Yilma, Sileshi (PhD)Hawi, Adicho2019-01-172023-11-112019-01-172023-11-112018-06http://etd.aau.edu.et/handle/12345678/15851Bridges that cross the rivers and valleys are vital components of the road network that contributes significantly to the national development and public daily life. Any damage or collapse of bridge can risk the lives of road users as well as create serious influence to the entire country. Ginchi Awash Bridge is found at 79.5km west of Addis Ababa Ethiopia, which is bounded in geographical coordinate of 38°35'E to 38°7'E longitude and 9°8'N to 9°1'N latitude. Ginchi Awash Bridge is the one which this thesis work is conducted on, in case the bridge is in risk due to the scour at the abutment and the river bed of the bridge structure. Hence this research provides the investigation of the effect of scouring on the hydraulic performance of the Bridge from the hydrological and hydraulic analysis. From the hydrological aspect the design flood at different return periods is estimated by Flood Frequency Analysis method and the peak discharge for 100 year return period is 291.04m v 3 /s. Based on the result from HEC-RAS model the significant bed scour was modeled and abutment local scour depth for the estimated design flood of 100 year return period is 4.12m at left abutment and 4.84m at right abutment and the contraction scour or bed scour is 1.66m. The total scour depth is the sum of local abutment scour depth and contraction scour depth which is 5.78m at left abutment and 6.50m at right abutment. This is mainly caused by constriction of the main channel and about 70.5 percent of river bed and bank material is sand and gravel which are rapidly eroded under water action. In addition to this the steady flow water surface profile is checked and the result shows that the water surface elevation of Ginchi Awash River at the Bridge is lower than the low chord elevation of the Bridge, so the flood could not over top even for design flood of 100 year return period. Finally the Scour mitigation methods are studied in HEC-RAS software. Taking into account the possible geotechnical failure repair and construction costs, constructing riprap at the bridge abutment is recommended and its detail design calculation is discussed.en-USBridgeFlood frequency AnalysisHEC-RASLocal Abutment ScourContraction ScourDegradationThesis