. Photo: Mark Vanner

Low inflows to the Hume Dam with dam wall in the distance.

(Photo: Mark Vanner)

Flow to South Australia in 2006–07 comprised an entitlement flow of 1,403 GL, compared to the normal minimum entitlement of 1,850 GL under the Murray-Darling Basin Agreement. A review of flow measurement is currently under way and any adjustments necessary will be carried over to deliveries in 2007–08.

The flow received in 2006–07 is the lowest total annual flow to South Australia since 1945 and is less than one-third of the median annual flow of 4,850 GL. At South Australia’s request, the monthly pattern of flows was altered in an effort to improve access to water in the Lower Lakes in South Australia.

The total volume of flow to South Australia for the past ten years is the lowest ten-year total volume on record (see Figure 6). South Australia has received above long-term median flows in only three of the past ten years.

Murray River system operations

Murray River system operations posed significant challenges throughout 2006–07. As inflow records progressively tumbled throughout the season, and advice was received from Snowy Hydro of significant reductions in expected Snowy Mountains Scheme releases, the risk of ‘emptying’ MDBC storages became very real. System operations were aimed at achieving a concurrent drawdown of storages as late in the year as possible to avoid any individual storage falling too low too early.

The Commission adopted interim minimum flow targets late in the year to begin conserving as much water as possible in 2007–08. River heights and flow rates at many locations across the system fell to levels not seen for many years.

Equitable sharing of a scarce resource in 2007–08 – establishing the rules

The interpretation of the Murray-Darling Basin Agreement’s application during the period of extremely low water resource availability was a key development late in 2006–07. This included devising options for sharing very small volumes of improvements equitably to ensure that sufficient water was available for critical urban, stock and domestic consumption and subsequently so that state water allocation systems and water markets could continue to function.

At the direction of the MDB Ministerial Council, the Commission agreed to new arrangements for water sharing for critical urban and stock use equally between New South Wales, Victoria and South Australia. A further equal share will be dedicated to providing dilution flows through the entire system, and a small environmental allocation will provide for critical environmental assets. Should inflows improve sufficiently, a transition to normal sharing arrangements would occur.

Towards the end of the reporting period, there were small improvements in water availability. Evaporation and transmission losses were lower than expected, and rainfall in autumn was average – though onto an extremely dry catchment, causing significantly lower than average inflows. These small increases will be shared in 2007–08 in accordance with the agreed principles.

The record low inflows of 2006–07 have profound implications for future water management in the Murray-Darling Basin. MDBC analysis has shown that extremely wet conditions – equivalent to the wettest 15 per cent on record – will be required to rebuild reserves in Murray River system storages to average volumes. Hence there is a significant risk that contingency measures will again be required to secure critical water supplies in 2007–08, as storage volumes are likely to be severely depleted.

Upper Murray River system

At the start of 2006–07, about 75 per cent of available water was stored in Dartmouth Reservoir. With the dry start to the season, transfers of water from Dartmouth to Hume Reservoir began in July and reached channel capacity rates in the Mitta Mitta River by early August.

By mid-spring, forecasts predicted that water levels at Hume would fall to the minimum operating level of 1 per cent over summer if extreme conditions continued. By agreement with landholders along the Mitta Mitta River, additional transfers from Dartmouth Dam between mid-November and late January 2007 avoided any rationing of water. Increased release rates from the Snowy Mountains Scheme later in summer, and the subsequent rise of Hume Reservoir, permitted a progressive reduction in transfers from Dartmouth Dam, where total storage at the end of June 2007 was 516 GL.

Total storage in Hume Reservoir reached 664 GL (22 per cent of capacity) early in July 2006 before beginning to fall under the extreme dry conditions. With low inflows persisting and then reaching new record low levels, storage in Hume continued to fall during 2006–07 – the peak of 664 GL was the lowest peak storage for a season since 1936. Storage at the end of June 2007 had reached 397 GL (13 per cent of capacity).

Mid-Murray

With Hume levels forecast to fall further, and potentially restrict outlet capacity, the water level in Lake Mulwala was allowed to rise in preparation for Yarrawonga Weir to become, in effect, the Murray’s primary regulating structure. It did not become necessary, however, to rely on Yarrawonga to perform this regulating function, and operating levels returned to normal later in the season.

An increase in rainfall from about January, which reduced demands and losses over the remainder of the season, combined with increased Snowy Mountain Scheme releases, meant there was no need for drawdowns from weir pools across the system.

Lake Victoria

Transfers of water from Hume Dam to Lake Victoria were managed throughout the season to balance the risks of extreme low levels occurring in either storage. Operations were on a knife edge for many months. Improved rainfalls in the later half of the season, combined with the introduction of carryover of high-security allocations by the states and early release by Snowy Hydro of water due to be delivered in 2007–08, resulted in higher than expected reserves being in storage at the end of the season, given the drought conditions.

Early in the year, the Commission considered departing from existing requirements to store any end-of-season reserves first in Lake Victoria. As conditions worsened, it became clear that the MDBC minimum reserve, as required by the Agreement, would be zero. Operations were then directed at having the water level in Lake Victoria as low as practical by the end of the season.

The actual storage in the lake at the end of June 2007 (284 GL or 42 per cent of capacity) was considerably healthier than expected, due to reduced diversions and losses upstream.

Lower Lakes

By mid-April, the Lower Lakes in South Australia had fallen to about 0.1 metres AHD (Australian Height Datum), in comparison to the normal level of 0.75 metres AHD, close to the record low level set in March 1968. This is below sea level for most of the tide cycle. Substantial efforts to reduce leakage of sea water through, under and around the barrages were made, but some inevitable leakage has resulted in elevated salinity levels in the reaches immediately upstream of the barrages.

