0.2-Percent-Annual-Chance Flood — The flood that has a 0.2-percent chance of being equaled or exceeded in any given year.
1-Percent-Annual-Chance Flood — The flood that has a 1-percent chance of being equaled or exceeded in any given year.
1-Percent-Annual-Chance Flood Elevation — See Base Flood Elevation (BFE).
2-Percent-Annual-Chance Flood — The flood that has a 2-percent chance of being equaled or exceeded in any given year.
6-Month Compliance Period — See Compliance/Adoption Period.
10-Percent-Annual-Chance Flood — The flood that has a 10-percent chance of being equaled or exceeded in any given year.
10-Year Flood — See 10-Percent-Annual-Chance Flood.
50-Year Flood — See 2-Percent-Annual-Chance Flood.
90-Day Appeal Period — See Appeal Period.
100-Year Flood — See 1-Percent-Annual-Chance Flood.
500-Year Flood — See 0.2-Percent-Annual-Chance Flood.
Accredited Levee - A levee that the Federal Emergency Management Agency (FEMA) has shown on a Flood Insurance Rate Map (FIRM) or Digital Flood Insurance Rate Map (DFIRM) as providing protection from the 1-percent-annual-chance or greater flood. This determination is based on the submittal of data and documentation as required by 44 CFR Section 65.10 of the NFIP regulations. The area landward of an accredited levee is shown as Zone X (shaded) on the FIRM or DFIRM except for areas of residual flooding, such as ponding areas, which will be shown as Special Flood Hazard Area (SFHA).
ADCIRC Coastal Circulation and Storm Surge Model - A numerical computer model for solving time-dependent, free surface circulation and transport problems in two and three dimensions. The model utilizes the finite element method in space allowing the use of highly flexible, unstructured grids.
Adjacent Grade - Elevation of the natural or graded ground surface, or structural fill, abutting the walls of a building.
Appeal - The formal objection to proposed or proposed modified Base Flood Elevations (BFEs), submitted by a community official or an owner or lessee of real property within the community during the statutory 90-day appeal period. An appeal must be based on data that show the proposed or proposed modified BFEs are scientifically or technically incorrect.
Appeal Period - The statutorily required 90-day period that is initiated when FEMA formally notifies community officials, residents, and other interested parties that FEMA is proposing new or modified Base Flood Elevations (BFEs) and/or new or modified base flood depths. To start the appeal period, FEMA sends a letter to the Chief Executive Officer and floodplain administrator of the affected communities, publishes a notice twice in the local newspaper(s) with wide circulation, and publishes a notice (called a Proposed Rule) in the FEDERAL REGISTER. During the 90-day appeal period, which begins on the date of the second publication of the BFE notice in the local newspaper(s), community officials or owners or lessees of real property within the community may appeal the proposed or proposed modified BFEs and/or base flood depths by submitting scientific or technical data to show that those BFEs or base flood depths are scientifically or technically incorrect. The 90-day appeal period is statutory and cannot be extended for any reason.
Application Forms - The comprehensive, easy-to-use forms that were implemented by FEMA in 1992 to facilitate the processing of requests for conditional and final revisions or amendments to NFIP maps.
Approved Model - A numerical computer model that has been accepted by FEMA for use in performing new or revised hydrologic or hydraulic analyses for NFIP purposes. All accepted models must meet the requirements set forth in Subparagraph 65.6(a) (6) of the NFIP regulations.
Approximate Study - A flood hazard study that results in the delineation of floodplain boundaries for the 1-percent-annual-chance (100-year) flood, but does not include the determination of BFEs or flood depths.
Area Not Included (ANI) - An area that is excluded from the mapping for a subject community because (1) the area is under the jurisdiction of another community or county and is shown on the mapping for that community or county, or (2) access to the area is limited for security reasons (e.g., military installations).
Armor Layer - The protective layer on a breakwater or seawall composed of "armor units."
Armor Units - A relatively large quarrystone or concrete shape that is selected to fit specified geometric characteristics or density.
Artificial Nourishment - The process of replenishing a beach with material (usually sand) obtained from another location.
As-Built - A term used to describe mapping and mapping-related data that reflect conditions within a floodplain based on flood-control and other structures being completed.
Astronomical Tide - The
Base Flood - The flood that has a 1-percent chance of being equaled or exceeded in any given year.
Base Flood Elevation (BFE) - The elevation of a flood having a 1-percent chance of being equaled or exceeded in any given year.
Base Map - The map of the community that depicts cultural features (e.g., roads, railroad, bridges, dams, and culverts), drainage features, and corporate limits.
Bathymetric Chart - A topographic map of the bed of the ocean, with depths indicated by contours (isobaths) drawn at regular intervals.
Bathymetry - The measurement of depths of water in oceans, seas, and lakes; also information derived from such measurements.
Beach - The zone of unconsolidated material that extends landward from the low water line to the place where there is marked change in material or physiographic form, or to the line of permanent vegetation (usually the effective limit of storm waves).
Beach Berm - A nearly horizontal plateau on the beach face or backshore, formed by the deposition of beach material by wave action or as part of a beach nourishment effort.
Beach Erosion - The carrying away of beach materials by wave action, tidal currents, littoral currents, or wind.
Beach Nourishment - The replacement of beach sand removed by ocean waters.
Beach Profile - A cross-section taken perpendicular to a given beach contour, the profile may include the face of a dune or seawall, extend over the backshore, across the foreshore, and seaward underwater into the nearshore zone.
Benchmark (BM) - A permanent monument established by any Federal, State, or local agency, whose elevation and description are well documented and referenced to the National Geodetic Vertical Datum of 1929 or the North American Vertical Datum of 1988.
Berm Breakwater - A rubble mound structure with horizontal berm of armor stones at about sea level, which is allowed to be (re)shaped by the waves.
Bluff - A high, steep bank or cliff.
Breakaway Wall - A wall that is not part of the structural support of the 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.
Buffer Area - A parcel or strip of land that is designed and designated to permanently remain vegetated in an undisturbed and natural condition to protect an adjacent aquatic or wetland site from upland impacts, to provide habitat for wildlife and to afford limited public access.
Building - See Structure.
Bulkhead - A structure or partition to retain or prevent sliding of the land.
Central Pressure Index (CPI) - The estimated minimum barometric pressure in the eye (approximate center) of a particular hurricane. The CPI is considered the most stable index to intensity of hurricane wind velocities in the periphery of the storm; the highest winds are associated with storms having the lowest CPI.
Channel - A naturally or artificially created open conduit that periodically or continuously contains moving water or which forms a connecting link between two bodies of water.
Chief Executive Officer (CEO) - The official of a community who has the authority to implement and administer laws, ordinances, and regulations for that community.
Coast - A strip of land of indefinite width (may be several kilometers) that extends from the shoreline inland to the first major change in terrain features.
Coastal A Zone - This is an area of special flood hazard extending inland to the limit of the 1.5- foot breaking wave.
Coastal Barrier Resources System (CBRS) - A system of protected coastal areas (including the Great Lakes. The areas within the CBRS are defined as depositional geologic features consisting of unconsolidated sedimentary materials; subject to wave, tidal, and wind energies; and protecting landward aquatic habitats from direct wave attack.
