Classifying the flow regime of data-limited streams in the wet-dry tropical region of Australia

SummaryMany studies have used hydrological variables derived from long-term discharge records to describe the flow regime of streams. However, many streams in the wet-dry tropics of Australia have little or no flow data available for such analysis. In this study, an analysis was undertaken to link significant hydrological variables to a selection of basic catchment characteristics. Long-term discharge records from streams within three relatively well-gauged catchments – Daly (Northern Territory), Fitzroy (Western Australia) and Flinders (Queensland) rivers – were analysed to classify streams into flow regime groupings. Hydrological variables based on flow variability, flood regime pattern and intermittency, were derived for the complete record of each stream. Cluster analysis indicated that streams could be classified broadly into (1) perennial, (2) seasonal, (3) dry seasonal, and (4) seasonal-intermittent. The coefficient of variation of total annual flow and mean annual number of zero flow days were the two most significant variables for classifying streams into flow regime groupings. A selection of broad-scale catchment characteristics based on digital elevation, topographical and geological data were derived for each long-term station within the three catchments. Significant relationships were fitted linking the two most influential hydrological variables, coefficient of variation of total annual flow and mean annual number of zero flow days, to these catchment characteristics. Long-term discharge data from test stations within five other catchments of the wet-dry tropics were used to validate the fitted relationships. Using hydrological variables based on catchment characteristics, most of the test stations were classified within the same flow regime group as that based on hydrological variables derived from flow data. This result indicates that the predicted hydrology variables can be used to broadly classify the flow regime of ungauged or data-limited streams within Australia’s wet-dry tropics.