Letters of Map Change (LOMCs) & Map Revisions

ASFPM Certified Floodplain Manager CFM

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1 Chapter 1: Overview & Context of Floodplain Management

History, Evolution & Goals of Floodplain Management Intergovernmental Roles & Responsibilities Professional Ethics & Public Communication in Floodplain Management

2 Chapter 2: Floodplain Mapping & Studies

Hydrology, Hydraulics & Flood Insurance Studies Flood Insurance Rate Maps (FIRMs), Flood Zones & Base Flood Elevations Regulatory Floodways & Encroachment Analysis Letters of Map Change (LOMCs) & Map Revisions Modern Mapping Tech, Vertical Datums & Map Interpretation

3 Chapter 3: NFIP Regulatory Standards & Development Administration

Local Ordinance Authority, Adoption & Permit Requirements Zone A & AE Regulatory Standards Zone V & VE Regulatory Standards (Coastal High Hazard) Regulatory Floodway Administration & No-Rise Certifications Manufactured Homes, Recreational Vehicles & Accessory Structures Utility & Building Service Protection & Enclosures Subdivision Standards, Site Design & Watercourse Alterations

4 Chapter 4: Substantial Improvement, Substantial Damage & Enforcement

Substantial Improvement (50% Rule Definitions, Cost Estimation, Market Value) Substantial Damage Determinations & Post-Disaster Inspections Variances, Appeals & Legal Considerations (Hardship vs Financial Convenience, Takings Law) Documentation, Permit Files, Elevation Certificates & Administrative Enforcement (Section 1316)

5 Chapter 5: Flood Insurance & Community Rating System

The National Flood Insurance Program (NFIP) & Standard Flood Insurance Policy (SFIP) Provisions Mandatory Purchase Requirement, Flood Zones & Coverage Limits Increased Cost of Compliance (ICC) Coverage The Community Rating System (CRS) & Insurance Rating Basics

6 Chapter 6: Flood Hazard Mitigation & Retrofitting

Structural vs Non-Structural Mitigation Strategies (Elevation, Acquisition, Relocation, Dry/Wet Floodproofing) Hazard Mitigation Planning & Benefit-Cost Analysis (BCA) Repetitive Loss & Severe Repetitive Loss Properties & Mitigation Funding (HMA, FMA, BRIC)

7 Chapter 7: Emergency Preparedness, Response & Recovery

Emergency Operations Planning, NIMS/ICS & NWS StormReady Program Post-Disaster Response, Safety & Debris Management Disaster Recovery, DRRA Section 1206 & FEMA Individual Assistance / Public Assistance

8 Chapter 8: Natural & Beneficial Functions of Floodplains

Natural Floodplain Functions (Storage, Conveyance, Groundwater Recharge, Water Quality) Ecological Resources, Wetlands, Riparian Corridors & Habitat Protection Protecting Natural Functions through Open Space, Green Infrastructure & No Adverse Impact (NAI)

Letters of Map Change (LOMCs) & Map Revisions

Key Takeaways Explain This Topic AI

A Letter of Map Amendment (LOMA) is used when natural high ground was inadvertently mapped within the SFHA.

A Letter of Map Revision based on Fill (LOMR-F) is used when artificial fill has been placed to raise land above the BFE.

A Letter of Map Revision (LOMR) officially updates the FIRM to reflect physical changes (like channelization) or better scientific data.

A Conditional Letter of Map Revision (CLOMR) provides FEMA's comment on a proposed project before it is built.

LOMCs are official amendments to the FIRM and can remove the mandatory flood insurance purchase requirement.

Last updated: August 2026

Letters of Map Change (LOMCs) & Map Revisions
The Need for Map Changes

Flood Insurance Rate Maps (FIRMs) are massive undertakings, often covering entire counties and utilizing topography with specific contour intervals. Because maps are drawn at a macro scale, they cannot capture every small topographic detail. Sometimes, a naturally high piece of ground is inadvertently shaded as being within the Special Flood Hazard Area (SFHA).

Furthermore, the physical world changes. Rivers migrate, new bridges are built, and developers alter the landscape. To keep the NFIP fair and accurate, FEMA provides mechanisms to correct and update FIRMs without having to republish the entire map. These mechanisms are collectively known as Letters of Map Change (LOMCs) .

An approved LOMC is a legal document that officially revises the effective FIRM. If a LOMC removes a structure from the SFHA, the mandatory flood insurance purchase requirement is waived by federal law, though lenders may still require it at their own discretion.

Letter of Map Amendment (LOMA)

A Letter of Map Amendment (LOMA) is used to correct a mapping error involving natural high ground .

If a property owner believes their home is on a natural hill that is actually higher than the Base Flood Elevation (BFE), but the map shows them in the SFHA, they can apply for a LOMA.

Key Requirement: The ground must be naturally high. No fill dirt can have been placed to raise the elevation.

Process: The owner hires a licensed surveyor to complete an Elevation Certificate. The surveyor must prove that the Lowest Adjacent Grade (LAG)—the lowest ground touching the foundation of the structure—is at or above the BFE.

Result: If approved, FEMA issues a LOMA stating the structure (or portion of the property) is removed from the SFHA and is now considered Zone X.

Letter of Map Revision based on Fill (LOMR-F)

A Letter of Map Revision based on Fill (LOMR-F) is similar to a LOMA, but it applies when the land was raised above the BFE using artificial fill .

Key Requirement: Fill was placed to elevate the site.

Process: Like a LOMA, a surveyor must prove the LAG is at or above the BFE. However, there is a critical additional step: The local floodplain manager must sign a Community Acknowledgment Form. This form confirms that the placement of fill complied with all local floodplain ordinances (e.g., it wasn't illegally dumped in a regulatory floodway without a No-Rise certification).

Result: The structure or property is officially removed from the SFHA.

Letter of Map Revision (LOMR)

While LOMAs and LOMR-Fs usually deal with single properties, a Letter of Map Revision (LOMR) is a major, physical update to the map's technical data.

A LOMR is used to officially revise the Base Flood Elevations, the flood zone designations, or the regulatory floodway boundaries. LOMRs are required when:

A community completes a major flood control project (like a levee or channelization).

A new bridge significantly alters the hydraulic profile of a river.

Better topographic data (like LiDAR) or more advanced hydraulic modeling proves the existing FIS is inaccurate.

Applying for a LOMR requires submitting detailed engineering data, including hydrologic and hydraulic models (like HEC-RAS), to FEMA for review. Once approved, the LOMR physically changes the map data for an entire stream reach.

Conditional Letter of Map Revision (CLOMR)

A Conditional Letter of Map Revision (CLOMR) is FEMA's formal comment on a proposed project that would, upon construction, affect the hydrologic or hydraulic characteristics of a flooding source and thus result in the modification of the existing regulatory floodway, the effective BFEs, or the SFHA.

Why use it? If a developer wants to build a project that will drastically alter the floodplain (requiring a future LOMR), they need assurance that FEMA will actually approve the changes once the project is done. A CLOMR provides this assurance before millions of dollars are spent on construction.

CLOMR Requirements: Under NFIP regulations, a community must apply for a CLOMR before permitting any project in a floodway that will cause a rise in the BFE > 0.00 feet, or any project in an AE zone without a floodway that will cause a rise > 1.0 foot.

Crucial Distinction: A CLOMR does not revise an effective FIRM. It is merely a letter stating, "If you build it exactly as proposed, we will approve the LOMR later." The map is not officially changed until the project is built and the final LOMR is approved.

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