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Menindee Lakes: the facts

In the past few years, the Darling River System along with the Menindee Lakes have been severely impacted by extreme drought conditions. This has resulted in particularly low and prolonged storage inflows, lower storage releases, and high evaporation rates. Operating the Menindee Lakes is challenging, and whenever water is released consideration is given to environmental impacts, community needs, and the requirements of downstream water users.

Storage volumes and levels

The total storage volume of Menindee Lakes at full supply level is 1,731 GL, with an ability to surcharge the lakes after seasonal inflows to a volume of 2,050 GL.

Drought

  • water storages in the northern Basin are at about 20% with some storages extremely low
  • in the Lower Darling, Menindee Lakes storages are low, around 5%
  • in the last 15 years, prolonged drought conditions have meant the Darling River system has experienced the three driest periods and lowest inflows to the Menindee lakes system on record
  • since December 2016, when the Menindee Lakes storage last peaked, there has been approximately 140 GL of inflows—measured at Wilcannia gauge

Evaporation and other losses

  • Menindee Lakes is estimated on average to lose 426 GL a year to evaporation, and up to 700 GL a year when the lakes are full
  • around 900 GL is estimated to have been lost from Menindee Lakes through evaporation between October 2016 and January 2019
  • total system losses from the lakes, including seepage, are estimated to be over 1200 GL between October 2016 and January 2019

The lakes are in a semi-arid area and are shallow with a large surface area. In most years they lose the equivalent of one Sydney Harbour of water to evaporation. These high evaporation rates are considered when making decisions on moving water within the lakes and and any releases.

Government operations of the lakes

  • WaterNSW manages the Menindee Lakes System
  • The Murray–Darling Basin Authority (MDBA) can access water in the lakes when they rise above 640 GL, and until the lakes drop below 480 GL.
  • Water accessed by the MDBA is on behalf of the joint governments of South Australia, Victoria and New South Wales and used to support entitlements in the River Murray.

The Menindee Lakes storage is owned and operated by New South Wales under the long-standing Murray–Darling Basin Agreement. This Agreement requires the MDBA to include the water held within the lakes as part of the shared resource of the River Murray System, and use the water in the lake when it's above 640 GL until it falls below 480 GL.

Once the storage volume within the lakes is less than 480 GL, the water held within the lakes is no longer considered a shared resource of the River Murray System, but is managed by New South Wales to meet local demands. Part of this includes water that cannot be released (called dead storage). The dead storage of the system is 125 GL.

Storing water in the upper lakes

  • Over the past six years river operators have been keeping as much water as possible in the upper lakes of Lakes Wetherell and Lake Pamamaroo.
  • The upper lakes primarily supply water to the local community and Broken Hill.
  • With low inflows, the importance of keeping water in these upper lakes for community needs is increasing.

When the lakes are below 480 GL, WaterNSW takes over the day-to-day operations of the lakes and have been working to ensure there is volume remaining in the ‘upper lakes’ to support local water needs. In the current drought conditions with low inflows, the distribution of water in the lakes is more important, and ensuring the upper lakes are accessible for the local community is a priority.

Releasing water from the lakes

Prior to July 2016, the Menindee Lakes system water storage was extremely low, following a record low inflow sequence.

As inflows arrived from upstream, the storage levels rose, and the New South Wales Government recommenced releases from Menindee Lakes into the Lower Darling.

The lakes continued to rise passing 640 GL in mid-October. This is when the water in the lakes was deemed to be part of shared resource in the River Murray System.

The MDBA, working with the state governments directed releases from the lakes into the Lower Darling from mid-October 2016 to mid-December 2017, when the lakes reached 480 GL. The MDBA worked closely with New South Wales to ensure water was retained in the upper lakes to secure a supply for local water users.

During this time, water was also released from Cawndilla into the Great Darling Anabranch for local needs.

Since mid-December 2017, with continued low inflows, New South Wales has implemented emergency drought operations at the lakes.

Releases from Menindee Lakes from July 2016–January 2019

Timeframe Releases for entitlements Releases for water for the environment Menindee Lakes system losses*
No shared resource available to the Murray from 27 July 2016 – 20 October 2016
  • 45 GL to re-start the system and meet local lower Darling entitlements and minimum passing flows (as released at Weir 32)
  • 20 GL – environmental water needs in the lower Darling from releases at Weir 32
Over 170 GL
TOTAL between Oct 16-Dec 17 45 GL 20 GL + 170 GL
Shared Resource (i.e.>640 GL) available to Murray from 21 October 2016 to 15 December 2017 (GL)
  • 24 GL for local Darling Anabranch water users from releases at Cawndilla, measured at Packers Crossing.
  • 444 GL for local lower Darling entitlements and Murray System requirements (approx. 50GL contributed to ADF) from releases at Weir 32
  • 100 GL – environmental use in Darling Anabranch from releases at Cawndilla
  • 125 GL – environmental water needs lower Darling from releases at Weir 32
Over 800 GL

TOTAL

(between Oct 16-Dec 17)

468 GL 225 GL 800 GL

No shared resource (i.e. <480GL) available to Murray from December 16 2017 to 10 January 2019

  • 40 GL to Lower Darling Anabranch entitlements and requirements from releases at Cawndilla, measured at Packers Crossing.
  • 83 GL to lower Darling entitlements and requirements from releases at Weir 32.
  Over 300 GL

TOTAL

(between Dec 17-Jan 19)

123 GL 0 GL + 300 GL

TOTAL

(between July 16-Jan 19)

636 G 245 GL + 1270 GL

Note: the figures in this table were updated on 29 January 2018

*Menindee Lakes System losses include evaporation and seepage and are determined using a water balance where the loss is calculated as: the change in storage volume plus the system inflows (measured at Wilcannia) less the system outflows (measured at Weir 32 on the lower Darling River, at Packers Crossing on the Great Darling Anabranch downstream of the Lake Cawndilla outlet and small volumes of pumped water). System losses are predominantly evaporation and seepage, and during periods of high flow, channel breakouts from the Darling River channel between Wilcannia and Menindee Lakes.

Improvements to Menindee in the future

Under the Basin Plan, reforms are being introduced to increase both the volume and management of flows from the northern Basin to the Menindee Lakes. These changes aim to improve water availability to the Menindee Lakes in the long-term.

The Basin Plan has also seen the New South Wales government, in partnership with all Basin governments, commit to reconfigure the Menindee Lakes through the Sustainable Diversion Limit Adjustment Mechanism.  The Menindee project will undergo extensive environmental analysis and community consultation before being finalised. Under the project, infrastructure and river operating rules will be changed.  These changes must meet stringent community and environmental conditions.

Improving the inflows and management of the Menindee Lakes will take time, the Basin Plan is a long-term plan, and we are six years into the 12 year plan.