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The lower Broken and Nine Mile creeks have been regulated for over 100 years, significantly altering their flow regimes. Pre-regulation, the creeks would have mainly flowed in winter and spring and the adjacent floodplain would have received more regular flooding from overbank flows. In summer and autumn, the creeks would have had much less flow, even reducing to pools and drying out completely. The creeks now flow at a relatively constant level from mid-August until mid-May with numerous weirs that support adjacent irrigated farming. This has resulted in changes to the way native animals use the creek. Previously, native fish would have moved into the creek when it was flowing and moved back out into the River Murray when it dried. The creek now provides year-round habitat for native fish, permanently holding water and with fish passage structures through all the weirs. Consequently, environmental water is used to support this permanent native fish habitat.

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

Environmental water provided in the lower Broken Creek can be sourced from both the Goulburn and Murray systems. Environmental water is released from the Goulburn system through the East Goulburn main channel and from the Murray system through the Yarrawonga main channel. The priority river reach for environmental watering is reach 3 (from Nathalia Weir Pool to the River Murray), with flows to this reach expected to also deliver the desired flows in reaches 1 and 2. The measurement point for target flows in lower Broken Creek is at Rices Weir.

Environmental watering objectives in the Lower Broken Creek

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Protect and boost populations of native fish (including the threatened Murray cod, golden perch and silver perch) by providing habitat flows and encouraging fish to migrate and spawn
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Control excessive build-up of azolla, 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

Lower Broken Creek and Nine Mile Creek support diverse and abundant native fish including the threatened Murray cod, golden perch, silver perch, unspecked hardyhead and Murray–Darling rainbowfish. The associated floodplain and wetland habitats support box-dominated grassy woodland and numerous threatened species of state and national conservation significance including buloke, the bush stone-curlew and the brolga.

Social and economic values

The lower Broken and Nine Mile creeks and associated floodplain and wetland habitats contain many important Aboriginal cultural heritage sites, provide water for agriculture and urban centres and support a variety of recreational activities such as fishing and bushwalking.

Conditions mid-2016

Unregulated (natural streamflows that can't be captured in major reservoirs or storages) winter flows were significantly lower in July–August 2015 than in the previous winter. There was no other significant rain that triggered unregulated flows in the systems for the remainder of the irrigation season.

Between the opening of the irrigation season on 15 August and the end of August, flows at Rices Weir averaged 240 megalitres (ML) per day. This was higher than normally targeted at this time of year and was a result of the delivery of the Goulburn system water quality reserve to dilute and flush irrigation channels of residual herbicide applied for the treatment of arrowhead, an aquatic weed. There were no negative effects recorded and the flows helped flush a build-up of azolla from the creek that developed during the low pre-irrigation-season flows.

Environmental watering started slightly later than normal in early September following the completion of the delivery of water from the Goulburn system water quality reserve. Flows reduced in September, averaging 162 ML per day, which helped minimise further azolla build-up.

Between October and the end of April the flow target was 250 ML per day, and flows generally ranged between 200 ML per day and 350 ML per day. As well as environmental water, Goulburn inter-valley transfer and Murray choke bypass flows contributed a significant proportion of the flows. The coordination of environmental and operational water deliveries helped achieve both environmental outcomes and delivery of water to downstream users.

In February a blue-green algae outbreak occurred in the Murray and made its way into the lower Broken Creek. In early March, a local heatwave increased water temperatures to close to 30oC. These two factors combined to result in low dissolved oxygen levels at Rices Weir for about a week. A proactive fish relocation project was initiated, capturing native fish and relocating them downstream of Rices Weir. All fish moved were in good condition and no other signs of stress (such as fish gulping for air at the surface) were observed. This indicates that either the fish were able to move to find better water quality in the immediate area or up and down the creek—there are fish ladders allowing passage along the creek and into the River Murray—or they were able to cope with the low dissolved oxygen levels until they improved.

The target flow at Rices Weir was reduced to 150 ML per day in May but with local rain and reduced irrigation demand it remained around 250 ML per day before ceasing at the end of the irrigation season on 15 May.

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

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

  • Minimise azolla growth

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

  • Maintain water quality, including dissolved oxygen levels above 5 mg/L

Winter/spring freshes (120–250 ML/day for up to 14 days in August–November)

  • Remove large azolla blooms

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

  • Increase native fish habitat during 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.

