Monitoring of gully erosion in an urban area using geoinformation technology

Gully erosion is one of the major causes of land degradation in most urban areas in Edo state of Nigeria. Many of the gullies have developed as a result of inappropriate land use, poor termination of drainage outlet, inadequate storm drainage facilities and in some cases, none availability of such drainage facilities where they are needed.The purpose of the study is to assess the volume of soil loss and sediments transport over a given area as a result of gully erosion. This paper discusses the use of GPS with Total Station Surveys, Remote Sensing and GIS in monitoring the Morphology and Land Degradation procesess within the Queen EdeCatchment Basin in Benin City. In the study, control points were established by method of differential GPS (DGPS), while detailed mapping of the Gully bed, Gully head, Gully banks and Finger were carried out using a total station Instrument. High resolution Ikonos Imageries were acquired and Georeferenced. Point coordinates and morphological parameters including depth, width, cross sectional areas and volume of soil loss were computed. The coordinates were exported into ARGIS environment as an EXCEL shape file. With the aid of ARCGIS software various maps including spot height, Contour and Digital Elevation Model (DEM) were generated. From the morphological parameters cross sectional drawings and bed profiles were produced. Results of the studies revealed that the Gully width varied from 15.6m to 99.5m while the depth varied from 0.5m to 13.8m, the width to depth ratio (WDR) vary from 1.6m to 41.7m. The volume of soil loss was 372, 775m3 over an area of 104.4m2 which is equivalent to 3.57 m3 / m2. Recent research in estimating Gully erosion in China and Spain produced results of 0.86 to 2.24 m 3/m2 and 2.11 m3/m2 respectively. The cross sections show that the Gully is U-shaped indicating a large catchment with large volume of discharge passing through the Gully. Analysis of the immediate catchment area around the Gullying showed that 17.4% of the land area is degraded by Gully, 30% by large sediment deposit and 52.6% by marsh land with mild to medium sediment deposit. The study revealed that GPS with total station surveys in combination with GIS and remote sensing can be used for monitoring gully morphology. The results of the study can be used for planning for further monitoring, gully erosion control and management within the catchment basin.