Review of May 2022 Operations
Rainfall recorded during May was below average at all Wimmera-Glenelg reservoirs. The highest recorded monthly rainfall total was at Lake Bellfield which received 49.0 mm (or 50% of the historic average). The lowest recorded monthly rainfall total was 23.0 mm at Taylors Lake (54% of the historic average).
Despite reservoirs recording below average rainfall during May, small volumes of inflow were again recorded at Lake Wartook and Rocklands Reservoir (440 ML in total). Inflow to the Grampians reservoirs for the water year to date (July 2021 to May 2022) increased to 74,090 ML, equivalent to 40% of the historic average for the same period.
Between 4 May 2022 and 1 June 2022, the total volume in storage decreased from 168,830 ML (30.1%) to 165,570 ML (29.6%), representing a total decrease of 3,260 ML. This was primarily the result of very little inflow, and water releases to supply entitlement holders.
The calculated net evaporation from reservoirs was approximately -180 ML during the month of May, with rain falling on reservoirs slightly exceeding evaporation. (Net evaporation considers rainfall on the reservoir as an evaporation offset).
During May, 1,360 ML of environmental water was released to waterways in the Wimmera catchment, inclusive of 640 ML passing flow releases from Lake Lonsdale. A total of 1,000 ML was released to the Glenelg River during the month.
Wimmera-Mallee Pipeline supplied recreation lakes received 106 ML during the month of May, and 28 ML was delivered to Wimmera-Mallee Pipeline connected wetlands during the month.
Consumptive entitlement holders collectively used 810 ML during May to supply their respective urban and rural demands.
June 2022 Operations
The Bureau of Meteorology (BoM) Climate Driver Update released on 24 May 2022 advised that climate models indicate a return to neutral El Niño Southern Oscillation (ENSO) during the southern hemisphere winter. Even if La Niña eases, forecast sea surface temperature pattern in the tropical Pacific still favour average to above average winter rainfall for eastern parts of Australia.
The Indian Ocean Dipole (IOD) is currently neutral, however it has become increasingly negative through late May. While BoM advised that all climate models surveyed indicate that a negative IOD event is likely to develop over the coming months, forecasts generally become more accurate from June. A negative IOD increases the chances of above average winter–spring rainfall for much of Australia.
BoM rainfall outlooks indicate a 60-70% chance of exceeding the median rainfall for June. However, reservoir inflows remain dependent on further rainfall events to saturate catchments and generate runoff. The Storage Manager will continue to monitor rainfall and catchment conditions through June, and will commence water harvesting activities should sufficient rainfall be received. 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.
With upgrade works at the Lake Fyans southern marina and boat ramp now complete, the Storage Manager has begun directing natural catchment flows to Lake Fyans. It is anticipated that water levels in Lake Fyans will increase slowly over the coming months.
A number of reservoirs are projected to remain at suitable levels throughout June 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.
Blue-Green Algae above the levels safe for recreational contact has 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.