FEMA National Flood Hazard Layer

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1. What is it?

The National Flood Hazard Layer (NFHL) is a dynamic, GIS-based database that consolidates flood hazard data from FEMA's Flood Insurance Rate Maps (FIRMs) and Flood Insurance Study (FIS) reports. It offers a nationwide view of flood hazards and presents this information through various interactive maps and tools. The NFHL contains data on flood zones, floodways, base flood elevations (BFEs), and other pertinent information necessary for floodplain management and insurance purposes.

Key Components

1. Flood Hazard Zones: The NFHL classifies flood hazards into various zones. For instance:

- **Zone A**: Areas subject to inundation by the 1-percent-annual-chance flood event.

- **Zone AE**: Areas with BFEs provided.

- **Zone VE**: Coastal areas with additional hazards due to storm-induced waves.

- **Zone X**: Areas of moderate or minimal flood hazard.

2. Base Flood Elevations (BFEs): BFEs indicate the elevation at which there is a 1-percent chance of flooding in any given year. These are critical for building and land use regulations, as they inform the minimum elevation requirements for structures.

3. Floodways: The NFHL identifies regulatory floodways, which are channels and adjacent lands that must be reserved to discharge the base flood without increasing the water surface elevation more than a designated height.

4. Coastal Flood Hazard Areas: These areas include information on coastal flood risks, wave heights, and erosion hazards, vital for coastal management and mitigation efforts.

Flood Zone descriptions

Zone A

Areas where there is a high risk of flooding. In communities participating in the NFIP, homeowners and businesses with federally backed mortgages must purchase flood insurance.

Zones V and VE

Zones V and VE are high risk coastal areas with an additional hazard from storm waves. These areas have a 26% chance of flooding over the life of a 30-year mortgage. In communities that participate in the NFIP, flood insurance is mandatory for federally backed mortgages.

Zone D

Areas where flood risk has not been determined and no flood hazard analysis has been conducted. Flood insurance rates are therefore proportionate to the uncertainty of the flood risk.

Zone B & X

Area of moderate flood hazard, usually between the limits of 100‐year and 500‐year floods. B Zones are also used to designate base floodplains of lesser hazards, such as areas protected by levees from 100‐year floods, or shallow flooding areas with average depths of less than 1 foot or drainage areas less than 1 square mile.

Zone C & X

Area of minimal flood hazard, usually depicted on Flood Insurance Rate Maps (FIRM) as above the 500‐year flood level. Zone C may have ponding and local drainage problems that don’t warrant a detailed study or designation as base floodplain. Zone X is the area determined to be outside the 500‐year flood limit and is protected by a levee from 100‐year floods.

Further information can be found:

https://www.floodsmart.gov/flood-zones-and-maps

https://www.fema.gov/flood-maps

2. How can I use it?

The NFHL is a valuable resource for:

• Floodplain Management: Assisting communities in implementing and enforcing floodplain management regulations.
• Insurance Underwriting: Helping insurers assess flood risks for properties to determine appropriate coverage and premiums.
• Land Use Planning: Informing decisions on zoning, development, and infrastructure projects to mitigate flood risks.
• Emergency Preparedness: Aiding in the development of evacuation routes and disaster response plans based on identified flood-prone areas.

3. How is the data created?

The NFHL is compiled by FEMA through the aggregation of data from Flood Insurance Rate Maps (FIRMs) and Flood Insurance Study (FIS) reports. These sources provide detailed information on flood hazards, including statistical analyses of flood data, hydrologic and hydraulic analyses, and historic rainfall and storm data. The data is then digitized and integrated into a GIS-based platform, allowing for dynamic mapping and analysis.

Flood Insurance Rate Map (FIRM)

Within the NFHL data you may see references to FIRM, this is the Flood Insurance Rate Map and is  the official map of a community on which FEMA has delineated the Special Flood Hazard Areas (SFHAs), the Base Flood Elevations (BFEs) and the risk premium zones applicable to the community.

4. Are there any limitations?

While the NFHL is a comprehensive tool for understanding flood hazards, users should be aware of certain limitations:

• Data Currency: The NFHL is updated as new data becomes available, but there may be delays between data collection, analysis, and publication.
• Resolution Variability: The level of detail in the NFHL can vary depending on the source data and the methods used in its creation.
• Assumptions and Uncertainties: The data is based on statistical analyses and models that incorporate assumptions and may have inherent uncertainties.

5. What data points are available?

The NFHL includes several key components:

• Flood Hazard Zones: Classifications indicating the level of flood risk in different areas.
• Base Flood Elevations (BFEs): The computed elevation to which floodwater is anticipated to rise during the base flood.
• Floodways: The channel of a river or other watercourse and the adjacent land areas that must be reserved to discharge the base flood without cumulatively increasing the water surface elevation more than a designated height.
• Coastal Flood Hazard Areas: Zones subject to inundation by tidal surges and wave action.

6. Where can I find out more?

For more detailed information, you can visit FEMA's official National Flood Hazard Layer website.

Note: This document is based on information available as of February 4, 2025. For the most current details, please refer to the official Addresscloud resources.