A Geographic Information System Approach to Morphometric Analysis of a Drainage Basin for Flood Vulnerability Potential, Southwest Nigeria

Abstract

Drainage-basin morphometry provides useful quantitative evidence for interpreting basin form, runoff response and flood-vulnerability potential, especially where direct hydrological observations are limited. This study evaluated the drainage characteristics of the Aye River sub-basin in south-western Nigeria and their implications for flood vulnerability potential. Shuttle Radar Topographic Mission digital elevation model data and ArcGIS Pro were used to derive linear, areal, relief and geometric parameters of the drainage system. The assessed parameters included stream order, stream length, bifurcation ratio, drainage density, stream frequency, channel maintenance, infiltration number, length of overland flow, basin relief, relief ratio, relative relief, ruggedness number, gradient ratio, length-area relation, lemniscate and form factor ratio. The basin covers 1463.69 km² and exhibits a dendritic drainage pattern, with streams extending to the seventh order. The computed values include drainage density of 0.76 km/km², stream frequency of 0.36, channel maintenance of 1.32, infiltration number of 0.27, length of overland flow of 0.66 and form factor ratio of 0.21. These values indicate coarse drainage texture, relatively low channel concentration and an elongated basin form, suggesting longer runoff duration. Flood-vulnerability mapping shows spatial variation across the basin, with moderately vulnerable areas occupying the largest proportion. The findings provide preliminary morphometric evidence for watershed management and future flood-risk assessment in the area.