Coastal Base Flood Elevations (BFEs) - The 1-percent-annual-chance flood elevations shown on a FIRM or DFIRM within the coastal high hazard area. Coastal BFEs can be calculated using the following equation: Stillwater Elevation + Wave Height = Coastal BFE.
Coastal Flooding - This is flooding that occurs along the Great Lakes, the Atlantic and Pacific Oceans, and the Gulf of Mexico.
Coastal Flood Study - The term used to describe the engineering analysis of flood hazards along the Gulf or Atlantic coast performed by FEMA using the ADCIRC computer model, with the results of that analysis being reflected on the Digital Flood Insurance Rate Maps and associated Flood Insurance Study reports for the affected counties.
Coastal High Hazard Area - An area of special flood hazard 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 actions from storms or seismic sources.
Coastal Processes - A collective term covering the action of natural forces on the shoreline and nearshore seabed.
Coastal Zone Management (CZM) - The integrated and general development of the coastal zone. Coastal Zone Management is not restricted to coastal defense works, but includes also a development in economical, ecological, and social terms. Coastline Management is a part of Coastal Zone Management.
Coastline - Technically, the line that forms the boundary between the coast and the shore; commonly, the line that forms the boundary between the land and the water, especially the water of a sea or ocean.
Code of Federal Regulations (CFR) - The codification of the general and permanent rules published in the NFIP by the Executive Departments and agencies of the Federal Government. NFIP regulations appear in Parts 59 through 77 of Title 44 of the CFR.
Comment - An objection to any information, other than BFEs, shown on an NFIP map that is submitted by community officials or interested citizens through the community officials during the appeal period.
Community - Any State or area or political subdivision thereof, or any Indian tribe or authorized tribal organization, or Alaska Native village or authorized native organization, which has the authority to adopt and enforce floodplain management regulations for the areas within its jurisdiction.
Community Assistance Call (CAC) - A telephone call made by FEMA RO staff or the State NFIP Coordinator to a community to supplement or replace a Community Assistance Visit.
Community Assistance Program (CAP) - An NFIP-funded FEMA program under which cost-shared funds are provided to States to provide technical assistance support to NFIP participating communities.
Community Assistance Visit (CAV) - A visit by FEMA or State NFIP Coordinator staff to a community to assess whether the community’s floodplain management program meets NFIP requirements.
Community Coordination Meeting - A meeting during which Project Team members discuss plans for a study/mapping project, interim results of a study/mapping project, and final results of a study/mapping project for a particular community or group of communities.
Community Identification Number (CID) - A six-digit code used by FEMA to identify each community that is potentially subject to flood hazards.
Community Information System (CIS) - An Oracle database system used by FEMA to track and report on all communities identified by FEMA as potentially floodprone, especially with regard to mapping actions, including Letters of Map Change, taken by FEMA to identify flood hazards in each community.
Community Map Repository (CMR) - This is the local office where the NFIP flood hazard maps and related products are kept for local use and viewing by citizens.
Community Rating System (CRS) - A FEMA initiative, established under the 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 voluntarily may reduce the flood insurance premium rates for property owners in the community by taking these additional actions.
Compliance/Adoption Period - The period that begins with the issuance of a Letter of Final Determination and ends when a new or revised DFIRM or FIRM becomes effective, during which a community must enact and adopt new or revised floodplain management ordinances required for participation in the NFIP.
Conditional Letter of Map Amendment (CLOMA) - The FEMA response to a requester, who believes his or her proposed structure when constructed on natural ground at or above the BFE, will be outside the 1-percent-annual-chance floodplain. CLOMAs may not be issued for unimproved or undeveloped property.
Conditional Letter of Map Revision (CLOMR) - The FEMA response to a community request for FEMA’s comment on proposed alterations to the floodplain conditions within that community. The CLOMR describes the effect of the proposed project, if constructed as proposed, on the effective FIRM, FBFM, and/or FIS report. A CLOMR often contains detailed information on conditions that must be met by a requester before FEMA will issue a final determination regarding revising the FIRM, FBFM, and/or FIS report.
Conditional Letter of Map Revision Based on Fill (CLOMR-F) - The FEMA response to a community request for FEMA’s comment on the effect(s) that a proposed project involving the placement of earthen fill within the SFHA will have on the SFHA designation for one or more legally defined parcels of land or one or more proposed structures.
Confluence - The junction of two or more river reaches or branches.
Consultation Coordination Officer (CCO) - The individual on the FEMA RO staff who is responsible for coordinating with a community on activities related to NFIP.
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.
Cooperating Technical Partners (CTP) Program Blue Book - A FEMA guidance document that outlines the unit cost approach FEMA uses in estimating the contributions of State agency, regional entity, university, community, and Indian Tribal entity partners who participate in map production in support of the FEMA Flood Hazard Mapping Program.
Countywide Format - A format used by FEMA to show flooding information for the entire geographic area of a county, including the incorporated communities in the county, on one set of FIRM or DFIRM panels and in one FIS report.
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.
Cultural Features - Railroads, airfields, streets, roads, highways, levees, dikes, seawalls, dams and other flood-control structures, and other prominent manmade features and landmarks shown on an NFIP map.
Current Effective Base Flood Elevations (BFEs) - See Effective Base Flood Elevations (BFEs).
Current Effective Date - See Effective Date.
Current Effective Flood Insurance Study (FIS) Report - See Effective Flood Insurance Study (FIS) Report.
Current Effective Map - See Effective Map.
Customer and Data Services (CDS) Contractor - A team of private-sector firms that, under contract to FEMA, maintains the archives of flood hazard mapping and related data and performs activities related to program development and program support, including maintenance of the Flood Hazard Mapping pages on the FEMA Website, operation of the FEMA Map Information Exchange, and operation of the FEMA Mapping Information.
De-Accredited Levee System - A levee system that was once shown on the FIRM or DFIRM as providing protection from the 1-percent-annual-chance or greater flood, but is no longer accredited with providing this protection because FEMA has not been provided with sufficient data and documentation to determine that the levee continues to meet the requirements of 44 CFR Section 65.10 of the NFIP regulations. The area landward of a de-accredited levee is shown as an SFHA.
Deep Water - Water so deep that surface waves are little affected by the ocean bottom. Generally, water deeper than one-half the surface wavelength is considered deep water.
Deep Water Wave - A wave for which the depth of water is greater than one-half the wave length.
Detailed Study - A flood hazard study that, at a minimum, results in the delineation of floodplain boundaries for the 1-percent-annual-chance flood and the determination of BFEs or flood depths.
Development - Any manmade 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.
Digital Elevation Model (DEM) - A digital file consisting of terrain elevations for ground positions at regularly spaced horizontal intervals, organized by quadrangle.
Digital Flood Insurance Rate Map (DFIRM) - A Flood Insurance Rate Map that has been prepared as a digital product, which may involve converting an existing manually produced FIRM to digital format, or creating a product from new digital data sources using a Geographic Information System environment. The DFIRM product allows for the creation of interactive, multi-hazard digital maps. Linkages are built into an associated database to allow users options to access the engineering backup material used to develop the DFIRM, such as hydrologic and hydraulic models, Flood Profiles, data tables, Digital Elevation Models, and structure-specific data, such as digital elevation certificates and digital photographs of bridges and culverts.
