This page contains answers to questions compiled from actual public questions about FEMA's coastal flood risk mapping and mitigation policies and activities.
Where FEMA shares responsibility with another Federal agency, they have been engaged in preparing the response. If you have a question that has not been answered here, please call 1-877-FEMA-MAP (1-877-336-2627) or e-mail FEMAMapSpecialist@riskmapcds.com.
Coastal Flood Hazard Mapping Questions
- Why did FEMA choose the 1-percent standard?
- I have never seen a flood here. Why is this area shown as a high risk flood zone?
- A recent hurricane hit near my house and it didn’t flood; are you sure these maps indicate the current flood risk in my area?
- What is the difference between a Zone VE and a Zone AE flood hazard designation?
- How does the preliminary map issuance change my flood insurance rate?
- Why does FEMA map coastal flood hazards?
- Why is FEMA creating new coastal maps when there are so many other public priorities?
- What different methodologies are used in performing coastal studies and why?
- Why are there multiple flood studies occurring in my community?
- Are the flood hazards shown on the Flood Insurance Rate Map based on historic coastal flood events?
- How accurate are coastal flood study results?
- How can coastal flood studies be made more accurate?
- If there is a margin of error in coastal flood studies, how can FEMA be sure that its flood insurance mandatory purchase requirement is not being applied to structures outside the Special Flood Hazard Area (SFHA)?
- At what scale are coastal flood studies performed?
- Are the flood study results appealable?
- Is it possible for community officials or individual property owners to appeal a coastal study when FEMA used supercomputers to obtain the results presented on the Flood Insurance Rate Map (FIRM)?
- Why isn't FEMA using the latest two-dimensional wave models to estimate wave effects over land?
- Why is the Base Flood Elevation (BFE) near my property different than the BFE near my neighbor’s property?
- What is the Limit of Moderate Wave Action (LiMWA)?
- How is the LiMWA mapped?
- How should I build in areas near the Limit of Moderate Wave Action (LiMWA)?
- Does the LiMWA impact flood insurance premiums?
- What is a Primary Frontal Dune (PFD)? How are the PFD lines drawn?
- How long does it take to conduct a coastal flood study?
- Why does a coastal study take so long?
- What stakeholders are involved in conducting a coastal flood study?
- Why is the modeling for a coastal study so complex?
- How long is the appeal process and compliance period?
- How is FEMA accounting for sea level rise and climate change on the FIRMs? Does sea level rise/climate change affect the FIRMs?
- How are the FEMA maps different from NOAA’s inundation/evacuation maps?
- Why isn’t our beach nourishment and/or dune construction project included in the coastal map study analysis and resulting mapping?
- How do you assure that the analysis includes enough information to depict the flood risk near my home?
- What is the Joint Probability Method?
- What is a synthetic storm?
- Does FEMA include tsunamis on the flood hazard maps?
- What is the Coastal Barrier Resources System (CBRS)?
- What is the CBRS digital conversion project?
- Why shouldn’t the FIRM be used to make CBRS determinations?
- Why are you mapping the Great Lakes now when lake levels are low?
- Why did FEMA remove some survey benchmarks?
- Why am I in the mapped SFHA if my house is on a dune above the BFE?
- Are extensive engineering studies needed in order to obtain a Letter of Map Amendment (LOMA)?
The base (1-percent-annual-chance, or 100-year) flood standard was adopted for the National Flood Insurance Program (NFIP) after various alternatives were considered. The standard constitutes a reasonable compromise between the need for building restrictions to minimize potential loss of life and property and the economic benefits of floodplain development. The Base (1-percent-annual-chance) Flood Elevation (BFE) has been adopted by the NFIP as the basis for floodplain management and flood insurance regulations.
FEMA understands it may seem unlikely that it will flood in your community, especially as you and possibly even your neighbors, parents, or others may not ever remember flooding there. But changes in your community can send water flowing in new directions, creating flood risks that never existed before.
Be aware that every flood and every storm is different. For instance, there were some communities in Louisiana that flooded during Hurricane Isaac (2012) but did not flood during Hurricane Katrina (2005). Although Isaac was much weaker than Katrina, Isaac moved very slowly and caused flooding in areas that the faster-moving, stronger Katrina had not.
FEMA is using the latest science and technology available to make your flood maps more accurate with the ultimate goal of protecting you, your home or business, and your community from flood-related losses. FEMA is also working with your local officials to use the information in your new flood map to better plan community development and protect your community from the devastation floods can cause.
Zone AE is the area subject to inundation by the base (1-percent-annual-chance) flood event. Zone VE is also area subject to inundation from the base flood, but with additional hazards due to storm-induced velocity wave action. Base Flood Elevations (BFEs) derived from detailed hydraulic analyses are shown. Mandatory flood insurance purchase requirements and floodplain management standards apply in both zones. Read more about the different flood hazard designations.
The issuance of a preliminary Flood Insurance Rate Map (FIRM) does not impact flood insurance rates. When FEMA releases a preliminary FIRM and Flood Insurance Study (FIS) report for a community, caution must be exercised in using this data. For insurance purposes, preliminary FIRMs and FIS reports cannot be used to make official flood determinations. The currently effective FIRM is the only official document for this purpose.
However, for regulatory purposes, preliminary FIRMs and FIS reports may be used by the community. Local regulations usually allow for the use of the best available data, and in most instances, the data provided on the preliminary FIRMs is much better than the older data on the currently effective FIRMs. The use of preliminary maps as "best available data" is only allowable when the preliminary data are more conservative than the effective data; i.e. the elevations of the base (1-percent-annual-chance) flood are higher or the Special Flood Hazard Area (SFHA) is more extensive. Please contact your community's floodplain administrator to determine whether preliminary data is being used by your community and whether it has any impact on construction or other use of your property.
