Review of June 2024 Operations
Below average rainfall totals were recorded across Grampians storages during June, with monthly rainfall totals between 24.4 mm and 57.4 mm recorded. These monthly rainfall totals were well below the historic average for each storage. The highest monthly rainfall total received was recorded at Moora Moora Reservoir with 57.4 mm (52% of the historic monthly average), followed by Lake Bellfield which recorded 44.6 mm (40% of the historic monthly average). The lowest monthly rainfall total was recorded at Taylors Lake, with 24.4 mm (55% of historic monthly average). Below average rainfall received during June represented the fifth consecutive month of below average rainfall across headworks storages.
Persistent dry catchment conditions limited inflow during June to 508 ML. Increasing the year-to-date inflow to 52,753 ML or 26.4% of the historic average). This ranks the 2023-24 year below the 90th percentile for cumulative natural inflows to storage based on all historic records.
Between 5 June and 3 July 2024, the total volume in storage decreased from 308,950 ML (55.1%) to 308,360 ML (55%), representing a total decrease of 590 ML (0.1% of total operating capacity).
The total monthly evaporation from all storages was less than rainfall received to storages for June, representing the first month since July 2023 negative net evaporation was recorded. Approximately -1.1 GL of net evaporated was calculated for headworks storages during the month. (Net evaporation considers rainfall on the reservoir as an evaporation offset).
Environmental demand from the headworks system continued during June with environmental releases from several storages persisting through the month, in recognition of the absence of natural catchment flows. A total of 298 ML of regulated environmental releases were made from Lake Wartook to the MacKenzie River and from Lake Lonsdale to Mt William Creek during the month.
A total of 14.2 ML was supplied to wetlands from the Wimmera-Mallee Pipeline during the month, and 4 ML was delivered to Wimmera-Mallee Pipeline connected recreation lakes.
Consumptive entitlement holders collectively used approximately 623 ML during June to supply their respective urban and rural demands.
July 2024 Operations and Climate Outlook
The Bureau of Meteorology (BoM) indicate that the El Niño-Southern Oscillation (ENSO) is currently neutral. However, due to a number of models suggesting a La Niña might form as early as September 2024, the ENSO outlook is currently listed as La Niña watch.
While climate indicators such as La Niña can provide broad indications of the expected climate, the long-range forecast provides better guidance for local rainfall and temperature patterns. Long-range forecasts for the Wimmera-Glenelg headworks area have been relatively optimistic, with early indications of average to above average rainfall conditions developing as the year progresses. These predictions 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 August to October period remain positive (average to slightly above average rainfall), current catchment conditions are likely to drive operational decision making over the next month, with the likelihood of transfers and contingency planning expected to increase.
The Indian Ocean Dipole (IOD) is currently neutral and is predicted to remain neutral until at least early spring.
The Southern Annular Mode (SAM) is currently neutral, as of 22 June. Forecasts indicate SAM is likely to become positive during late June before returning to neutral by early July.
Rainfall outlooks indicate a 40-45% chance of rainfall exceeding the median during July. Daytime temperatures are expected to remain elevated, with the BOM projecting a >60% chance of exceeding median max temperatures for the remainder of July. Given the expected dry conditions throughout July, the operational focus will 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 July 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.