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River Murray operations 17-24 August 2016

Welcome to our report on river operations in the Murray for the river week ending 24 August 2016.

You can find the full weekly report including more rainfall and inflow figures, pics, graphs and data as a word or PDF document under the river info section of our website.

Rainfall and inflows

Last week, the highest weekly total in Queensland was 89 mm in the East Darling Downs. The highest in New South Wales was 89 mm at Glenn Innes.

In the southern Basin, Perisher Valley received 52 mm while in Victoria the highest totals were in the upper ranges with 134 mm recorded at Mt Buller. In South Australia, 34 mm fell at Pinnaroo.

Over the coming 8 days the Bureau of Meteorology is forecasting in excess of 25 mm for much of the basin with some regions forecast to receive over 50 mm.

Rainfall over the weekend increased stream flows in the Murray tributaries. Significant streamflow rises could be expected if the rainfall forecast by the BoM eventuates. See the full weekly report for more details.

Total in storage

MDBA total storage increased by 165 GL this week, with the active storage now 5,133 GL (61% capacity).

River operations

  • Unregulated flows continue in the Murray system

  • Environmental water releases from Hume cut back

Unregulated flows are currently available in the Murray and Edward River systems downstream of Hume Reservoir. Forecast rain may permit an extension of unregulated flows in the Murray downstream of Hume. The unregulated flows are providing extra opportunities for environmental watering along the Murray. Environmental managers and system operators are working closely to achieve the best possible overall environmental outcomes from the Barmah-Millewa Forest down to the Coorong.

At Dartmouth Reservoir, the storage volume increased by 27 GL to 2,177 GL (56% capacity). The release from Dartmouth was around 1,200 ML/day due to the release of AGL entitlement water for hydroelectricity generation, but has now been reduced back to the minimum release of 200 ML/day.

At Hume Reservoir, the storage volume increased by 121 GL to 2,596 GL (86% capacity). MDBA may soon commence ‘airspace management’ releases aimed at providing a measure of flood protection, balanced against ensuring Hume fills to maximise water availability prior to demand emerging.

In recent weeks Hume Dam has provided considerable flood protection to communities downstream. However, as the storage approaches its full supply level (3,005 GL), the dam will have reduced capacity to mitigate future floods. Further details about flood management at Hume Dam are available on the MDBA website. Regular updates on Hume storage levels and releases will be provided in future weekly reports, however communities are reminded that all Flood Watches and Warnings are issued by the Bureau of Meteorology. In addition, community members living close to the river downstream of Hume Dam are reminded of the WaterNSW Early Warning Network (EWN) service. This service alerts people when the River Murray increases to relatively high levels in the stretch downstream of Hume Dam to Albury via SMS, email or voice message notifications. More information including how to register are provided on the WaterNSW website.

Environmental water releases from Hume Reservoir have been supplementing inflows from the downstream Kiewa and Ovens rivers to enable releases from Yarrawonga Weir to target a maximum downstream Tocumwal height of 3.0 m. This maximum target at Tocumwal is aimed at maintaining low level inundation of the downstream Barmah-Millewa forest. The release of environmental water from Hume is being ceased as weekend rainfall increased the inflows from the Kiewa and Ovens rivers. These natural inflows may result in the level at Tocumwal increasing above 3.0 m in the coming days. Releases of environmental water from Hume may be restarted later in the week if the forecast height at Tocumwal falls below 3.0 m.

Releases from Yarrawonga Weir have fluctuated around 15,000 ML/day this week and are currently near 15,900 ML/day. The release is expected to remain around this rate over the coming days.

On the Edward River, the flow through the Edward Offtake has gradually receded to 1,850 ML/day while the Gulpa Offtake has receded to 650 ML/day. Downstream at Toonalook, the flow has fallen from around 10,000 ML/day down to 5,200 ML/day this week and is forecast to continue receding this coming week.

At Stevens Weir, the gates are being reinstalled and the downstream flow has dropped to around 4,200 ML/day. Over the coming week the flow is expected to further reduce. Downstream on the Edward River at Moulamein the flow is at 6,600 ML/day and close to a peak, while small returns from the natural flooding of the Koondrook-Perricoota Forest are entering the Wakool River through Thule and Barbers Creeks. The Wakool at Stoney Crossing continues to rise and is expected to peak this coming week. At Kyalite the flow is 11,100 ML/day and rising, with a peak expected in the coming days.

