The prediction of floods resulting from sudden dam failure is an important component of a dam safety assessment. It enables one to predict the inundated area, the flood depth and the travel time of the flood wave due to a sudden release of huge amounts of uncontrolled water. Numerical simulation models for different dam failure situations have been presented over more than 100 years. The prediction of dam break floods in the field is normally accomplished using the NWS DAMBRK model, Boss DAMBRK model, the Mike 11 model, the newly developed HEC-RAS dam break model or other similar models. However the application of these hydrodynamic simulation models requires considerable time and budget. Advantages of using a simple Finite Difference Diffusive (FD DIFFUSIVE) scheme over a higher order numerical model in computing dam break flow in a real field situation with complex topography is investigated. Complexities arise when the flood wave as a result of dam failure moves over a natural flood plain topography having significant changes in bed elevations, bed slopes and bed frictions at each computational grid. To explore the merit of the proposed FD DIFFUSIVE scheme, it is compared with the TVD MacCormack scheme through their application in two hypothetical dam failure situations with complex topography; one located on the Himalayan river Dibang, with a wide flood plain downstream, and the other on the river Kynsy, which has a steep narrow downstream channel. The simulation model with FD DIFFUSIVE scheme is found to be highly stable and well applicable for these complex hypothetical failure situations. The ease of implementation, less computational runtime and the ability to handle flows in sub critical, mixed and highly super critical flow conditions are favorable features of the presented model. It provides accurate predictions for maximum flood depths, peak arrival time and flood wave travel time, which are the most important parameters for practicing field engineers and planners.

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