Constraints Management Strategy

35.Murrumbidgee

The Murrumbidgee supports a rich assemblage of river channel and floodplain habitats, including the Mid-Murrumbidgee Wetlands and Lowbidgee Wetlands. The Murrumbidgee is also an important tributary of the River Murray.

Potential constraints to environmental water delivery in the Murrumbidgee include: the low level Mundarlo Bridge; the channel capacity of the Tumut River; the channel capacity of the Murrumbidgee River near Balranald; and possible third party inundation and impeded access impacts, particularly around the upper Yanco Creek, Collingullie and Darlington Point. Additionally, high flows may cover sections of low-lying local roads or require the closing of stormwater gates in areas such as Wagga Wagga.

Consultation

Consultation has begun with stakeholders in the Murrumbidgee. Those involved include riparian landholders, irrigators, local councils and agencies involved in river management and operations. Consultation has focused on communicating the scope of the work and gaining feedback on potential impacts (positive and negative) of potential environmental flows.

Key issues raised by stakeholders during the public comment period included the importance of:

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  ongoing discussions with local people to understand the potential impacts of addressing constraints and developing appropriate options to mitigate any impacts
  
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  further work to refine potential flow regimes; as impacts are driven not only by the height of additional flows, but also by the duration, frequency and timing of flows
  
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  providing accurate, timely and easily-accessible information about river flows, particularly when media reports may contain inaccuracies which can have significant impacts on tourism
  
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  recognising the needs of all water users including irrigators, towns, communities, recreational users and the environment
  
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  effective management of environmental watering events; including understanding the impact when environmental flows are followed by natural events
  
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  considering if dam imbalance (as a result of large ‘piggy-back flows’) could reduce reliability of supply
  
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  considering a wide range of mitigation options not just flood easements; including enhancing flood mitigation works, en route storages, constructed floodways and formed waterways to channel flows and land topography projects
  
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  understanding local riverine impacts of higher flows such as erosion, bank slumping and tree fall
  
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  considering infrastructure, agricultural production, risk of localised flooding with stormwater gate closures and social and economic impacts that may be associated with higher flows.
  

36.Priority actions for 2014

Further work is required to understand the range of third party impacts and includes:

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  working with environmental water managers and ecologists to better define and refine the optimal flow height, frequency, duration and seasonality of environmental deliveries
  
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  verifying modelling and mapping of inundation areas already undertaken for the Murrumbidgee mainstem
  
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  development of modelling and mapping of potentially affected watercourses not previously undertaken; particularly for Old Man/Beavers Creek and the Upper Yanco Creek system
  
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  working with landholders to validate the above mapping and identify the types and scale of any potential impacts
  
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  identifying and undertaking a preliminary assessment (through literature review and community input) of potential mitigation measures, including a regulator at the Yanco Creek offtake.
  

Figure Schematic drawing of the Lower Darling between Menindee and Wentworth

37.

38.Lower Darling

The Lower Darling River System is located in south-western New South Wales at the lower end of the Darling River, upstream of its junction with the River Murray at Wentworth. All catchments in the northern Murray–Darling Basin drain into the Barwon–Darling River, which is separated from the Lower Darling by Menindee Lakes. The region contains a number of important environmental assets including Menindee Lakes, the Darling River, Great Darling Anabranch and a number of billabongs, wetlands and floodplains.

The MDBA has identified the main constraints to delivering higher environmental flows as the channel capacity downstream of Weir 32 and the operational strategy and storage release capacity of the Menindee Lakes system.

Consultation

Detailed consultation on constraints in this area has not occurred with landholders and the community to date, because work on some of the issues identified as constraints in the Lower Darling is already being undertaken through the Menindee Lakes Water Savings Project. MDBA did meet with around 20 members of the Lower Darling community — this meeting focused more broadly on the draft Constraints Management Strategy rather than local issues associated with potential higher flows. Given that consultation has been delayed in the Lower Darling there was limited additional local feedback provided during the public comment period.

The feedback received included:

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  current status of the Menindee Water Savings Project and the interdependencies with the Constraints Management Strategy
  
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  importance of working with communities, particularly local irrigators, to:
  

build the understanding of how the Lower Darling and the Darling Anabranch function and the potential impacts of changes in flow regimes

identify potential options to mitigate impacts of higher flows such as floating pumps

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  the need to ground-truth with the community, and to validate the models and assumptions that are used to identify the impacts of constraints
  
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  importance of explaining that the Constraints Management Strategy is about local outcomes as well as allowing more water to be delivered downstream
  

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  impacts of higher flows such as bank erosion, trees falling into the river and the anabranch.
  

39.Priority actions for 2014

During 2014 the Commonwealth and NSW governments will continue (in consultation with the Victorian and South Australian governments) to progress the range of issues that underpin the development of the Menindee Lakes Water Savings Project, including issues that impact on the Lower Darling key focus area. Additional work will include the identification of issues relevant to the Constraints Management Strategy not covered in the Menindee Lakes Water Savings Project; and the scoping of those issues.

These activities are to include:

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  further development of inundation mapping for a range of flow scenarios
  
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  continued liaison with the Lower Darling community: to increase the understanding of flow pathways under the mapped flow scenarios and identify potential third party impacts and benefits that would result from higher flows
  
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  identify and describe potential mitigation strategies to address third party impacts that may result from higher flows.
  

Figure Schematic drawing of the Gwydir