In this study, a two-dimensional hydraulic routing model was applied to a sudden failure scenario for the Atasu Dam in Trabzon, Turkey. The goal was to simulate spreading and propagation of a dam break flood wave along a narrow valley into a downstream city center with many buildings. Flow properties along the downstream were routed according to diffusive and dynamic wave models represented by Saint-Venant equations. Maximum flow depth, maximum flow velocity, and time moment of the maximum flow depth maps are shown in a Geographic Information System environment. The results predict that flow depths could reach approximately 8 m in the residential area, and this would be achieved approximately 32 min after the dam-break event. Houses in a large section of the city center would be under the maximum flow depths. The results of this study demonstrate that these two approaches can determine potential risk areas of a floodplain due to natural hazards and facilitate preparation of emergency action plans.