VEWH - Werribee system

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 Werribee River and its tributaries continue to be a place of significance for Traditional Owners and their Nations. The Registered Aboriginal Parties (RAPs) in the Werribee River area are the Wathaurung Aboriginal Corporation (on the western side of the Werribee River) and the Wurundjeri Land and Compensation Cultural Heritage Council Aboriginal Corporation (on the eastern side of the river in the upper catchment).

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

Maintain the cover of in-stream, riverside and estuary plants

Protect and increase populations of native fish by improving pool habitat and stimulating fish including black bream and galaxiids to migrate and spawn 

Maintain populations of frogs by providing suitable habitat

Maintain populations of waterbugs to break down dead organic matter and support the river’s food chain

Maintain pool water quality for native fish, frogs, waterbugs and platypus

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 and economic values

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

The Werribee River and its tributary the Lerderderg River support 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, birdwatching, canoeing, kayaking and bushwalking.

In the lower reaches, the river meanders through the Werribee River Park and Werribee Park Tourism Precinct (which includes the Open Range Zoo, National Equestrian Centre, Shadowfax Winery, Mansion Hotel and Spa, Western Treatment Plant, Refectory and Golf Club) which attracts more than a million visitors a year to the region. The Werribee River Trail and Federation Trail bike paths are popular recreational cycling routes.

Conditions 2018

After a wet 2016–17, winter 2017 was one of the driest winters on record for the Werribee system. Drier conditions prevailed across the catchment with below-average rainfall and higher-than-average temperatures in spring, summer and autumn 2017–18. Small volumes of water for the environment were delivered to protect and maintain current ecological objectives in the Werribee system.

Water for the environment was delivered into Pyrites Creek (reach 6) from Lake Merrimu in spring 2017. High flows were delivered at the beginning of October 2017 and flows were reharvested in Melton Reservoir for later use. A second fresh in November 2017 was passed through Melton Reservoir to meet flow objectives in the lower Werribee River. These flows flushed organic matter from benches and supported the recruitment and growth of native vegetation along the creek. No water for the environment 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.

Flows in the lower Werribee River in 2017–18 were low all year, except for a few freshes that resulted from storms in spring/summer. The fresh delivered to Pyrites Creek in
November 2017, combined with water held in storage — reharvested flows from Pyrites Creek low flows and the October fresh — was released from Melton Reservoir to deliver a large fresh to the lower Werribee River. Water for the environment was delivered in the lower Werribee River in autumn 2017, to maintain water quality and support native fish habitat and recruitment. Monitoring in the last two years in the lower Werribee River has detected a higher catch rate of young-of-year galaxiid species following high freshes in November 2016 and November 2017. These flows provide suitable conditions for diadromous native fish to complete their lifecycles — to disperse and breed — in southern Victoria's coastal rivers.

Another exciting discovery in the lower Werribee River was the presence of a young-of-year Australian grayling caught in November 2016 and an another, older one, caught in autumn 2017. These represent the first and second records of Australian grayling in the Werribee River system, and it is likely due to improved fish passage in the Werribee River thanks to recently constructed fishways and managed flows.

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)	Provide frog and waterbug habitat Promote 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 Promote longer-distance movement of native fish through reach 9, including black bream
Autumn low flows 10 ML/day during March–May¹	Provide flows to allow native diadromous fish to move between the freshwater river and saltwater estuary to complete their life cycle Provide habitat for waterbugs and native fish, and support plant growth in reach 9
Summer/autumn/winter freshes (up to 3 freshes of 80 ML/day² for 2 days during January–May)	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

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. This is usually the last watering action in a year, so duration is matched to remaining available water in Melton Reservoir.

² 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.

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

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
Department of Environment, Land, Water and Planning Landholders including Zoos Victoria Southern Rural Water Victorian Environmental Water Holder Werribee River Community Advisory Group including representatives of Melton and Wyndham councils, Werribee Riverkeeper, Werribee South Fishing Club, Werribee and District Anglers Club, Western Water, Port Phillip and Westernport CMA