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The four reaches in the Werribee system that can receive water for the environment are Pyrites Creek between Lake Merrimu and Melton Reservoir (reach 6), the Werribee River between Melton Reservoir and the Werribee Diversion Weir (reach 8), the Werribee River between the Werribee Diversion Weir and Werribee Park Tourism Precinct (reach 9) and the Werribee estuary below the Werribee Park Tourism Precinct (the estuary).

Environmental watering that targets environmental objectives in reach 9 and the estuary is delivered from Melton Reservoir and therefore also benefits reach 8. Water for the environment released from Lake Merrimu is re-harvested in Melton Reservoir, where it can be held and released at an appropriate time to achieve environmental objectives in the lower Werribee River.

Waterway manager
Traditional Owners
Storage manager
Environmental water holder

System map

Werribee System
Grey river reaches have been included for context. The numbered reaches indicate where relevant environmental flow studies have been undertaken. Coloured reaches can receive environmental water.

Environmental watering objectives in the Werribee River

Fish icon
Protect and increase populations of native freshwater fish species including galaxiids Protect and increase populations of black bream in the estuary
Maintain native frog populations
Landscape icon
Maintain channel beds and pool habitats Maintain clean substrate surfaces to support biological processes
Platypus icon
Maintain the platypus population
Plant icon
Maintain the health and increase the cover of in-stream, streamside and estuary plants Limit the spread of terrestrial plants, and promote the recruitment of native waterdependent plant species on the banks and benches of waterways
Maintain and enhance the population of waterbugs, to break down dead organic matter and support the river’s food chain
Water icon
Maintain oxygen and salinity levels in pools

Environmental values

The Werribee system supports a range of native fish including river blackfish, flathead gudgeon, short-finned eel, tupong, Australian smelt, several species of galaxiids, and a large population of black bream in the estuary. Several species of frogs and diverse waterbug communities inhabit the upper reaches and platypus are present in the lower reaches. The freshwater-saltwater interface of the Werribee River estuary is a regionally significant ecosystem due to the many aquatic plants and animals it supports, providing nursery habitat for juvenile freshwater fish species and estuarine species such as black bream.

Recent conditions

Total rainfall in the Werribee system during 2019–20 was close to the long-term annual average, but rainfall was not evenly distributed across all reaches or storages. Pykes Creek Reservoir and Melton Reservoir both spilled in winter and spring 2019, which delivered large flows to the lower Werribee River. Inflows to Lake Merrimu remained low throughout the year, and environmental flows provided some flow in Pyrites Creek in spring 2019. By early March 2020, holders of high-reliability water shares in the Werribee system had received 100 percent allocations, and holders of low-reliability water shares had received 60 percent allocations. Small volumes of inflows into Lake Merrimu were attributed to the environmental entitlement throughout 2019–20.

Most of the potential watering actions for the lower Werribee River were delivered in 2019–20. Natural events provided regular freshes throughout the year, and water for the environment was used to deliver additional summer freshes and some low flows in June 2020. One of the summer freshes was used to flush an algal bloom that developed in the lower Werribee River during early summer. Low flows during autumn and winter were achieved by passing flows delivered by the storage manager.

In Pyrites Creek, water for the environment was used to deliver low flows and two spring freshes. These flows connected habitat pools for frogs, waterbugs and native fish, flushed sediment from pools and supported the recruitment and growth of native vegetation in the stream and along the margins of the banks. About one-third of flow in Pyrites Creek seeps into groundwater reserves or evaporates, but all flow that

Traditional Owner cultural values and uses

Melbourne Water has made initial contact with Wathaurung Aboriginal Corporation (Wadawurrung) and Wurundjeri Woi-Wurrung Cultural Heritage Aboriginal Corporation, to discuss environmental watering in the Werribee system.

Social, recreational and economic values and uses

In planning the potential watering actions in Table 1, Melbourne Water considered how environmental flows could support values and uses including:

  • water-based recreation (such as fishing)
  • riverside recreation and amenity (such as improved water quality for communities)
  • tourism (such as Werribee Zoo).

