An approach for assessing the physical condition of rivers at the catchment scale

Contemporary approaches for assessing the condition of river systems focus primarily on biological information. Increasingly, natural resource managers are becoming interested in the physical condition of river systems. Rivers are naturally complex physical systems that change in time and space, and therefore challenge many traditional scientific approaches for assessing their character. One solution to this problem is the use of hierarchy theory which provides a graded organizational structure to interpret river complexity. However, most geomorphic characterizations of rivers fail to acknowledge the importance of the nested organisation of river systems and scale, thus often misinterpret form-process links. This study outlines a typology for a geomorphic characterization of rivers that can be used to assess their physical condition. It focuses on a specific level within the geomorphic river hierarchy. For this study, a set of criteria are outlined for developing a quantitative river classification scheme. This involves the use of fifteen geomorphic variables in a desktop based taxonomic river typing scheme. Variables are extracted from digital data, using both an automated GIS module developed specifically for such an exercise and combined with manually extracted data. These physical data are analysed using a series of multivariate analyses. The applicability of the approach is demonstrated in the Namoi catchment, NSW, at the basin scale. The physical condition of the river network is based on the community of river types and is assessed by considering the richness, composition and diversity of river types. The applicability of the approach for river management is also outlined.