Below are commonly used terms and acronyms that are related to floodplain management. 


The terms listed below will regularly be used by local flooplain managers and City officials, as well as by Federal Emergency Management Agency (FEMA) staff, Mississippi Emergency Management Agency (MEMA) staff and those involved with the National Flood Insurance Program (NFIP).


Additional definitions specific to the City of Bay St. Louis and its floodplain management can be found in the Flood Damage Prevention Ordinance No. 603-10-2015.




0.2-Percent-Annual-Chance Flood—This is the flood that has a 0.2-percent chance of being equaled or exceeded in any given year (also known as the 500-year flood).


1-Percent-Annual-Chance Flood—This is the flood that has a 1-percent chance of being equaled or exceeded in any given year (also known as the base, or so-called 100-year, flood).


2-Percent-Annual-Chance Flood—This is the flood that has a 2-percent chance of being equaled or exceeded in any given year.


10-Percent-Annual-Chance Flood—This is 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.


100-Year Flood—See 1-Percent-Annual-Chance Flood.


500-Year Flood—See 0.2-Percent-Annual-Chance Flood.


Base Flood—This is the flood that has a 1-percent chance of being equaled or exceeded in any given year.  The base flood is also referred to as the 1-percent-annual-chance flood or the 100-year flood.


Base Flood Elevation (BFE) —This is the elevation of a flood having a 1-percent chance of being equaled or exceeded in any given year.  The BFE is also referred to as the 1-percent-annual-chance flood elevation or the 100-year flood elevation.


Base Map—This is the map of the community that depicts cultural features (e.g., roads, railroad, bridges, dams, culverts), drainage features (e.g., rivers, creeks, streams, shorelines), and corporate limits. 


Bench Mark (BM)—This is 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.


Building—See Structure.


Channel—This is 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.


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—See Undeveloped Coastal Barrier.


Coastal Barrier Resources System (CBRS)—This is 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 Flooding—This is flooding that occurs along the Great Lakes, the Atlantic and Pacific Oceans, and the Gulf of Mexico.


Coastal Flood Study—This is the term used to describe the engineering analysis of flood hazards along the Mississippi Gulf coast performed by FEMA.  The results of that study is reflected on the Digital Flood Insurance Rate Maps (DFIRM) and associated Flood Insurance Study (FIS).


Coastal High Hazard Area—This is 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.


Code of Federal Regulations (CFR)—This is the codification of the general and permanent rules published in the Federal Register by the Executive Departments and agencies of the Federal Government.  The NFIP regulations are printed in Parts 59 through 77 of Title 44 of the CFR.


Community—This is 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)—This is a telephone call made by FEMA Regional Office staff or the State NFIP Coordinator to a community to supplement or replace a Community Assistance Visit.


Community Assistance Program (CAP)—This is a FEMA program, funded by the NFIP, under which cost-shared funds are provided to States to provide technical assistance support to communities that are participating voluntarily in the NFIP.  The purpose of the CAP is to identify, prevent, and resolve floodplain management issues in NFIP participating communities before a flood occurs, or before poor performance or noncompliance warrant enforcement and intervention by FEMA.


Community Assistance Program-State Support Services Element (CAP-SSSE)—This is a program through which FEMA provides funding to States to provide technical assistance to communities participating in the NFIP and to evaluate community performance in implementing NFIP-compliant floodplain management activities.


Community Assistance Visit (CAV)—This is a visit by FEMA Regional Office staff or the State NFIP Coordinator to a community to assess whether the community’s floodplain management program meets NFIP participation requirements.


Community Flood Hazard Area (CFHA)—This is an area, as has been determined by the Floodplain Administrator (or other delegated, designated, or qualified community official) from available technical studies, historical information, and other available and reliable sources, which may be subject to periodic inundation by floodwaters that can adversely affect the public health, safety and general welfare.  This includes areas downstream from dams.


Community Information System (CIS)—This is 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)—This is a FEMA initiative, established under the NFIP, to recognize and reward communities that have implemented floodplain management measures beyond the minimum required by NFIP regulations. 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.