DFIRM Database - A database designed to facilitate collecting, storing, processing, and accessing data developed by FEMA, enabling Mapping Partners to share the data necessary for the DFIRM production and conversion process. Where possible, all mapping and engineering data elements are linked to physical geographic features and georeferenced. The use of a Geographic Information System as a component of the DFIRM database provides the ability to georeference and overlay the mapping and engineering data, allowing the database to support a variety of existing and forthcoming engineering and mapping products.
Digital Orthophoto Quadrangle (DOQ) - Photographic maps distributed by the U.S. Geological Survey. A DOQ is an aerial photograph that is adjusted to remove distortions caused by variations in terrain and the camera lens to produce a photograph that displays features in their planimetrically correct location. This term is sometimes used loosely to mean any photographic map produced by this process.
Digital Terrain Model (DTM) - A land surface represented in digital form by an elevation grid or lists of three-dimensional coordinates.
Duration - In wave forecasting, the length of time the wind blows in nearly the same direction over the fetch, or "generating area."
Effective Base Flood Elevations (BFEs) - The BFEs that are shown on the effective map (FIRM or DFIRM) that is in effect for a community for flood insurance and floodplain management purposes.
Effective Date - The date on which the NFIP map for a community becomes effective and all sanctions of the NFIP apply.
Effective Map - The NFIP map issued by FEMA, usually a FIRM or DFIRM, that is in effect as of the date shown in the title block of the map as "Effective Date", "Revised", or "Map Revised" and is to be used by the community and others for flood insurance and floodplain management purposes.
Elevation Certificate - The form, developed by FEMA, to be used to provide elevation information necessary 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 or Letter of Map Revision Based on Fill.
Elevation Reference Mark (ERM) - Temporary vertical control monument established by a FEMA Study Contractor during the performance of a study or restudy.
Embankment - Fill material, usually earth or rock, placed with sloping sides and with a length greater than its height. Usually an embankment is wider than a dike.
Embayment - An indentation in the shoreline forming an open bay.
Emergency Phase - The phase of the NFIP that was implemented, on an emergency basis, to provide a first-layer amount of insurance on all insurable structures before the effective date of the initial FIS report and FIRM.
Emergency Program - See Emergency Phase.
Encroachment - Construction, placement of fill, or similar alteration of topography in the floodplain that reduces the area available to convey floodwaters.
Erosion - The process by which floodwaters lower the ground surface in an area by removing upper layers of soil.
Erosion Analysis - The analysis of the short- and long-term erosion potential of soil or strata, including the effects of flooding or storm surge, moving water, wave action, and the interaction of water and structural components.
Estuary - The part of a river that is affected by tides; the region near a river mouth in which the fresh water of the river mixes with the salt water of the sea.
External Data Request (EDR) - A request from a State, community, or other non-FEMA source for the archived technical and administrative support data developed and maintained by FEMA for the NFIP.
Extraterritorial Jurisdiction (ETJ) Limits - Areas outside of a community's corporate limits where the community has authority to regulate zoning and issue building permits.
Eye - The roughly circular area of comparatively light winds that encompasses the center of a severe tropical cyclone. The eye is either completely or partially surrounded by the eyewall cloud.
Eyewall/Wall Cloud - An organized band or ring of cumulonimbus clouds that surround the eye, or light-wind center of a tropical cyclone. Eyewall and wall cloud are used synonymously.
Federal Emergency Management Agency (FEMA) - The component of the U.S. Department of Homeland security that oversees the administration of the NFIP.
Federal Insurance and Mitigation Administration (FIMA) - The component of FEMA Headquarters that, among other responsibilities, administers the NFIP.
Federal Register - The document, published daily by the Federal Government, which presents regulation changes and legal notices issued by Federal agencies. FEMA publications in the NFIP include Proposed, Interim, and Final Rules for BFE determinations and Final Rules concerning community eligibility for the sale of flood insurance.
Fee-Charge System Administrator (FCSA) - The individual that is responsible for processing and maintaining records of payments submitted to the National Flood Insurance Fund for conditional and final map change requests and requests for technical and administrative support data.
FEMA Map Assistance Center (FMAC) - See FEMA Map Information Exchange (FMIX).
FEMA Map Information Exchange (FMIX) - The FEMA customer service center staffed by Map Specialists who are specially trained to answer specific questions about NFIP mapping and related issues, including the following: how to obtain maps and other NFIP products from the FEMA Map Service Center; levee resources; status of active and completed studies/mapping projects, conditional and final map revision requests, and conditional and final map amendment requests; technical and administrative support data available from the FEMA archives.
Fetch - The distance along open water or land over which the wind blows.
Fill - Soil that is brought in to raise the level of the ground. Depending on where the soil is placed, fill may change the flow of water or increase flood elevations. Fill may be used to elevate a building to meet NFIP requirements. Sometimes fill is combined with other methods of elevation such as pilings or foundation walls. Placement of fill requires a local permit from the community.
Final Base Flood Elevations (BFEs) and Base Flood Depths - The 1-percent-annual-chance flood elevations and flood depths that a participating community must use for permitting and floodplain management purposes once FEMA publishes a Final Rule in the FEDERAL REGISTER and before the DFIRM becomes effective.
First-layer coverage - The maximum amount of structural and contents insurance coverage available under the Emergency Phase of the NFIP.
Fiscal Year - The 12-month period that begins on October 1 and ends on September 30.
Flood - A general and temporary condition of partial or complete inundation of normally dry land areas from (1) the overflow of inland or tidal waters or (2) the unusual and rapid accumulation or runoff of surface waters from any source.
Flood Boundary and Floodway Map (FBFM) - The floodplain management map issued by FEMA that depicts, based on detailed flood hazard analyses, the boundaries of the 1-percent-annual-chance (100-year) and 0.2-percent-annual-chance (500-year) floodplains and, when appropriate, the regulatory floodway. The FBFM does not show flood insurance risk zone designations or BFEs.
Flood-Control Storage - Storage of water in reservoirs to abate flood damage.
Flood Elevation Determination Docket (FEDD) - A file maintained by FEMA that includes all correspondence between FEMA and the community concerning a flood study; reports of meetings held among FEMA representatives, community representatives, the State NFIP Coordinator, private citizens, FEMA and community contractors, or other interested parties; relevant publications (e.g., newspaper notices, NFIP notices); Letter of Final Determination; a copy of the FIS report; a copy of the FIRM or DFIRM; and a copy of the FBFM if one was published.
Flood-Frequency Curve - A graph showing the number of times per year on the average that floods of certain magnitudes are equaled or exceeded.
Flood-Frequency Analysis - An analytical technique that involves using observed annual peak flow data to calculate statistical information, such as mean values, standard deviations, skewness, and recurrence intervals. These statistical data are then used to construct frequency distributions, which are graphs and tables that tell the likelihood of various discharges as a function of recurrence interval or exceedence probability.
Flood Hazard Boundary Map (FHBM) - The initial insurance map issued by FEMA that identifies, based on approximate analyses, the areas of the 1-percent-annual-chance (100-year) flood hazard within a community.
Flood Gate - A gravity outlet fitted with vertically-hinged doors, opening if the inner water level is higher than the outer water level, so that drainage takes place during low water.
Flood Hazard Mapping Program - The program undertaken by FEMA to conduct FISs and prepare reports and maps delineating flood hazards in floodprone communities throughout the United States.
