Community information. Management of Menindee Lakes 2010 ... · 2011/074 (15 March 2011) Source:...
6
The NSW Office of Water is a separate office within the Department of Environment, Climate Change and Water INTRODUCTION The NSW Office of Water, together with State Water Corporation and in consultation with local communities and stakeholders, is managing releases from the Menindee Lakes to the Lower Darling River and Great Darling Anabranch as floods from northern NSW and Queensland pass through the Darling River System. This is the seventh information paper produced to provide information on the inflows, levels, operations and management of the Menindee Lakes. The Queensland flood peaks of January 2011 are now passing into and through the Menindee Lakes and flood operations are reaching a critical stage. CURRENT FLOW MANAGEMENT Two storm events in March, the first delivering around 70 mm on 9 and 10 March and the second up to 30 mm on 19 to 21 March in the area from Wilcannia to Menindee (with higher rainfall in the latter event south of Menindee) has produced significant local runoff. Consequently, greater than expected inflows to Menindee Lakes are now occurring. The Darling River at Wilcannia is falling after a flood peak of 10.5 m (38,500 ML/d) on 21 March, as is the Talyawalka Creek at the Barrier Highway after a peak of 30,500 ML/d on 19 March. These peaks, together with the recent local runoff, will cause inflows to Menindee Lakes to reach at least 50,000 ML/d in the next 5 to 10 days. Upstream of Wilcannia the Darling River at Tilpa is now 22,700 ML/d and falling sharply. The reduction in flows in the Lower Darling through Weir 32, which had commenced on 12 March, has had to be stopped after the heavy rainfall in mid-March. Flows through Weir 32 are down from a peak of 37,000 ML/d, and have been held for the past week at 28,000 ML/ d to pass on the additional inflows. There is a likelihood of further rainfall in April therefore outflows will be increased to around 30,000ML/d at Weir 32 (or about 150mm), and the release from Cawndilla Outlet to the Anabranch will also be increased from the current 600ML/d to 1,500ML/d to accommodate the additional inflows. Current predictions are that this will be sufficient to manage the inflows. Further increases to the Darling River at Weir 32 will become necessary if inflows are greater than anticipated over the next week or so, or further significant rainfall occurs in the area. Total storage in the lakes is now 1,800,000 megalitres which is 105 per cent capacity and maximum surcharge capacity is 2,050,000 ML (118 per cent of capacity). WHAT THIS MEANS In effect, the recent rainfall has set back relief from flooding around Menindee by at least two weeks, as it will now be difficult to get flows at Weir 32 down to around 18,000 ML/d before mid to late April. Further delays can be expected if significant additional rainfall is received. The longer term outlook for autumn (March to May) is that there is a good chance (60 per cent) that at least median rainfall conditions will be received. With the lakes currently at full capacity, weather systems are being closely monitored to enable us respond to any new flood threat. Community information Management of Menindee Lakes 2010-2011 March 25, 2011
Transcript of Community information. Management of Menindee Lakes 2010 ... · 2011/074 (15 March 2011) Source:...
The NSW Office of Water is a separate office within the Department of Environment, Climate Change and Water
INTRODUCTIONThe NSW Office of Water, together with State Water Corporation and in consultation with local communities and stakeholders, is managing releases from the Menindee Lakes to the Lower Darling River and Great Darling Anabranch as floods from northern NSW and Queensland pass through the Darling River System.
This is the seventh information paper produced to provide information on the inflows, levels, operations and management of the Menindee Lakes.
The Queensland flood peaks of January 2011 are now passing into and through the Menindee Lakes and flood operations are reaching a critical stage.
CURRENT FLOW MANAGEMENTTwo storm events in March, the first delivering around 70 mm on 9 and 10 March and the second up to 30 mm on 19 to 21 March in the area from Wilcannia to Menindee (with higher rainfall in the latter event south of Menindee) has produced significant local runoff. Consequently, greater than expected inflows to Menindee Lakes are now occurring.
The Darling River at Wilcannia is falling after a flood peak of 10.5 m (38,500 ML/d) on 21 March, as is the Talyawalka Creek at the Barrier Highway after a peak of 30,500 ML/d on 19 March. These peaks, together with the recent local runoff, will cause inflows to Menindee Lakes to reach at least 50,000 ML/d in the next 5 to 10 days. Upstream of Wilcannia the Darling River at Tilpa is now 22,700 ML/d and falling sharply.
The reduction in flows in the Lower Darling through Weir 32, which had commenced on 12 March, has had to be stopped after the heavy rainfall in mid-March. Flows through Weir 32 are down from a peak of 37,000 ML/d, and have been held for the past week at 28,000 ML/ d to pass on the additional inflows.
