Review of January 2025 Operations
Well below average rainfall totals were recorded across Grampians storages during January, with all storages recording rainfall below the monthly average. The highest rainfall total received was at Mt Cole with 27.8 mm (62% of the historic monthly average), followed by Moora Moora Reservoir with 18.2 mm (38% of the historic monthly average). The lowest monthly rainfall total was received at Rocklands Reservoir, with 8.2 mm (28% of historic monthly average). Below average rainfall received during January represented 12 consecutive months of below average rainfall across headworks storages.
Below average rainfall in January failed to generate meaningful inflow to storages with 638 ML (excluding Taylors Lake) being recorded. January inflow was equivalent to 18.2% of the historic average. Year to date inflow increased to 25,096 ML, or 14.7% of the historic average for the same time period.
Between 1st January to 5th February, the total volume in storage decreased from 276,680 ML (49.4%) to 254,630 ML (45.5%) representing a total decrease of 22,050 ML (3.9% 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 January, with approximately 14.2 GL of net evaporation calculated from headworks storages during the month. High net evaporation throughout the summer period is expected to be the main influence on storage levels over the next few months.
Recent fire activity in the Grampians National Park has limited operational access to a number of storages through January. Although deliveries were able to continue from effected storages, operational staff weren’t able to adjust releases during this period. Access restrictions are expected to remain until fire activity ceases.
Environmental deliveries from the headworks system continued through January, with 170 ML of environmental water released to the Mackenzie River / Burnt Creek systems. Releases from Taylors Lake to Wimmera River re-commenced, with 820 ML released during January. Releases to the Glenelg River continued, with 1,900 ML of regulated environmental flow from Rocklands Reservoir, and 220 ML from Moora Moora reservoir to the upper Glenelg River.
A total of 360 ML was delivered to Wimmera-Mallee Pipeline connected recreation lakes during January.
Consumptive entitlement holders collectively used approximately 2,170ML during January to supply respective urban and rural demands.
February 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 continue to suggest average to slightly above average rainfall conditions over the next few months. Previous predictions of favourable rainfall conditions have so far failed to develop, with consistent dry conditions being experienced across the headworks system since late December 2023 / early January 2024. While predictions for the February to March period are neutral to slightly positive, dry catchment conditions are likely to drive operational decision making over the next month, 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 until the end of the forecast period (April 2025).
The Southern Annular Mode (SAM) is negative, and is expected to remain negative until mid-February.
Rainfall outlooks indicate a less than 50% chance of rainfall exceeding the median during February and a 50% chance of rainfall exceeding the median between March to May. 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 February, 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 February 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) and 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.