River Murray operations 24-31 May 2017

2 June 2017

Welcome to our summary report on River Murray operations for the week ending 31 May 2017.

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

Rainfall and inflows

Most of the rain recorded this week fell along the southern ranges and in northeast New South Wales. The highest totals were recorded in the Southern Alps including 93 mm at Mount Buller AWS and 55 mm at Mount Buffalo. In South Australia, 26 mm was recorded at Meadows and Woodside and 22 mm at Mount Compass in the Lofty ranges. Little or no rain was recorded in Queensland and central and north western NSW. Rain across the upper catchments saw a rise in stream flows along upper Murray tributaries.

May 2017 Summary

Rainfall during May was mostly around average across much of the Murray-Darling Basin, although patchy areas scattered around the basin recorded rainfall above or below average. Overall, the BoM reports that area-averaged rainfall across the Murray-Darling Basin in May was 25.8 mm and that May 2017 was the 47th driest May in 118 years of records. Temperatures during May were mostly above average in the north of the Basin and average to below average in the southern Basin. The BoM reports that the Australian mean daily maximum temperature in May 2017 ranked equal 9th warmest on record, however this was influenced by warmer temperatures in the north and west of Australia. River Murray system inflows during May totalled around 168 GL, which is below the month’s long-term median of 281 GL. In comparison with the historical record since 1891, only about 22% of previous monthly totals for May have been lower than the inflows observed in May 2017. Rainfall during May resulted in a small net gain (negative evaporative loss) at Hume storage.

Autumn 2017 Summary

Rainfall was average to above-average across most of the Murray-Darling Basin in autumn 2017. Across the Basin as a whole, the BoM reported area-averaged rain for autumn 2017 totalled 115.7 mm, ranking it the 81st wettest autumn out of 118 years of records. Temperatures across the Basin were generally above average during autumn. The BoM reports that the Australian mean daily maximum temperature ranked 7th warmest on record. Autumn inflows to the River Murray System totalled around 498 GL, compared with the long term median of 624 GL. In comparison with the historical record since 1891, only about 38% of previous autumn totals have been lower than the inflows observed in autumn 2017.

Autumn rainfall
Source: Bureau of Meteorology
Murray-Darling Basin rainfall across autumn 2017

2016-17 Water Year Summary

The beginning of June marks the transition to a new ‘water year’ for the River Murray system as the commencement of the winter-spring period is typically when tributary inflows increase and headwater storages begin to be replenished. The water year is used by the MDBA to manage and report on system inflows, demands and storage levels across a 12 month period in a way that best matches the system’s hydrological and demand cycle.

Rainfall

Rainfall in 2016-17 was above average across most of the Basin. 2016-17 was significantly wetter than 2015-16 and the wettest year basin-wide since 2011-12. Of particular note, rainfall for the winter and spring period was ‘very much above average’ across most of the Basin with highest on record totals across large parts of central New South Wales and in a small area of the Victorian Alps. In addition, September 2016 was the Basin’s wettest September on record. More information is available in the BoM’s Special Climate Statement 58 – record September rains continue wet period in much of Australia. Rainfall over summer and autumn was closer to average, although South Australia, western Victoria and northeast NSW were generally wetter than average, whilst western Queensland and north western NSW were drier than average (Map 7).

Temperature

Overall, temperatures across much of the Basin were above average for the 2016-17 water year. While conditions during spring 2016 were generally cooler than average, summer 2016–17 saw prolonged and, at times, extreme heat across the Basin. Temperatures in January and February were notable due to the maximum temperatures reached and the record period of consecutive days of high temperatures above threshold values. More information is available in the BoM’s Special Climate Statement 61—exceptional heat in southeast Australia in early 2017. Temperatures in March 2017 were also notable with some parts of north central Victoria recording their highest on record mean March temperatures.

Inflows

River Murray System inflows during 2016-17 water year were around 14,800 GL – almost twice the long-term median of around 8,000 GL putting 2016-17  in the wettest 14% of years on record. By comparison, inflows in 2015-16 totalled 3,050 GL with 4,400 GL in 2014-15. Inflows to Menindee Lakes were around 1,800 GL putting 2016-17 in the wettest 30% of years on record. This follows three years of almost no inflows. By comparison, the long-term median inflow is 865 GL. 

