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Lower Broken and Nine Mile creeks have been regulated for over a century. Before regulation, the creeks would have had most of their flow in winter and spring and then contracted to isolated pools or dried out during summer and autumn. The adjacent floodplain would have also flooded regularly. The creeks now have numerous weirs that maintain a relatively constant flow from mid-August until mid-May to support irrigated agriculture. These modifications have changed the way native animals use the creek. Previously, native fish would have moved into the creek when it was flowing and returned to the River Murray as it dried. Both creeks now provide year-round habitat for native fish, and fish passage structures allow fish to move between weir pools. Water for the environment is used to support these permanent fish habitats, by providing flows to trigger fish movement and support fish passage, control water quality and flush azolla as necessary.

The lower Broken Creek is operated separately to the upper Broken Creek and the Broken River, because regulated water is delivered to the lower Broken Creek from the Goulburn and Murray systems via the irrigation channel network.

Water for the environment can be provided to the lower Broken Creek from the Goulburn system through the East Goulburn Main Channel and from the Murray system through the Yarrawonga Main Channel. Water is released into the lower Broken Creek from several irrigation area regulators along the length of the lower Broken Creek. The main priority for environmental watering in the lower Broken Creek system is to maintain minimum flows throughout

the year. Particular attention is given to reaches 1 and 2 during the non-irrigation season, when flow can stop. The next priority is to deliver freshes in winter and spring to trigger fish movement and spawning, maintain water quality and manage azolla blooms in reaches 3 and 4. The measurement point for environmental flows in the lower Broken Creek is at Rices Weir.

Some of the environmental flow targets for the lower Broken Creek are partly or wholly met by operational water releases (inter-valley transfers [from the Goulburn to the Murray] or choke bypass flows [when bypassing the Barmah choke in the Murray]) that are delivered to meet downstream demands. These operational deliveries mainly occur during peak irrigation demand between spring and autumn. Water for the environment may be used to supplement these operational releases and to deliver recommended flow components that are not met by the operational releases.

System map

Environmental watering objectives in the Lower Broken Creek

Fish icon
Protect and increase native fish populations including the threatened Murray cod, golden perch and silver perch
Platypus icon
Protect platypus populations, particularly outside the irrigation season

Protect rakali (water rat) populations, particularly outside the irrigation season
Protect turtle populations, particularly outside the irrigation season
Plant icon
Avoid the excessive build-up of azolla

Maintain the cover and condition of native in- stream and littoral vegetation communities
Insect icon
Maintain the diversity and abundance of waterbug populations
Water icon
Maintain dissolved oxygen levels suitable for aquatic animals

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 feature reserves. The associated floodplain and wetland habitats support box-dominated grassy woodland communities and numerous species of state and national conservation significance including river swamp wallaby-grass and the Australasian bittern.

Recent conditions

The lower Broken Creek system experienced below- average rainfall, record high temperatures and little unregulated flow during 2018–19. Water for the environment was used in combination with operational water to maintain flow in the creek, where possible.

Lower Broken Creek had particularly low flow during June and July 2018, due to lower-than-average rainfall and maintenance works at Katandra Weir and surrounding irrigation areas. Goulburn-Murray Water was forced to close the fish ladders in lower Broken Creek for a number of weeks during this period, to maintain critical weir pool habitat.

The low winter flow led to a build-up of azolla downstream of Nathalia in July 2018. Six blockages were identified, where azolla blanketed whole sections of the creek. Water for the environment was used to deliver a fresh at the start of the irrigation season in August. The fresh peaked at 450 ML per day at Rices Weir and successfully flushed azolla and stimulated fish movement.

Flows between September and December 2018 varied from 206 ML per day to 332 ML per day and often failed to meet the minimum-flow target of 250 ML per day, which is what is needed to maintain adequate fish habitat.

A combination of water for the environment and operational water maintained dissolved oxygen levels in the lower Broken Creek through summer 2018–19. This was particularly important in the wake of record high temperatures in January 2019, which increased the risk of low dissolved-oxygen levels in the weir pools.

The environmental flow study for the lower Broken Creek was updated in 2019. The study improved the scientific rationale for the current environmental flow regime and developed new objectives and flow recommendations for the flowing reaches upstream of Nathalia. One of the main amendments is a recommendation for minimum flows in reaches 1 and 2 over the non-irrigation season, to provide critical habitat for aquatic animals and protect in-stream vegetation.

There is limited formal and ongoing monitoring of ecological conditions in the lower Broken Creek, but the Broken Environmental Water Advisory Group observed when it met in February 2018–19 that:

  • lower Broken Creek is looking better than it has since the 1990s
  • golden perch and large Murray cod are being caught, and fishing has improved
  • a platypus was recently sighted in a permanent weir pool in the Nine Mile Creek at Wunghu. The platypus sighting was verified by several fishers and community members and is the first sighting in the reach.

Scope of environmental planning

Potential environmental watering actions and objectives for the lower Broken Creek

Potential environmental watering action

Functional watering objective

Environmental objectives

Year-round low flows of up to 200 ML/day in reaches 3 and 4 and 100 ML/day in reaches 1 and 21

  • Provide native fish passage through fish ladders
  • Provide suitable foraging habitat for platypus and rakali (water rats),
    and support the movement of juvenile platypus and rakali
  • Provide habitat for turtles including protection from exposure to cold
    in winter
  • Provide flowing water habitat and avoid winter drawdown of weir
    pools for fish, vegetation, waterbugs, platypus and turtles
  • Limit suspended sediment and maintain suitable dissolved oxygen
    conditions
Fish iconPlatypus iconTurtle iconPlant iconInsect iconWater drop icon

Winter/spring/summer/autumn high flows (up to 300 ML/day in reaches 3 and 4 during July to May)

  • Provide habitat for fish and support fish movement, spawning and
    recruitment
  • Flush and mobilise azolla and maintain oxygen levels in summer
Fish iconPlant iconWater drop icon

Winter/spring freshes (up to three freshes of 450ML/day during July to October)

  • Flush and mobilise azolla, if it blooms
  • Trigger fish migration and movement
Fish iconPlant icon

1Primarily planned for the irrigation season between mid-August and mid-May, but it may be delivered year-round subject to supply constraints. Constraints may mean these flows may not be delivered in the non-irrigation season.

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
  • Individual landholders who are on the Broken Environmental Water Advisory Group
  • Commonwealth Environmental Water Office
  • Goulburn-Murray Water
  • Parks Victoria
  • Victorian Environmental Water Holder
  • Nathalia Angling Club Numurkah Angling Club
  • Taungurung Land and Waters Council
  • Yorta Yorta Nation Aboriginal Corporation