An alphabetical list of defined key terms used on this website is provided on this page.
ADCIRC (ADvanced CIRCulation) Model
A computer model used for modeling coastal storm surge which results in the generation of stillwater elevations associated with storm events. For detailed information on the ADCIRC model, visit the ADCIRC website.
Advisory Base (1% Annual Chance) Flood Elevation [ABFE]
The coastal water surface elevation of a flood having a 1% annual chance of being equaled or exceeded in any given year. It is expressed in feet referenced to the North American Vertical Datum of 1988 (NAVD88) and can reflect the elevation of an Advisory Flood Zone V or A.
Advisory Base Flood Elevation Data
FEMA created Advisory Base Flood Elevation (ABFE) maps to show a more current picture of flood risk for coastal New Jersey and New York communities after Hurricane Sandy. For most communities, ABFE information has now been replaced by preliminary Flood Insurance Rate Maps as the most recent flood hazard data available from FEMA. Information about how the Advisory information was developed is available in the New York/New Jersey Coastal Advisory Flood Hazard Information Development Report.
Advisory 0.2% Annual Chance Flood Elevation
The coastal water surface elevation of a flood having a 0.2% annual chance of being equaled or exceeded in any given year. It is expressed in feet referenced to the North American Vertical Datum of 1988 (NAVD88).
Advisory Base Flood Elevation (ABFE) Zones
A map layer which indicates whether an area is designated as a V or A flood hazard zone and which provides the 0.2% Advisory Flood Elevation and the 1% Advisory Base Flood Elevation (ABFE) in feet referenced to the North American Vertical Datum of 1988 (NAV88) for the zone.
Advisory Flood Hazard Zones
Indicates the Advisory flood hazard zone associated with the location:
- Advisory Zone V is the area subject to high velocity wave action (a 3-foot breaking wave) from the 1% annual chance coastal flood. Zone V is subject to more stringent building requirements than other zones because these areas are exposed to a higher level of risk.
- Advisory Zone A is the area subject to storm surge flooding from the 1% annual chance coastal flood. These areas are not subject to high velocity wave action but are still considered high risk flooding areas.
- Advisory Shaded Zone X is an area of moderate coastal flood risk outside of Advisory Flood Hazard Zones V and A up to the 0.2% annual chance flood level.
Advisory Flood Hazard Zones V and A
The Advisory 1% annual chance floodplain includes both A and V Advisory flood hazard zones:
Advisory Zone V is the area subject to high velocity wave action (a 3-foot breaking wave) from the 1% annual chance coastal flood. Zone V areas are exposed to a higher level of risk than other flood zones.
Advisory Zone A is comprised of the area subject to storm surge flooding from the 1% annual chance coastal flood. These areas are not subject to high velocity wave action but are still considered high risk flooding areas.
Advisory Limit of the 1% Annual Chance Flood Hazard Area
The limit of the Advisory 1% annual chance floodplain. The advisory 1% annual chance floodplain includes both V and A Advisory flood zones.
Advisory Map Panels
The Advisory Map Panels layer shows the map paneling scheme used to produce the New Jersey and New York Advisory flood hazard information.
Advisory Shaded Zone X
Advisory Zone V-A Boundary
The division between the Advisory flood hazard Zones V and A. This is where the high velocity wave action greater than 3 ft in height is anticipated to end for a coastal 1% annual chance flood. Zone V is subject to more stringent building requirements than other zones because these areas have a higher level of risk.
AO Zone Depth
An area of high flood risk subject to inundation by 1% annual-chance shallow flooding where average depths are between one and three feet. Average flood depths derived from detailed hydraulic analyses are shown in this zone.
An appeal is part of the regulatory process detailed in Part 67 of the National Flood Insurance Program (NFIP) regulations that allows interested parties to provide feedback on the preliminary FIRM and FIS report. To be considered an appeal, a submittal must:
- Include data that shows the proposed flood hazard information is scientifically or technically incorrect
- Include the needed revisions to the FIRM and/or Flood Insurance Study (FIS) report, in digital format (e.g. digital boundaries of revised floodplains)
- Be received during the statutory 90 day appeal period.
