Tarago River

The Tarago River rises in the Tarago State Forest and flows into the Tarago Reservoir at Neerim (Figure 3.3.1). The reservoir harvests inflows from all upstream tributaries to supply towns on the Mornington Peninsula and around the Western Port area. Water is released from the reservoir to supply downstream irrigators. Below the reservoir, the Tarago River flows close to the town of Rokeby before meeting the Bunyip River at Longwarry North. From there, the Bunyip River flows through a modified, straightened channel — Bunyip Main Drain — that discharges into Western Port. The Bunyip Main Drain supplies many irrigators in the catchment.

Water available under the Tarago environmental entitlement is stored in and released from Tarago Reservoir. This water is primarily used to meet environmental objectives in reach 2, which is between the reservoir and the confluence of the Tarago and Bunyip rivers. Water for the environment that is delivered to reach 2 also supports environmental flow recommendations in reach 6 (Bunyip Main Drain).

Year-round passing flows in the Bunyip and Tarago rivers are stipulated under both the environmental entitlement and Melbourne Water’s bulk entitlement. These passing flows are generally sufficient to meet the minimum low-flow requirements in summer/autumn, but are much less than the recommended minimum flows in winter/spring; and they do not provide any of the freshes or higher flows that are needed throughout the year to support environmental outcomes.

Water releases to meet irrigation demands create variable flow patterns in the Tarago and Bunyip rivers throughout the year. The magnitude and timing of these releases can influence environmental outcomes, and Melbourne Water continues to work with Southern Rural Water to optimise the shared value derived from irrigation releases.

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

Increase populations of native fish, including threatened species (such as the Australian grayling)

Maintain channel form and structure

Increase platypus populations

Increase native streamside and aquatic plant communities on the riverbank and in the channel

Increase the diversity and biomass of waterbugs, to support aquatic foodwebs

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

Environmental values

The Tarago system contains several significant and threatened native animal and plant species, including Australian grayling, long pink-bells, tree geebung and swamp bush pea. The upper catchment (reach 2) has healthy streamside vegetation and diverse in-stream habitat that supports platypus and native fish, including river blackfish, tupong, short-finned eels and mountain galaxias. The lower catchment (reach 6) has been highly modified, but it still contains patches of remnant vegetation and is a key migration pathway for Australian grayling. It also has healthy platypus populations.

Traditional Owner cultural values and uses

Melbourne Water is working with the Registered Aboriginal Parties within the Tarago system — the Bunurong Land Council Aboriginal Corporation, the Wurundjeri Woi Wurrung Cultural Heritage Aboriginal Corporation and the Gunaikurnai Land and Waters 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 the Tarago and Bunyip rivers, including the environmental watering program.

Bunurong Land Council Aboriginal Corporation has expressed a desire to be more involved in environmental flows planning and management in the Tarago River.

Wurundjeri Woi Wurrung Cultural Heritage Aboriginal Corporation is interested in undertaking a program of work to determine cultural values and uses in the Tarago River using their preferred method.

There are more opportunities for Melbourne Water and the VEWH to work with the Traditional Owner groups to identify and integrate cultural values and their flow requirements into the environmental watering program on an ongoing basis.

Recent conditions

The mean temperatures in the Tarago River catchment during 2021-22 were above the long-term average. Rainfall was close to the long-term average, except during spring and January, which were wetter than average. This follows wetter-than-average conditions in 2020-21. The Tarago Reservoir continually spilled from March 2021 to January 2022, and a combination of high tributary inflows and reservoir spills caused minor flooding in the Tarago River during October 2021, which connected with many streamside billabongs. The VEWH held 100 percent or more2 of its entitlement volume in Tarago Reservoir (3,000 ML share of storage) from the beginning of the water year (July 2021), and inflows to the reservoir quickly replenished the VEWH’s supply whenever it was used throughout the year.

Water for the environment was managed in line with a wet climate scenario throughout 2021-22 as a response to the frequent reservoir spills. All watering actions planned for winter and spring of 2021 in the Tarago River were fully achieved from natural tributary flows and spills from Tarago Reservoir. Water for the environment was used to deliver summer/autumn freshes in January and February 2022 and an autumn high flow in March.