Flood Insurance Rate Map (FIRM) - The insurance and floodplain management map produced by FEMA that identifies, based on detailed or approximate analyses, the areas subject to flooding during a 1-percent-annual-chance (100-year) flood event in a community. Flood insurance risk zones, which are used to compute actuarial flood insurance rates, also are shown. In areas studied by detailed analyses, the FIRM shows BFEs to reflect the elevations of the 1-percent-annual-chance flood. For many communities, when detailed analyses are performed, the FIRM also may show areas inundated by 0.2-percent-annual-chance (500-year) flood and regulatory floodway areas.
Flood Insurance Rate Zones - See Flood Insurance Risk Zones.
Flood Insurance Risk Zones - The zones, also referred to as "risk premium rate zones" and "flood insurance rate zones", shown on a FIRM or FHBM that are used to determine flood insurance premium rates for properties in a mapped area. Flood insurance risk zones include SFHAs and non-SFHA areas.
Flood Insurance Study (FIS) - See Study/Mapping Project.
Flood Insurance Study (FIS) Report - A document, prepared and issued by FEMA, that documents the results of the detailed flood hazard assessment performed for a community. The primary components of the FIS report are text, data tables, photographs, and Flood Profiles.
Flood Interval - The interval between the transit of the moon over the meridian of a place and the time of the following flood.
Flood Map Modernization (Map Mod) - The multiyear effort undertaken by FEMA to perform flood hazard assessments and produce new or updated flood maps and related products for communities throughout the United States. Through Map Mod, FEMA (with the help of its contractors and mapping partners) will transform flood maps into a more reliable, easier-to-use, and readily available product.
Flood Map Project - See Study/Mapping Project.
Flood Mitigation Assistance (FMA) Program - The program through which FEMA provides funding to States and communities for measures that reduce or eliminate the long-term risk of flood damage to buildings, manufactured homes, and other structures insurable under the NFIP. The FMA Program provides grants for mitigation planning and projects with a goal of reducing claims under the NFIP.
Floodplain - Any land area that is susceptible to being inundated by water from any source.
Floodplain Administrator (FPA) - The community official who is responsible for implementing and enforcing floodplain management measures and for monitoring floodplain development.
Floodplain Management - The operation of a program of corrective and preventative measures for reducing flood damage, including, but not limited to, emergency preparedness plans, flood-control works, and floodplain management regulations.
Floodplain Management and Insurance (FMI) Branch - The component of the Mitigation Division in the FEMA Regional Office that helps reduce flood losses by providing affordable flood insurance for property owners; by encouraging communities to adopt and enforce floodplain management regulations that mitigate the effects of flooding on new and improved structures; and by working to reduce risk to life and property through the use of land use controls, building practices, and other tools.
Floodplain Management Regulations - The zoning ordinances, subdivision regulations, building codes, health regulations, special-purpose ordinances, and other applications of enforcement used by a community to manage development in its floodplain areas.
Floodproofing - Any combination of structural and nonstructural additions, changes, or adjustments to structures that reduce or eliminate flood damage to real estate or improved real property, water and sanitary facilities, structures, and their contents.
Flood Profile - A graph showing the relationship of water-surface elevation to location, with the latter generally expressed as distance above the mouth for a stream of water flowing in an open channel.
Flood Protection System - Those physical works for which funds have been authorized, appropriated, and expended and which have been constructed specifically to modify flooding to reduce the extent of the area subject to a "special flood hazard" and the extent of the depths of the associated flooding. Flood protection systems typically include hurricane tidal barriers, dams, reservoirs, levees, or dikes.
Flood Risk Open House - The term used to describe the public meeting, held after the formal Preliminary DFIRM Community Coordination Meeting with community officials, to familiarize the public with the coastal analysis and resulting DFIRM and FIS report.
Floodwall - A long, narrow concrete or masonry wall built to protect land from flooding.
Floodway - See Regulatory Floodway.
Floodway Fringe - The portion of the 1-percent-annual-chance (100-year) floodplain that is not within the regulatory floodway and in which development and other forms of encroachment may be permitted under certain circumstances.
Footprint - The land area occupied by a structure.
Freeboard - A factor of safety usually expressed in feet above a flood level for purposes of floodplain management.
Frontal Dune - A ridge or mound of unconsolidated sandy soil, extending alongshore landward of the sand beach and defined by relatively steep slopes abutting markedly flatter and lower regions on each side.
Gabion - A rock-filled cage of wire or metal that is placed on slopes or embankments to protect them from erosion caused by flowing or fast-moving water.
Geographic Information System (GIS) - A system of computer hardware, software, and procedures designed to support the capture, management, manipulation, analysis, modeling, and display of spatially referenced data for solving complex planning and management problems.
Generating Area - In wave forecasting, the continuous area of water surface over which the wind blows in nearly a constant direction.
Government Printing Office - See U.S. Government Printing Office (GPO).
Hazard - An event or physical condition that has the potential to cause fatalities, injuries, property damage, infrastructure damage, agricultural loss, damage to the environment, interruption of business, and other types of loss or harm.
Hazards U.S. Multi-Hazard (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 state-of-the-art 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.
Hazard Mitigation Assistance (HMA) Branch - The component of the Mitigation Division in the FEMA Regional Office that administers the Hazard Mitigation Grant Program, Pre-Disaster Mitigation Program, Flood Mitigation Assistance Program, Repetitive Flood Claims Program, and Severe Repetitive Loss Program.
Hazard Mitigation Grant Program (HMGP) - The program, authorized under Section 404 of the Stafford Act, under which FEMA provides grants to States and local governments to implement long-term hazard mitigation measures after a presidential disaster declaration. The purpose of the HMGP is to reduce the loss of life and property due to natural disasters and to enable mitigation measures to be implemented during the immediate recovery from a presidentially declared disaster.
Headquarters (HQ) - The FEMA office in Washington, DC.
High-Velocity Wave Action - A condition in which wave heights or wave runup depths are greater than or equal to 3.0 feet.
High-Water Mark (HWM) - A physical mark, such as a mud line, that designates the location and elevation of floodwaters from a storm event.
Highest Adjacent Grade - The highest natural elevation of the ground surface prior to construction next to the proposed walls of a structure.
High Water (HW) - The maximum height reached by a rising tide. The height may be solely due to the periodic tidal forces or it may have superimposed upon it the effects of prevailing meteorological conditions.
Higher High Water (HHW) - The higher of the two high waters of any tidal day.
Holland B Coefficient - A parameter used in some hurricane wind models to control the peakedness of the hurricane wind profile.
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.
Hydraulic Analysis - An engineering analysis of a flooding source carried out to provide estimates of the elevations of floods of selected recurrence intervals.
Hydraulic Computer Model - A computer program that uses flood discharge values and floodplain characteristic data to simulate flow conditions and determine flood elevations.
Hydraulic Methodology - Analytical methodology used for assessing the movement and behavior of floodwaters and determining flood elevations and regulatory floodway data.
Hydrologic Analysis - An engineering analysis of a flooding source carried out to establish peak flood discharges and their frequencies of occurrence.
Hydrologic Unit Code (HUC) - A unique code, consisting of two to eight digits, used to identify units (watersheds) in the U.S. Geological Survey’s four-level classification system.
Hydrology - The science encompassing the behavior of water as it occurs in the atmosphere, on the surface of the ground, and underground.
