HYDROLOGY OF OSUN RIVER SOUTHWESTERN NIGERIA

Abstract

This research assessed the water resources potential of Osun River Basin for data generation in river projects planning and design. The river takes its source from Igede-Ekiti in Southwestern Nigeria and discharges into Lagos lagoon in Gulf of Guinea. Direct measurement of the discharge at some points along a river has a reasonable cost implication and it is time consuming. This can similarly be achieved by using stage- discharge relationship (Rating Curve). The retaining capacity of the Osun River could be estimated using mass curve diagram developed in the study. Hydrological study of Osun river basin was done from the available rainfall and stream flow records of years 1982 -2013. The data was taken from the Hydrometric Department of the Ogun-Osun River Basin Development Authority (OORBDA). The Rainfall analysis indicated no apparent trend. The flood frequency analysis of Osun River was carried out using Gumbel’s distribution and Powell’s distribution. Maximum flood discharges were estimated for different recurrence intervals of 2, 5, 10, 25, 50, 100, 200 and 400 years. Powell distribution forecast higher flood for the different return periods which makes the method more acceptable in designing an erosion mitigating structures. The study would contribute to the knowledge of hydrology of Osun River. The data obtained in this study would be useful information for future studies of the basin. The study would further contribute to the improvement of future water resources development plans in the region.