Review of January 2021 Operations
January saw above average rainfall totals recorded across the Grampians reservoirs, with rainfall ranging from 100% to 377% of the monthly average. The highest rainfall total for the month was recorded at Lake Bellfield with 145.8 mm (319% of average), followed by 132 mm recorded at Mt Cole Reservoir (316% of average). The lowest rainfall total recorded for the month was Taylors Lake with 24.8 mm (100% of average).
Despite above average rainfall having been recorded at many reservoir locations, key reservoir catchment areas did not receive the higher rainfall totals recorded in adjacent areas. This coupled with dry catchment conditions and high daytime temperatures for much of the month saw inflow to reservoirs of only 750 ML, or 21% of the January average. Total 2020-21 year to date inflow increased to 63,820 ML (59,540 ML excluding Taylors Lake), equivalent to 35% of the historic average inflow for the same period (170,300 ML excluding Taylors Lake).
During January, the total volume in storage decreased from 204,510 ML (36.6%) to 191,730 (34.3%), representing a total decrease of 12,780 ML.
Calculated net evaporation from reservoirs was approximately 5,460 ML for the month; with evaporation from reservoirs exceeding rainfall. This was lower than forecast for the month due to above average rainfall. (Net evaporation considers rainfall on the reservoir as an evaporation offset)
Water for the environment totalling 2,466 ML was released to waterways in the Wimmera catchment during the month, and 1,295 ML was released from Rocklands Reservoir to the Glenelg River.
Wimmera-Mallee Pipeline supplied recreation lakes received 191 ML during the month of January, and no water was delivered to Wimmera-Mallee Pipeline connected wetlands.
Consumptive entitlement holders collectively used 1,651 ML during January to supply their respective urban and rural demands.
Planned February 2021 Operations
The Bureau of Meteorology (BOM) in its most recent Climate Driver Update advised that the current La Niña event has likely peaked in terms of sea surface temperature. However, associated impacts such as increased rainfall are expected to persist across eastern states into early autumn.
The Indian Ocean Dipole (IOD) index remains in a neutral phase, and generally does not have an impact on climatic conditions throughout summer and autumn months.
Beyond monitoring of catchment flows for harvesting opportunities during early February (primarily the Wimmera River, as a result of significant rainfall in its catchment during late January), the Storage Manager’s operational focus for February will continue to remain on the delivery of entitlement holders’ water requirements. Should further rainfall events eventuate, the Storage Manager is well positioned to transition to the planning and coordination of water harvesting activities. However, sporadic rainfall events spaced between periods of warm daytime temperatures often do not generate significant runoff during the summer months.
A number of reservoirs are projected to remain at suitable levels through 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 current restrictions and recreation activities permitted at each reservoir.
Blue-Green Algae above the levels safe for recreational contact have been recorded at 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.
Note: 1 ML = 1 megalitre = 1 million litres