Review of February 2025 Operations
Well below average rainfall totals were recorded across Grampians storages during February, with the exception of Lake Bellfield which experienced a localised high intensity rainfall event. The highest monthly rainfall total received was at Lake Bellfield with 44.4 mm (119% of the historic monthly average), followed by Lake Wartook with 16.6 mm (46% of the historic monthly average). The lowest monthly rainfall total was received at Rocklands Reservoir, with 0.2 mm (1% of historic monthly average). Below average rainfall received during February represented 13 consecutive months of below average rainfall across headworks storages.
Below average rainfall in February failed to generate meaningful inflow to storages with 35 ML (excluding Taylors Lake) being recorded. February inflow was equivalent to 1.75% of the historic average. Year to date inflow increased to 25,131 ML, or 14.6% of the historic average for the same time period.
Between 5th February to 5th March 2025, the total volume in storage decreased from 254,630 ML (45.5%) to 235,410 (42%) representing a total decrease of 19,220 ML (3.5% of total operating capacity).
High daytime temperatures and very limited rainfall has effectively shut-down all storage catchments with future harvesting from unregulated systems reliant on catchments receiving sufficient rainfall to recommence flow, which during summer is unlikely.
The total monthly evaporation from all storages was significantly greater than rainfall received to storages for February, with approximately 11,740 ML of net evaporation calculated from headworks storages during the month. High net evaporation throughout the Autumn period is expected to be the main influence on storage levels over the next few months.
Recent fire activity in the Grampians National Park limited operational access to a number of storages in early February. Although deliveries were able to continue from impacted storages, operational staff weren’t able to adjust releases during this period.
To support entitlement holder demand and reduce the risk of BGA in Lake Fyans, a 3,000 ML headworks transfer from Lake Bellfield commenced in late February. The expected duration of the transfer is just over two weeks and will ensure enough volume is held in Lake Fyans to support entitlement holder demand, recreational use of the lake and provide improved water quality outcomes.
Environmental deliveries from the headworks system continued through February, with 200 ML of environmental water released to the Mackenzie River / Burnt Creek systems. Releases from Taylors Lake to Wimmera River continued, with 595 ML released during February. Releases to the Glenelg River continued, with 2,515 ML of regulated environmental flow from Rocklands Reservoir, and 35 ML from Moora Moora reservoir to the upper Glenelg River.
A total of 220 ML was delivered to Wimmera-Mallee Pipeline connected recreation lakes during February.
Consumptive entitlement holders collectively used approximately 1,780 ML during the month to supply respective urban and rural demands.
March 2025 Operations and Climate Outlook
The Bureau of Meteorology (BoM) indicate that the El Niño-Southern Oscillation (ENSO) is likely to remain neutral.
Long-range forecasts for the Wimmera-Glenelg headworks area suggest average to below average rainfall conditions over the next few months. Dry catchment conditions and an outlook for below average rainfall over the next few months are likely to drive operational decision making throughout Autumn, with additional monitoring likely required for less resilient storages such as Lake Wartook.
The Indian Ocean Dipole (IOD) has returned to a neutral state and is likely to remain neutral until the end of the forecast period (April 2025).
The Southern Annular Mode (SAM) is neutral, and is expected to remain neutral until mid-March.
Rainfall outlooks indicate a 65-70% chance of rainfall exceeding the median for the remainder of March and a 35-45% chance of rainfall exceeding the median between April to June. Daytime temperatures are expected to remain elevated, with the BOM projecting a >80% chance of exceeding median max temperatures for the March to May period. Unless average to above average rainfall conditions develop throughout March, the operational focus will continue to focus on contingency planning for less secure storages, based on entitlement holder demand estimates for the 2024-25 water year.
Reservoirs are projected to hold suitable levels during March 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 Blue-Green Algae warnings issued for Green Lake (Horsham), Lake Lonsdale and Taylors Lake. Information on all current algae warnings, as well as general information on Blue-Green Algae, is available from the GWMWater Algae Warnings webpage.