Scope of environmental watering

Table 1 Potential environmental watering actions and objectives for the Werribee system

Potential environmental watering action

Functional watering objective

Environmental objective

Pyrites Creek (reach 6)

Spring fresh (one to four freshes of 40 ML/day for two days during September to October)

  • Drown terrestrial plant species that encroach into the waterway
  • Increase the growth and recruitment of streamside and in-stream vegetation
  • Scour silt, biofilms and algae from substrates to maintain the quality and quantity of food and habitat for waterbugs
  • Wet depressions adjacent to the stream that frogs can use for breeding
Frog iconPlant iconInsect icon 

Spring/summer high flow (one to three high flows of 130 ML/day for two days during September to December)

  • Drown terrestrial plant species that encroach into the waterway
  • Increase the growth and recruitment of streamside and in-stream vegetation
  • Transport carbon to drive aquatic food webs
  • Scour silt, biofilms and algae from substrates to maintain the quality and quantity of food and habitat for waterbugs
  • Wet depressions adjacent to the stream that frogs can use for breeding

Frog iconMountain iconsPlant iconInsect icon

Winter/spring/summer low flow (two ML/day [or natural] during June to December)

  • Maintain access to food and habitat for waterbugs, native fish and frogs
  • Increase the growth and recruitment of in-stream vegetation

Fish iconFrog iconPlant iconInsect icon

Lower Werribee River (reaches 8, 9 and the estuary)

Summer/autumn fresh (one to five freshes of 80 ML/ day for two days during November to May)

  • Support the growth and recruitment of water-dependent streamside vegetation
  • Flush silt and scour biofilms and algae from substrates on the stream bed and maintain pools and channel dimensions
  • Maintain access to habitat and improve water quality for native fish, frogs and platypus
  • Provide enough flow for native fish to move downstream past natural or artificial barriers
  • Maintain the quality and quantity of food and habitat for waterbugs

Fish iconFrog iconMountain iconsPlatypus iconPlant iconInsect iconWater drop icon

Winter/spring fresh (one to two freshes of 350 ML/day for three days during June to October)
  • Support the growth and recruitment of water-dependent streamside vegetation
  • Flush silt and scour biofilms and algae from substrates on the stream bed and maintain pools and channel dimensions
  • Provide movement cues and enough flows for fish to move upstream past natural and artificial barriers
  • Maintain water quality and quantity of food and habitat for waterbugs and platypus
  • Wet depressions adjacent to the stream that frogs can use for breeding

Fish iconFrog iconMountain iconsPlatypus iconPlant iconInsect iconWater drop icon

Summer/autumn low flow (six ML/day during December to May)

  • Maintain the growth and recruitment of in-stream vegetation
  • Support the growth and recruitment of water-dependent streamside vegetation
  • Maintain water quality and food in pool habitats for native fish
  • Maintain access to habitat for native fish, frogs, platypus and waterbugs
  • Maintain flow through pool habitats to allow mixing or suppression/dilution of saline groundwater intrusion

Fish iconFrog iconMountain iconsPlatypus iconPlant iconInsect iconWater drop icon

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

Fish iconFrog iconPlatypus iconPlant iconInsect iconWater drop icon

Engagement

Table 2 shows the partners, stakeholder organisations and individuals with which Melbourne Water engaged when preparing the Werribee system seasonal watering proposal.

Seasonal watering proposals are informed by longer-term regional catchment strategies, regional waterway strategies, environmental flow studies, water management plans and other studies. These incorporate a range of environmental, cultural, social and economic perspectives and longerterm integrated catchment and waterway management objectives. For further details, refer to the Port Phillip and Western Port Regional Catchment Strategy and Melbourne Water's Healthy Waterways Strategy.

Table 2 Partners and stakeholders engaged in developing the Werribee system seasonal watering proposal

Partner and stakeholder engagement
  • Werribee Riverkeeper
  • Department of Environment, Land, Water and Planning | Water and Catchments
  • Southern Rural Water
  • Western Water
  • Environment Protection Authority
  • Parks Victoria (land manager)
  • Port Phillip and Westernport Catchment Management Authority
  • Wyndham City Council
  • Zoos Victoria
  • Werribee Anglers Club
  • Melbourne University – research collaborators
  • Monash University
  • Arthur Rylah Institute (Department of Environment, Land, Water and Planning)
  • Boon Wurrung Foundation
  • Bunurong Land Council Aboriginal Corporation
  • Wurundjeri Woi-Wurrung Cultural Heritage Aboriginal Corporation
  • Wathaurung Aboriginal Corporation

Page last updated: 24/07/20