Review of April 2021 Operations
Rainfall received during April was well below average across all Grampians reservoirs, with rainfall ranging from 19% to 69% of the monthly average. The highest rainfall totals for the month were recorded at Lake Bellfield with 26.6 mm (69% of average) and Lake Wartook with 26.2 mm (68% of average). The lowest rainfall total for the month was recorded at Taylors Lake with 4.6 mm (20% of average).
Well below average rainfall resulted in only 240 ML of inflow being recorded to Grampians reservoirs during April. This inflow equates to approximately 10% of the historic average inflow for the month. Total 2020-21 year to date inflow increased to 60,525 ML (excluding Taylors Lake), which is equivalent to 34% of the historic average inflow for the same period (176,600 ML excluding Taylors Lake).
During April, the total volume in storage decreased from 167,550 (29.9%) to 162,390 (29%), representing a total decrease of 5,160 ML, and the lowest end of April volume since 2015.
Calculated net evaporation from reservoirs was approximately 3,100 ML for the month; with evaporation from reservoirs exceeding rainfall. (Net evaporation considers rainfall on the reservoir as an evaporation offset)
Water releases for the environment totalling 225 ML were made to waterways in the Wimmera catchment during the month, and 1,242 ML was released from Rocklands Reservoir to the Glenelg River.
Wimmera-Mallee Pipeline supplied recreation lakes received 230 ML during the month of April, and 9.6 ML was delivered to Wimmera-Mallee Pipeline connected wetlands.
Consumptive entitlement holders collectively used 915 ML during April to supply their respective urban and rural demands.
Planned May 2021 Operations
The Bureau of Meteorology (BoM) in its most recent Climate Driver Update advised that the El Niño Southern Oscillation (ENSO) remained neutral and will remain in this state until at least September.
The Indian Ocean Dipole (IOD) index is currently neutral and forecast to remain so at least through early winter.
Despite neutral conditions, the BoM are indicating an increased chance of rainfall exceeding the median for May. The past accuracy of mid to late May rainfall outlooks, however, is between 45% - 50%.
Much of the key Grampians catchment areas remain very dry. As a result, the Storage Manager’s operational focus for May is anticipated to primarily centre on the delivery of entitlement holders’ water requirements. Should significant rainfall events be experienced during the month, the Storage Manager is well positioned to transition to the planning and coordination of water harvesting activities.
A number of reservoirs are projected to remain at suitable levels through May 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, including any restrictions in place to comply with the Victorian Government’s COVIDSafe Settings.
Blue-Green Algae above the levels safe for recreational contact have been recorded at 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.
Note: 1 ML = 1 megalitre = 1 million litres