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The Tarago River has its headwaters in the Tarago State Forest and it flows into the Tarago Reservoir at Neerim. Downstream of the reservoir, the river flows close to the town of Rokeby before meeting the Bunyip River (of which it is a major tributary) at Longwarry North. The downstream reach towards Western Port Bay supplies many irrigators in the catchment.

Water available under the Tarago environmental entitlement is stored in and released from Tarago Reservoir. Reach 2 is the target reach as it has high ecological value with a diversity of native fish and patches of native fringing vegetation. Deliveries to reach 2 often result in the desired flows in reach 6 (see system map below).

Waterway manager
Storage manager
Environmental water holder

System map

Tarago 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 Tarago River

Insect icon
Provide habitat and nourishment for waterbugs which provide energy, break down dead organic matter and support the river’s food chain
Fish icon
Protect and boost native fish populations including threatened species (the Australian grayling and river blackfish) by providing habitat and encouraging fish to migrate and spawn
Plant icon
Encourage healthy and diverse riverside vegetation
Platypus icon
Maintain and improve habitat for platypus

Environmental values

The Tarago system contains several significant and threatened native plant and animal species including the Australian grayling, long pink-bells, tree geebung and swamp bush-pea. The upper catchment has healthy riparian vegetation and in-stream habitat diversity that supports native fish including river blackfish and mountain galaxias. While the lower catchment has been highly modified, it contains good patches of remnant vegetation and healthy populations of Australian grayling and platypus.

Social and economic values

There are several reserves, picnic areas and designated fishing locations along the length of the Tarago system as well as a popular caravan park and public land in the headwaters. These all contribute to the social and recreational value of the Bunyip and Tarago rivers. Many irrigators rely on water from the Tarago system and urban supplies are also provided from the storage.

The Tarago River runs through the traditional lands of the Kurnai and Kulin Nations. The waterways of this region would have been a focus for Aboriginal communities before European settlement due to their permanent water supply and associated resources. Aboriginal people have a continuing connection to the waterways of this region. In recent times the Robin Hood Reserve on the Tarago River has been an important meeting place for Traditional Owners.

Conditions mid-2016

Spills from Tarago Reservoir between June and November 2015 provided increased flows and variability in the river downstream of the reservoir, resulting in achievement of most of the targeted environmental flows in winter. While small spills occurred into late spring, conditions began to dry due to below-average spring rainfall. The dry conditions continued in summer and autumn.

Environmental water was released to provide two summer freshes (small pulses of water), the first in December 2015 and the second in February 2016. These events improved habitat availability for animals and helped clear sand bars of encroaching vegetation. An autumn fresh was delivered in April and piggybacked on some unregulated flows following local rainfall. Initial monitoring results showed that the release was successful in triggering Australian grayling spawning.

Significant monitoring continues to be undertaken in the Tarago system. The results show a clear link between environmental flow pulses and Australian grayling spawning with the length of the pulse being critical to successful spawning. Monitoring of platypus also showed the environmental watering has substantial benefits for this iconic animal including improvements to habitat, increased movement opportunity and more food (waterbugs).

Scope of environmental planning

Table 1. Potential environmental watering actions and objectives for the Tarago River

Potential environmental watering

Environmental objectives

Summer/autumn freshes (5 freshes of 100 ML/day for 4 days each in December–May)

  • Prevent vegetation growing on sand bars, encourage scour hole creation and improve water quality and maintain habitat for aquatic species, particularly fish

Autumn high flow (1 high flow of 100 ML/day for 2 days during April–May)

  • Trigger downstream dispersal and spawning of Australian grayling

Spring/summer high flow (1 high flow of 280 ML/day for 4 days during October–December)

  • Migration of Australian grayling and inundation of barriers, providing for fish passage

Winter/spring freshes (up to 4 freshes of 280 ML/day for 3 days during June–November)

  • Generate habitat variability for waterbugs, prevent sedimentation and provide sufficient depth for fish passage

Summer/autumn low flows (12 ML/day [or natural] during December–May)1

  • Maintain water quality and provide habitat for river blackfish, Australian grayling, platypus and waterbugs

Winter/spring low flows (100 ML/day [or natural] during June–November)2

  • Inundate marginal habitats for juvenile fish
  • Increase riverbed habitat availability for waterbugs
  • Promote establishment and recruitment of diverse riparian vegetation types and prevent terrestrial vegetation encroachment

1 Summer/autumn low flows are generally provided by passing flows under the environmental entitlement but during dry conditions it may be necessary to supplement these flows using environmental water.

