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Floodplain Terminology: What You Need to Know

April 4, 2022
Susanna Pho, CFM

In floodplain management there are a host of terms that are difficult to understand if they don’t inform your work on a day-to-day basis. Our team at Forerunner is comprised of individuals with wide ranging backgrounds and everyone joins with a varying degree of floodplain management knowledge, so we’re acutely aware of the learning curve involved in mapping terminology to real-world regulations and situations. To help ourselves and others, we put together this list of terms and acronyms that occur frequently in the work of our partner communities and in our product development. We’re hoping it can help you, whether you are a permitting clerk looking to brush up on floodplain knowledge, a resident trying to understand your flood risk better, or a floodplain professional looking for a resource to share with community members.

Community Rating System (CRS)

The Community Rating System (CRS) Program is a voluntary program that was created by FEMA to encourage communities to engage in flood mitigation activities. Credits for these activities are awarded to participating communities – for every 500 credits earned, communities move up one CRS Class. A CRS Class 9 community receives a 5% discount on NFIP flood insurance premium costs and a CRS Class 1 (the highest Class) community receives a 45% discount. These discounts can be quite large in communities with high flood insurance penetration – in some cases, CRS participation can result in millions of dollars in savings for flood insurance purchasers across a community. If you’re curious about the CRS, check out this blog post where we discuss considerations for participation. If your community is already participating in the CRS, you might find our CRS Guide useful.

Special Flood Hazard Area (SFHA)

If you live in a Special Flood Hazard Area (SFHA) this means that at least part of your property sits in an area with a 1 percent chance of being inundated by flood waters in any given year. Within the SFHA, there are different zones that correspond to different types of hazards. These are called flood zones. There are many different flood zones but the ones that are most common are:

  • X: Areas subject to flooding by the 0.2-percent annual chance flood event. These are considered to be lower risk than A, AE, V, and VE zones and are not included in the Special Flood Hazard Area (SFHA)
  • A: Areas subject to inundation by the 1-percent annual chance flood event that don’t have Base Flood Elevations (BFEs) calculated. Sometimes A zones are called “Approximate A” zones.
  • AE: Areas subject to flooding by the 1 percent annual chance flood event that have Base Flood Elevations (BFEs) calculated (the E in AE stands for “elevation”!). Coastal AE zones also exist. These are areas of special flood hazards extending inland to the limit of the 1.5-foot breaking wave.
  • V: Areas along coasts subject to inundation by the 1-percent annual chance flood event with additional hazards associated with storm-induced waves.
  • VE: Areas along coasts subject to flooding by the 1-percent annual chance flood event with additional hazards associated with storm-induced waves. These are different from V zones in that (like AE zones) they have Base Flood Elevations (BFEs) calculated.

The SFHA is what must be regulated through floodplain management in order for your community to participate in the National Flood Insurance Program (NFIP). If that’s confusing, think of it like this: the Special Flood Hazard Area (SFHA) is the area of concern for the National Flood Insurance Program (NFIP). Determining whether or not a structure sits within a SFHA can be difficult for those not well-versed in reading flood maps. To help with this, Forerunner has a series of internal and public-facing tools to better communicate and document flood risk. Using the FEMA Flood Map Service Center is also a great first step in figuring out a property’s flood risk level.

Elevation Certificates (ECs)

Elevation Certificates are surveyor completed forms that document a structure’s flood risk. They play a big role in helping floodplain managers evaluate development for compliance and are often required as part of the construction permitting process in Special Flood Hazard Areas (SFHAs). Until recently, ECs were also used as a primary document for rating NFIP flood insurance policies. While Risk Rating 2.0 has changed this, ECs still play an important role in helping individuals advocate for lower premiums.

For communities participating in the Community Rating System (CRS), a minimum requirement of participation involves a yearly review of new Elevation Certificates issued. If clerical or surveying errors are found on the form, the community risks losing its CRS Class as well as the associated discount on flood insurance for its residents. We recently launched an Elevation Certificate Error Detection feature to help our partner communities ensure that their ECs are free from error, which helps them retain their CRS discount and alleviate the review burden on their floodplain management departments.

We wrote a blog post that details common errors and challenges that hinder EC accuracy, in case you’d like to dig in further.

Base Flood Elevation (BFE)

Often referred to in acronym form (BFE), you can think of base flood elevation as the elevation of surface water resulting from a flood that has a 1 percent chance of equaling or exceeding that level in any given year. This means that “homes in areas with a BFE have a 1 percent annual chance of seeing a flood reach the area’s BFE” (FEMA). The BFE can be shown on a Flood Insurance Rate Map (FIRM) for AE and VE zones (under the zone designation if available). In some areas, particularly those that experience riverine flooding, BFEs are harder to determine and require cross section interpolation or a look at the community’s Flood Insurance Study (FIS). BFEs are important to floodplain management in that they often serve as regulatory thresholds for development and building permits – in many NFIP participating communities, new construction and substantial improvement is required to have lowest floors elevated above BFE.

