Spatial Analysis of Flood Risk Zones in The Usuma Watershed Federal Capital Territory, Nigeria

This study examined flood risk zones within the Usuma Watershed in the Federal Capital Territory (FCT), Nigeria, with the aim of identifying spatial patterns of flood vulnerability and informing sustainable flood risk management. The objectives were to map flood-prone areas, analyze flood frequency, and evaluate the biophysical and anthropogenic factors contributing to flood risks. Data were collected through satellite imagery, Shuttle Radar Topography Mission (SRTM) digital elevation data, hydrological datasets, and field observations. The Analytical Hierarchy Process (AHP) and Geographic Information Systems (GIS) were used for data analysis, allowing for the integration of thematic layers including slope, elevation, land use/land cover, rainfall, drainage density, Soil Permeability Index (SPI), and Topographic Wetness Index (TWI). The study reveals that areas of very high to high flood risk accounted for approximately 24.51% and 24.25% of the watershed respectively, predominantly in the central, southern, and eastern portions of the floodplain, including communities such as Gwagwalada, Kuje, and parts of Abuja Municipal Area Council. Flood frequency analysis between 2018 and 2023 showed that the worst flood event occurred in 2022, during which about 70,058 hectares were inundated. Key factors influencing flood risk included low elevation, moderate slopes, high rainfall, sparse vegetation, and dense drainage networks. Based on the findings, the study recommended the enforcement of land use regulations in high-risk areas, the development of sustainable urban drainage systems, regular updates to flood risk maps, and community-based early warning systems. The study concluded that spatial analysis techniques offer critical insights for flood risk reduction, and its approach can serve as a model for other flood-prone regions in Nigeria and across sub-Saharan Africa.