Picture: Lake Fyans

Review of October 2023 Operations

Below average rainfall was recorded at all Wimmera−Glenelg System reservoirs during October. The highest rainfall total for the month was 39.4 mm, recorded at Lake Bellfield (48% of the October average). The lowest rainfall total was recorded at Lake Lonsdale, which received 10.8 mm (22% of the October average).

The total inflow to reservoirs for October was 2,200 ML (8% of October average). Multiple months with below average rainfall combined with historically warm conditions in September appear to have dried out the catchment to the point where inflow has ceased to a number of headworks storages. The total year to date inflow is 46,900 ML (excluding Taylors Lake to allow for statistical comparison) which equates to 31% of the annual historic average inflow for the July to October period.

Between 4 October 2023 and 1 November 2023, the total volume in storage decreased from 425,560 ML (76.0%) to 411,690 ML (73.5%), to representing a decrease of 13,870 ML (2.5%).

The total monthly calculated net evaporation from all reservoirs continued to increase, with warmer daytime temperatures, reduced rainfall and longer daylight hours experienced across headworks storages. Approximately 9,510 ML evaporated from the headworks during the month of October, with evaporation from the reservoirs exceeding rainfall. (Net evaporation considers rainfall on the reservoir as an evaporation offset).

Considering the drying conditions, environmental demand from the headworks system increased during October. A total of 2,878 ML of passing flows was released from Rocklands Reservoir to the Glenelg River. In addition to 803 ML of regulated releases from Taylors Lake to the Wimmera River and 156 ML of regulated releases from Lake Wartook to the MacKenzie River and Burnt Creek systems.

A total of 70 ML was supplied to wetlands from the Wimmera-Mallee Pipeline during the month, and 247 ML was delivered to Wimmera-Mallee Pipeline connected recreation lakes.

Consumptive entitlement holders collectively used approximately 813 ML during October to supply their respective urban and rural demands.

November 2023 Operations and Climate Outlook

The Bureau of Meteorology (BoM) continue to report that El Niño and a positive Indian Ocean Dipole (IOD) are established and likely to remain into 2024. El Niño typically results in decreased winter-spring rainfall for eastern parts of Australia. A positive IOD has the potential to supress spring rainfall in our region, potentially intensifying the drying effect of El Niño.

Rainfall outlooks indicate a low chance of exceeding median rainfall (25-30%) during November. It is expected that inflows to headworks will continue to recede or cease completely in November. It is expected operational focus will turn to supplying entitlement holders in the coming month. Environmental Water Managers have already placed orders with the Storage Manager and environmental demand from the headworks is expected to increase as pick-up recedes and catchments further dry out.

Reservoirs are projected to hold suitable levels during November 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.

There are currently no Blue-Green Algae warnings issued for lakes within the Wimmera – Glenelg Headworks System. Information on all current algae warnings as well as general information on Blue-Green Algae is available from the GWMWater Algae Warnings webpage.