Glossary
 
An alphabetical list of defined key terms used on this website is provided on this page.

A


ADCIRC (ADvanced CIRCulation) Model

A numerical computer model used for modeling coastal storm surge which results in the generation of stillwater elevations associated with storm events. For additional technical information on the ADCIRC model, visit the ADCIRC homepage.

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. In New Jersey and New York, State and local officials, property owners, builders and others are encouraged to use ABFEs to make informed decisions about rebuilding, and to reduce the impact of future flood events.

Advisory Base Flood Elevation Data

FEMA has created Advisory Base Flood Elevation (ABFE) maps to show a more current picture of flood risk for certain communities affected by Hurricane Sandy. The Advisory information can help communities better understand current flood risks and ensure structures are rebuilt stronger and safer to reduce the impact of similar events in the future. ABFE maps can be accessed through the View FEMA Flood Hazard Data page. Information about the methodologies, assumptions and data sources used to develop the Advisory information is available through the New York/New Jersey Coastal Advisory Flood Hazard Information Development Report.

FEMA is now in the process of releasing preliminary work maps followed by preliminary Flood Insurance Rate Maps (FIRMs) which are based on the same underlying data as the ABFE maps, but include the results of a more refined analysis of shoreline conditions, including the effects of erosion and wave runup. 

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 a zone 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. Different ABFE zones are distinguished by yellow lines.

Advisory Flood Hazard Zones

Indicates the lettered Advisory flood hazard zone associated with the location:
  • Advisory Zone V is comprised of 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 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 Shaded Zone X is comprised of areas 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 comprised of 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 hazard zones. 

Advisory Map Panels

The Advisory Map Panels layer on the FEMA Advisory Base Flood Elevations map shows the map paneling scheme used to produce the New Jersey and New York Advisory flood hazard information. The symbology shown for each map panel in this layer indicates its current availability: 
  • Green: Advisory information for the panel is currently available
  • Yellow: Advisory information for the panel is partially available
  • Diagonal hatching: Advisory information is not yet available for the panel. 
If there is no panel outline shown on the map, currently there are no plans to produce Advisory flood hazard information for that area.
To download a .pdf version of a map panel from the interactive ABFE map showing the Advisory information (once available), simply click on the desired map panel while the Advisory Map Panel layer is turned on and click on the ‘PDF Map Hyperlink’ field in the pop up window. The .pdf map panels are produced at a scale of 1” = 1,000 feet. 

Advisory Shaded Zone X

The Advisory Shaded Zone X map layer shows areas of moderate coastal flood risk outside the regulatory 1% annual chance flood but within the limits of the 0.2% annual chance flood level. 

Advisory Zone V-A Boundary

The division between the Advisory flood hazard Zone V and Advisory flood hazard Zone 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, also known as the coastal high hazard area, is subject to more stringent building requirements than other zones because these areas are exposed to 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.

Appeal

An appeal is part of the regulatory process detailed in Part 67 of the National Flood Insurance Program (NFIP) regulations. To be considered an appeal, technical data must be submitted during the statutory 90-day appeal period that follows the release of the preliminary FIRM and FIS report. Appeals concern additions or changes to the flood hazard information shown on the preliminary FIRM and must be based on technical data that demonstrates the proposed flood hazard information is scientifically or technically incorrect. Appeals address Base Flood Elevations (BFEs), base flood depths, Special Flood Hazard Area (SFHA) boundaries or Zone designations, and/or regulatory floodway delineations. The flood hazard information shown on the preliminary FIRM and in the FIS report is developed by experienced engineers and mapping professionals using the latest engineering methods and computer models. As a result, an appeal of the flood hazard information requires similar detailed technical data to demonstrate the preliminary flood hazard information is scientifically or technically incorrect. 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 Advisory 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.

B


Base Flood

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 Elevations (BFEs) are typically shown on Flood Insurance Rate Maps (FIRMs).

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 the flood profile in the Flood Insurance Study (FIS) report.

In coastal areas, BFEs are calculated using 4 components: 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).  

Bathymetry

The measurement of water depths in oceans, seas, and lakes; also information derived from such measurements.

Breakaway Wall

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.

