An investigation on Tana Beles diversion head-work is carried out for this research work andrnattempt is made to understand the failure problems encountered. This serve for differentrnpurposes such as for construction of new diversion structure (either as replacement for existingrnstructures, or as an entirely new structure), rehabilitation of existing structures (from minorrnrepairs to complete re-engineering either to maintain existing function, or to meet newrnrequirements). rnHydrology and hydraulic analysis, structural analysis and evaluation of the foundationrncondition of the weir has been made to investigate the causes for the failure of the weir. rnThe hydrology analyses is made by Hec-hms and the result shows that the peak flood used forrnthe design of the weir is smaller than the result obtained in this investigation, but the water wayrnof the weir built can accommodate the estimated peak flood. Models used for the hydrologyrnanalysis include Global Mapper, Arc-GIS, Hec-Geohms and Hec-hms. On the other side,rnhydraulic design is evaluated and the evaluation exposes the absence of concrete floor, absencernof energy dissipater and protection works on the hydraulic design of the weir and clogging ofrnunder sluice as a cause for the failure of the weir. The structural analysis involves checkingrnstability analysis of the weir against overturning, sliding and shear. Surveying data upstreamrnand downstream of the weir is collected and foundation condition were investigated byrncomparing the collected surveying data with the design bed level.in addition to this the appliedrnfoundation treatment is evaluated by comparing it with standards and found that the mainrnstructure was built on weak foundation which activates the weir failure. This investigationrnshows that the main cause of Tana Beles weir failure is due to the weak foundation conditionrnof the weir and absence of the necessary concrete floor and energy dissipater on its design.rnFinally, the remedial design for the weir is recommended.