Limit of Moderate Wave Action (LiMWA)

The LiMWA demarcates the inland limit of the Coastal A Zone — an area of the Special Flood Hazard Area where base flood wave heights may reach between 1.5 and 3 feet. Coastal A Zones are A and AE Zones that sit between the LiMWA and a V Zone or the coast. Construction in V zones is often subjected to stricter regulations than construction in A zones. Some communities in the U.S. choose to enforce V zone design standards in Coastal A zones as a way to extend the extent of stricter V zone regulations in peri-coastal areas. It can be difficult to figure out whether or not a specific structure is in a Coastal A Zone. To make this a bit easier, Forerunner incorporates Coastal A Zone and LiMWA logic into our web-based dashboard. The LiMWA can also be identified using FEMA’s Map Service Center.

Substantial Improvement/Substantial Damage (SI/SD)

In NFIP participating communities, local governments are required to enforce minimum floodplain standards for new construction and substantial improvements. Substantial Improvements are defined as any reconstruction or additions made where the cost of these changes are equal to or exceed 50% of the market value of the building before the construction began. Substantial Damage is a type of Substantial Improvement. While we typically use 50% of market value threshold to determine whether or not a substantial damage applies, the damage cost is determined as the amount of money needed to return a structure to its pre-damage state.

FEMA’s Substantial Improvement/ Substantial Damage Desk Reference is a great comprehensive resource to understand SI/SD and how it may apply to your own property. We have also published an SI/SD guide on our website that offers a more in-depth breakdown of the topic.  

CAV/CAC: Community Assistance Visit/Community Assistance Contacts

CAVs/CACs (or Community Assistance Visits/Contacts) are pre-determined visitations by FEMA staff members to participating NFIP communities to provide technical assistance and ensure compliance with federal requirements. “A CAV consists of a tour of the floodplain, an inspection of community permit files, and meetings with local appointed and elected officials” (FEMA). These community visits allow officials to address any administrative issues or violations that residents are later notified of and provided with the opportunity to rectify. Once deadlines are established, residents within a community have a period of time to act accordingly or it can impact their community’s standing in the program.

CACs are different from CAVs in that they are much less comprehensive and typically involve checking-in with communities in good standing over the phone. FEMA utilizes a risk-based approach to determine whether a community needs a CAV or CAC and this is based on the community’s flood risk. Conversations involved in a CAC allow for FEMA or the NFIP State Coordinator to understand if the floodplain management program is being implemented efficiently and effectively.

LFE: Lowest Floor Elevation

Defined by the National Flood Insurance Program, the lowest floor elevation identifies the lowest enclosed area in a property. This can include the basement or, if you do not have a basement, the main/first floor of your home. Floodplain managers often use the LFE as the elevation for enforcing regulations. For example, in an AE zone a structure’s LFE will likely have to be elevated above the site’s BFE. While this elevation is immensely important for regulation, it can be fairly complicated to determine a structure’s LFE. It’s identified using a structure’s Elevation Certificate and the complex logic found in FEMA’s Lowest Floor Guide. To help alleviate some of the burden of determining the LFE, Forerunner automatically identifies the LFE for structures with ECs for our partner communities.  

Letters of Map Change (LOMC)

LOMCs are FEMA-issued documents that signify the acceptance of a request to alter a community’s Flood Insurance Rate Map (FIRM). The documentation needed to successfully complete this request may include surveys, maps, engineering studies, elevation certificates, or photographs of the property. LOMC documents include Letters of Map Amendments (LOMAs), Letters of Map Revision (LOMRs), and Letters of Map Revision Based on Fill (LOMR-Fs). These documents recognize any changes with a property’s placement within a floodplain and can help to correct any inaccuracies with mapping. They are often acquired by property owners wanting to remove the flood insurance purchase requirement for an area or to change the construction requirements for a property. To find copies of LOMCs you can contact your local building officials, zoning administrators, or FEMA. If you are curious about the process of submitting an LOMC and which document applies to your property, the LOMC webpage on the Wisconsin Department of Natural Resources’ website is a great comprehensive resource.


Sometimes communities want to go above and beyond enforcing minimum floodplain standards by requiring that new construction and substantial improvement is constructed well above a property’s base flood elevation (BFE), instead of at BFE. A common way of doing this is adopting a freeboard requirement. Freeboard is an additional elevation amount added to the BFE as a factor of safety. It can help ensure that new construction is built high enough to accommodate things like future sea level rise. This can be confusing, so here’s an example: If a community doesn’t have a freeboard requirement and a new house is constructed on a site with a BFE of 2 ft, the lowest floor of the house will just have to sit at 2 ft elevation according to NFIP minimum standards. If that community has a 3 ft freeboard ordinance, however, that same house would have to be built at 5 ft elevation (2 ft BFE + 3 ft freeboard).

At Forerunner, our work is centered on enabling better compliance and communication in our partner communities. If you are interested in our work and our mission, please feel free to check out our other blog posts or subscribe to our monthly newsletter to receive product updates and hear about what we have been up to!


Substantial Damage Desk Reference

FEMA Flood Map

Home Builder’s Guide to Coastal Construction

The Forerunner Guide to Substantial Improvement and Substantial Damage

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