The NSW Office of Water is a separate office within the Department of Environment, Climate Change and Water

INTRODUCTIONIn consultation with a community reference group, the NSW Office of Water, together with State Water Corporation are managing releases from the Menindee Lakes to the Lower Darling River and Great Anabranch to minimise the impacts on private property, maximise environmental benefits downstream and to make sure that the lakes are full when the floods have passed.

CURRENT FLOW MANAGEMENTHeavy rainfall in the past week along the Darling and particularly in the Lower Darling produced an immediate small rise in Menindee storage and a corresponding increase in flows to the Lower Darling through Weir 32. These were accommodated within the current flow management regime. State Water was quick to check structures, banks and access roads for any deterioration. While there were some local problems and wash-outs caused by the rain, the overall flooding has not been significantly affected by the latest inflows.

NSW rainfall totals (mm) week ending 8 February 2011 (Product of the National Climate Centre)

Community information Management of Menindee Lakes 2010-2011February 10, 2011

www.water.nsw.gov.au NSW Office of Water | Issue 4 – February 10, 2011 page 2

Management of Menindee Lakes 2010-2011 – February 10, 2011

In the north, along the Barwon River, the peak flows have just passed Walgett where the river today is flowing at 38,000 ML/d and falling. This peak will pass Brewarrina and reach Bourke over the next 7 to 10 days. The peak from the Queensland flooding last month is nearing the lower reaches of the Culgoa River system with river at Mundiwa peaking yesterday at 64,500 ML/d. This peak will reach Bourke over the next 5 to 8 days, however, the Culgoa and Bokhara Rivers will continue to drain into the Darling River for many weeks.

Interestingly, the Narran system has received large volumes of water on this occasion and Narran Lake is full. With additional water still to arrive there is a possibility water will flow to the Darling for the first time in decades.

The satellite imagery clearly shows the flood extents through the Culgoa-Bokhara and Narran systems and also an accumulation of water upstream of Wilcannia. There appears to be a backing up of peak flows to Wilcannia, that is diverting more water into effluents and flood runners including the Talyawalka Creek anabranch. Flows in the Talyawalka at the Barrier Highway have increased today to 8,500 ML/d while flows through Wilcannia are at 33,600 ML/d and continuing to rise slowly. Flows through Wilcannia are expected to continue to rise slowly over the next few weeks to around 36,000 ML/d.

Image: MODIS Australia6.2011039.aqua.721.1km, dated 8 February 2011.

Source: NASA/GSFC, MODIS Rapid Response 2011.

At Menindee Lakes, the Main Weir gates have been opened, providing maximum through-flow of water as well as allowing fish passage. Without storing these inflows and with system losses, primarily to evaporation, the total lakes’ storage continues to slowly decline. Currently the Lakes are holding 1,686,000 ML – 97.4% of capacity. This provides about 360,000 ML of airspace. It is estimated some 1,500,000 ML of inflows are yet to arrive at Menindee.

FUTURE FLOW MANAGEMENT

Flows into the Lower Darling through Weir 32 are currently around 33,000 ML/d. They will increase slowly in response to inflows to the Lakes

At this stage it is intended that peak inflows will be attenuated through the lakes system using some of the airspace currently available and thereby limit any further flood threat to Menindee township. At these levels there continues to be some access difficulties in and around the township but it is unlikely that difficulties will increase unless a significant weather system brings more heavy rainfall and more large inflows.

www.water.nsw.gov.au NSW Office of Water | Issue 4 – February 10, 2011 page 3

Management of Menindee Lakes 2010-2011 – February 10, 2011

Nearly half of the Lower Darling flows are passing naturally into the Great Darling Anabranch and, combined with releases from Lake Cawndilla of 1,750 ML/d, are flowing through the entire Anabranch system to the Murray River.

High flows at Pooncarie and Burtundy are expected to continue for at least a two months and will only recede when the release from Menindee is slowly reduced to capture peak inflows and fill the Lakes at the end of the floods.

The situation is being closely monitored and information will updated and distributed regularly.

