Morphometric Analyses of Osun Drainage Basin, Southwestern Nigeria

This study evaluated some morphometric parameters with a view to assessing the infiltration potential of Osun Drainage Basin (ODB), Southwestern Nigeria. Input data were derived from SPOT DEM using ArcGIS 10.3 platform. ODB has an area extent of 2,208.18 km2, and is drained by 1,560 streams with total length of 2,487.7 km. The Relief Ratio (5.6) suggests that ODB is characterized by topographic high and topographic low. Thus, infiltration potential would be low as surface runoff would have less time to infiltrate before entering the drainage channels. The computed values of Drainage Texture (0.52), Stream Number (1,560), Total Stream Length (2,487.7 m) and Main Stream Length (119 m) indicate that larger percentage of annual rainwater would leave ODB as river discharge. Stream Frequency, Basin Perimeter, Length of Overland Flow and Drainage Density influence Infiltration Number across the basin. Infiltration Number increases with increasing Stream Frequency (r = 0.95) and Drainage Density (r = 0.78); and Length of Overland Flow increases with decreasing Drainage Density (r = -0.83), Stream Frequency (r = -0.51) and Infiltration Number (r = -0.45). The study concluded that basin’s infiltration potential is moderate as suggested by the mean Infiltration Number.