Review of September 2019 Operations
A monthly total of 7,470 ML inflow was received to reservoirs during September (6,805 ML excluding Taylors Lake). Year to date inflows for the 2019/20 season increased to 49,305 ML (41,910 ML excluding Taylors Lake), which is equivalent to 34% of the historic average inflow for the same period (122,300 ML excluding Taylors Lake inflow).
During September, the volume in storage increased slightly, from 244,880 ML (43.8%) to 248,540 (44.4%). The last week in September saw a decline in overall storage volume, indicating catchments have started to dry. With the Bureau of Meteorology predicting an increase in daily temperatures and below average rainfall for October, it is anticipated that the volume held in storage will begin to decline as water is delivered to entitlement holders and lost to evaporation.
Rainfall recorded at Grampians reservoirs ranged between 42% and 63% of average during September. The highest rainfall for the month was 61.2 mm, recorded at Lake Bellfield (56% of average), followed by 58.0 mm recorded at Moora Moora (53% of average). Lake Lonsdale recorded the lowest rainfall total with 24.2 mm, which equates to 42% of the monthly average.
Calculated net evaporation from reservoirs was approximately 620 ML for the month; with monthly evaporation exceeding rainfall for the first time since April 2019 (Net evaporation considers rainfall on the reservoir as an evaporation offset).
There were no environmental water releases in either the Wimmera or Glenelg catchments during the month of September. Passing flows releases commenced at Rocklands Reservoir in late September in response to a reduction in natural flows occurring in the Glenelg River downstream of Rocklands Reservoir.
Wimmera-Mallee Pipeline supplied recreation lakes received 330 ML throughout the month of September, and Wimmera-Mallee Pipeline connected wetlands received 3.4 ML.
Consumptive entitlement holders collectively used 964 ML during September to supply urban and rural demands.
The transfer of water between Rocklands Reservoir and Taylors Lake concluded in late September. The duration of the transfer was able to be shortened due to higher than forecast catchment flows, which were able to be harvested to Taylors Lake. This reduced the overall volume required from Rocklands Reservoir, and subsequently enabled a supply of 1,300 ML to be made to Green Lake near Horsham.
Planned October 2019 Operations
The Bureau of Meteorology (BOM)
in their most recent El Niño -Southern Oscillation (ENSO) outlook have stated that all models currently indicate ENSO-neutral conditions will remain for the rest of 2019. This indicates that other climate drivers are more likely to influence Australian weather for the remainder of the year.
A very strong positive Indian Ocean Dipole (IOD) is expected to persist until the end of spring. Typically, positive IOD events have resulted in below average winter–spring rainfall for southern and central Australia, and above average daytime temperatures for the southern two-thirds of Australia. Climate model outlooks indicate a positive Indian Ocean Dipole is likely to drive Australia's weather for the rest of 2019, meaning the likelihood of a drier than average spring remains.
The Storage Manager will continue to maximise water harvesting to storages during October, however the opportunities to harvest will be dependent on rainfall during the month. Should catchments continue to dry through October, the focus of reservoir operations will predominantly centre on delivery of water to entitlement holders, and operational actions to maximise headworks efficiency.
Many reservoirs are anticipated to remain at suitable levels through October 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