Increased Cost of Compliance (ICC) - The insurance coverage, an endorsement to a Standard Flood Insurance Policy, that is made available to policyholders for homes or businesses that are damaged by a flood. ICC coverage allows policyholders to meet certain building requirements in their community to reduce future flood damage before they repair or rebuild their home or business.
Interior Drainage Systems - Systems associated with levee systems that usually include storage areas, gravity outlets, pumping stations, or a combination thereof.
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.
Joint Probabability Method-Optimal Sampling (JPM-OS) - A statistical procedure for selecting the optimal configuration of hypothetical hurricanes required to develop storm surge frequency curves.
Landmark - A conspicuous object, natural or artificial, located near or on land, which aids in fixing the position of an observer.
Legally Defined Parcel of Land - Parcel of land for which a metes and bounds description or a plat has been recorded. Structure may exist on legally defined parcels of land.
Letter of Determination Review (LODR) - A FEMA response to a request from a borrower and lender that FEMA provide its concurrence or disagreement with the lender’s determination on whether the borrower’s building is in the SFHA shown on the effective NFIP map.
Letter of Final Determination (LFD) - The letter in which FEMA announces its final determination regarding the flood hazard information, including (when appropriate) proposed and proposed modified BFEs and base flood depths, presented on a new or revised FIRM, FIS report, and (when appropriate) FBFM for a particular community. In the LFD, FEMA begins the adoption/compliance period and establishes the effective date for the new or revised FIRM/DFIRM, FIS report, and/or FBFM.
Letter of Map Amendment (LOMA) - An official determination by FEMA that a property has been inadvertently included in an SFHA as shown on an effective FHBM, FIRM, or DFIRM and is not subject to inundation by the 1-percent-annual-chance flood. Generally, the property is located on natural high ground at or above the BFE or on fill placed prior to the effective date of the first NFIP map designating the property as within an SFHA. Limitations of map scale and development of topographic data more accurately reflecting the existing ground elevations at the time the maps were prepared are the two most common bases for LOMA requests.
Letter of Map Change (LOMC) - A collective term used to describe official amendments and revisions to NFIP maps that are accomplished by cost-effective administrative procedures and disseminated by letter.
Letter of Map Change Revalidation (LOMC-VALID) Letter - A letter issued by FEMA, immediately before the effective date of a revised FIRM, new DFIRM, or revised DFIRM, to notify community officials about LOMAs, LOMR-Fs, and LOMRs that will remain in effect after the new or revised FIRM or DFIRM is published.
Letter of Map Revision (LOMR) - A letter issued by FEMA to revise the effective FIRM/ DFIRM, FBFM, and/or FIS report for a community to change BFEs, floodplain and floodway boundary delineations, and/or flood insurance risk zone designations.
Letter of Map Revision Based on Fill (LOMR-F) - A LOMC issued by FEMA when FEMA determines that a legally defined parcel of land or structure has been elevated above the BFE based on the placement of earthen fill after the date of the first NFIP map.
Levee - A manmade 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.
Levee-Impacted Area - The floodplain area landward of a levee system for which the levee system provides some level of flood protection or risk reduction.
Levee Owner – A Federal or State agency, a water management or flood control district, a local community, a levee district, a nonpublic organization, or an individual considered the proprietor of a levee.
Levee System - A flood protection system that consists of a levee, or levees, and associated structures, such as closure and drainage devices, which are constructed and operated in accordance with sound engineering practices.
LIght Detection and Ranging (LIDAR) System - An airborne laser system, flown aboard rotary or fixed-wing aircraft, that is used to acquire x, y, and z coordinates of terrain and terrain features that are both manmade and naturally occurring. LIDAR systems consist of an airborne Global Positioning System with attendant base station(s), Inertial Measuring Unit, and light-emitting scanning laser.
Limit of Moderate Wave Action (LimWA) - A line within the SFHA designated Zone AE on a DFIRM that marks the inland limit of the area inundated by the 1-percent-annual-chance, 1.5- foot breaking wave. The LimWA is provided on the DFIRM, for informational purposes, because these moderate waves can cause damage to structures; the damage would not be as severe as the damage caused by the 1-percent-annual-chance, 3- foot breaking waves.
Local Newspaper - The community newspaper, identified by the CEO or other designated community official, in which FEMA publishes notices at the beginning of a Flood Map Project, at the beginning of the appeal period, and at other times during the processing of a new or revised FIRM or DFIRM when required.
Lot - A parcel of land for which a metes and bounds description or a plat has been recorded and on which one or more structures may be built.
Lowest Adjacent Grade (LAG) - The lowest natural elevation of the ground surface next to a structure.
Lowest Finished Floor Elevation (LFFE) - The lowest floor of the lowest enclosed area (including basement) of a structure.
Manning’s n - A coefficient of roughness, used in a formula for estimating the capacity of channel to convey water.
Manufactured Home - Any building that is transportable in one or more sections, which is built on a permanent chassis and designed to be used with or without a permanent foundation when connected to the required utilities. Park trailers, recreational vehicles, and other similar vehicles are not considered manufactured homes.
Map Amendment - A change to an effective NFIP map that results in the exclusion from the SFHA of an individual structure or legally defined parcel of land that has been inadvertently included in the SFHA (i.e., no alterations of topography have occurred since the date of the first NFIP map that showed the structure or parcel to be within the SFHA.
Map Assistance Center - See FEMA Map Information Exchange (FMIX).
Mapping Information Platform (MIP) - An online portal for the Map Mod program that provides numerous sets of hazards data and a suite of tools for use by FEMA approved map-generating partners. The MIP is also being used to help deliver and standardize digital maps and other geospatial products as part of the National Spatial Data Infrastructure.
Mapping Needs Update Support System (MNUSS) - The computerized database system that is used by FEMA and its Flood Hazard Mapping Partners to compile information on mapping needs nationwide.
Mapping Activity Statement (MAS) - An agreement signed by FEMA and a participant (community, regional agency, or State agency) in the CTP Program under which the participant will complete specific mapping activities.
Mapping Project - See Study/Mapping Project.
Map Revision - A change to an effective NFIP map that is accomplished by a LOMR or a Physical Map Revision.
Map Service Center (MSC) - The FEMA facility through which flood maps and an array of related products are distributed in electronic form.
Marsh - A wetland dominated by herbaceous or nonwoody plants often developing in shallow ponds or depressions, river margins, tidal areas, and estuaries.
Mean High Water (MHW) - The average height of the high waters over a 19-year period.
Mean Higher High Water (MHHW) - The average height of the higher high waters over a 19-year period.
Mean Low Water (MLW) - The average height of the low waters over a 19-year period.
Mean Lower Low Water (MLLW) - The average height of the lower low waters over a 19-year period.
Mean Sea Level (MSL) - The average height of the surface of the sea for all stages of the tide over a 19-year period, usually determined from hourly height readings.
Minimally Floodprone Community - A community that FEMA has determined to be subject to inundation by the 1-percent-annual-chance (100-year) flood, but for which existing conditions indicate that the area is unlikely to be developed in the foreseeable future. The criteria used by FEMA to evaluate a community’s development potential are as follows: (1) Floodplains are publicly owned and designed for open space or preservation; (2) Zoning laws, sanitary codes, subdivision regulations, shore land regulations, or community regulations effectively prohibit floodplain development; (3) Surrounding land use or topography effectively limits the development potential; (4) Population is decreasing or stable, and there is no foreseeable pressure for floodplain development; and (5) Floodplains are remote and uninhabited, and future development is unlikely.