The designation of a submittal as an appeal provides certain appellant rights, including the opportunity for the affected community to have data reviewed by a Scientific Resolution Panel.
More information is available in FEMA’s Criteria for the Appeal of Flood Insurance Rate Maps.
Area of MOderate Wave Action (MOWA)
The portion of the 1% annual chance coastal flood hazard area referenced by building codes and standards, where wave heights are between 1.5 and 3 feet, and where wave characteristics are deemed sufficient to damage many National Flood Insurance Program (NFIP)-compliant structures on shallow or solid wall foundations.
A flood having a 1% chance of being equaled or exceeded in any given year. The base flood is the national regulatory standard used by the National Flood Insurance Program (NFIP) and all Federal agencies for the purposes of requiring the purchase of flood insurance and regulating new development.
Base Flood Depth
The depth shown on the Flood Insurance Rate Map for Zone AO that indicates the depth of water above the highest adjacent grade—the highest point of the ground level immediately next to a building—resulting from a flood that has a 1-percent chance of equaling or exceeding that level in any given year.
Base Flood Elevation (BFE)
The elevation shown on the Flood Insurance Rate Map (FIRM) for Zones AE, AH, A1-30, or VE that indicates the water surface elevation resulting from a flood that has a 1-percent chance of occurring in any given year.
In riverine areas, BFEs are plotted as lines at different points along the stream on the FIRM which correspond to elevations in the flood profile in the Flood Insurance Study (FIS) report.
In coastal areas, BFEs are calculated by taking into account: 1) the storm surge stillwater elevation, 2) the amount of wave setup, 3) the wave height above the storm surge stillwater elevation, and 4) the wave runup above the storm surge stillwater elevation (where present).
The measurement of water depths in oceans, seas, and lakes; also information derived from such measurements.
A wall that is not part of the structural support of a building and is intended through its design and construction to collapse under specific lateral loading forces, without causing damage to the elevated portion of the building or supporting foundation system.
A structure protecting a shore area, harbor, anchorage, or basin from waves.
A structure or partition built to retain or prevent sliding of the land.
Coastal A/AE Zone
The portion of the Special Flood Hazard Area landward of a V zone (i.e., areas where wave heights are computed as less than 3 feet) that is mapped as an A zone on the FIRM. While the wave forces in coastal A zones are not as severe as those in V zones, the capacity for the damage or destruction of buildings is still present.
Coastal Barrier Resources Act (CBRA) Zones
The Coastal Barrier Resources Act (CBRA) established the John H. Chafee Coastal Barrier Resources System (CBRS), a defined set of geographic units along the Atlantic, Gulf of Mexico, Great Lakes, U.S. Virgin Islands, and Puerto Rico coasts. Most new Federal expenditures and financial assistance (including flood insurance) are prohibited within the CBRS, with some exceptions. The U.S. Fish and Wildlife Service is responsible for administering CBRA. CBRS boundaries shown on FEMA mapping products are for informational purposes only. For the best available CBRS boundary data, visit: http://www.fws.gov/cbra/Maps/Mapper.html. For additional information on the CBRA and the CBRS, visit: http://www.fws.gov/cbra.
The wearing away of land and the removal of beach or dune sediments by wave action, tidal currents, wave currents, or drainage. Waves, generated by storms, wind, or fast moving motor craft, cause coastal erosion which may take the form of long-term losses of sediment and rocks or a temporary redistribution of coastal sediments; erosion in one location may result in the buildup of sediment in other places nearby.
Coastal High Hazard Areas (V/VE Zones)
The Special Flood Hazard Area extending from offshore to the inland limit of a primary frontal dune along an open coast, and any other area subject to high-velocity wave action from storms or seismic sources. Typically, this is the area where the computed wave heights for the base flood are 3 feet or more. V zones are subject to more stringent building requirements and different flood insurance rates than other zones shown on the FIRM because these areas have a higher level of risk than other areas.
