VEWH - Yarra system

Up to 400,000 ML per year (long-term average diversion limit) can be harvested from the Yarra system for consumptive use in Melbourne and surrounding areas. The Upper Yarra, O’Shannassy and Maroondah reservoirs harvest water from headwater tributaries, and a pump station at Yering Gorge is used to divert water from Birrarung (Yarra River) to Sugarloaf Reservoir.

Flow in the upper reaches of Birrarung (Yarra River) is influenced by tributaries (such as Armstrong Creek, McMahons Creek, Starvation Creek, Woori Yallock Creek, Watts River and Little Yarra River). Urbanised tributaries (such as Olinda Creek, Mullum Mullum Creek, Diamond Creek, Plenty River and Merri Creek) provide additional water to the middle and lower reaches of Birrarung (Yarra River).

Environmental flows can be released from the Upper Yarra, Maroondah and O’Shannassy reservoirs to support ecological processes and environmental outcomes in downstream river reaches and wetlands. The priority environmental flow reaches in Birrarung (Yarra River) are reaches 2 and 5, shown in Figure 3.2.1. Reach 6 is also a priority in summer and autumn to

manage poor water quality upstream of Dights Falls, as flow targets in reach 5 may not be sufficient. Water for the environment delivered to reaches 2 and 5 will help meet flow targets in other reaches.

Plenty River rises from the slopes of Mount Disappointment in the Great Dividing Range about 50 km north of Melbourne. It flows downstream through rural and semi-rural areas and Plenty Gorge before joining Birrarung (Yarra River) near Viewbank, east of Banyule Flats Reserve. Yan Yean Reservoir is located off the waterway, north of Plenty Gorge, and it receives flows from Toorourrong Reservoir via a channel. The Plenty River has not received managed environmental flows before, but there may be opportunities to deliver water for the environment from Yan Yean Reservoir in the coming years.

System map

Environmental watering objectives in the Yarra River

Protect and increase populations of native fish, including threatened species (such as the Australian grayling, Macquarie perch and river blackfish)

Maintain the population of frogs, particularly on the mid-Birrarung (Yarra River) floodplain

Maintain the form of the river channel

Scour silt from riffles and clean cobbles

Maintain the population of resident platypus

Maintain native streamside and aquatic vegetation on the riverbank and in the channels

Increase the growth of threatened wetland plant species to rehabilitate shallow marsh, deep marsh and freshwater meadows on the floodplain and billabongs

Provide wetted habitat area for waterbirds

Maintain and increase the abundance and diversity of waterbugs to support aquatic food webs

Improve water quality in river pools, ensuring adequate oxygen concentration in the water to support fish, crustaceans and waterbugs

Environmental values

The upper reaches of Birrarung (Yarra River) (reaches 1-3) provide habitat for a range of native fish species, including river blackfish, mountain galaxias and common galaxias, and they have good-quality streamside and aquatic vegetation. The middle and lower reaches of Birrarung (Yarra River) (reaches 4-6) flow through forested gorges, cleared floodplains and some highly-urbanised areas, and they support several populations of native fish including Australian grayling, river blackfish, Macquarie perch and tupong. Macquarie perch were introduced to Birrarung (Yarra River) last century, and the population is now considered one of the largest and most important in Victoria.

The Plenty River (reach 9) provides habitat for waterbugs and native fish species (such as common galaxias). Platypus have been detected in the Plenty River in the past, but none have been recorded in recent surveys.

Billabongs are an important feature of the Birrarung (Yarra River) floodplain between Millgrove and Yering Gorge and in the lower reaches around Banyule Flats near Heidelberg. The billabongs support distinct vegetation communities and provide foraging and breeding habitat for waterbirds and frogs. Except in very high flows, most billabongs are disconnected from Birrarung (Yarra River).

Recent conditions

Rainfall in the Birrarung (Yarra River) catchment in 2021-22 was above the long-term average, and tributary inflows significantly contributed to flow in Birrarung (Yarra River) and the Plenty River throughout the year. Maroondah Reservoir, O’Shannassy Reservoir and Yan Yean Reservoir all spilled for prolonged periods during the year. Natural flow events frequently exceeded in-channel flow targets during winter and spring, with the largest event reaching about 3,700 ML per day at Millgrove (reach 2) and about 7,400 ML per day at Warrandyte (reach 5) in October. Maintenance work at Upper Yarra Reservoir required operational releases to Birrarung (Yarra River) during October to November 2021. These operational releases replaced the need for environmental flows that were planned during that time. The operational releases were adjusted where possible to align with environmental flow needs, and they largely met the expected watering effects. Ecological monitoring downstream of the Upper Yarra Dam was undertaken in 2021, and follow-up monitoring will take place in 2022 to study the effects of the operational releases. This was undertaken with members of the Narrap Team, and the continuing presence of populations of river blackfish was noted.

