HEC-RAS has the ability to perform Dam or Levee breaching analyses. User can perform a breach analysis on multiple Dams and/or levees simultaneously within the same unsteady flow run (There is no limit to the number of breach locations). Breach data can be entered for a any and all Dams (Inline Structures) and Levees (Lateral Structures), however there is an option to turn specific locations on or off for any specific analysis.
The breach data entered, and the erosion process used in HEC-RAS for a Dam or a Levee is almost identical. Dams are entered as Inline Structures in HEC-RAS, and Levees are entered as Lateral Structures. Both types of structures have a breaching option, and the breaching editor used is almost identical. There are some minor differences in the data entered. Most of the differences are in how it is applied hydraulically in the model.
Currently the user has two Breaching Methodologies to choose from, either "User Entered Data" or "Simplified Physical". The User Entered Data method requires the user to enter all of the breach information (i.e. breach size, breach development time, preach progression, etc…). The Simplified Physical breaching method allows the user to enter velocity versus breach down-cutting and breach widening relationships, which are then used dynamically to figure out the breach progression versus the actual velocity being computed through the breach, on a time step by time step basis.
Note: The documentation in this chapter for dam and levee breaching is just an overview of how to use the User Interface to enter the data. For a more detailed discussion of Dam and Levee Breach, please go to the section on Dam and Levee Breaching in Chapter 14 of this Manual (Advanced Features for Unsteady Flow Analysis)
Dam (Inline Structure) Breach.
This option allows the user to perform a Dam Breaching analysis. The breach data is stored as "Plan" information. This is done so the user can try different breach locations, sizes, etc, without having to re-run the geometric pre-processor. However, the user can get to the breach data in two different ways. First there is a button on the Inline Structure editor that is labeled Breach (Plan Data). Second, from the Unsteady Flow Simulation Manager, the user can select Dam (Inline Weir) Breach from the Options menu. When either option is selected, the following window will appear (Figure 7-58).

Figure 7 58. Dam Breach Editor
As shown in Figure 7-58, the user selects a particular Inline Structure to perform the breach on. At the top left of the editor is an option labeled: Breach This Structure - This check box is used to decide if the program will perform the breach or not. In order for the breach to occur this box must be checked. This box was added to allow the user to turn certain breaches on or off, without losing the user entered breach information.
Next the decision needs to be made as to whether the user is going to compute the breach dimensions and development time and enter it as "User Entered Data", or if they want to use the "Simplified Physical" breaching option (his option requires velocity versus erosion rate information).