River Murray Operations 6/3/15

[Member]

River Murray Ops Update – 6 March - MDBA   

Welcome to our weekly report of river operations on the Murray. This one takes a look back at February 2015 and covers the river week ending 4 March.


A look back at last month

February was a relatively hot and dry month across most of the Murray-Darling Basin. In the southern Basin, temperatures for the month were generally above average, with a large section of the Murray valley experiencing temperatures very much above average. Along with the heat, rainfall for February was below average throughout much of the Murray valley, as well as large sections of southern Queensland and north-east NSW. Across the Basin as a whole, the Bureau of Meteorology has reported area-averaged rain totalling 19.9 mm, which is 51% below the long-term February mean.



The PS Cumberoona being carefully navigated out of Wodonga creek (photo credit Fraser Knolls).

River Murray System inflows (excluding Snowy Scheme, Darling River and managed environmental inflows) were around 92 GL for February, which is approximately half the long-term monthly average. This inflow volume was almost identical to the inflow received in February 2014.

Estimated evaporation losses from MDBA storages for February 2015 are in the full river ops report. Lake Victoria is estimated to have lost similar volumes of water this month compared to January 2015, whilst Dartmouth and Hume are estimated to have lost slightly more compared to last month (4 GL and 3 GL respectively). Menindee Lakes is estimated to have recorded similar evaporation losses to last month. Lake Menindee, the largest of the four main lakes, is empty and recorded nil evaporation from storage. However, ongoing loss of moisture from the dry lake bed would have continued.


River operations

MDBA total storage decreased by 128 GL this week, with the active storage now 4,219 GL (50% capacity).

At Dartmouth Reservoir, the storage decreased by 10 GL to 3,038 GL (79% capacity). The release, measured at Colemans gauge, was reduced this week from 2,500 ML/day to 600 ML/day as bulk transfers of water downstream are no longer required. The release is expected to remain at 600 ML/day over the coming month.

At Hume Reservoir, the storage volume decreased by 77 GL to 1,110 GL (37% capacity). Releases from Hume this week were able to be scheduled to meet both downstream needs and assist the navigation of the paddle steamer ‘Cumberoona’ from a slipway in Wodonga Creek downstream to Lake Mulwala (see picture). The Murray-Darling Basin Authority considers community activities when undertaking river operations and aims to assist where operationally possible. The release from Hume is now being increased to around 20,000 ML/day in response to rising downstream demand.

A combination of factors led to a drop in the Lake Mulwala pool level over the week, which fell from 124.75 m AHD to 124.63 m AHD. Diversions from the major irrigation offtakes at Lake Mulwala started the week steady at around 5,000 ML/day, then quickly increased following the weekend up to 6,000 ML/day coinciding with reduced inflows arriving from Hume. Strong westerly winds experienced at Yarrawonga throughout the week pushed water from Lake Mulwala back upstream, resulting in reduced water levels at Yarrawonga Weir. Most of this water pushed upstream returns back to the weir pool once the winds either abate or change direction. Depending on prevailing winds, the pool level is expected to rise back above 124.70 m AHD by Sunday. This phenomenon of a water body fluctuating in height due to outside forces is known as a ‘seiche’, and can occur at all major water storages. Primary drivers for seiches include strong winds, intense inflow events, and earthquakes. Releases from Yarrawonga Weir for the coming week are planned to be between 9,000 ML/day and 10,000 ML/day.

On the Edward River system, the combined flow through the Edward River and Gulpa Creek offtakes is steady at around 1,900 ML/day. Diversions to Wakool Main Canal averaged 600 ML/day for the week and the flow downstream of Stevens Weir is around 2,300 ML/day.

On the Goulburn River, the flow at McCoys Bridge has receded from 1,900 ML/day to 1,170 ML/day as the last of a pulse of water released from Lake Eildon enters the Murray. The flow at McCoys Bridge is planned to remain at around 1,000 ML/day over the coming week. At Torrumbarry Weir, diversions from National Channel are around 2,400 ML/day and the downstream release is around 6,600 ML/day and gradually falling.

Further downstream, inflows into the Murray from the lower Murrumbidgee River are around 750 ML/day at Balranald. This flow is expected to recede to a base flow of around 180 ML/day over the coming week.

Following consultation with the local community, a start date of 20 May has been selected for commencement of the major works at Mildura Weir this winter. The works will require closure of the lock for three to four months, as well as removal of the weir for up to ten weeks. Further advice and updates on the works will be provided in coming months.

At Menindee Lakes (currently managed by NSW), the storage volume decreased by 10 GL to 108 GL (6% capacity). Releases into the lower Darling are around 150 ML/day at Weir 32. Upstream of the storage, the slow moving flow event making its way down the upper Darling is still yet to reach Wilcannia.

At the confluence of the Darling and Murray Rivers at Wentworth, the flow is around 8,200 ML/day and rising as the pulse of water released from the Goulburn River last month passes downstream.

At Lake Victoria, the storage volume has decreased by 31 GL to 265 GL (39% capacity). The daily flow to South Australia is targeting around 9,800 ML/day for the first half of March as increased environmental water is passed downstream for barrage outflows into the Coorong. The flow to South Australia is planned to reduce back to around 6,500 ML/day in the second half of March, due to works on the Lake Victoria outlet which will limit the volume of water that can be delivered across the border. The planned flow for the second half of March is still greater than the normal March entitlement flow of 6,000 ML/day.

At the Lower Lakes, the 5-day average water level in Lake Alexandrina decreased 2 cm this week to 0.55 m AHD. Releases from the barrages are targeting flows into the Coorong of 2,000 ML/day or greater when conditions permit.

Source: freeflow.mdba.gov.au/2015/03/06/river-murray-ops-update-6-march/