Guide to Floodplains

What Is a Floodplain?

A floodplain is a flat area of land that is susceptible to flooding from various sources of water, such as creeks, rivers, lakes, and oceans. According to FEMA, a floodplain includes any land that is at risk of being inundated by floodwaters, which can come from several different causes. This includes:

Coastal floodplains, where land is flooded by storm surges or rising tides.
Riverine floodplains, which are areas along rivers or creeks that flood when water levels rise and overflow the banks.
Local floodplains, which refer to areas outside of official FEMA flood zones, where flooding can occur due to heavy rainfall or poor drainage in urban areas.

Flooding can happen in many different types of landscapes and can be caused by factors like rainfall, storms, or coastal surges. Understanding your specific flood risk requires knowing which type of floodplain you’re dealing with—whether riverine, coastal, or local. It’s important to note that many FEMA flood maps don’t currently include areas that are vulnerable to local flooding or urban flood zones.

Where It Rains, It Can Flood

Many people don’t fully grasp the risks associated with floodplains. For example, homes that aren’t elevated in the 1% annual chance floodplain have a 26% likelihood of being damaged over the course of a 30-year mortgage.

Flood risks can evolve over time due to factors such as new development, shifts in weather patterns, and other environmental changes. To help communities assess and address these risks, FEMA’s Risk Mapping, Assessment, and Planning (Risk MAP) program provides tools for better flood risk understanding and encourages proactive mitigation planning. Through more accurate flood maps, risk assessment resources, and community outreach, Risk MAP empowers local areas to make informed decisions that reduce flood risks.

By identifying hazards, anticipating recovery challenges, and prioritizing mitigation actions before a disaster strikes, communities can significantly lower long-term risks and prevent future damage. Effective hazard mitigation planning is essential for making communities more resilient to disasters.

As part of the Risk MAP initiative, FEMA will use watershed boundaries to guide future studies. This watershed-based approach will foster collaboration among local governments, tribes, businesses, and non-profits, enabling them to share flood risk information, pool resources, and identify broader opportunities for mitigation. Together, these groups can develop a shared vision for reducing flood risks and strengthening community resilience.

Base Flood Elevation (BFE) and Development Regulations

Base Flood Elevation (BFE) is a critical reference in floodplain management, required until a regulatory floodway is designated.

In Zones A1–30 and AE on a community’s Flood Insurance Rate Map (FIRM), no new construction, substantial improvements, or other forms of development (including the placement of fill) are allowed unless it is demonstrated that the proposed development will not raise the water surface elevation of the base flood (the flood event with a 1% annual chance of occurring) by more than one foot at any point within the community.

The Special Flood Hazard Area (SFHA) refers to land that is expected to be inundated by the base flood, which has a 1% chance of being equaled or exceeded in any given year. This area represents the high-risk flood zone and requires specific management practices to reduce flood damage and risks to property and life.

Flood Hazard Maps

Flood maps, officially called Flood Insurance Rate Maps (FIRMs), are created by FEMA to show the flood risk in specific areas. These maps display flood zone designations, floodplain boundaries, roads, landmarks, and the Base Flood Elevation (BFE).

Communities use FIRMs to better understand flood risks and make informed decisions on how to manage or reduce those risks.
Lenders rely on FIRMs to determine whether flood insurance is required for a property.
Individuals consult FIRMs to decide where to live and what to build based on the flood risk in a particular area.

FIRMs are publicly available at no cost through the FEMA Flood Map Service Center.

FIRMs indicate the likelihood of flooding in a given area. For example, properties located in the 1% annual chance floodplain (also known as the 100-year floodplain)

Areas and Zones

Special Flood Hazard Areas (SFHAs) are high-risk flood zones, marked on flood maps with zones starting with the letters ‘A’ or ‘V’. These areas have a 1% annual chance of flooding (also known as the 100-year floodplain). Flood insurance is available to all property owners and renters in these zones, and lenders require mandatory flood insurance for properties in SFHAs.

