Mapping Gully Erosion Sites in Imo State Using UAV and GIS

Gully erosion is one of the most severe forms of land degradation in South East Nigeria, destroying farmland, undermining road infrastructure, and displacing rural communities in Imo State. This study maps and characterises active gully erosion sites in Orlu and Oru East Local Government Areas of Imo State using UAV photogrammetry and GIS analysis. A multi-rotor UAV with an RGB sensor is deployed to survey fourteen identified gully systems, generating high-resolution orthomosaics at five-centimetre ground sampling distance and Digital Elevation Models at ten-centimetre resolution. Gully morphological parameters, including length, width, depth, and volume, are extracted from the DEMs and compared with measurements from a 2019 field survey to quantify gully progression. Topographic attributes and land cover conditions are examined using GIS overlay to identify site-specific driving factors. Results indicate active gully retreat averaging 2.8 metres per year across surveyed sites, with the largest volumes of soil loss recorded in sites adjacent to unpaved access roads and areas of exposed laterite substrate. The study produces a spatial inventory that supports the Imo State Ministry of Environment and the Ecological Fund Office in prioritising remediation investment and selecting appropriate bioengineering intervention packages. Keywords: gully erosion, UAV, GIS, Imo State, land degradation.