Channel dynamically changes in response for the variation of flow and sediment transport. rnSediment variation is because of land use change, composition of channel bank and bed materialrnwhile for variation of discharge is because of climate change, as a result channel become altered.rnThis channel change cause to flooding, channel bed and bank instability consequently destructionrnof infrastructure constructed along a river, irrigation area, home and other property in adjoiningrnarea. Assessing channel stability and provide stabilization measure is critical to prevent suchrndamage. rnThe objective of this study is evaluating channel stability investigation and recommend appropriaternmitigation measure of Mersa river, Awash basin Ethiopia. HEC-RAS5.0.7 model with BSTEMrn(its extension) was developed to evaluate Mersa river bed and bank stability, quantify in depth orrnmass sediment erosion amount and identify flood prone area. To achieve the objective both filedrninvestigation such as river cross section data collected, soil sample taken and experimental tasksrnsuch as sieve analysis, triaxial compression test are carried out. rnHEC-RAS model simulation with Yang sediment transport formula is best fit for study reach asrncompare to Meyer Peter and Muller sediment transport method. For entire simulation period anrnaverage aggradation was 1.24m and 0.98m at upstream and downstream reach respectively,rnwhereas average degradation on both upstream and downstream reach was 1.25m. The averagernsediment eroded generated from Mersa river was 22.47kt/yr. Both aggradation and degradationrnwere observed on the study reach but Mersa river reach more affected by erosion than deposition.rnMersa river bank stability and toe erosion assessed by BSTEM of HEC-RAS was safe and againrnbank toe neither aggrade nor degrade in response to the flow. Additionally, Water surface of Mersarnriver was computed using steady flow analysis shows that flood over top above the bank, adjacentrnarea (Mersa town) were affected by flood and the reality also true. The reality shows people aroundrnthat loss their farm land and different property due to flood. Finally, this investigation presentedrnthat channel bed was unstable while bank was stable. Different stabilization measures like Gabionrnbank, Check dam and drop structure were recommended to prevent flood prone area from floodrnand to control channel bed instability.