Coastal flood maps represent “snapshots” of flood risk for a local area at the time the study was performed. Flood maps can become obsolete as physical conditions change, or as our understanding of local flooding and flood effects improves. Obsolete flood maps have consequences for life safety (individuals may be living at risk and not know it), insurance reasons (flood insurance premiums may no longer reflect actual flood risk) and for land use and building permit reasons (development, building design, and post-flood recovery decisions are no longer tied to the nature and severity of flood hazards). Thus, it is in the best interest of the community and its citizens to maintain up-to-date flood hazard maps.
New flood studies are undertaken and flood maps are updated for a number of reasons, including:
Better topographic data;
A longer period of record to characterize coastal flood events;
Improved flood modeling procedures; and
Changes in land use and land characteristics, shoreline erosion, construction of flood barriers, etc.
According to FEMA’s records, eight of the top 10 most expensive disasters in our Nation were caused by hurricanes. During these disasters, thousands of homes were destroyed, lives were disrupted, and many people were killed. Understanding coastal risks and then taking steps to make our homes and communities more resilient makes sense both on an economic and human level.
FEMA recognizes that communities have many priorities competing for their time, attention, and funding. FEMA also believes that public safety is a top priority of all communities. Understanding the flood risk for a community and taking action to mitigate that risk saves lives, property, and the heartache caused by a flood.
Coastal flood study methods and the specific modeling software used are tailored to the coastline characteristics and the nature of coastal flood events. For example, the Wave Height Analysis for Flood Insurance Studies (WHAFIS) model is used for analyses of low-lying areas subject to overland flooding and waves. However, WHAFIS is not appropriate for analysis of coastal dune or bluff areas that are subject to erosion and wave runup; other procedures and models are used in these areas. Some studies consider hurricane effects while others consider northeasters or Pacific storms or tsunamis; some studies consider multiple flood types. Great Lakes studies consider fluctuating lake levels and ice cover.
However, all coastal flood studies:
Include the effects of tides, storm surges and waves;
Consider historical coastal flood events that have affected the study area;
Use historical data to validate flood, wave and erosion analyses; and
Determine the flood level with a 1-percent chance of being equaled or exceeded in any given year.
In the late 1990s through the mid-2000s, FEMA made a significant effort to convert paper maps into a digital format to increase their usefulness in flood risk analyses and associated flood risk mitigation efforts. In recent years, as part of the initiation of the Risk Mapping, Assessment, and Planning (Risk MAP) program, FEMA is investigating entire watersheds instead of individual counties because this made the most sense scientifically. Floods do not stop at political boundaries.
Although new maps may have been issued recently, much of the underlying study information in coastal areas across the U.S. has not been updated for decades. In recent years, FEMA has initiated studies along the entire populated U.S. coastline because of the significant and sometimes dangerous flood risks along the coast. Where possible, FEMA has combined these studies, but in some cases studies have overlapped. FEMA requests your patience and support as we seek to better understand this country’s coastal flood risks, and equip communities and families with appropriate information so they may protect themselves from catastrophic loss.
For coastal flood hazard mapping, the existing repository of historical observational data (e.g. hurricane winds and barometric pressure, high-water marks, wave conditions, pre- and post-storm beach profiles) is relatively small, and therefore insufficient for use in predicting coastal flood elevations. As a result, when performing coastal studies, FEMA and mapping partners rely more heavily on the modeling of wave and erosion processes and storm surge (water that is pushed toward the shore by the force of winds swirling around a storm) to predict coastal flood elevations.
FEMA works to create the most accurate FIRMs possible. Accuracy can be impacted by the quality of the underlying data, and the assumptions and approximations that must be made when conducting a coastal study. The accuracy of a coastal study depends directly on several parameters:
The accuracy and resolution of data (i.e. topographic, bathymetric, wind, and water level data);
The length of the historical water level and wave records;
The incidence and severity of coastal flood events affecting the study area; and
The number and quality of coastal flood high water marks and hydrographs (used to calibrate computer models used in the study).
In an effort to improve the accuracy and resolution of topographic and bathymetric data, FEMA and mapping partners (U.S. Army Corps of Engineers, National Oceanic and Atmospheric Administration, and others) are using Light Detection and Ranging (LiDAR) technology to gather data for many coastal studies. This topographic collection approach represents a higher level of accuracy over traditional methods.
Study accuracy also depends on:
The resolution of the computer model grids and the ability of the grids to duplicate small-scale topographic, bathymetric, and land use features;
The ability of the modeling schemes and algorithms to capture the physics of water flow, wave mechanics, and in some cases, erosion of dunes during the base flood; and
The ability of statistical procedures to estimate the 1-percent-annual-chance flood conditions with a high degree of confidence.
Because of the wide variety of factors that affect study results, no single benchmark exists for assessing study accuracy.
FEMA readily shares methodology and data, and welcomes new information that will make the mapped flood hazard information even more accurate. It is important to note, however, that even when SFHAs are mapped with high precision for existing conditions, new residential and commercial development and natural changes in weather patterns may, over time, change conditions sufficiently to require a restudy to update the study to the new conditions.
If there is a margin of error in coastal flood studies, how can FEMA be sure that its flood insurance mandatory purchase requirement is not being applied to structures outside the Special Flood Hazard Area (SFHA)?
FEMA’s coastal flood studies and coastal flood hazard mapping, like all other hazard studies and maps, are not perfect. Some uncertainty will always be associated with Special Flood Hazard Area (SFHA) limits and Base (1-percent-annual-chance) Flood Elevations (BFEs). Through our modeling procedures, FEMA strives to reduce the uncertainty and to calculate the average of the likely range of BFEs.
In other words, the elevations and lines shown on the FIRMs are just as likely to under-predict the true 1-percent-annual-chance flood conditions as they are to over-predict them.
