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System overview
The Yarra River flows west from the Yarra Ranges above Warburton, through the Yarra Valley and then opens out into a wider plain as it meanders through the suburbs and city of Melbourne before entering Port Phillip Bay. Over time, the lower Yarra River (below Warrandyte) has been straightened, widened and cleared of natural debris as Melbourne has developed.
Up to 400,000 ML per year (long-term average diversion limit) can be harvested from the Yarra River system for consumptive use in Melbourne and surrounding areas.
The Upper Yarra, O’Shannassy and Maroondah reservoirs harvest water from headwater tributaries, and a pump station at Yering is used to divert water from the Yarra River to Sugarloaf Reservoir.
Flow in the upper reaches of the Yarra River is influenced by tributaries (such as Armstrong Creek, McMahons Creek, Starvation Creek, Woori Yallock Creek, Watts River and Little Yarra River). Urbanised tributaries (such as Olinda Creek, Mullum Mullum Creek, Diamond Creek, Plenty River and Merri Creek) provide additional water to the middle and lower reaches of the Yarra River.
Environmental flows can be released from the Upper Yarra, Maroondah and O’Shannassy reservoirs to support ecological processes and environmental outcomes in downstream river reaches and wetlands. The priority environmental flow reaches in the Yarra River are reaches 2 and 5, shown in Figure 3.2.1. Water for the environment that is delivered to reaches 2 and 5 will help meet flow targets in downstream reaches.
Plenty River rises from the slopes of Mt Disappointment in the Great Dividing Range about 50 km north of Melbourne. It flows downstream through rural and semi-rural areas and Plenty Gorge before joining the Yarra River near Viewbank, east of Banyule Flats Reserve. Yan Yean Reservoir is located off the waterway, north of Plenty Gorge, and it receives flows from Toorourrong Reservoir via a channel. The Plenty River has not received managed environmental flows before, but there may be opportunities to deliver water for the environment from Yan Yean Reservoir from 2020–21 onwards.
Environmental values
The upper Yarra River (reaches 1–3) provides habitat for
a range of native fish species including river blackfish, mountain galaxias and common galaxias, and has good- quality streamside and aquatic vegetation. The middle and lower Yarra River (reaches 4–6) flows through forested gorges, cleared floodplains and some highly-urbanised areas, and supports several populations of native fish including Australian grayling, river blackfish, Macquarie perch and tupong. Macquarie perch was introduced to the Yarra River last century, and the population is now considered one of the largest and most important in Victoria.
The Plenty River (reach 9) provides habitat for waterbug populations and native fish species (such as common galaxias and river blackfish). Platypus have been detected in the Plenty River in the past, but none have been recorded in recent surveys.
Billabongs are an important feature of the Yarra River floodplain between Millgrove and Yering Gorge and in the lower reaches around Banyule Flats near Heidelberg. The billabongs support distinct vegetation communities and provide foraging and breeding habitat for waterbirds and frogs. Except in very high flows, most billabongs are disconnected from the Yarra River.
Environmental watering objectives in the Yarra River, Plenty River and Yarra billabongs
3.2 Yarra system
    Protect and increase populations of native fish including threatened species (such as the Australian grayling, Macquarie perch and river blackfish)
    Maintain the population of frogs, particularly on the mid-Yarra floodplain
      Maintain the form of the river channel Scour silt from riffles and clean cobbles
     Maintain the population of resident platypus
   Increase, strengthen and maintain native streamside and aquatic vegetation on the riverbank and in the channels
Increase, strengthen and maintain the growth of threatened wetland plant species to rehabilitate shallow marsh, deep marsh and freshwater meadows on the floodplain and billabongs
    Protect and increase communities of waterbugs, which break down dead organic matter and support the river’s food chain
    Improve water quality in river pools, ensuring adequate oxygen concentration in the water to support fish, crustaceans and waterbugs
Victorian Environmental Water Holder | Seasonal Watering Plan 2020–21 | 89

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