The term comment is used for any feedback on the preliminary FIRM or FIS report from an interested party that does not meet the requirements outlined for appeals as outlined in Title 44, Chapter I, Part 67 of the Code of Federal Regulations (44 CFR Part 67). This includes feedback about road names, jurisdictional boundaries, or other base map features or concerns about proposed flood hazard information that don’t meet the requirements for an appeal.
Community Rating System (CRS)
A FEMA initiative, established under the National Flood Insurance Program (NFIP), to recognize and reward communities that have implemented floodplain management measures beyond the minimum NFIP requirements. Under the CRS, those communities that choose to participate may reduce the flood insurance premium rates in the community from 5 to 45% based on the types of activities they perform.
Compliance/ Adoption Period
The 6-month period in the FIRM update process that begins with the issuance of a Letter of Final Determination and ends when a new or revised FIRM becomes effective, during which a community must adopt new or revised floodplain management ordinances required for participation in the National Flood Insurance Program.
Consultation Coordination Officer (CCO) Meeting
The CCO Meeting is held by FEMA and its partners for communities after the issuance of the preliminary FIRM and the Resilience Meeting (if held). The purpose of the CCO meeting and associated public Open House is to present the preliminary FIRM and data to community officials and the general public. During this meeting, differences between the new and the effective FIRM will be presented, along with an overview of the appeals and map adoption processes.
The difference in elevation represented by each contour line on a topographic map or its digital equivalent.
Cooperating Technical Partners (CTP) Program
A FEMA program to create partnerships with NFIP communities, regional agencies, and State agencies that have the interest and capability to become more active participants in the FEMA flood hazard mapping program.
Facilities that, if damaged, would present an immediate threat to life, public health, and safety. Critical and essential facilities include, but are not limited to, hospitals, emergency operations centers, water systems, and utilities.
Cross sections of riverine flooding sources are taken by surveyors and engineers to gather information about the size and geometry of the stream channel, bridges and culverts along the stream, and the elevation of the ground. This information is used to accurately model the flood hazards for the stream. Cross sections are shown on the FIRM and the flood profiles and other tables in the Flood Insurance Study (FIS) report.
Any man-made change to improved or unimproved real estate including, but not limited to, buildings or other structures, mining, dredging, filling, grading, paving, excavation or drilling operations or storage of equipment or materials.
In wave forecasting, the length of time the wind blows in nearly the same direction over the fetch, or “generating area.”
Effective Flood Hazard Zone
The lettered flood zone associated with the location shown on the effective FIRM. Zones include the following:
- Zone VE: The area subject to high velocity wave action (a 3-foot breaking wave) from the 1% annual chance flood. VE zones are subject to more stringent building requirements than other zones because these areas are exposed to a higher level of risk. Base Flood Elevations (BFEs) are established for VE zones.
- Zone A/AE: The area subject to inundation from the 1% annual chance flood. These areas are not subject to high velocity wave action but are still considered high risk flooding areas. AE zones have BFEs established. A zones are areas studied by approximate engineering methods and do not have BFEs established.
- Zone X (Shaded): Areas of moderate coastal flood risk outside the 1% annual chance flood up to the 0.2% annual chance flood level.
Effective Flood Insurance Rate Map (FIRM)
The official National Flood Insurance Program map of a community which shows Special Flood Hazard Areas and flood risk zones. The FIRM is used to determine flood insurance rates and requirements and for floodplain management activities and regulation.
Effective Flood Insurance Rate Map (FIRM) Panel Number
This field indicates the current effective community FIRM panel number which applies for the particular location in the What is my BFE? address lookup tool.
For insurance purposes, a non-basement building which has its lowest elevated floor raised above ground level by foundation walls, shear walls, posts, piers, pilings, or columns.