Please note that flood risk exists even for structures located outside the SFHA. Past floods have exceeded the 1-percent-annual-chance flood and future floods may as well. About one in five NFIP claims come from property owners whose structures are located outside the mapped SFHA.
Often the coastlines of entire states or an entire area, such as the Great Lakes, are included in one coastal study. Due to the large scale of FEMA’s coastal flood studies, many are performed using clusters of high-powered computers to calculate components (e.g. storm surge, wave conditions) of a coastal flood. Such computing power is necessary to capture the physics of water moving over highly detailed topography and bathymetry.
The computer models calculate water levels and wave effects in areas that can be several hundred miles across, at hundreds of thousands (or sometimes millions) of points every few seconds during each simulation. Typically, 100 to 200 storms or coastal flood events are simulated for a coastal flood study.
FEMA is sensitive to the needs of property owners and community officials who believe the flood hazard information shown on a new or updated FIRM or accompanying Flood Insurance Study (FIS) is incorrect. Therefore, the study procedures, data, and results are documented throughout a coastal flood study and are available for review by those individuals or communities considering an appeal.
Although it is true that replicating an entire coastal flood study will be time-consuming and expensive, a review of the study documentation can help focus an appeal on certain aspects of the study, including, but not limited to, the following:
Quality of the topography and bathymetry used in the models;
Validation of the models using historical flood events;
Selection of flood events modeled;
How those events are parameterized in the models;
Methods by which water levels from individual simulations are combined statistically; and
Overland wave hazard modeling.
The first and last items listed above (topography and overland wave hazard modeling) have a significant influence on the Base (1-percent-annual-chance) Flood Elevations (BFEs) and Special Flood Hazard Area (SFHA) boundaries and/or zone designations (Zones VE or AE) produced by a coastal flood study, and do not require high-powered computers and sophisticated models to appeal. In fact, challenging results based on these two items is no more complicated today than it was before the advent of supercomputers. Many appeals and revision requests are still submitted and granted using local topographic data, desktop computers, and readily-available models.
The latest models resolve the flow of water or waves in two horizontal directions, and they are referred to as 2-D models. Simpler, 1-D models resolve flow or waves in one direction. Each has advantages and disadvantages. For now, FEMA uses both types of models. It uses 2-D wave models in the ocean and in bays, and a 1-D model—Wave Height Analysis for Flood Insurance Studies (WHAFIS) – over land.
On a large scale, 2-D wave models offer certain advantages over simplified wave analyses—the 2-D models better capture the physics of wave propagation, account for waves changing direction in response to bathymetric features.
However, the 2-D models still have some unresolved technical and computational issues related to overland wave propagation:
The 2-D wave models do not have the resolution required to capture small details and changes in topography and land use/land cover. Grid cells are usually hundreds of feet across, and physical features must be smoothed or averaged over each grid cell. Using smaller grid cells on land necessitates using smaller time steps in the model and drives up the time and cost required to complete the analysis.
The 2-D models lack a robust method for calculating wave dissipation effects (of vegetation, buildings and other obstructions) comparable to the procedures developed for FEMA’s 1-D (WHAFIS) method.
WHAFIS captures the key aspects of waves moving along a specified transect over land and has been used successfully applied to many flood studies and flood map revisions.
The use of WHAFIS on land does not eliminate the use of 2-D wave models seaward of the shoreline. 2-D wave models are still used by modern flood studies to transform waves from deep water to the shoreline, at which point the 2-D wave characterization can be used as an input to WHAFIS. WHAFIS will be eventually be replaced as 2-D models become able to handle topography and development characteristics on a finer scale; but until that time, FEMA will continue to use WHAFIS.
Please also note that Letters of Map Revision (LOMRs) that are based on better topography or changed site conditions can now be carried out with relatively little effort and at modest cost using WHAFIS. Use of a 2-D overland wave model would make these map revisions more challenging and expensive. At some point in the future, when 2-D models overcome the technical issues mentioned above, and as their use becomes more widespread, flood studies and flood map revisions using the 2-D overland wave models will become feasible.
Even a small difference in the 1-percent-annual-chance water level or wave height can change a BFE from one whole foot to another. Larger differences in BFEs can result when:
The scale of the Flood Insurance Rate Map (FIRM) prevents mapping every whole foot BFE (flood zones would be too narrow to see on the FIRM) so BFEs are mapped two or more feet apart; and
In instances where wave run-up determines BFEs, changes in dune/bluff/structure slope can result in adjacent BFEs that have differences of several feet.
The Limit of Moderate Wave Action (LiMWA) is the location where the 1-percent-annual-chance wave height equals 1.5 feet. FEMA began showing the LiMWA on Flood Insurance Rate Maps to communicate the higher risk that exists in the area. Because the 1.5-foot breaking wave in the LiMWA zone can potentially cause foundation failure, communities are encouraged to adopt building construction standards similar to Zone VE in those areas.
Residents and business owners living or working in the LiMWA zone should be aware of the potential wave action along with floating debris, erosion and scour that could cause significant damage on their property. They are encouraged to build safer and higher to minimize the risk to life and property.
To learn more about LiMWA and other coastal flood zones, view the Coastal Zones/LiMWA animation.
Like any other Base (1-percent-annual-chance) Flood Elevation (BFE) zone break or Special Flood Hazard Area (SFHA) boundary on a coastal FIRM, the LiMWA’s position is calculated along overland wave propagation analysis transects, and interpolated between the transects. Transect locations are selected so they are representative of topographic and land use/land cover characteristics on either side. Interpolation takes these same factors into consideration.
