River Murray operations 19- 26 July 2017

28 July 2017

Welcome to our summary report on River Murray operations for the week ending 26 July 2017.

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

Rainfall and inflows

Rainfall was scarce across the northern Basin this week. In the south, weak cold fronts delivered rainfall that was mostly confined to the Victorian and southern New South Wales ranges. In Victoria, 49 mm fell at Mt Buller and 47 mm at Mt Buffalo, whilst 27 mm was recorded at Cabramurra in New South Wales.

This week’s rainfall provided only minor streamflow responses in the upper Murray tributaries. The upper Mitta Mitta River at Hinnomunjie averaged around 500 ML/day, while the upper Murray at Biggara averaged close to 700 ML/day. These flow rates are quite low for this time of year, reflecting the below average rainfall experienced in June and so far in July.

Downstream of Hume Reservoir, inflow from the Kiewa River to the Murray was 1,500 ML/day, while in the Ovens, the flow at Wangaratta increased slightly from 1,750 ML/day at the start of the week to close to 2,350 ML/day.  

Mitta Mitta
Source: Hugo Bowman, MDBA.
The Mitta Mitta arm of Hume Reservoir slowly filling.

Total in storage

MDBA total storage rose by 35 GL this week, with the active storage now 5,805 GL (68% capacity).

River operations

Over the last fortnight, the Executive Director of River Management and the General Manager of Assets completed the annual inspection of the major water assets in the River Murray System. Following the inspection, the Senator J S Collings trophy was awarded to the most effectively maintained asset - Dartmouth Dam (see Photo 1). Congratulations to the team at Dartmouth who continue to develop and implement innovative engineering solutions to maintain or replace a range of asset components.

  • At Hume Reservoir, the storage increased by 36 GL to 2,265 GL (75% capacity). Increases to Hume storage are continuing to be driven by the consistently high releases from the Snowy Hydro Scheme. 
  • Given the dry conditions experienced in June and July, MDBA is planning to commence transfers from Hume to Lake Victoria in the next week to ensure Lake Victoria has sufficient volume to supplement downstream demands during the peak of the irrigation season. 
  • At Yarrawonga Weir, releases have followed the estimated natural flow and were increased to 7,500 ML/day before reducing to 7,200 ML/day. The additional releases to protect winter base flows downstream in the River Murray have been made on behalf of environmental water holders. Releases of this magnitude are likely to be sustained over the coming weeks as transfers from Hume to Lake Victoria commence. Diversions to Yarrawonga Main Channel remained low this week. Diversions to Mulwala Canal are expected to commence next week in anticipation of early season irrigation demands.
  • Downstream of Yarrawonga Weir, the regulators into the Barmah-Millewa forest remain open to facilitate a winter watering of the forest. This watering action will benefit native fish and improve the transfer of valuable nutrients from the floodplain to the river to increase ecosystem productivity. Water used in the forest is being debited from water accounts held by the environmental water holders.
  • On the Edward River system, the gates at Edward and Gulpa Offtakes remain clear of the water. Flows through the Edward and Gulpa offtakes are currently near 1,000 ML/day and 300 ML/day respectively and may continue to vary over the winter period in response to river level fluctuations in the Murray at Picnic Point. At Stevens Weir, the pool level has remained around 4.0 m (local gauge) with the downstream release averaging 750 ML/day.
  • The environmental pulse in the Goulburn River continues to recede. The flow at McCoy’s bridge has fallen to around 1,300 ML/day and is expected to decrease to 1,000 ML/day over the coming days. The environmental flows in the Goulburn River were planned by the Goulburn Broken CMA. More information can be found on the GMW factsheet and the Goulburn Broken CMA website.
  • The Torrumbarry weir pool level is 85.96 m AHD and will be raised to 86.0 m AHD (5 cm below full supply level (FSL)) in the coming days. The current flow over the weir is around 5,000 ML/day, and is expected to average a similar rate over the coming week. Diversions into National Channel remain around 450 ML/day to maintain winter base flows along Gunbower Creek for the benefit of native fish. Next week diversions to National Channel are expected to increase to 1,500 ML/day in order to fill irrigation channels and storages within the irrigation district in readiness for the start of the irrigation season.
  • The flow in the Murrumbidgee River at Balranald averaged just under 1,200 ML/day and is likely to remain relatively steady over the coming week. Around mid-August the flow at Balranald is expected to increase as a ‘river fresh’ is delivered along the Murrumbidgee targeting a flow rate of 20,000 ML/day upstream at Wagga Wagga. The aim of the fresh is to improve the health of wetlands along the mid-Murrumbidgee River as well as deliver instream benefits throughout the mid and lower Murrumbidgee River system. This event is expected to deliver significant inflows, at within-channel rates, to the Murray in August. Further environmental benefits will accrue as the flows are passed down the Murray to South Australia. Further information is available on the NSW Office of Environment & Heritage website.
  • At Euston weir, the pool level is currently 47.36 m AHD (24 cm below FSL). The pool level is expected to be varied over the coming weeks as part of the weir pool variability program. The downstream release has continued to reduce this week and is now below 10,500 ML/day and will recede towards 8,000 protML/day in the coming days.
  • On the Darling River, the total storage volume in the Menindee Lakes decreased by 6 GL to 759 GL (44% capacity). Inflows to the lakes continue at low rates, with the upstream flow at Wilcannia around 300 ML/day. Releases from Menindee Lakes to the Lower Darling River at Weir 32 continue to target 400 ML/day. This release is above the minimum release for this time of year (200 ML/day) due to the release of environmental water to benefit native fish in the lower Darling.
  • At the junction of the Darling with the Murray, releases from Wentworth weir peaked at 12,000 ML/day before decreasing to 10,500 ML/day. The flow will continue to recede over the next week as the peak from the Goulburn pulse travels further downstream. Small flows continue to enter the Murray from the Great Darling Anabranch.
  • Lock 9 remains close to FSL while Lock 8 is almost 100 cm below FSL and Lock 7 around 25 cm below FSL. Varying pool levels helps restore a more natural wetting and drying cycle to riverbanks and adjacent wetlands within the influence of the weir pool.
  • At Lake Victoria, the storage volume increased by 2 GL to 424 GL (63% capacity). Over the coming months MDBA will manage the filling of Lake Victoria in line with the Lake Victoria Operating Strategy. The strategy aims to maximise water security whilst minimising the impact on vegetation and aboriginal cultural heritage sites around the lake.
  • The flow to South Australia reached 11,500 ML/day a week ago influenced by environmental water from the Goulburn pulse event. Flow has since decreased to around 10,000 ML/day. Further recessions of flows are expected to continue into August.
  • At the Lower Lakes, the 5-day average water level in Lake Alexandrina increased by 4 cm to 0.75 m AHD. Releases through the barrages were managed to avoid intrusion of seawater during high swells and tides, whilst providing an attractant flow for pouched lamprey which characteristically migrate upstream at this time of year to breed.

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