Review of March 2025 Operations
Localised heavy rainfall was recorded at a number of storages during March with storages recording both well above and below average totals. The highest rainfall total received was at Moora Moora Reservoir with 50.2 mm (134% of the historic monthly average), followed by Lake Lonsdale with 50 mm (180% of the historic monthly average). The lowest monthly rainfall total was received at Toolondo Reservoir, with 8.6 mm (38% of historic monthly average). Although a number of storages recorded above average rainfall for the month of March, the total rainfall across all headworks storages remained below average, representing the 14th consecutive months of below average rainfall across headworks storages.
Below average rainfall in March failed to generate meaningful inflow to storages with 940 ML (excluding Taylors Lake) being recorded. March inflow was equivalent to 52% of the historic average for the month. Year to date inflow increased to 26,070 ML, or 15% of the historic average for the same time period.
Between 5th March 2025 to 2nd April, the total volume in storage decreased from 235,410 (42%) to 223,820 ML (40%) representing a total decrease of 11,590 ML (2% of total operating capacity).
High daytime temperatures and 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 March, with approximately 8,460 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.
To support entitlement holder demand and reduce the risk of BGA in Lake Fyans, a 3,200 ML headworks transfer from Lake Bellfield was completed in March. This transfer increased the volume in Lake Fyans to approximately 14,200 ML (77% of operating capacity) ensuring capacity to satisfy entitlement holder demand, recreational use of the lake and provide improved water quality outcomes.
Environmental deliveries from the headworks system continued through March, with the following deliveries taking place:
- Lake Wartook delivered 184 ML of environmental water to the Mackenzie River / Burnt Creek systems.
- Lake Fyans delivered a small flow of approximately 100 ML to Mt William Creek.
- Releases to the Glenelg River continued, with 1,541 ML of regulated environmental flow from Rocklands Reservoir.
A total of 203 ML was delivered to Wimmera-Mallee Pipeline connected recreation lakes during March.
Consumptive entitlement holders collectively used approximately 1,715 ML during the month to supply respective urban and rural demands.
April 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.
The Southern Annular Mode (SAM) is neutral, with a tendency towards positive values over April.
Rainfall outlooks indicate a 50% chance of rainfall exceeding the median for the remainder of April 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 April to June period. Unless average to above average rainfall conditions develop throughout April, 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 April 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. Information on all current algae warnings, as well as general information on Blue-Green Algae, is available from the GWMWater Algae Warnings webpage.