Page 128 - VEWH Seasonal Watering Plan 2020-21
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 3.7 Barwon system
Table 3.7.1 Potential environmental watering actions and objectives for the upper Barwon River
  Potential environmental watering action
  Functional watering objectives
  Environmental objectives
  Summer/autumn low flow (continuous 0.5–30 ML/day during December to May)
• Maintain an adequate depth of permanent water in the channel/pools to support resident fish, platypus and waterbugs
• Promote the recruitment of native aquatic vegetation
• Reduce encroachment by terrestrial plants into aquatic zone
• Provide minimum velocity to maintain mixing in pools
                 Summer/autumn freshes (two freshes of nine to 35 ML/day for two days during December to May: east branch only)
    • Provide longitudinal connectivity with water over riffles to allow fish to move between pools to breed, feed and find new habitats
• Submerge woody debris and clean hard surfaces to provide breeding substrate
• Maintain waterbug communities in the dry period by flushing organic matter into the channel to provide food after inundating benches
• Maintain emergent and streamside vegetation on terraces, the channel edge and lower bank
• Provide minimum velocity to mix and flush pools
                  Winter/spring low flow (continuous 10–50 ML/day or natural during April to November)
 • Maintain an adequate water depth in the channel/pools to support fish and platypus foraging and breeding habitat
• Maintain an adequate depth of permanent water in the channel to promote the recruitment of aquatic and streamside plants and to limit the encroachment of terrestrial species
• Provide minimum velocity, to mix pools
            Scenario planning
Table 3.7.2 outlines the potential environmental watering and expected water use under a range of planning scenarios.
The upper Barwon environmental entitlement can only support a small proportion of the environmental flow recommendations for the upper Barwon River. The highest- priority potential watering actions under all scenarios are summer/autumn low flows and freshes. The size of these events is likely to be less than recommended in the latest environmental flows study, due to system constraints and expected water availability.
Watering actions in the east branch of the Barwon River will be prioritised, because it has higher environmental values than the west branch and because relatively small flows
in the east branch have the potential to deliver significant environmental outcomes. Some low flows may be delivered down the west branch under dry, average or wet scenarios to help meet target flow objectives further downstream.
An additional 18,000 ML of water for the environment
is required to achieve the remaining potential watering actions (tier 1b) in the upper Barwon River. The tier 1a watering actions described here should help to maintain current environmental values and conditions in the upper Barwon River, but larger environmental entitlements and complementary works that address non-flow-related impacts in the catchment will be needed to significantly improve environmental conditions.
It is intended to carry over up to 500 ML at the end of 2020–21 to ensure the highest-priority flows can be achieved under any scenario in the following year.
    126 | Victorian Environmental Water Holder | Seasonal Watering Plan 2020–21

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