Devilish Tasmanian Streams: Testing a Referential Approach for the Rapid Assessment of Stream Physical Form Condition

The Natural Resource Management (NRM) organisations in Tasmania commissioned the development of a Tasmanian River Condition Index (TRCI) to enable a statewide assessment of the condition of its streams, incorporating the assessment of physical form. The initial approach that was tested was to use an existing Environmental Domain Analysis (EDA) based on a total of 30 separate inputs which included various measures of topography, litho-structure, climate, the mapped extent of relict geomorphic systems and, specific process provinces (eg Pleistocene glacial limits and karst landscapes) The outputs of the EDA allowed regions of similar fluvial system drivers to be produced (Fluvial Landscape Mosaics) that were independent of anthropogenic disturbance. Within the FLMs pre-European styles of stream were predicted (TasWide Styles), and due to the abundance of pristine streams in Tasmania, it was hoped that reference sites could be found for the dominant Style in each FLM. A comparison of field and desktop-based stream characterisation (based on the RiverStyles method) was used to test the validity of using the FLMs to predict the distribution of TasWide Styles. Detailed field measurements at the site scale were also undertaken in 3 catchments to define the character of reference and test reaches, given the context provided by FLMs and TasWide Styles. These types were also assessed across a disturbance gradient. Whilst a good correlation was found between FLMs and TasWide Styles at a regional scale, the results of the field testing did not give sufficient confidence for this technique to be used for condition assessment at this stage for two reasons: 1. there was a high degree of heterogeneity (using detailed field measures) in sampled reference sites which precluded clear definition of reference character; 2. the scale, and type, of data used to define Fluvial Mosaics and TasWide Styles do not appear to define the character of the river as described by the field measures. A modified approach is now being explored using a combination of GIS landuse data to determine disturbance upstream of a site, and field measures to be assessed against a conceptual model of degradation for each Taswide Style in the context of FLMs.