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 Rokeby before meeting the Bunyip River at Longwarry North. From there, the Bunyip River flows through a modified, straightened channel called Bunyip Main Drain that discharges into Western Port. The Bunyip Main Drain supplies many irrigators in the catchment.

Water available under the Tarago and Bunyip Rivers Environmental Entitlement 2009 is stored in and released from Tarago Reservoir. This water is primarily used to meet environmental objectives in reach 2, between the reservoir and the confluence of the Tarago and Bunyip rivers, as Figure 3.3.1 shows. Water for the environment 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 contribute toward meeting the minimum low-flow requirements in summer/autumn and winter/spring, but they are less than the recommended minimum flows. The passing flows do not provide any of the freshes or greater flows that are needed throughout the year to support environmental outcomes.

Water released to meet irrigation demands creates 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 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 interested Traditional Owner groups and the Registered Aboriginal Party within the
Tarago system – the Bunurong Land Council Aboriginal Corporation – to develop and strengthen relationships and to increase Traditional Owners’ involvement in the planning and delivery of water for the environment. As of January 2023, one overarching partnership agreement had been finalised between Melbourne Water and the Gunaikurnai Land and Waters Aboriginal Corporation that frames relations and obligations between the two organisations. Discussions were also occurring with the Bunurong Land Council Aboriginal Corporation to determine whether similar partnership agreements would benefit Bunurong. The intent is for Traditional Owners to be active partners in the planning, delivering and monitoring water for the environment associated with the Tarago and Bunyip rivers.

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

Melbourne Water and the VEWH will continue 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 environmental 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, so visitors and long-term residents of the Glen Cromie Caravan Park can enjoy the additional flow in the river.

Scope of environmental planning

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

Potential environmental watering action	Expected watering effects	Environmental objective
Tarago River (targeting reach 2)
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 freshes (three 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

Page last updated: 01/07/22