3D Mapping and Morphometric Investigation of Gully Erosion Using Geoinformation Approach

Gully erosion is an active process in the Fergusson catchment; a sub-catchment of the Daly river, Northern Australia. Adverse effects of gully erosion include removal of vast amount of soil, sediments increase in the water channels and poor water quality. Identification and mapping of gullies is crucial for the quantification of sediment production. Advanced spatial technologies and availability of high resolution imagery have made it possible to examine and analyse the landform features in detail. Cartosat-1 stereo imagery (2.5m resolution) is used to map erosion features along 58 km upstream of the junction of the Daly and Fergusson rivers. A high resolution Digital Surface Model (DSM) is produced from the stereo pairs using Image Analysis and Stereo Analyst for ArcGIS software. The DSM represents the terrain in three dimensions and offers an opportunity for three dimensional (3D) mapping and visualization of gully features. The position, size and form of 83 gullies are recorded, ranging in size from 205 to 127112.6 Sq m. The geomorphometric properties of each gully, including length, width, depth and volume, were calculated using a Geographic Information System (GIS). These features were used to develop a classification of gully form and the spatial distribution of gully type was analysed in relation to channel and catchment properties. The correlation between the volume of gully erosion and width/depth and length/depth was determined in order to develop an understanding of gully evolution process. Furthermore drainage area and slope relationship is determined for cluster of gullies by subdividing the drainage area to examine mapped gullies.