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Flooding in Ilorin city has become a yearly occurrence. Mapping and evaluation of flood risk areas along Asa River in Ilorin metropolis was carried out using the Geographic Information System (GIS) and remote sensing. The technique used includes conversion of Digital Terrain Model (DTM) to Triangulated Irregular Network (TIN) format. The geometric data was obtained from TIN through the use of United States Army Corps of Engineers, Hydrologic Engineering Centre, Geo River Analysis System (USACE HEC-geoRAS) in GIS. The obtained geometric data, Manning’s roughness coefficient (n), Expansion and contraction coefficient values and steady flow data of the River were used in HEC-RAS. The n values of 0.035, 0.016 and 0.02 were used for the channel, 0.045, 0.016 and 0.03 were used for the overbank and 0.2 was used for the bridges. Contraction and expansion co efficient value of 0.1 and 0.3 were used for channel and 0.3 and 0.5 were used for the bridges. Gumbel equation was used to estimate the flow for return period of 10, 50 and 100 years and the values of 155.13, 213.44 and 221.43 m 3 /s were obtained respectively. Delineated map was then compared with TIN terrain model to generate inundation map. The map revealed that some areas in Ilorin such as Coca-Cola Road, Baba Ode, Unity road, Obo Road, Taiwo-Isale, Amilengbe, Isale Koko, Mubo Phase 1, Mubo Phase 11, Royal Valley and Akerebiata prone to flood disasters. Estimated maximum top width for inundated area along the river ranges from 900.74 to 2375.11m. Keywords :-GIS, River Asa, DEM, Flood risk, HEC-RAS, Ground slope

Mapping and Evaluation of Flood Risk Areas along Asa River using Remote Sensing and GIS Techniques