![]() The speed varies over the development time according to the first quarter cycle of a sine wave. The Sine Wave method causes the breach to grow quickly in the early part of breach development and more slowly as it reaches maximum size. ![]() The Linear method causes the breach to grow in equal increments of depth and width from initiation to the end of the development time. Current progression method options are: linear, sine wave, and user curve. The progression method determines how the breach grows from initiation to maximum size during the user-specified development time. The development time defines the total time (in hours) for the breach to form, from initiation to reaching the maximum breach size. Once the breach has been triggered, the development of the breach is determined using a selected progression method over the development time. For the Specific Time method, the breach will begin opening at the specified time regardless of the reservoir pool elevation. For the Duration at Elevation method, the reservoir elevation must remain at or above a specified elevation for a specified length of time in order to initiate the breach. For the Elevation method, the breach will begin forming as soon as the reservoir reaches a specified elevation. There are three methods for triggering the initiation of the failure: elevation, duration at elevation, and specific time. Only one dam break can be included in the reservoir. In order to model a dam break, the Outflow Structures routing method must be used. At a certain size, RAS would be more meaningful, since it includes the ability to manage a nonlevel pool. Typically dam breaks would be modeled in HEC-HMS only for periodic assessments. For both types of breach methods, a trigger method, development time, and progression method are used to define when the failure initiates, how long it takes to attain maximum breach opening, and how the breach develops during the development time. Two types of dam failure can be modeled in HEC-HMS, overtop and piping. Sometimes it is of interest to model a scenario in which there is a dam failure.
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