Since 2019, scientists have used passive integrated transponder (PIT) tag readers to track the movement of migratory fish in response to environmental flows in the Tarago. The results from tracking highlight the importance of high flows to support the migration and spawning patterns of Australian grayling, tupong and short-finned eel. The PIT tag readers also allow managers to adaptively manage flows during the season. For example, in 2021, waterway managers cancelled a planned flow to trigger the movement of fish because PIT tag readers indicated that fish had already responded to natural high flows. Cancelling the planned flow conserved water for the environment for other high-priority watering actions later in the year.

Social, recreational and economic values and uses

In planning the potential watering actions in Table 3.3.1, Melbourne Water considered how environmental flows could support values and uses, including:

water-based recreation (such as fishing and swimming)
riverside recreation and amenity (such as cycling, camping, caravanning, short- and long-term visiting and walking)
community events and tourism (such as visiting and residing in the Glen Cromie Caravan Park)
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).

If the timing or management of planned environmental flows may be modified to align with a community benefit, this is acknowledged in Table 3.3.1 with the following icon.

Watering planned to support peaks in visitation (e.g. camping or other public activities on long weekends or school holidays)

Melbourne Water may time the release of a summer fresh in the Tarago River to coincide with long weekends in January or March 2023, so visitors and long-term residents of the Glen Cromie Caravan Park can enjoy the additional flows in the river.

Scope of environmental planning

Table 1 Potential environmental watering actions, expected watering effects and associated environmental objectives for the Tarago River

Potential environmental watering action	Expected watering effects	Environmental objective
Winter/spring low flow (75 ML/day [or natural] during June to November)	Prevent the encroachment of terrestrial vegetation in the channel Wet the banks to promote streamside vegetation growth Maintain an adequate depth through riffles to allow access to habitats for fish and platypus Mix pools to maintain water quality and increase habitat for fish and macroinvertebrates during wetter months
Winter/spring fresh(es) (one to two freshes with a peak of 100-200 ML/ day for two days during June to September)	Flush sediment and scour biofilm from stream substrate and large woody debris to maintain habitat for macroinvertebrates and fish, including river blackfish Create extra depth to allow greater fish movement between pools and reaches Cue the downstream migration of species, including eel and tupong Wet the banks and low benches to maintain the fringing aquatic vegetation
Spring high flows (two to three high flows with a peak of 200-300 ML/day for two days in a seven- to-10-day duration during September to October)	Form and maintain scour holes around large wood Prevent the encroachment of terrestrial vegetation into the channel Cue the upstream migration of juvenile diadromous fish (e.g. Australian grayling) from the sea or estuary into the river Wet the higher benches to maintain the fringing aquatic vegetation and ensure vertical zonation of the fringing vegetation Encourage female platypus to select a nesting burrow higher up the bank to reduce the risk of greater flow later in the year flooding the burrow when juveniles are present
Summer/autumn low flow (20 ML/day [or natural] during December to May)	Maintain adequate depth through riffles to support waterbugs and allow access to habitats for fish and platypus Maintain adequate foraging habitat in pools for fish and platypus Maintain water quality (especially oxygen concentration) in pools
Summer/autumn fresh(es) (four to five freshes of 75 ML/day for two days during December to May)	Flush fine silt from hard substrates and around large woody debris to maintain habitat for native fish in low-flow periods Allow the localised movement of native fish Prevent terrestrial vegetation growth on sandbars Maintain water quality by aeration in times of low flow
Autumn high flow (one high flow with a peak of 100 ML/day for two days in a minimum seven-day duration during April to May)	Cue the downstream migration and spawning of diadromous fish (e.g. Australian grayling) Assist the dispersal of juvenile platypus

Scenario planning

Table 3.3.2 outlines potential environmental watering and expected water use under a range of planning scenarios.

The Tarago River requires similar watering actions every year, although the magnitude of low flows and the frequency of high flows will naturally be less under a dry climate scenario than under a wet or average climate scenario. Natural catchment inflows, mandated passing flows and reservoir spills will meet many of the required watering actions and provide natural flow variation throughout the year, especially under a wet climate scenario. Water for the environment will be used where possible to deliver critical flow components that are not met by other means.

Under a dry climate scenario, water for the environment will likely be used to deliver summer/autumn freshes and top up low flows to maintain water quality and adequate habitat for native fish and platypus. Melbourne Water will monitor water levels and water quality throughout the year and adjust releases as necessary to limit stress on existing plants and animals. There is unlikely to be enough supply under a dry scenario to deliver spring high flows to cue the upstream migration of Australian grayling from the estuary to the river, deliver autumn high flows for Australian grayling movement and spawning or help platypus select breeding burrows. The inability to deliver high flows is a low risk in dry years because fish and platypus will naturally have lower breeding rates. The risk is lower than normal in 2022-23 because the Tarago system has had multiple, large flow events and good breeding conditions during the last two to three years.