Building codes use the LiMWA to identify the “Coastal A Zone” (e.g., the area where base flood wave heights are between 1.5 and 3 feet), where certain design and construction requirements are instituted. Because of the presence of damaging waves, VE Zone design, construction, and certification practices are recommended, though not required by the National Flood Insurance Program, in the LiMWA. Recommendations include:
Use open foundations (pile or pier) designed to resist all base flood conditions (waves, high velocity flow, erosion and scour, floodborne debris);
Since waves and debris will be impacting the floor joists and other foundation elements during the base flood, elevate the bottom of the lowest horizontal structural member supporting the lowest floor above the base flood wave crest elevation;
Use flood-resistant materials above the level of the walking surface of the lowest floor in the event that future flooding exceeds the lowest floor level;
Assure that connections between the foundation and the elevated building are capable of withstanding simultaneous wind and flood forces;
Use the space below the lowest horizontal structural member for parking, access, or storage only. Adding sufficient freeboard to allow parking beneath the building will not only reduce future flood damages, but will also lower flood insurance premiums; and
Use screens or latticework if space below the elevated floor must be enclosed.
No. The LiMWA currently has no bearing on flood insurance premium rates. Zone AE areas that are both seaward and landward of the LiMWA will be rated the same for flood insurance purposes.
A PFD is defined as a continuous or nearly continuous mound or ridge of sand with relatively steep seaward and landward slopes immediately landward and adjacent to the beach and subject to erosion and overtopping from high tides and waves during major coastal storms. The inland limit of the primary frontal dune occurs at the point where there is a distinct change from a relatively steep slope to a relatively mild slope.
Areas designated as Zone VE, by definition, must at a minimum extend to the inland limit of the PFD. Primary frontal dunes are mapped as Zone VE because of their important role as the first line of defense against flooding. The Zone VE designation ensures that dunes are not subject to manmade alterations in a way that could increase potential flood damage. The Zone VE designation also reflects the potential risk of erosion and undermining of structures that exists for primary frontal dunes.
Taken as a whole, the mapping process, from inception to final map adoption, can take several years.
There are three primary reasons for the length of a study from project inception through final map adoption:
Coordination with multiple stakeholder groups;
Complex modeling; and
The appeal process and compliance period.
It is important for our Nation to have accurate flood hazard information. This information is used by communities to plan for disaster resiliency and by individual property owners to protect themselves and their assets. Coastal flood studies are complicated and many stakeholders may be involved in their development, including:
Other Federal agencies such as the U.S. Army Corps of Engineers, National Oceanic and Atmospheric Administration, U.S. Geological Survey, or U.S. Fish and Wildlife Service;
Multiple State agencies including the State National Flood Insurance Program (NFIP) Coordinator, the State Hazard Mitigation Officer, State emergency managers, State dam safety officials, and others;
Regional authorities such as water boards and planning commissions;
Several local community officials including the local floodplain administrator, planning/zoning officials, emergency managers, and Chief Executive Officers (e.g. Mayors, City/Town Managers, County/Parish Executives and their communications staff); and
Private sector and non-profit organizations who are also interested in the coastal FIRMs, especially engineers, environmental scientists, surveyors, realtors, developers, mortgage bankers, and the non-profit organizations that support them such as universities and professional societies.
Because coastal studies can involve the entire coastline of a state or multiple states as in the case of the Great Lakes Coastal Flood Study, the number of stakeholders who have an interest or relevant information for the study is multiplied dramatically. FEMA must engage hundreds or even thousands of communities. This coordination takes time, but FEMA believes the ultimate product is improved with their involvement.
In addition to the stakeholder engagement and coordination needed, coastal studies are technically complex. Coastal flood studies use sophisticated computer models and complex statistical analyses covering areas that are hundreds of miles across, capturing detailed ground elevations, land characteristics, and modeled surge and waves.
Gathering and formatting the input data requires attention to detail and exacting quality control. Running the models and checking the outputs requires time. Translating the verified outputs into Special Flood Hazard Areas (SFHAs) and Base (1-percent-annual-chance) Flood Elevations (BFEs) is the next step, which is guided by FEMA’s guidelines and standards. Draft maps must be checked carefully (and revised, when necessary) before Preliminary versions of FIRMs are created and distributed to communities and other stakeholders. Everything must be documented and reviewed.
Once a preliminary FIRM is produced and distributed, the review and appeal period can extend for one year or more. After a standard review and comment period, a meeting is scheduled by FEMA’s Regional Office staff and community officials. Unless significant technical concerns are raised before or during that meeting, FEMA will then initiate a statutory 90-day appeal period whenever new or revised flood hazard information is proposed. During this period, community officials and property owners have the opportunity to submit appeals and comments regarding the BFEs shown on the preliminary FIRM or in the accompanying FIS report. When the 90‑day period is complete and all appeals have been resolved, a six-month “adoption/compliance” period begins. During this time, the community enacts any new or modified floodplain management ordinances required for participation in the National Flood Insurance Program.
FEMA maps coastal flood hazards based on existing shoreline characteristics, and wave and storm climatology at the time of the flood study. In accordance with the current Code of Federal Regulations, FEMA does not map flood hazards based on anticipated future sea levels or climate change. Over the lifespan of a study, changes in flood hazards from sea level rise and climate change are typically not large enough to affect the validity of the study results.
In accordance with the Biggert-Water Flood Insurance Reform Act of 2012, FEMA is to establish a Technical Mapping Advisory Council that will provide recommendations to FEMA on flood hazard mapping guidelines—including recommendations for future mapping conditions, the impacts of sea level rise and future development. FEMA will be required to incorporate future risk assessment in accordance with the recommendations of the Council.
