Ecological processes in large rivers are controlled by their flow variability. However, it is difficult to find measures of hydrological variability that characterize groups of rivers and can also be used to generate hypotheses about their ecology. Multivariate analyses of the hydrographs of 52 rivers worldwide revealed distinctive patterns of flow variability that were often correlated with climate. For example, there were groups of rivers that corresponded broadly with ‘tropical’ and ‘dryland’ climates. However, some rivers from continental climates occupy both extremes of this range, illustrating the limitations of simple classification. Individual rivers and groups of rivers may also have different hydrographic ‘signatures’, and attempts to combine measures of hydrological variability into indices mask biologically significant information. This paper identifies 11 relatively independent measures of hydrological variability that help categorize river types and are each associated with aspects of fish biology. Ways are suggested by which the Flood Pulse Concept can be expanded to encompass hydrological variability and accommodate differences among groups of rivers from different climatic regions. Such recognition of the complex role of hydrological variability enhances the value of the concept for river conservation, management and restoration.

The ecosystem concept should be reappraised as a basic model for rivers, with regard for flow as an organizing variable. This would facilitate comparisons between the large rivers of humid climates, where flow regimes are comparatively regular, and those of arid and semi-arid areas, where river regimes are highly variable. Ecosystem processes might be modelled by combining the river continuum and flood pulse concepts, with refinements to accommodate a complex flood pulse (e.g. variations in stage amplitude, timing, duration, rates of rise and fall). Patch boundaries (ecotones) such as the riverine littoral zone warrant close study because they strongly influence the structure and dynamics of the ecosystem. The general model needs a quantitative basis, perhaps focused on the balance of processes involved in the physical transport and biological transformation of carbon. The ultimate test of such a model will be in its capacity to predict the effects of flow regulation. Further development, however, is limited by data. In both research and management monitoring programmes need to be established to provide information and to develop a sustained, comprehensive approach to dryland rivers as ecosystems.

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1. Dryland rivers are a focal point of life. Highly variable flows that underpin the ecology of these rivers are the antithesis of requirements for regular water for irrigation. Proposals exist to divert water for irrigation on the dryland rivers, Cooper Creek and the Paroo River in central Australia, that cross political boundaries of three Australian states (Queensland, South Australia and New South Wales). 2. Poorly‐planned water resource developments on dryland rivers incur unacceptably high ecological costs. Debate about the future of Cooper Creek and the Paroo River is challenging traditional political accountabilities for management hitherto focused on land rather than water. Diversion of water for irrigation threatens high conservation values of these unregulated rivers and livelihoods of rural communities who rely on floods. The current process whereby a Government water agency in one political jurisdiction assesses and judges the merits of proposals that have ecological consequences is restrictive. We critique current mechanisms for assessment, and approval of proposals to divert water from dryland rivers in Australia. 3. An alternative is to begin with a discussion of the impacts of such proposals and ecological and social values under threat that involves a ‘collaborative’ resource management partnership between scientists, landholders and conservationists. Two scientific workshops on Cooper Creek and the Paroo River distilled such a process. This paper reviews the background to these workshops and their importance for decisions on sustainable management of dryland rivers and their floodplain wetlands. Scientific workshops involve the wider community in decision‐making that is traditionally the province of water managers and developers. Transparency, independence and a catchment focus remain challenges for decision‐making on the Paroo and the Cooper but the foundations were laid by the workshops. © 1998 John Wiley & Sons, Ltd.

1. We take issue with a proposal to irrigate cotton crops from Cooper Creek, as the development would be in sharp contrast to the ‘boom‐and‐bust’ character of the local environment. In dryland rivers the flow regime is influenced by aseasonal climatic phenomena like the Southern Oscillation, so that patterns are highly variable and averages are virtually meaningless. Some irrigation developments on dryland rivers have been planned during periods that were unusually wet and, as a result, present levels of water use are not sustainable.  2. Long, dry periods are the norm in dryland rivers. The biota tolerate drought and respond to occasional floods that may have long‐enduring effects (riparian trees, for example, may live for centuries). All are sensitive to the rates of rise and fall and the amplitude, duration and frequency of floods. Where the flood pulse is erratic, as in Cooper Creek, species with opportunistic traits are likely to dominate. Base flows and seasonal variations imposed by irrigation use present a very different physical environment for these species. The plan to tap the Cooper headwaters would amplify the impacts because this region is a refuge for flora and fauna.  3. In general, we contend that the Cooper Creek ecosystem could not accommodate a competitor for water that is vital for its own maintenance, and that the irrigation proposal could be rationalized only in the sophistry of short‐term economics. © 1997 John Wiley & Sons, Ltd.

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In dryland rivers, interactions between flow variability and complex geomorphology expose floodplain wetlands to long-term patterns of flooding and drying and highly variable short-term events. We consider whether the abundance and diversity of fish, macroinvertebrate and zooplankton communities in wetlands of the Coongie Lakes complex are influenced by long-term water regimes. To relate biological changes to changes in water regime, mean values of assemblage indices were ranked and correlated against ranked frequency of drying (i.e. water retention) in each waterbody. As water-retention time increased, fish species diversity (richness, evenness) and disease incidence rose, and fish species dominance and macroinvertebrate abundance decreased. The more mobile species of fish utilised the habitats and food resources provided by newly flooded waterbodies. We conclude that fish populations utilise wetlands with a variety of water regimes, and reductions in the frequency of inundation will decrease fish diversity with sequential losses of less mobile species.