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Catchment Polygons, National Geochemical Survey of Australia, 2011

Note: This metadata describes the dataset in accordance with the ANZLIC (Australia New Zealand Land Information Council) Core Metadata Guidelines Version 2.

Dataset citation

ANZLIC unique identifier: ANZCW0703014235

Title: Catchment Polygons, National Geochemical Survey of Australia, 2011


Custodian: Geoscience Australia

Jurisdiction: Australia



This dataset was created for the National Geochemical Survey of Australia (NGSA) to help determine the location of target sites for sampling catchment outlet sediments in the lower reaches of defined river catchments. Each polygon represents a surface drainage catchment derived from a national scale 9 second (approximately 250 m) resolution Digital Elevation Model. Catchments were extracted from an unpublished, interim version of a nested catchment framework with an optimal catchment area of 5000 km2. Only catchments from the Australian mainland and Tasmania were included. In order to generate catchments approaching the optimal area, catchments with an area of less than 1000 km2 were excluded from the dataset, while other small catchments were amalgamated, and catchments much larger than 5000 km2 were split.

ANZLIC search words:

  • GEOSCIENCES Geochemistry
  • SOIL Chemistry
  • WATER Hydrology

Spatial domain:

locality map

Geographic extent name: AUSTRALIA EXCLUDING EXTERNAL TERRITORIES - AUS - Australia - Australia

Geographic extent polygon: 112 -10, 154 -10, 154 -44, 112 -44, 112 -10,

Note: The format for each Geographic extent name is: Name - Identifier - Category - Jurisdiction (as appropriate) See GEN Register

Geographic bounding box:
North bounding latitude: -10 °
South bounding latitude: -44 °
East bounding longitude: 154 °
West bounding longitude: 112 °

Data currency

Beginning date: 2007-07-01

Ending date: 2011-06-30

Dataset status

Progress: Complete

Maintenance and update frequency: Not Known


Stored data format:
DIGITAL - shp ArcView shape file ArcView Geographic GDA94
DIGITAL - ArcSDE ArcSDE feature class ArcGIS Geographic GDA94

Access constraints:

? Commonwealth of Australia (Geoscience Australia) 2011. This material is released under the Creative Commons Attribution 3.0 Australia Licence (

Free Data Download

Data quality


The Centre for Resource and Environmental Studies (CRES - now the Fenner School of Environment and Society) at the Australian National University extracted catchments with an average area of approx. 5000 km2 from an unpublished, interim version of a nested catchment framework (Stein, 2006). Main stem sub-catchment units less than 2500 km2 in area were combined with the upstream tributary catchment, and closed (internally draining) basins of combined area less than 10,000 km2 were iteratively aggregated with a lower neighbouring catchment via the lowest point on the drainage divide. The catchments were derived using a multi-flow extension of an early version of the GEODATA 9 second Flow Direction Grid (ANZLIC unique identifier: ANZCW0703012015) associated with the GEODATA 9 second Digital Elevation Model (DEM) Version 3 (Hutchinson et al. 2008; ANZLIC unique identifier: AW0703011541).

Geoscience Australia then used ESRI ArcGIS? software (v.9.1) (ESRI, 2007) and ArcHydro? Tools (v.1.2 beta) (Maidment and Djokic, 2000) to generate a higher resolution catchment coverage of Australia (threshold area 500 km2) from the 9 second DEM. This high-resolution coverage was used to guide the disaggregation of over-sized polygons in the CRES coarse-scale catchment coverage and bring them within an optimal area range of 4000-6000 km2. Catchment polygons with areas less than this range were, where appropriate, aggregated with neighbouring polygons to again achieve an optimal area. Decisions on which polygons to aggregate or disaggregate were guided by information obtained from these datasets:

- NATMAP Raster Premium 2005 (includes 1:250,000 scale topographic and cultural information for the whole of Australia), along with a Landsat 7 national mosaic (Geoscience Australia, 2007);

- Shuttle Radar Topography Mission (SRTM) 3 second (~90 m) v.2 digital elevation model (NASA, 2007).

Applying the method outlined above, an iterative series of edit, clean and build processes in ArcINFO? resulted in the final national catchment coverage. ArcHydro? Tools (v.1.2 beta) was then used to generate an outlet point for each catchment. These points were used as target sites for field sampling of catchment outlet sediments. Point location adjustments were made manually, if necessary, following consultation with State/Territory Geological Surveys and/or assessment against other environmental datasets. Adjustments were made to account for factors such as proximity to sources of contamination, inaccessibility, or false outlet point placement (e.g. points on the Gulf of Carpentaria which were auto-generated in tidal mangrove swamps).