Breakwater

A structure protecting a shore area, harbor, anchorage, or basin from waves.

Bulkhead

A structure or partition built to retain or prevent sliding of the land.

C


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 or AE 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.

Coastal Erosion

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 (SFHA) 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 are exposed to a higher level of risk than other coastal flooding areas. 

Comment

A comment addresses information in the preliminary FIS report or on the preliminary FIRM that does not involve new or changed flood hazard information. Comments can address corporate limits, jurisdictional boundaries, road names, base map changes, and requests for incorporation of changes resulting from a Letter of Map Revision (LOMR). By FEMA definition, the term “comment” may also apply to concerns with flood hazard data that were submitted outside the statutory 90-day appeal period.

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 for property owners in the community by taking these additional actions.

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 enact and 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. 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. 

Cooperating Technical Partners (CTP) Program

An innovative FEMA program to create partnerships between FEMA and participating 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.

Critical Facilities

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 Section

Cross sections of riverine flooding sources are taken by surveyors and engineers to obtain 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.  

D


Development

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.

Duration

In wave forecasting, the length of time the wind blows in nearly the same direction over the fetch, or "generating area."

E


Effective Flood Hazard Zone

Indicates the lettered flood zone associated with the location shown on the effective Flood Insurance Rate Map and will be usually be populated with one of the following lettered zones described below. Effective FIRM data in the 'What is My BFE' tool report is derived from FEMA's National Flood Hazard Layer.
  • Zone VE: The area subject to high velocity wave action (a 3-foot breaking wave) from the 1% annual chance coastal 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: Areas of moderate coastal flood risk outside the regulatory 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 on which FEMA has delineated Special Flood Hazard Areas and flood risk zones.  The FIRM is used to determine flood insurance rates and requirements and for community floodplain management purposes. 

Effective Flood Insurance Rate Map (FIRM) Panel Number

This field indicates the current effective community FIRM panel number which applies to the particular location in the What is my BFE? address lookup tool. 

Elevated Building

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.

Erosion

See 'Coastal Erosion'.

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 updated preliminary Flood Insurance Rate Maps for New York City and certain New Jersey communities.
  • Digital building footprint information for New York City provided by the Department of Information Technology and Telecommunications, City of New York.
  • 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.
All ground elevations are approximate. You will need to consult with a licensed surveyor to determine the actual elevation of your home.  


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F


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.

Federal Register

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.

Flood

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. To learn more about flood hazards and ways to keep safe from floods, visit FEMA’s disaster preparedness site, Ready.gov.

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, the Base Flood Elevations (BFEs), and the risk premium zones applicable to the community. The FIRM is used to determine who must buy flood insurance 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.

FIRM Database

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 will indicate whether the preliminary FIRM panel is part of a community-based or a countywide FIRM.  It will also indicate whether the particular 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

The official report which usually accompanies the Flood Insurance Rate Map (FIRM), provided by FEMA that contains additional technical information on the flood hazards identified on the FIRM.

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 regulatory 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) and Flood Insurance Study (FIS) report. 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. Opportunities for incorporating Risk MAP products into local mitigation planning efforts are also presented during this meeting.

Floodplain

Any land area susceptible to being inundated by water from any source.

Floodplain Management Regulations

Zoning ordinances, subdivision regulations, building codes, health regulations, special purposes 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.

Floodproofing

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.

Freeboard

A factor of safety usually expressed in feet above a flood level for purposes of floodplain management.

G


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 geographic data.   
 

H


HAZUS-MH

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.

Hurricane

A tropical cyclone, formed in the atmosphere over warm ocean areas, with a well-defined counter-clockwise circulation and 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. To learn more, including ways to prepare and keep safe from hurricanes, visit the Ready.gov Hurricanes webpage.

Hydraulic Analysis

An engineering analysis of a flooding source developed to provide estimates of the elevations of floods of selected recurrence intervals.

Hydrologic Analysis

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.

J


Jetty

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.

L


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 (SFHA). LOMAs are usually issued because a property has been inadvertently mapped as being in the floodplain, but is actually on natural high ground above the Base Flood Elevation (BFE).

