Nashe Dam Fail and Risk Analysis

Nashe earth fill dam was constructed for the aim multi-purpose use (hydroelectric power and irrigation). While the construction of this dam many peoples around Dam were immigrated from their residential to another places including to the town. This research focused on the dam fail analysis by considering overtopping and piping failure mode. The input data were collected from Min. of Water and Energy, Federal Democratic Republic of Ethiopia (FDRE). The dam breach parameters were determined by applying the principle with Von Thun and Gillette. In dam break analysis the first step is model setup by using three dimensions (x, y and Z) of the downstream. By applying overtopping model, the peak discharge 8761.23m3/sec was obtained, which was more than 7.33 times the probable maximum flood and by applying piping mode, the peak discharge was obtained is 8620.85 m3/sec which was more than 7.21 times the probable maximum food at the nearby location of the dam. This indicates that, the peak outflow development during raining season was greater than inflow discharge flood (IDF) used as upper boundary condition for breach parameters. So it was summarized that high peak outflow and risk were developed to downstream by overtopping mode as compare by piping mode during occurrence of dam breach. As from the sensitivity analysis it was concluded, the effect of breach time on discharge is more sounded than the water level increase. This Dam Break modeling results obtained by studies could be used as flood mappings to assist the societies/communities for future planning developments in the flood prone areas/zones in advance.