Approximate BFE

In this article:

• How to measure an approximate BFE
• Forerunner's logic for approximate BFE measurements
• How to update an approximate BFE value

The Approximate Base Flood Elevation (BFE) measurement tool in Forerunner is designed to help riverine communities overcome the challenges of manually calculating BFE values. This feature allows users to measure approximate BFEs directly within the platform, streamlining flood data management for communities without automated BFE values on their Flood Insurance Rate Maps (FIRMs).

Note: the approximate BFE values provided are estimates and should be treated as such; they do not represent the official BFE for the property. Please refer to the associated Flood Insurance Study (FIS) to verify these values.

How to measure an approximate BFE

For properties in riverine communities without FEMA-provided BFE values, you can use Forerunner's Approximate BFE measurement tool to estimate these flood elevation values.

Note: the approximate BFE feature is something that needs to be turned on in your Forerunner account by your Forerunner contact. Please reach out to us for assistance on getting your account configured!

Once configured in your account, here's how to measure an approximate BFE value:

1. Find the property you are looking to measure a BFE for, and if no BFE is provided by FEMA, click the Add button next to the BFE row to initiate the measurement workflow.
2. Choose the two cross sections closest to the property. The selected cross sections will be highlighted and shown in the modal for easy selection or deselection.
   1. Please note that the cross sections need to have a continuous profile baseline running through them as Forerunner takes the measurement along the profile baseline that intersects the two cross sections.
   2. Please note, both cross sections also must have BFE values associated with them
3. Forerunner will calculate an approximated BFE value based on the relative position of the property between the two cross sections along the profile baseline. Ensure that the selected cross sections are connected by a continuous profile baseline for accurate calculations.
4. Click Save to save the value on the property
   1. When you save the value, Forerunner will display a warning indicating to your team and members of your public that the value is an approximation and should not be used as the official BFE for the structure.

Things to note:

• The measurement tool is available for properties without FEMA-provided BFEs. For properties in both riverine and coastal areas, Forerunner will display FEMA-generated BFEs if available.
• The tool supports BFE measurements in all zones, including X and X500 zones, as some communities regulate these areas.
• Forerunner will only calculate BFEs if valid cross sections with BFE values are present.

Forerunner's logic for approximate BFE measurements

In Forerunner, we use the property's latitude and longitude to locate the nearest point on the profile baseline between the two selected cross sections. We then calculate the property's relative distance along this baseline and interpolate the approximate BFE by averaging the two cross sections, adjusting based on the property's position between them. This gives an estimated BFE specific to the property's location relative to the profile baseline.

Please note: Forerunner will only calculate approximate BFEs if valid cross sections with BFE values are present. If cross sections do not have BFE values, we do not have enough information to determine the approximate BFE and you should refer to the FIS profile for more information.

How to update an approximate BFE

You can manually update an approximate BFE if you've calculated the value using the FIS, a raster dataset, or another method. To do this, simply click the underlined approximate BFE value, enter the new value, and click Save to save the value on the property.

If you prefer to add a value manually without using the measurement tool’s calculation, click Add manually to input your value directly.