Bridges are crucial for transporting people and goods, but their failures can be catastrophic, resulting in loss of life and property. This study assessed the flood stage of selected bridges (Alaafin Avenue, Seven-Up, and Oluyole) along the Ona River, Ibadan, Nigeria, using a one-dimensional model called the Hydraulic Engineering Center-River Analysis System (HEC-RAS). The model requires two major input data: geometric and steady flow data. The geometric features of the study area (stream centerline, riverbanks, flow paths, cross-sections, and bridges) were generated from the Digital Elevation Model (DEM) in HEC-GeoRAS, an extension of ArcMap GIS. The MapWindow Soil and Water Assessment Tool (MWSWAT) was used to predict flow. The input data for the model include DEM, Land use, soil map data, and meteorological data obtained from the Nigerian Meteorological Agency (NIMET). The flood stages of the three bridges were predicted in the HEC-RAS model and the results showed that Alaafin Avenue, Seven-Up and Oluyole bridges had predicted flood stages of 1.5 m, 1.6 m, and 2.5 m and a freeboard minimum clearance of 2 m, 0.3 m, and 0.5 m respectively. However, the predicted flow (75.25 m³/s) was compared with the corresponding value of the flow in ERA (2002) for a free board minimum clearance. It was shown that only Alaafin Avenue Bridge is safe while Seven-Up and Oluyole bridges are prone to inundation by approximated values of 0.3 m and 0.5 m respectively. Therefore, regular inspection and maintenance of bridges are recommended to prevent inundation.

Impounded reservoirs provide beneficial functions such as flood control, recreation, hydropower and water supply but they also carry potential risks. Spontaneous dam break phenomenon can occur and the resultant flooding may cause substantial loss of life and property damage downstream of the dam. A hypothetical dam break on Asa Dam located in Ilorin, Kwara State, Nigeria was analyzed using United States Army Corps of Engineers (USACE), Hydrologic Engineering Center’s River Analysis System (HEC-RAS) computer model. Unsteady flow simulation was performed using geometric data obtained from Digital Terrain Model (DTM) with 100-year, 24 hr flow event. The HEC-RAS was used in concert with HEC-GeoRAS to assess the flood hazard along the Asa River channel starting from the dam axis and approximately 12 km towards the downstream as a result of the dam break. The highest discharge Q (1913.66 m3/s) and the highest peak stage (277.35 m) just below the dam were produced with breach width of 130.86 m and time of failure of 1.45 hours. The outcome of the analysis showed that in the event of such failure of Asa dam, some areas which include industrial and residential sections along the river channel are at very high risk of being inundated due to the significant difference in the value of the produced water surface elevation and existing ground elevation affecting thousands of people living along the channel immediate vicinity. http://dx.doi.org/10.4314/njt.v36i1.39

Nigeria's Jebba sub-basins are synonymous to frequent flooding, high rate of erosion, depletion of soil nutrients and unsustainable water use. The uncontrolled flooding may be a result of numerous factors related to topography, geology, climate and human activity.  The present work was an attempt to describe the application of Geographical Information System (GIS) and Digital Elevation Model (DEM) for the estimation of morphometric characteristics of eight sub-basins in the upstream watershed of Jebba reservoir, Nigeria. Morphometric characteristics such as topographic, areal, relief and network were determined. Soil Conservation Service (SCS) technique was applied to estimate hydrographs. The study revealed that sub-basin number 3 had the lowest time of concentration and maximum depth of runoff while sub-basin number 2 had maximum ratio of circulation of 1.8 and it is tagged as the area that is highly prone to flood. The peak runoff in the sub-basins ranged between 330.10 and 924.86 m3/s (25-year return period) and for 100-year intervals ranged between 502.69 to 1408.40 m3/s. The estimated peak runoffs can be adopted for designing and constructing erosion control structures in the catchment area.