knowledge for managing Australian landscapes Technical report Ecohydrological regionalisation of Australia: A tool for management and science Principal Investigators: Brad Pusey1, Mark Kennard1, Mike Hutchinson2 and Fran Sheldon1 Project Associates: Janet Stein2, Julian Olden3 and Steve McKay1 Affiliations: 1.Australian Rivers Institute, Griffith University, Nathan, Queensland 2. Fenner School of Environment and Society, Australian National University, Canberra ACT 3. School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington, USA Funding: This project was funded by the Land & Water Australia Innovation Program with additional start-up funds provided by the Australian Rivers Institute, Griffith University. Published by: Land & Water Australia Product Code: PN22591 Project Number: GRU36 Electronic ISBN: 978-1-921544-73-6 Program: Innovation Postal address: GPO Box 2182, Canberra ACT 2601 Office Location: Level 1, The Phoenix 86-88 Northbourne Ave, Braddon ACT Telephone: 02 6263 6000 Facsimile: 02 6263 6099 Email [email protected] Internet: lwa.gov.au Land & Water Australia © April 2009 Disclaimer The information contained in this publication is intended for general use, to assist public knowledge and discussion and to help improve the sustainable management of land, water and vegetation. It includes general statements based on scientific research. Readers are advised and need to be aware that this information may be incomplete or unsuitable for use in specific situations. Before taking any action or decision based on the information in this publication, readers should seek expert professional, scientific and technical advice. To the extent permitted by law, the Commonwealth of Australia, Land & Water Australia (including its employees and consultants) the authors, and its partners do not assume liability of any kind whatsoever resulting from any person’s use or reliance upon the content of this publication. Project objectives • To develop and validate continental-scale ecohydrological classifications of Australia’s rivers using a combination of empirical and deductive approaches. • To assess the extent to which within-drainage variation in regime exceeds variation at broader spatial scales (i.e. confounds regional classification) and understand the factors responsible for this variation. • To test whether the developed classification is consistent across all key ecologically relevant aspects of the riverine flow regime. • To provide a rigorous foundation for the incorporation of ecohydrological principles into scientific investigation and management of Australia’s rivers. Project final milestones • Final validated continental-scale ecohydrological classifications of Australia’s rivers. • Consistency of the classifications across key ecologically relevant aspects of the flow regime. • Understanding of the extent to which within-drainage variation in flow regime exceeds variation at broader scales. • Clear documentation of the River Analysis Package (RAP). • Flow data prepared and stored according to Land & Water Australia guidelines. • Knowledge and adoption plan completed. An introduction to the project’s aims and methodologies underpinning the examination are given in Appendix 1. a) and b) Continental-scale classification of Australia’s rivers and validation Empirical classification A review of classification methods and of other hydrological classifications for Australia and elsewhere was undertaken (Appendix 2). A review of anthropogenic factors influencing streamflow in unregulated streams was undertaken (Appendix 3). These reviews provide the background to the process of classifying contemporary streamflow data and the context in which classifications relate to the natural flow regime. From these reviews, we constructed a protocol for the classification, outlining all significant methodological steps required. Flow information was obtained for 830 gauges. The minimum period of record within these 830 gauges was 15 years. Whilst this relatively short record length was initially considered sub-optimal for the estimation of some flow metrics, their inclusion greatly increased geographic coverage and accordingly, substantial work was undertaken to estimate, and control for, the effect of the inclusion of these short-record length gauges in the classification. Significant work was also undertaken in screening the data to satisfy our criteria for inclusion and infilling periods of missing record (see Appendix 4). Classification was undertaken using a Bayesian soft clustering technique. The resultant classification (Appendix 5) was composed of 12 groups broadly separated according to 1 predictability, timing of flows and degree of intermittency. The fidelity of group membership was very high for the majority of gauges and groups. Comparison of classification outputs resulting from the total data set, long term gauge data only and short term gauge data only, revealed high concordance, thus lending confidence in the final classification in which all 830 gauges were included. Similarly, the use of different error terms (based on the long or short gauge records) to inform the clustering process did not result in widely divergent classification outcomes. Many of the classification groups were very widely distributed but a clear distinction between tropical/subtropical and temperate regions was detected. ANOSIM (Analysis of similarity) and regression tree analysis revealed that flow regime group membership could be significantly predicted based on a limited set of landscape oriented variables, thus allowing greater confidence in the outcome of the modelled (deductive) classification process. Comparison of the classification scheme with other regionalisation/classification schemes (not necessarily hydrological) at the continental scale was undertaken. Concordance was frequently poor. For example, the Australian Water Resources Advisory Council (AWRAC) basin classification is a poor description of flow regime variation except at the broadest scale of tropical versus temperate. Nonetheless, AWRAC drainage divisions remain a convenient construct for discussion of differences in flow regime type. Deductive classification A spatial framework was developed to supply the spatial units for the deductive classification and the representation of surface drainage pathways necessary for the attribution of catchment climatic and landscape characteristics on which the classification is based (Appendix 7). It was derived using new methods of drainage analysis that accommodate the uncoordinated and distributary drainage systems found over much of the Australian continent, underpinned by the latest revision of the national 9 second digital elevation model (DEM). Although the significant delays in the completion of the DEM update affected the timelines for this task this was justified by the improved accuracy of the outcomes that resulted. We generated a number of environmental classifications of the 1.2 million stream reaches with a non-hierarchical clustering method, varying the sets of attributes, their weighting and transformations and the number of groups (Appendix 8). A 30 group ‘hydroecological/environment’ classification was selected for further analysis, based on its ability to recover the flow regime classes generated by the empirical classification, its classification strength and the ease with which the classification might be communicated. The groups are primarily differentiated by attributes describing the catchment climate and water balance and secondarily by attributes characterising catchment morphology, substrate and vegetation cover. The performance of the classification was mixed. The classification strength was relatively high (75% of that for a comparable empirical classification). The groups differentiated significant variation in flow characteristics though less reliably for those metrics describing the frequency and duration of extreme events. However, the classes defined by the empirical classification were only moderately well recovered by the hydroecological environment groups. We suggested some ways in which this might be improved including better characterisation of some hydrological processes, notably those that control the groundwater contribution to streams, and alternative classificatory strategies. These would be the subject of future research. The classification is available from the author (Stein). It is provided as a Geographic Information System (GIS) layer of the stream network with associated attribute tables indicating the group membership and summary statistics of both the environmental attributes from which it was derived and the flow metrics. c) Spatial variation at different scales As mentioned above, the clear distinction between the flow regimes present in northern and southern Australia was one outcome of the classification and not surprisingly reflects differences in climate. Arid zone streams (Divisions VII, X and XII) grouped with tropical divisions (see 2 Appendix 6). These arid zones divisions contained a low diversity of flow regime types. More flow regime types were present in southern than northern Australia, reflecting the greater complexity of the landscape and weather patterns generating stream runoff. Division I in northern Australia and Division II in southern Australia were the most hydrologically diverse. Northern flow regime types were distributed across the region with little spatial pattern. In southern Australia, two flow types (6 and 9: predictable