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), 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 downstream of 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.

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 fish including black bream and galaxiids

Maintain the population of frogs

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, riparian 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 the population of waterbugs, to break down dead organic matter and support the river’s food chain

Maintain dissolved 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 macroinvertebrate 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

The Werribee system experienced below-average rainfall for most of 2017–18 and 2018–19. Storms in November and December 2018 and January 2019 provided some natural events after a very dry winter/spring period.

Pyrites Creek (reach 6) is an ephemeral system that naturally flows from winter until early summer (depending on local inflows) and then dries out over summer/autumn. Water for the environment is delivered to reinstate parts of this natural flow regime. In 2018–19, water for the environment was used to deliver low flows and two freshes (in October and December 2018) to Pyrites Creek (reach 6) from late spring 2018 until early summer. These flows flushed organic matter from benches and supported the recruitment and growth of native vegetation in the stream and along the margins of the banks. A significant proportion of flow in Pyrites Creek seeps into groundwater reserves or evaporates, but all flow that reached Melton Reservoir was re-harvested for later use.

The lower Werribee River had lower-than-average flows for much of 2018–19. The only notable natural event was an unseasonal storm in January 2019 that delivered a large fresh. Water for the environment was released from Melton Reservoir to deliver three freshes and a low flow to the lower Werribee River in autumn 2019. These flows helped to maintain water quality and allowed native fish, platypus and waterbugs to access feeding and breeding habitat.

Low water availability and dry climate conditions meant that the recommended spring freshes were not achieved in the lower Werribee in 2017–18 or 2018–19. Spring freshes help support the migration of native fish between the marine and estuary environments into freshwater reaches of the Werribee River, and the lack of these flows helps to explain why fewer migratory fish have been detected in routine fish surveys in the lower Werribee River over the last two years.

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 freshes (up to three freshes of 30 ML/day for two days during September to October)	Drown terrestrial plant species that cannot tolerate being inundated Increase the growth and recruitment of riparian and in-stream vegetation Scour silt, biofilms and algae from substrates to maintain the quality and quantity of food and habitat for waterbugs Inundate depressions adjacent to the stream that frogs can use for breeding
Spring/summer high flows (up to three high flows of 130 ML/day for two days during September to December)	Drown terrestrial plant species that cannot tolerate being inundated Increase the growth and recruitment of riparian 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 Inundate depressions adjacent to the stream that frogs can use for breeding
Winter/spring/summer low flows (2 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
Lower Werribee River (reaches 8, 9 and the estuary)
Spring/summer freshes (up to two freshes of 50–80 ML/day for two days during November to December)	Drown terrestrial species and support the growth and recruitment of water-dependent riparian 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 to support native fish recruitment in the estuary Maintain the quality and quantity of food and habitat for waterbugs Inundate depressions adjacent to stream that frogs can use for breeding
Year-round low flows (10 ML/day)¹	Maintain the growth and recruitment of in-stream vegetation Support the growth and recruitment of water-dependent riparian 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
Summer/autumn freshes (up to five freshes of80 ML/day² for two days during November to April)	Drown terrestrial species and support the growth and recruitment of water-dependent riparian 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
Winter/spring/summer freshes (up to four freshes of 350 ML/day for three days during June to December)	Drown terrestrial species and support the growth and recruitment of water-dependent riparian 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 Inundate depressions adjacent to stream that frogs can use for breeding
Increased winter/spring low flows (up to 80 ML/day or natural during June to November)	Provide flows to allow fish to move upstream past natural and artificial barriers Support the growth and recruitment of water-dependent riparian 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

¹The original recommendation from the flow study (Ecological Associates 2005, Jacobs 2014) is for 89 ML per day for four days throughout autumn. Construction of a fishway has reduced the required flow rate, and less flow is required to enable fish movement.

² The original recommendation from the flow study (Ecological Associates 2005, Jacobs 2014) is for 137 ML delivered in one day. The recommendation has been revised due to operational constraints to be 160 ML delivered over two days. Monitoring has shown that this achieves the hydraulic and water quality objective.

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 Parks Victoria Port Phillip and Westernport CMA Zoos Victoria Melton Shire Council Wyndham City Council Southern Rural Water Victorian Environmental Water Holder Department of Environment, Land, Water and Planning Werribee Anglers Club

Page last updated: 12/12/19