Review of September 2018 Operations
A total of 3,660 ML inflow was received into reservoirs during September, with total inflows of 37,420 ML received for the 2018-19 year to date. This is equivalent to 29% of the historic average inflow for the same period (122,300 ML excluding Taylors Lake inflow).
During September, the volume in headworks reservoirs decreased from 293,210 ML (52.4%) to 290,070 (51.8%).
Rainfall was approximately 20% of average across Grampians reservoirs during September. The highest rainfall for the month was 25.6 mm, recorded at Lake Bellfield, followed by 18.8 mm received at Lake Wartook. Taylors Lake received the least rainfall for the month with 6.6 mm recorded. With rainfall for the month well below average and warmer temperatures, net evaporation from reservoirs was 2,823 ML for the month; with evaporation exceeding rainfall, (Net evaporation considers rainfall on the reservoir as an evaporation offset).
Passing flow releases from Rocklands Reservoir to the Glenelg River commenced early in September, with a total of 600 ML released during the month. Environmental water releases began later in the month in the Wimmera catchment, with a total of 230 ML delivered to the Wimmera River from Taylors Lake, and 238 ML supplied to the lower MacKenzie River from a combination of Lake Wartook and Moora Moora Reservoir. No passing flows were released from Lake Lonsdale, with these being withheld in storage.
Wimmera-Mallee Pipeline supplied Recreation Lakes received 291 ML throughout the month of September, with top-up supplies commencing for a number of lakes. 46 ML was supplied to Wimmera-Mallee Pipeline connected wetlands within the Mallee, North Central and Wimmera Catchment Management Authority areas.
Consumptive entitlement holders collectively used 1,173 ML during September to supply urban and rural demands.
During September, the Storage Manager utilised water stored in Moora Moora Reservoir to meet environmental water demands for the lower MacKenzie River and concurrently supply the Wimmera-Mallee Pipeline Supply System 6 balancing storages. This is an operational contingency measure to reduce the volume of demand from Lake Wartook over the 2018-19 season, and provide a greater reserve in storage for 2019-20 season, should conditions remain dry.
On 3 September, a concurrent transfer commenced from Rocklands Reservoir to both Taylors Lake and Toolondo Reservoir. The Storage Manager determined that a transfer of up to 5,000 ML is necessary to support supply from Taylors Lake over the 2018-19 season. With the volume in Rocklands Reservoir at the start of September being above 130 GL, and tracking close to the ‘Average’ inflow scenario presented in the July to September supplement to the Annual Operating Plan, a 5,000 ML transfer to Toolondo Reservoir was determined to be appropriate.
Planned October 2018 Operations
The Bureau of Meteorology (BoM) in their most recent climate outlook have predicted a 25% to 30% chance of above average rainfall during October. BoM reports that the El Niño Southern Oscillation (ENSO) outlook remains at ‘El Niño WATCH’ status. This indicates a 50% chance of El Niño conditions developing in the coming months, which is twice the normal likelihood for a given year. During El Niño events, rainfall in eastern Australia has historically been below average during spring, with warmer daytime temperatures also occurring. The Storage Manager will continue to monitor BoM climate outlooks and consider this information in its planning activities.
The Storage Manager’s operational focus for October will include water transfer activities and supply of entitlement holder requirements. The supply of accumulated passing flow obligations is anticipated to commence during the month for the Wimmera catchment, and to continue in the Glenelg catchment. Wimmera catchment ‘regulated’ environmental flows are anticipated to continue throughout the month. Regulated environmental flows from Rocklands Reservoir to the Glenelg River are anticipated to commence once passing flows obligations have been delivered.
Transfers from Rocklands to Toolondo Reservoir and Taylors Lake will continue into October. Flows into Toolondo Reservoir will conclude on 15 October upon the supply of 5,000 ML. Transfers flows will continue passing onwards to Taylors Lake for the remainder of October to complete this transfer and supply to Green Lake near Horsham.
A transfer from Lake Bellfield to Lake Fyans will be satisfied in early October, transferring a total of 800 ML. This will increase water levels to those planned for in the Annual Operating Plan under ‘dry’ inflow conditions, and will support water quality and recreation opportunities in Lake Fyans. The opportunity to transfer this water has been taken while natural flows persist in Fyans Creek below Lake Bellfield, to minimise transfer losses. The Annual Operating Plan included a volume of up to 3,000 ML for transfers to Lake Fyans prior to the summer months.
Further information in relation to water transfers are described in the Storage Manager’s Annual Operating Plan.
Reservoirs are expected to remain at suitable levels through September for a range of recreational activities, including boating at reservoirs where this is permitted. Please refer to the Reservoir information page for further information on water levels and recreation activities permitted at each reservoir.
Blue-Green Algae blooms can be more common during the warmer summer months. 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.