Flood Vulnerability Mapping: A Case Study of Okoko Basin, Osogbo

Abstract

This study employed Geographic Information System (GIS) and remote sensing approach to analyze the flood vulnerability areas in the Okoko basin area of Osogbo in Osun state, Southwestern Nigeria. High-resolution imageries, a Topographic map of the study area and a TCX software program (Version 2.0) were integrated using ArcGis (10.7). Some of the causative factors for flooding in the watershed were taken into account which are: Land use, Distance of buildings to drainage, Digital Elevation Model, and Slope. This study aimed at mapping the flood-vulnerable areas along the Okoko basin of Osogbo. In developing a flood risk/flood hazard map of the study area, and determining the level of expected disaster, a multi-criteria analysis was utilized. The factors considered were ranked in five classes with the highly vulnerable areas having the highest score of “5”. These factors were weighed according to the estimated significance of causing flooding. The study revealed that the study area has an estimated area of 17.85 km2 of which 14.2 km2 falls within the vulnerable areas while 3.6 km2 is on the least vulnerable areas. Moreover, out of 16,829 buildings in the study area, 8204 buildings were found susceptible to flood disasters. This research attempts to equip decision-makers to make accurate decisions and also serves as a mitigation measure for flood disaster management.