A minimum of two inputs are required to simulate a hydraulic event in HEC-FIA. These inputs are point locations and hydraulic data. Some computation methods discussed in this section require a third input, terrain data.

Point Locations

In HEC-FIA, structure and critical infrastructure inventories are described in point shapefiles. Although other damageable elements are not stored as points, during computations the elements are converted to point locations. Hydraulic information is then evaluated at these explicitly input or internally generated point locations. This conversion and evaluation process is true for all components of every damageable element recorded in the software, including impact response curves and warning scenario nodes.

Inundation Data

Inundation data contains information about hydraulic characteristics that drive the consequence computations of HEC-FIA. The inundation data required for HEC-FIA should be prepared by an experienced hydraulic engineer in conjunction with an economist familiar with the computational procedures in HEC-FIA. A variety of hydraulic modeling programs are suitable for this preparation, including HEC-RAS (River Analysis System; including two-dimensional output), HEC-HMS (Hydrologic Modeling System), HEC-ResSim (Reservoir System Simulation), MIKE 21 (DHI, Denmark), or FLO-2D (FLO-2D Software, Inc.), among others. Inundation data can be imported into HEC-FIA in four formats: 1) cross sections/storage areas; 2) grids; 3) a combination of grids and cross sections/storage areas; and, 4) common computation points. The characteristics of each of these data types are described in the following paragraphs.

Cross Sections/Storage Areas

Cross section and storage area shapefiles provide HEC-FIA with georeferenced locations at which hydrographs contained in a DSS (HEC's Data Storage System) file should be applied. Time-series information is exchanged between DSS files and HEC-FIA at each of the geo-referenced cross section and storage area locations. Cross section shapefiles are used to define regions for the application of interpolated hydrographs. Each region is defined by connecting the ends of adjacent cross sections with straight lines. The storage area shapefiles are used to describe the extents of the storage area within each storage area-linked hydrograph, which should be applied.

Grids

Grids can be used to define hydraulic characteristics throughout a study area. The five hydraulic characteristics that can be represented by grids in HEC-FIA are maximum depth; maximum instantaneous depth-times-velocity; arrival time for life loss calculations; arrival time for agricultural calculations; and, flood duration for agricultural calculations. Structures will be assigned hydraulic characteristics based on the value of the grid cell for each grid in which the structure point is contained.
Hydraulic grid datasets can be imported into HEC-FIA in many gridded formats, including a tagged image file (*.tif); ArcInfo® ASCII grid (.asc); ArcGrid® (*.flt); Segmented Multi-Resolution Multi-Parameter (*.smrmp); and, tile map service (*.tms) format. HEC-FIA will prompt users to convert the files into the .tif format for more efficient operation once the file has been imported.
A depth grid represents the maximum depth reached in a given cell. HEC-FIA will use the depth grid to calculate damage to structures, damage to agricultural assets, and life loss consequences. Depth grids are typically generated using the HEC-RAS Mapper tool if HEC-RAS is the hydraulic model used to produce the results for a study.
An instantaneous depth-times-velocity grid represents the maximum product of depth and velocity calculated for each time step in the hydraulic simulation. Depth-times-velocity grids can be generated from HEC-RAS using the HEC-RAS Mapper tool.
An arrival time grid represents the time that floodwaters of a given depth (usually two feet for life loss and any value greater than zero feet for agricultural damage) reach each cell. When modeling the evacuation process for life loss, HEC-FIA assumes that after a given depth is reached, the individuals remaining in a structure will no longer be able to evacuate successfully, thus they will remain in the structure for the flood event. In HEC-FIA, this portion of the population is termed as "Not Mobilized". The arrival time grid for agricultural damage calculations is used to determine when the flood arrives compared to the planting and harvesting times. Arrival time grids can be can be generated from HEC-RAS using the HEC-RAS Mapper tool.
Duration grids contain information about the duration of time that a cell is inundated greater than zero feet. Duration grids can also be developed using the HEC-RAS Mapper tool.

HDF5 HEC-RAS Output

First introduced in HEC-FIA 3.3, the Holdout - RAS HDF inundation configuration is used for Flood Damages Reduced calculations. Instead of HEC-DSS files or Geotiffs, this inundation configuration requires the native HEC-RAS results in .hdf format (in the format of *p##.hdf). This format reduces compute time and storage needs, eliminating the need for the creation and storage of bulky Geotiffs. The max depth at any location within the project extent is accessed directly by HEC-FIA to calculate damage to structures. Currently this format is only used to calculate direct damage (structures) within a Flood Damages Reduced computation.

Grids and Cross Sections/Storage Areas

The grids and cross sections inundation datasets utilize a combination of the two datasets. The ability to use two datasets can also be useful when using gridded data for depth and arrival time, which is typically more accurate, while using cross sections to warn the population based on a depth exceedance threshold drawn from the hydrograph data (Impact Response Table). Structures will be assigned hydraulic characteristics first based on any gridded data that has been imported. After all of the gridded data inputs have been assigned, the program will reference the cross section-linked DSS files to define the remaining variables for the computations.

Common Computation Points

A common computation point (CCP) shapefile provides HEC-FIA with geo-referenced locations along a stream alignment to which hydrographs contained in a DSS file should be applied. Time-series information is exchanged between DSS files and HEC-FIA at each of the geo-referenced common computation points. Hydraulic characteristics for each section of the stream alignment are linearly interpolated based on the hydraulic characteristics of the bounding common computation points.

Terrain Model

A terrain model in HEC-FIA is defined by importing a Digital Elevation Model (DEM). The DEM represents the ground elevation for the region being studied in a gridded format, which is used to provide elevation data for the structure inventory. The HEC-FIA User's Manual should be used to determine the types of terrain model files that can be imported.