Conditional Letter of Map Amendment (CLOMA)—This is 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)—This is the FEMA response to a community request for FEMA 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 NFIP map and Flood Insurance Study 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 map and/or report.


Conditional Letter of Map Revision Based on Fill (CLOMR-F)—This is the FEMA response to a community request for FEMA comment on the effect(s) that a proposed project involving the placement of earthen fill within the Special Flood Hazard Area (SFHA) will have on the SFHA designation for one or more legally defined parcels of land or one or more proposed structures.


Consultation Coordination Officer (CCO)—This is the individual on the FEMA Regional Office staff who is responsible for coordinating with a community on activities related to the NFIP.


Countywide Format—This is the 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 NFIP map and in one report.


Cultural Features—This is the term used to describe 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)—These are the BFEs that are shown on the effective NFIP map that is in effect for a community for flood insurance and floodplain management purposes.


Current Effective Date—This is the date on which the NFIP map for a community becomes effective and all sanctions of the NFIP apply.


Current Effective Flood Insurance Study (FIS) Report—This is a document, prepared and issued by FEMA with the current effective map, that documents the results of the flood hazard assessment performed for a community or a county.  The primary components of the FIS report are text, data tables, photographs, and Flood Profiles.


Current Effective Map—This is the NFIP map issued by FEMA, usually a Flood Insurance Rate Map, 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.


Data Layer—This is the term used to describe data having similar characteristics being contained in the same plane or overlay (e.g., roads, rivers) of a Geographic Information System.  Usually, information contained in a data layer is thematically related and is designed to be used with other data layers.  Multiple data layers are combined to create Digital Flood Insurance Rate Maps.


Dataset—This is a named collection of logically related data records arranged in a prescribed manner.


Design Flood Event—This is the greater of two events: (1) the base flood, affecting those areas shown as Special Flood Hazard Areas on the Flood Insurance Rate Map for a community; or (2) the flood corresponding to the area designated as a flood hazard area on the Flood Hazard Boundary Map for a community or otherwise legally designated.


Detailed Study—This is 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 base flood depths.


Development—This is 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 Data—These are data displayed, recorded, or stored in binary notation.


Digital Elevation Model (DEM)—This is a file with terrain elevations recorded for the intersection of a fine-grained grid and organized by quadrangle as the digital equivalent of the elevation data on a topographic base map.


Digital Flood Insurance Rate Map (DFIRM)—This is a Flood Insurance Rate Map (FIRM) 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, multihazard digital maps.  Links 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; DEMs; and structure-specific data, such as digital elevation certificates and digital photographs of bridges and culverts.


Digital Flood Insurance Rate Map (DFIRM) Spatial Database—This is a database that was designed to facilitate collecting, storing, processing, and accessing data developed by FEMA, enabling FEMA Mapping Partners and contractors 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 Spatial Database provides the ability to georeference and overlay the mapping and engineering data, allowing the database to support a wide variety of existing and forthcoming FEMA engineering and mapping products.


Digital Orthophoto Quadrangle (DOQ)—This is the photographic map 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)—This is a land surface represented in digital form by an elevation grid or lists of three-dimensional coordinates.


Effective Date—See Current Effective Date.


Effective Flood Insurance Study Report—See Current Effective Flood Insurance Study (FIS)


Report Effective Map—See Current Effective Map.


Elevation Certificate—This is 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.


Encroachment—This is the term used to describe construction, placement of fill, or similar alteration of topography in the floodplain that reduces the area available to convey floodwaters.


Erosion—This is the process by which floodwaters lower the ground surface in an area by removing upper layers of soil.


External Data Request (EDR)—This is 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.


Federal Emergency Management Agency (FEMA)—This is the component of the U.S. Department of Homeland Security that oversees the administration of the NFIP.


Federal Information and Processing Standards (FIPS) Code—This is the unique five-digit number that is assigned to each county in the United States.  This number is made up of a two-digit state code followed by a three-digit county code.  The FIPS code is the first five digits of panel numbers for FIRMs or DFIRMs prepared in the Countywide Format.


