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The Werribee River flows south-east from the Wombat State Forest near Ballan before dropping through the Werribee Gorge to Bacchus Marsh and then flowing into Port Phillip Bay at Werribee. The Lerderderg River is a major tributary that joins the river at Bacchus Marsh. The main storages in the Werribee system are Pykes Creek Reservoir, Melton Reservoir and Merrimu Reservoir.

The priority river reaches for environmental flow delivery in the Werribee system are the reach downstream of Lake Merrimu (reach 6), the reach within Werribee (reach 9) and the estuary. These support a diverse range of native fish species, waterbugs and platypus. Flows targeting the estuary are expected to provide some benefits to reach 8 and water may also be delivered for environmental objectives in this reach under suitable conditions. Environmental water released from Lake Merrimu can be reharvested in Melton Reservoir, minus en route losses. It can then be held and re-released from Melton at a later date to achieve environmental objectives in the lower Werribee River. Flows are measured downstream of Lake Merrimu (reach 6), downstream of Melton Reservoir (reach 8) and at the Werribee Diversion Weir for reach 9 and the estuary.

Waterway manager
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

Plant icon
Maintain diverse macrophytes (large water plants) and shrubs to provide shade and food for organisms further up the food chain
Fish icon
Protect and increase native fish populations including black bream and galaxiids by providing pool habitat and flows for fish to move upstream and downstream and encouraging fish to spawn
Maintain habitat for frogs
Provide or improve habitat for waterbugs
Water icon
Maintain pool water quality for fish and platypus and inundate estuary salt marshes with brackish water
Landscape icon
Move built-up silt from riffles (in the shallower parts of the river)

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. A highly diverse community of frogs and waterbugs 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).

Social, cultural and economic values

The Werribee River is a much-needed resource for agriculture, industry, recreation and tourism. The system provides irrigation water for agricultural industries throughout the Bacchus Marsh and Werribee areas (including the market gardens at Werribee South) and domestic water for Melton and Bacchus Marsh.

The Werribee River and its tributary the Lerderderg River flow past popular camping and hiking spots in the Wombat State Forest and Lerderderg State Park. Along its length, the Werribee River provides opportunities for recreational activities including fishing, bird watching, passive boating (such as canoeing and kayaking) and bushwalking.

In the lower reaches, the river meanders through the Werribee River Park and Werribee Park Tourism Precinct. The precinct includes the Werribee Open Range Zoo, National Equestrian Centre, Mansion Hotel & Spa and Werribee Park Golf Club, and it contributes more than $116 million a year to the Wyndham local government area. The Werribee River Trail and Federation Trail bike paths are popular recreational cycling routes.

Werribee is an Aboriginal word meaning backbone or spine. Significant Aboriginal cultural heritage sites including fish traps, artefacts and burial sites have been found along the riverbanks and escarpments. The Werribee River continues to be a place of significance for the Wurundjeri, Wadawurrung and Boon Wurrung (Bunurong) people, who are the Traditional Owners in the region.

Conditions mid-2017

Above-average rainfall in winter/spring 2016 ended a four-year dry spell in the Werribee River. Melton Reservoir spilled in September 2016, and unregulated flows passed through the system from September to November 2016. Environmental water helped extend flows in the lower Werribee River in November. Large spring flows are important for the ecology of the lower Werribee River and would have naturally occurred in most years. River regulation has significantly reduced the frequency of large spring-flow events and they now occur only in wet years when the reservoirs spill.

The current environmental entitlement in the Werribee system is not sufficient to deliver large-flow events. An additional 1,100 ML was made available to the environment in 2015–16 and it was carried over specifically to deliver a large, spring flow. The release in November 2016 was the largest single release of environmental water in the Werribee catchment to date. Environmental water was also used to deliver freshes to the lower Werribee River in autumn to maintain water quality and support native fish habitat and recruitment.

Environmental water was delivered to Pyrites Creek (reach 6) from Lake Merrimu in spring 2016. A high-flow event was delivered at the beginning of September, before the spring rains. A second high-flow event was delivered in November, after the wet conditions had ended. These flow events flushed organic matter from benches and supported the recruitment and growth of native vegetation along the creek. The first event passed through to the lower Werribee River as Melton Reservoir was spilling at the time. The second event was re-harvested in Melton Reservoir and reused in the large fresh delivered to the lower Werribee River in November. No environmental water was released from Lake Merrimu to Pyrites Creek in summer/autumn, as a wet winter/spring followed by a dry (cease-to-flow) summer/autumn is the natural cycle of this creek.

