Applying Satellite Remote Sensing and GIS Tools in the Study of Gully Erosion

Abstract

Aim: Gully erosion is the most obvious form of soil erosion in southeastern Nigeria mainly because of the remarkable impressions the gullies make which are also visible manifestation of the physical loss of land due to erosion. In the literature, there are various accounts of the number of gully sites in Imo State as well as the likely causes of the gullies. The very great depths of some of these gullies and the failure of some control measures strongly suggest that they may actually result from interplay of exogenic (such as weathering) and endogenic (tectonic) forces. The aim of this study therefore was to integrate satellite remote sensing data of the study area with GIS to highlight gully erosion hotspots as well as create a database of erosion sites and attributes. Development of 3D – Digital Terrain Models (DTM) of the area for the purpose of studying topography, characteristics and patterns of gully sites. Integration of the DTMs with processed satellite images to generate data for slope analysis and other spatial attributes of gullying. Study Population: Gully Erosion profiles in Imo State, Nigeria. Duration of Study: 24 months. Methodology: SRTM data and SPOT 5 satellite imageries of Imo State were studied and utilizing the opportunities offered by Remote Sensing and GIS. Google earth images and ground truth were used to confirm gully spots and maps were then generated with vital spatial datasets on the spatial distribution and development of gully erosion in Imo State. Results: The Digital Elevation Model (DEM) data revealed a correlation of low values with areas of high gully erosion susceptibility. There is also a relationship between the drainage, lineament density and gully erosion in the study area. Gullies are concentrated in the northern western section of Imo State and area underlain by the transition zone between Benin Formation and Bende-Ameki Formation while the Northeast flank though on the same relief height is not that affected because of the shale component of the soil, however, this areas is heavily dissected by streams in dendritic pattern. Finally, a correlation was found to exist between the lineament trend and the strike directions of most gully erosions in the area indicating structural control of gully initiation in the area.