Water for the environment was managed in line with the wet scenario throughout 2021-22. Natural rain events, combined with larger-than-normal inflows from the O’Shannassy River and operational releases from the Upper Yarra and Maroondah reservoirs, achieved most of the planned watering actions in the Yarra River for 2021-22. Natural rain events inundated many of the Birrarung (Yarra River) billabongs during the year. Water for the environment was used to help meet winter/spring high flow, winter fresh and summer fresh requirements in the Birrarung (Yarra River). In the Plenty River, natural rain events achieved most of the high-priority planned watering actions, but a faulty release pipe at Yan Yean Reservoir prevented any opportunity to supplement natural flows with water for the environment. Melbourne Water will undertake maintenance during 2022-23 and review opportunities for environmental flow releases in the Plenty River in 2023-24.

Yering Backswamp has received water for the environment annually since 2013. The site was inundated naturally in June, September and October 2021, and it was allowed to gradually dry out by February 2022 in accordance with the site’s management plan. Annulus Billabong received water for the environment for the first time from October to December 2020, and it was filled again in September 2021 to support the growth of threatened wetland plant species and provide habitat for frogs, waterbugs and eels. This delivery was undertaken safely and successfully during a COVID-19 lockdown period, providing great recreational opportunities for local visitors. Bolin Bolin Billabong was filled in 2017 with a combination of natural overbank flows and water for the environment, which were delivered via a temporary pump. It filled again naturally in 2018, 2020 and on three occasions in 2021. Bolin Bolin Billabong was then drawn down over the summer months of 2021-22. Vegetation monitoring has detected a decrease in the cover and diversity of exotic plant species within Bolin Bolin Billabong since 2017. The inlet between the river and the billabong was modified in March 2022 to better facilitate the long-term delivery of water for the environment.

Birdlife Australia conducted bird surveys at four Yarra billabongs in 2021-22. The surveys aimed to compare bird responses at watered and dry billabongs, but Yering Backswamp, Spadonis Billabong, and some parts of Birrarung Billabong naturally filled and prevented a direct comparison. The surveys still provided useful information about how birds are using the Yarra billabongs. Initial results indicate that some species respond very quickly to environmental flows, with a family of day-old wood ducks observed at Annulus Billabong only one week after watering commenced. Other notable observations include nankeen night-heron at Annulus Billabong and buff-banded rail at Birrarung Billabong.

Melbourne Water has installed real-time water-quality monitoring instruments in Birrarung (Yarra River) at Millgrove and upgraded the water-quality monitoring buoy in the lower reaches of the river. These complement the other four water-quality monitoring stations along Birrarung (Yarra River) and will help inform decisions about the delivery of water for the environment

Traditional Owner cultural values and uses

Melbourne Water is working with the Registered Aboriginal Parties within the Yarra system — the Wurundjeri Woi Wurrung Cultural Heritage Aboriginal Corporation, the Bunurong Land Council Aboriginal Corporation and the Taungurung Land and Waters Council Aboriginal Corporation — to develop and strengthen relationships with them and to increase Traditional Owners’ involvement in the planning and delivery of water for the environment. As of May 2022, three overarching partnership agreements were being drafted that will frame relations and obligations with the organisations. The intent is for Traditional Owners to be active partners in the planning, delivery and monitoring of all works and deliveries of water for the environment associated with Birrarung (Yarra River), the Plenty River and Yarra billabongs, including the environmental watering program.

Increasing the involvement of Traditional Owners in environmental water planning and management and ultimately providing opportunities to progress towards self-determination within the environmental watering program is a core commitment of the VEWH and its agency partners. This is reinforced by a range of legislative and policy commitments, including the Water Act 1989, the Victorian Aboriginal Affairs Framework and the 2016 Water for Victoria, and in some cases, agreements under the Traditional Owner Settlement Act 2010.

Where Traditional Owners are more deeply involved in the planning and/or delivery of environmental flows for a particular site, their contribution is acknowledged in Table 3.2.1 with an icon. The use of this icon is not intended to indicate that these activities are meeting all the needs of Traditional Owners but is incorporated in the spirit of valuing their contribution and indicating progress towards deeper involvement.

