Under very extreme conditions a flood that threatens to overtop a dam may be combined with strong winds that generate waves in the reservoir. Prolonged wave overtopping or a combination of wave overtopping followed by constant overflow may cause erosion of the dam crest and downstream face, leading to a dam breach. If these conditions occur in a reservoir with a long dam and an uneven crest, the dam may start to breach at multiple locations. If the breach at one location develops rapidly, the reservoir pool may be drawn down fast enough to "starve" other breach locations so that the dam will only breach from one location; otherwise, the dam may breach at multiple locations. A three-dimensional numerical dam breach model was developed at the Utah State University to simulate this problem. The model incorporates the topography of the entire dam site and does not unrealistically limit the breach representation to a single dam height throughout the length of the dam. Breaches can be located anywhere along the length of the dam. The two-dimensional Shallow Water Equations are solved at each breach location to calculate the flow characteristics. Three-dimensional slope stability along the main flow direction in the breach channel is checked using Bishop's simplified method before the dam fully breaches through. Multiple breaches are modeled under the actions of wind generated waves and wave overtopping. The uneven elevations of the dam crest are considered. Currently, the model is developed only for a non-cohesive soil dam, although it is proposed to extend it to cohesive dams and zoned dams with an impermeable core. In this paper, we present the effects of wind direction and wind velocity on multiple breaches for a hypothetical large long dam and reservoir. We also report the three-dimensional breach process given by our model.
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