Location Height (m) Flow (ML/d) Comment

Boggabilla 1.19 1,802 Falling (Peak 270,000 on 14/1/11)

Mungindi 3.71 1,101 Falling

Collarenebri (total) - 29,421 Falling

Walgett 10.94 38,286 Falling (Peak 40,260 on 6/2/11)

Brewarrina (total) - 38,022 Rising

Bourke 12.16 72,155 Rising (Note: New rating table after recent gaugings)

Louth 11.87 74,827 Rising

Tilpa 12.16 74,238 Rising

Wilcannia 10.13 33,636 Rising slowly

Weir 32 6.94 33,073 Steady

Pooncarie 7.06 18,325 Rising slowly

Burtundy 7.00 17,783 Steady

River data from 9 February 2011

below left – View of Irrigation Rd, South Menindee, facing North – photo courtesy of Barry Philp, State Water, Menindee

below right – Paddle steamers on the Darling at Tulney Point Station – photo courtesy of Rachel Strachan, Tulney Point Station

www.water.nsw.gov.au NSW Office of Water | Issue 4 – February 10, 2011 page 4

Management of Menindee Lakes 2010-2011 – February 10, 2011

Darling River flows and Menindee Storage volume

Darling River Flows and Menindee Storage Volume

0

20,000

40,000

60,000

80,000

100,00029

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Flow

(ML/

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1,500,000

1,600,000

1,700,000

1,800,000

1,900,000

2,000,000

2,100,000

2,200,000

Stor

age

Volu

me

(ML)

Bourke Flow

Weir 32 Release

Wilcannia Flow

Forecast Conditions -approximate only.

Menindee Storage

WHAT THIS MEANS The outlook for the Lower Darling is for flows of about 20,000 ML/d (7.4m gauge height) and minor flooding at Burtundy by late February, similar to the event of 1998 (21,600 ML/d and 7.7m) but much smaller than the huge flood of 1976 (59,000 ML/d and 9.7m) at Burtundy. Flows in the Murray River at the Darling confluence are considerably more, in the vicinity of 80,000ML/d, creating some backwater effects at the bottom of the Darling and the Anabranch.

Current releases from the Menindee Lakes are:

ML/d

Main weir 34,100

Lake Wetherell outlet 325

Lake Pamamaroo outlet -

Lake Menindee outlet -

Lake Cawndilla outlet 1,750

Total 36,175

HOW THIS FLOOD COMPARES TO PREVIOUS EVENTSThis section is shown to enable the comparison of the current flood events with previous floods.

Year Max height at Bourke (m)

Total volume at Bourke (GL)

Max height at Wilcannia (m)

Total flows at Wilcannia (GL)

Max height Weir 32 (m)

1988 12.57 3,500 10.19 2,600 5.10

1996 12.39 2,500 9.85 2,400 5.18

1998 13.78 9,700 10.83 4,200 7.45

2001 12.28 3,300 9.75 2,250 6.21

2010 10.78 2,370 9.43 2,400 5.44

www.water.nsw.gov.au NSW Office of Water | Issue 4 – February 10, 2011 page 5

Management of Menindee Lakes 2010-2011 – February 10, 2011

© State of New South Wales through the Department of Environment, Climate Change and Water, 2011 This work may be freely reproduced and distributed for most purposes, however some restrictions apply. Contact the Department of Environment, Climate Change and Water for copyright information.

Disclaimer: While every reasonable effort has been made to ensure that this document is correct at the time of publication, the State of New South Wales, its agencies and employees, disclaim any and all liability to any person in respect of anything or the consequences of anything done or omitted to be done in reliance upon the whole or any part of this document. This information does not constitute legal advice. Users are advised to seek professional advice and refer to the relevant legislation, as necessary, before taking action in relation to any matters covered by this information sheet.

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ENVIRONMENTAL MANAGEMENTLake Wetherell is currently at 52 per cent capacity; its lowest level since it was filled by the December 2009 floods. This is providing essential drying of the floodplain to avoid deterioration of vegetation and improves habitat for native species. However, with the volumes of water expected to reach Menindee, all of the lakes are expected to be surcharged to their capacity in the coming weeks and months.

Releases are continuing from Lake Cawndilla to the Great Anabranch, providing much needed environmental benefits after such a long drought. Flows are continuous for the length of the Anabranch to the Murray River and are filling some of the Anabranch Lakes that are listed in the Directory of Important Wetlands in Australia.

COMMUNICATION AND ADDITIONAL INFORMATIONThe NSW Office of Water and State Water will continue to prepare and publish this series of information sheets every two weeks where possible.

A regional committee, that includes representatives of water users from the Menindee, Lower Darling and Great Anabranch has been established to ensure that available information is distributed about river levels and flow management.

The Office of Water and State Water will continue to work with the SES, local police and Councils.

WHERE DO I GO FOR ADDITIONAL INFORMATION? NSW State Water office in Cawndilla Street Menindee.

SES free call 132 500

NSW Office of Water: call Bunty Driver T 03 5898 3910 or visit the website www.water.nsw.gov.au