River Health in the New South Wales Lower North Coast, Hunter and Central Coast Catchments

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A report of AusRivAS assessments 1994 - 1999
Grant Hose and Eren Turak
Environment Protection Agency, 2004
ISBN 0 642 55099 9 ISSN 1447-1280

3. Australian River Assessment System (AusRivAS) Explained (continued)

3.2 The AusRivAS predictive models

AusRivAS is a computer package that contains a number of predictive models. The development of these predictive models were based on the British RIVPACS assessment system models (River Invertebrate Prediction and Classification System, Wright 1993).

AusRivAS models are used to predict the aquatic macroinvertebrate fauna that are likely or expected to be found at any given site were it to be in a reasonable natural condition. In essence, the assessment describes the macroinvertebrate fauna that could be present in the absence of environmental stresses such as water pollution; stream bank erosion, habitat loss nutrient enrichment, altered hydrology etc.

To undertake an assessment using AusRivAS, it is necessary to collect both biological and environmental data from the identified test site using the AusRivAS sampling protocols. The models use the environmental data to predict the types of invertebrates that are expected to be present at the site. The models' predictions are based upon the pooling of the macroinvertebrate reference data collected from sites that are determined to be environmentally similar. The AusRivAS models' predicted invertebrate fauna is a hypothetical representation of the reference condition for that specific site. A score is then derived from comparison of the macroinvertebrates actually collected from that site with those predicted for that site. This score is called the O/E (Observed/Expected) value.

AusRivAS assessments are affected by a number of factors including, site geography, the time of the year, the habitat, and the method of sorting. The influence of these elements is further discussed below.

  1. The geographic area.
    Particular models have different geographic areas of reference. In NSW, the large-scale models cover either the entire state or are divide it into east (coast) and west (inland). There are also regional models developed by the Cooperative Research Centre for Freshwater Ecology (CRCFE) that cover smaller areas such as the South Coast and the Snowy Mountains regions.
  2. The time of year of collection.
    The season or time of year of sampling is likely to have some influence on the composition of the macroinvertebrates found. For most of NSW the combined season model is applicable, with the seasons defined as Autumn = March to June, Spring = October to December. There are also single season models (autumn or spring). In addition to these State wide models there is a summer model for the Snowy Mountains region that has been developed by the Co-operative Research Centre for Freshwater Ecology (CRCFE).
  3. The stream habitat.
    In NSW, the two habitats used for assessments are riffles and edges. The riffles areas are defined as areas of broken water with rapid current that has some cobble and/or boulder substratum. Edges are defined as areas along the stream bank with little or no current.
  4. Details of the sampling protocol.
    All large-scale models for NSW are based on analyses of field picked samples where live animals were separated from samples in sorting trays in the field. Details of sample handling protocols are given in Turak and Waddell (2001a). In contrast, the regional models developed by the CRCFE are based on analyses of animals picked under a microscope from samples that were preserved in ethanol.