Active storage

MDBA active storage started the 2016-17 water year at 2,560 GL, or around half the long-term average for start of June. Significant inflows over winter and spring increased the water in storage to a peak of 7,400 GL in mid-December 2016. Over the remainder of the water year the total active storage reduced to 5,470 GL by the end of May 2017. This is around 400 GL more than the long-term average for this time of year. On 1 June 2016, water in storage at Menindee was only 49 GL as a result of extremely low inflows for three years in a row. However, significant inflows during the second half of 2016 refilled Menindee storage to a peak of 1,585 GL in mid-December. This is around 150 GL shy of the full supply volume (1,730 GL). Releases during 2016-17 to supply demands in the lower Darling and the River Murray system, along with evaporation losses and releases to the Anabranch reduced the water in storage to 780 GL by the end of May.

Operations

With a relatively low volume of water in storage following dry conditions in 2015-16, operations at the start of winter were initially focused on storing water. However, operations soon transitioned to airspace management at Hume Reservoir as rainfall and resulting runoff continued into spring. Flood operations at Hume Reservoir commenced in early September and continued until late November, with a peak release of 80,000 ML/day in early October. More details on operations across the system is in the full report.

Early Outlook for 2017-18

BoM’s 3 month outlook for June to August is generally for drier conditions over the southern half of Australia. However, there is no clear signal for the upper Murray catchment. Both the Pacific (ENSO) and Indian (IOD) ocean climate indicators remain ‘neutral’ however some models surveyed by BoM suggest a ‘late-onset’ El Niño which may suppress spring rains although these outlooks have been weakening over recent months.

Hume and Dartmouth storages are currently relatively full for this time of year (only 16% and 50% of years (respectively) have had higher storage volumes at end of May). Scenarios prepared by MDBA for planning purposes suggest that Hume Dam could fill later in spring 2017 if inflow conditions during winter and spring are near average or wetter (reasonably wet inflow conditions would be required to spill Dartmouth Dam). MDBA is meeting with local government and SES representatives in Albury in early June to discuss storage management at Hume Dam and the possibility of flooding over the coming winter-spring period.

With the volume in Menindee Lakes above 480 GL, water stored in the lakes could be available to the MDBA for release to meet River Murray system demands during the coming 2017–18 water year. When MDBA directs releases will depend on future inflows, evaporative losses, local use and Murray inflows and demands. MDBA remains committed to working with WaterNSW to ensure that as much of the 480 GL as is reasonably practicable is stored in the upper two lakes (Lakes Wetherell and Pamamaroo) when the 480 GL trigger is reached to maximise water available to meet Broken Hill and lower Darling critical needs.

In the southern Basin, opening water availability for 2017–18 is expected to be higher than last year. South Australia has announced that its River Murray water access entitlement holders will receive 100% of their allocation. Similarly, New South Wales has indicated that there is sufficient resource to assure full allocation for all lower Darling licence categories. NSW Murray and Murrumbidgee general security allocations are expected to commence with at least 4% and 9% of entitlement (respectively). When added with carry over, water availability for general security users could average close to 47% and 39% of entitlement (respectively). In Victoria, high reliability water holders are expected to start 2017–18 with 50% of entitlement or better in the Murray system and 30% of entitlement or better in the Goulburn system.

Total in storage

The total MDBA storage increased by 31 GL this week, and total active storage is now 5,471 GL (64% capacity).

