Page 52 - VEWH Seasonal Watering Plan 2020-21
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 2.2. Latrobe system
Table 2.2.1 Potential environmental watering actions and objectives for the Latrobe River (continued)
  Potential environmental watering action
  Functional watering objectives
    Environmental objectives
  Winter/spring low flow (620 ML/day during June to November)
• Wet benches to maintain habitat and support the growth of emergent macrophyte vegetation
• Maintain oxygen levels in pools and maintain sediment (sands and silts) in suspension to prevent pools filling and depositing on substrates, helping to maintain habitat for waterbugs and breeding substrate for river blackfish
• Longitudinal connectivity to allow movement/dispersal of aquatic animals
             1 This fresh may involve inundating private land if delivered at higher magnitude, and it will be subject to obtaining landholder agreement. The magnitude of delivery depends on the relative contribution possible from the Thomson system.
Scenario planning
Table 2.2.2 outlines the potential environmental watering and expected water use under a range of planning scenarios.
Under all scenarios, summer/autumn freshes are a high priority in the Latrobe system. At durations of one to five days, these events aim to maintain the physical form of the river bed and improve water quality by flushing sediments and mixing water in pools, which supports aquatic animals including waterbugs. Longer duration freshes (seven to
10 days) will also meet water quality, fish and vegetation objectives for the Latrobe estuary and are a high priority under dry, average and wet scenarios. To meet the flow requirements for the Latrobe estuary, these longer-duration freshes need to coincide with releases in the Thomson River, as the full estuary fresh cannot be delivered from Blue Rock Reservoir without inundating some private land.
Summer/autumn low flows are a high priority under a drought scenario, to maintain oxygen and connectivity between pools. Water for the environment is unlikely to be required to deliver these flows under other scenarios because they are expected to be met naturally.
If more environmental water is available under a drought scenario, it may be used to increase the duration of summer/autumn low flows and/or deliver a summer/autumn estuary fresh. Under a dry scenario, extra environmental water would be used to deliver an additional summer/ autumn estuary fresh.
Winter/spring freshes will improve environmental outcomes under average and wet scenarios. They are considered a high priority under a wet scenario, but there may not be enough available water to deliver them under an average scenario, so they are identified as a tier 1b priority. Large winter/spring freshes may wet private land and therefore landholder agreements will be needed before they are delivered as a managed environmental flow.
Winter/spring low flows and freshes are considered a lower priority under drought and dry scenarios. No tier 2 watering actions have been identified for the Latrobe River under average or wet scenarios, as natural inflows are expected to meet the remaining demands.
            50 | Victorian Environmental Water Holder | Seasonal Watering Plan 2020–21

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