Under average and wet conditions, natural inflows will likely provide a greater proportion of the recommended low flows throughout the year, and the larger supply of water for the environment will potentially be used to deliver more freshes to improve the condition and size of native fish and platypus populations. Delivering two winter/spring freshes is a priority under average and wet climate scenarios to consolidate recent environmental gains by creating more opportunities for fish movement, boosting biofilm and macroinvertebrate productivity and improving the growth and survival of new fringing vegetation. Delivering an autumn high flow to cue Australian grayling migration and spawning is always a high priority under a wet climate scenario to optimise natural breeding success. Australian grayling require suitable breeding conditions about two out of every three years. Given the Tarago River has had high autumn flows (and Australian grayling recruitment) in each of the last two years, delivering an autumn high flow is a lower priority in 2022-23 under dry and average climate scenarios if the supply of water for the environment is insufficient.

As a minimum, 1,000 ML should be carried over into 2023-24 to ensure critical summer and autumn low flows and freshes can be delivered if the climate becomes very dry and there is low allocation.

Planning scenario table

Table 3.3.2 Potential environmental watering for the Tarago system under a range of planning scenarios

Planning scenario	Dry	Average	Wet
Expected river conditions	Low streamflow Some reduction in passing flow Irrigation releases likely	Average streamflow Partial freshes naturally provided	Above-average streamflow Partial or full freshes naturally provided Irrigation releases unlikely
Predicted supply of water for the environment	3,000 ML	3,500 ML	4,500 ML
Potential environmental watering – tier 1 (high priorities)	Tier 1a (can be achieved with predicted supply)
	Winter/spring low flow (partially achieved) Winter/spring fresh (one fresh) Summer/autumn low flow Summer/autumn freshes (four freshes)	Winter/spring low flow (partially achieved) Winter/spring freshes (two freshes) Summer/autumn low flow Summer/autumn freshes (four freshes)	Winter/spring low flow (partially achieved) Winter/spring freshes (two freshes) Summer/autumn low flow Summer/autumn freshes (five freshes) Autumn high flow (one high flow)
	Tier 1b (supply deficit)
	Winter/spring low flow Spring high flow (one high flow) Autumn high flow (one high flow)	Winter/spring low flow Spring high flow (one high flow) Summer/autumn fresh (one fresh) Autumn high flow (one high flow)	Winter/spring low flow Spring high flow (one high flow)
Potential environmental watering – tier 2 (additional priorities)	N/A
Possible volume of water for the environment required to achieve objectives	1,850 (tier 1a) 5,900 ML (tier 1b)	2,450 ML (tier 1a) 5,150 ML (tier 1b)	3,450 ML (tier 1a) 2,900 ML (tier 1b)
Priority carryover requirements	1,000 ML

Engagement

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

Partner and stakeholder engagement
Friends of Robin Hood Reserve Waterwatch co-ordinators Department of Environment, Land, Water and Planning \| Water and Catchments Melbourne Water Service Delivery Parks Victoria Southern Rural Water Baw Baw Shire Council Cardinia Shire Council Environment Protection Authority Port Phillip and Westernport Catchment Management Authority Individual landholders Glen Cromie Caravan Park Local Anglers VRFish Melbourne University – research collaborators Monash University Arthur Rylah Institute (Department of Environment, Land, Water and Planning Boon Wurrung Foundation Bunurong Land Council Aboriginal Corporation Wurundjeri Woi-Wurrung Cultural Heritage Aboriginal Corporation

Partner and stakeholder engagement

Friends of Robin Hood Reserve
Waterwatch co-ordinators
Department of Environment, Land, Water and Planning | Water and Catchments
Melbourne Water Service Delivery
Parks Victoria
Southern Rural Water
Baw Baw Shire Council
Cardinia Shire Council
Environment Protection Authority
Port Phillip and Westernport Catchment Management Authority
Individual landholders
Glen Cromie Caravan Park
Local Anglers
VRFish
Melbourne University – research collaborators
Monash University Arthur Rylah Institute (Department of Environment, Land, Water and Planning
Boon Wurrung Foundation
Bunurong Land Council Aboriginal Corporation
Wurundjeri Woi-Wurrung Cultural Heritage Aboriginal Corporation

Page last updated: 01/07/22