Review of June 2020 Operations
Rainfall totals recorded at Grampians reservoirs during June were below average at all reservoirs, with recorded rainfall ranging from 26% to 79% of the monthly average. The highest rainfall total for the month was 86.2 mm recorded at Lake Wartook (79% of average), followed by Lake Bellfield with 59.8 mm (55% of average). Taylors Lake recorded 11.6 mm, the lowest rainfall total for the month (26% of average).
June rainfall resulted in around 6,570 ML of inflow to reservoirs (38% of the historic June average). Total inflow for the 2019/20 season (July 2019 to June 2020) was 64,810 ML (56,610 ML, excluding Taylors Lake), which is equivalent to 28% of the historic average inflow. The 2019/20 year has been the third consecutive year where inflows to reservoirs have been less than one third of the historic average.
During June, the total volume in storage increased by 6,610 ML, from 165,770 ML (29.6%) to 172,380 ML (30.8%).
Calculated net evaporation from reservoirs was approximately -880 ML for the month; with rainfall on reservoirs exceeding evaporation (Net evaporation considers rainfall on the reservoir as an evaporation offset).
Environmental water releases during the month of June consisted of releases from:
• Lake Wartook to the MacKenzie River and Burnt Creek, and
• Rocklands Reservoir to the Glenelg River (passing flow obligations).
Wimmera-Mallee Pipeline supplied recreation lakes received 7 ML throughout the month of June, and Wimmera-Mallee Pipeline connected wetlands received 15 ML.
Consumptive entitlement holders collectively used 730 ML during June to supply their respective urban and rural demands.
Planned July 2020 Operations
The Bureau of Meteorology (BOM) in their most recent El Niño-Southern Oscillation (ENSO) outlook have advised that Niño–Southern Oscillation (ENSO) remain neutral. However, cooling in the tropical Pacific Ocean has continued, and the majority of climate models indicate this cooling trend may be close to La Niña thresholds by early spring. Subsequently, BoM have upgraded the ENSO outlook to “La Niña Watch”. La Niña events during spring are typically accompanied by above average rainfall for northern, eastern and southern parts of Australia.
Despite recent cooling in the eastern Indian Ocean, some climate models still indicate that that a negative Indian Ocean Dipole (IOD) may develop during late winter or early spring. Negative IOD events typically coincide with increased winter-spring rainfall for southern parts of Australia.
While there was again only a small volume inflow to reservoirs during June, catchment conditions at the beginning of July remain primed for further inflows. With regular rainfall events through July, it is anticipated that an increase in runoff will be observed, however the extent of this will be dependent on the frequency and magnitude of rainfall events. Where possible, natural inflows to waterways downstream of reservoirs will be used to service entitlement holder demands, in order to preserve water in storage.
The Storage Manager’s operational focus for July will be water harvesting activities in response to rainfall events, and as catchment runoff is observed.
Although many reservoirs are anticipated to remain at suitable levels through July for a range of recreational activities, some restrictions may remain in place to comply with the Victorian Government’s Coronavirus response. Please refer to GWMWater'sReservoir information page for further information on current restrictions and recreation activities permitted at each reservoir.
While Blue-Green Algae blooms are generally less common during the cooler months, it is still possible for these to occur. Recent Blue-Green Algae warnings for reservoirs can be found on the Storage Manager News Feed and all current warnings are available from the GWMWater Algae Warnings webpage.
Note: 1 ML = 1 megalitre = 1 million litres