GIS-Based Morphometric Analysis, Peak Discharge Estimation, and Mcda-Ahp Flood Susceptibility Mapping of Yenagoa Metropolis, Bayelsa State, Nigeria

Abstract

Yenagoa Metropolis in Bayelsa State, Nigeria, lies within the deltaic lower Nun River basin and experiences recurrent, severe flooding that causes widespread loss of life and damage to infrastructure. This study applied a GIS-based framework integrating morphometric analysis, peak discharge estimation using the Rational Method, and Multi-Criteria Decision Analysis with the Analytic Hierarchy Process (MCDA-AHP) to produce a quantitative flood susceptibility map across eight delineated sub-watersheds. The Copernicus DEM GLO-30 (30 m resolution) was processed in ArcMap 10.8 using the D8 flow-direction algorithm to delineate a principal watershed of 946.39 km² comprising eight sub-watersheds ranging in area from 33.31 km² to 237.62 km². Twelve morphometric parameters spanning linear, areal, and relief categories were computed for each sub-watershed and subjected to Pearson correlation analysis. Peak discharge was estimated at the 25-year return period using the IDF model of Egop (2025) and the Kirpich (1940) time-of-concentration formula, yielding discharges ranging from 13.60 m³/s to 46.40 m³/s. A Flood Susceptibility Index (FSI) was derived through a weighted linear combination of thirteen criteria using AHP weights computed from a 13 × 13 pairwise comparison matrix (CR = 0.0033 < 0.10). Sub-Watersheds 3, 6, and 1 were classified as High susceptibility (FSI = 0.65 to 0.71), four sub-watersheds as Moderate (FSI = 0.53 to 0.56), and one as Low (FSI = 0.30). The High susceptibility zone encompasses 398.12 km², representing 42.07% of the total watershed area. The resulting flood susceptibility map provides a spatially explicit, evidence-based decision-support tool for infrastructure design, urban planning, and flood risk management in Yenagoa Metropolis.