Water Week

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Murray-Darling Basin Commission to lower Euston Lakes from Murray River

Posted by waterweek on 4 October 2007

Euston flow was now 1960 ML/day; the “normal” flow range was 30,000 to 56,000 ML/day. The local towns were at level four restrictions Murray-Darling Basin Commission (MDBC) Chief Executive Dr Wendy Craik said the emergency needs had forced the Murray-Darling Basin Commission (MDBC) to further lower the NSW-Victoria Euston Weir Pool and its associated Lakes. The lakes were on the NSW side of the river and the town of Robinvale on the Victoria side. Water was pumped from the Euston Weir pool to supply the Robinvale Irrigation District in Victoria private diverters in NSW, for almonds and olives, and urban supplies. The widre area is called Sunraysia (centred around Mildura, including Red Cliffs, Merbein and Robinvale), administered by Lower Murray Water Authority (LMW)

Robinvale may have to cart water: The weir services Robinvale Irrigation District in Victoria, private diverters in NSW and town water supplies. Euston Weir is located 1 110 km upstream of the river mouth, and 1 420 km downstream of the source. It is located downstream of all of the major tributaries of the River Murray, with the exception of the Darling River.

Very low flow: The current flow art Euston was 1960 ML/day. “Normal:” flow range 30,000 to 56,000 ML/day was Euston Weir is located in the Sunraysia region on the River Murray near Euston (NSW) and Robinvale (Victoria). Euston Weir raises the water in the River Murray to a level so that it permanently inundates the Euston lakes; Dry Lake and Lake Benanee. Lake Carrringay would also be inundated if it were not for levee banks isolating it, which allows the lakebed to be used for agriculture.

The rules: The system was under emergency management as the approximate flows for removal and reinstatement of Euston Weir were:

For weir Removal:
• lowest flow 40,000 ML/day,
• highest flow 50,000 ML/day
Reinstatement was:
• lowest flow 30,000 ML/day;
• highest flow 56,000 ML/day.

The emergency plan: Murray-Darling Basin Commission (MDBC) Chief Executive Dr Wendy Craik the the emergency plan was to:,

• reduce evaporative losses across the system;

• increase water availability to users during this extremely difficult period”.

Extreme conditions: “Under extreme conditions more evaporative savings will be needed over summer and autumn. How these savings will be made will be kept under review. There is a difficult trade-off between avoiding unnecessary impact on the weir pool users and the other options to reduce evaporation. The Euston Lakes Users Group will continue to be consulted in developing all options. The rate of lowering will be reduced if there is significant rain or higher river flows. On the other hand, hot weather may lead to the weir pool level being temporarily drawn down at a slightly faster rate. In this event, extra water will be released from upstream storages to return the pool level to the original schedule.

We appreciate that lowering the weir pool will impact some river users, but we are operating the river system on a knifes edge to maximise overall water availability.

Dry Lake and Lake Benanee on empty: Dry Lake and Lake Benanee will be refilled when conditions improve and when we are able to supply the water. In the meantime, we advise river diverters, boat skippers and other river users to take the lower weir pool levels into account in their activities, Dr Craik said.

No more flows to Euston Lakes: An estimated 25 GL evaporative losses can be saved by reducing the surface area of the Euston Lakes. The Euston Weir pool level was gradually lowered to 25cm below full supply level in August as the first stage in a series of water savings measures, Dr Craik said. At that time, we warned that the level of the weir pool might need to be lowered further unless inflows improved substantially.

The normal conditons: Under normal circumstances, Eustons associated Lake Benanee and Dry Lake are maintained at full supply level (47.60m) and evaporative losses are replaced each day by flows from the river. However, by gradually lowering the weir pool level to match the evaporation rate, no net flow into the lakes will occur.

Gradually lowering Euston Weir pool: This water can then be saved and redirected to users throughout the Murray Valley, Dr Craik said. Euston Weir pool is currently 47.34m AHD, which is 26 cm below full supply level. “We plan to begin gradually lowering Euston Weir pool on Monday 1 October, initially at a rate of about 3-5 cm per week. We expect the pool level to fall to about 0.5 m below full supply level by early November”.

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