HYDRAULIC PERFORMANCE EVALUATION OF CROSS DRAINAGE STRUCTURES (THE CASE OF BOKOJI TO KERSA ROAD, OROMIA REGION)

Abstract

Drainage problem is a major concern in the functionality of road. Raise in traffic interruption, structures damage and loss of life can be caused due to poor drainage. To cope with these problems, it is essential to determine the functionality routine of such structures through hydrologic and hydraulic investigation. The study attempted to analyze hydraulic performance of drainage structures found along Bokoji-Kersa road. Different datasets (spatial, hydrological, metrological, survey data) and models (SCS CN and HEC-RAS) were used. Arc-Hydro and image classification tools of ArcGIS, Easy-fit program, statistical methods (Gumble and Lognormal) are employed as processing tools to prepare model inputs. Watershed delineation, land use land cover classification, generation of IDF curves, peak discharge estimation, and steady flow simulation of water surface profile were the active tasks conducted in the study. It was found that the existing Katar Bridge has insufficient size even to convey 320.20m3/s peak design flow of 50 year return period. The resulted water surface elevation was 2496.82m, whereas the lower cord elevation of the Bridge is 2496m. Moreover, the hydraulic capacities of some drainage structures are adequate but inefficient. Limitations in the hydraulic and hydrologic investigation during the design and construction phase were identified as the cause of the problems. Subsequently, causes of gully erosion at the outlet and blockage by sediment led to reduced functionality, traffic interruption, and loss of propert