Non-Special Flood Hazard Areas are moderate-to-low risk zones, represented on flood maps with zones starting with ‘B’ or ‘X-shaded’. These areas have a 0.2% annual chance of flooding (also referred to as the 500-year floodplain). While flood insurance is available at a lower cost for property owners and renters, it is not required by lenders, though they may still mandate it in some cases.

Undetermined Flood Hazard Areas are areas where flood risks have not been fully assessed or determined. These zones are marked with the letter ‘D’ on flood maps, indicating that flood hazards are possible but not yet officially identified.

What is Base Level Engineering (BLE)?

Base Level Engineering (BLE) is a method used to generate detailed, watershed-wide flood hazard information. It relies on foundational hydrologic and hydraulic engineering models to produce key flood data, including floodplain boundaries, flood depths, and water surface elevation grids. BLE uses high-resolution ground elevation data and advanced modeling software, all developed in compliance with FEMA’s Standards for Flood Risk Projects. The results align with the Zone A flood mapping designation.

Although BLE data does not immediately replace a community’s official Flood Insurance Rate Map (FIRM), it provides valuable flood risk information that can help local communities determine Base Flood Elevations (BFEs) for Zone A areas and other newly identified flood-prone regions. Communities can choose to adopt this data for local planning by updating their ordinances.

BLE data offers critical insights that can aid a variety of stakeholders, including floodplain managers, emergency responders, residents, business owners, insurance agents, and surveyors, helping them make more informed decisions about flood risk and management.

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What is a Letter of Map Change (LOMC)?

A Letter of Map Change (LOMC) is an official document issued by FEMA that modifies or clarifies the flood zone designation of a specific property or area on the Flood Insurance Rate Map (FIRM). The LOMC is used when a property owner or community requests a change to the flood zone or floodplain boundaries, usually because of new information or changes in the physical landscape.

There are different types of LOMCs, including:

Letter of Map Amendment (LOMA): This is issued when a property or structure is determined to be outside of the Special Flood Hazard Area (SFHA), meaning it is not at risk of flooding from the base flood. A LOMA can remove the property from the mandatory flood insurance requirement.
Letter of Map Revision (LOMR): This is used when FEMA revises the flood zone designation or boundaries due to changes in flood risk, such as improvements to flood control infrastructure, changes in river channels, or updated data. A LOMR can affect a larger area, like a community or watershed.
Letter of Map Revision Based on Fill (LOMR-F): This is issued when a property has been elevated with fill, and the new elevation is shown to be above the base flood elevation, potentially removing the property from the floodplain.

An LOMC helps property owners, developers, and communities clarify flood risks and may result in reduced insurance costs or changes in development regulations. To request a LOMC, applicants must submit detailed documentation and supporting evidence, such as elevation certificates, hydrologic data, or engineering studies, to FEMA for review.

An applicant might request a Letter of Map Change (LOMC) for several reasons, primarily to clarify or modify the flood zone designation of a property or area. Common scenarios include:

Remove Property from the Floodplain (LOMA)

Purpose: If a property is incorrectly shown within a Special Flood Hazard Area (SFHA) on a FEMA Flood Insurance Rate Map (FIRM), the property owner may request a Letter of Map Amendment (LOMA) to remove the property from the floodplain.
Benefit: Being removed from the floodplain can reduce the property owner’s flood insurance requirements. If FEMA determines the property is outside of the 1% annual chance floodplain (100-year floodplain), the property owner may not be required to purchase flood insurance.

Revised Flood Zone Designation (LOMR)

Purpose: A Letter of Map Revision (LOMR) is requested if the flood zone designation or boundaries need to be updated due to changes in flood risk. This might occur after new flood control measures (such as levees or dams) are implemented, or if better flood data becomes available.
Benefit: A LOMR may reduce the flood risk designation for an area or alter floodplain boundaries, which can affect development regulations or insurance requirements.

