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Lower Broken Creek is the section of Broken Creek that flows from the confluence with Boosey Creek near Katamatite to the River Murray near Barmah. Nine Mile Creek is an anabranch that leaves lower Broken Creek at the East Goulburn Main Channel and rejoins it downstream of Numurkah. Both waterways are collectively referred to as the lower Broken Creek. 

The lower Broken and Nine Mile creeks and associated floodplain continue to be an important place for Traditional Owners and their Nations. The RAP for this system is the Yorta Yorta Nation Aboriginal Corporation, who were involved in preparing the lower Broken Creek seasonal watering proposal.

System map

Environmental watering objectives in the Lower Broken Creek

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Protect and increase populations of native fish including the threatened Murray cod, golden perch and silver perch by maintaining habitat (water level and quality), allowing fish passage and stimulating fish to migrate and spawn
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Control excessive build-up of azolla, which is a native aquatic plant that can lower water quality in the creek when significant blooms occur
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Maintain healthy water oxygen levels

Environmental values

The lower Broken Creek and Nine Mile Creek support a diverse and abundant native fish community including the threatened Murray cod, golden perch, silver perch, unspecked hardyhead and crimson-spotted rainbowfish (also known as the Murray-Darling rainbowfish). Sections of the lower Broken and Nine Mile creeks have been reserved as state park and natural features reserve. The associated floodplain and wetland habitats support box-dominated grassy woodland communities and numerous threatened species of state and national conservation significance including river swamp wallaby-grass and the Australasian bittern.

Social and economic values

The lower Broken and Nine Mile creeks and associated floodplain and wetland habitats provide water for agriculture and urban centres and support a variety of recreational activities (such as fishing and bushwalking).

Conditions 2018

A dry winter and spring in 2017 meant there was little unregulated flow in the lower Broken Creek, so water for the environment was used to maintain target flows. A winter low flow was delivered before higher flushing flows in August and September 2017, which were delivered to break up and move azolla, which blanketed over 2 km of the creek in several locations. A combination of weir pool manipulation and physically disrupting the azolla significantly reduced the amount of azolla and prevented a further build-up. Hot weather in October 2017 caused much of the remaining azolla to shrink and die, and higher flows that were delivered to provide fish passage helped to break up the remaining blockages and flush the azolla from the system.

In response to a large rainfall event forecast in early December 2017, water levels in the Murray Valley irrigation channels were lowered by increasing outfalls into the lower Broken Creek. The outfalls increased flow in the creek above 700 ML per day for a short period.

Water for the environment was used to maintain dissolved oxygen levels in the lower Broken Creek through summer. Between January and March 2018, average daily flow past Rices Weir was reasonably steady, with a combination of environmental flow releases and Goulburn inter-valley transfer deliveries maintaining target flow rates.

A recent fish population survey in the lower Broken Creek indicates natural spawning and recruitment is occurring and that reaches with a high density of submerged wood, which provides fish habitat, have the highest abundance of native fish. Murray cod larvae were recorded in the creek for the first time, and adult golden perch were abundant. The lack of juvenile golden perch and the detection of golden perch movement in response to increases in flow and water temperature in spring support the theory that the population is primarily maintained by migration from the River Murray. Murray cod were detected moving throughout the lower Broken Creek system during late winter and spring, which highlights the benefit of delivering environmental flows outside of the irrigation season.

Scope of environmental watering

Table 1 Potential environmental watering actions and objectives for the lower Broken Creek

Potential environmental watering

Environmental objectives

Year-round low flows (40 ML/day)1

  • Provide native fish passage through fish ladders

Winter/spring low flows (120 ML/day in August–November)

  • Minimise azolla growth

Spring/summer/ autumn low flows (150–250 ML/day in October–May

  • Minimise azolla build-up 
  • Maintain dissolved oxygen above 5 mg/L

Winter/spring freshes (up to 500 ML/day in August–November)

  • Manage azolla blooms 
  • Trigger fish migration

Spring/summer low flows (250 ML/day in September–December)

  • Increase the availability of native fish habitat during the migration and breeding seasons

1 Primarily during the irrigation season between mid-August and mid-May, but it may be delivered year-round subject to supply constraints.

Risk management

In preparing its seasonal watering proposal, Goulburn Broken CMA considered and assessed the risks of environmental watering and identified mitigation strategies. Program partners continually reassess risks and mitigation actions throughout the water year

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
  • Broken Environmental Water Advisory Group (comprising community members) 
  • Commonwealth Environmental Water Office 
  • Goulburn Broken Catchment Wetland Advisory Group (with representation of Goulburn Valley Landcare, Field & Game Australia, Moira Shire, Greater Shepparton City Council, Turtles Australia, Parks Victoria, Trellys Fishing and Hunting and Kinnairds Wetland Advisory Committee) 
  • Goulburn-Murray Water * Murray–Darling Basin Authority (River Murray Water) 
  • Parks Victoria 
  • Taungurung Clans Aboriginal Corporation 
  • Victorian Environmental Water Holder 
  • Yorta Yorta Nation Aboriginal Corporation