Mitigation - A sustained action taken to reduce or eliminate long-term risk to people and property from flood hazards and their effects. Mitigation distinguishes actions that have a long-term impact from those are more closely associated with preparedness for, immediate response to, and short-term recovery from specific events.
Mitigation Directorate - See Federal Insurance and Mitigation Administration (FIMA).
Monochromatic Waves - A series of waves generated in a laboratory; each wave has the same length and period.
National Elevation Dataset (NED) - The primary elevation data product of the U.S. Geological Survey. The NED is a seamless dataset with the best available raster elevation data of the conterminous United States, Alaska, Hawaii, and territorial islands.
National Flood Insurance Fund (NFIF) - The fund used as the funding mechanism for the NFIP.
National Flood Insurance Program (NFIP) - Federal Program under which flood-prone areas are identified and flood insurance is made available to the owners of the property in participating communities.
Non-Floodprone Community - See Non-SFHA Community.
Non-Participating Community - A community that has been identified by FEMA as being floodprone but has chosen not to participate in the NFIP.
Non-SFHA Community - A community that FEMA has determined not to be subject to inundation by the 1-percent-annual-chance flood. The FEMA guidelines employed for determining whether a community is designated as a "non-SFHA community" are that the Special Flood Hazard Areas (SFHAs) are less than 200 feet wide and all drain less than 1 square mile, or physiographic features that preclude floodplain development exist in the community.
Otherwise Protected Area (OPA) - An undeveloped coastal barrier within the boundaries of an area established under Federal, State, or local law, or held by a qualified organization, primarily for wildlife refuge, sanctuary, recreational, or natural resource conservation purposes.
Overtopping - The passing of water over the top of a structure as a result of wave runup or surge action.
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.
Participating Community - Any community that voluntarily elects to participate in the NFIP by adopting and enforcing floodplain management regulations that are consistent with NFIP standards.
Partnership Agreement - An agreement, sometimes referred to as a Memorandum of Agreement, that is signed by FEMA and a community, regional agency, or State agency that wishes to participate in the CTP Program. The Partnership Agreement is a broad statement of principle, emphasizing the value of the NFIP's three components of insurance, floodplain management, and mapping.
Physical Map Revision (PMR) - A revision made by FEMA to an effective FIRM/DFIRM, FBFM, and/or FIS report based on community-supplied data. FEMA issues PMRs when (1) changes resulting from the requested revision are extensive, affecting significant portions of a FIRM/DFIRM panel or multiple FIRM/DFIRM panels; (2) revision will add significant SFHAs to the effective FIRM/DFIRM; or (3) revision will result in an increase in the BFEs and/or regulatory floodway for an extended area.
Ponding - The result of runoff or flows collecting in a depression that may have no outlet, subterranean outlets, rim outlets, or manmade outlets such as culverts or pumping stations. Impoundments behind manmade obstructions are included in this type of shallow flooding as long as they are not backwater from a defined channel or do not exceed 3.0 feet in depth.
Pre-Disaster Mitigation (PDM) Program - The program through which FEMA assists States, Indian Tribal governments, and local governments with cost-effective hazard mitigation activities that complement a comprehensive mitigation program. The program provides applicants with an opportunity before disasters strike to raise risk awareness and reduce disaster losses through planning and project grants.
Preferred Risk Policy (PRP) - A flood insurance policy that offers low-cost coverage to owners and tenants of eligible structures located in moderate-risk areas (i.e., Zone B, Zone C, Zone X, Zone X (shaded)) on the current effective FIRM or DFIRM.
Preliminary Base Flood Elevations (BFEs) - The BFEs that are shown on the Preliminary DFIRM and in the Preliminary FIS report before the 90-day appeal period begins.
Preliminary DFIRM - The NFIP map that reflects the initial results of a Flood Map Project that is performed by or for FEMA. The Preliminary DFIRM is provided to CEOs and floodplain administrators of all affected communities before the 90-day appeal period is initiated.
Preliminary DFIRM Community Coordination (PDCC) Meeting - The formal meeting that FEMA Regional Office staff and mapping partners hold with community officials to discuss the results of a study/mapping projected presented on a Preliminary DFIRM and in a Preliminary FIS report.
Preliminary Flood Insurance Study (FIS) Report - The report that reflects the initial results of a Flood Map Project that is performed by or for FEMA. The Preliminary FIS report is provided to CEOs and floodplain administrators of all affected communities before the 90-day appeal period is initiated.
Primary Frontal Dune (PFD) - 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 PFD occurs at the point where there is a distinct change from a relatively steep to a relatively mild slope.
Procedure Memorandum (PM) - A guidance document issued by FEMA to implement updates to the requirements documented in FEMA’s Guidelines and Specifications for Flood Hazard Mapping Partners or Document Control Procedures Manual; to provide additional clarification of procedures to be followed by FEMA and Mapping Partners that are not documented in these two documents; and to establish new procedures and policies for FEMA and Mapping Partners that will be incorporated at a later date.
Production and Technical Services (PTS) Contractor - A team of private-sector firms (including firms specializing in engineering, information technology (IT), and program management) that provides a variety of engineering services under contract to FEMA, including performing flood studies/mapping projects (including coastal analyses); reviewing and processing flood studies/mapping projects performed by mapping partners; reviewing and processing appeals and other comments submitted during the 90-day appeal period for studies/mapping projects as well as requests for CLOMAs, LOMAs, CLOMRs, LOMRs, CLOMR-Fs, LOMR-Fs, and LODRs; preparing technical and administrative support data for storage in FEMA archives; and providing updates for FEMA Web and IT reporting systems as required.
Program Management (PM) Contractor - A team of private-sector firms that, under contract to FEMA HQ, performs a variety of program management activities in support of the Risk MAP initiative, including the development and implementation of a National Outreach Strategy.
Project Scoping - The stage during the mapping process that entails: conducting background research and community outreach; determining what flood hazard data can be used in the revised flood hazard analyses and/or transferred without change to the new DFIRM and FIS report; identifying other data needed to complete the mapping project and sources of those data; establishing priority levels for flooding sources to be analyzed and mapped; determining DFIRM format requirements; developing schedules and cost estimates for the various components of the study/mapping project; and assigning project tasks to project team members and developing appropriate contracts or agreements for assigned work.
Proposed Base Flood Elevations (BFEs)/Depths and Proposed Modified Base Flood Elevations (BFEs)/Depths - Those BFEs and base flood depths that FEMA posts on the FEMA Website and in the FEDERAL REGISTER at the start of the 90-day appeal period.
Protest - See Comment.
Public Assistance (PA) Program - The program through which FEMA provides Federal funding to State and local governments, and some nonprofit organizations, to respond to, recover from, and mitigate the future effects of disasters. The primary goal of the PA program is to help communities and their citizens recover from catastrophic disasters.
Quadrangle - A U.S. Geological Survey (USGS) topographic map.
Quality Assurance/Quality Control (QA/QC) Reviews - The reviews of the Flood Insurance Study reports, maps, and related products and data performed to ensure compliance with FEMA standards.
Radius of Maximum Winds - The distance from the eye of a hurricane, where surface and wind velocities are zero, to the place where surface wind speeds are maximum.
Recurrence Interval - The average interval of time within which a given flood will be equaled or exceeded once.