Elevated Property Above Base Flood Elevation (LOMR-F)

Purpose: A property owner who has elevated their property above the Base Flood Elevation (BFE) with fill may request a Letter of Map Revision Based on Fill (LOMR-F) to have the property removed from the floodplain. The fill must be shown to raise the property above the BFE to qualify.
Benefit: This may remove the property from flood risk zones, potentially lowering or eliminating the need for flood insurance.

Correct Flood Zone Errors

Purpose: An applicant may request a LOMC if they believe there is an error in the way a flood zone is mapped for their property, such as inaccurate floodplain boundaries or misclassified flood zone designations.
Benefit: Correcting the flood zone could ensure the property is classified accurately, leading to potentially lower insurance premiums and fewer development restrictions.

Clarify Property’s Flood Risk Status

Purpose: A property owner or developer might request a LOMC to clarify the flood risk status of a property before purchasing it, developing it, or obtaining a loan.
Benefit: By clarifying whether the property is in a high-risk or low-risk area, the applicant can make more informed decisions regarding flood insurance, construction, and compliance with local floodplain management regulations.

Development and Construction Considerations

Purpose: When planning construction or substantial improvements on a property, an applicant may seek a LOMC to determine whether the property falls within a flood zone and whether it is subject to specific building codes, elevation requirements, or floodplain development restrictions.
Benefit: Understanding flood risks can help with project planning, ensuring the development meets local building codes and floodplain regulations, and possibly reducing costs for flood protection.

In all these cases, the applicant must provide supporting documentation, such as elevation certificates, hydrologic data, or engineering studies, to substantiate their claim and demonstrate that the requested change is justified.

What is Involved in Requesting a Letter of Map Change (LOMC)?

Requesting a Letter of Map Change (LOMC) involves a series of steps and the submission of specific documentation to FEMA to support the change in flood zone designation or mapping. The process ensures that FEMA has sufficient information to evaluate the request and determine whether the property or area qualifies for a change in flood status.

Here’s what is typically involved in requesting a LOMC:

1. Determine the Type of LOMC Needed

Letter of Map Amendment (LOMA): Used to remove a property or structure from the Special Flood Hazard Area (SFHA).
Letter of Map Revision (LOMR): Used to update flood zone boundaries, typically due to changes in flood risk or the environment (e.g., new flood control measures or better data).
Letter of Map Revision Based on Fill (LOMR-F): Used when a property has been elevated with fill and the new elevation is above the Base Flood Elevation (BFE), potentially removing the property from the floodplain.

2. Gather Required Documentation

To support your request, you must provide FEMA with sufficient evidence, which typically includes:

Elevation Certificate: For a LOMA or LOMR-F request, an Elevation Certificate is often required. This certificate provides precise information about the elevation of the building or property relative to the Base Flood Elevation (BFE).
Floodplain Data: Hydrologic and hydraulic data may be required, especially for LOMRs that propose changes to flood zone boundaries.
Site Plans or Survey Maps: Detailed site plans, property surveys, or boundary maps may be needed to show the property’s location relative to flood zones and floodplain boundaries.
Other Engineering Reports: If applicable, detailed engineering studies or reports that show changes in flood risk (e.g., flood control infrastructure, drainage improvements) may be necessary.

3. Complete the LOMC Request Form

Applicants must fill out a LOMC Request Form available on FEMA’s website. This form requires the applicant to provide:
- Property details (address, legal description, flood zone, etc.).
- Reason for the request (e.g., new flood data, elevation change, map error).
- Contact information for the property owner or applicant.

4. Submit the Request to FEMA

Submit the completed LOMC form along with all required documentation (e.g., elevation certificates, maps, engineering studies) to FEMA for review.
The application can typically be submitted online through the FEMA Map Service Center (MSC) or directly to FEMA’s Map Change Program.