The Flood Insurance Rate Maps (FIRMs) produced by FEMA and the Hurricane Inundation/Evacuation Maps produced by the National Oceanic and Atmospheric Administration’s (NOAA) maps are fundamentally different. NOAA’s Hurricane Inundation/Evacuation Maps depict areas that are subject to hurricane surge inundation for established storm intensities (usually the Saffir-Simpson scale). The FIRMs depict the areas subject to inundation by the 1-percent-annual-chance flooding and the water surface elevations having a 1-percent-annual-chance of exceedance.
There are no consistent probabilities of flooding associated with the NOAA inundation/evacuation maps. There are no storm categories associated with FIRMs. There are also differences between the models and the underlying methodologies. For example, NOAA’s maps do not incorporate wave effects while FIRMs do.
Thus, there is no direct or consistent comparison between Special Flood Hazard Areas (SFHAs) shown on FIRMs and surge inundation areas shown on Hurricane Inundation/Evacuation Maps; or between Base Flood Elevations (BFEs) and water elevations produced by NOAA’s SLOSH (Sea Lake and Overland Surges from Hurricanes) model. For example, the area flooded by the base flood at one location may be roughly equivalent to Category 2 hurricane inundation, but at another nearby area, it may be closer to a Category 1 inundation or a Category 3 inundation.
Beaches are dynamic in nature as they are likely to continue to erode over time due to winds and waves, which reduces the effects of nourishment projects on flood hazards landward of the beach. Therefore, without regular maintenance, a raised or widened beach is only temporary. When coastal flood hazard mapping studies are performed, FEMA takes beach nourishment projects into consideration only when the project is significant (i.e., has the dimensions necessary to affect 1-percent-annual-chance flood hazards) and will be maintained for many years. Dunes are also dynamic as they are subject to erosion, overwash, and could be washed away during major storms. Many nourishment projects incorporate a dune – either new or rebuilt – at the landward edge of the beach, although in some cases dunes are enlarged or constructed separately.
Not all nourishment projects will affect the 1-percent-annual-chance flood hazard – either because the project is small, the dune lacks vegetation, the community cannot demonstrate a commitment to future maintenance, or other reasons. FEMA’s experience evaluating these projects shows:
Many nourishment projects have beach elevations that are too low to alter upland wave hazards;
One-time projects without assurance of future maintenance will only have a temporary effect on flood hazards; and
Newly constructed dunes lack long-standing vegetation, making them more susceptible to erosion.
In order to assure that the analysis includes enough information to accurately depict the flood risk as accurately as possible, FEMA uses the Joint Probability Method.
The Joint Probability Method (JPM) is a statistical approach to determine extreme water levels based on a large number of combinations of storm parameters. This is the primary method used to predict the 1-percent-annual-chance storm surge elevation for a coastal flood study. The JPM describes tropical storms using five or six parameters (central pressure, storm size, forward speed, direction, point of landfall or exit or closest approach, and wind speed variation with distance from storm center). Probability distributions are developed for each of the parameters based on local climatology. All possible parameter combinations are simulated using a hydrodynamic model constructed to faithfully represent the bathymetry, topography, and ground cover of the study area.
The JPM was developed in 1975 and has been modified since that time. The most recent modification was to optimize the parameterization of storm characteristics and reduce the number of storm simulations that must be performed to estimate 1-percent-annual-chance flood levels; this method is known as JPM-OS (Joint Probability Method – Optimal Sampling).
A synthetic storm is a hypothetical storm that is created using combinations of storm parameters derived from the historical storm record. Because severe coastal storms tend to occur infrequently in a given local area, observed storms do not capture all plausible combinations of important storm parameters. Synthetic storms are created to capture this variability by sampling the statistical distributions of observed storm parameters, and combining these to create additional storms for coastal flood study simulations.
Depending on the study area, tsunami flooding could be a contributor to the 1-percent-annual-chance flood event. In those specific areas, tsunamis have been included in the FEMA flood hazard analysis. Typically, tsunami flooding has a longer recurrence interval than the 1-percent-annual-chance event and therefore is not included in most FEMA Flood Insurance Studies. Check with your local community or FEMA Regional Office to determine if tsunamis are included in your study.
The Coastal Barrier Resources Act (CBRA) of 1982 established the John H. Chafee Coastal Barrier Resources System (CBRS), a defined set of coastal barrier units located along the Atlantic, Gulf of Mexico, Great Lakes, U.S. Virgin Islands, and Puerto Rico coasts. These areas are delineated on a set of official maps that are maintained by the Department of the Interior through the U.S. Fish and Wildlife Service (FWS). Most new Federal expenditures and financial assistance, including Federal flood insurance, are prohibited within the CBRS. CBRA does not prevent development, and it imposes no restrictions on development conducted with non-Federal funds. Congress enacted CBRA to minimize the loss of human life, wasteful Federal expenditures, and the damage to natural resources associated with coastal barriers. Because of the implications of CBRA on FEMA programs (such as the National Flood Insurance Program), CBRS boundaries are also shown for informational purposes on FEMA's Flood Insurance Rate Maps (FIRMs). For more information, please visit the FWS’s CBRA website.
FWS is collaborating with FEMA to conduct a digital conversion of the CBRS maps by 2016. The CBRS digital conversion effort is being conducted concurrently with FEMA’s large-scale effort to modernize its coastal FIRMs. The digital conversion effort will accomplish the following: (1) ensure that the CBRS boundaries depicted on FEMA’s FIRMs are the same as the boundaries depicted on FWS’s official CBRS maps; (2) fulfill FWS’s responsibility under CBRA to update the CBRS maps at least once every five years to account for natural changes such as erosion and accretion (mandated by Section 3 of P.L. 101-591); and (3) replace the entire set of CBRS maps in a timely and cost-effective manner. Replacing the existing CBRS maps with more accurate and user-friendly updated maps will significantly improve the administration and implementation of CBRA, thereby reducing the number of Federal flood insurance policies, and other financial assistance, provided within the CBRS in error.
