Volume 3 Issue 3

Authors: Shakirudeen Odunuga; Saheed A. Raji

Abstract: Flood frequency analysis and inundation mapping of lower Ogun River basin was implemented using the Gumbel probability distribution method. This method was however tested with Log Pearson Type III to ascertain the best fitting statistical measure for hydrological fluxes using Chi Square. Basin delineation data was extracted from the topographic maps of Ilaro SE 1, 2, 3 & 4 which covers the study area while gauge height data at Adiyan intake was used as the principal data for flood frequency assessment and inundation modelling based on (Tr) return periods 2, 5, 10, 25, 50 and 100 years. The results showed modelled water level values of 2.22 metres, 2.24 metres, 2.28 metres, 2.38 metres, 2.55 metres, and 2.90 metres for each of the return periods. Consequent upon this, the inundated area is projected to increase to almost 30% of the area from an initial 23% for most of the scenarios. These findings provide clearer picture for the pattern of hydrological fluxes of the lower Ogun River Basin. Sustainable planning and developmental measures that consider the modelled pattern of hydrological fluxes of the study area were recommended for decision making on urban areas.

Keywords: Flood estimation; Flood modelling, Floodplain; Gumbel distribution; Log Pearson Type III and Return period.