Defining Dam Crest Geometry for HEC-HMS Storage Areas

The Dam Crest Geometry data panel of the Storage Area Data dialog box will be enabled when Outflow Structures is selected as the routing method. Otherwise, this data panel entry is disabled (i.e., grayed out). The dam crest geometry is used to model the discharge flowing over the top of the dam.
Dam Crest Geometry data panel of the Storage Area Data dialog box

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

Dam Crest Geometry

The data table under this section contains the following parameters:

Dam Crest Type
This dropdown combo box entry defines how the dam crest geometry is to be defined. This dropdown combo box provides the following entries:
1. None (default)
2. Level
3. Non-Level
Overflow Direction
This dropdown combo box entry defines where the overflow is being routed. This dropdown combo box provides the following entries:
1. Main (default)
2. Auxiliary
Weir Overflow Discharge Coef
This entry defines the weir overflow discharge coefficient for flow going over the top of the dam. Clicking the adjacent […] button displays the Weir Discharge Coefficient lookup dialog box.

Level Dam Crest

This section will only be enabled if the selected row in the Dam Crest Geometry data table has the Level option selected for the Dam Crest Type entry. Otherwise, this section is disabled (i.e., grayed out).
Level Dam Crest

This section contains the following options:

Dam crest elevation
This entry defines the crest elevation of a level dam.
Dam crest length
This entry defines the length of the level dam crest. Clicking the adjacent [Pick] button will cause the dialog box to temporarily disappear and allow the user to measure the length of the dam crest from the Map View.

Non-Level Dam Crest

This section will only be enabled if the selected row in the Dam Crest Geometry data table has the Non-Level option selected for the Dam Crest Type entry. Otherwise, this section is disabled (i.e., grayed out). This section allows the user to define 8-Point or Original dam crest geometry. Note that the software allows the user to cut the cross sections from the underlying terrain model and then simplify the cross section for the 8-point crest geometry used.
Non-Level Dam Crest