Picture: Lake Fyans

Review of December 2023 Operations

Above average rainfall totals were recorded at all storages during December. This was due to widespread rainfall events at the start and end of December. The highest monthly rainfall total received was recorded at Mt Cole (104.6mm, or 232% of historic monthly average), while the lowest was Lake Toolondo (50.2mm or 167% of historic monthly average). Other significant rainfall totals were recorded at Moora Moora (94.2mm or 174% of historic monthly average) and Lake Lonsdale (81.8mm or 251% of historic monthly average).

Although headworks storages experience well above average monthly rainfall totals, previous months of below average rainfall and high evaporation meant most rain fell on dry catchments, with runoff also limited by dry conditions between rainfall events. This limited the generation of inflow with 2,360 ML recorded to storages through December (excluding Taylors Lake to allow for statistical comparison), representing 50.3% of the historic monthly average (4,700 ML).  Year to date inflow increased to 49,840 ML or 30.0% of historical average to January.

Between 6 December 2023 and 3 January, the total volume in storage decreased from 393,380 ML (70.2%), to 384,800 ML (69.0%), representing a decrease of 8,580 ML (1.2%).

The total monthly calculated net evaporation from all reservoirs was lower than expected in December, with multiple rainfall events helping to negate evaporation from headworks storages. Approximately 7,090 ML of net evaporated was calculated for headworks storages during the month of December, with evaporation from the reservoirs exceeding rainfall. (Net evaporation considers rainfall on the reservoir as an evaporation offset).

Environmental demand from the headworks system remained consistent throughout November. A total of 3,440 ML of passing flows was released from Rocklands Reservoir to the Glenelg River and 340 ML of passing flows released from Lake Lonsdale to the Mt William Creek. In addition, a total of 930 ML of regulated releases were delivered from Lake Wartook to the MacKenzie River and Burnt Creek systems.

A total of 7.6 ML was supplied to wetlands from the Wimmera-Mallee Pipeline during the month, and 288 ML was delivered to Wimmera-Mallee Pipeline connected recreation lakes.

Consumptive entitlement holders collectively used approximately 1,260 ML during December to supply their respective urban and rural demands.

January 2024 Operations and Climate Outlook

The Bureau of Meteorology (BoM) continue to report that El Niño and a positive Indian Ocean Dipole (IOD) are established and likely to remain into 2024. However the influence of El Niño  on Australian rainfall usually reduces during summer, especially in eastern states. The BoM also notes that high-impact rainfall events can occur during El Niño years. A positive IOD also continues to influence Australian weather patterns, but has likely peaked and is expected to ease in January.

Rainfall outlooks indicate an above average chance of exceeding median rainfall (65-70%) during January. Even with above average rainfall, it is expected that inflow to headworks storages will be negligible during January, unless consistent heavy rainfall events occur across the headworks system. It is expected the operational focus will continue by be supplying entitlement holders in the coming month.

Reservoirs are projected to hold suitable levels during 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.

There is currently a Blue-Green Algae warning issues for Lake Toolondo. Information on all current algae warnings as well as general information on Blue-Green Algae is available from the GWMWater Algae Warnings webpage.