Structure Inventory

What is a Structure Inventory?

A structure inventory is a data set that consists of attributes of unique or groups of structures in the floodplain relevant to flood damage analysis.

What is the Purpose of a Structure Inventory?

A structure inventory is needed to calculate the consequences - in dollar-denominated terms - of flooding for the range of possible flood events.

Where Do I Get a Structure Inventory?

Modern approaches for putting together a structure inventory include the National Structure Inventory and/or the use of publicly-available data such as county tax records and Google Earth.

Below is an image of a structure inventory for Muncie, Indiana taken from the National Structure Inventory. The attributes of the structure, such as structure type and location, have been refined by reviewing Google Maps and Google Maps Street View imagery and editing the attribute table with geospatial software.

Working with Structure Inventories in HEC-FDA

HEC-FDA accepts point shapefile structure inventories only. The points in the shapefile represent the structure locations. Modifications to the structure inventory (e.g., to reflect non-structural actions) should be imported as distinct point shapefiles instead of the use of modules. The required attributes for each structure include:

• Structure ID
• Dollar-denominated structure value
• Occupancy type
• First-floor elevation or ground elevation and foundation height

Upon import, you need to select whether the first floor elevation or the ground elevation and foundation height will be used. If ground elevation and foundation height are selected, you will need to identify the source of ground elevation (structure inventory or terrain file). Optional attributes include:

• Beginning damage depth
• Content value
• Other value
• Year in service
• Number of structures
• Metadata/notes

Each field in the structure inventory must be of an expected data type. The types are consistent with the data types served by the National Structure Inventory and are listed below:

Differences Between HEC-FDA Versions 1 and 2

1. HEC-FDA Version 2.0 does not handle flat file structure inventories (i.e., tab-delimited text files). A structure inventory must be in the form of a point shapefile. 
2. The structure inventory no longer requires information about stations because the software can read the data set to understand where the structures are located. This means that revising impact area delineations to match structural alternatives throughout plan formulation is clean and easy.  
3. Structure modules will not be used in HEC-FDA Version 2.0. To reflect differences in structure inventories between project conditions or analysis years, import separate structure inventories. Only one structure inventory will be used for a given stage-damage compute, so each imported structure inventory should contain all structures required for a given project condition - analysis year combination. 
4. Stage-direct damage functions were entered into study data as part of the structure inventory in HEC-FDA Versions 1. In HEC-FDA Versions 2, a stage-direct damage function is entered into study data as a manually-entered stage-damage function. 

Steps to Import a Structure Inventory

A structure inventory is imported using a point shapefile, where the attribute table must have the following attributes: unique ID, dollar-denominated structure value, occupancy type, and either both foundation height and ground elevation or just the first floor elevation. Identify whether first floor elevation or foundation height will be used, and if foundation height, identify whether the ground elevations will come from the structure inventory or a terrain file. Select optional attributes and identify what occupancy type names in the structure inventory correspond to which occupancy types in the study database. 

To import a structure inventory:

1. Right-click on Structure Inventories under Economics in the Study Tree and select Import From Shapefile.
   
2. Give the imported inventory a useful Name and Description (optional, but recommended).
3. Identify the path of the shapefile. From the Structure Inventory Shapefile box, click the browser ellipse button to navigate to the appropriate point shapefile and click Open.
4. From the Required Attributes panel, select the first floor elevation source:
   1. First Floor Elevation – Select this option if the shapefile contains an attribute with the structure first floor elevation. When selected a First Floor Elevation required attribute dropdown list will be provided below the Structure ID and Occupancy Type dropdown lists.
   2. Ground Elevation and Foundation Height – Select this option to have the first floor elevation calculated from the structure ground elevation and foundation height. Selecting this option requires users to select the Ground Elevation Source either from an imported terrain file or from the selected structure inventory shapefile. 
      

      HEC-FDA will notify users if the required attributes have not been selected in the import wizard (e.g., Structure ID was left blank), or if a terrain file has not been imported and the From Terrain File is selected. 

5. Identify required attributes and any optional attributes.
   
6. Click Next.
7. The next window requires users to identify the occupancy types for the structures. Select source of occupancy types (e.g., NSIOccTypes MuncieOccTypes), and match imported occupancy types to occupancy types in the structure inventory.
   
8. Click Finish.

Duplicates Not Needed

1. If a given study data item is the same for multiple project conditions, then that study data item need not be duplicated. For example, assume that you have a flow-frequency function for the existing condition of a given impact area, but the flow-frequency function is also representative of the hydrologic conditions of the future-without project condition, and all with-project conditions. In that case, create one frequency function, and select the same frequency function for each of the Scenarios. 
2. Except for terrain and the set of impact areas, many items can be created for a given study data element. For example, multiple structure inventories can be imported.