An administrative tool of the National Flood Insurance Program that is used to provide elevation information needed to ensure compliance with community floodplain management ordinances, to determine the proper insurance premium rate, and to support a request for a Letter of Map Amendment.
Estimated Ground Elevation
The estimated ground elevation in the What is My BFE? Report has been derived from the following sources:
- Detailed topographic data used to develop the preliminary FIRMs.
- Digital building footprint information for New York City provided by the City’s Department of Information Technology and Telecommunications.
- Building footprint information for Monmouth County, and parts of Bergen, Essex and Hudson County, New Jersey.
- Parcel boundary information for Atlantic, Bergen, Burlington, Cape May, Hudson, Monmouth, Ocean, Union Counties, and portions of Essex and Middlesex Counties, New Jersey.
- Building footprint information for Westchester County, New York provided by the Westchester County GIS Agency (giswww.westchestergov.com).
All ground elevations are approximate. You will need to consult with a licensed surveyor to determine the actual elevation of your home.
Federal Emergency Management Agency (FEMA)
FEMA is the part of the Department of Homeland Security working to support citizens and first responders to ensure that as a nation we work together to build, sustain, and improve our capability to prepare for, protect against, respond to, recover from, and mitigate all hazards. FEMA employees work all over the country – at FEMA Headquarters, the ten regional offices, the National Emergency Training Center, Center for Domestic Preparedness/Noble Training Center, and other locations – to support the larger emergency management team.
The FEMA Region II office supports New York, New Jersey, Puerto Rico and the U.S. Virgin Islands.
The document, published daily by the Federal Government, which presents regulation changes and legal notices issued by Federal agencies. FEMA publications related to the National Flood Insurance Program that are published in the Federal Register include Proposed and Final Flood Hazard Determination Notices and Final Rules concerning community eligibility for the sale of flood insurance.
A condition of partial or complete inundation of normally dry land areas from: (1) the overflow of inland or tidal waters, (2) the unusual and rapid accumulation or runoff of surface waters from any source, or (3) Mudslides.
Flood Insurance Rate Map (FIRM)
Official map of a community on which FEMA has delineated the 1% annual chance (base) floodplain or Special Flood Hazard Area, Base Flood Elevations (BFEs), and flood zones applicable to the community. The FIRM is used to determine flood insurance rates and requirements and where floodplain development regulations apply. Once effective, FIRMs are available through the local community map repository and online through the FEMA Map Service Center.
A database containing digital flood hazard information shown on the FIRM, designed for use with specialized Geographic Information System (GIS) software. Users can integrate local data sets with the information in the FIRM database in order to assist with floodplain management or mitigation planning measures. The FIRM database is provided to your community once a FIRM becomes effective and will also be available for download through the FEMA Map Service Center.
FIRM Panel Type
This field in the Preliminary FIRM Data Viewer indicates whether the preliminary FIRM panel is part of a community-based or a countywide FIRM. It will also indicate whether the panel is printed. Unprinted panels may be included in the FIRM paneling scheme, but since there are currently no flood hazards mapped on the panel, are not actually printed.
Flood Insurance Study (FIS) report
Flood Hazard Zone
Flood hazard zones are lettered based on the level and type of flood risk:
- Zone V/VE: An area of high flood risk subject to inundation by the 1% annual-chance flood event with additional hazards due to storm-induced velocity wave action (a 3-foot or higher breaking wave).
- Zone A/AE: An area of high flood risk subject to inundation by the 1% annual-chance flood event.
- Zone AO: An area of high flood risk subject to inundation by 1% annual-chance shallow flooding where average depths are between one and three feet.
- Shaded Zone X: Areas of moderate flood risk within the 0.2% annual chance floodplain; or areas of 1% annual chance flooding where average depths are less than 1 foot, where the drainage area is less than 1 square mile, or areas protected from this flood level by a levee.
- Unshaded Zone X: Areas of low flood risk outside the 1%- and 0.2%-annual chance floodplains.
- Zone D: Areas where flood hazards are undetermined but flooding is possible.
