Welcome to our report on river operations in the Murray for the river week ending 7 December.
You can find the full weekly report including more rainfall and inflow figures, pics, graphs and data under the River Murray system section of our website.
Spring 2016 Summary
Regular frontal systems in combination with north-west cloud bands that streamed across from the Indian Ocean delivered above-average rainfall throughout most of the Murray-Darling Basin in spring 2016. Across the Basin as a whole, the Bureau of Meteorology (BoM) reported area-averaged rain for spring totalling 187.4 mm, 64% above the long-term seasonal mean. Temperatures across the Basin were below average during spring.
Following on from high winter inflows, spring inflows to the River Murray System (excluding Snowy Scheme, Darling River and managed environmental inflows) totaled around 8,500 GL, which is only exceeded in about 8% of years.
The peak flows inundated parts of the mid-Murray floodplain that had not seen water in over 20 years. Leaf litter that had accumulated over two decades subsequently leached high amounts of dissolved organic carbon into floodwaters. While such a process is a vital part of the riverine food web, assisting large-scale recruitment events, the magnitude of carbon released from this year’s flooding has resulted in widespread hypoxic blackwater throughout large parts of the River Murray system as well as the Lachlan and Murrumbidgee systems.
November 2016 Summary
November saw the return to near-average rainfall for much of the southern Murray–Darling Basin, and below average rainfall in much of the northern Basin. Overall, the BoM reported that area averaged rain for November was 22.3 mm, 44% below the long-term monthly mean. For the Murray catchments, this was the first month without above average rain since May this year. Temperatures across the Murray-Darling Basin were near-average in November.
With catchments wet from 6 months of above-average rainfall prior to November, November’s near-average rainfall still resulted in well-above average inflows. Inflows to the River Murray System during November (excluding Snowy Scheme, Darling River and managed environmental inflows) totalled just under 1,500 GL, well-above the month’s long-term average of around 790 gigalitres (GL).
Rainfall and inflows
Patchy light rain fell across much of the Murray-Darling Basin this week, with moderate falls mainly confined to areas of the Great Dividing Range. In Queensland the heaviest falls were in the East Darling Downs with 50 mm recorded at Stanthorpe. In New South Wales Emmaville received 38 mm while further south in Victoria 27 mm of rain fell at Lake Dartmouth. Only light rain was recorded in South Australia this week.
Relatively light rainfall in the upper Murray catchments provided only short-lived flow increases this week. Biggara on the upper Murray receded to 770 ML/day before briefly rising to 1,200 ML/day. At Hinnomunjie, on the Mitta Mitta River upstream of Dartmouth Reservoir, the flow has receded from 800 ML/day to 660 ML/day. The flow in the Ovens River at Wangaratta averaged 1,700 ML/day. With 10 – 25 mm of rainfall expected across the catchments on Thursday (8th December) some modest tributary rises are expected.
Total in storage
MDBA total storage increased by 117 GL this week to 7,385 GL (86% capacity). The bulk of this increase was due to continuing high inflows into the Menindee Lakes.
River operations
Yarrawonga releases to continue fluctuating around 15,000 ML/day for another week
Current flow peak enters South Australia
Releases gradually increased from the Menindee Lakes
Hypoxic ‘blackwater’ remains in the lower Murrumbidgee River, and on the Murray from the Murrumbidgee junction downstream into South Australia. Dissolved oxygen readings continue to improve in the Murray upstream of the Murrumbidgee junction and in the Edward-Wakool system. The MDBA, together with New South Wales, Victorian and South Australian agencies, will continue to monitor dissolved oxygen levels.
At Dartmouth Reservoir, the storage volume increased by 10 GL this week, to 2,973 GL (77% capacity). The release remains at the minimum flow of 200 ML/day at Colemans gauge.
The storage volume at Hume Reservoir decreased by 61 GL this week to 2,883 GL (96% capacity). Release from Hume Reservoir peaked at 21,000 ML/day this week before being gradually reduced to 13,200 ML/day as downstream demands wound back.
At Yarrawonga Weir, the release has fluctuated around 15,000 ML/day over the last few weeks and will remain near this rate until mid-December before being gradually reduced in the following weeks. These flows include environmental water which is aiming to provide benefits in Barmah-Millewa Forest and at sites further downstream.
Flows through the Edward River offtake have remained near 1,600 ML/day while the Gulpa Creek offtake has slowly receded to 650 ML/day. The flow at Toonalook on the Edward River continues to slowly recede, falling from near 4,700 ML/day at the start of this week to 4,350 ML/day.
Inflows to the Murray from the Goulburn River have gradually lowered to near 1,100 ML/day, while the Campaspe River is now contributing less than 100 ML/day.
The flow at Torrumbarry Weir has reduced from 11,000 ML/day to around 8,150 ML/day this week, but is expected to level out over the next fortnight. Diversions through National Channel are currently near 3,000 ML/day.
The flow at Swan Hill continues to recede, falling from near 14,000 ML/day to 9,300 ML/day, but is expected to steady later this week. With contributions from the Wakool River quickly receding, the flow in the Murray at Wakool Junction fell from 42,700 ML/day to 27,600 ML/day this week, and is expected to continue receding over the coming weeks.
On the Murrumbidgee River at Balranald, the flow has fallen from around 20,000 ML/day to 14,000 ML/day this week, and at this stage is expected to return to channel capacity in mid-late December. Downstream on the Murray at Euston, the flow has fallen to 59,000 ML/day and is expected to continue receding into the New Year. With levels quickly falling, the weir is scheduled to be reinstated from Thursday (8th December).
Flows continue to decrease at Mildura Weir, Wentworth Weir and Locks 7, 8 & 9. This recession will continue over the coming weeks with these weirs expected to be reinstated before Christmas. Further information about the reinstatement of these weirs will be provided in next week’s Weekly Report. For the latest flood warning for Wentworth, see the BoM website.
The volume stored in the Menindee Lakes increased by 143 GL this week to 1,544 GL (89% capacity). The release, measured at Weir 32, was increased from 710 ML/day up to around 1,750 ML/day. A portion of this water is environmental water aimed at supporting the growth and dispersal of Murray Cod that have spawned in the Lower Darling River over the past few months - see the media release from WaterNSW and a joint media release from the Commonwealth Environmental Water Office and the NSW government.
At Lake Victoria, the storage volume has increased by 24 GL this week to 659 GL (97% capacity), with current operations aiming to fill the lake in the coming weeks. A flow of 3,500 ML/day is being maintained through the outlet regulator to provide better quality water in Rufus River. These releases are aimed at providing some refuge for native fish from surrounding hypoxic conditions. Despite high volumes of hypoxic water entering Lake Victoria, monitoring across the lake has shown dissolved oxygen levels within the lake have remained relatively high. Dissolved oxygen readings downstream of the outlet of Lake Victoria (start of Rufus River) have remained above 4.5 mg/L over the last few weeks. In contrast, dissolved oxygen concentrations in the Murray upstream of the junction with the Rufus River have been below 1 mg/L for almost three weeks.
After peaking near 94,600 ML/day last week, the flow to South Australia has slowly receded to around 91,000 ML/day. The flood peak is expected to reach Lock 3 by 16 December and Lock 1 by 22 December—see DEWNR’s latest high flow advice.
The 5-day average level in the Lower Lakes is 0.77 m AHD with high barrage releases expected to continue to New Year.
Photo courtesy: Brian Twomey, NSW Department of Primary Industries
Water from the Rufus River mixing with hypoxic blackwater from the Murray.
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Published on:
Friday, December 9, 2016