Flood Plain Determination on River Ofiki Catchment, South Western Nigeria

Abstract

Floods and erosion are the most devastating natural hazards, which lead to the loss of lives, properties and resources. It has therefore become important to create easily read, rapidly accessible flood and erosion risk maps, which will prioritize the mitigation effects and cost-effective research work for preparing flood and erosion risk maps in River Ofiki catchment.

Geographic Information System (GIS) were used in this research work to map out the flood and erosion risk areas. The study area map was extracted from Google Earth and was then imported into ArcGIS software for the achievement of the set objectives. The land use map was generated from the input map obtained from Google Earth by using the ArcGIS software. The Digital Elevation Measurement (DEM) was derived by transforming the contour lines extracted from the Federal Survey map into point features using the interpolating icon in the ArcGIS Toolbox Drainage map was derived by using the basic function in the spatial analyst toolbox of ArcGIS. The floodplains were formulated using the Actual runoff map and the Triangulated Irregular Network (TIN) and the erosion map was generated by combining the flow length, flow accumulation, slope map and the land use map.

The erosion risk map showed that 34% of the study area is susceptible to high erosion risk while 49% of the study area is susceptible to moderate erosion risk and 17% of the study area is susceptible to low erosion risk. The flood risk map showed that 45% of the study area is highly vulnerable to flooding while 28 and 27% are moderately and low vulnerable to flooding, respectively. Flood and erosion risk maps are vital components for creating easily-read, rapidly-accessible maps that can facilitate the administrators and planners to identify areas of low, moderate or high risk and prioritize mitigation and response efforts.