Federal Register—This is the document, published daily by the Federal Government, that presents regulation changes and legal notices issued by Federal agencies.  FEMA publications in the Federal Register include Proposed, Interim, and Final Rules for BFE determinations; Compendiums of Flood Map Changes, published twice each year; Final Rules concerning community eligibility for the sale of flood insurance; and Notices announcing clarifications of procedures and requirements.


FEMA Map Assistance Center (FMAC)—This is the FEMA customer service center staffed by Map Specialists who are specially trained to answer specific questions about NFIP mapping and related issues, including: 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.  FMAC Map Specialists will link callers with other FEMA service and fax numbers and the FEMA Web site and provide information regarding, or copies of, FEMA products, brochures, and publications.  The FMAC number is 1-877-FEMA MAP (1-877-336-2627).


Fill—This is 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 BFEs and Base Flood Depths—These are 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.


Fiscal Year (FY)—This is the 12-month period that begins on October 1 and ends on September 30.


Flood—This is 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 Elevation Determination Docket (FEDD)—This is the file maintained by FEMA that includes all correspondence between FEMA and a 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,Federal Register Proposed and Final Rules); Letter of Final Determination; a copy of the Flood Insurance Study report; and a copy of the FIRM or DFIRM.


Floodflow-Frequency Curve—This is a graph showing the number of times per year on the average that floods of certain magnitudes are equaled or exceeded.


Flood-Frequency Analysis—This is 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)—This is the initial insurance map issued by FEMA that identifies, based on approximate analyses, the areas of the 1-percent-annual-chance flood hazard within a community.  The FHBM is the NFIP map used during the Emergency Phase of participation in the NFIP.


Flood Hazard Mapping Program—This is the program undertaken by FEMA to conduct flood hazard studies and prepare reports and maps delineating flood hazards in floodprone communities throughout the United States.


Flood Insurance Rate Map (FIRM)—This is 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 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 and/or base flood depths 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 the 0.2-percent-annual-chance (500-year) flood and regulatory floodway areas.


Flood Insurance Rate Zones— See Flood Insurance Risk Zones.


Flood Insurance Restudy (RFIS)—This is a revised study of flood hazards performed for a community that already has a current effective FIRM.


Flood Insurance Risk Zones—These are the zones, also referred to as “risk premium rate zones” and “flood insurance rate zones,” shown on a FIRM/DFIRM, or FHBM that are used to determine flood insurance premium rates for properties in the community covered by the FIRM/DFIRM or FHBM.  The flood insurance risk zones include Special Flood Hazard Areas (i.e., Zones A, A1-30, AE, A0, A99, AH, AR, AR/A, AR/A1-30, AR/AE, AR/A99, V, V1-30, VE, V0) and areas outside Special Flood Hazard Areas (i.e., Zones B, X, D, M, N, P, E).


Flood Insurance Study (FIS)—This is the initial study of flood hazards performed for a community that does not have a current effective FIRM or DFIRM. 


Flood Insurance Study (FIS) Report—This is a document, prepared and issued by FEMA, that documents the results of the detailed flood hazard assessment performed for a community or a county. The primary components of the FIS report are text, data tables, photographs, and Flood Profiles.


Flood Map Modernization (Map Mod)—This is the multiyear initiative undertaken by FEMA in support of the NFIP 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) is transforming flood maps into a more reliable, easier-to-use, and readily available product.  Updated, digital flood maps will become the platform for identifying multiple hazards—not just floods.  Through Map Mod, FEMA is achieving the following goals: create a premier hazard map collection and technically advanced delivery system to support risk management; achieve effective program management by sharing responsibilities and aligning partner missions; build and maintain mutually beneficial partnerships by communicating hazard risk information; and establish better understanding of where to obtain flood hazard data and how to use the information for sound mitigation decisions.


Flood Map Project—See Mapping Project.


Flood Mitigation Assistance (FMA) Program—This is 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—This is any land area that is susceptible to being inundated by water from any source.


Floodplain Management—This is 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 Regulations—These are 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.


Floodprone Area—See Floodplain.