Subsequent to field sampling, minor adjustments to a small number of catchment boundaries were made manually using ArcGIS? software. These adjustments related primarily to catchments where samples had been collected just outside their designated catchment bounds, and generally involved extending the boundary closest to the catchment outlet downstream, usually resulting in a net change to the affected catchment areas of <100 km2.


References are listed under Additional Metadata.

The current nested catchment framework is distributed by the Bureau of Meteorology as the 'Geofabric': (last accessed 9 Nov 2011)

Further information on the methods used to generate the NGSA catchments and target sampling sites can be found in Lech, M.E., Caritat, P. de, McPherson, A.A. 2007. National Geochemical Survey of Australia: Field Manual. Geoscience Australia, Record 2007/09, 53 pp.

Positional accuracy:

For 50% of the continent the 9 Second DEM has local relief not exceeding 4 metres and standard elevation error not exceeding around 10 metres. This standard error is only twice the stated 5 metre error for the TOPO-250K point elevation source data (Geoscience Australia 2006). As the local relief of the DEM increases the elevation errors increase. Thus a further 30% of the DEM has standard error not exceeding around 15 metres, a further 15% has standard error not exceeding around 35 metres, a further 4% of the DEM has standard error not exceeding around 50 metres and the remaining 1% of the DEM has standard error not exceeding around 60 metres. The maximum absolute errors across the DEM cells are naturally larger than the standard errors. These range from 20-40 metres for the lower relief 50% of the continent up to around 200 metres for high relief areas. There are isolated instances of errors as large as 300 metres in complex highland areas.

Version 3 of the DEM underestimates the elevations of peaks by an average of just 5 metres. Version 3 of the DEM has improved the representation of streamlines and catchment boundaries by upgrading the ANUDEM algorithms and by adding significant numbers of additional data points in areas where the catchment boundaries had been less accurately defined. Comparisons of the rasterised streamlines defined by the 9 Second Flow Direction Grid with corrected TOPO-250K streamline data indicate that the rasterised streams respect these streamlines to within the limits of accuracy achievable at the 9 second scale. The average positional error of the gridded streamlines is around 1/4 of one grid cell or 60 metres. Approximately 95% of the gridded streamlines lie within 125 metres of the mapped streamline network and virtually all are within 270 metres.

Attribute accuracy:

This dataset is accurate to the best of our ability as at 09 November 2011.

Logical Consistency:

This digital dataset has been visually verified.


The National Geochemical Survey of Australia required catchments to have an average area of approximately 5000 km2. As many coastal catchments have areas significantly less than this value, a minimum threshold area value of 1000 km2 was established and used to eliminate small catchments from the shapefile. Accordingly, many of the coastal catchments are not included and the shapefile does not extend to the coastline in many areas.

Contact information

Contact organisation: Commonwealth of Australia (Geoscience Australia) (GA)
Contact position: Manager Client Services
Mail address: Cnr Jerrabomberra Ave and Hindmarsh Dr
Mail address: GPO Box 378
Locality: Canberra
State: ACT
Country: Australia
Postcode: 2601
Telephone: 02 6249 9966
Facsimile: 02 6249 9960
Electronic mail address:

Metadata information

Metadata date: 2013-03-08

Additional metadata

Metadata reference XHTML:

Metadata reference XML:

Lineage References:

Geoscience Australia 2007. NATMAP raster, NATMAP raster premium 2005 release. (last accessed 9 Nov 2011).

Hutchinson M.F., Stein J.A., Stein J.L., Anderson, H. and Tickle, P. 2008. Geodata 9 Second DEM and D8 -Digital Elevation Model Version 3 and Flow Direction Grid User Guide. Fenner School of Environment and Society, ANU and Geoscience Australia, 43 p. (last accessed 9 Nov 2011).

Maidment, D. and Djokic, D. 2000. Hydrologic and hydraulic modelling support with Geographic Information Systems. ESRI, California. 216 p.

NASA 2007. Shuttle radar topography mission - the mission to map the world. Available at: (last accessed 9 Nov 2011).

Stein, J. L. 2006. A continental landscape framework for systematic conservation planning for Australian rivers and streams. Unpublished PhD Thesis, Centre for Resource and Environmental Studies, Australian National University, Canberra.

Authors:McPherson, A.A. Cooper, M. Stein, J.L. Hutchinson, M. F. Lech, M.E. De Caritat, P.