5. FEMA Review Process

FEMA evaluates the submission to determine whether the requested map change is justified. This may include reviewing the flood data, elevations, and other technical details provided in the application.
The review process may take several weeks or months depending on the complexity of the request and the documentation provided.

6. Receive the LOMC Decision

After FEMA completes its review, it will issue a Letter of Map Change (LOMC) decision. This could be:
- Approved: If FEMA agrees with the request, the LOMC is issued, and the flood zone status of the property is officially updated.
- Denied: If FEMA does not have sufficient evidence or the request does not meet the required criteria, the LOMC will be denied.
The LOMC letter will outline the specifics of the change and provide instructions for updating local records and any flood insurance implications.

7. Implement Changes

If the LOMC is approved, the change in flood zone designation is reflected in FEMA’s flood maps. The property owner or applicant may then use the LOMC to adjust flood insurance requirements or comply with local building regulations.
Local governments may update floodplain management ordinances or development standards based on the new flood zone information.

8. Appeal Process (If Denied)

If your request for a LOMC is denied, you can appeal FEMA’s decision. This involves submitting additional supporting data or corrections to the existing information to address FEMA’s concerns.
Appeals should be submitted within a specified timeframe after receiving the denial.

Key Considerations When Requesting a LOMC:

Accuracy is Crucial: The success of your request depends on the accuracy and completeness of the documentation provided. Inaccurate data or insufficient evidence may delay the process or result in a denial.
Professional Assistance: It can be beneficial to work with a surveyor, engineer, or floodplain manager to ensure the submission meets FEMA’s technical requirements.
FEMA’s Review Time: The process can take time, often several weeks to months, depending on the complexity and completeness of the request.

By requesting a LOMC, property owners and developers can potentially reduce flood insurance costs, clarify flood risk, and avoid unnecessary floodplain development restrictions.

You can submit the following types of Letter of Map Change (LOMC) requests online through the FEMA Map Service Center (MSC):

1. Letter of Map Amendment (LOMA)

Purpose: This type of LOMC is used to remove a property or structure from the Special Flood Hazard Area (SFHA) (the high-risk flood zone). If the property is shown incorrectly on FEMA’s Flood Insurance Rate Map (FIRM) as being in a floodplain, a LOMA can be requested to remove it.
Online Submission: You can submit a LOMA request online if the property meets specific criteria (e.g., if it is shown to be elevated above the Base Flood Elevation (BFE)).

2. Letter of Map Revision Based on Fill (LOMR-F)

Purpose: This LOMC is requested when a property has been elevated using fill material to raise the ground level above the Base Flood Elevation (BFE). This change can remove the property from the floodplain, which may reduce or eliminate the requirement for flood insurance.
Online Submission: You can submit a LOMR-F request online, provided that you have documentation to prove the property has been elevated above the BFE (typically requiring an Elevation Certificate).

3. Letter of Map Revision (LOMR) (in some cases)

Purpose: A LOMR is typically requested when flood zone boundaries or flood elevations need to be changed, often due to new flood data, flood control measures, or changes in flood risk. In some cases, if the request is simple enough (such as a minor map correction or update), it may be submitted online.
Online Submission: FEMA accepts online LOMR submissions in cases where the revision involves relatively straightforward changes to flood zones or floodplain boundaries. However, more complex requests may require paper submission or additional documentation

The MT–EZ, MT–1, and MT–2 paper forms, as well as the Online LOMC submission process, are all used to request Letters of Map Change (LOMC) from FEMA, but they differ in terms of complexity, the types of changes they address, and the submission process. Here’s a breakdown of each:

