Social and economic impacts of the Basin Plan in Victoria February 2017

11.3Impacts in geographic industry centres

The impact of future scenarios would be expected to be concentrated in the same communities and geographic industry centres that were identified to be relatively vulnerable to impacts from the Basin Plan (as identified in Chapter 10).

Impacts from reduced potential milk production would be concentrated in GMID, with flow on effects in towns where dairy processing occur.

Drought impacts that require significant rationalisation of horticultural developments would involve competition between horticultural farms in Victoria, NSW and SA with adjustment expected (to varying degrees) in all States.

2. Environmental outcomes and benefits

   1. The method used to determine SDLs

The Commonwealth Water Act 2007 requires the Basin Plan to limit the amount of water that can be taken from the Murray-Darling Basin for use over the long-term. The Basin Plan aims to do this through the establishment of new long-term sustainable diversion limits (SDLs), which come into effect in 2019.

These SDLs will replace the existing cap on water use and are set at both catchment and Basin-wide scales. The Water Act 2007 requires these limits to be determined through an assessment of the Environmentally Sustainable Level of Take, or ESLT. To fulfil that requirement, the MDBA assessed how much water can be taken from the Basin without compromising the environment (MDBA 2011a).

The MDBA (2011b) developed a method for determining the ESLT, which it presented in a report along with the outcomes of the assessment. The method involved adopting the basin-wide objective to achieve a healthy-working basin and then determining associated ecological objectives. More specific flow-related ecological targets were then set. The MDBA (2011a) then designed flow targets to protect or reinstate ecologically significant parts of the flow regime in order to sustain:

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  the current extent of water-dependent habitats and vegetation communities in a healthy, dynamic and resilient condition — for their intrinsic values as well as the habitat they provide for conservationally-significant fauna
  
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  viable populations of conservationally-significant fauna by providing recruitment opportunities, recolonisation opportunities and refuge habitat
  
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  ecosystem functions that support these targets.
  

Ultimately flow targets, based on ecological needs, were determined for selected sites along the Basin’s rivers. The locations were called hydrologic indicators sites. A simplified outline of the process is shown in Figure . The flow targets included flow volume, duration, timing and frequency. Comparing achievement of the flow targets for a range of water recovery scenarios was one of the major factors in determining the 2,750 GL water recovery target and corresponding basin-wide SDL.

Figure : Simplified outline of the method used to determine the ESLT (Source: Figure 2, Young et al. 2011)

The method used to determine the ESLT relies strongly on two assumptions (Overton et al. 2014). The first is that meeting the flow requirements at the hydrological indicator sites will result in flow requirements being met across the whole reach represented by the site. The flow targets were based mainly on the flow or habitat requirements for recruitment opportunities of native fish, healthy condition of vegetation, and successful breeding of water birds. The second assumption was that by achieving the flow targets a range of additional biodiversity, ecosystem function, and ecosystem resilience targets specified under the Basin Plan, but not specifically modelled, would also be met.

Other uncertainties included the:

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  estimates of the flow metrics required by plant and animal populations, especially flow frequency (MDBA 2011b)
  
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  practicality of delivering the flows represented in the hydrological models
  
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  uncertainties inherent in the hydrological models – they are only a coarse representation of reality (although the best representation available at the time)
  
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  ecological health of environmental assets is determined by a range of factors of which flows are just one element.
  

The inherent uncertainty in environmental outcomes was recognised by scientific reviewers of the ESLT method (Young et al. 2011, page 30):

Give the uncertainties involved the Panel strongly recommends the MDBA commit to an adaptive approach to implementation of the Basin Plan informed by a well-designed ongoing environmental monitoring and evaluation program that supports longer-term knowledge generation in order to iteratively refine the ESLT and SDLS.

An interpretation of what, ecologically, can be realistically achieved with the Basin Plan under the proposed SDLs has not yet been clearly articulated, either at the site level or the Basin level.

And by the MDBA (2012, pg 2)

The results contained in this report are for a selection of scenarios, and the outcomes presented are indicative of a feasible change in flow regime given the modelled level of reduction in diversions... the final outcomes achieved may be different to those contained in this report.

Following the determination of the ESLT governments formally recognised, through the inclusion of an SDL Adjustment Mechanism in the final Basin Plan, that additional environmental outcomes can be achieved by better use of the available environmental water. The adjustment mechanism includes the supply measures program that enables more efficient use of environmental water to reduce the water recovery from consumptive purposes while achieving equivalent environmental outcomes.

The above discussion does not mean that the Basin Plan won’t deliver significant environmental gains. It simply means that the specifics about what outcomes can be achieved are uncertain. The following section about the potential environmental outcomes delivered by the Basin Plan must be read in this context, recognising that significant effort has gone into better understanding the potential environmental outcomes since the ESLT was determined.

2.