Watering planned and/or delivered in partnership with Traditional Owners to support cultural values and uses

There are many places of tangible and intangible cultural significance for the Wurundjeri Woi wurrung people on the lower Birrarung floodplain. Where possible, Melbourne Water and the Wurundjeri Woi Wurrung Cultural Heritage Aboriginal Corporation will work together to link water for the environment with cultural outcomes for the Wurundjeri Woi wurrung people.

Watering of Annulus, Banyule and Bolin Bolin billabongs is aligned with the aspirations of Wurundjeri Woi wurrung Elders. The Wurundjeri Woi Wurrung Cultural Heritage Aboriginal Corporation’s Narrap Team is the Wurundjeri Woi wurrung natural resource management team and is active in the planning, delivery and monitoring of all works on the lower Yarra (Birrarung) floodplain. The Narrap Team continues to monitor associated environmental values (such as vegetation, eels and water quality). Watering also aligns with a landscape-scale approach for billabong watering in the lower Birrarung, which has been developed in consultation with Wurundjeri Woi wurrung people.

A vegetation monitoring and water-quality monitoring project is continuing at the billabongs with the Wurundjeri Woi Wurrung Cultural Heritage Aboriginal Corporation’s Narrap Team, the University of Melbourne and Melbourne Water. The group has been monitoring the vegetation watering outcomes and held an on-Country knowledge-sharing day to discuss learnings.

Monitoring is underway at Annulus Billabong following a delivery of water for the environment in 2021-22, and similar work will likely be undertaken in 2022-23. The Narrap Team is also undertaking weed control and revegetation at Annulus Billabong and Bolin Bolin Billabong.

Social, recreational and economic values and uses

In planning the potential watering actions in Table 3.2.1, Melbourne Water considered how environmental flows could support values and uses, including:

water-based recreation (such as kayaking, canoeing, fishing and swimming)
riverside recreation and amenity (such as birdwatching, camping, picnicking, cycling, running and walking)
community events and tourism (such as the Moomba Festival and the Inflatable Regatta)
socioeconomic benefits (such as for diverters for irrigation, stock needs and domestic use: water levels and water quality can rely on the delivery of water for the environment, particularly in summer).

Scope of environmental watering

Table 3.2.1 describes the potential environmental watering actions in 2022-23, their expected watering effect (that is, the intended physical or biological effects of the watering action) and the longer-term environmental objectives they support. Each environmental objective relies on one or more potential environmental watering actions and their associated physical or biological effects.

Table 3.2.1 Potential environmental watering actions, expected watering effects and associated environmental objectives for the Yarra system

Potential environmental watering action	Expected watering effects	Environmental objectives
Birrarung (Yarra River) The highest-priority reaches for Birrarung (Yarra River) are reaches 2 (upper Birrarung) and 5 (lower Birrarung); water delivered to these reaches generally benefits other reaches
Winter/spring low flow (June to November) Reach 2: 80-350 ML/day Reach 5: 350-750 ML/day	Physically mix pools to minimise the risk of stratification and low oxygen Maintain access to habitats for fish, waterbugs and platypus Wet bank vegetation to promote growth
Winter/spring freshes (two freshes for three to seven days during June to November) Reach 2: 700 ML/day Reach 5: 2,500 ML/day	Scour sediment and biofilm from gravel in riffles to improve spawning opportunities for Macquarie perch Wet native streamside vegetation on the banks of the river to promote growth Provide cues for upstream migration of juvenile migratory fish (e.g. Australian grayling and tupong)
Winter/spring high flow (one high flow for 14 days during August to September) Reach 2: 700 ML/day Reach 5: 2,500 ML/day	Scour sediment and biofilm from gravel in riffles Provide prolonged wetting to favour flood-tolerant native vegetation in the streamside zone Provide cues for upstream migration of juvenile migratory fish (e.g. Australian grayling and tupong) Trigger spawning of Macquarie perch
Summer/autumn low flow (December to May) Reach 2: 80 ML/day Reach 5: 200 ML/day Reach 6: 300-450 ML/day	Physically mix pools to minimise the risk of stratification and low oxygen Maintain access to habitats for fish, waterbugs and platypus
Summer/autumn freshes (three freshes for two days during December to May) Reach 2: 350 ML/day Reach 5: 750 ML/day	Flush pools to prevent a decline in water quality Scour sediment and biofilm from gravel in riffles and pools to maintain habitat quality for fish and waterbugs Provide opportunities for the localised movement of fish and platypus Wet the banks of the river to maintain flood-tolerant vegetation on the banks
Autumn high flow (one high flow for seven to 14 days during April to May) Reach 2: 560 ML/day Reach 5: 1,300 ML/day	Cue the migration of Australian grayling Scour sediment and biofilm from gravel in riffles and pools to maintain habitat quality for fish and waterbugs
Yarra billabongs
Annulus Billabong (partial fill in winter/spring)	Wet the wetland bed to support the growth of threatened wetland plant species to rehabilitate shallow marsh, deep marsh and freshwater meadows Provide habitat for frogs, waterbirds, waterbugs and eels
Bolin Bolin Billabong (partially fill in winter/ spring)	Wet the deepest part of the wetland to about 200 cm to provide habitat for frogs, waterbugs and eels Wet the remaining area of the wetland to about 50-100 cm to support the growth of threatened wetland plant species and encourage the regeneration of spreading aquatic herbs
Yering Backswamp (fill in autumn/winter/spring)	Wet the deepest parts of the wetland to about 80 cm to provide habitat for fish, frogs and waterbugs Wet remaining areas of the wetland to about 40-60 cm to support the growth of threatened wetland plant species and encourage the regeneration of spreading aquatic herbs
Banyule Billabong (fill in spring/summer)	Wet the wetland bed to support the growth of aquatic and semi-aquatic vegetation Inundate the wetland to prevent the encroachment of terrestrial vegetation Provide habitat for native fish, frogs and waterbirds
Burke Road Billabong (fill in spring/summer)	Wet the wetland bed to support the growth of aquatic and semi-aquatic vegetation Inundate the wetland to prevent the encroachment of terrestrial vegetation Provide habitat for frogs and waterbirds

