Review of April 2025 Operations
Below average rainfall totals were recorded across Grampians storages during April. The highest rainfall total received was at Moora Moora Reservoir with 23.2 mm (36% of the historic monthly average), followed by Lake Fyans with 21.8 mm (60% of the historic monthly average). The lowest monthly rainfall total was received at Mt Cole, with 4 mm (8% of historic monthly average).
With rainfall below average rainfall totals recorded across all headworks storages, April represented the 15th consecutive months of below average rainfall across Grampians headworks storages, with many storages having received approximately 50% of their average yearly rainfall to date.
Well below average rainfall in April failed to generate any inflow to storages. Year to date inflow remained at 26,290 ML, or 14.9% of the historic average for the same time period. 2024/25 is currently ranked as the second lowest inflow year of record (1900-2024).
Between 2nd April to 7th May 2025, the total volume in storage decreased from 223,820 ML (40%) to 212,000 (37.8%), representing a total decrease of 11,820 ML (2.2% of total operating capacity).
Moderate 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.
The total monthly evaporation from all storages was greater than rainfall received to storages for April, with approximately 3,940 ML of net evaporation calculated from headworks storages during the month. The calculated net evaporation received in April was well below that calculated for March (8,460 ML), representing a noticeable decrease in daytime temperatures.
Environmental deliveries from the headworks system continued through April, with the following deliveries taking place:
- Releases from Lake Wartook delivered 149 ML of environmental water to the Mackenzie River / Burnt Creek systems.
- Releases from Taylors Lake delivered 2,238 ML of environmental water to the Wimmera River.
- Releases from Rocklands Reservoir delivered 2,092 ML of environmental water to the Glenelg River.
A total of 223 ML was delivered to Wimmera-Mallee Pipeline connected recreation lakes during April.
Consumptive entitlement holders collectively used approximately 1,862 ML during the month to supply respective urban and rural demands.
May 2025 Operations and Climate Outlook
The Bureau of Meteorology (BoM) indicate that the El Niño-Southern Oscillation (ENSO) is neutral and likely to remain neutral until at least September.
Long-range forecasts for the Wimmera-Glenelg headworks area suggest well below average rainfall conditions over the next few months. Dry catchment conditions and an outlook for below average rainfall are likely to result in a delayed start to system inflows leading into winter.
The Indian Ocean Dipole (IOD) is currently in a neutral state and likely to remain neutral until at least August.
The Southern Annular Mode (SAM) is neutral, with a tendency towards positive values over May.
Rainfall outlooks indicate a less than 25% chance of rainfall exceeding median over May and a 50% chance of rainfall exceeding the median for the June / July period. Daytime temperatures are expected to remain elevated, with the BOM projecting a >80% chance of exceeding median max temperatures for the June to August period. Unless average to above average rainfall conditions develop throughout May, 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 May 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.