Flood-Loss Reduction and Channel Maintenance along Ogunpa River, Ibadan: Application of Hec-Ras Modelling
1*Olayiwola, O.O., 2Adegbola, A.A., 3Olaniyan O.S. and *4Okesiji. S.O.
1,2,3Department of Civil Engineering, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria.
4Department of Civil Engineering, African Institute of Science Administration and Commercial Studies, Lome, Togo.
DOI: 10.36108/laujoces/6202.61.0252
Abstract
Flooding poses a persistent hazard in rapidly urbanizing sub-Saharan cities, worsened by landuse changes and infrastructural deficits. In Ibadan, Nigeria, the Ogunpa River catchment experiences recurrent inundation. This study evaluates the hydrological and hydraulic dynamics of the river to identify critical channel maintenance requirements and flood-loss reduction strategies using integrated multi-model approach. Runoff was estimated using the Soil Conservation Service Curve Number (SCS-CN) method based on daily rainfall data (1970–2021) obtained from the Nigerian Meteorological Agency (NIMET). Spatial analysis and watershed delineation were conducted using ArcGIS 10.3 with Landsat 8 imagery and Digital Elevation Models. Hydraulic behavior was simulated using a one-dimensional HEC-RAS model, parameterized with field measurements of channel geometry and flow velocity. Analysis revealed increasing rainfall variability and a reduction in flow velocity from 0.36m/s upstream to 0.25m/s downstream, indicating significant sedimentation. Complementary socio-spatial data (n=200) identified waste mismanagement and encroachment as key aggravating factors, despite moderate community risk perception (mean = 2.41). The hydraulic inefficiency of the Ogunpa River is driven by both morphological constraints (sedimentation) and anthropogenic interference. Effective flood risk mitigation requires a dual approach: engineering interventions (desilting, channel widening) and policy enforcement (building setbacks, waste management). This study demonstrates the efficacy of coupling hydraulic modelling with social assessment to inform urban drainage planning.
Keywords: Flood risk, HEC-RAS, channel maintenance, Ogunpa River, Ibadan, urban hydrology, flood-loss reduction.