Flood Risk Review Meeting
The Flood Risk Review Meeting occurs after the release of preliminary work maps and before the release of the preliminary Flood Insurance Rate Map (FIRM). It is a technically- focused meeting organized by FEMA and its partners that gives community officials the opportunity to review the draft Risk MAP products, including the preliminary work maps and certain draft flood risk datasets.
Any land area susceptible to being inundated by water from any source.
Floodplain Management Regulations
Zoning ordinances, subdivision regulations, building codes, health regulations, special purpose ordinances (such as a floodplain ordinance, grading ordinance and erosion control ordinance) and other applications of police power. The term describes such state or local regulations, in any combination thereof, which provide standards for the purpose of flood damage prevention and reduction.
Any combination of structural and nonstructural additions, changes, or adjustments to structures which reduce or eliminate flood damage to real estate or improved real property, water and sanitary facilities, structures and their contents.
Floodway / Regulatory Floodway
The channel of a river or other watercourse and the adjacent land areas that must be reserved in order to discharge the base (1%-annual-chance) flood without cumulatively increasing the water surface elevation more than a designated height.
A factor of safety usually expressed in feet above a flood level for purposes of floodplain management.
Geographic Information System (GIS)
A system of computer hardware, software, and procedures designed to support the capture, display, management, analysis, and modeling of spatially referenced data.
Hazard Analysis Methodology
The methods used to develop the flood hazards included on the Flood Insurance Rate Map. Different methods apply based on the types of flood hazards (e.g. coastal or riverine) shown. Learn about the methodology used to prepare the New York/New Jersey coastal flood study on the Coastal Mapping Basics page.
A nationally applicable standardized methodology, developed by FEMA under contract with the National Institute of Building Sciences for estimating potential losses from earthquakes, hurricane winds, and floods. HAZUS-MH uses GIS software to map and display hazard data and the results of damage and economic loss estimates for buildings and infrastructure. It also allows users to estimate the impacts of earthquakes, hurricane winds, and floods on populations.
A tropical cyclone, formed in the atmosphere over warm ocean areas, with sustained winds of 74 miles per hour or higher. Hurricanes can cause catastrophic damage to coastlines and even several hundred miles inland. Hurricanes can create storm surges along the coast and cause extensive damage from heavy rainfall. Floods and flying debris from the excessive winds are often the deadly and destructive results of these weather events.
An engineering analysis of a flooding source developed to establish peak flood discharges and their frequencies of occurrence. The results of the hydrologic analysis will be used when developing the hydraulic analysis performed to estimate flood elevations of selected recurrence intervals, such as the 1% annual chance flood.
Increased Cost of Compliance (ICC) Coverage
Flood insurance through the National Flood Insurance Program includes ICC Coverage, which covers property owner expenses, above and beyond the cost to repair the physical damage the structure actually sustained from a flooding event, to comply with mitigation requirements of State or local floodplain management ordinances or laws. Acceptable mitigation measures are elevation, floodproofing, relocation, demolition, or any combination of these measures.
A structure built out into the water to restrain currents and/or stabilize a shoreline. Jetties are commonly built at the mouths of rivers or tidal inlets to help deepen and stabilize the channel.
Letter of Map Amendment (LOMA)
An official amendment, by letter, to an effective FIRM. A LOMA establishes a property’s location in relation to the Special Flood Hazard Area. LOMAs are usually issued because a property has been inadvertently mapped as being in the floodplain due to map scale limitations, but is actually on natural high ground above the Base Flood Elevation.
Letter of Map Revision (LOMR)
An official revision, by letter, to an effective FIRM and sometimes the accompanying Flood Insurance Study (FIS) report. A LOMR may change flood zones, flood zone boundaries, Base Flood Elevations (BFEs), or other map features. The LOMR is accompanied by an annotated copy of the affected portions of the FIRM and FIS report.
