What is Terrain Data?

A terrain is a spatial data set that contains the ground elevations throughout a particular area.

What is the Purpose of Terrain Data?

The terrain is used to identify the ground surface elevation across an area of interest. Terrain data takes the form of a raster file in a geospatial environment. Each pixel in a raster file contains a value that indicates the ground surface elevation at that point. Below is an example of terrain data from Muncie, Indiana. 

Muncie Terrain Data

Where Can I Find Terrain Data?

You can obtain terrain data from the data used in the HEC-RAS modeling, from the US Geological Survey (USGS), or by working with a geographic information system (GIS) specialist.

Working with Terrain Data in HEC-FDA

Study Configuration Considerations

The only prerequisite for importing terrain data is the creation of an HEC-FDA Version 2.0 study. Review Create New Study from Scratch for more information on how to create a new HEC-FDA Version 2.0 study.

To import terrain data in FDA 2.0, right-click Terrain at the top of the contents pane and left-click Import Terrain. See below image.


Give the terrain a name, click the ellipsis, and navigate to the appropriate folder to select your terrain file. See below image. Select Ok and your terrain will be imported.



Terrain File

Please note that only 1 terrain file may be imported. Import terrain as a HEC-RAS terrain. A RAS Terrain is a .hdf file paired with one or more .tif files. Select the .hdf file when importing your terrain and ensure the accompanying files are included in the same subdirectory. A terrain file is required if you're relying on hydraulic data in HDFs or if you do not have elevation data in your structure inventory (e.g. only foundation heights but no ground elevations). 

Differences Between HEC-FDA Versions 1 and 2

Terrain data (ground elevation) is used the very same way in HEC-FDA Version 2 as it was used in Version 1 - to calculate the depth of flooding. The only difference is the way that the data was imported. In HEC-FDA Version 1, ground elevations had to be imported as part of the structure inventory. In HEC-FDA Version 2, terrain data can be imported to identify the ground elevations at structures if the ground elevation data does not already exist in the structure inventory. Also, terrain data will be required if using the native HEC-RAS output format (HDF) for hydraulic data sets. 

Steps to Import Terrain Data

  1. Right click on Terrain in the study tree and click Import Terrain.
  2. Give the terrain a useful name.
  3. Identify the path of your terrain data set.
  4. Click OK.