Review of June 2021 Operations
Rainfall received during June was above average for all headworks storages with the exception of Rocklands Reservoir, which recorded 59.2 mm or 85% of the historic average. The highest monthly rainfall total was recorded at Mt Cole Reservoir (159.4 mm or 231% of the historic average), with the lowest monthly total being recorded at Taylors Lake (53.2 mm or 121 % of the historic average).
A total of 9,740 ML of inflow was recorded to Grampians reservoirs during June. This inflow equates to approximately 55% of the historic average inflow for the month. Total 2020-21 inflows finished the year at 65,240 ML (excluding Taylors Lake), which is equivalent to 33% of the historic average inflow for the same period (199,600 ML excluding Taylors Lake).
During June, the total volume in storage increased from 160,450 (28.6%) to 175,140 ML (31.3 %) representing a total increase of 14,690 ML.
Calculated net evaporation from reservoirs was approximately -2,790 ML for the month; with rainfall received onto reservoirs exceeding evaporation. (Net evaporation considers rainfall on the reservoir as an evaporation offset)
Water releases for the environment totalling 19 ML were made to waterways in the Wimmera catchment during the month. No water was released from Rocklands Reservoir to the Glenelg River in June.
Wimmera-Mallee Pipeline supplied recreation lakes received 70 ML during the month of June, and 22 ML was delivered to Wimmera-Mallee Pipeline connected wetlands.
Consumptive entitlement holders collectively used 720 ML during June to supply their respective urban and rural demands.
Planned July 2021 Operations
The Bureau of Meteorology (BoM) in its most recent Climate Driver Update advised that the El Niño Southern Oscillation (ENSO) remains neutral and is likely to remain in this state until November 2021.
The Indian Ocean Dipole (IOD) is currently negative and is forecast to remain negative throughout the winter and spring period. A negative IOD increases the chances of above average winter and spring rainfall for parts of southern Australia.
With Grampians catchment well primed to produce runoff following above average rainfall in June, further rainfall events are anticipated to result in runoff and additional inflow to reservoirs. The extent of water harvested remains contingent on rainfall across key catchment areas.
The Storage Manager’s operational focus for July will primarily centre on monitoring of catchment conditions and flows, and coordinating water harvesting in response to rainfall events. Consistent flow is already being observed within a number of Grampians catchment waterways.
A number of reservoirs are projected to remain at suitable levels through July 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