Regional Mitigation Divisions - The components of the FEMA Regional Offices that, among other responsibilities, administer the NFIP.
Regional Offices (ROs) - The FEMA offices located in Boston, Massachusetts; New York, New York; Philadelphia, Pennsylvania; Atlanta, Georgia; Chicago, Illinois; Denton, Texas; Kansas City, Missouri; Denver, Colorado; San Francisco, California; and Bothell, Washington.
Regional Support Centers (RSCs) - The PTS contractor offices that provide Risk MAP-related technical and program support services to the FEMA RO in support of the Risk MAP initiative.
Regular Phase - The phase of a community’s participation in the NFIP when more comprehensive floodplain management requirements are imposed and higher amounts of insurance are available. The FIRM forms the basis for this phase of participation in the NFIP.
Regular Program - See Regular Phase.
Regulatory Floodway - A floodplain management tool that is the regulatory area defined as the channel of a stream, plus any adjacent floodplain areas, that must be kept free of encroachment so that the base flood discharge can be conveyed without increasing the BFEs more than a specified amount. The regulatory floodway is not an insurance rating factor.
Repetitive Flood Claims (RFC) Program - A grant program, authorized by the Bunning-Bereuter-Blumenauer Flood Insurance Reform Act of 2004, through which FEMA provides funds to assist States and communities reduce flood damages to insured properties that have had one or more claims to the NFIP.
Risk Analysis (RA) Branch - The component of the Mitigation Division in the FEMA RO that applies engineering and planning practices in conjunction with advanced technology tools to identify hazards, assess vulnerabilities, and develop strategies to manage the risks associated with natural hazards.
Risk Analysis Division (RAD) - The component of the Federal Insurance and Mitigation Administration Directorate at FEMA HQ that applies engineering and planning practices in conjunction with advanced technology tools to identify hazards, assess vulnerabilities, and develop strategies to manage the risks associated with natural hazards.
Risk Insurance Division (RID) - The component of the Federal Insurance and Mitigation Administration Directorate that helps reduce flood losses by providing affordable flood insurance for property owners and by encouraging communities to adopt and enforce floodplain management regulations that mitigate the effects of flooding on new and improved structures.
Risk Reduction Division - The component of the Federal Insurance and Mitigation Administration Directorate that works to reduce risk to life and property through the use of land use controls, building practices, and other tools. These activities address risk in both the existing built environment and in future development, and they occur in both pre- and post-disaster environments.
Riverine Flooding - The overbank flooding of rivers and streams.
River Mile Marker (RMM) - A marker that indicates the distance in miles from a reference point on a river or other major watercourse.
RUNUP - A computer program that uses stillwater elevation, shore profile and roughness, and incident wave condition input information to compute a wave runup elevation that is consistent with the most detailed guidance available.
Saffir-Simpson Scale - A scale (Categories 1 through 5) that measures a hurricane’s intensity to give an estimate of the potential property damage and flooding expected. Wind speed is the determining factor in the scale.
Scientifically Incorrect Base Flood Elevations (BFEs) - Those BFEs determined through analyses in which the methodologies used and/or assumptions made are inappropriate for the physical processes being evaluated or are otherwise erroneous.
Scoping Meeting - The meeting where FEMA, community officials, and other stakeholders come together to discuss, and perhaps finalize, the scope for a particular study/mapping project (including the areas to be studied) and the task assignments.
Seawall - 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 seawall is typically more massive and capable of resisting greater wave forces than a BULKHEAD.
Second-layer coverage - Limit of coverage equal to the amounts made available under the Emergency and Regular Phases of the NFIP.
Section 65.10 Requirements - The NFIP regulatory criteria for the evaluation and mapping of areas protected by levee systems, which are presented at Title 44, Chapter 1, Section 65.10 of the Code of Federal Regulations.
Sediment - Fragmental material that originates from the weathering of rocks and is transported by, suspended in, or deposited by water or air or is accumulated in beds by other natural occurrence.
Sediment Cell - A length of coastline in which interruptions to the movement of sand or shingle along the beaches or near shore sea bed do not significantly affect beaches in the adjacent lengths of coastline.
Self-Sustaining Beach - A beach that has either natural or engineered sand retention that can be stable through the continued supply of natural sediment sources, without and mechanical nourishment needed over a long period.
Severe Repetitive Loss (SRL) Program - A grant program, authorized by the Bunning-Bereuter-Blumenauer Flood Insurance Reform Act of 2004, which allows FEMA to provide funding to reduce or eliminate the long-term risk of flood damage to severe repetitive loss structures insured under the NFIP.
Shallow Flooding - Unconfined flows over broad, relatively low relief areas, such as alluvial plains; intermittent flows in arid regions that have not developed a system of well-defined channels; overbank flows that remain unconfined, such as on delta formations; overland flow in urban areas; and flows collecting in depressions to form ponding areas. For NFIP purposes, shallow flooding conditions are defined as flooding that is limited to 3.0 feet or less in depth where no defined channel exists.
Sheet Runoff - The broad, relatively unconfined downslope movement of water across sloping terrain that results from many sources, including intense rainfall and/or snowmelt, overflow from a channel that crosses a drainage divide, and overflow from a perched channel onto deltas or plains of lower elevation. Sheet runoff is typical in areas of low topographic relief and poorly established drainage systems.
Shore - The narrow strip of land in immediate contact with the sea, including the zone between high and low water lines.
Shoreline Management - The development of strategic, long-term and sustainable coastal defense and land-use policy within a sediment cell.
Significant Wave - A statistical term relating to the 1/3 highest waves of a given wave group and defined by the average of their heights and periods.
Significant Wave Height - The average of the1/3 highest waves of a given wave group.
Significant Wave Period - An arbitrary period generally taken as the period of 1/3 highest waves of a given wave group.
Simulating WAves Nearshore (SWAN) Model - A third-generation phase-averaged wave model for the simulation of waves in waters of deep, intermediate and finite depth. It is suitable for use as a wave hindcast model.
Sea, Lake, and Overland Surge from Hurricane (SLOSH) Model - A computer model run by the National Hurricane Center to estimate storm surge heights and winds resulting from historical, hypothetical, or predicted hurricanes (by taking into account pressure, size, forward speed, track, winds).
Slab-on-Grade Foundation - The type of foundation in which the lowest floor of the house is formed by a concrete slab that sits directly on the ground.
Slough - A small muddy marshland or tidal waterway which usually connects other tidal areas.
Sluice - A structure containing a gate to control the flow of water from one area to another.
Sounding - A measured depth of water. On hydrographic charts, the soundings are adjusted to a specific plane of reference called a sounding datum.
Special Conversion - An action taken by FEMA to convert a community to the Regular Phase of the NFIP without preparing a FIRM with detailed flood risk zones. The exact action taken depends on whether FEMA determines the community is "non-floodprone" or "minimally floodprone".
Special Flood Hazard Area (SFHA) - The area delineated on a NFIP map as being subject to inundation by the base flood. SFHAs are determined using statistical analyses of records of riverflow, storm tides, and rainfall; information obtained through consultation with a community; floodplain topographic surveys; and hydrologic and hydraulic analyses.
Standard Flood Insurance Policy (SFIP) - The flood insurance policy issued by FEMA or an insurer pursuant to an arrangement with FEMA pursuant to Federal statutes and regulations. State - Any State, the District of Columbia, the territories and possessions of the United States, the Commonwealth of Puerto Rico, and the Trust Territory of the Pacific Islands.
