For fragility curve sampling to work in HEC-WAT, the RAS model alternative (plan) must be setup for levee breaching.
1.To ensure the RAS model alternative (plan) for the current HEC-WAT simulation is setup correctly, from the HEC-WAT main window (Figure 17.4), from the Toolbar, click
. The HEC-RAS main window will open (Figure 17.7).

Figure 17.7 HEC-RAS Main Window
2.From the HEC-RAS Toolbar click , or from the Run menu, click Unsteady Flow Analysis. The HEC-RAS Unsteady Flow Analysis dialog box will open (Figure 17.8).
3.From the HEC-RAS Unsteady Flow Analysis dialog box (Figure 17.8), from the Options menu, click Levee (Lateral Structure) Breach, the Levee (Lateral Structure) Breach Data Editor will open (Figure 17.2). Note: Fragility curves may also be associated with inline structures (i.e., dams). This data can be entered on the Dam (Inline Structure) Breach Data Editor. The following example will only provide descriptions for the definition of levee breach information. However, the data requirements are similar for inline structures.

Figure 17.8 HEC-RAS – Unsteady Flow Analysis Dialog Box
5.From the HEC-RAS Levee (Lateral Structure) Breach Data Editor (Figure 17.2), the user will need to select breach options (Figure 17.9) for the defined lateral structure at a location. The user will need to select Breach This Structure, select a breach method from the Breach Method list (default – User Entered Data), select a failure mode from the Failure Mode list, and select WS Elev from the Trigger Failure at list as the trigger failure option.

Figure 17.9 HEC-RAS – Levee Breach Options
6.From the Failure Mode list (Figure 17.9), HEC-RAS currently has two different breaching methods - piping and overtopping. The user must specify only one of these modes, even if the fragility curve combines the probability of failure due to both modes. If the levee is going to overtop and fail then select the Overtopping failure mode. If the breach is expected to initiate from a piping failure mode and progress upwards and downwards until a complete breach has occurred, the Piping failure mode should be selected.
7. The user must define a trigger failure, from the Trigger Failure at list (Figure 17.9). For HEC-WAT 1.0, the user should select WS Elev. The WS Elev+Duration and Set Time options should not be selected for an FRA compute. However, if the user does select the WS Elev+Duration or the Set Time option and an FRA compute has been selected, then the trigger failure at option is automatically switched to the WS Elev. The trigger failure elevation is used by HEC-RAS to begin initiation of the lateral structure breach. The breach is initiated when the computed water surface elevation exceeds the trigger elevation and is not dependent on the selected failure mode.
8. When the user is finished configuring breach information for the study area in the RAS model alternative. From the Unsteady Flow Analysis dialog box (Figure 17.8), from the File menu, click Save Plan to save changes. From the File menu, click Exit, the Unsteady Flow Analysis dialog box will close (Figure 17.8). From the HEC-RAS main window (Figure 17.7), from the File menu, click Exit, the HEC-RAS main window will close (Figure 17.7).
9.If the RAS model alternative in the HEC-WAT FRA simulation has all of the above set, then the user can go on to defining fragility curve alternatives and input data in HEC-WAT.