River Murray operations 15-22 March 2017

24 March 2017

Welcome to our summary report on River Murray operations for the week ending 22 March 2017.

You can find the full weekly report under the River Murray system section of our website.

Rainfall and inflows

Heavy rain along Australia’s east coast pushed further inland this week with humid and unstable conditions affecting large parts of the Murray–Darling Basin. The stormy nature of the rain meant totals were patchy, with some gauges receiving significant falls, while nearby locations largely missed out. Conditions in the far west and South Australia were mostly dry.

The highest weekly totals in Victoria fell across the north and north-east and included 78 millimetres (mm) at Osbornes Flat, 67 mm at Mt Hotham, 53 mm at Wodonga and 36 mm at Tatura. Totals in NSW were highest over the northern tablelands and north-western plains and included 144 mm at Emmaville, 131 mm at Glen Innes, 100 mm at Condobolin, 98 mm at Pindari Dam and 76 mm at Walgett. Further south, totals included 82 mm at Forbes, 61 mm at Crookwell, 61 mm at Moulamein and 59 mm in the ACT at Tuggeranong. Totals in Queensland were heaviest over the Warrego catchment and the eastern Darling Downs and included 84 mm at Bollon, 72 mm at Beardy Junction and 61 mm at both Wallangarra and Glenorie.

There were modest increases to stream flows along upper Murray tributaries towards the end of the week that have raised rates marginally from base flow levels. On the Mitta Mitta River, the flow at Hinnomunjie bridge increased from around 150 to 500 megalitres per day (ML/day). On the upper Murray at Biggara, flows have increased from 200 to 500 ML/day. On the Ovens River, hot and mostly dry weather has meant flows during recent weeks have been at quite low rates - although at around 100 ML/day, the flow at locations such as Bright was still relatively good for the late summer period (see photo below). Following this week’s rain, flows have increased, with Bright’s current flow rate close to 200 ML/day. For contrast, peak flows at the Bright gauge during the flood period last October were in excess of 9,000 ML/day.

Total in storage

Total MDBA storage decreased 149 gigalitres (GL) this week, with the active storage now 5,684 GL (66% capacity).

River operations

System operations

Operations during recent weeks continue to focus on releasing sufficient water from storage to meet system demands and steer towards targets at key locations, including Lake Victoria; while also aiming to conserve water and deliver it efficiently. However, actual releases and river flows are highly affected by both forecast and observed weather and demand conditions. Current Bureau of Meteorology outlooks suggest warm and dry conditions are more likely during the autumn period, however uncertainty always remains and significant rain events always remain a possibility. These can alter prevailing conditions and change system trends quickly. With significant water able to be supplied from the Menindee Lakes and via trade deliveries from the Murrumbidgee and Goulburn valleys, release requirements from Hume Reservoir remain quite low compared to many other years.

This combination of factors may result in quite low and variable flows along the mid-reaches of the River Murray during coming weeks, including the Easter period. River users are therefore advised to maintain a close eye on conditions and keep up to date via the MDBA Weekly Report when planning recreational or other activities.

