Yilma, Sileshi (PhD)Wendmagegnehu, Taye2019-12-092023-11-112019-12-092023-11-112019-05http://etd.aau.edu.et/handle/12345678/20336Arsema Bridge was constructed on Jemo River, Jemo River is tributary of Little Akaki River which is the sub catchment of Akaki basin and study area has an inclusive area of 73.3 Square Kilometer, Arsema Bridge built as River crossing structure to connect the ring road from German round about to Lebu Mebrate Haile under Addis Ababa city Administration. It had been built just before 15 years ago and currently the Bridge faces a serious problem of sediment aggradations both at the left and right side of the abutment, and trash accumulation on the entrance of the Bridge. Due to this; overtopping of the Bridge and flooding of residential house were observed frequently. HEC- HMS modeling was used to determine peak discharge of 2, 5, 10, 25, 50 and 100 year return periods and then 67, 97.6, 117, 136.1, 154.5 and 174.9 m /sec results were found, subsequence HECRAS Modeling was used to determine water surface profile level, performance of existing bridge when difference return period peak discharge pass through it and sediment transport at the bridge location based on the current river sectional profiles however the bridge accommodate only up to 10 year return flow. Then Q50 was used to analysis before and after bridge constructed, then after the water surface elevation is 2214.36m and 2214.57m amsl respectively however existing bridge high chord is 2213.684m amsl i.e. 0.676m and 0.886m difference before and after the bridge constructed, this show us the existing bridge is submerged as per previously estimated flood. After detail analysis of the result and discussion I recommend the appropriate remedial measure for sedimentation aggradations and trash accumulation as well as flooding of the residential house, HECRAS was used with combination of HEC- RAS Mapping: to redesign of Bridge with Trash Trap Screen and Flood Hazard map, the result show us road surface finishing level has to increase at least 0.766 m high at the bridge and refill both left and right side of the bridge up to 150 m length as per road profile; to accommodate the redesigned bridge high chord of 2214.45m amsl, residential house upstream to bridge has to consider flood protection or guide wall up to 2.0m high depending on their OGL against the flood hazard map, relocate of all utilities line which are pass through bridge and period clearing of trash trap screen is highly recommended as main mitigation measure.en-USBridgeHEC Geo HMSHEC _HMSflood frequency analysisHEC_RASRAS mappingtrash accumulationsediment aggradationsThesis