The percentage of catchment area with agriculture (cropping, improved pasture) on steep slopes in Australia's Intensive Landuse Zone was used as an indicator in the assessment catchment condition, during the National Land and Water Resources Audit . Steep slopes were defined as slopes equal to or greater than 3%.
Agriculture on steep slopes increases the likelihood of soil erosion by sheetwash, and by rill and gully erosion . Erosion increases the transport of soil, particulate nutrients and organic matter into waterways. The main issue in coastal waterways relates to the enhanced sediment loads.
More information and maps of agriculture on steep slopes can be found at the Catchment Condition Online Maps website . Appendix I (pp. 311-312) in Volume 2 of the Australian Catchment, River and Estuary Assessment, 2002 contains a map of Australia's River Basins and Drainage Divisions in which each river basin has been assigned a number. These catchment numbers can be matched to a large number of coastal waterways in pages 316-363 of the same document. The 'agriculture on steep slope scores' for a large number of river basins are available in Appendix B (pp 65-76) of the Assessment of Catchment Condition in Australia's Intensive Land Use Zone: A biophysical assessment at the national scale .