Geospatial analysis of factors driving gully erosion: a case study from Southeastern Nigeria

Gully erosion studies are usually complex and expensive due to the multiple nature of the causative factors, heterogeneity of the underlying geologic materials, and the high volume of point source data required within a given area. For this reason, thorough gully erosion studies are rarely carried out, especially in developing countries with few resources allocated to environmental studies. Thus, it becomes difficult in solving problems arising from such a geologic hazard in those areas. However, the availability of data emanating from remotely sensed operations can be utilized in solving complex gully erosion problems using modern geospatial analytical tools. Consequently, a gully erosion susceptibility study was carried out in Anambra State, Southeastern Nigeria, by integrating remotely acquired geomorphologic and environmental data with the geotechnical information that was derived from field and laboratory investigations. The integrated geomorphologic, environmental, and geotechnical data were analysed with analytical tools such as ArcGIS, Google Earth, and Microsoft Excel, following the frequency ratio method. Results from the study revealed that slope angle, soil plasticity, angle of internal friction, cohesion, and population density contributed about 20%, 23%, 20%, 18%, and 9%, respectively, to soil’s susceptibility to gullying. Slope angle positively correlated with the frequency of gully erosion, whereas population density, plasticity, cohesion, and angle of internal friction negatively correlated with the frequency of gully erosion. The spatial distribution of the data revealed areas that are susceptible to gullying in their various degrees, thus providing affordable information for proper environmental planning and development.