Floodprone Community—This is a term used to describe any community that is subject to inundation by the 1-percentannual-chance flood.


Flood Profile—This is 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—This is the physical works for which funds have been authorized, appropriated, and expended and which have been constructed specifically to modify flooding in order 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, levee systems, or dikes.


Floodwall—This is a long, narrow concrete or masonry wall built to protect land from flooding.


Floodway—See Regulatory Floodway.


Floodway Fringe—This is the portion of the 1-percent-annual-chance floodplain that is not within the regulatory floodway and in which development and other forms of encroachment may be permitted under certain circumstances.


Freeboard—This is a factor of safety, usually expressed in feet above a flood level, for purposes of floodplain management. "Freeboard'' tends to compensate for the many unknown factors that could contribute to flood heights greater than the height calculated for a selected size flood and floodway conditions, such as wave action, bridge openings, and the hydrologic effect of urbanization of the watershed.


Geographic Information System (GIS)—This is 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.


Grandfathering— To recognize policyholders who have either built in compliance with the flood map and/or remained loyal customers of the NFIP by maintaining continuous coverage, FEMA has "grandfather" rules.  These rules allow such policyholders to benefit in the rating for that building.  For such buildings, the insured has the option of using the current rating criteria for that property or having the premium rate determined by using the BFE and/or flood insurance risk zone on the map in effect when the building was originally constructed (for those built in compliance) or when coverage was first obtained (for those with continuous coverage).


Hazard—This is 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.


Hazard Mitigation—This is the sustained action taken to reduce or eliminate long-term risk to people and their property from hazards.


Hazard Mitigation Grant Program (HMGP)—This is 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.


High-Water Mark (HWM)—This is a physical mark, such as a mud line, that designates the location and elevation of floodwaters from a storm event.


Hydraulic Analysis—This is an engineering analysis of a flooding source carried out to provide estimates of the elevations of floods of selected recurrence intervals.


Hydraulic Computer Model—This is a computer program that uses flood discharge values and floodplain characteristic data to simulate flow conditions and determine flood elevations.


Hydraulic Methodology—This is an analytical methodology used for assessing the movement and behavior of floodwaters and determining flood elevations and regulatory floodway data.


Hydrograph—A graph showing stage, flow, velocity, or other properties of water with respect to time.


Hydrologic Analysis— This is an engineering analysis of a flooding source carried out to establish peak flood discharges and their frequencies of occurrence.


Hydrology—This is 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)—This is 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—These are systems associated with levee systems that usually include storage areas, gravity outlets, pumping stations, or a combination thereof.


Joint Probability Method (JPM)—This is a method for evaluating and modeling coastal storm surges pioneered by the National Oceanic and Atmospheric Administration and used in early FEMA coastal surge studies.  In the JPM approach, hurricanes are defined by give parameters: track angle, track position, forward speed, storm radius to maximum winds, and central pressure depression.


Legally Defined Parcel of Land—This is a 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)—This is 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 Special Flood Hazard Area shown on the effective NFIP map.


Letter of Final Determination (LFD)—This is the letter in which FEMA announces its final determination regarding the flood hazard information, including (when appropriate) BFEs or base flood depths, presented on a new or revised DFIRM and in a new or revised FIS report.  By issuing the LFD, FEMA begins the compliance period and establishes the effective date for the new or revised DFIRM and FIS report.


Letter of Map Amendment (LOMA)—This is an official determination by FEMA that a property has been inadvertently included in an SFHA as shown on a current effective FHBM, FIRM, or DFIRM and is not subject to inundation by the 1percent-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 a Special Flood Hazard Area.  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)—This is a collective term used to describe official amendments and revisions to National Flood Insurance maps that are accomplished by a cost-effective administrative procedure and disseminated by letter.


Letter of Map Change Revalidation (LOMC-VALID) Letter—This is a letter issued by FEMA, immediately before the effective date of a revised FIRM or DFIRM, to notify community officials about LOMCs that will remain in effect after the FIRM or DFIRM is published.


Letter of Map Revision (LOMR)—A letter issued by FEMA to revise the FIRM, DFIRM, and/or FIS report for a community to change BFEs or base flood depths, floodplain and floodway boundary delineations, and/or coastal high hazard areas.


