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In this section you will find detailed information, including national overviews and state and regional level assessments, from the 2000-2002 National Land and Water Resources Audit theme assessments.
Australian Catchment, River and Estuary Assessment 2002
National Land and Water Resources Audit, 2002
ISBN 0 642 37125 3
Visualising catchments
Photo: CSIRO
Catchments can be presented at a range of scales from subcatchment to total river basin. This assessment found that a catchment size of 500 km² provided sufficient detail to be useful at both the national scale and the catchment management scale. Other visualisations that were trialled included:
- a 5 x 5 km grid;
- State government-defined catchment management areas;
- Australian Water Resources Council river basins;
- bioregions (Interim Biological Regionalisation of Australia); and
- a combination of river basins and bioregions.
These gave different visualisations and were useful, depending on the purpose of the analysis.
For assessment reporting in this report each indicator and aggregate index output is presented at three scales:
- 5 x 5 km grid, taking data sets and creating values for each 5 x 5 km cell (115 226 in total);
- 500 km2 catchments based on the Centre for Resource and Environmental Studies, Australian National University, 1:250 000 digital elevation model and creating values from the data for each 500 km² catchment (3718 in total); and
- Australian Water Resources Council river basins (197 in the assessment area).
Assessment limitations
Integration across biophysical condition data only
- Productivity (e.g. agriculture, forestry, fish production), ecosystem services (e.g. quality of life, conservation, recreation) and social and economic factors were not included in the biophysical definition of catchment condition used for this assessment.
Circularity through linked data sets
- Some key data sets such as land use, soil distribution and vegetation used to derive catchment scale indicators are linked (e.g. most land uses require the clearing of native vegetation and occur on the better quality soils). False precision and bias due to the inter-correlation of variables used in deriving an index can occur.
Quality of available spatial data
- Only biophysical data that are readily available were used. These included satellite imagery, topographic and digital elevation model data, computed or derived indicators (e.g. erosion, soil wetness, salinity risk), data from the Audit, data from State and Territory governments, and existing geographic information system data in the national archive (e.g. vegetation, soils, geology). Data sets have differing levels of data quality. Care has been taken in the selection of data sets to avoid compounding of errors.
Time constraints
- Restricted Audit timelines meant that some Audit data sets were not available in time for incorporation (e.g. Australian Soil Resources Information System, soil acidity, river condition and estuary condition).
Thresholds of condition
- For all biophysical aspects of a catchment there will be a threshold of condition (e.g. induced soil acidity should not be allowed to go below pH of 4.8 as major changes to soil structure, condition and ability to support production occur at these low pH levels [NLWRA 2001b]). Likewise, if our goal is to maintain biodiversity, loss of species accelerates greatly when less than 30% of native vegetation remains (James & Saunders CSIRO 2001). Review of the five-class rating from better to poorer to incorporate thresholds is essential if we are to base our natural resource management on a target-based approach.
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