Dams are built for water supply, hydropower, flood mitigation and irrigation purposes to support development for the benefit of mankind. However in the event of dam break, the great energy stored in the impounded reservoir will cause colossal and significant loss of human lives, and damage to properties and infrastructures. The damage is compounded by short warning time available. As a result of the high potential hazard dam failure poses to the downstream area, a dam break flood analysis becomes very important. Dam break flood analysis on Lower Usuma Dam was carried out using parametric simulation tool, BOSS DAMBRK hydrodynamic flood routing model. This was employed to determine the maximum peak discharge hydrograph, flood travel times, peak to time stage, and the flood water velocities for a reach length of one kilometre downstream of the dam. These parameters would provide the basis for adequate planning and prediction of downstream hazard potentials in the event of failure. An inflow hydrograph with a peak of 17,591 m3/s was adopted for the simulation and a peak discharge hydrograph of 17,623 m3/s was obtained. A maximum flow velocity of 2.64 m/s having a peak discharge of 17,592 m3/s at 0.1 km downstream was obtained. The sudden drop in velocity from 2.64 m/s at station 2 (0.1 km) to 1.54 m/s at station 5 (1.0 km) with a peak discharge of 15,685 m3/s showed that the flood peak velocity steadily reduced as the flood wave attenuated downstream the dam due to the geometry of the river channel. In the event of failure of Lower Usuma dam, some areas within the one kilometre reach length downstream considered would suffer significant inundation due to flood released from the reservoir. Therefore, development activities within this region should be controlled.

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