The new ‘water year’ has began! Read this week’s full weekly report about water volumes and expected upstream and downstream water intakes. Have a peek at the May 2012 summary while you’re at it!
MDBA active storage increased by 69 GL this week and is now 7,626 GL (89%). The beginning of June and the start of winter marks the transition to a new ‘water year’ for the River Murray system and the commencement of the winter-spring period is typically when tributary inflows increase and headwater storages are 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 usual hydrological and demand cycle.
The 2011-12 water year saw a notable deviation from this cycle, and like the 2010-11 year, was characterised by rain and inflow patterns that were considerably different from the long term average (see diagrams on page 7). Most notably, record rainfall and system inflows took place during late summer and early autumn 2012 when in a more typical year the system is drying out. These weather and inflow conditions have pushed water storages in the River Murray system to very high levels for this time of the year. Since the addition of Dartmouth Reservoir to the suite of River Murray system storages in 1979, the ‘end of May’ total combined volume held in Dartmouth, Hume, Menindee and Lake Victoria has never been higher than at the end of the 2011-12 water year.
At Dartmouth Reservoir, the storage volume increased over the last week by 40 GL to 3,270 GL (85% capacity). High inflows are expected at Dartmouth over the coming week however the storage is expected to increase by another 1% during this period. The chance of Dartmouth spilling this winter/spring has now increased to about 50%, which is relatively high given that Dartmouth has only spilled 6 times since it was completed in 1979 (with no spill since 1996). The release, measured at Colemans remains at 200 ML/day.
At Hume Reservoir, the storage increased by 34 GL to 2,747 GL (91% capacity). Release remained at the minimum value of 600 ML/day. However with inflows now increasing, the release at Hume is expected to be increased to about 5,000 ML/day in the coming days to manage airspace heading into winter. MDBA will review short and long-term rainfall outlooks on a daily basis throughout the coming months in order to provide as much airspace for flood mitigation as practicable given Hume’s primary role as a water conservation storage. Downstream communities are reminded that with the storage near full, heavy rainfall would result in significant flooding, and that the operation of Hume Dam cannot always provide the level of protection achieved in recent years when the level was well down prior to major inflows. June 2012 is FloodSafe Month; see the SES NSW site for more information on how you can be better prepared.
Downstream at Yarrawonga, the pool level in Lake Mulwala is currently 124.71 m AHD. The release at Yarrawonga Weir has decreased with the recession of inflows from the previous week’s rain and is currently 4,100 ML/day. The release is expected to be increased during the week as inflows once again rise following the latest rain.
On the Edward-Wakool System, flow through the Edward and Gulpa offtakes remains at low levels whilst works continue at Stevens Weir. Downstream at Toonalook, the flow has decreased to 370 ML/day and should continue receding towards 300 ML/day this week. The flow at Stevens Weir fell slightly during the week to around 500 ML/day and will likely continue falling next week . Downstream on the lower Edward and Wakool Rivers, flows are now receding at all gauges.
On the Goulburn River, the flow at McCoys peaked at 3,200 ML/day on 1 June but has since receded to the current flow of 2,000 ML/day. The flow should recede further in the coming days. At Torrumbarry Weir, the flow increased to a peak of 7,900 ML/day but is now receding as inflows from the Goulburn River decrease. The flow should decrease to below 7,000 ML/day later this week.
On the Murrumbidgee River, the flow at Balranald continues to recede, decreasing from 10,000 to 8,700 ML/day this week. At Euston, the recession continues and the flow is now 17,500 ML/day. The flow should decrease more slowly over the coming days before higher flows in transit from Torrumbarry temporarily halt the recession later in the week.
On the Darling River, the flow at Wilcannia has remained quite steady at around 3,400 ML/day this week and with extended base flows continuing in the upper Darling tributaries, is expected to continue flowing steadily through the winter months even without any significant rain in the upper catchments. At the Menindee Lakes, inflow has averaged around 4,200 ML/day and the total storage volume decreased by 12 GL to 1,918 GL (111% capacity). Release from Menindee Lakes (measured at Weir 32) has been decreased to 4,000 ML/day. The release will continue to be reduced by around 250 ML/day each day over the coming week. Downstream on the lower Darling River, the flow at Burtundy is now falling away more quickly, with the flow decreasing from 17,800 to 11,400 ML/day over the last 7 days.
At Wentworth, the Murray receded to 34,400 ML/day and will decrease to below 30,000 ML/day this week. At Lake Victoria, outflow from the storage has been decreased in order to commence increasing the stored volume, which increased by 7 GL during the week to 365 GL (55%).
The flow to South Australia decreased to 30,000 ML/day, and will continue receding during the week ahead. Downstream at Lock 1, the flow has fallen away as expected and is now at 42,600 ML/day. At the Lower Lakes, the 5 day average level for Lake Alexandrina decreased to 0.72 m AHD (3 cm below full supply). Salinity levels in the Lower Lakes continue to fall slowly with on-going inflow from the Murray. Recent heavy local rainfall and water exchange between Lake Alexandrina and Lake Albert during high lake levels has also influenced salinity, with recent salinity measurements in Lake Albert decreasing to some of the lowest observed since early 2008.