Hypsometric Analysis and Watershed Morphometry of River Osun Basin Using GIS and SRTM DEM

Understanding watershed morphometry is fundamental to hydrological analysis, erosion susceptibility assessment, and water resource development planning. This study undertakes hypsometric analysis and morphometric characterisation of the River Osun basin in South West Nigeria using GIS and a Digital Elevation Model derived from SRTM data. The basin boundary is delineated using automated watershed delineation tools in ArcHydro, and linear, areal, and relief morphometric parameters are computed following the classification framework established in geomorphological literature. Hypsometric curves and integral values are computed for both the whole basin and seven sub-basins to assess geomorphic maturity and relative erosion susceptibility. Results indicate that the Osun basin is predominantly monadnock to monadnock-in-pediplain stage, with hypsometric integrals ranging from 0.38 to 0.61 across sub-basins. Sub-basins with higher integrals, indicating youthful stages with higher energy gradients, are concentrated in the upper Iragbiji and Esa-Oke headwater zones, which coincide with areas of documented streambank erosion. Bifurcation ratios and drainage texture values indicate dendritic drainage patterns consistent with the geological homogeneity of the underlying basement complex formation. Findings provide hydrological characterisation data relevant to the Osun-Osogbo Cultural Landscape conservation management and the Osun State Ministry of Water Resources. Keywords: watershed morphometry, hypsometric analysis, GIS, River Osun, SRTM DEM.