Flashflood Hazard Assessment in Yewa South Lga

In the bid to accomplish the Sustainable Development Goals, several attempts have been made in Yewa South LGA to accomplish environmental sustainability (SDG7) and reduce the adverse effects of climate change (SDG13). The area has witnessed recurrent flash floods with deleterious effect to lives and properties due to anthropogenic factors coupled with incessant torrential rainfall events which are the major drivers of flood vulnerability in the area. Previous studies have adopted the use of GIS, Remote sensing or an integration both techniques with associated challenges. This study adopts the use of Hydrologic Engineering Centre’s Hydrologic Modelling System with Geographic Information Systems (HEC-GeoHMS) to evaluate the relationship between rainfalls, terrain characteristics, run off and stream flow as an alternative flood mitigation scheme. The catchment area was divided into forty-five sub basins over a 10m DEM, the run off hydrographs simulated and the hydrological characteristics modelled by using rainfall data between 1<sup>st</sup> June, 2022 – 31<sup>st</sup> May, 2023 as well as discharge data from Ogun-Osun River basin Development Authority (O-ORBDA). the model parameters were optimized for calibration and the calibrated model was thereafter validated using three statistical evaluation criteria which showed that there is a good simulation between the observed and estimated values (Rep = -2.24%, REv = 6.67%, NSE = 95.03%, and R<sup>2</sup> = 0.83). Further analysis of the results showed that the flash flood is induced mainly by hydrologic characteristics of the area. This work therefore proposes to mitigate flood in Yewa South Local Government Area of Ogun State by modelling how excess water runs on the terrain thereby creating flash floods. The model will serve as an input for putting mitigation measures in place to arrest flash floods.