REGULATED RIVERS: RESEARCH & MANAGEMENT Regul. Riers: Res. Mgmt. 16: 403–420 (2000) USING DISASTER TO PREVENT CATASTROPHE: REFERENCING THE IMPACTS OF FLOW CHANGES IN LARGE DRYLAND RIVERS FRAN SHELDON a,b , MARTIN C. THOMS a,c, *, OLIVER BERRY b AND JIM PUCKRIDGE a,b a Co -operatie Research Centre for Freshwater Ecology, Uniersity of Canberra, Belconnen, ACT 2601, Australia b Department of Enironmental Biology, Uniersity of Adelaide, Adelaide, South Australia 5005, Australia c Uniersity of Canberra, Belconnen, ACT 2601, Australia ABSTRACT This paper outlines the hydrological change associated with water resources development for six rivers within the Murray-Darling Basin. Hydrological change was assessed using simulated data from the Integrated Quantity and Quality Model (IQQM) and a range of relatively simple flow statistics: the annual proportional flow deviation; the frequencies of medium or high flow events; and the durations of low or no-flow events. The changes in physical properties, water quality and biological characteristics within the six river systems were assessed from the literature and summarized. This information was used to construct a series of hypothetical curves (reference curves) summarizing ecological response to hydrological change. The suitability of these response curves was then checked using data from a seventh river, Cooper Creek, a relatively major pristine endorheic system in central Australia. Reference curves appear to be an effective tool for assessing the likely ecological responses of river systems to increased hydrological change. Copyright © 2000 John Wiley & Sons, Ltd. KEY WORDS: ecological response; hydrology; regulation; river INTRODUCTION It is difficult to predict the environmental impacts on large rivers when their flow regimes are altered. Knowledge of their natural (or pre-development) hydrology and the links between their hydrology, morphology and ecology is required. Long-term hydrological data are available for many river systems, but there are few corresponding physical and biological data sets that can indicate the natural cause and effect processes associated with flow changes. In some instances, the modelling of relevant processes in the presence and absence of human activities has proved successful (Maheshwari et al., 1995), but this also relies on the existence of data on flows and ecosystems. Information about pre-impact conditions (‘natural’ structure and functioning) may also be obtained from palaeoecological studies: that is, studies of historic and prehistoric conditions (Thoms et al., 1999). Here, the physical, chemical and biological characters of sediments offer an opportunity to reconstruct the nature and timing of ecosystems’ responses to natural and human disturbances. However, this painstaking work is slow compared to the time scales at which river managers and scientists operate (Cullen, 1990) and is often considered inappropriate in the face of rapid institutional change. In environmental impact studies it is common to compare pristine or non-impacted sites and test or impacted sites (e.g. Gurnell and Petts, 1995; Richter et al., 1995; Norris and Thoms, 1999). The prediction usually relies upon assessing a group of flow statistics from the river in question in comparison to statistics for similar river systems in which hydrological change and environmental impact have been documented. If the rivers have similarly variable flows, this method provides a reasonable way of estimating flow-related ecological impact (e.g. Poff and Ward, 1989; Gehrke, 1997). It is relatively quick and inexpensive (cf. Norris and Thoms, 1999) and may provide a useful tool for managers attempting to assess the level of ecosystem change given a known level of hydrological change. * Correspondence to: Co-operative Research Centre for Freshwater Ecology, University of Canberra, Belconnen, ACT 2601, Australia. Copyright © 2000 John Wiley & Sons, Ltd. Receied 24 March 1999 Reised 10 July 1999 Accepted 18 July 1999