2 Winter/spring low flows are unlikely to be delivered as the volume required would severely affect the ability to provide other environmental flow events.

Scenario planning

The highest-priority releases in the Tarago system are summer/autumn freshes (to provide habitat and improve water quality) and an autumn high flow (to provide migration cues for Australian grayling). An autumn high flow is important to deliver in most years as Australian grayling are short-lived (to around three years old) so regular successful breeding is needed. There may not be sufficient water in drought conditions to deliver the event but this flow has been provided in five of the past six years so absence of the flow in 2016–17 does not pose a significant risk. Under wetter conditions, we expect that in addition to summer/autumn releases environmental water may contribute to delivery of some winter/spring flows, building on natural flows in the system to improve habitat for waterbugs and fish movement along the river.

Another priority release is the spring freshes to support the movement of juvenile Australian grayling back into the Tarago system. This event usually occurs naturally but drier springs have led to only the partial delivery of this flow. Anecdotal evidence suggests that the fish move on these partial events, which will be monitored in spring 2016.

The number of watering actions increases from the drought to the wet scenarios, thus increasing the volume of environmental water required. Carrying water over into 2017–18 is important under all conditions, to provide a secure ability to deliver summer and autumn freshes in the following year.

Table 2 Potential environmental watering for the Tarago system under a range of planning scenarios

Planning scenario

Drought

Dry

Average

Wet

Expected river conditions

  • Very low streamflows
  • Reduced passing flows
  • Irrigation releases likely
  • Low streamflows
  • Some reduction to passing flows
  • Irrigation releases likely
  • Average streamflows
  • Partial freshes naturally provided
  • Some irrigation releases likely
  • Above-average streamflows
  • Partial-to-full freshes naturally provided
  • Irrigation releases unlikely

Expected availability of environmental water

  • 1,500 ML carryover
  • 200 ML allocation
  • 1,700 ML total
  • 1,500  ML carryover
  • 500–1,000 ML allocation
  • 2,000–2,500 ML total
  • 1,500 ML carryover
  • 1,000–2,200 ML allocation
  • 2,500–3,700 ML total
  • 1,500 ML carryover
  • 2,200–3,500 ML allocation
  • 3,700–5,000 ML total

Potential environmental watering – tier 1 (high priorities)

  • Summer/autumn freshes
  • Summer/autumn freshes
  • Autumn high flows (partial event)
  • Summer/autumn freshes
  • Autumn high flows
  • Spring high flows (partial event)
  • Summer/autumn freshes
  • Autumn high flows
  • Spring high flows
  • Winter/spring freshes

Potential environmental watering – tier 2 (additional priorities)

  • Spring high flows (partial event)
  • Spring high flows (partial event)
  • Autumn high flows (full event)
  • Spring high flows (full event)
  • N/A

Possible volume of environmental water required to achieve objectives1

  • 1,000 ML (tier 1)
  • 800 ML (tier 2)
  • 1,000–1,500 ML (tier 1)
  • 1,200 ML (tier 2)
  • 1,500–2,700 ML (tier 1)
  • 1,200 ML (tier 2)
  • Up to 3,500  ML (tier 1)

Priority carryover requirements

  • 500 ML
  • 1,000 ML

1 Environmental water requirements for tier 2 actions are additional to tier 1 requirements.

Risk management

In preparing its seasonal watering proposal, Melbourne Water considered and assessed risks and identified mitigating strategies relating to implementing environmental watering. Risks and mitigating actions are continually reassessed by program partners 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.