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Scenario planning
Table 5.6.4 outlines the potential environmental watering and expected water use under a range of planning scenarios. Watering actions have only been considered for drought to average scenarios, because the storage is likely to spill under wet conditions, and therefore it will not be possible to accumulate passing flows to deliver environmental flows.
Low flow in summer/autumn is the highest-priority potential watering action across all (drought to average) scenarios, to support aquatic habitats for fish, platypus and waterbugs, and to support aquatic and fringing vegetation in the river.
It should be possible to maintain continuous low flow targets under dry and average conditions, but less water will be available under drought conditions, so it may only be possible to deliver pulsed low flow to maintain refuge habitats
Under dry and average conditions, accumulated passing flows are planned to be used to deliver summer/autumn freshes to support vegetation recruitment, maintain aquatic habitats and clean river substrates. The number of freshes delivered will depend on the available water and observed conditions in the river.
If more water is available under drought conditions, it is planned to be set aside to support critical watering actions in 2021–22 and/or used to increase the magnitude or duration of low flow if conditions in the river deteriorate. Additional water will go to delivering tier 2 priorities which are freshes in summer/autumn (across all scenarios) and in winter/spring (in the drought scenario).
The carryover priority is to bank passing flows in the river for 2021–22 watering actions (700 ML).
Table 5.6.4 Potential environmental watering for the Coliban River under a range of planning scenarios
5.6 Campaspe system
 Planning scenario
  Drought
  Dry
  Average
   Expected river conditions
   • Little or no natural flow
   • Some natural flow
   • Some natural flow
   Expected availability of water for the environment
 • Little passing flow accumulated for use in other times of the season
• Reliant on carryover from 2019–20 year
 • Increase in passing flows, with minimal risk of storage spills
• Maximum accumulation of passing flows
• Withheld flows for use at other times in the season
 • Moderate to high passing flows but reduced ability to accumulate flows due to possible storage spills
 Potential environmental watering – tier 1a (high priorities)
   • Pulsed summer/autumn low flow
• Summer/autumn low flow (reduced magnitude)
   • Summer/autumn low flow (reduced magnitude)
• One to two summer/ autumn freshes
   • Summer/autumn low flow (reduced magnitude)
• One to two summer/ autumn freshes
   Potential environmental watering – tier 1b (high priorities with shortfall)
 • Set aside 2021–22 carryover
• Increased magnitude of summer/autumn low flow
 • Increased magnitude of summer/autumn low flow
 • Increased magnitude of summer/autumn low flow
 Potential environmental watering – tier 2 (additional priorities)
   • Two winter/spring freshes
• Two summer/autumn freshes
   • Increased magnitude of two summer/autumn freshes
   • Increased magnitude of two summer/autumn freshes
   Possible volume of environmental water required to achieve objectives
 • 1,200 ML (tier 1a)
• Tier 1b and 2 – dependent on water resources and river conditions
  • 1,600 ML (tier 1a)
• Tier 1b and 2 – dependent on water resources and river conditions
  • 2,500 ML (tier 1a)
• Tier 1b and 2 – dependent on water resources and river conditions
  Priority carryover requirements
  • Accumulate passing flows for 2021–22 (700 ML)
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