Scenario planning

Due to regulation of the lower Broken and Nine Mile creeks, their environmental water needs are relatively fixed from year to year and independent of annual climatic conditions.

During the season, the environmental water flows of the lower Broken Creek can vary and focus on maximising the habitat and movement of fish, maintaining water quality and flushing azolla through the system. The required volume to meet these objectives decreases from a dry to a wet scenario as unregulated flows would contribute a greater amount under wetter conditions.

Table 2 Potential environmental watering for the lower Broken Creek under a range of planning scenarios

Planning scenario

Dry

Average

Wet

Expected river conditions

  • Some unregulated flows in winter
  • No unregulated flows throughout the irrigation season (mid-August–May)
  • No diversion of unregulated River Murray flows available
  • No unregulated flows from October–May
  • Unregulated flows in winter/spring
  • Diversion of unregulated River Murray flows available mid-August–October

 

  • Unregulated flows in winter/spring
  • No unregulated flows from November–May
  • Diversion of unregulated River Murray flows available mid-August–November

Potential environmental watering

  • Year-round low flows
  • Winter/spring medium flows
  • Summer/autumn medium flows
  • Winter/spring freshes
  • Year-round low flows
  • Winter/spring medium flows
  • Summer/autumn medium flows
  • Winter/spring freshes
  • Spring/summer high flows

Possible volume of environmental water required to achieve objectives

  • 62,000 ML
  • 61,000 ML
  • 50,000 ML

Risk management

In preparing its seasonal watering proposal, Goulburn Broken Catchment Management Authority considered and assessed risks and identified mitigating strategies relating to the implementation of environmental watering. Risks and mitigating actions are continually reassessed by program partners throughout the water year.

Engagement

Waterway managers meet communities on environmental watering regionally, although other program partners also play a role.

In each region of Victoria, community engagement on environmental watering happens when environmental watering objectives and priorities are scoped (long term and annually), when delivering environmental water, and when reporting on environmental watering results.

In the Goulburn Broken region communities are involved in decisions about the Goulburn River and wetlands, Broken River and wetlands and the Murray River and wetlands. This happens through formal advisory groups: Environmental Water Advisory Groups focusing on rivers, a wetland advisory group and the Barmah Millewa Operations Advisory Group.

Who is engaged and how

Recreational users

Through formal advisory groups, recreational users provide local advice and raise opportunities for 'shared benefits' including whether the timing of environmental watering may align with key recreational events such as cod and duck opening. Recreational users are informed of environmental water deliveries and provide data that assists with reporting on the outcomes of environmental watering.

Goulburn-Murray Water directly engages with recreational user groups that use Goulburn-Murray Water water storages for recreation through planned consultations and meetings to discuss storage levels and potential impacts of environmental water releases from storages.

Environment groups

Through formal advisory groups, environment groups provide local knowledge, land management advice and advocate for the environment. They are also informed of environmental water deliveries and provide data that assists with reporting on the
outcomes of environmental watering.

Landholders/farmers

Through formal advisory groups, farmers and landholders (who often own land with river frontages) provide local knowledge and land management advice. They are also informed of environmental water deliveries and provide data that assists with reporting on the outcomes of environmental watering.

Traditional Owners

Through the Goulburn Broken Catchment Management Authority Indigenous Facilitator, the Yorta Yorta Nation (responsible for managing some land and reserves in the region) is given the opportunity to provide input to seasonal watering proposals through annual briefings with the Catchment Management Authority.

There are Yorta Yorta representatives from the Goulburn Broken region who are members of the Murray Lower Darling Rivers Indigenous Nations. The Victorian Environmental Water Holder, the Commonwealth Environmental Water Holder and the Murray Darling Basin Authority engage Murray Lower Darling Rivers Indigenous Nations on strategic (often longer term) issues related to environmental watering.

Councils

Through the wetland advisory group (due to their role as land managers for some wetlands), Councils provide local advice.
They also support local advertising during water delivery and share data for reporting.

Goulburn-Murray Water consults with the Greater Shepparton City Council and the Moira Shire Council regularly on water management, including on environmental water management.

General public

The Goulburn Broken Catchment Management Authority communicates through their website, media releases, advertisements in local papers, a column in Country News, in the Goulburn Broken Catchment Management Authority bi-monthly newsletter, social media, radio, community forums and partnered research.