River Murray operations 12-19 July 2017

21 July 2017

Welcome to our summary report on River Murray operations for the week ending 19 July 2017.

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

Rainfall and inflows

At the start of the week, a cold front delivered light to moderate isolated falls to eastern South Australia. This was followed by a second cold front combined with a complex low producing widespread rainfall and some thunderstorms along the southeast coast of South Australia, across much of Victoria and into southeast NSW.

In the north, the middle of the week saw a mid-level trough and associated surface trough strengthened, resulting in light to moderate falls in northern NSW and Queensland.

Whilst rainfall totals in the Riverina and Murray Lands were small, between 15- 80 mm of rainfall was recorded across the Australian Alps for this week. Despite these falls, a limited streamflow response was observed this week.

The Mitta Mitta River at Hinnomunjie Bridge rose only 300 ML/day to a peak of 680 ML/day. The upper Murray at Biggara peaked around 1,000 ML/day while the Ovens River, measured at Rocky Point, increased to 1,400 ML/day.

Overall, streamflow responses are much lower than this time last year reflecting dryer catchment conditions.

Lamprey
Photo: SARDI
Sampling of pouched Lamprey at the barrages.

Water Availability

On the 17 July, NSW Murray general security allocation increased by 2 per cent and is now 13 per cent of entitlement for the 2017/18 water year. With an average carryover of about 42 per cent, the overall general security water availability is 55 per cent of entitlement. High security allocations remain at 97%.

In Victoria, high-reliability water shares in the Murray and Goulburn systems remain unchanged at 66% and 36% respectively.

Given the reasonable water availability and the below average rainfall over irrigation districts during June and July so far, diversions for irrigation are expected to start early this water year.

Total in storage

MDBA total storage rose by 40 GL this week, with the active storage now 5,771 GL or 67% capacity.

River operations

  • At Dartmouth Reservoir, the storage volume increased by 2 GL to 3,028 GL (79% capacity). Releases from Dartmouth, measured at Colemans gauge, continued at the minimum flow rate of 200 ML/day.
  • At Hume Reservoir, the storage increased by 40 GL to 2,229 GL (74% capacity). Increases to Hume storage are continuing to be driven by the consistently high releases from the Snowy Hydro Scheme.
  • The release from Hume averaged around 2,000 ML/day this week and varied in response to forecast rainfall and environmental targets downstream of Yarrawonga. Releases above the minimum are meeting winter environmental flow targets in the Murray downstream at Yarrawonga Weir. The additional releases to protect winter base flows downstream in the River Murray have been made on behalf of environmental water holders.
  • Over the coming week, releases from Hume Dam will vary to mimic natural flow conditions downstream of Yarrawonga up to 10,000 ML/day (channel capacity). This water would be released on behalf of the Commonwealth Environmental Water Holder for the purpose of providing environmental benefits along the length of the Murray.
  • At Yarrawonga Weir, the pool level is 124.81 m AHD (9cm below full supply level (FSL)). With dry conditions persisting diversions through Mulwala and Yarrawonga Main Channel are expected to begin in early August. Murray Irrigation is considering opening the Mulwala Canal Offtake on Monday 24 July and the Wakool Main canal offtake on Monday 31 July for channel filling purposes.  Releases from the Yarrawonga weir averaged 5,200 ML/day downstream this week.
  • Downstream of Yarrawonga Weir, the regulators into the Barmah-Millewa forest were opened last week. Traditionally these regulators were only opened when river flows downstream of Yarrawonga would result in the Barmah Choke channel capacity being exceeded. This new operation will provide connectivity between the river and the floodplain in winter and into spring when river flows are below channel capacity. This will benefit native fish and improve the transfer of valuable nutrients from the floodplain to the river to increase productivity. 
  • 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 800 ML/day and 250 ML/day respectively and will 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 is around 4.0 m (local gauge) and will vary between 3.8 m and 4.0 m over winter to provide connectivity for fish and protect instream habitat in the Colligen and Yallakool Creeks and downstream in the Wakool River. 
  • On the Goulburn River, the flow at McCoy’s bridge continued to recede this week and is currently 3,200 ML/day. The flow is expected to continue to recede towards 1,000 ML/day over the coming week. The environmental flows in the Goulburn River have been planned by the Goulburn Broken CMA. More information can be found on the GMW factsheet and the Goulburn Broken CMA website.
  • On the Campaspe River, the small environmental flow passing Rochester has receded to 100 ML/day.
  • At Torrumbarry the weir pool level is 85.84 m AHD. This is 21 cm below the FSL in accordance with the weir pool variability program. The weir will be gradually raised during July to around 86.0 m AHD (5 cm below FSL). Diversions into National Channel continued at around 420 ML/day to maintain winter base flows along Gunbower Creek for the benefit of native fish. With the Goulburn flows receding, the flow over Torrumbarry Weir has reduced to 8,500 ML/day and is forecast to recede to around 6,000 ML/day over the coming week.
  • Inflow from the Murrumbidgee River averaged 1,400 ML/day this week. Environmental agencies are planning to deliver a ‘river fresh’ along the Murrumbidgee River and Yanco Creek systems starting later in July. The fresh includes targeting a flow rate of around 20,000 ML/day at Wagga Wagga.  
  • At Euston weir, the pool level is currently 47.35 m AHD (25 cm below FSL). The pool level is expected to be varied over the coming weeks, also as part of the weir pool variability program. The release downstream of Euston weir peaked at 12,200 ML/day on Monday and has receded to 11,800 ML/day.
  • Downstream of Euston at Hattah Lakes, pumping of environmental water into the lakes continues at pump capacity of 1,000 ML/day. Pumping around this rate is expected to continue until early October 2017. Delivery of this water will build upon the ecological outcomes resulting from the natural flooding that occurred in 2016, and continue to improve the ecological health of this wetland system.
  • On the Darling River, the total storage volume in the Menindee Lakes decreased by 2 GL and is currently 765 GL (44% capacity). Inflows to the lakes are continuing at low rates, with the daily flow, measured at Wilcannia, around 400 ML/day. Releases from Menindee Lakes to the lower Darling River at Weir 32 are currently 400 ML/day. This is above the normal minimum of 200 ML/day at this time of year. The additional water is being released on behalf of environmental water holders to benefit native fish in the lower Darling River.
  • At the junction of the Darling and Murray rivers at Wentworth, flow has increased to 12,000 ML/day. Downstream of the weir, inflows from the Great Darling Anabranch continue at very low rates.
  • Lock 9 is currently at FSL while at Locks 8 and 7, the pool levels are currently 96 cm and 20 cm below FSL respectively. Pool levels are varied to help 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 remained at 423 GL (62% capacity) this week. 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.
  • This week, flow to South Australia increased to 11,500 ML/day. The increase in flow is largely due to the peak of the Goulburn environmental water pulse flowing across the border. The flow is expected to 
  • Remain around 10,000 ML/day over the coming week. Whilst flow to South Australia is higher, South Australia’s Department of Environment, Water and Natural Resources (DEWNR) is planning to undertake modest weir pool lowerings of 8 cm (within normal operating ranges) at Locks 2, 5 and 6 during July for ecological benefits. Further information can be found at DEWNR’s WaterConnect website and media release.
  • At the Lower Lakes, the 5-day average water level in Lake Alexandrina decreased by 1 cm to 0.71 m AHD. Releases through the barrages were stepped up early in the week to over 10,000 ML/day. A key objective of this pulse was to provide an attractant flow for pouched lamprey which characteristically migrate upstream at this time of year to breed.

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