During the evacuation portion of the life loss computation in HEC-FIA, the time it takes for people in a given structure to evacuate safely (defined as the time from leaving a structure to reaching a safe location) can be defined by either:

  • Entering the exact time (minutes) it takes for the inhabitants of each structure to reach a safe location, or
  • Providing a hazard area boundary and nominal evacuation velocity (mph) and letting HEC-FIA compute the time required for the inhabitants of each structure to evacuate to safety.

Typically, a hazard area boundary and nominal velocity is entered in HEC-FIA to estimate the evacuation times for a given event. The hazard area boundary should be determined by creating a polygon that represents the extents of flooding where depth is greater than two feet. Each flood event being simulated has a separate hazard area boundary. To create a hazard area boundary, follow the steps in the following sections.

Reclassify Depth Grid Cells

The following steps assist the user in creating a polygon representing the Hazard Boundary, which represents everything with two feet of flooding or greater. This polygon can be utilized for evaluating where structures evacuate in an HEC-FIA simplified LifeSim computation. Reclassify depth grid cells for the maximum depth grid to values of one (1) if greater than two feet deep and two (2) if less than or equal to two feet deep:

  1. Start ArcMap. The ArcMap window opens. By default, a new empty map is selected, click OK.

    Figure: ArcMap - New Empty Map

  2. If the Spatial Analyst Toolbar is not available from the ArcMap window, right-click on the empty area next to the Menu Bar. From the shortcut menu, click Spatial Analyst, the Spatial Analyst Toolbar appears in the ArcMap window in the toolbar area.
  3. From the Spatial Analyst Toolbar, click Spatial Analysis and then select Reclassify from the shortcut menu . The Reclassify dialog box opens.
  4. Input raster is the maximum depth grid (depth0) for the flood scenario being assessed. From the Input raster list, select the depth grid file or by clicking next to the Input raster list.
  5. A Choose an input raster browser opens. Browse to the location of the depth grid file, click on the depth grid filename and then click Add. The Choose an input raster browser closes, and the filename of the grid appears in the Input raster box on the Reclassify dialog box.
  6. Leave the Reclass field box blank.

  7. Default values appear in the Set values to reclassify box. These values (both old and new) need to be reset. Set all values less than or equal to two (2) feet to a new value of two (2) and values from two (2) feet up to the highest value in the depth grid to a new value of one (1). For an example, see the figure below. Note that when entering the old value range a space is required on both sides of the dash (enter 0 - 2, not 0-2).

    Figure: Toolbar Setup Shortcut Menu


    Figure: Spatial Analyst Toolbar


    Figure: Reclassify Dialog Box


    Figure: Set Values to Reclassify

  8. In the Output raster box, type the desired pathname for the depth grid or click to browse to the place where the grid is to be saved.
  9. Click OK. The hazard area grid is created. When that is finished, the Reclassify dialog box closes and the hazard area boundary grid displays in the ArcMap® window.

Generate a Polygon Shapefile of the Hazard Area Boundary

Generate a polygon shapefile that represents the hazard area boundary (can be done in ArcMap or ArcCatalog):

  1. If the ArcToolbox Pane is not present, click ArcToolbox  on the Standard Toolbar and the ArcToolbox Pane displays in the ArcMap or ArcCatalog window.

  2. From the ArcToolbox Tree, double-click Conversion Tools, double-click From Raster, and then double-click Raster to Polygon. The Raster to Polygon dialog box opens.

    Figure: Raster to Polygon Dialog Box

  3. The input raster file is the hazard area boundary grid that was created in the previous section. Select the location of the hazard area boundary grid by clicking next to the Input raster box . Browse to the location of the hazard area boundary grid, and select it. Click Add, the Input raster browser closed, and the path and the name of the selected hazard area boundary file appears in the Input raster box on the Raster to Polygon dialog box.
  4. The Field box should be set to VALUE; this option is used to assign values from the cells in the hazard area boundary file to the polygons in the shapefile.
  5. By default the software stores the output shapefile to the same directory as the selected hazard area boundary grid. In the Output polygon features box, the path and the default name for the shapefile appears. Change this name to symbolize the depth grid it represents (i.e., normal_fail_hazardarea.shp).
  6. Select Simplify polygons so that the software smoothes the polygons into simpler shapes.
  7. Click OK. The Raster to Polygon dialog box closes and the Raster to Polygon Compute dialog opens. This dialog box notifies the user of the status of the compute and how long it took to create the binary file. When finished viewing information, click Close. The Raster to Polygon Compute dialog box closes.

Editing the Hazard Area Boundary Shapefile

All polygons with a value of one (1) in the output polygon dataset represent the hazard area boundary. Edit the polygon shapefile and select all polygons with a value of two (2) and delete them. To edit the hazard area boundary shapefile:

  1. From the Editor Toolbar click Editor (Figure B.19), from the shortcut menu click Start Editing.

    Figure: Start Editing

  2. Right-click on the shapefile that was created in the previous section. From the shortcut menu, click Open Attribute Table. The attribute table for the hazard area polygon file opens.
  3. Click Options. From the shortcut menu, click Select by Attributes. The Select by Attributes dialog box opens.

  4. Double-click on "GRIDCODE", in the SELECT * FROM shapefile name WHERE box "GRIDCODE" appears. Click the equals sign button and then enter 2.

    Figure: Open Attribute Table Menu Item


    Figure: Attribute Table

  5. Click Apply, in the attribute table all the rows with a GRIDCODE equal to two (2) are highlighted in a cyan color. If the shapefile is displayed in the ArcMap window, the same items are highlighted in cyan.
  6. Click Close, the Select by Attributes dialog box closes.
  7. From the attribute table dialog box click the Delete key . All of the highlighted rows are deleted. Click to close the attribute table.
  8. From the Editor Toolbar click Editor. From the shortcut menu click Save Edits. Now the hazard area boundary shapefile has been edited to contain only the polygons that delineate areas where the maximum depth is greater than two feet.

  9. Repeat all steps in this section for each depth grid in the study.

    Figure: Select by Attributes Dialog Box