Picture: Lake Fyans

Review of March 2024 Operations

Well below average rainfall totals were recorded at all storages during March. The highest monthly rainfall total received was recorded at Mt Cole (3.8 mm, or 10% of historic monthly average). Widespread rainfall received in early April has not been captured in these rainfall totals, which are calculated monthly. It’s important to note that this rainfall did contribute to small increases in volume held in storages during the assessment period and will be captured in the April rainfall figures reference in the next resource assessment.

With warm conditions prevailing and little to no rainfall across headworks storages, calculated inflow totalled 140 ML for the month. Year to date inflow increased to 52,190ML or 30% of historical average to March.

Between 28th February and 3rd April, the total volume in storage decreased from 350,600 (62.6%) to 327,270 (58.4%) representing a total decrease of 23,330 ML (4.2% of total operating capacity).

The total monthly calculated net evaporation from all reservoirs was above the resource assessment allowance for March, with warm dry conditions increasing evaporation from headworks storages. Approximately 11.82 GL of net evaporated was calculated for headworks storages during the month of March, with evaporation from reservoirs far exceeding rainfall. (Net evaporation considers rainfall on the reservoir as an evaporation offset).

Environmental demand from the headworks system remained consistent throughout March. A total of 3,220 ML of regulated environmental released were made from Rocklands Reservoir to the Glenelg River. In addition to 1,310 ML of regulated releases to the MacKenzie River and Burnt Creek systems from Lake Wartook. A total of 1,040 ML of passing flow was released from Lake Lonsdale to the Mt William Creek.

A total of 17.5 ML was supplied to wetlands from the Wimmera-Mallee Pipeline during the month, and 215 ML was delivered to Wimmera-Mallee Pipeline connected recreation lakes.

Consumptive entitlement holders collectively used approximately 1,380 ML during March to supply their respective urban and rural demands.

April 2024 Operations and Climate Outlook

The Bureau of Meteorology (BoM) have observed that the El Niño continues to weaken and is near its end, with models indicating conditions will likely reach a neutral state by the end of April 2024.

While the majority of international models are predicting a La Niña by late winter, El Niño and La Niña predictions made in early autumn tend to have lower accuracy than predictions made at other times of the year. The reliability of El Niño / La Niña forecasts improves beyond May and should be used with caution during Autumn.

The Indian Ocean Dipole (IOD) is currently above the positive threshold but is considered to be neutral. Sustained values of the IOD index above the threshold are required for an IOD event to form.

The Southern Annular Mode (SAM) is currently positive, as of 2 April. Forecasts indicate SAM will remain positive for almost a week before it returns to neutral.

Rainfall outlooks indicate a less than average chance (25-35%) of rainfall exceeding the median during April. Daytime temperatures are expected to remain elevated, with the BOM projecting a >65% chance of exceeding median max temperatures for the remainder of April. Given the expected dry conditions, the operational focus for April will continue to be supplying entitlement holders.

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 is currently a Blue-Green Algae warning issues for Green Lake (Horsham) and Lake Wallace (Edenhope). Information on all current algae warnings as well as general information on Blue-Green Algae is available from the GWMWater Algae Warnings webpage.