Page 115 - VEWH Seasonal Watering Plan 2020-21
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Table 3.5.1 Potential environmental watering actions and objectives for the Werribee system (continued)
3.5 Werribee system
  Potential environmental watering action
  Functional watering objectives
   Environmental objectives
  Increased winter/spring low flow (up to 80 ML/day or natural during June to November)
• Provide flows to allow fish to move upstream past natural and artificial barriers
• Drown terrestrial plant species and support the growth and recruitment of water-dependent streamside vegetation
• Maintain permanent pools and increase the extent of habitat for waterbugs, platypus and frogs
• Maintain flow through pool habitats to allow mixing or suppression/dilution of saline groundwater
                Scenario planning
Table 3.5.2 outlines the potential environmental watering and expected water use under a range of planning scenarios.
The highest-priority potential watering actions for Pyrites Creek under all scenarios are spring freshes, spring/ summer high flows and winter/spring/summer low flows. These flows will maintain connected aquatic habitats from winter to summer, maintain streamside and in-stream vegetation zones and periodically wet channel margins that can support frog breeding. Fish and other aquatic animals will retreat to permanent pools that are maintained by groundwater in summer and autumn. The highest- priority watering actions for the lower Werribee River under all scenarios are summer/autumn freshes and winter/ spring freshes. Passing flows and operational deliveries for irrigation customers are expected to meet most low-flow requirements in the lower Werribee River, but managed environmental flows are important to control water quality and provide regular opportunities for fish and platypus to move throughout the lower Werribee River and to support streamside and aquatic vegetation.
The number of freshes delivered to both Pyrites Creek and the lower Werribee River will vary between dry, average and wet scenarios, depending on water availability. Water for the environment may be used to supplement summer/autumn low flows in the lower Werribee River under a wet scenario, but more environmental water would need to be secured
to deliver these flows under dry or average scenarios. A minimum of 980 ML is planned to be carried over into 2021–22 to ensure high-priority flows can be delivered to Pyrites Creek (reach 6) and the lower Werribee River, if environmental water allocations are low.
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