Letter of Map Revision Based on Fill (LOMR-F)—This is a letter 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 for the area in which the parcel of land or structure is located.


Light Detection and Ranging (LIDAR) System—This is 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)—This is 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.


Long-Term Recovery Office—This is an office established by FEMA near a disaster site following a presidentially declared disaster.  The Long-Term Recovery Office, which is staffed by both Federal and State employees, is established to provide support to State and local community officials, business, and citizens during the period of reconstruction following a disaster.  Long term recovery is the year-round focus of the office, with particular attention paid to helping communities recover in a way that better prepares them for future disasters. 


Lot—This is 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)—This is the lowest natural elevation of the ground surface next to a structure.


Lowest Finished Floor Elevation (LFFE)—This is the lowest floor of the lowest enclosed area (including basement) of a structure.


Lowest Floor—This is the lowest floor of the lowest enclosed area (including basement) of a structure.  An unfinished or flood resistant enclosure, usable solely for parking of vehicles, building access, or storage in an area other than a basement area is not considered a building's lowest floor.


Manufactured Home—This is 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—This is 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 Assistance Center (FMAC).


Map Modernization—See Flood Map Modernization.



Mapping Project—This is any activity undertaken by FEMA or a mapping partner to create a new or updated DFIRM, including detailed studies, limited detailed studies, approximate studies, and floodplain boundary redelineations based on updated topographic information.


Map Revision—This is a change to an effective NFIP map that is accomplished by a LOMR or a Physical Map Revision.


Map Service Center (MSC)—This is the FEMA facility through which flood maps and an array of related products are distributed in hardcopy or electronic form. The MSC is available online at


Mississippi Coastal Improvement Program (MsCIP)—This is the program undertaken by the U.S. Army Corps of Engineers to determine the nature and level of hurricane protection and environmental restoration for coastal Mississippi.


Mississippi Emergency Management Agency (MEMA)—This is the State agency that has primary responsibility for coordinating NFIP activities within the State of Mississippi.  MEMA has entered into a Partnership Agreement with MDEQ and FEMA to produce flood hazard mapping for the Mississippi Gulf Coast.


Mitigation—This is 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—This is the component of FEMA that, among other responsibilities, administers the NFIP.


Mitigation Division—See Mitigation Directorate.


National Flood Insurance Fund (NFIF) —This is the fund used as the funding mechanism for the NFIP.


National Flood Insurance Program (NFIP) — This is the Federal program under which floodprone areas are identified and flood insurance is made available to the owners of the property in participating communities.


Non-Participating Community—This is a community that has been identified by FEMA as being floodprone but has chosen not to participate in the NFIP.


Otherwise Protected Area (OPA)—This is 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.


Participating Community—This is any community that voluntarily elects to participate in the NFIP by adopting and enforcing floodplain management regulations that are consistent with the standards of the NFIP.


Physical Map Revision (PMR)—This is a revision made by FEMA to a FIRM, DFIRM, 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 or DFIRM panel or multiple FIRM or DFIRM panels; (2) the revision will add significant SFHAs to the current effective FIRM or DFIRM; or (3) the revision will result in an increase in the BFEs and/or regulatory floodway.


Ponding—This is 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—This is 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)—This is 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.



Primary Frontal Dune—This is a continuous or nearly continuous mound or ridge of sand with relatively steep seaward and landward slopes immediately landward and adjacent to the beach and subject to erosion and overtopping from high tides and waves during major coastal storms.  The inland limit of the primary frontal dune occurs at the point where there is a distinct change from a relatively steep slope to a relatively mild slope.


Public Assistance (PA) Program—This is 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.


Recurrence Interval—This is the average interval of time within which a given flood will be equaled or exceeded once.



Regulatory Floodway—This is 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.


Risk Mapping, Analysis, and Planning (Risk MAP)—This is a seamless FEMA initiative aimed at reducing losses of life and property through effective local mitigation activities enable by quality flood hazard data, risk assessments, and mitigation planning.  Risk MAP will provide an integrated national assessment of risks based on digital flood hazard data and Web-accessible data.  Risk MAP information and tools will help communities develop informed mitigation plans that will reduce losses from natural hazards.


