Alluvial gully erosion is a dominant sediment source of many large rivers draining into the Gulf of Carpentaria. Recent field reconnaissance and aerial survey has highlighted that gullies have a considerable impact on the landscape. In order to understand alluvial gully erosion it is essential that a detailed survey of the nature and extent of alluvial gully erosion be undertaken. Remote sensing is the only practical approach for undertaking this assessment due to the extent and nature of gully erosion in Australia's tropical rivers. In this paper a two level method for mapping gully erosion in Australia's tropical rivers is reported that uses Aster (Advanced Spaceborne Thermal Emission and Reflection Radiometer) satellite image data as the regional level data source. The first level is a data centred remote sensing overview and the second level is a remote sensing image analysis method. Results of a pilot study looking at a 600km2 section of the Mitchell River demonstrate feasibility of the method. The results illustrate a variable scale approach for mapping alluvial gully extent and density with potential for a range of regional scale mapping applications.