A man-made structure, usually an earthen embankment, designed and constructed in accordance with sound engineering practices to contain, control, or divert the flow of water so as to provide protection from temporary flooding. While levees can help reduce the risk of flooding, they do not eliminate the risk. For additional information on levees and levee risk, visit FEMA’s Living With Levees Homepage.
Light Detection and Ranging (LiDAR)
LiDAR is a state-of-the-art method for collecting accurate elevation information using an instrument that measures distance to a reflecting object by emitting timed pulses of laser light and measuring the time between emission and reception of reflected pulses. Additional information on LiDAR can be found in the LiDAR video at FEMA.gov.
Limit of Advisory Base Flood Elevations
The Limit of Advisory Base Flood Elevations depicts the location at which the dominant flood hazard transitions from the 1% annual chance coastal Advisory Base Flood Elevation (ABFE) to the riverine flood hazard presented on the effective Flood Insurance Rate Map (FIRM).
Limit of Moderate Wave Action (LiMWA)
The LiMWA depicts the limit of the Area of Moderate Wave Action (MOWA), the portion of the 1% annual chance coastal flood hazard area referenced by building codes and standards, where base flood wave heights are between 1.5 and 3 feet, and where wave characteristics are deemed sufficient to damage many National Flood Insurance Program (NFIP)-compliant structures on shallow or solid wall foundations. Read FEMA’s LiMWA fact sheet for more information.
The effort to reduce loss of life and property by reducing the impact of disasters. For more information on mitigating flood risk, visit the Reducing Risk page.
National Flood Insurance Program (NFIP)
In 1968, Congress created the National Flood Insurance Program (NFIP) to help provide a means for property owners to financially protect themselves. The NFIP offers flood insurance to homeowners, renters, and business owners if their community participates in the NFIP. Participating communities agree to adopt and enforce ordinances that meet or exceed FEMA requirements to reduce the risk of flooding.
National Geodetic Survey Benchmark
National Geodetic Survey Benchmarks are shown on Flood Insurance Rate Maps (FIRMs) where available. To obtain current elevation, description, and/or location information for benchmarks shown on preliminary or effective FIRMs, please contact the Information Services Branch
of the National Geodetic Survey at (301) 713-3242, or visit its website.
National Geodetic Vertical Datum (NGVD) of 1929
Historically, NGVD 29 was the standard vertical datum used by the federal government for mapping projects. However, the North American Vertical Datum of 1988 (NAVD 88) is now the national standard. There are also many other different vertical datums available. Elevations on some older FIRMs are still referenced to NGVD 29. To learn more about vertical datums, visit the Vertical Datum FAQ.
A nor’easter is a cyclonic storm that moves along the east coast of North America. It’s called “nor’easter” because the winds over coastal areas blow from a northeasterly direction. Nor’easters may occur any time of the year, but are most frequent and strongest between September and April.
In addition to heavy snow and rain, nor’easters can bring gale force winds greater than 58 miles per hour. These storms can produce rough seas, coastal flooding and beach erosion. (Source: National Oceanic and Atmospheric Administration)
North American Vertical Datum (NAVD) of 1988
A vertical datum established for vertical control surveying in the Unites States. It replaces the National Geodetic Vertical Datum of 1929. To learn more about vertical datums, visit the Vertical Datum FAQ.
Overland Wave Modeling
In conjunction with storm surge modeling, overland wave modeling is conducted to determine Base Flood Elevations (BFEs) and coastal flood hazards. Overland wave modeling consists of the determination of wave heights, wave setup values, simulations of inland wave propagation, as well as computing wave runup scenarios. Typically, the Wave Height Analysis for Flood Insurance Studies (WHAFIS) model is used to perform overland wave modeling for FEMA flood studies.
The mass of water representing the part of the wave advancing up a beach that runs over the highest part of a berm or other structure and that does not flow directly back to the sea or lake in which the wave originated.
