Review of December 2021 Operations
Rainfall recorded during December was well below average across the Wimmera-Glenelg reservoirs. The highest monthly rainfall total was recorded at Mt Cole Reservoir (22.0 mm or 49% of the historic average). The lowest monthly total was 3.6 mm recorded at Toolondo Reservoir (12% of the historic average).
Catchment conditions were very dry through December, with high daytime temperatures and windy conditions. There was no inflow recorded to any of the Grampians reservoirs during December.
Between 1 December 2021 and 5 January 2022, the total volume in storage decreased from 240,210 (42.9%) to 219,150 (39.1%), representing a total decrease of 21,060 ML. This was the combined result of high evaporation, no inflow, and increased deliveries to entitlement holders.
The calculated net evaporation from reservoirs was approximately 10,500 ML during the month of December, with evaporation from storages exceeding rainfall. (Net evaporation considers rainfall on the reservoir as an evaporation offset).
During this month 342 ML of environmental water was released to waterways in the Wimmera catchment, and 2,080 ML to the Glenelg River. In addition, 1,220 ML of passing flow obligations were released from Rocklands Reservoir to the Glenelg River.
Wimmera-Mallee Pipeline supplied recreation lakes received 200 ML during the month of December, and 2 ML was delivered to Wimmera-Mallee Pipeline connected wetlands during the month.
Consumptive entitlement holders collectively used 1,720 ML during December to supply their respective urban and rural demands.
January 2021 Operations
The Bureau of Meteorology (BoM) advised that the El Niño Southern Oscillation (ENSO) is now exhibiting a La Niña event. The current La Niña event is expected to persist until late autumn. La Niña events increase the chances of above-average rainfall for eastern parts of Australia during spring and summer.
The Indian Ocean Dipole (IOD) has returned to a neutral state, with all climate models indicating the IOD will remain neutral through to May 2022. A neutral IOD is not expected to have a significant influence on weather patterns and rainfall.
The Storage Manager’s operational focus for January will remain on coordinating deliveries to entitlement holders, including the delivery of environmental flows. The Storage Manager will continue to closely monitor catchment conditions, and should suitable opportunities arise, coordinate routine water harvesting activities in response to rainfall events. Water harvesting is undertaken in accordance with Storage Management Rules, the Storage Manager’s Annual Operating Plan, and takes into consideration factors such as water quality and environmental objectives.
A number of reservoirs are projected 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 GWMWater’s Reservoir information page for further information on water levels and recreation activities permitted at each reservoir.
Embankment upgrade works at Lake Fyans are planned to commence in early 2022. Water levels will still remain within the normal operating range for this time of year.
Blue-Green Algae above the levels safe for recreational contact have been recorded at Lake Lonsdale and Toolondo Reservoir. Information on all current algae warnings as well as general information on Blue-Green Algae is available from the GWMWater Algae Warnings webpage.