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 3.3 Tarago system
Scenario planning
Table 3.3.2 outlines the potential environmental watering and expected water use under a range of planning scenarios.
Summer and autumn freshes are considered high priority under all climatic conditions. These freshes aim to top up pool habitats and improve water quality, which helps to maintain the quality and quantity of available habitat for
fish, macroinvertebrates and platypus. Freshes temporarily increase river depth in riffles and run habitats between pools, allowing native fish to move within and between reaches. Freshes also wet sand bars and lower sections of the riverbank, which helps to prevent the encroachment and growth of unwanted terrestrial species in the waterway.
An autumn high flow is needed to cue Australian grayling
to spawn. As this is a short-lived species, the autumn high flow should be delivered in at least two out of every three years. In average and wet years, this increases to an annual requirement. The autumn high flow was partially achieved in 2018–19 and fully achieved in 2019–20. Hence, full delivery of an autumn high flow is a tier 2 priority for 2020–21, although a partial autumn high flow using a lesser volume of water may be delivered under dry and average conditions.
Under average and wet scenarios, a spring high flow may be delivered to support the migration of native fish. This flow has not been achieved with environmental flows since 2012–13, and although reach 6 has received some natural spring high flows, reach 2 has not. The spring high flow will encourage movement and cue the upstream migration of juvenile native fish species including Australian grayling, common galaxias and tupong.
The spring high event is a higher priority than the winter/ spring freshes, because previous monitoring has shown it triggers more fish to move.
A carryover volume of 700–1,000 ML is required to support high-priority actions (such as summer/autumn freshes) in 2021–22.
      100 | Victorian Environmental Water Holder | Seasonal Watering Plan 2020–21

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