Due to protracted dry and warm conditions, and declining dissolved oxygen values in the lower Werribee, Melbourne Water will deliver a small spring low flow release.
The last significant rainfall impacting flows in the lower Werribee was a short duration event on the 18-19 October. Since that time dry and warm conditions have persisted, which has necessitated bringing a release forward.
Melbourne Water will commence a spring low flow release of approximately 225 megalitres (ML) of water for the environment for the lower Werribee River from Tuesday 12 November to Friday 15 November.
The release will commence from Melton Reservoir and pass over the lower Werribee Diversion Weir on Wednesday 13 November to Friday 15 November with a peak flow of 80 megalitres per day. This will achieve the winter/spring low flow magnitude as set out in the Seasonal Watering Plan 2024-25.
Every year, Melbourne Water release environmental water flows into the Werribee River to mimic the river’s natural flow patterns. They do this in conjunction with the Victorian Environmental Water Holder (VEWH) and Southern Rural Water (SRW).
The specific objectives of this release are to:
- Mitigate declining dissolved oxygen values in the Werribee River below the lower diversion weir
- Provide sufficient depth to allow fish to move upstream past natural and artificial barriers
- Facilitate the downstream movement of diadromous fish to the estuary
- 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, fish, platypus and frogs
- Maintain flow through pool habitats to allow mixing or suppression/dilution of saline groundwater
Environmental flow release in numbers…
- Melbourne Water will release approximately 225 ML of water into the Werribee River system from 12 – 15 November.
- The spring low flow is expected to be a peak flow of 80ML/d for two days (13-14 Nov) downstream of the Lower Werribee diversion weir. The flow volumes will then gradually ramp down on the following two days to avoid stranding aquatic fauna.
- They expect minor increases in the water level which is well within the natural seasonal variation of the river system. A river level rise of approximately 20cm on current conditions may be experienced downstream of the lower diversion weir. River level rise experienced between Melton Reservoir and the lower diversion weir will be well within current operations of the river, as experienced in recent days and weeks.
- Flow conditions will be monitored throughout the release.
This information is kindly provided by Melbourne Water, the water manager for the Werribee River.
More information can be found here Water for the environment | Melbourne Water