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 insurance risk zones, flood zone boundary delineations, planimetric features, and/or Base Flood Elevations (BFEs). LOMRs are generally based on the implementation of physical measures that affect the hydrologic or hydraulic characteristics of a flooding source and thus result in the modification of the existing regulatory floodway, the effective BFEs, or the Special Flood Hazard Area (SFHA) or flood zone designations. The LOMR is generally accompanied by an annotated copy of the affected portions of the FIRM and FIS report.

Levee

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 and at NOAA’s Digital Coast website, which includes a free online training module. 

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, as presented on the effective Flood Insurance Rate Map (FIRM).  Users should access the Effective FIRM to get further information on their flood hazard beyond this limit.

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.
 
 
 

M


Mitigation

The effort to reduce loss of life and property by lessening the impact of disasters. For more information on hazard mitigation, visit FEMA’s Mitigation Homepage.

N


National Flood Insurance Program (NFIP)

The Federal Program under which floodprone areas are identified and flood insurance is made available to the owners of the property in participating communities. For more information on the NFIP, visit Floodsmart.gov. 

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 at http://www.ngs.noaa.gov. 

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. Some older FIRMs are still use NGVD 29. To learn more about vertical datums, visit the Understanding Vertical Datums page.

Nor’easter

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. These storms usually develop between Georgia and New Jersey within 100 miles of the coastline and generally move north or northeastward.
Nor’easters typically become most intense near New England and the Canadian Maritime Provinces. 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

The vertical control datum established for vertical control surveying in the Unites States of America based upon the General Adjustment of the North American Datum of 1988. It replaces the National Geodetic Vertical Datum of 1929. To learn more about vertical datums, visit the Understanding Vertical Datums page.

O


Overland Wave Modeling

In conjunction with storm surge modeling, overland wave modeling is conducted to determine Base Flood Elevations (BFEs) and to delineate 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.

Overwash

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.

P

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. 

Once released, the preliminary work maps, including user guides and other learning resources, will be made available through this website on the View FEMA Flood Hazard Data page. Property owners and community officials can easily look up flood zone and Base Flood Elevation (BFE) information for their property using the “What is my BFE?” address lookup tool.

Preliminary Flood Insurance Rate Map (FIRM)

A FIRM that is not yet effective that reflects the initial results of a flood map project 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 example, dunes above the 1% annual chance flood level are included in the SFHA (typically mapped as a VE Zone on a FIRM), which protects PFDs from manmade impacts or physical alterations that could increase potential flood damage. 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. 

 

R


Resilience Meeting

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 first opportunity to review the preliminary FIRM and FIS report and additional 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.

S


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 to evaluate the threat from storm surge, and emergency managers use this data to determine which areas must be evacuated. SLOSH output is used by the National Hurricane Program (NHP) when conducting Hurricane Evacuation Studies as a hazard analysis tool for assisting with the creation of state and local hurricane evacuation plans or zones. 

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).

Sea Wall

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 coastal water surface elevation of a flood having a 1% annual chance of being equaled or exceeded in any given year shown on the community Flood Insurance Rate Map (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 and Advisory 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. Preliminary BFEs for riverine areas should be obtained by accessing the preliminary Flood Insurance Study report flood profile for the flooding source, which can also be accessed through the map’s pop up window.  

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 the coastal Base Flood Elevations.

Storm surge

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 needed to handle the complexities of integrating these large quantities of data and performing the necessary simulations. To learn more about coastal storm surge, visit the Coastal Mapping Basics page of this website or NOAA’s State of the Coast website.

Subsidence

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)

Swale

The depression between beach ridges.

T


Transect

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.

Tropical Storm

A tropical cyclone with maximum sustained (1-minute average) winds of 39 to 73 miles per hour.

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Watershed

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 (cross sections of the shoreline) in a study area. Additional information on WHAFIS is available in FEMA’s Atlantic Ocean and Gulf of Mexico Guidelines Update.

Wave Propagation

The transmission of waves through water.

Wave Runup

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.

Wave Setup

The increase in the water level caused by the onshore mass transport of water that occurs due to waves breaking during a storm. Wave setup is affected by the wave height, the speed at which waves approach shore, and the nearshore slope.