1. MT–EZ Form

Purpose: The MT–EZ form is a simplified request for a Letter of Map Amendment (LOMA) or Letter of Map Revision Based on Fill (LOMR-F). It is used when the property owner believes the property is incorrectly shown in a Special Flood Hazard Area (SFHA) and is eligible for removal.
Used For:
- LOMA: To remove a property or structure from the floodplain if it is located above the Base Flood Elevation (BFE).
- LOMR-F: To remove a property from the floodplain after it has been elevated using fill material to meet or exceed the BFE.
Eligibility: Only simple cases where the request is clear and doesn’t require complicated data or studies. Typically, no engineering analysis or complex documentation is needed.
Paper Form Submission: Available in paper form (MT–EZ) or can be submitted online (for certain requests) via FEMA’s Map Service Center (MSC).
Process: If the request is straightforward, the MT–EZ form is filled out and submitted, along with necessary documentation like an Elevation Certificate for a LOMR-F. FEMA will evaluate it based on the information provided and issue a decision.

2. MT–1 Form

Purpose: The MT–1 form is used to request a Letter of Map Amendment (LOMA), Letter of Map Revision (LOMR), or Letter of Map Revision Based on Fill (LOMR-F). It is more detailed than the MT–EZ form and is used for more complex requests that may involve larger changes or additional flood data.
Used For:
- LOMA: Similar to MT–EZ but for more complex situations (i.e., cases requiring additional evidence or more detailed documentation).
- LOMR: Used when requesting changes to flood zone boundaries or flood elevations due to new flood data or changes in flood risk (such as new flood control measures or updated studies).
- LOMR-F: Same as MT–EZ but used for more detailed fill-based elevation requests.
Eligibility: This form is appropriate for cases where the flood zone change is not clear-cut, or when more data and documentation are required.
Paper Form Submission: This form is a paper submission and requires more detailed supporting documentation, such as site surveys, elevation certificates, engineering reports, or hydrologic data.
Process: A more involved process than the MT–EZ, requiring careful preparation of supporting documents. FEMA reviews the application, which may take longer.

3. MT–2 Form

Purpose: The MT–2 form is used to request a Letter of Map Revision (LOMR) or a Letter of Map Revision Based on Fill (LOMR-F) for more complex or large-scale changes. It is the most detailed of the forms and typically involves multiple properties or a broader change in flood risk.
Used For:
- LOMR: Changes to the floodplain map, including modifications to flood zone boundaries, flood elevations, or flood hazard areas, often due to infrastructure changes, improved data, or major flood control projects.
- LOMR-F: For large or more complicated fill-based elevation requests where multiple structures or substantial data may be involved.
Eligibility: Used for complex cases that involve detailed engineering studies, flood risk reassessments, or significant changes in flood mapping.
Paper Form Submission: Like the MT–1, this form requires detailed documentation, which might include engineering studies, flood modeling, hydrologic reports, and survey data.
Process: Requires the submission of a substantial amount of data, and the review process is more thorough and time-consuming. FEMA evaluates the supporting documentation before issuing the LOMR or LOMR-F.

4. Online LOMC (LOMC Online Submission Portal)

Purpose: The Online LOMC submission process allows property owners to request certain LOMCs directly through FEMA’s Map Service Center (MSC). This process is faster, more streamlined, and is designed for less complex requests.
Used For:
- LOMA: The online portal is often used for simple LOMA requests where a property owner believes their property is incorrectly included in the floodplain.
- LOMR-F: For simpler fill-based elevation changes (provided the documentation is straightforward).
Eligibility: The online process is designed for simpler cases, such as properties that are clearly above the BFE or have been elevated with fill. If the case is too complex, FEMA will require a paper submission (MT–1 or MT–2).
Process: The online process is user-friendly, allowing property owners to fill out the necessary forms, upload supporting documentation (e.g., Elevation Certificate, survey, etc.), and submit it directly to FEMA for review. It can be completed faster than paper submissions.
Documentation: For LOMA and LOMR-F, applicants will need to provide an Elevation Certificate or other basic documentation to prove the property’s elevation or flood risk.

