National Flood Hazard Cross Sections from FEMA FIRM Databases

Cross section lines represent channel surveys and interpolated data used in hydraulic models for calculating flood elevations. The data originates from FEMA's Flood Insurance Rate Map (FIRM) databases and is continually updated with Letters of Map Revision (LOMRs). It supports floodway data tables and the planimetric depiction of flood hazards.

Use Cases

• Analyze cross section line locations to validate or cross-reference flood profiles shown in FIS reports.
• Use the data for hydraulic modeling to calculate flood elevations based on channel survey inputs.
• Integrate cross section information with FIRM panels to assess floodway boundaries and zone designations like Zone AE or Zone A.

Strengths

• Data is developed with horizontal control specifications consistent with 1:12,000-scale mapping.
• The minimum horizontal positional accuracy for base map features is the NSSDA radial accuracy of 38 feet.
• Data is stored in the North American Datum of 1983, Geodetic Reference System 80 coordinate system.

Limitations

• Specific row counts, column definitions, and sample data are unavailable, limiting initial assessment of data structure and volume.
• Access to certain base map standards requires a username and password via the Knowledge Sharing Site (KSS).
• The description focuses on procedural and accuracy standards rather than the specific attributes contained within the cross-section records.

Provenance

Source

FEMA's Flood Insurance Rate Map (FIRM) databases, via the Louisville Metro Government.

Collection Method

Developed from channel surveys and high-accuracy elevation data for hydraulic modeling, with updates via Letters of Map Revision (LOMRs).

Freshness

Last updated on 2025-07-30, with new data added continually.

Geography

National coverage within the United States, as part of the National Flood Hazard Layer (NFHL).