Balancing use and protection for scarce water resources

In many parts of the world, and especially arid and semi-arid regions, water resources are over-allocated to the extent that even very large rivers are being reduced to no-flow conditions in their downstream reaches during dry seasons. The emerging process of environmental flow assessment has been designed to help maintain or improve environmental conditions in rivers by predicting how much water should remain in the river in order to meet the needs of the ecosystem and the non-consumptive requirements of people. There are now many methods for making these predictions, and countries worldwide have adopted policy and legislation to include environmental flows in a process of sustainable water resource management. However, the implementation and provision of the environmental flows, once they have been calculated, has been problematic, because of the perceived competing needs for consumptive use. Australia, as one of the few countries to commence providing environmental flows, now faces the new challenge of demonstrating their benefits and incorporating climate change. This paper looks at case studies of environmental flow assessment in small and large rivers in different parts of the world, and examines the factors which mitigate for and against implementation, including perceptions of climate change impacts. These factors are then compared with the situation in the Murray-Darling Basin, Australia. We conclude that whilst science underpins the ethical need for action and frames the biophysical basis of policy solutions, it is rarely a limiting factor for implementation. Rather the different social, economic, cultural and governance systems are more often the main factors which lead to success, failure or delay in implementation of environmental flows.