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Flooding in the Barmah–Millewa Forest depends on flows in the River Murray. A natural narrowing of the river (known as the Barmah choke) restricts flow and results in overbank flooding when flows downstream of Yarrawonga Weir exceed the channel’s capacity. This restriction influences both the operation of Yarrawonga Weir and the upper limit of environmental flows that can be delivered to the forests.

The delivery of irrigation water during summer and autumn is managed to minimise unseasonal flooding of the forest. Regulators along the River Murray remain closed during summer and autumn to restrict flow through low-lying flood runners. The delivery of water to Barmah Forest is also limited by an imposed flow constraint downstream of Yarrawonga Weir to prevent flooding of private land. The current constraint limits releases to a maximum of 18,000 ML per day until the end of September (with potentially affected landholder support) and to 15,000 ML per day for the rest of the year. To overcome this constraint, most environmental flows are directed into Barmah and Millewa forests via regulators rather than overbank flows. It is currently not possible to achieve the desired flooding depth and duration for floodplain marsh vegetation in both forests at the same time without natural flooding.

Water management at Barmah–Millewa Forest seeks to build on unregulated flows and the delivery of consumptive and operational water en route to optimise environmental outcomes when possible. As Barmah–Millewa Forest is located towards the upper reaches of the regulated portion of the River Murray, water for the environment delivered to the forest can often be used again at sites further downstream, as part of multi-site watering events.

System map

Environmental watering objectives in Barmah Forest

Provide habitat for native fish and increase the population
Maintain or increase the habitat available for frogs
Connected icon
Enable nutrient cycling (particularly carbon) between the floodplain and river through connectivity
Maintain or increase the habitat available for turtles including the broad-shelled turtle
Plant icon
Enhance the health of river red gum communities and aquatic vegetation in the wetlands and watercourses and on the floodplain

Promote the growth of floodplain marsh vegetation communities, particularly the extent of Moira grass growing in these areas
Provide feeding and nesting habitat for the successful recruitment of colonial nesting waterbirds
Provide early-season flushing of the lower floodplain to cycle nutrients during cooler conditions and reduce the risk of poor water quality events in summer

Environmental values

The Barmah–Millewa Forest is the largest river red gum forest in Australia and the most-intact freshwater floodplain system along the River Murray. The forest supports important floodplain vegetation communities including the threatened Moira grass plains and is a significant feeding and breeding site for waterbirds including bitterns, ibis, egrets, spoonbills and night herons. Significant populations of native fish, frogs and turtles also live in the forest’s waterways. Barmah Forest is known to support 74 plant and animal species protected under state and national legislation.

Recent conditions

Forest regulators were opened in July 2018 to allow water to pass through Barmah Forest while the flow in the River Murray was below channel capacity. From September 2018, the volume of operational transfers between Hume Reservoir and Lake Victoria increased and exceeded the channel capacity. These operational transfers caused sustained low-level flooding of the Barmah floodplain. Water for the environment was released in November and December 2018 to enhance the low-level flooding and optimise environmental outcomes triggered by the operational transfers. All flows reduced in late December 2018, and the forest dried out over the rest of summer and autumn.

Around 30 percent of the Barmah floodplain was inundated in spring, resulting in an excellent vegetation response for wetland plants in the shallow freshwater marshlands. Exceptional growth and flowering of Moira grass was recorded, and it was observed to grow in parts of its former range where it has not been recorded for many years. This was an important outcome for a species that has suffered a 90 percent decline in extent since 1930.

Waterbirds also responded to the spring/summer flood. Many species were observed breeding or calling throughout the wetlands including Australasian and little bitterns, and relatively small numbers of colonial nesting waterbirds (such as cormorants, ibis and night herons) also bred. In most years, additional environmental flows are provided during summer to help birds complete their breeding, but this was not required in 2018–19 due to the relatively low numbers of colonial waterbird nests.

Most of the operational flows in spring 2018 were directed through Barmah Forest to optimise the transfers to Lake Victoria. As a result, only around five percent of the Millewa Forest floodplain was inundated. Watering low-lying wetlands in Millewa Forest will be the priority objective if overbank environmental flows occur in 2019–20.

Scope of environmental watering

Table 1 Potential environmental watering actions and objectives for Barmah Forest

Potential environmental watering action

Functional watering objective

Environmental objective

Winter/spring low flows to
various waterways in Barmah Forest (variable flow rates during July to December)

  • Provide flow in forest waterways to maintain habitat for native fish and turtles
  • Facilitate the movement of native fish between floodplain waterways and the river
  • Remove accumulated organic matter to cycle carbon to the river system and minimise the risk of anoxic blackwater
Fish iconTurtle iconJigsaw icon Water drop icon 

Spring/summer freshes (inchannel) in the River Murray channel (up to three events of at least 500 ML/day of variability for eight days during October to December)

  • Trigger spawning of native fish species, primarily golden and silver perch

Fish icon

Spring/summer freshes (drought) to Gulf and Boals
creeks (100 ML/day for three to five days as required
during November to April)

  • Maintain critical drought-refuge areas in Barmah Forest to provide habitat for native fish and turtle populations
  • Flush drought-refuge pools to maintain water quality

Fish iconTurtle iconWater drop icon

Spring/summer/autumn low flows to floodplain waterways
including Sandspit, Gulf, Big Woodcutter, Boals, Island
and Punt Paddock Lagoon (200 ML/day for 30 to 60 days
during November to April)1

  • Provide flows to replenish refuge areas and maintain water quality
  • Provide flows to replenish permanent waterways, to maintain fish and turtle populations
  • Maintain connectivity to the river
  • Remove accumulated organic matter, cycle carbon to the river system and minimise the risk of anoxic blackwater

Fish iconTurtle iconJigsaw icon Water drop icon

Spring inundation of floodplain marshes (variable flow rates up to 18,000 ML/day downstream of Yarrawonga Weir for three months during September to December)1

  • Provide flooding of sufficient duration to allow the growth of floodplain marsh vegetation in open plains
  • Provide water to in-forest wetlands and low-lying floodplain areas to create foraging opportunities for birds and increase available habitat for turtles, frogs and small-bodied native fish

Fish iconFrog iconTurtle iconPlant iconHeron icon

Targeted wetland watering to Boals Deadwood, Reedy Lagoon and Top Island wetlands (200–400 ML/day for four and a half months during  September to February)

  • Provide a cue to initiate waterbird breeding or maintain a breeding event
  • Maintain wetland vegetation to provide habitat for colonial nesting and flow-dependent waterbirds

Plant iconHeron icon

Autumn/winter low flows in the River Murray (up to
4,000 ML/day downstream of Yarrawonga in May to June)

  • Increase water depth in the River Murray channel to provide habitat for large-bodied native fish in the River Murray and unregulated
    anabranches in Barmah–Millewa Forest

Fish icon

1 Likely to target Millewa Forest in 2019–20, unless the Murray–Darling Basin Authority directs operational transfers via Barmah Forest.

Engagement

Table 2 shows the partners organisations with which Goulburn Broken CMA engaged when preparing the Barmah Forest seasonal watering proposal.

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

Table 2 Partners engaged in developing the Barmah Forest seasonal watering proposal

Partner and stakeholder engagement
  • Commonwealth Environmental Water Office
  • Department of Environment, Land, Water and Planning
  • Goulburn-Murray Water
  • Murray-Darling Basin Authority
  • New South Wales Office of Environment and Heritage
  • Parks Victoria
  • Victorian Environmental Water Holder
  • Yorta Yorta Traditional Owner Land Management Board