What is an Index Point?

An index point is the location in a given impact area at which the input relationships are defined (e.g., flow-frequency, stage-discharge). In other words, the index point is the location for which the risk equation is calculated.

What is the Purpose of an Index Point?

An index point is only required if you need to retrieve water surface elevations from the hydraulics data set to create graphical stage-frequency functions, which can otherwise be entered into the study directly. Otherwise, the location of the index point becomes a hydraulics modeling concern alone. 

How Can I Develop Index Point Data?

Index points may be developed by creating a point shapefile using GIS software, placing points (x-y coordinates) at the index locations. 

Working with Index Points in HEC-FDA

Differences Between HEC-FDA Versions 1 and 2

  • The primary difference between Versions 1 and 2 is that index points are optional. Index points will only be used to retrieve a graphical stage-frequency function from a hydraulics data set.
  • In Version 1, index points were identified using a river station. The use of river stations is how we tricked HEC-FDA Version 1 to consume geographic information. HEC-FDA Version 2 can natively process geospatial data. Hence, index points are identified as x-y coordinates and are imported using the point shapefile. 
  • Sometimes, the best index points vary by alternative plan. In HEC-FDA Version 2, you can import multiple sets of index points to accommodate retrieval of graphical frequency functions at the correct locations by alternative plan. 

Steps for Importing Index Points

Impact Areas FDA icon Index points are only required when imported water surface elevations in hydraulics will be used to retrieve graphical stage-frequency functions. In other words, index points are not explicitly used for anything else within HEC-FDA, but remain an important concept. Import index points in the form of a point shapefile (only one index points dataset can be imported into a study).

  1. If desired, create index points for the study. Index points should be created when retrieving graphical stage-frequency from water surface elevations in hydraulics. From the Study Tree, right-click on Index Points and select the create new command.
    Create New Index Points study tree shortcut command
  2. From the Create New Index Points dialog, enter the name and description for the data. Click the browser ellipse button to navigate to the appropriate file and click Open to set the shapefile path. Then select the unique name (a field of the attribute table). Click OK to import the dataset.
    Create New Index Points example completed