There is a likelihood of further rainfall in April therefore outflows will be increased to around 30,000ML/d at Weir 32 (or about 150mm), and the release from Cawndilla Outlet to the Anabranch will also be increased from the current 600ML/d to 1,500ML/d to accommodate the additional inflows. Current predictions are that this will be sufficient to manage the inflows. Further increases to the Darling River at Weir 32 will become necessary if inflows are greater than anticipated over the next week or so, or further significant rainfall occurs in the area.
Total storage in the lakes is now 1,800,000 megalitres which is 105 per cent capacity and maximum surcharge capacity is 2,050,000 ML (118 per cent of capacity).
WHAT THIS MEANS In effect, the recent rainfall has set back relief from flooding around Menindee by at least two weeks, as it will now be difficult to get flows at Weir 32 down to around 18,000 ML/d before mid to late April. Further delays can be expected if significant additional rainfall is received.
The longer term outlook for autumn (March to May) is that there is a good chance (60 per cent) that at least median rainfall conditions will be received. With the lakes currently at full capacity, weather systems are being closely monitored to enable us respond to any new flood threat.
Community information Management of Menindee Lakes 2010-2011March 25, 2011
www.water.nsw.gov.au NSW Office of Water | Issue 7 – March 25, 2011 page 2
Management of Menindee Lakes 2010-2011 – March 25, 2011
Updated satellite imagery confirms significant overbank flow and the filling of lakes and billabongs in the Talyawalka and Anabranch systems. High flows have also continued in the Three Mile Creek which leaves the Darling River near Lake Wetherell and joins the Talyawalka Creek in its westward run back to the Darling River below Weir 32. It is quite rare for these lower reaches of the Talyawalka Creek to flow and it has been more than ten years since they last received water.
Full supply level of Menindee Lakes is 1,731,000 ML. The current management strategy is to fill the lakes to a maximum storage of about 2,000,000 ML (surcharged to 116 per cent of capacity) in mid to late April and then to reduce flows and water levels in the Lower Darling at a rate that will minimise the potential for riverbank damage.
Figure 1 Darling River flood operations - Image: MODIS Australia6 Subset - Terra 250m Bands 7-2-1 Image for 2011/074 (15 March 2011) Source: NASA/GSFC, MODIS Rapid Response 2011.
www.water.nsw.gov.au NSW Office of Water | Issue 7 – March 25, 2011 page 3
Management of Menindee Lakes 2010-2011 – March 25, 2011
The Sydney to Perth railway line approaching Menindee has remained open throughout the flooding. The water rose a further 0.65 m from that pictured, to a peak on 11 March.
Photo: 11 January 2011 – Courtesy Barry Philp State Water, Menindee
Peak of flooding around Menindee township.
Photo: 12 March 2011 – Courtesy Barry Philp State Water, Menindee
The Main Weir at Menindee, discharging approximately 33,000 ML/d into the Lower Darling River. A peak outflow of nearly 36,000 ML/d occurred on 9 March 2011.
In the background is Lake Pamamaroo at 100 per cent capacity and its inlet regulator can be seen to the top right.
Photo: 17 February 2011 – Courtesy Barry Philp State Water, Menindee
www.water.nsw.gov.au NSW Office of Water | Issue 7 – March 25, 2011 page 4
Management of Menindee Lakes 2010-2011 – March 25, 2011
RIVER LEVELS
Location Height (m) Flow (ML/d) Comment
Bourke 4.62 4,252 Falling (Peak 88,000 on 14/2/11)
Talyawalka (BH) 4.20 23,840 Falling (Peak 30,500 ML/d on 19/3/11)
Wilcannia 10.45 37,883 Falling (Peak 38,500 on 21/3/11)
Weir 32 6.70 28,009 Steady (Rising to 30,000 ML/d)
Pooncarie 7.42 23,736 Steady
Burtundy 7.23 18,975 Steady
River data from 25 March 2011
Darling River Flows and Menindee Storage Volume
Darling River Flows and Menindee Storage Volume
0
20,000
40,000
60,000
80,000
100,000
01-O
ct-1
0
15-O
ct-1
0
29-O
ct-1
0
12-N
ov-1
0
26-N
ov-1
0
10-D
ec-1
0
24-D
ec-1
0
07-J
an-1
1
21-J
an-1
1
04-F
eb-1
1
18-F
eb-1
1
04-M
ar-1
1
18-M
ar-1
1
01-A
pr-1
1
15-A
pr-1
1
Flow
(ML/
d)
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
Darling River Flows and Menindee Storage Volume
River data from 10 March 2011
OUTLOOK FOR MENINDEE TOWNSHIP AND THE LOWER DARLING
Current water levels will continue in and around Menindee township until at least the middle of April, before the reduction of flows can be resumed. Once the inflow fall and the downstream recession begins again, it will take another 12 days (without rainfall) to reach flows of 18,000 ML/d at Weir 32 with is the flow rate at which access to most properties is possible.
