Spatial analysis of anthropogenic river disturbance at regional and continental scales: identifying the wild rivers of Australia

A method for assessing anthropogenic river disturbance is described. The grid-based spatial modeling procedure computes indices of disturbance for individual stream sections. These indices rank streams along a continuum from near-pristine to severely disturbed. The method couples geographical data, recording the extent and intensity of human activities known to impact on river condition, with a Digital Elevation Model (DEM) used for drainage analysis. It was developed to produce the first nation-wide assessment of river disturbance from which Australia's least disturbed or 'wild' rivers were identified. A national summary of the extent and the potential impact of human activities is presented, calculated from the disturbance index values computed for more than 1.5 × 106 stream sections with a total length of over 3 × 106 km. Index values close to the undisturbed end of the continuum are rare, especially among large rivers. Most of the least disturbed streams are predicted to lie within the monsoonal tropical north or the arid/semi-arid center of the continent. The disturbance indices generated provide a comprehensive and consistent characterization of river and catchment disturbance that has applications beyond the identification of wild rivers. These include identification of priorities for rehabilitation and restoration; development of systematic survey strategies for aquatic, riparian and estuarine biota and identification of reserve networks for river systems. However, these applications depend on validating the correlation between river disturbance indices and intensively sampled physical and biological indicators of river condition