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Recent conditions
The Macalister River catchment has observed ongoing
very dry climatic conditions over the last three years.
Rainfall has been below average and temperatures warmer than average. In June 2019, the storage level at Lake Glenmaggie was exceptionally low: just 6.1 percent of the full reservoir capacity. Opening allocations of 45 percent towards high-reliability water shares were declared by the storage manager, and this increased to 80 percent by mid-August after inflows improved the water storage level. Despite the dry start, continued inflows over spring led to full allocations for high-reliability water shares by the end of September 2019, boosting water available for environmental watering. Low-reliability water shares also increased throughout the year in response to inflows, reaching full allocation in April 2020.
As of 1 June 2020, Lake Glenmaggie had not spilled in 2019–20. This is an unusual occurrence: historically, Lake Glenmaggie spills most years, as it is a relatively small reservoir in a productive water catchment. 2019–20 was the second consecutive year without a spill, demonstrating how dry the system has been in recent times. Without a spill, the natural high and bankfull flows that usually occur in the Macalister River in winter/spring were absent, but above Maffra Weir the river flowed steadily for most of the year, because water for irrigation and urban supply is delivered between Lake Glenmaggie and the offtake at Maffra Weir. Below Maffra Weir, some moderate natural flows occurred in spring and late summer after heavy rainfall.
Environmental flows were delivered year-round to provide several objectives in the Macalister system. Flows were delivered over winter to maintain habitat for aquatic animals and to support the establishment of in-stream vegetation. This included a winter fresh in August 2019, and again in June 2020, which aimed to cue the downstream migration of tupong and Australian bass towards the Latrobe estuary for breeding and spawning. A spring fresh was delivered in early November 2019, to encourage juvenile fish to migrate into the Macalister River from their estuary nurseries as
well as to wet bankside vegetation and enable native seed dispersal.
In autumn 2020, a fresh to cue the downstream migration of Australian grayling towards the Latrobe River estuary for spawning was delivered. This event coincided with an equivalent fresh in the Thomson River system to optimise fish responses across both systems.
All tier 1a watering actions planned for 2019–20 under both a dry and average scenario were met. As Lake Glenmaggie did not spill, there were no tier 1b actions, either with releases of water for the environment or natural and operational flows in the system.
Scope of environmental watering
Table 2.4.1 describes the potential environmental watering actions in 2020–21, their functional watering objectives (that is, the intended physical or biological effect of the watering action) and the longer-term environmental objective(s) they support. Each environmental objective relies on one or more potential environmental watering actions and their associated physical or biological functions.
2.4 Macalister system
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