Picture: Lake Fyans

Review of December 2019 Operations

December was the second consecutive month in the 2019/20 water year where no measurable inflow was recorded at any reservoir. Year to date inflows for the 2019/20 season remain at 50,760 ML (42,740 ML excluding Taylors Lake), which is equivalent to 25% of the historic average inflow for the same period (166,300 ML excluding Taylors Lake inflow).

During December, the volume in storage decreased from 230,050 ML (41.1%) to 212,270 ML (37.9%). Very warm day time temperatures through much of the month resulted in very high evaporation losses from reservoirs, and substantial losses were observed in the natural waterways used to deliver water to entitlement holders.

Rainfall recorded at Grampians reservoirs ranged between 18% and 3% of average during December. The highest rainfall for the month was 7 mm, recorded at Moora Moora Reservoir (13% of average), followed by 5.4 mm recorded at Lake Fyans (18% of average). Lake Bellfield recorded the lowest rainfall total with 1.4 mm, which equates to just 3% of the monthly average.

Calculated net evaporation from reservoirs was approximately 10,830 ML for the month; with monthly evaporation far exceeding rainfall (Net evaporation considers rainfall on the reservoir as an evaporation offset).

Environmental water releases from Lake Wartook were supplied to the MacKenzie River and Burnt Creek, and from Rocklands Reservoir to the Glenelg River. Water for the environment was also supplied to the Lower Mt William Creek and Wimmera River from Lake Lonsdale. An environmental watering trial in the upper Glenelg River, using water from Moora Moora Reservoir, concluded during December.

Wimmera-Mallee Pipeline supplied recreation lakes received 213 ML throughout the month of December, and Wimmera-Mallee Pipeline connected wetlands received 3 ML.

Consumptive entitlement holders collectively used 1,623 ML during December to supply urban and rural demands.


Planned January 2020 Operations

The Bureau of Meteorology (BOM)

in their most recent El Niño -Southern Oscillation (ENSO) outlook have stated that the strong positive Indian Ocean Dipole (IOD) which has driven much of the climate in recent months is continuing to weaken. The El Niño–Southern Oscillation (ENSO) remains neutral. International climate models forecast ENSO to remain neutral until at least autumn 2020. When ENSO is neutral, it has limited influence on Australian and global climate.

It is anticipated that the focus of reservoir operations during January will predominantly centre on routine delivery of water to entitlement holders, and operational actions to maximise headworks efficiency.

Many reservoirs are anticipated to remain at suitable levels through January for a range of recreational activities. Recreation users are reminded to take care and abide by signage at reservoirs. Please refer to theReservoir information page for further information on water levels and recreation activities permitted at each reservoir.

Blue-Green Algae blooms can be more common during warmer months. Recent Blue-Green Algae warnings for reservoirs can be found on the Storage Manager News Feed and all current warnings are available from the GWMWater Algae Warnings webpage.


1 ML = 1 megalitre = 1 million litres