River operations

  • At Dartmouth Reservoir, the storage volume increased by 6GL to 3,010 GL (78% capacity). The release from Dartmouth, measured at Colemans, remained steady at around 200 ML/day. The release will increase to around 1,200 ML/day from 1 June for the purposes of electricity generation. The duration of this increased release is dependent upon electricity demands over the coming days.
  • At Hume Reservoir, the storage volume increased by 31 GL to 1,960 GL (65% capacity). Releases from Hume Reservoir increased from 900 ML/day to 3,000 ML/day early in the week and are currently 2,200 ML/day. These releases are currently above the normal minimum of around 600 ML/day as additional water is delivered on behalf of the environmental water holders to maintain higher base flows in the Murray for the benefit of native fish.
  • At Lake Mulwala, the pool level is currently 124.68 m AHD. The level is expected to remain around 124.7 m AHD over the coming week. The release downstream of Yarrawonga Weir has increased to 4,200 ML/day and is expected to vary between around 3,800 ML/day and 4,200 ML/day in the coming week. This is well above the minimum flow rate of 1,800 ML/day which is likely to have been reached late this week without additional water being released from Hume to maintain the higher base flows.
  • Inflows to the Edward-Wakool system remained steady this week, with flows through the Edward River and Gulpa Creek offtakes currently around 430 ML/day and 150 ML/day respectively. With the regulator gates at these structures currently clear of the water, inflows to the Edward-Wakool system can be expected to fluctuate over winter in response to the changes in river levels downstream of Yarrawonga Weir. Flow downstream of Stevens Weir averaged 300 ML/day. The weir pool 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 in the Yallakool Creek and downstream in the Wakool River. Visit the WaterNSW website for more information.
  • On the Goulburn River, the flow at McCoys Bridge is targeting 940 ML/day, with water above the minimum flow of 350 ML/day being provided for the environment. An environmental flow pulse for the Goulburn River is currently planned for late June. More information will be provided in future weekly reports. On the Campaspe River, the flow at Rochester is around 60 ML/day.
  • At Torrumbarry, the weir pool level is currently at 85.85 m AHD, or 20 cm below the full supply level (FSL). In the coming weeks, as part of the weir pool variability program, the pool level is expected to be varied, with the level planned to decrease as much as 50 cm below FSL. Visit the MDBA website for more information.
  • Inflow from the Murrumbidgee River remained mostly steady at around 400 ML/day (measured at Balranald), but is now increasing. The flow will continue to rise and is likely to reach around 1,000 ML/day in the coming week.
  • At Euston Weir, the pool level has remained around the FSL (47.60 m AHD). The flow rate downstream of the weir has averaged 6,100 ML/day and is likely to ease below 6,000 ML/day over the coming week.
  • On the Darling River, the total storage volume in the Menindee Lakes decreased by 13 GL and is currently 779 GL (45% capacity). Inflows to the lakes are continuing at low rates, with the daily flow continuing to recede (currently around 500 ML/day measured at Wilcannia). Releases from Menindee Lakes to the lower Darling River at Weir 32 are continuing around 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. Releases from Cawndilla outlet decreased from 700 ML/day to 300 ML/day this week as part of the delivery of water to the Great Darling Anabranch for the benefit of native fish. These flows will continue to be gradually wound back with rates around 100 ML/day expected by late next week.
  • At the junction of the Darling and Murray rivers at Wentworth the flow is currently steady at around 6,700 ML/day. Downstream of the weir, inflows from the Great Darling Anabranch are slowly receding and contributing around 700 ML/day.
  • At Lake Victoria, the storage level is currently 24.5 m AHD (396 GL). Over the coming months, MDBA will manage the filling of Lake Victoria so that the storage volume peaks as late in the year as possible. This strategy aims to encourage the growth of foreshore vegetation and helps protect against erosional impacts on aboriginal cultural heritage, whilst maximising the storage available to help supply flow to South Australia during next summer and autumn.
  • Flow to South Australia reduced from 7,000 ML/day to 5,000 ML/day during the week as inflows to Lake Victoria were managed to target a lake level of 24.5 m AHD on 31 May in accordance with the Lake Victoria operating strategy. The flow to South Australia will gradually reduce to 4,000 ML/day over the coming days and remain around this rate for approximately two weeks. This steady flow is being targeted to facilitate ‘run-of-the-river’ salinity monitoring from the SA border to the lower lakes. This monitoring is typically undertaken annually and provides valuable information about the intrusion of salt into the River Murray. The results are used to calibrate salt modelling and help inform salt interception scheme (SIS) operations.
  • At the Lower Lakes, the 5-day average water level in Lake Alexandrina has increased to 0.66 m AHD. Barrage gates were mostly closed this week in order to manage reverse flows of sea water due to high tides and large swells. Only small releases occurred through Tauwitchere, briefly at the start of the week and again at the end of the week.

 

 

 


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