Geospatial Analysis of Topographic and Hydrological Controls on Flood Susceptibility

Abstract

This study evaluates the influence of topographic and hydrological factors on flood susceptibility in the South–South region of Nigeria using Geographic Information Systems (GIS), Remote Sensing, and the Analytical Hierarchy Process (AHP). Digital Elevation Model (DEM), slope, aspect, drainage density, stream density, flow direction, and distance from river variables were analysed to determine their contribution to flooding. The results show that elevation ranges from approximately 13 m in low-lying coastal areas (Delta, Rivers, Bayelsa, and Akwa Ibom States) to about 256 m in elevated inland areas (Cross River and parts of Edo State). Slope analysis indicates that coastal areas are dominated by very gentle slopes (0°–3.37°), which promote water accumulation and increase flood susceptibility. Aspect results further reveal that much of the coastal region is predominantly flat (−1), limiting directional flow and enhancing water stagnation. Hydrological analysis shows that drainage density is mainly very low to moderate (0 89.89 km/km²), indicating high infiltration but increased water retention, while localized high values (89.9–134.8 km/km²) enhance runoff. Stream density is highest (228.1–811 km/km²) in Delta, Bayelsa, and Rivers States, whereas lower values occur in Edo and Cross River. Flow direction exhibits a dominant east–west pattern, with accumulation values ranging from 1–16, indicating runoff convergence. Distance-to-river analysis shows that large areas lie within 0 1,000 m of river channels. Flood susceptibility is highest in coastal zones and lowest in inland elevated areas. The study demonstrates that terrain morphology and hydrological network characteristics are key determinants of flooding in the region and highlights the effectiveness of geospatial techniques in flood susceptibility assessment and management in the South–South region of Nigeria