Scenario planning

Table 3.2.2 outlines potential environmental watering and expected water use under a range of planning scenarios.

In the Yarra system, current scenario planning is considered only under dry, average and wet climate scenarios. A combination of the highly reliable environmental allocation (17,000 ML each year) and high carryover volume from 2021-22 will provide sufficient supply for most required watering actions in 2022-23, and there is no need to significantly restrict watering actions in very dry or drought conditions.

Environmental flow planning in Birrarung (Yarra River) primarily focuses on providing sufficient low flow throughout the year to maintain habitat for aquatic life and providing high flows at critical times to support the migration and breeding requirements of native fish. Summer/autumn low flows and freshes, a winter/spring high flow and winter/spring low flows and freshes are needed to achieve these outcomes under all climate scenarios, but the extent to which these flows are likely to be met by natural tributary inflows varies between dry, average and wet scenarios. Water for the environment will be used to fill the main deficits under each scenario, where possible.

Winter/spring high flows are required at least once every two years to support Macquarie perch breeding and the upstream migration of Australian grayling and tupong. The recommended winter/spring high flow for Birrarung (Yarra River) has only been met twice since 2017-18, and it is therefore a high priority under all scenarios in 2022-23. Autumn high flows are required in at least two of every three years to support Australian grayling breeding, and they are the lowest tier 1 priority action under average and dry scenarios for 2022-23 because they have been delivered in the two previous years. Ensuring priority carryover requirements into 2022-23 means there may not be enough water to deliver the autumn high flow under dry and average scenarios. Autumn high flows are still a priority under wet conditions because other environmental cues and resources will likely favour strong native fish recruitment.

Melbourne Water is delivering a landscape-scale approach to watering floodplain billabongs that considers the ecosystem services different billabongs provide, as well as which billabongs need to be watered at any given time to support regionally important plant and animal populations. There are numerous billabongs throughout the Birrarung (Yarra River) catchment that are drier than natural due to river regulation and modifications to natural flow paths. Ensuring some billabongs are inundated at any given time is necessary to provide habitat for waterbirds and frogs, including some species that are rare or threatened.

Melbourne Water’s landscape assessment has identified watering at Yering Backswamp, Bolin Bolin Billabong, Annulus Billabong, Banyule Billabong and Burke Road Billabong as high priorities under all scenarios in 2022-23. These wetlands are ephemeral — they have a wet then dry cycle — except for the deep section in Bolin Bolin Billabong, which aims to be kept permanently inundated. The proposed watering will maintain their preferred wet-dry frequency, which will help support native vegetation communities and provide food and potential breeding opportunities for frogs and waterbirds when they are inundated. If all billabongs miss out on a natural inflow, which is possible under a dry scenario, resources may limit Melbourne Water from actively watering all sites in spring and summer.

A target carryover volume of between 10,350 and 12,000 ML (depending on the climate scenario) has been determined to supplement natural flows and deliver the highest-priority flows in 2023-24.