State Coordinating Agency - See State NFIP Coordinator.
State NFIP Coordinator - The agency of the State government, or other office designated by the Governor of the State or by State statute at the request of FEMA, to assist in the implementation of the NFIP in that state.
State Plane Coordinates - A system of X,Y coordinates defined by the U.S. Geological Survey for each state. Locations are based on the distance from an origin within each state.
STeady State Irregular Wave (STWAVE) - An easy-to-apply, flexible, robust, half-plane model for nearshore wind-wave growth and propagation.
Stillwater Flood Elevation (SWEL) - Projected elevation that flood waters would assume, referenced to National Geodetic Vertical Datum of 1929, North American Vertical Datum of 1988, or other datum, in the absence of waves resulting from wind or seismic effects.
Stillwater Flood Level (SWFL) - Rise in the water surface above normal water level on the open coast due to the action of wind stress and atmospheric pressure on the water surface.
Storm Surge - The water that is pushed toward land from the high winds of a major storm (e.g., hurricane). Storm surge is usually estimated by subtracting the normal or astronomic high tide from the observed storm tide.
Storm Tide - The combined effect of storm surge, existing astronomical tide conditions, and breaking wave setup.
Structural Fill - See fill.
Structure - For floodplain management purposes, a walled and roofed building, including a gas or liquid storage tank that is principally above ground, as well as a manufactured home. For flood insurance purposes, a walled and roofed building, other than a gas or liquid storage tank, that is principally above ground and affixed to a permanent site, as well as a manufactured home on a permanent foundation.
Study/Mapping Project - Any activity undertaken by FEMA, separately or in partnership with a mapping partner, to create a new or updated DFIRM, including detailed engineering studies, approximate engineering studies, and floodplain boundary redelineations based on updated topographic information.
Subcritical Flow - Flow with a mean velocity that is less than the critical velocity; in other words, tranquil flow.
Substantial Damage - 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.
Substantial Improvement - Any reconstruction, rehabilitation, addition, or other improvement of a structure, the cost of which equals or exceeds 50 percent of the market value of the structure before the "start of construction" of the improvement.
Summary of Map Actions (SOMA) - A list, generated by FEMA and delivered to the community that summarizes the LOMAs, LOMR-Fs, and LOMRs that are or will be affected by a physical update to an effective FIRM/DFIRM.
Supercritical Flow - Flow with a mean velocity that is greater than the critical velocity; i.e., rapid flow.
Surge - See storm surge.
Swale - The depression between the beach ridges.
Swash - The rush of water up onto the beach face following the breaking of a wave.
Swell - Wind-generated waves that have traveled out of their generating area.
Technical Support Data Notebook (TSDN) - The format for the FEMA-maintained file that contains all of the technical and administrative support data for a community for which FEMA published an NFIP map and all revisions to that map.
Technically Incorrect Base Flood Elevations (BFEs)/Depths - Those BFEs and base flood depths determined through analyses in which the methodologies used have not been applied properly, are based on insufficient or poor-quality data, or do not account for the effects of physical changes that have occurred in the floodplain.
Temporary Benchmark (TBM) - A benchmark established for a particular study/mapping project or community.
Tidal Benchmark - A benchmark whose elevation has been determined with respect to mean sea level at a nearby tide gage; the tidal bench mark is used as reference for that tide gage.
Topographic Map - A map on which elevations are shown by means of contour lines.
Transect - Cross section taken perpendicular to the shoreline to represent a segment of coast with similar characteristics.
Triangulated Irregular Network (TIN) - A set of non-overlapping triangles developed from irregularly spaced points that are used to represent the facets of a surface.
Tropical Cyclone - A warm-core non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters, with organized deep convection and a closed surface wind circulation about a well-defined center.
Tropical Depression - A tropical cyclone with some rotary circulation at the water surface, with maximum sustained wind speeds of up to 39 miles per hour. The tropical depression is the second phase in the development of a hurricane.
Tropical Disturbance - A tropical cyclone that maintains its identify for at least 24 hours and is marked by moving thunderstorms and with slight or no rotary circulation at the water surface. Winds are not strong. It is a common phenomenon in the tropics and is the first discernable phase of hurricane development.
Tropical Storm - A tropical cyclone with maximum sustained (1-minute average) winds of 39 to 73 miles per hour.
Undeveloped Coastal Barrier - Any land area adjacent to the Atlantic Ocean, Pacific Ocean, or Great Lakes, where flood insurance will not be available for new or substantially improved structures. These areas are protected by law to discourage development and to preserve dunes, beaches, and wildlife habitats.
Universal Transverse Mercator (UTM) Grid - A system of plane coordinates based on 60 north-south trending zones, each 16 degrees of longitude wide, that circle the globe.
Unnumbered A Zones - Flood insurance risk zones, designated Zone A on a FIRM or DFIRM, that are based on approximate studies.
U.S. Government Printing Office (GPO) - The Federal Government office that is responsible for producing printed copies of Federal Government resources and delivering them to the originating Federal agency offices for distribution. GPO works directly with the FEMA Map Service Center on the distribution of flood maps and related products.
Velocity Zone/V Zone - See Coastal High Hazard Area.
Violation - The failure of a structure or other development to be fully compliant with a community’s floodplain management regulations.
Watershed - An area of land that drains into a single outlet and is separated from other drainage basins by a divide.
Water-Surface Elevations (WSELs) - The heights of floods of various magnitudes and frequencies in the floodplains of coastal or riverine areas, in relation to a specified vertical datum.
Wave - A ridge, deformation, or undulation of the water surface.
Wave Amplitude - The magnitude of the displacement of a wave from a mean value. An ocean wave has an amplitude equal to the vertical distance from stillwater level to wave crest.
Wave Crest - The highest part of a wave; that part of the wave above the stillwater level.
Wave Crest Elevation - The elevation of the crest of the wave.
Wave Crest Length - The length of a wave along its crest, sometimes called crest width.
Wave Forecasting - The theoretical determination of future wave characteristics, usually from observed or predicted meteorological phenomena.
Wave Generation - The creation of waves by natural or mechanical means; the creation and growth of waves caused by a wind blowing over a water surface for a certain period of time. The area involved is called the “generating area” or “fetch.”
Wave Height - The vertical distance between the wave crest and the wave trough.
Wave Height Analysis for Flood Insurance Studies (WHAFIS) - A computer program that uses representative transects (selected considering major topographic, vegetative, and cultural features) to compute wave crest elevations in a given study area.
Wave Hindcasting - The use of historical synoptic wind fields to calculate characteristics of waves that probably occurred at some past time.
Wave Propagation - The transmission of waves through water.
Wave Runup - The rush of wave water up a slope or structure.
Wave Runup Depth - The vertical distance between the maximum wave runup elevation and the eroded ground elevation.
Wave Runup Elevation - The elevation, referenced to NGVD29, NAVD88, or other datum, reached by wave runup.
Wave Setup - The increase in the stillwater surface near the shoreline, due to the presence of breaking waves.
Wave Steepness - The ratio of the wave height to the wave length.
Wind Field - The three-dimensional spatial pattern of winds.
Wind Waves - The waves being formed and built up by the wind; any wave generated by wind.