Review of November 2024 Operations
Below average rainfall totals were recorded across Grampians storages during November, with all storages recording rainfall below the monthly average. The highest rainfall total received was at Mt Cole with 50.6 mm (83% of the historic monthly average), followed by Moora Moora Reservoir with 32.2 mm (54% of the historic monthly average). The lowest monthly rainfall total was received at Lake Fyans, with 16 mm (42% of historic monthly average). Below average rainfall received during November represented the tenth consecutive month of below average rainfall across headworks storages.
Below average rainfall in November struggled to generate meaningful inflow to storages with 1,550 ML (excluding Taylors Lake) being recorded. November inflow was equivalent to 13.8% of the historic average. Year to date inflow increased to 23,940 ML, or 14.8% of the historic average for the same time period.
Between 6 November and 4 December, the total volume in storage decreased from 308,220 ML (55.0%) to 295,030 ML (52.7%) representing a total decrease of 13,190 ML (2.3% of total operating capacity).
There were limited opportunities to harvest unregulated catchment flow during November with only minor flows recorded on the upper Glenelg River, MacKenzie River and upper Wimmera River. Even with some natural catchment flow observed in the system during November, increasing daytime temperature leading to higher daily evaporation ensured any flows were short lived. Any future harvesting from unregulated catchments will be reliant on catchments receiving sufficient rainfall to recommence flow.
The total monthly evaporation from all storages was greater than rainfall received to storages for November, with approximately 9.81 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.
Environmental deliveries from the headworks system continued through November, with 215 ML of environmental water released to the Mackenzie River / Burnt Creek systems. Releases to the Mt William / Wimmera River system continued, with 1,550 ML released from Lake Lonsdale and 760 ML from Taylors Lake. Releases from Rocklands Reservoir to the Glenelg River recommenced, with 1,535 ML of regulated environmental flow, 560 ML of passing flow and 780 ML of Glenelg River Compensation Flow released.
A total of 215 ML was delivered to Wimmera-Mallee Pipeline connected recreation lakes during November.
Consumptive entitlement holders collectively used approximately 1,345 ML during November to supply respective urban and rural demands.
December 2024 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 January 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 been below the negative IOD threshold since mid-October. However, the majority of climate models indicate the IOD will return to a neutral state in December.
The Southern Annular Mode (SAM) is neutral, having been positive for most of November. SAM is expected to become positive over the coming fortnight.
Rainfall outlooks indicate a 50% chance of rainfall exceeding the median during December and a 50-55% chance of rainfall exceeding the median between January and March. Daytime temperatures are expected to remain elevated, with the BOM projecting a >80% chance of exceeding median max temperatures for the January to March period. Unless average to above average rainfall conditions develop throughout December, the operational focus will continue to shift towards 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 December 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 is currently a Blue-Green Algae warning issued for Green Lake (Horsham). Information on all current algae warnings, as well as general information on Blue-Green Algae, is available from the GWMWater Algae Warnings webpage.