Review of May 2019 Operations
Minor inflows were observed to Rocklands Reservoir, Lake Wartook, Lake Lonsdale and Lake Fyans during May. In total, there was 2,800 ML of inflow received, increasing the 2018-19 year to date inflows to 40,920 ML (or 38,340 ML excluding Taylors Lake). This is equivalent to 21% of the historic average inflow for the same period (182,500 ML excluding Taylors Lake inflow).
During May, the volume in headworks reservoirs increase only slightly, from 190,890 ML (34.1%) to 191,220 ML (34.2%).
Rainfall across the Grampians catchments was above average during May. The highest rainfall for the month was 135 mm, recorded at Lake Wartook (137% of average), followed by 123.4 mm recorded at Lake Bellfield (125% of average). Toolondo Reservoir was the only storage to record less rainfall than the average, with 39.4 mm (80% of average). Calculated net evaporation from reservoirs was approximately -1,860 ML for the month; with rainfall exceeding evaporation for the first time since August 2018 (Net evaporation considers rainfall on the reservoir as an evaporation offset).
Environmental water releases continued in both the Wimmera and Glenelg catchments, with a total of 1,477 ML delivered to the Wimmera River from Taylors Lake, and 246 ML supplied to the lower MacKenzie River and Burnt Creek from Lake Wartook. A total of 1,670 ML was released from Rocklands Reservoir to the Glenelg River, including 230 ML of the Glenelg River Compensation Flow.
Wimmera-Mallee Pipeline supplied recreation lakes received 94 ML throughout the month of May, with top-up supplies made to number of lakes. Water supply to Wimmera-Mallee Pipeline connected wetlands within the Mallee region continued, with 17 ML delivered in May. The watering of a number of wetlands within the Wimmera region commenced, with a total of 5 ML delivered.
Consumptive entitlement holders collectively used 1,223 ML during May to supply urban and rural demands.
Planned June 2019 Operations
The Bureau of Meteorology (BOM) in their most recent El Niño -Southern Oscillation (ENSO) outlook have stated climate models remain close to El Niño thresholds, but are expected to ease away from El Niño thresholds, becoming neutral during winter. BoM have downgraded their ENSO outlook to “El Niño WATCH”. This suggests a 50% chance of El Niño conditions developing during 2019, which is still double the chance of normal. During El Niño events, rainfall in south eastern Australia has historically been below average during winter and spring, with warmer daytime temperatures also occurring.
The Indian Ocean Dipole (IOD) is now positive, with recent warming in the Indian ocean causing the threshold to be exceed. All but one of the models surveyed suggest positive IOD levels will be maintained throughout winter. To be considered an event, these values would need to be sustained for at least two months. A positive IOD often results in below average winter–spring rainfall over southern and central Australia.
Above average rainfall received in May made a significant contribution to priming catchments, and further rainfall during June is anticipated to starting producing runoff to reservoirs and waterways. As the catchment becomes saturated and inflows begin to occur, the Storage Manager’s operational focus will transition to water harvesting operations.
Many reservoirs are anticipated to remain at suitable levels through June for a range of recreational activities. Recreation users are reminded to take care and abide by signage at reservoirs. Please refer to theReservoir information page for further information on water levels and recreation activities permitted at each reservoir.
Blue-Green Algae blooms can be more common during warmer months. Recent Blue-Green Algae warnings for reservoirs can be found on the Storage Manager News Feed and all current warnings are available from the GWMWater Algae Warnings webpage.
1 ML = 1 megalitre = 1 million litres