An Impossible Prescription: Why Science Cannot Determine Environmental Water Requirements for a Healthy Murray-Darling Basin

The concept of environmental water requirements (EWRs) is central to Australia’s present approach to water reform. Current decision-making regarding environmental water relies strongly on the notion that EWRs necessary to meet targets associated with ecological objectives for asset sites can be scientifically defined, thus enabling the ecological outcomes of alternative water management scenarios to be evaluated in a relatively straightforward fashion in relation to these flow thresholds or targets. We argue, however, that the ecological objectives and targets currently underpinning the development of EWRs in the Murray-Darling Basin are insufficient to permit the identification of exact water requirements or flow thresholds. Because of the dynamic and heterogeneous nature of the Murray-Darling Basin and the myriad ways in which it is valued by people, we also assert that it is unlikely that adequate ecological objectives and targets from which to determine EWRs could ever be formulated. We suggest that the current emphasis on the concept of EWRs in environmental water planning conflates science and values, perpetuating a “how much is enough?” myth whereby the significance of the social, cultural and political dimension in environmental decision-making is diminished. We support an alternative paradigm in which the contribution of ecological science to water policy and management decisions focuses on understanding ecological responses of water-dependent ecosystems and their biota to alternative management scenarios and linking these responses to the ecosystem services and human values which they support.