Current Operations

  • At Dartmouth Reservoir, the storage volume decreased by two gigalitres to 2,990 GL (78% capacity). The release from Dartmouth, measured at Colemans, was held at 300 ML/day throughout the week.
  • The Hume Reservoir storage volume decreased 73 GL this week and is currently 2,042 GL (68% capacity). Releases at the beginning of the week were increased to a rate of 18,000 ML/day in response to rising water orders downstream. This was Hume’s highest release rate so far in 2017. However, as forecasts for rain began emerging and then strengthened, the release was cut back over several days in anticipation of likely reductions to demands downstream. The release is now back at 7,800 ML/day, although higher releases are likely in a few days’ time if drier weather returns.
  • At Lake Mulwala diversions to Mulwala Canal and Yarrawonga Main Channel decreased considerably through the week as rain moved across irrigation districts. The diversion to Mulwala Canal decreased from 6,500 to 3,900 ML/day and may decrease further. Diversions to Yarrawonga Main Channel decreased from around 2,400 ML/day to 500 ML/day. In response to these rain rejections, the pool level has increased and is now at the normal maximum operating target of 124.90 m Australian Height Datum (AHD). Similar high pool levels are expected over the coming days before decreasing.
  • The release downstream of Yarrawonga Weir started the week at 8,000 ML/day but has since been increased to the current rate of 9,500 ML/day to help manage the pool level rise. The release remains below the downstream channel capacity of around 10,000 ML/day and will be stepped back towards 8,000 ML/day once conditions permit.
  • Inflows to the Edward-Wakool system have remained fairly steady throughout the week, with around 1,600 ML/day flowing through the Edward River Offtake and just under 350 ML/day through the Gulpa Creek Offtake. At Stevens Weir, there were high diversions into the Wakool Main Canal at the beginning of the week of around 1,300 ML/day, however these have since fallen back following the rain to around 1,000 ML/day. Downstream of Stevens Weir, the flow has increased slightly and is currently at 1,000 ML/day.
  • On the Goulburn River, flows at McCoys Bridge continue to recede with the current rate at 3,000 ML/day. This flow includes the tail end of an environmental delivery as well as a component of IVT water that continues to be delivered to the Murray. Flow rates of around 1,200 ML/day are expected by early April.
  • At Torrumbarry Weir, the pool remains at the full supply level (FSL) of 86.05 m AHD, while diversions to National Channel were decreased from around 3,400 to 2,800 ML/day. The downstream flow receded slightly during the early part of the week but has since increased to the current rate of around 6,000 ML/day in response to rainfall and the reduced National Channel diversion. The flow is expected to remain around 6,000 ML/day for a few more days before receding during early April. Actual flow rates during April will depend on the weather and resultant demand conditions that transpire.
  • On the Murrumbidgee River at Balranald, flows remained fairly steady at around 550 ML/day before a slight rise during the last couple of days. The current flow is 700 ML/day with similar rates expected during the coming week.
  • Downstream at Euston Weir, the pool level is currently 47.53 m AHD (7 cm below FSL) and will be further reduced to around 20 cm below FSL over the coming days as part of the weir pool variability program. The flow rate downstream of Euston has remained fairly steady at around 5,000 ML/day with similar rates expected in the coming days.
  • In the northern Basin, rainfall during the last couple of weeks has resulted in some reasonably significant streamflow responses along the upstream reaches of several tributaries. The Bureau of Meteorology has issued minor to moderate flood warnings for a number of rivers including the McIntyre, Moonie and Bogan. However, responses have been fairly short in duration and at this stage, volumes flowing into the Barwon-Darling River are expected to remain small unless there is further heavy rain in the coming days and weeks.
  • Downstream at the Menindee Lakes the total storage volume decreased by 36 GL to the current volume of 950 GL (55% capacity). The release from Menindee Lakes into the lower Darling River has decreased slightly with the flow at Weir 32 currently 1,900 ML/day. This release rate will be reduced during the coming week in response to changing forecast downstream requirements, with flows of 1,500 ML/day expected in a few days’ time. See the media release for more details. At the Lake Cawndilla outlet, the release by NSW is currently around 1,100 ML/day. The bulk of this release is environmental water for the Great Darling Anabranch and this action is expected to continue over the coming weeks.
  • At the confluence of the Darling and Murray Rivers at Wentworth, flows have remained steady. A flow of 5,700 ML/day has continued for several days. A slow recession is expected for the coming week.
  • Downstream at Lock 8, the weir pool level is currently 32cm below FSL. The pool level will remain around this level for a few more days. Starting late March, the pool level is expected to be gradually lowered again, to around one metre below FSL. At Lock 7, the weir pool level is currently 10 cm below FSL and will be varied around FSL for a few more days. Starting late March, the pool level is expected to be gradually lowered again, to around 90 cm below FSL by early April.
  • At Lake Victoria, the storage volume decreased by 38 GL to 376 GL (56% capacity). The level will continue to drop away during the coming week. The flow into South Australia peaked at 11,200 ML/day on 18 March with rates boosted by the delivery of environmental flow pulses released from upstream storages several weeks’ ago. The flow rate during mid-March has been a little lower than was previously expected due to additional trades of water out of South Australia to users upstream. Downstream at Lock 1, the flow increased to a peak of 7,400 ML/day on 21 March and is now slowly receding. The current flow is 7,100 ML/day.
  • At the Lower Lakes, the 5-day average water level in Lake Alexandrina decreased 2 cm to 0.59 m AHD. Releases through the barrages are continuing, although gates at Goolwa and Mundoo barrage have been closed at times to manage reverse flows of sea water due to high tides and large swells. This has reduced the total release, which has been around 4,000 ML/day during recent days.

Low flows Bright
Low flows Bright Will Lucardie
Low early autumn flows along the Ovens River near Bright have increased slightly following this week's rain. Photo courtesy Will Lucardie, MDBA.

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