The development of potential flooding from a dam failure requires several elements; the hydrologic scenario, the possible dam failure modes, breach parameters that are associated with the failure modes, and the routing and mapping of the consequent discharge hydrograph. The unsteady flow routing model, HEC-RAS, is often used for the computation and display of downstream impacts resulting from hypothetical dam failures. Estimation of the breach parameters, such as width and development time, has typically done external to the model. This paper presents recent research into the use of several breach process models to define HEC-RAS breach parameters. The process models evaluated incorporate several mechanisms for simulating breach development; including vertical erosion due to sediment transport, breach widening, side slope collapse, and head cutting. The use of such process models to provide information regarding the time-history of breach development for use in HEC-RAS is described.
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