Since 2006, CBRS boundaries have been placed on updated FIRMs by FWS through an interagency agreement with FEMA. However, the CBRS boundaries shown on the FIRMs are for informational purposes only and can serve as a first alert that a property may be located within the CBRS. Until the digital conversion effort is completed for the entire CBRS (projected completion timeframe is 2016), there may be discrepancies in the depiction of CBRS unit boundaries on the FIRMs and on the official CBRS maps maintained by FWS. The official CBRS maps can be viewed and downloaded.
Because the official CBRS maps can be difficult to interpret, in November 2012, FWS released to the public an interactive CBRS mapper that can be used to help determine whether a property may be located within the CBRS. The CBRS mapper is available. The digital CBRS boundaries depicted in the mapper are the best available representations of the official CBRS boundaries and should not be relied on for determining whether a property located close to a CBRS boundary is “in” or “out” of the CBRS (i.e., the area identified within the “CBRS Buffer Zone” on the mapper). If a property is covered by or touches the “CBRS Buffer Zone”, an official determination from FWS is recommended. Information on how to request an official CBRA determination from FWS is available.
The water levels in the Great Lakes region are cyclical. While these past few years have seen lower water levels, these levels are expected to rise in the coming years based on historical trends. The flood levels used in this flood risk analysis study take the average of 50 years of data into consideration, thereby providing the most accurate depiction of the overall flood risk in your area. More information about the Great Lakes Coastal Study.
When completing detailed engineering studies, FEMA, or its mapping partners, establishes temporary benchmarks, also called elevation reference marks, in the vicinity of the floodplain to aid in data collection.
Upon publication of the studies, FEMA initially chose to include such information on the FIRMs and within the Flood Insurance Study report. However, FEMA and, in some instances, the community do not actively maintain these temporary benchmarks.
Because it cannot be guaranteed that the benchmarks have remained undisturbed, FEMA elects not to include such benchmark information on subsequent FIRM revisions. If you have difficulty locating a specific benchmark, it is suggested that you contact the community or the National Geodetic Survey for an inventory of active benchmarks.
In some VE zones, it is not uncommon to have ground elevations at or above the Base (1-percent-annual-chance) Flood Elevation (BFE), particularly along shorelines with well-developed dune fields. Having a mapped Zone VE with a BFE at or below grade seems counterintuitive, but it is possible because of two VE Zone mapping considerations:
Dune erosion: Dunes can erode during the base flood (or lesser floods), resulting in a substantial lowering of the pre-storm grade to a level below the mapped BFE. The BFE is mapped based on surge and waves passing over the lowered ground surface.
The presence of a primary frontal dune: VE zones are mapped to the inland extent (heel) of the primary frontal dune. The BFE on the seaward face of the dune will be extended as a horizontal line from the seaward toe, through the dune feature, to the location of the heel.
It is not FEMA’s intention that homeowners pay for extensive engineering studies to obtain supporting documentation for a LOMA request. For most LOMA requests, the only elevation information that must be submitted is the Lowest Adjacent Grade (LAG) – the elevation of the lowest ground touching the structure, including stairs, attached deck, or garage – or the lowest lot elevation, which must be certified by a licensed land surveyor or professional engineer who is authorized by State or local law to certify elevation information. You may find it less expensive to provide the certified LAG or lowest lot elevation in a letter from a professional surveyor or engineer or to complete Section B of the MT-EZ forms packet, than to obtain a complete property survey or Elevation Certificate. You may also wish to contact the FEMA Map Information eXchange, toll free at 1-877 FEMA MAP (1‑877‑336‑2627) for assistance with the LOMA process. Interested applicants can apply for LOMCs online.
Coastal Floodplain Management Questions
- What are some mitigation actions that coastal communities can take?
- Can a community require higher BFEs to encourage higher building standards?
- My home was destroyed in a fire and my local building code official is telling me I have to elevate my replacement home due to flood concerns. My homeowners insurance will not cover the additional cost to elevate. How is that fair?
- Is it considered “new construction” if I replace my home after a disaster event?
- Can I build on my property in the floodplain?
- I can’t afford to elevate my home out of the floodplain. Is there any assistance available for me?
Mitigation is best employed at the time a coastal building is planned and designed, because that affords an opportunity to maximize mitigation benefits while minimizing mitigation costs. For new construction, mitigation efforts can best be directed at the following:
If a property owner has an existing building and wants to make it more hazard resistant, the building can be “retrofitted.” While it is preferable to design and build in a hazard-resistant method originally, there are steps an owner of an existing building can take, particularly with respect to wind and wind-driven rain resistance. Improving the flood resistance of an existing building often involves elevating the building on a new foundation.
For more information, see the wealth of information in FEMA’s building science guidance. Other helpful websites include:
Consult the building code official and floodplain administrator, as well as others with knowledge of local construction requirements and hazards. Discuss design options with a knowledgeable insurance agent—before the design is finalized—in order to maximize any insurance discounts that may be available.
Understand the risk of building along the coast and select a parcel that is not on the shoreline and preferably is not in an SFHA. If a property has not yet been acquired, select a parcel that has a stable shoreline, or if the shoreline is erosional, select a parcel with a low erosion rate; select a parcel that is large enough to accommodate construction without encroaching on sand dunes or a bluff edge; a generous setback from dunes, bluffs and shorelines is recommended.
If a property has been acquired, site the building on the portion of the parcel away from dunes, bluffs, eroding shorelines and sensitive site features. If the land is on the shoreline, consider other uses, including donating/selling the land to a land trust to keep as open space. Investigating whether there is transfer/purchase of development rights program in your community is another option to consider.
