VEWH - Werribee system

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), Wirribi Yaluk (Werribee River) between Melton Reservoir and the Werribee Diversion Weir (reach 8), Wirribi Yaluk (Werribee River) between the Werribee Diversion Weir and Werribee Park Tourism Precinct (reach 9) and the Werribee River estuary below the Werribee Park Tourism Precinct.

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 lower Wirribi Yaluk (Werribee River).

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

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

Maintain channel beds and pool habitats Maintain clean substrate surfaces to support biological processes

Maintain the platypus population

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

Maintain oxygen and salinity levels in pools

Environmental values

The Werribee system supports a range of native fish including Australian grayling, 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, a diverse waterbug community and platypus inhabit the upper and 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, and it provides nursery habitat for juvenile freshwater fish species and estuarine species (such as black bream).

Recent conditions

The Werribee system catchment experienced wetter-than-average conditions in autumn 2020 and throughout 2020-21. High rainfall in autumn 2020 caused Pykes Creek Reservoir and Melton Reservoir to fill and spill, and both storages spilled on several occasions throughout late spring and summer 2020-21. Allocations against high-reliability water shares in Melton Reservoir reached 100 percent by December 2020, and low-reliability water shares reached 80 percent by March 2021. In contrast, Lake Merrimu had below-average inflows and contributed only a small volume to the environmental entitlement in 2020-21.

Pyrites Creek did not have any significant natural high-flow events in 2020-21. Water for the environment was used to deliver a spring fresh, a spring/summer high flow and maintain low flows to the end of December. These flows enabled connections

between habitat pools for native fish, frogs and waterbugs. The flows supported the recruitment and growth of native vegetation within the creek and on the banks, and it flushed sediment from pools along the length of the reach. Most of the water delivered during the high flow in September and the fresh in December was re-harvested at Melton Reservoir and used to deliver watering actions in lower Wirribi Yaluk (Werribee River).

Spills from Melton Reservoir provided some large natural flows through reaches 8 and 9 and the Werribee River estuary during spring and summer. Water for the environment was used to deliver a partial spring/summer high flow in September to support the upstream migration of native fish from the estuary. Small environmental flows were delivered during summer and autumn to freshen the lower reaches and flush algal blooms that developed near the Werribee Zoo. The storage manager’s increased passing flows below the Werribee Diversion Weir met the low-flow watering actions during late summer, autumn and winter.

Water for the environment was managed in the Werribee system in accord with an average climate scenario in 2020-21. Most planned watering actions were fully met. The spring high flow in Pyrites Creek and winter/spring fresh in the lower Wirribi Yaluk (Werribee River) were only partially delivered due to capacity constraints at reservoir outlets, but the expected watering effects and environmental objectives for these flows were likely met.

Delivering a partial winter/spring fresh in 2021-22 under dry and average conditions and a full winter/spring fresh under wet conditions will remain a high priority, to support black bream recruitment following a fish death event in early 2020 linked to low oxygen and an excess influx of nutrients in stormwater.

Traditional Owner cultural values and uses

Melbourne Water has made initial contact with the Wadawurrung Traditional Owners Aboriginal Corporation and Wurundjeri Woi wurrung Cultural Heritage Aboriginal Corporation to discuss environmental watering in the Werribee system.

There are more opportunities for Melbourne Water and the VEWH to work with the Traditional Owner groups to identify and better integrate cultural values and their flow requirements into the environmental watering program on an ongoing basis.

The Wadawurrung Traditional Owners Aboriginal Corporation has reviewed the environmental values for the Werribee system and has identified the following values that also have cultural significance to Wadawurrung Traditional Owners.

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Reach	Extent	Key environmental values with cultural significance to the Wadawurrung
8	Wirribi Yaluk (Werribee River)
9	Wirribi Yaluk (Werribee River) between Wyndham Vale and Bluestone Ford
Estuary	Werribee River downstream of Bluestone Ford

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 canoeing, fishing, kayaking and swimming)
riverside recreation and amenity (such as picnicking)
community events and tourism (such as Werribee Zoo)

Scope of environmental watering

Table 1 Potential environmental watering actions, expected watering effects and associated environmental objectives for the Werribee system

Potential environmental watering action	Expected watering effects	Environmental objectives
Pyrites Creek (reach 6)
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
Spring fresh(es) (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 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 Improve water quality and the quantity of food and habitat for waterbugs, frogs and native fish Wet depressions adjacent to the stream that frogs can use for breeding
Spring/summer high flow(s) (one to three high flows of 130 ML/ day for two days during September to December)	Maintain access to food and habitat for waterbugs, native fish and frogs Increase the growth and recruitment of in-stream vegetation
Lower Werribee River (reaches 8, 9 and the estuary)
Winter/spring low flow (up to 80 ML/day during June to November)	Provide flow 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
Winter/spring fresh(es) (one to four freshes of 250-350 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 flow 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
Summer/autumn low flow (10 ML/day during December to May)	Increase the growth and recruitment of in-stream and water-dependent streamside vegetation Maintain access to habitat and improve water quality for native fish, frogs, platypus and waterbugs Maintain flow through pool habitats to allow mixing or suppression/ dilution of saline groundwater intrusion
Summer/autumn fresh(es) (one to five freshes of 80 ML/day for two days during November to May)	Increase 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 of water within pools by dispersing azolla and blue- green algae blooms

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

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: 22/01/21