Local rainfall and reduced evaporation rates late in the year saw lake levels rise gradually to 0.18 metres AHD by the end of June 2007.

Menindee Lakes

Menindee Lakes began the season at 268 GL, under NSW control in accordance with the Agreement. Inflows were effectively zero throughout the entire year, but heavy local rainfall brought temporary minor rises in summer. The lakes remained under NSW control and had fallen to 94 GL at the end of June 2007. The lakes will revert to MDBC control when next they reach 640 GL.

The Murray component of the Snowy Mountains Scheme

Total active storage in the Snowy Mountains Scheme at the end of April 2007 was 770 GL.

As at 1 May 2006, the required annual release from Murray 1 Power Station was 989 GL. The actual release from Murray 1 Power Station for the 12 months to 30 April 2007 was 1,074 GL. The partner governments had agreed in 2005–06 that any advances made under the flexibility arrangements of the Murray Water deal made in that year would not be immediately available for allocation but would be held over to be used in the following year. This means that, of the 1,074 GL released, 217 GL was not available for allocation in 2006–07, and has been held in upper Murray storages as a resource to be made available in 2007–08.

Contingency planning for 2007–08

In response to the record low Murray River system inflows in winter–spring 2006, and MDBC forecasts of extremely low reserves at the end of the 2006–07 season, the Prime Minister convened a Water Summit of all partner governments on 7 November 2006.

First Ministers were advised that, if 2006–07 season inflows were repeated in 2007–08, there would be just enough water to provide for critical human needs.

First Ministers established a Senior Officials Group to consider the emerging threat to critical water supply needs in 2007–08 and provide a report outlining contingency planning by late December 2006. The membership of the Senior Officials Group included partner governments and the Murray-Darling Basin Commission. MDBC coordinated hydrologic analysis for the Murray River system. State water resource management agencies coordinated Murrumbidgee and Goulburn hydrologic analysis and provided contingency options for individual town water supplies.

Contingency measures

MDBC assisted the Department of Prime Minister and Cabinet to prepare the first Senior Officials Group report to First Ministers on 23 December 2006. In addition to defining the scope of the crisis, the report considered a range of contingency measures including:

  • evaporation savings
  • reduced winter minimum regulated flow targets in the Murray River system
  • reduced reserve targets in Lake Victoria
  • early pumping of water to Adelaide metropolitan storages
  • lowering of Adelaide water supply pump station offtakes
  • a number of market measures to acquire additional reserves, and
  • construction of a temporary weir at Wellington.

As the year progressed, it became evident that the focus should initially be on the first five of these measures. The option of using water market measures would have needed to be exercised early in the irrigation year.

The last option, to construct a temporary weir near Wellington, was considered a measure of last resort, probably due to its high cost, estimated at more than $100 million.

Both options, however, will need to be reviewed in the light of inflows received in early 2007–08. If these remain very low, these two contingency measures may become necessary.

During the first half of 2007, MDBC continued to support the Senior Officials Group and by providing papers to its meetings and updated hydrologic analysis in three further reports to First Ministers. MDBC staff also assisted in the drafting and review of each report’s entire contents. Overview summaries of the reports were published on the Prime Minister’s and Department of Environment and Water Resources websites.

Communication about the drought

The Commission made significant efforts in 2006–07 to keep partner governments, water users and the broader community up to date with the unfolding drought situation.

Frequent drought updates, operational updates and media releases supplemented the normal reporting arrangements.

Drought-affected wheat crop. Photo: Arthur Mostead

Drought-affected wheat crop, Ouyen, Victorian Mallee.

(Photo: Arthur Mostead)

River operations and the water delivery system

Murray River operations are conducted by a team based in the head office of the MDBC and three state government constructing authorities or their agencies. Twenty-one Commission staff and 128 associated constructing authorities are effectively dedicated to water operations.

Water resource modelling

MDBC modellers are responsible for the maintenance and development of the Commission’s river models and hydrographic data management systems. This group also provides training and guidance to the modellers working on specific projects and is available to investigate other water resource issues as they arise.

Water scarcity has increased demand for forecast information from river operators and partner governments. The MDBC’s modelling group has continued to supply and refine forecasts of water availability and to provide the systems for assessing options for short-term operations. The likelihood of future outcomes is estimated by using the inflows and climatic conditions experienced in each of the last 116 years, and using and improving MSM_Bigmod (the model of the Murray and Lower Darling rivers) to conduct simulations using those observations.

Drought contingency planning

MSM_Bigmod performed well under the drought conditions, though some changes have been made to ensure it accurately reflects system behaviour and incorporates management decisions.

The modelling group has been involved in generating flow and salinity forecasts to inform decisions made about securing Adelaide’s water supply, and in formulating special water-sharing arrangements to allow priority water needs along the length of the Murray River to be met.

Water monitoring data for Murray River

MDBC has an ongoing commitment to fund the monitoring and operation of state hydrometric networks, and collection and provision of hydrometric data for water and salinity management in the Murray River system at key locations. In early 2007 a new Operations Services Unit was created, which will be dedicated to the management of hydrometric stations and hydrographic data for the Commission.

The very low river levels experienced during autumn 2007 presented difficulties for river operators, as existing flow rating tables for many sites had not been calibrated to determine a flow at these low levels. As a consequence, there was an increased level of field flow measurements during this period to allow development of rating tables that provided accurate assessment at low flows.