Preliminary Work Maps
The preliminary work maps created for certain New Jersey/New York communities are an interim product created by FEMA in the development of preliminary Flood Insurance Rate Maps (FIRMs). The preliminary work maps reflect the full results of an ongoing coastal flood hazard study for the New York/New Jersey coast. For most communities, the preliminary work maps have now been replaced by the preliminary FIRMs as the most recent flood hazard data available from FEMA.
Preliminary Flood Insurance Rate Map (FIRM)
A FIRM that is not yet effective that reflects the initial results of a flood study performed by or for FEMA. The preliminary FIRM is provided to the Chief Executive Officer (e.g., Mayor, County Commissioner, etc.) and floodplain administrator for each affected community and is available to all citizens for review both online or through the local community map repository (often the community planning or zoning office).
Primary Frontal Dune (PFD)
A primary frontal dune (PFD) is a continuous or nearly continuous mound or ridge of sand with relatively steep seaward and landward slopes immediately landward of and adjacent to the beach. PFDs are subject to erosion and may be vulnerable to overtopping or breaching from high water levels and waves during coastal storms. Because dunes can help reduce coastal flood hazards, the National Flood Insurance Program has established special mapping, insurance, and floodplain management criteria designed to help communities protect dunes. For more information about PFDs, see FEMA’s fact sheet on the topic.
Provisional Hurricane Sandy Storm Surge Elevation
Observed storm surge flood elevations from Hurricane Sandy, collected by the U.S. Geological Survey (USGS). These elevations, expressed in feet referenced to the North American Vertical Datum of 1988 (NAVD88), represent provisional USGS high water marks and storm tide sensors.
The Resilience Meeting occurs after the issuance of the preliminary FIRM and FIS report. During this meeting organized by FEMA and its partners, community officials will have the opportunity to review the preliminary FIRM and FIS report and draft flood risk datasets and products. Ways the community can incorporate the Risk MAP products into ongoing risk assessment and planning efforts are also discussed during this meeting.
Risk Mapping, Assessment, and Planning (Risk MAP)
The FEMA program that provides flood information and tools that can be used by communities to enhance flood hazard mitigation planning efforts and to take action to better protect their citizens. Through more precise flood mapping products, risk assessment tools, and planning and outreach support, Risk MAP strengthens local ability to make informed decisions about reducing risk. For more information on Risk MAP, visit the FEMA Risk MAP homepage.
Sea, Lake, and Overland Surge from Hurricanes (SLOSH)
SLOSH is a computerized model developed by FEMA, the U.S. Army Corps of Engineers (USACE), and the National Weather Service (NWS) to estimate storm surge depths resulting from historical, hypothetical, or predicted hurricanes by taking into account a storm’s pressure, size, forward speed, forecast track, wind speeds, and topographical data. SLOSH is used by State and local officials to evaluate the threat from storm surge and to determine which areas must be evacuated.
Sea Level Rise
An increase in sea level caused by a change in the volume of the world’s oceans due to temperature increase, deglaciation (uncovering of glaciated land because of melting of the glacier), and ice melt (Source: NOAA).
A solid barricade, often concrete or stone, built at the water’s edge to protect the shore and to prevent inland flooding. Generally built parallel to the shore, a sea wall is typically more massive and capable of resisting greater wave forces than a bulkhead.
Simulating WAves Nearshore (SWAN) Model
A computer model that is often used to estimate wave generation and propagation in conjunction with the ADCIRC model when modeling the effects of coastal storm surge.
Special Flood Hazard Area (SFHA)
The land area covered by the floodwaters of the base (1%-annual-chance) flood on the FIRM. The SFHA is the area where the National Flood Insurance Program’s (NFIP’s) floodplain management regulations must be enforced and the area where the mandatory purchase of flood insurance applies. The SFHA includes Zones A, AO, AH, A1-30, AE, A99, AR, AR/A1-30, AR/AE, AR/AO, AR/AH, AR/A, VO, V1-30, VE, and V.