Elevate the lowest floor of the building above the Base (1-percent-annual-chance) Flood Elevation (BFE). Adding freeboard (a factor of safety usually expressed in feet above a flood level for the purposes of floodplain management) will reduce the likelihood and severity of flood damage, and will yield substantial flood insurance premium discounts.
Where appropriate, use VE Zone foundations in AE Zones. Use a deep and open foundation (piles or columns) that can resist erosion and allow flood water and waves to pass through unobstructed. This may be appropriate in areas designated as LiMWAs on the FIRM and other areas known to the community to be at high risk.
Consider maintaining natural buffers along shorelines (i.e., keep vegetation in its natural state).
Design all aspects of the elevated building to resist wind and wind-driven rain. Protect all windows, doors, and openings by using shutters or by constructing using impact-resistant glazing. Building codes have minimum design and construction requirements, but these do not necessarily translate into a wind-resistant and watertight building. Post-storm investigations often reveal deficiencies in buildings subject to less than design wind speeds.
Use a “Best Practices” design philosophy rather than a “Code Minimum” approach. Consider design and construction that meets higher standards such as those described in the Fortified program.
FEMA’s post-disaster investigations.
FEMA’s Coastal Construction Manual for a comprehensive approach to planning, siting, designing, constructing, and maintaining homes in the coastal environment.
The International Code Council website for information on I-Codes and code books.
Yes. Though participating communities are required to adopt the most current Flood Insurance Rate Map (FIRM), communities are free to regulate to higher standards than the flood hazard information shown on the latest FIRM.
In building code terms, this means adopting a design flood greater and higher than that which is shown on FEMA’s latest flood map. Some communities take new maps with lower Base (1-percent-annual-chance) Flood Elevations (BFEs) as an opportunity to require freeboard, without requiring buildings to be elevated higher than has been customary. By maintaining locally-required building elevations at or near prior BFEs, property owners may be eligible to receive substantial flood insurance premium discounts, both individually and as a community via the Community Rating System (CRS) discount points—which benefits all of its citizens.
My home was destroyed in a fire and my local building code official is telling me I have to elevate my replacement home due to flood concerns. My homeowners insurance will not cover the additional cost to elevate. How is that fair?
FEMA recognizes that communities have many priorities competing for their time, attention, and funding. FEMA also believes that public safety is a top priority of all communities. Understanding your community’s hazard risks and taking action to mitigate that risk saves lives, property, and the heartache caused by disasters.
The elevation requirement is based on the flood risk to your property. Your original home was probably built before the latest flood study and maps were completed for your area. The community adopts floodplain management regulations and periodically adopts new flood maps to minimize flood risk to development, and in return for reducing flood risk, the Federal government makes flood insurance and other assistance available to residents of the community. One such floodplain management regulation is that new construction must be elevated to the Base (1-percent-annual-chance) Flood Elevation (BFE), or higher if the community requires elevation above the BFE.
This situation arises when a homeowner in a flood hazard area does not carry flood insurance and the home is damaged by a flood. Homeowner’s insurance will not cover the cost of elevation unless the owner purchased separate coverage that pays for the costs of meeting whatever building requirements exist when a building is rebuilt. If the owner had carried flood insurance, however, the flood policy would have paid up to $30,000 toward the cost of elevation.
While it may seem unfair to have this requirement, studies have found for every $1 spent on mitigation, such as elevating above the floodplain, approximately $4 is saved in losses avoided.There may be grants or low-interest loans available that will help you rebuild at the required elevation. You should check with the community floodplain administrator.
New construction includes anything that is normally thought of as a “new” building, as well as any building that is a replacement for an existing building that is heavily damaged or destroyed, regardless of the cause (“substantially damaged” according to community and National Flood Insurance Program (NFIP) regulations). The NFIP defines substantial damage as “damage of any origin sustained by a structure whereby the cost of restoring the structure to its pre-damaged condition would equal or exceed 50 percent of the market value of the structure before the damage occurred.” The requirement that replacements of substantially-damaged buildings must be elevated to or above the BFE is central to the long-term goal of reducing flood damage in a community. Owners can continue to occupy and use non-conforming buildings until such time as those buildings are substantially damaged. After that, any replacement building must conform to the latest flood elevation requirements.
Development may take place within the SFHA if it complies with local floodplain ordinances, which must meet Federal requirements. Communities participating in the National Flood Insurance Program (NFIP) must at least require that new construction or substantial improvements of residential structures in the SFHA be elevated so that the lowest floor (including the basement) is at or above the Base (1-percent-annual-chance) Flood Elevation. A community in the NFIP must also require permits for all new development in the SFHA and ensure that the construction materials and methods will minimize future flood damage. Permit files must document how buildings were actually constructed.
The floodplain management requirements for the SFHA are designed to prevent new development from increasing the flood threat and to protect new and existing buildings from anticipated flood events. FEMA works closely with states and local communities to identify flood hazard areas and risks. When a community joins the NFIP, it agrees to adopt the required floodplain management regulations and to ensure that its enforcement procedures meet NFIP requirements. In return, the Federal Government makes flood insurance available for almost every building and its contents within the community.
Please note that communities are encouraged to adopt higher standards than those of the NFIP. Check with your local officials for information regarding your community’s specific floodplain development standards, which may include further limits on development in the SFHA.
Under the minimum National Flood Insurance Program regulations, you are not required to elevate your home out of the floodplain unless you are located within a Special Flood Hazard Area (SFHA) and if you’re making substantial improvements to your home, or if your home has been damaged and you are now required to meet certain building requirements.
The only times that you may be required to elevate your home within a SFHA is when you’re making significant improvements to your home or if your home has been severely damaged and you are now required to meet certain building requirements.
