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Flood Terms
| Term | Acronym | Definition |
|---|---|---|
| Base flood | The flood having a 1 percent chance of being equaled or exceeded in any given year. Also referred to as the 100-year flood. The base flood is used by the National Flood Insurance Program as the basis for mapping, insurance rating, and regulating new construction | |
| Base flood depth | A measurement of the base flood in feet above ground, used for shallow flooding | |
| Base floodplain | The area of water and land inundated by the base flood | |
| Basin | See watershed | |
| Bench marks | Monuments on the ground that show the elevation of the spot above sea level | |
| Channel | Defined landforms that carry water | |
| Community | A city, county, township, Indian tribe or authorized tribal organization, Alaska Native village or authorized native organization, or other local government with the statutory authority to adopt and enforce floodplain regulations and participate in the National Flood Insurance Program | |
| Community Assistance Program | CAP | A FEMA program that funds state activities that help communities in the NFIP |
| Community Rating System | CRS | A program that provides a flood insurance premium rate reduction based on a community's floodplain management activities |
| Dam breach inundation area | The area flooded by a dam failure | |
| Damage Survey Report | DSR | A form completed by disaster assistance staff to determine the repair and reconstruction needs of public and private nonprofit facilities |
| Detailed studies | Flood hazard mapping studies that are done using hydrologic and hydraulic methods that produce base flood elevations, floodways, and other pertinent flood data | |
| Development | Any man-made change to improved or unimproved real estate, including but not limited to buildings or other structures, mining, dredging, filling, grading, paving, excavation or drilling operations or storage of equipment and materials | |
| Discharge | The amount of water that passes a point in a given period of time. Rate of discharge is usually measured in cubic feet per second (cfs) | |
| Dry Floodproof | To protect a building and its contents from flood damage by taking measures to seal the building so that flood waters cannot enter | |
| Elevation Certificate | 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. | |
| Elevation reference marks | See bench marks | |
| Emergency Alert System | EAS | Emergency Alert System Replaced the Emergency Broadcast system in 2002 |
| Emergency Operations Center | EOC | A facility that houses communications equipment that is used to coordinate the response to a disaster or emergency |
| Enabling legislation | State laws that authorize communities to perform governmental activities, such as enacting and enforcing regulations | |
| Encroachment review | An analysis to determine if a project will increase flood heights or cause increased flooding downstream | |
| Federal Emergency Management Agency | FEMA | Most of the National Flood Insurance Program field work and community coordination are done by the 10 FEMA Regional Offices |
| Federal Insurance Administration | FIA | FIA was the part of the Federal Emergency Management Agency that administered the National Flood Insurance Program. This is now the responsibility of FEMA's Mitigation Division |
| Flash flood | A flood in hilly and mountainous areas that can develop within minutes after a heavy rain. Can also occur in urban areas where pavements and drainage improvements speed runoff to a stream | |
| Flood | A general and temporary condition of partial or complete inundation by water in normally dry land areas | |
| Flood Boundary Floodway Map | FBFM | An official map of a community, on which the Federal Emergency Management Agency has delineated the regulatory floodway Recent Flood Insurance Studies show the floodway on the FIRM and do not include an FBFM |
| Flood fringe | The portion of the floodplain lying outside of the floodway | |
| Flood Hazard Boundary Map | FHBM | An official map of a community published by FEMA that delineates the approximate boundary of the floodplain. The FHBM is generally the initial floodplain boundary map and is eventually superseded by a FIRM |
| Flood hazard mitigation | All actions that can be taken to reduce property damage and the threat to life and public health from flooding | |
| Flood Insurance | Unlike a standard insurance policy, flood insurance covers losses to your property caused by flooding. | |
| Flood Insurance Rate Map | FIRM | An official map of a community on which FEMA has delineated both the Special Flood Hazard Areas and the risk premium zones applicable to the community |
| Flood Insurance Study | A report published by FEMA that is issued along with the community's FIRM. The study contains such background data as the base flood discharges and water surface elevations that were used to prepare the FIRM | |
| Flood Mitigation | The measures a community takes to correct and prevent flood risks. Efforts include zoning, rules for building in floodplains, and special-purpose floodplain ordinances | |
| Flood Mitigation Assistance | FMA | A grant program that supports plans and projects for mitigating losses to insured buildings funded by the National Flood Insurance Program |
| Flood of record | The highest known flood level for the area as recorded in historical documents | |
| Flood Zone | Land area described in terms of its risk of flooding | |
| Floodplain | Any land area susceptible to being inundated by flood waters from any source | |
| Floodproofing | Protective measures added to or incorporated in a building that is not elevated above the base flood elevation to prevent or minimize flood damage. "Dry floodproofing" measures are designed to keep water from entering a building. "Wet floodproofing" measures minimize damage to a structure and its contents from water that is allowed into a building | |
| Floodway | The channel of a river or other watercourse and that portion of the adjacent floodplain that must remain open to permit passage of the base flood without cumulatively increasing the water surface elevation more than a designated height (usually one foot) | |
