Tarago River

The Tarago River rises in the Tarago State Forest and flows into the Tarago Reservoir at Neerim. 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 plant and animal 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 and mountain galaxias. The lower catchment (reach 6) has been highly modified, but still contains patches of remnant vegetation and healthy populations of Australian grayling and platypus.

Traditional Owner cultural values and uses

Melbourne Water has made initial contact with Boon Wurrung Foundation, Bunurong Land Council Aboriginal Corporation and Wurundjeri Woi wurrung Cultural Heritage Aboriginal Corporation to discuss environmental watering in the Tarago/Bunyip system.

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

Wurundjeri Woi wurrung Cultural Heritage Aboriginal Corporation is interested in undertaking a program of work to determine cultural values and uses in the Tarago system 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 Tarago River catchment received above-average rainfall in winter and spring 2020, which delivered significant inflows into the storage. Tarago Reservoir filled and spilled in October 2020, January 2021 and April 2021. The Tarago environmental entitlement received its full allocation — 3,000 ML share of storage — in July 2020, and use throughout the year was replenished by frequent inflows. Opportunistic use of water held under the Tarago Reservoir airspace agreement contributed significantly to planned environmental watering actions. Rainfall also contributed to flows in the Tarago and Bunyip rivers downstream of the reservoir.

Natural inflows and storage spills maintained the recommended low flows in the Tarago River throughout much of 2020-21, and they also delivered five winter/spring freshes and three summer/autumn freshes. Water for the environment was used to deliver an additional winter/spring fresh in September 2020 and one summer/autumn fresh in January 2021.

Water for the environment was managed in line with an average climate scenario throughout 2020-21. All planned potential watering actions were met. Melbourne Water delivered a winter/spring high flow in September using environmental water held under the airspace agreement. This temporary arrangement between the VEWH, the storage manager and other entitlement holders allows the VEWH to save its share of inflows in spare reservoir capacity if its share of storage is full. This can help reserve enough environmental water to provide for some of the higher flow requirements that VEWH would otherwise not have sufficient water for.

The high flow improved water quality downstream of the reservoir and provided opportunities for the upstream migration of juvenile native fish species including Australian grayling, common galaxias and tupong. It is the first time since 2012-13 that water for the environment has been used to deliver a winter/spring high flow in the Tarago River.

Water for the environment was used to deliver a summer/ autumn fresh at the end of January to flush sediment and organic material from the river bed. The fresh coincided with a public holiday, which improved conditions for riverside campers and other visitors. An autumn high flow may be delivered using water for the environment in May 2021 to cue Australian grayling to spawn.

Between 1,500 and 2,000 ML of water for the environment will be carried over in the Tarago system to help meet critical priorities in 2021-22 including summer and autumn freshes and an autumn high flow.

Social, recreational and economic values and uses

In planning the potential watering actions in Table 1, Melbourne Water considered how environmental flows could support values and uses including:

riverside recreation and amenity (such as day visitors, short- and long-term visitors and camping)
socio-economic benefits (such as irrigators and stock and domestic users)

If the timing or management of planned environmental flows may be modified to align with a community benefit, this is acknowledged in Table 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 2020, so visitors and long-term residents of the Glen Crombie 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 Maintain water quality through an increased low flow to flush the system and wet additional habitat for fish and macroinvertebrates
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 such as 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 higher flow later in the year flooding the burrow when juveniles are present
Summer/autumn low flows (20 ML/day [or natural] during December to May)	Maintain an adequate depth through riffles to support waterbugs and allow access to habitats for fish and platypus Maintain adequate foraging habitat for fish and platypus Maintain water quality and increase oxygen in pools
Summer/autumn fresh(es) (one 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)	Form and maintain scour holes around large wood Cue the downstream migration and spawning for diadromous fish (e.g. Australian grayling) Assist the dispersal of juvenile platypus

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: 22/01/21