Static Base Flood Elevation
The static Base Flood Elevation (BFE) shown on the community FIRM for A or Z flood hazard zones. On effective FIRMs, these elevations may either be referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29) or the North American Vertical Datum of 1988 (NAVD 88).
All BFEs listed in the ‘What is My BFE’ tool report are referenced to NAVD 88; in cases where elevations are actually referenced to NGVD 29 on the effective FIRM, a conversion factor has been applied so that these elevations are also referenced to NAVD 88.
Note that on FEMA’s interactive GeoPlatform Maps, if an area has a static BFE, the elevation will be listed in the map’s pop up window. Otherwise, a value of “-9,999.00” will be shown. This will typically occur for riverine AE flood zones.
Stillwater Elevation (SWEL)
The projected elevation of floodwaters in the absence of waves resulting from wind or seismic effects. In coastal areas, stillwater elevations are determined when modeling coastal storm surge; the results of overland wave modeling are used in conjunction with the stillwater elevations to develop Base Flood Elevations.
Storm surge is the water, combined with normal tides, that is pushed toward the shore by strong winds during a storm. This rise in water level can cause severe flooding in coastal areas, particularly when the storm coincides with the normal high tides. The height of the storm surge is affected by many variables, including storm intensity, storm track and speed, the presence of waves, offshore depths, and shoreline configuration. To model the effects of coastal storm surge, sophisticated computer models, such as ADCIRC and SWAN, are used. Watch a video about storm surge to learn more.
A gradual settling or sudden sinking of the Earth’s surface owing to subsurface movement of earth materials. Subsidence is a global problem, and in the United States, more than 17,000 square miles in 45 states, an area roughly the size of New Hampshire and Vermont combined, have been directly affected by subsidence. (Source: NOAA)
Damage of any origin sustained by a building whereby the cost of restoring the building to its before-damaged condition would equal or exceed 50 percent of the market value of the building before the damage occurred.
Any reconstruction, rehabilitation, addition, or other improvement of a building, the cost of which equals or exceeds 50 percent of the market value of the building before the start of construction of the improvement. Substantial improvement includes buildings that have incurred “substantial damage,” regardless of the actual repair work performed. The term does not, however, include either any project for improvement of a building to correct existing state or local code violations or any alteration to a “historic building,” provided that the alteration will not prevent the building’s continued designation as a historic building.
The depression between beach ridges.
A surveyed cross section taken perpendicular to the shoreline to represent a segment of coast with similar characteristics. Transect data is used when performing overland wave modeling and mapping for a coastal flood study.
A tropical cyclone with maximum sustained (1-minute average) winds of 39 to 73 miles per hour.
The base measurement point (or set of points) from which elevations are determined. Historically, the standard datum used by the federal government was the National Geodetic Vertical Datum of 1929 (NGVD 29). However, the North American Vertical Datum of 1988 (NAVD 88) is now the national standard. There are also many other different vertical datums available. To learn more about vertical datums, visit the Vertical Datum FAQ.
The area of land where all of the water that is under it or drains off of it goes into the same place (Source: Environmental Protection Agency).
Wave Height Analysis for Flood Insurance Studies (WHAFIS)
The WHAFIS model has been used to perform coastal flood studies since 1980 to incorporate the effects of wind-bourne wave action on FIRMs for communities along the Atlantic and Gulf Coasts. WHAFIS uses various input data to calculate wave heights, wave crest elevations, flood insurance risk zone designations, and flood zone boundaries along transects in a study area. Additional information on WHAFIS is available in FEMA’s Atlantic Ocean and Gulf of Mexico Guidelines Update.
The transmission of waves through water.
The rush of water that extends inland when waves come ashore. Wave runup effects are computed as a part of the overland wave analysis and are added to the stillwater elevations computed from the storm surge model when developing Base Flood Elevations in coastal areas.
The increase in the water level caused by the onshore mass transport of water that happens due to waves breaking during a storm. Wave setup is affected by the wave height, the speed at which waves approach the shore, and the slope of the shore.
See ‘Flood Hazard Zone’