Inflows to the Murray from the Goulburn River receded this week to 3,700 ML/day at McCoys Bridge before increasing to 4,300 ML/day and are expected to rise to around 4,500 ML/day. On the Murray at Torrumbarry Weir, the weir pool is currently 85.80 m AHD (25 cm below FSL) and will be raised to 85.90 m AHD next week before returning to Full Supply Level (FSL) in the coming weeks. The downstream flow has receded to 22,300 ML/day and will continue to fall away this week.

Gunbower and Koondrook-Perricoota Forest have been naturally inundated since early August due to the high flows at Torrumbarry. Inundation of these sites would have been significantly higher without regulation.

At Balranald on the Murrumbidgee River, the flow has reduced from 8,400 ML/day to 7,600 ML/day and is expected to remain close to this rate over the coming week. Downstream on the Murray at Euston, the flow has increased to 35,600 ML/day and is expected to peak this week. Euston weir pool is currently around 20 cm below FSL but may be increased closer to FSL in the next couple of weeks.

A near-full Murrumbidgee River looking upstream towards the Balranald Weir. Photo: Sophie Gatacre - WaterNSW

On the Darling River at Menindee Lakes the storage increased 21 GL to 182 GL (11% capacity).

Releases from Lake Wetherell into the lower Darling River commenced 29 July. Flows at Weir 32 are currently near 150 ML/day. Further downstream, the flow at Burtundy peaked at 1,200 ML/day last week before reducing to the current rate of 650 ML/day. The flows from the lower Darling have now reached the Murray at Wentworth (see Photo 2). Given the high flows in the Murray, only a minor and short-lived rise in salinity is expected as the flow front from the Darling passes downstream into South Australia.

Lower Darling
Flows from the lower Darling have reached the Murray at Wentworth. Photo courtesy of NSW Department of Primary Industries.

On the Murray at Lock 9 the weir pool is currently 12 cm above FSL and at Lock 8 the weir pool is 50 cm above FSL. The river is flowing freely through Lock 7 as the stop logs have been fully removed. The higher flows are resulting in the current river height being around 80 cm above FSL. The gates at the Mullaroo offtake regulator have been laid flat to maximise the flow into the Mullaroo Creek.

The total storage at Lake Victoria was reduced by 4 GL this week to 554 GL (82% capacity). MDBA has lowered Lake Victoria over the last month to minimise disturbance to Aboriginal cultural heritage material. MDBA operates in accordance with the Lake Victoria Operating Strategy (LVOS), which requires the period of time that the water level in Lake Victoria is held high to be minimised in order to limit erosion and allow for revegetation to protect important cultural heritage. The MDBA has now reduced the outflows from, and begun increasing the inflows to, Lake Victoria in order to fill the lake by the end of the current unregulated flow event. If forecast rainfall does eventuate then it is possible that unregulated flows may extend which would further delay the filling of Lake Victoria. MDBA will continue to assess the upstream inflows to determine operations at Lake Victoria.

The flow to South Australia averaged 29,300 ML/day this week and is expected to be slightly lower over the coming week.

Lock 6 will be progressively raised by up to 50 cm to ensure flow through the Chowilla anabranch is maintained. This raising of the Lock 6 water level is important for the management of water quality and protection of important habitat for native fish.

Downstream at the Lower Lakes, flows through the barrages continue, albeit at lower rates than last week. Releases are being made to help improve water quality in Lake Albert and the Coorong, and to assist in scouring sand from the Murray Mouth. The 5-day average water level in Lake Alexandrina increased this week to 0.82 m AHD.

Periodic reductions in the water level in Lake Alexandrina enables the higher salinity water of Lake Albert to drain out. Subsequent raising of Lake Alexandrina allows fresher water to then flow back into Lake Albert. The current lake level cycling operation has been made possible by favourable tidal and weather conditions combined with the assurance of high unregulated flows passing over the SA border which enables the Lower Lakes to be raised again in the future. Salinity levels at Lake Albert have already decreased significantly in recent months, down from an average of around 2,250 EC (μS/cm) in April 2016 to current levels of around 1,800 EC (μS/cm). It is anticipated that there could be further reductions in Lake Albert salinity levels as a result of current operations.

Homepage Image: 
Lower Darling
Site Context: 
Grid View Image: 
Lower Darling
Published on: 
Friday, August 26, 2016

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