Defining Dam Breach for HEC-HMS Storage Areas

The Dam Breach data panel Storage Area Data dialog box is enabled when Outflow Structures is selected as the routing method. Otherwise, this data panel entry is disabled (i.e., grayed out).
Dam Breach data panel Storage Area Data dialog box

The following sections describe how to interact with the Dam Breach data panel of the Storage Area Data dialog box.

Breach Control

The Breach structure checkbox option allows the user to toggle on and off the breaching of the structure. The checkbox is checked by default.

Breach Dimensions

This section contains the following options:
Breach Dimensions

Dam top elevation
This entry defines the top elevation of the dam face. The dam failure may be initiated at a lower elevation than the top elevation, depending upon the dam breach type (i.e., overtopping or piping failure). This information is used to constrain the top of the breach opening as it grows.
Breach final bottom elevation
This entry defines the bottom elevation of the breach trapezoidal opening in the dam face when the breach is fully developed.
Breach final bottom width
This entry defines the bottom width of the breach trapezoidal opening in the dam face when the breach is fully developed.
Breach left side slope (V:H)
This entry defines the left-side slope of the breach trapezoidal opening in the dam face when the breach is fully developed.
Breach right side slope (V:H)
This entry defines the right-side slope of the breach trapezoidal opening in the dam face when the breach is fully developed.
Breach formation time
This entry defines the total time required for the breach opening to fully develop after it has been initiated.

Breach Failure Details

This section contains the following options:
Breach Failure Details

Breach flow direction
This dropdown combo box entry defines where the dam failure flow is being routed. This dropdown combo box provides the following entries:
1. Main (default)
2. Auxiliary
Breach failure type
This dropdown combo box entry defines the mode of dam failure to be computed. This dropdown combo box provides the following entries:
1. Overtopping (default)
2. Piping
Piping coefficient
This entry defines the orifice coefficient used in the piping failure computations. This coefficient represents the energy losses as water moves through the opening. This entry is disabled (i.e., grayed out) if the Breach failure type has been set to Overtopping. Clicking the […] button displays an Orifice Piping Coefficients lookup dialog box.
Initial piping elevation
This entry defines the elevation at which the piping orifice flow initiates the failure computations. This entry is disabled (i.e., grayed out) if the Breach failure type has been set to Overtopping.
Breach trigger
This dropdown combo box entry defines the mode in which the dam failure is initiated. This dropdown combo box provides the following entries:
1. Exceeds WS Elevation (default)
2. Exceeds WS Elev & Time
3. Date & Time

Based upon the selected entry, the additional sections are shown to the user for purposes of defining the dam breach data.

Triggered by Exceeding WS Elevation

This section will be enabled when the Exceeds WS Elev is selected as the breach trigger. The Breach trigger elevation entry defines the water surface elevation at which the dam failure is initiated.
Triggered by Exceeding WS Elevation

Triggered by Exceeding WS Elevation & Time Duration

This section will be enabled when the Exceeds WS Elev & Time is selected as the breach trigger.
Triggered by Exceeding WS Elevation & Time Duration

This section contains the following options:

Breach threshold elevation
This entry defines the water surface elevation that the storage area pool has remained at or exceeded for the specified Duration above threshold time for the breach to initiate.
Duration above threshold
This entry defines the total continuous time required above the specified Breach threshold elevation prior to initiating breach.

Triggered at Date & Time

This section will be enabled when the Date & Time is selected as the breach trigger.
Triggered at Date & Time

This section contains the following options:

Start date
This entry defines the date on which the dam failure is initiated.
Start time
This entry defines the time at which the dam failure is initiated.