If you are required to elevate your home due to recent flood damage and you have a standard flood insurance policy, your coverage (specifically the Increased Cost of Compliance (ICC) portion of your coverage) will pay up to $30,000 to comply with your community’s building requirements if the home is damaged more than 50 percent of the market value. To learn more about ICC coverage, visit the ICC Coverage page or call your local floodplain manager or insurance agent.
Coastal Flood Insurance Questions
- Why does FEMA promote development in the floodplain by offering flood insurance?
- Why am I required to purchase flood insurance?
- When am I required to purchase flood insurance?
- Who determined that I was required to purchase flood insurance?
- What information should I bring with me to meet with a flood insurance agent?
- Can I shop around for flood insurance?
- Where can I find out more about insurance rates in my vicinity?
- Why should I purchase flood insurance?
- What can I do to get the cost of my flood insurance premium to be as low as possible?
- Are there any modifications that I can make to my home to reduce my flood insurance rate?
- How do flood insurance rates change when the new FIRMs become effective?
The National Flood Insurance Program (NFIP) does not seek to encourage unwise development in high-risk flood hazard areas. The NFIP was created by Congress to offer flood insurance in return for participating local community's adoption and enforcement of flood-resistant design and construction standards. The NFIP program is estimated to save the Nation $1.6 billion annually in avoided flood losses.
Congress changed the law in 1973 to mandate flood insurance coverage for many properties. Since this time, Federally regulated lending institutions cannot make, increase, extend, or renew any loan secured by improved real property located in a Special Flood Hazard Area in a participating community, unless the secured building and any personal property securing the loan were covered for the life of the loan by a flood insurance policy. Changing the law was necessary because, after major flooding disasters, it became evident that relatively few individuals in eligible communities who sustained flood damage had purchased flood insurance.
In accordance with the Flood Disaster Protection Act of 1973 and the National Flood Insurance Reform Act of 1994, flood insurance is required for all structures in a Special Flood Hazard Area (SFHA) that carry a home mortgage loan backed by a federally regulated lender or servicer. For virtually every mortgage transaction involving a structure in the United States, the lender reviews the current National Flood Insurance Program maps to determine the property’s location relative to the published SFHA. This review occurs anytime a Federally backed loan is can made, increased, extended, or renewed.
The mortgage lender, or a determination company hired by the mortgage lender, typically determines whether a structure is in a SFHA, and if flood insurance is required. If they determine that a home or business is located in a high-risk area, they then inform the owner or potential buyer that flood insurance is required to receive the loan.
If you have an elevation certificate, which verifies the elevation of the lowest floor of your house, you should bring it with you for any meeting with a flood insurance agent. This is especially important if your house/building is in a Special Flood Hazard Area, since rates in SFHAs can vary depending on how high your building is relative to the Base (1-percent-annual-chance) Flood Elevation. Visit floodsmart.gov for a list of questions to bring to your meeting.
The National Flood Insurance Program is a Federal program offering flood insurance that can be purchased from most leading insurance companies. Rates are set and do not differ from company to company or agent to agent.
Go to www.FloodSmart.gov to rate your risk, estimate your premiums, and find an agent in your area.
Just a few inches of water from a flood can cause tens of thousands of dollars in damage. From 2007 to 2011, the average residential flood claim amounted to almost $30,000. Flood insurance is the best way to protect yourself from devastating financial loss. Flood insurance is available to homeowners, renters, condo owners/renters, and commercial owners/renters. Costs vary depending on how much insurance is purchased, what it covers and the property's flood risk.
FEMA knows that flood insurance, especially when it becomes required unexpectedly, may be difficult for people to afford. Flood insurance helps protect you from the financial burden that flooding can cause – the average flood insurance claim from 2007 to 2011 was around $30,000. There are things you can do to make flood insurance as affordable as possible:
Increase your deductible (if allowed by your lender); and
Purchase an elevation certificate that provides details that can help determine how to reduce the flood risk specific to your home or business. This involves hiring a surveyor to visit your property. Your insurance agent or local floodplain administrator can then use your elevation certificate to help identify opportunities to protect your home from flooding and reduce your insurance premium (e.g., installing flood vents, removing an enclosure, etc.).
Also, if your community participates in the National Flood Insurance Program’s Community Rating System (CRS), you could qualify for a flood insurance discount of between five and 45 percent if your property is in the Special Flood Hazard Area. Communities that participate in CRS may also have elevation certificates on file for individual homes or businesses. Check with your tax assessor’s office or planning and zoning commission to determine if an elevation certificate is available for your home or business.
Your insurance agent can help you work through all of the options to make sure your payments are as low as possible. Visit www.FloodSmart.gov or call 1-888-379-9531 to learn more about flood insurance.
Yes. If a property owner has an existing building and wants to make it more hazard resistant and reduce flood insurance premiums, the building can be “retrofitted.” While it is preferable to design and build in a hazard-resistant method originally, there are steps an owner of an existing building can take, particularly with respect to wind and wind-driven rain resistance. Improving the flood resistance of an existing building often involves elevating the building on a new foundation. FEMA provides hazard mitigation grants to states for activities such as structure elevation, property acquisition, and flood-proofing. When completed, these activities can reduce or eliminate risk, which may result in lower flood insurance rates.
As shown in the chart below, options exist to save money while protecting property.
If Maps Show...
These Requirements, Options, and Savings Apply
Change from low-risk (Zone C or Zone X unshaded) or moderate-risk (Zone B or Zone X shaded) zone to a high-risk SFHA (Zone A, Zone AE, or Zone VE)
Flood insurance is mandatory. Flood insurance will be federally required for most mortgage holders. Insurance costs may rise to reflect the true (high) risk.
Change from high-risk to low- or moderate-risk zone
Flood insurance is optional but recommended. The risk in the area has only been reduced, not removed. Flood insurance can still be obtained at lower rates. Between 20-25 percent of all flood insurance claims come from low- and moderate-risk areas.