Flow Characteristics of Streams in the Tropical Rivers Region

Dene Moliere, John Lowry, Grant Staben and Chris Humphrey - NT Environmental Research Institute of the Supervising Scientist , 29 August, 2006

A multi- disciplinary project, known as the Tropical Rivers Inventory and Assessment Project, is aiming to categorise the ecological character of rivers throughout Australia’s wet -dry tropical rivers region. As part of this project, efforts are underway to characterise the flow regime of streams within this mostly undisturbed, and relatively data- limited, region in order to be in a position to properly assess the impacts of potential development. In general, the tropical rivers region experiences a distinct wet season from October to April, and a dr y season for the remainder of the year. Stream flow, as a consequence, is highly seasonal. Long- term discharge records from streams within three relatively well -gauged catchments – Daly (NT) , Fitzroy (WA) and Flinders (Qld) rivers – have been analysed to c lassify streams into flow regime units. Hydrological variables based on flow variability, flood regime and intermittency, were derived for the complete record of each stream. Cluster analysis indicated that streams could be classified broadly into (1) pere nnial, (2) seasonal, (3) dry seasonal, and (4) seasonal -intermittent streams. 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 units. Howeve r, many streams throughout the region have little or no flow data available for such analysis. A selection of basic catchment characteristics (including mean annual rainfall, mean catchment slope and drainage density) were derived for each long- term statio n within the three catchments. Significant relationship s were fitted which link 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. The predicted hydrology variables can be used to broadly classify the flow regime of ungauged or data- limited streams within the wet -dry tropical rivers region.