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 Westernport region and is used to manage flows for downstream irrigators. Downstream of the reservoir, the 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 Westernport Bay. 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, as Figure 3.3.1 shows. 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. Downstream of Tarago Reservoir at Drouin West, this equates to the lesser of 12 ML per day or natural flows. The magnitude of these passing flows is generally sufficient to meet the minimum low-flow requirements in summer/autumn, but it is much less than the recommended minimum flows in winter/ spring; and it does 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 and maintain native riparian and aquatic plant communities on the riverbank and in the channel

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

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 (reach 2) has healthy riparian vegetation and diverse in-stream habitat that support platypus and native fish including river blackfish and mountain galaxias. The lower catchment (reach 6) has been highly modified, but it still contains patches of remnant vegetation and healthy populations of Australian grayling and platypus.

Recent conditions

The Tarago catchment experienced below-average rainfall in 2018–19, resulting in low inflows to the Tarago Reservoir. Despite the dry conditions, local rainfall delivered three winter/spring freshes at the start of the water year. Water for the environment was used to deliver an autumn fresh and an autumn high flow, to trigger Australian grayling spawning.

Melbourne Water has funded the Arthur Rylah Institute to investigate Australian grayling flow requirements in the Bunyip-Tarago system since 2008. That work has clearly demonstrated that Australian grayling migrate and spawn in response to environmental flows that are delivered at specific times of the year. The research program is progressing to a long-term tagging study from 2019.

Scope of environmental planning

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

Potential environmental watering action	Functional watering objective	Environmental objective
Summer/autumn freshes (up to five freshes of 75 ML/day for two days each during December to May)	Scour sediment from holes and around large woody debris to maintain habitat for native fish in low-flow periods Allow the localised movement of resident fish Prevent terrestrial vegetation growth on sandbars Maintain water quality by aeration through times of low flow
Autumn high flow (one fresh with a peak of 100 ML/day maintained for two days in a minimum seven-day fresh duration during April to May)	Cue spawning for diadromous fish (such as Australian grayling) Allow the downstream movement of Australian grayling Assist the dispersal of juvenile platypus
Spring high flow (one to two freshes during September to October with two to three days in a minimum sevento- 10 day fresh at a peak of 200–300 ML/day)	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 (such as Australian grayling) from the sea or estuary into the river Wet higher benches to maintain the fringing aquatic vegetation and ensure vertical zonation of the fringing vegetation Provide a cue for platypus to select nesting burrows above high water level
Winter/spring freshes (two freshes of 100–200 ML/day at peak for one to two days during June to September)	Prevent sediment build-up and remove biofilm from large woody debris to maintain habitat for macroinvertebrates and fish including river blackfish Maintain access to habitats by ensuring sufficient depth through riffles to allow fish movement between pools and reaches Cue the downstream migration of species such as eel and tupong Inundate the banks, wetting the lower benches to maintain the fringing aquatic vegetation
Winter/spring low flows (75 ML/day [or natural] during June to November)	Prevent the encroachment of terrestrial vegetation in the channel Wet the banks to promote riparian vegetation growth Maintain an adequate depth through riffles to allow access to habitats for fish and platypus Maintain water quality through increased low flows to flush the system and inundate additional habitat for fish and macroinvertebrates Maintain foraging habitat for 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 Environmental Protection Authority Parks Victoria Port Phillip and Westernport CMA Baw Baw Shire Council Cardinia Shire Council Melbourne Water Service Delivery Parks Victoria Victorian Environmental Water Holder Glen Cromie Caravan Park Local Anglers VRFish Boon Wurrung Foundation Bunurong Land Council Aboriginal Corporation

Page last updated: 12/12/19