Development of Flood Prone Area Map for Igbokoda Township using Geospatial Technique

Abstract

Rapid urbanization has greatly increased the volume of runoff generated in many developed areas and subsequently resulting in flooding. This study evaluated the flood prone area of Igbokoda town in Ondo State and developed a flood risk map to facilitate proper planning and future flood mitigation. Scientific technique of GIS was used to identify flood risk areas within the study area. The Landsat 5 (TM), Landsat 7 (ETM+) and Landsat 8 (LC) images for 1986, 1999 and 2013 coupled with STRM 90 m DEM data of the area were used to identify three categorized risk zones. A total of 339 basins were delineated and stream network on the landscape of this area were carved. Hydrological and vegetation cover analyses were conducted using the satellite imageries obtained from United States Geological Surveys Archive online over the study area for three different epochs 1986, 1999 and 2013. There was a sharp decrease in area of vegetation cover from 1986 (19,630 ha) to 1999 (16,527.36 ha) and in 2013 (12,246.80 ha). The hydrological analysis results revealed that a major part of the residential area within the largest basin delineated was associated with low elevation and high slope angle. The combined stream network and slope of the area were used in developing flood risk zones. Three zones were specified: high, medium, and low flood risk zones. The total area covered by the high risk zone was 28.5615 km2 while the area of the medium and small risk zones were 15.94759 km2 and 31.3619 km2 respectively. It is recommended that an increased awareness on flood risk zone should be created among the populace of Igbokoda to guide them in further development.