Planning scenario table

Table 3.2.2 Potential environmental watering for the Yarra system under a range of planning scenarios

Planning scenario	Dry	Average	Wet
Expected river conditions	Low streamflow year- round Lack of unregulated freshes and high flow Passing flows are not likely to meet the minimum environmental flow recommendations Potential poor water quality, particularly in summer Pools may stratify Plenty River may experience cease-to-flow events	Minimum passing-flow recommendations are likely to be met Natural flow may provide some freshes, but its duration and/or magnitude will likely be less than recommended environmental flow Potentially poor water quality, particularly in summer Pools may stratify Small reservoirs may spill Overbank flow is not likely	Passing-flow recommendations are likely to be met High, natural flow will occur, most likely in winter/spring Major spills from reservoirs may occur Some natural wetting of billabongs may occur
Predicted supply of water for the environment	41,400 ML
Birrarung (Yarra River) (targeting reach 2 and 5)
Potential environmental watering – tier 1 (high priorities)	Tier 1a (can be achieved with predicted supply)
	Winter/spring low flow Winter/spring freshes (two freshes) Winter/spring high flow (one high flow) Summer/autumn low flow Summer/autumn freshes (three freshes) Targeted billabong watering (Annulus, Bolin Bolin, Yering, Banyule, Bourke Road)	Winter/spring low flow Winter/spring freshes (two freshes) Winter/spring high flow (one high flow) Summer/autumn low flow Summer/autumn freshes (three freshes) Targeted billabong watering (Annulus, Bolin Bolin, Yering, Banyule, Bourke Road)	Winter/spring low flow Winter/spring freshes (two freshes) Winter/spring high flow (one high flow) Summer/autumn low flow Summer/autumn freshes (three freshes) Autumn high flow (one high flow) Targeted billabong watering (Annulus, Bolin Bolin, Yering, Banyule, Bourke Road)
	Tier 1b (supply deficit)
	Autumn high flow (one high flow)	Autumn high flow (one high flow)	N/A
Potential environmental watering – tier 2 (additional priorities)	N/A
Possible volume of water for the environment required to achieve objectives	25,650 ML (tier 1a) 11,600 ML (tier 1b)	25,850 ML (tier 1a) 8,800 ML (tier 1b)	25,250 ML (tier 1a)
Priority carryover requirements	12,000 ML	10,350 ML	12,000 ML

Engagement

Table 2 shows the partners and stakeholder organisations with which Melbourne Water engaged when preparing the Yarra 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 Yarra system seasonal watering proposal

Partner and stakeholder engagement
Cannibal Creek Water Monitoring Group Environment Victoria Friends of Mt Cannibal Flora and Fauna Reserve Friends of Robin Hood Reserve Independent community members Native Fish Australia Waterwatch Coordinators Department of Environment, Land, Water and Planning Melbourne Water (Service Delivery) Southern Rural Water Aboriginal Victoria Baw Baw Shire Council Cardinia Shire Council Commissioner for Environmental Sustainability Victoria Environment Protection Authority Victoria Parks Victoria Port Phillip and Westernport CMA Victorian Fisheries Authority Individual landholders Glen Cromie Reserve Local anglers VRFish Aquatic Pollution Prevention Partnership Arthur Rylah Institute (Department of Environment, Land, Water and Planning) Australian Platypus Conservancy Cesar Australia Melbourne Water subject matter experts Research collaborators at Melbourne University Boon Wurrung Foundation Bunurong Land Council Aboriginal Corporation Wurundjeri Woi wurrung Cultural Heritage Aboriginal Corporation

Partner and stakeholder engagement

Cannibal Creek Water Monitoring Group
Environment Victoria
Friends of Mt Cannibal Flora and Fauna Reserve
Friends of Robin Hood Reserve
Independent community members
Native Fish Australia
Waterwatch Coordinators
Department of Environment, Land, Water and Planning
Melbourne Water (Service Delivery)
Southern Rural Water
Aboriginal Victoria
Baw Baw Shire Council
Cardinia Shire Council
Commissioner for Environmental Sustainability Victoria
Environment Protection Authority Victoria
Parks Victoria
Port Phillip and Westernport CMA
Victorian Fisheries Authority
Individual landholders
Glen Cromie Reserve
Local anglers
VRFish
Aquatic Pollution Prevention Partnership
Arthur Rylah Institute (Department of Environment, Land, Water and Planning)
Australian Platypus Conservancy
Cesar Australia
Melbourne Water subject matter experts
Research collaborators at Melbourne University
Boon Wurrung Foundation
Bunurong Land Council Aboriginal Corporation
Wurundjeri Woi wurrung Cultural Heritage Aboriginal Corporation

Page last updated: 01/12/22