Key Differences:

Form Type	Complexity	Used For	Submission Method	Eligibility
MT–EZ	Simple	LOMA, LOMR-F (basic, clear cases)	Paper or online	Simple cases, limited supporting documentation (e.g., Elevation Certificate).
MT–1	Moderate	LOMA, LOMR, LOMR-F (more complex cases)	Paper submission	Requires more documentation like site surveys, elevation certificates, etc.
MT–2	Complex	LOMR, LOMR-F (larger-scale or detailed changes)	Paper submission	Requires engineering studies, hydrologic data, and extensive supporting documents.
Online LOMC	Simple to Moderate	LOMA, LOMR-F (for straightforward cases)	Online submission	Simple cases (no complex engineering data needed), faster and easier to submit.

An Elevation Certificate (EC) is a critical document that provides the elevation of a property in relation to the Base Flood Elevation (BFE), which is used to determine flood risk and insurance requirements.

The Elevation Certificate will include:

Property address and legal description.
Information about the lowest floor elevation, including basements.
The Base Flood Elevation (BFE) for the property.
The flood zone designation and the date of the FEMA map used for the assessment.
Any floodproofing measures taken for the building.
The elevation of the property relative to the BFE, which will determine flood insurance rates.

If you need the certificate for a Letter of Map Change (LOMC) or flood insurance, ensure the Elevation Certificate meets the current FEMA standards and is accurate for your property’s Base Flood Elevation (BFE).

The Elevation Certificate should be filled out by a licensed surveyor or a licensed engineer with expertise in measuring property elevation and understanding flood risk. These professionals ensure that the Elevation Certificate is accurate, complete, and meets FEMA’s standards.

The Riverine Hydrology and Hydraulics Form (Form 2) is typically used in the context of FEMA’s Letter of Map Change (LOMC) requests, especially when there are changes to floodplain boundaries or Base Flood Elevations (BFEs) along riverine (river or stream) areas. This form requires detailed hydrological and hydraulic data to assess the impact of proposed changes (such as new development, flood control measures, or revised flood risk assessments) on floodplain conditions.

Form 2 should be completed by a qualified professional with expertise in hydrology and hydraulics.

The Riverine Hydrology and Hydraulics Form (Form 2) requires detailed information, such as:

Flow data for the riverine area (typically for the 1% annual chance flood, or the Base Flood).
Hydraulic analysis of how the floodwaters behave in the area (such as flood elevations, floodway delineations, etc.).
Impact of proposed development or changes (e.g., levee construction, flood control measures, or changes to river or stream channels).
Floodplain boundary delineation, especially if the proposed change will impact the flood hazard zone as shown on FEMA’s Flood Insurance Rate Maps (FIRMs).
Base Flood Elevation (BFE) changes and how they affect the surrounding area.

The Riverine Structures Form (Form 3) should be completed by a licensed professional engineer or hydrologist with expertise in hydraulics, riverine floodplain analysis, and the impact of riverine structures on flood behavior. These professionals will assess how structures like levees, dams, and bridges affect Base Flood Elevations (BFEs), floodplain boundaries, and flood risk in riverine environments. In some cases, a Certified Floodplain Manager (CFM) may assist in reviewing or overseeing the form.

The Riverine Structures Form (Form 3) requires the professional to provide detailed information on how specific structures impact the riverine floodplain. This may include:

Impact on flood elevations: How the structure affects the Base Flood Elevation (BFE), which is the elevation expected to be equaled or exceeded by floodwaters in the 100-year flood event.
Floodplain boundaries: Changes to the floodplain boundary as a result of the riverine structure (e.g., levee, dam).
Floodway impact: Whether the structure affects the floodway or prevents floodwaters from flowing through the area as they normally would.
Hydraulic modeling and calculations: Results from hydraulic models that assess the flow of water around the structure and the resulting changes to the floodplain.
Flood risk changes: How the structure alters flood risk in the area and its potential effect on surrounding properties and infrastructure.