Riverine Flooding—This is the overbank flooding of rivers and streams.


Scale—This is a representative fraction of a paper map distance to ground distance.


Sediment—This is 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.


Shallow Flooding—These are 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—This is 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.


Slab-on-Grade Foundation—This is the type of foundation in which the lowest floor of the house is formed by a concrete slab that sits directly on the ground.


Special Flood Hazard Area (SFHA)—This is the area delineated on an NFIP map as being subject to inundation by the 1-percent-annual-chance 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.


Stage—This is the height of a water surface above an established datum plane.


Standard Flood Insurance Policy (SFIP)—This is the single-peril (flood) insurance policy issued by FEMA, or by an insurer in accordance with an arrangement with FEMA, pursuant to Federal statutes and regulations.  The SFIP pays for direct physical damage to insured property up to replacement cost or Actual Cash Value of the actual damages or the policy limit of liability, whichever is less.


State—This is the term used to describe any State or Commonwealth, 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—This is 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.  In Mississippi, the State NFIP Coordinator is MEMA.


State Plane Coordinates—This is 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.


Stillwater Flood Elevation (SWEL)—This is the projected elevation that floodwaters would assume, referenced to the 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)—This is the rise in the water surface above normal water level on the open coast caused by the action of wind stress and atmospheric pressure on the water surface.


Storm Surge – This is the water that is pushed toward land from the high winds of a major storm (e.g., hurricane).


Structure—This is, 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.


Substantial Damage—This is damage of any origin sustained by a structure whereby the cost of restoring the structure to its before damaged condition would equal or exceed 50 percent of the market value of the structure before the damage occurred.


Substantial Improvement—This is 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)—This is a list, generated by FEMA and delivered to the community CEO and floodplain administrator at specific milestones, that summarizes the LOMAs, LOMR-Fs, and LOMRs that are or will be affected by a physical update to a FIRM or DFIRM.


Temporary Bench Mark (TBM)—This is a bench mark established for a particular study/mapping project or community (previously referred to as an Elevation Reference Mark).


Transect—This is a cross section taken perpendicular to the shoreline to represent a segment of coast with similar characteristics.


Transitional Recovery Office (TRO)—This is an office established by FEMA near a disaster site following a presidentially declared disaster.  The TRO is established to provide support to State and local community officials, business, and citizens during the period of reconstruction following a disaster.


Triangulated Irregular Network (TIN)—This is a set of non-overlapping triangles developed from irregularly spaced points that are used to represent the facets of a surface.


Undeveloped Coastal Barrier—This is any land area adjacent to the Atlantic Ocean, Pacific Ocean, Great Lakes, or Gulf of Mexico where flood insurance will not be available for new or substantially improved structures.  These areas are protected by law to discourage development in an attempt to preserve dunes, beaches, and wildlife habitats.


Unnumbered A Zones—These are flood insurance risk zones, designated “Zone A” on an FHBM, FIRM, or DFIRM, that are based on approximate studies.



Velocity Zone/V Zone—See Coastal High Hazard Area.


Violation—This is the failure of a structure or other development to be fully compliant with a community’s floodplain management regulations.  A structure or other development without an Elevation Certificate, other certifications, or other evidence of compliance required in Section 60.3 of the NFIP regulations is presumed to be in violation until such time as that documentation is provided.


Watershed—This is an area of land that drains into a single outlet and is separated from other drainage basins by a divide.


Water-Surface Elevations (WSELs)—These are 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 Height—This is the vertical distance between the wave crest and the wave trough.


Wave Runup—This is the rush of wave water up a slope or structure.


Wave Setup—This is the increase in the stillwater surface near the shoreline, due to the presence of breaking waves.


Zone Division Line/Gutter—This is the boundary, shown on a FIRM or DFIRM, dividing SFHAs of different BFEs, base flood depths, flow velocities, or flood insurance risk zone designations.