Urban Flood Mapping and Vulnerability Assessment in Ilorin, Kwara State, Nigeria

Abstract

Most urban cities have suffered from natural disasters especially flooding whose frequency and intensity have increased due to human activities with devastating consequences on sanitation, human health, and property. This research employed the use of geographic information systems (GIS) as a tool in mapping and monitoring floods in Ilorin, Kwara State with a view to developing a flood risk map for urban management. The specific objectives include identifying flood-prone areas, assessing urbanization and land-use changes and their implications on flooding. A total of 220 copies of pre-tested questionnaires were administered and 163 retrieved to evaluate anthropogenic activities and their consequences on this phenomenon. Shuttle Radar Topographic Mission (SRTM) Digital Elevation Model (DEM) data and Landsat Thematic Mapper (TM), Enhanced Thematic Mapper Plus (ETM+) and Landsat 8 Operational Land Imager (OLI ) images for 1984, 2000, and 2015 respectively were used to generate flood, vulnerability, and land use maps. The result shows that there was a rapid increase in built-up areas from 41.642 km² in 1984 to 167.911 km² in 2000 and subsequently to 239.49 km² in 2015. Urbanization resulted in increased paved and unpaved compacted surfaces at the expense of vegetation cover and increased surface runoff possibly leading to floods. Similarly, flood vulnerability maps were produced which classified the area into; high, medium, and low vulnerable areas. The research identified factors affecting flooding at Ilorin to include developmental activities on flood plains and land use/cover changes. Enlightenment, development control, and GIS-based flood vulnerability map for urban management were recommended as a way forward.