HYDROLOGIC AND HYDRAULIC INVESTIGATION AND MITIGATION OF FLOODING IN NSUKKA METROPOLIS

Urban flooding is increasingly driven by climate change and expanding impervious surfaces, which often overwhelm existing drainage infrastructure. This study evaluates flood risk in Nsukka, Enugu State, Southeastern Nigeria, by assessing the condition and capacity of its stormwater drainage system. The objectives were to: (i) examine the existing drainage network, (ii) develop and compare redesigned drainage structures with the current system, and (iii) analyze catchment characteristics to rank sub-catchments based on floodwater generation per unit area. Esri ArcGIS, Autodesk Civil 3D, and Bentley CivilStorm were used for sub-catchment delineation, hydrologic and hydraulic analyses, peak flow estimation, and drainage design. Field surveys revealed widespread channel blockage, siltation, illegal drainage connections, and unauthorized flood protection structures. Results showed that about 41% of existing drains are incapable of conveying peak flows even under ideal operating conditions. Many drains are severely undersized, making them susceptible to overtopping during rainfall events with return periods of less than one year. The analysis also revealed significant variation in runoff generation among sub-catchments, indicating the need for location-specific flood mitigation measures rather than uniform interventions. The findings provide a basis for targeted drainage rehabilitation and flood management in Nsukka. Beyond the study area, the integrated assessment approach offers a replicable framework for evaluating flood risk, upgrading drainage infrastructure, and supporting climate-resilient stormwater management in rapidly urbanizing cities worldwide.