Image of the Month - December
Mapping gullies at the speed of light
Mapping gullies in the Burdekin catchment
How do you find gullies in an area bigger than Greece?
The Burdekin catchment stretches for 130 000 square kilometres across north Queensland, with thousands of creeks and channels. With such a large area to investigate, scientists have turned to satellite and laser technologies to work out where gullies are likely to occur. By identifying gully hotspots, landholders, natural resource management groups and government agencies can target their efforts to reduce erosion and the amount of sediment-laden water flowing into the Great Barrier Reef.
Gullies are difficult to map as they are so variable in occurrence across the landscape. They are generally easier to identify in high resolution imagery, but this imagery can be expensive to obtain across large areas. However, high resolution imagery is available in Google Earth for some areas of the Burdekin catchment. Scientists used this available imagery combined with other landscape information to model the presence of gullies across the whole Burdekin catchment.
Queensland Government scientists recently returned from fieldwork in the Burdekin, where they validated the model and gathered additional data. The image above shows a 3D model of a gully on the Spyglass Beef Research Station captured using a terrestrial laser scanner. The scanner sends out multiple pulses of infrared light, then records how long it takes for the light to bounce off an object and return. This information is then processed to generate an accurate 3D image of the gully shape. By capturing repeated scans of the same locations over time, the scientists can develop models to observe the changes to the gullies, especially after major rainfall events. This provides detailed information about gully processes and movement of soil in gully systems. The information can then be used by geomorphologists and water quality modellers to assess landscape change and sediment loads in waterways, as well as provide information for on-ground remediation activities.
This project is funded through the Reef Wise Farming Research and Development Program, which aims to provide science-based tools and support to help land managers reduce water quality impacts in Reef catchments. The scientists are part of the Queensland Government Remote Sensing Centre, which develops innovative techniques for monitoring and managing Queensland’s natural resources.
Bartley, R., Hawdon, A., Post, D.A., Roth, C.H., 2007. A sediment budget for a grazed semi-arid catchment in the Burdekin basin, Australia. Geomorphology, 87 (4), pp. 302-321.
U. Gilad, R. Denham and D. Tindall., 2012. Gullies, Google Earth and the Great Barrier Reef: A remote sensing methodology for mapping gullies over extensive areas. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B8, 2012, XXII ISPRS Congress, 25 August – 01 September 2012, Melbourne, Australia.
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Last updated 7 January 2013