The outlook for the Lower Darling remains largely unchanged with flows at Pooncarie and Burtundy remaining fairly steady at around 20,000 ML/d and minor flooding at Burtundy during March and April. This is similar to flows in 1998 (21,600 ML/d and 7.7 metres) but much smaller than that of 1976 (59,000 ML/d and 9.7 metres) at Burtundy. In the absence of further storms and significant inflows, the river at Burtundy is likely to begin falling during May.
Flows in the Murray River downstream of the Darling River junction remain high. Flows fell in mid February, and remain steady through mid March. They have subsequently risen in recent days to about 65,000 ML/d.
With high Murray flows, it is probable that the Menindee Lakes will remain near full throughout autumn and winter.
www.water.nsw.gov.au NSW Office of Water | Issue 7 – March 25, 2011 page 5
Management of Menindee Lakes 2010-2011 – March 25, 2011
Current releases from the Menindee Lakes are:
ML/d
Main weir 26,500
Lake Wetherell outlet 2,200
Lake Pamamaroo outlet -
Lake Menindee outlet -
Lake Cawndilla outlet 600
Total 29,300
HOW THIS FLOOD COMPARES TO PREVIOUS EVENTSThe table below shows a comparison of the current flood events with previous floods.
YearMax height at
Bourke (m)Total volume at
Bourke (GL)Max height at Wilcannia (m)
Total flows at Wilcannia (incl.
Talyawalka Ck) (GL)
Max height Weir 32 (m)
1988 12.57 3,500 10.19 2,900 5.10
1990 12.99 9,000 11.0 8,150 7.37
1998 13.78 9,700 10.83 6,700 7.45
2001 12.28 3,300 9.75 2,250 6.21
2010 10.78 2,370 9.43 2,400 5.44
2011 12.56 5,800 10.5 5,000* 7.10
* Predicted values
ENVIRONMENTAL MANAGEMENTLake Wetherell is now at 93 per cent of capacity and rising after a period of drawdown to around 50 per cent of capacity. Lakes Pamamaroo, Menindee and Cawndilla are currently at 120 per cent, 104 per cent and 103 per cent respectively. All the lakes will continue to rise into April to near maximum surcharge capacity. Given that the high flows in the Murray River are continuing, the lakes will probably remain high into winter.
Flows are continuing to pass into the many lakes and billabongs of the Talyawalka system and the surrounding landscape is still being watered from periodic storms. Healthy flows are being observed in flood-runners that rarely receive water and the aerial imagery shows expansive areas of growth in native vegetation.
The Anabranch continues to flow its full length to the Murray, replenishing water storages and refuge pools along the way and providing connectivity of riparian vegetation and native habitat. Nearly all the lakes along the Anabranch have received water, most for the first time in 10 years. Lakes Nearie and Popiltah continue to receive water while Travellers Lake, Mindona Lake and Popio Lake can be seen near full in the bottom left hand corner of Figure 1.
There has been substantial inundation of floodplains along the Darling River during this event. As flows recede back to within channel, and floodplains begin to drain back to the river, there is potential for ‘blackwater’ to be produced. Blackwater is a natural phenomenon that is high in carbon and depleted of oxygen caused by the breakdown of organic material. If it makes its way into weir pools or refuge pools where it cannot be diluted and fish cannot escape, they may suffocate and die.
Extensive blackwater events have occurred from flooding along the Murray River this year, and a recent occurrence has been observed in the Darling River at Bourke.
The NSW Office of Water is ensuring that water quality instrumentation is distributed and accessible in key locations along the river to provide early detection of low dissolved oxygen levels and potential blackwater, particularly in the wake of the current Darling River floods.
www.water.nsw.gov.au NSW Office of Water | Issue 7 – March 25, 2011 page 6
Management of Menindee Lakes 2010-2011 – March 25, 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.
NO
W 11_100
The improved flow in the Lower Darling is attracting increasing numbers of larger vessels as visitors enjoy access to this region by boat. Boat owners are asked to minimize the wash from vessels as this can be damaging to riverbanks, and especially so as water levels begin to fall. Saturated river banks are heavy and vulnerable to damage (slumping).
COMMUNICATION AND ADDITIONAL INFORMATIONFlows and water levels are being closely monitored and information will be updated and distributed by the NSW Office of Water and State Water fortnightly, or more frequently if necessary.
A regional committee that includes representatives of water users from the Menindee, Lower Darling and Great Anabranch has been established. The committee convenes weekly to ensure that local knowledge and conditions are incorporated into flow management strategies and that appropriate information about river levels and flow management is made available to the community.
The NSW Office of Water and State Water Corporation will continue to work with the SES, local police and councils as required.
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
