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Lake Nillahcootie has a storage capacity that is about half the mean annual flow of its upstream catchment, so it fills in most years. The operation of Lake Nillachootie has modified the river’s natural flow pattern; winter/spring flows are less than natural because a large proportion of inflows are harvested, while summer/autumn flows are higher than natural because water is released to meet downstream irrigation demands. These impacts are most pronounced in the reach between Lake Nillahcootie and Hollands Creek. Downstream of Hollands Creek, the river retains a more- natural flow pattern due to the contribution of tributary inflows. The catchment has been extensively cleared for agriculture including dryland farming (such as livestock grazing and cereal cropping) and irrigated agriculture (such as dairy, fruit and livestock).

Water is released from Lake Nillahcootie to meet downstream demand and minimum-flow requirements specified under the bulk entitlement for the Broken River system. Releases from storage may be less than 30 ML per day as tributary inflows immediately below the storage (such as from Back Creek) can supply much of minimum- flow requirements specified in the bulk entitlement.

The upper Broken Creek is defined as the 89-km stretch of creek from the Broken River (at Caseys Weir) to the confluence with Boosey Creek near Katamatite. The upper Broken Creek flows across a flat, riverine plain and has naturally low run off from its local catchment. It receives flood flows from the Broken River, although the frequency of these floods has been reduced by earthworks and road construction.

Upper Broken Creek has been regulated for more than a century. Before 2007, water was diverted into upper Broken Creek at Casey’s Weir to meet local demand, but recent water-savings projects have reduced the demand on the creek. There are now low flows throughout the year between Caseys Weir and Waggarandall Weir. Flows downstream of Waggarandall Weir are mainly influenced by rainfall and catchment run off. These changes have reduced the amount of permanent aquatic habitat.

Delivery of water for the environment to the Broken River is primarily constrained by the availability of water. Usually, the available volume of water for the environment is well short of the volume required to deliver the desired flow components. Deliveries of water for the environment to the upper Broken Creek are also restricted by channel capacity and by the need to avoid flooding low-lying adjacent land.

System map

Environmental watering objectives in the Upper Broken Creek

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Increase native fish populations
Platypus icon
Maintain platypus populations
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Maintain in-stream vegetation
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Support a wide range and high biomass of waterbugs, to break down dead organic matter and support the river’s food web
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Maintain water quality

Environmental values

The Broken River retains one of the best examples of healthy in-stream vegetation in a lowland river in the region. A range of native submerged and emergent plant species including eelgrass, common reed and water ribbons populate the bed and margins of the river. These plants provide habitat for a range of animals including small- and large-bodied native fish species. Murray cod, Macquarie perch, golden perch, silver perch, river blackfish, mountain galaxias and Murray-Darling rainbowfish all occur in the Broken River. The river also supports a large platypus population.

The upper Broken Creek area is dominated by unique box riparian vegetation and remnant plains grassy woodland.

It supports numerous threatened species including brolga, Australasian bittern, buloke and rigid water milfoil. Much of the high-quality native vegetation in the region is set aside as a natural features reserve. Upper Broken Creek supports a variety of native fish species including carp gudgeon, Murray cod, golden perch and Murray-Darling rainbowfish, as well as platypus and common long-necked turtle.

Both the Broken River and upper Broken Creek are listed in the Directory of Important Wetlands in Australia.

Recent conditions

Dry conditions were the dominant feature of flows in the Broken River and upper Broken Creek in 2018–19. Isolated rainfall events between August and December 2018 delivered a few small, natural freshes in the Broken River downstream of Lake Nillahcootie, which benefitted native fish and in-stream vegetation. Winter/spring flows in the upper Broken Creek were below minimum-flow requirements for most of the time, although two small, natural freshes helped maintain water quality and broad environmental values.

Environmental flows commenced in May 2019, to help maintain minimum-flow levels in the Broken River under ongoing dry conditions. These flows aim to maintain habitat and prevent the loss of aquatic vegetation, waterbugs and native fish leading into winter 2019.

Scope of environmental planning

Potential environmental watering actions and objectives for the lower Broken Creek

Potential environmental watering action

Functional watering objective

Environmental objectives

Summer/autumn fresh in upper Broken Creek (one fresh of up to 100 ML/day for 10 days during December to May)

  • Maintain water quality, particularly dissolved oxygen levels, in refuge pools
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Summer/autumn low flows in upper Broken Creek (up to 10 ML/day for 30–60 days during December to May)

  • Maintain pool and riffle habitat for native fish populations and waterbugs
  • Maintain access to habitat and food resources for platypus
  • Maintain habitat for in-stream vegetation
Fish iconPlatypus iconPlant iconInsect icon

Winter/spring low flows in upper Broken Creek (up to 15 ML/day for 30–60 days during June to November)

  • Maintain pool and riffle habitat for native fish populations and waterbugs
  • Maintain access to habitat and food resources for platypus
  • Maintain habitat for in-stream vegetation
Fish iconPlatypus iconPlant iconInsect icon

Year-round low flows in the Broken River (up to 30 ML/day for 40–100 days)

  • Maintain riffles, slackwater and pools to provide diverse hydraulic habitat for native fish, aquatic plants, platypus and waterbugs
  • Maintain habitat for in-stream and fringing aquatic vegetation and prevent terrestrial vegetation colonising the stream bed
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Summer/autumn freshes in the Broken River (one fresh of 400–500 ML/day for two to five days during December to May)

  • Scour sediment around large wood and turn over bed sediments to replenish biofilms and increase productivity
  • Provide flow cues to stimulate native fish breeding and migration
  • Provide flow to maintain in-stream and fringing aquatic vegetation
  • Maintain longitudinal connectivity for native fish passage
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Engagement

Table 2 shows the partners and stakeholder organisations with which the Goulburn Broken CMA engaged when preparing the Broken system seasonal watering proposal.

Seasonal watering proposals are informed by longer-term plans such as regional catchment strategies, regional waterway strategies and environmental water management plans and other studies. These plans incorporate a range of environmental, cultural, social and economic perspectives and longer term integrated catchment and waterway management objectives. For further details, refer to the Goulburn Broken Regional Catchment Strategy and Goulburn Broken Waterway Strategy.

Table 2 Partners and stakeholders engaged in developing the Broken system seasonal watering proposal

Partner and stakeholder engagement
  • Goulburn Valley Environment Group
  • Individual landholders
  • Commonwealth Environmental Water Office
  • Goulburn-Murray Water
  • Parks Victoria
  • Victorian Environmental Water Holder
  • Taungurung Land and Waters Council
  • Yorta Yorta Nation Aboriginal Corporation