The Basin Plan (MDBA, 2012) aims to achieve a healthy, sustainable, working Basin by balancing environmental, economic and social considerations. A key component of the plan is ‘sustainable diversion limits’ (SDLs). These are the maximum amount of surface and groundwater that can be taken from the Basin for agricultural and human consumptive use. The Murray–Darling Basin Authority (MDBA) estimated that the environmentally sustainable level of take is 10,873 gigalitres per year (GL/y), averaged over the long term. This has been set as the current SDL. This is, on average, 2,750 GL/y less than what was used in the Basin in June 2009.
The Basin Plan allows SDLs to be increased or decreased (within limits) as long as environmental, social and economic outcomes are maintained or improved. SDLs can be increased if changes to infrastructure or water management or river operating practices enable the same environmental outcomes to be achieved with less water. The plan includes details of an ‘environmental equivalence test’ which the MDBA will use to assess whether environmental outcomes are maintained if the SDL is increased. CSIRO has developed a method to test the environmental equivalence of potential SDL adjustments — the Ecological Elements Method.
The Ecological Elements Method compares environmental outcomes at the regional scale for benchmark and SDLadjusted scenarios. The test requires the region environmental outcome score for the SDL-adjusted scenario to be equivalent or higher than the score for the benchmark scenario. The region is the southern connected Basin of the Murray-Darling Basin.
The challenge for CSIRO was to develop and implement Schedule 6 of the Basin Plan, which was the method used to assess the environmental equivalence between scenarios.
CSIRO led a team that developed the Ecological Elements Method. The method uses 12 elements from three ecological classes: vegetation, waterbirds and fish. It takes into account the life cycles, breeding and recruitment requirements to define stress and recovery times for each ecological element (expressed as preference curves). The development of the method involved developing the preference curves and rules which relate ecological response to changes in flow, metrics for weighting environmental significance and rules for combining scores to provide an aggregate environmental outcome score at the region scale. The method was based on published literature sources and the expert knowledge of scientists and consultants engaged as part of the CSIRO-led team. It also took account of input from an independent review panel, Basin governments, and the MDBA. The method is consistent with requirements of the Basin Plan (Chapter 7 and Schedule 6), including that the method be independently reviewed. An independent panel of scientists have reviewed the method at key stages throughout the method development and subsequent trial (Jones et al. 2014; Jones et al. 2015).
Capability is drawn from freshwater ecologists, hydrologists, informatics specialists, spatial analysts, remote sensing and quantitative ecologists. Resourcing from Griffith University, the Australian National University and private contractors were used to complement skills within the project team.
Using existing knowledge, ecological and hydrological information was used to develop a method that looked at state and transition changes.
The SDL adjustment required an amendment to the Basin Plan (2012) in Parliament, with a revised SDL. This amendment was accepted by both houses of parliament on the 9 May. The amendment outlined a package of projects aimed at improving how water recovered for the environment is used, with the aim of getting the best possible environmental outcomes from it.
A CSIRO valuation estimated that the benefit of CSIRO research in the SDL Adjustment was approximately $215 million.