Scope of environmental watering

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

Potential environmental watering

Environmental objectives

Pyrites Creek (reach 6)

Spring/summer freshes (up to 3 freshes of 30 ML/day for 2 days in September–December)

  • Improve waterbug habitat by scouring silt and sand from riffles
  • Promote vegetation growth
Spring/summer high flows (up to 3 high flows of 130 ML/day for 2 days in September–December)
  • Flush organic matter from benches
  • Increase the recruitment and growth of riparian vegetation

Winter/spring/summer low flows (2 ML/day [or natural] in June–December)

  • Create riffle habitat for waterbugs
  • Provide frog habitat
  • Promote the growth of aquatic plants
  • Allow fish movement between pools

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

Spring/summer freshes (up to 2 freshes of 50–80 ML/day for 2 days in November–December)

  • Promote juvenile black bream recruitment
  • Promote longer-distance movement of fish through reach 9
Winter/spring/summer low flows (10 ML/day in June–December)
  • Maintain suitable conditions for black bream spawning and recruitment
  • Provide habitat for waterbugs and fish and support vegetation growth
    in reach 9

Autumn low flows 10 ML/day during March–May

  • Allow downstream migration of diadromous fish — fish that move between freshwater and saltwater to complete their life cycle — to the estuary
  • Provide habitat for waterbugs and fish
  • Support vegetation growth in reach

Summer/autumn freshes (up to 3 freshes of 80 ML/day1 for 2 days during January–April)

  • Maintain pool water quality for fish and platypus in reach 9
  • Increase the recruitment of juvenile black bream in the estuary
  • Scour silt and algae from riffles in reach 8

Winter/spring/summer freshes (up to 4 freshes of 350 ML/day for 3 days during June–December)

  • Increase the diversity of riparian vegetation in reaches 8 and 9
  • Provide fish movement cues (all)
  • Inundate saltmarsh vegetation with brackish water in the estuary

1 Recommendation is for 137 ML delivered in one day. The recommendation has been revised due to operational constraints to be 160 ML delivered over 2 days. Monitoring has shown that this achieves the hydraulic and water quality objective.

2 If this watering action is not delivered in 2015–16, it may be delivered in 2016–17 using the 1,100 ML of additional water provided in 2015–16. This is not shown in the scenario planning table below as it is intended to be delivered in 2015–16 at the time of writing.

Risk management

In preparing its seasonal watering proposal, Melbourne Water considered and assessed the risks of environmental watering and identified mitigation strategies. Program partners continually reassess risks and mitigation actions throughout the water year.

Engagement

Waterway managers meet communities on environmental watering regionally, although other program partners also play a role.

In each region of Victoria, community engagement on environmental watering happens when environmental watering objectives and priorities are scoped (long term and annually), when delivering environmental water, and when reporting on environmental watering results.

Communities in the Melbourne region are involved in decisions about the Tarago, Yarra and Werribee river systems through each system's Environmental Water Advisory Group.

Who is engaged and how

Recreational users

Through formal advisory groups coordinated by Melbourne Water, representatives of recreational user groups are engaged. Advisory group members receive notifications about planned environmental water deliveries via the community bulletin.

For recreational users, safety related to higher water levels are a key concern.

On occasion, Melbourne Water informs recreational users directly about environmental watering (such as the Werribee fishing club or Canoes Victoria).

Environment groups

Representatives of environment groups are engaged through formal advisory groups coordinated by Melbourne Water. Advisory group members receive notifications about planned environmental water deliveries via the community bulletin.

Melbourne Water has informal relationships with various environment groups (such as Landcare, Birdlife Australia, Yarra Riverkeepers, Environment Victoria and Waterwatch) and meet with these groups on an as-needs basis.

Some groups, such as Waterwatch, share monitoring information with Melbourne Water.

Landholders/farmers

Through the Yarra Diversions newsletter, diversions licence holders receive information and updates on environmental watering.

Landholders and farmers are engaged through formal advisory groups coordinated by Melbourne Water. Advisory group members receive notifications about planned environmental water deliveries via the community bulletin.

Traditional Owners

Melbourne Water is doing a collaborative project with the Wurundjeri Tribe Land and Compensation Heritage Council and the Victorian Environmental Water Holder to document the Wurundjeri cultural values in the Yarra river system. The aim of this project is to increase understanding of values that can be supported with environmental water to achieve shared benefits for Aboriginal people from environmental watering (Aboriginal environmental outcomes).

Councils

Through formal advisory groups coordinated by Melbourne Water, Council representatives (from various local councils across region) are engaged. Advisory group members receive notifications about planned environmental water deliveries via the community bulletin.

Melbourne Water publishes an annual two-pager for each Council about activities undertaken in their catchment, including delivery of environmental flows.

General public

Melbourne Water communicates and engages with the general public through their website, media releases and Facebook and Twitter. Melbourne Water community bulletins are posted on their webpage, Facebook and Twitter, and issued to media contacts.