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

Abstract

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 little resources allocated to environmental studies. Thus, it becomes di cult in solving problems arising from such geologic hazard in those areas. However, the availability of data emanating from remotely sensed operations can be utilized in solving complex gully erosional problems using modern geospatial analytical tools. Consequently, gully erosion studies within the study area were carried out by integration of geomorphologic and environmental data which were acquired remotely, and geotechnical information derived from eld and laboratory investigations of the underlying geologic materials. The integrated geomorphologic, environmental, and geotechnical data was 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 and population density were positively correlated with the frequency of gully erosion, whereas plasticity, cohesion, and angle of internal friction were negatively correlated with 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.

Comparative analysis of the expansion rate and soil erodibility factor of some gullies in Nnewi and Nnobi, Southeastern Nigeria

“…Gully erosion, triggered by fast-flowing water eroding soil and creating channels, is exacerbated by increased slope instability during wet seasons, causing steep gully slope walls to fail due to heightened pore pressure levels 4 , 5 , 12 , 13 . The vulnerability of soil to water erosion is determined by geological, geomorphological, and climatic conditions within the area 4 , 13 .…”

“…Rainfall amplifies existing gullies as surface runoff erodes more soil 19 . The influx of pollutants from increased population and urbanization contributes to alkaline surface runoff, further eroding soil 12 .…”