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

  1. Right click on Index Points under Impact Areas in the Study Tree and select Import Index Points
  2. Give the set of index points a useful name and description
  3. Identify the location (path) of the index points shapefile
  4. Click OK