| Geographic information system | GIS | Computer based map systems that allow the user to keep a map updated easily and to correlate geographic information with other data, such as tax records on properties |
| Hazard Mitigation Grant Program | A FEMA disaster assistance grant that funds mitigation projects | |
| HEC-2 | A computer model used to conduct a hydraulic study, which produces flood elevations, velocities and floodplain widths | |
| HEC-RAS | A computer model used to conduct a hydraulic study, which produces flood elevations, velocities and floodplain widths | |
| Human intervention | Actions that must be taken by one or more persons before floodwaters arrive in order for a building to be floodproofed | |
| Hydrodynamic force | The force of moving water including the impact of debris at high velocities | |
| Hydrologic cycle | The natural cycle that circulates water throughout the environment to maintain an overall balance between water in the air, on the surface and in the ground | |
| Hydrology | The science dealing with the waters of the earth. A flood discharge is developed by a hydrologic study | |
| Hydrostatic pressure | The pressure put on a structure by the weight of standing water The deeper the water, the more it weighs and the greater the hydrostatic pressure | |
| Increased Cost of Compliance | An additional claim payment made to a flood insurance policy holder to help cover the cost of bringing a substantially damaged or repetitively damaged building into compliance with the community's floodplain management ordinance | |
| Individual and Family Grants | A disaster assistance grant that helps people with their unmet needs (ie, needs not helped by other disaster assistance programs) | |
| Insurance Services Office | ISO | An insurance organization that provides support to FEMA on implementation of the Community Rating System |
| Lateral pressure | The amount of pressure imposed sideways by standing water. Deep water exerts more lateral pressure than shallow water | |
| Letter of Map Amendment | LOMA | Documents issued by FEMA that officially remove a property and/or structure from the Special Flood Hazard Area. To obtain a LOMA or LOMR the applicant must submit mapping and survey data for the property, much of which is available from the municipality in which the property is located. Call 702.267.3022. |
| Letter of Map Revision | LOMR | |
| Limited Map Maintenance Project | A small-scale restudy of a Flood Insurance Study | |
| Manufactured home | A building that is transportable in one or more ways, which is built on a permanent chassis and is designed for use with or without a permanent foundation when attached to the required utilities It includes single- and double-wide mobile homes | |
| Mitigation Division | The FEMA office that sets national policy for the NFIP and administers the mapping program | |
| Movable bed streams | A type of flooding that features uncertain flow paths | |
| Mudflow | See mudslide | |
| Mudslide | A condition where there is a river, flow or inundation of liquid mud down a hillside | |
| Multi-objective management | An approach to planning and funding local programs that involves a variety of local interests and concerns | |
| National Environmental Policy Act | NEPA | A Federal law that requires agencies to evaluate the environmental impact of a proposed project |
| National Flood Insurance Program | NFIP | Established by Congress in 1968, the goals of the National Flood Insurance Program are to reduce future flood damage through floodplain management and to provide people with flood insurance |
| National Geodetic Vertical Datum | NGVD | National Geodetic Vertical Datum of 1929. The national datum is based on mean sea level. It was known formerly as the "Mean Sea Level Datum of 1929" (MSL) |
| National Oceanic and Atmospheric Administration National Weather Service | NOAA | Federal agency focused on the condition of the oceans and the atmosphere. |
| Non-structural flood protection measures | Administrative tools for controlling flooding and flood damage, including regulations on development, building codes, property acquisition and structure relocation, and modification of existing buildings | |
| No-rise Certification | A certification by an engineer that a project will not cause a set increase in flood heights | |
| National Weather Service | NWS | Short version of National Oceanic and Atmospheric Administration National Weather Service |
| Ordinance | The generic term for a law passed by a local government | |
| Overbank flooding | Flooding that occurs when downstream channels receive more rain or snowmelt from their watershed than normal, or a channel is blocked by an ice jam or debris and excess water overloads the channels and flows out onto the floodplain | |
| Planned development | A regulatory approach that allows a developer to design the entire area while individual requirements may be relaxed to allow for open space, mixed land uses, and other variances to traditional zoning rules | |
| Planned Unit Development | PUD | |
| Ponding | Runoff that collects in depressions and cannot drain out, creating a temporary pond | |
| Post-FIRM building | For insurance rating purposes, a post-FIRM building was constructed or substantially improved after December 31, 1974, or after the effective date of the initial Flood Insurance Rate Map of a community, whichever is later. For a community that participated in the NFIP when its initial FIRM was issued, post-FIRM buildings are the same as new construction and must meet the National Flood Insurance Program's minimum floodplain management standards | |
| Potable Water | Water fit to drink | |
| Pre-FIRM building | For insurance rating purposes, a pre-FIRM building was constructed or substantially improved on or before December 31, 1974, or before the effective date of the initial Flood Insurance Rate Map of the community, whichever is later Most pre-FIRM buildings were constructed without taking the flood hazard into account | |
| Probability | A statistical term having to do with the size of a flood and the odds of that size of flood occurring in any year | |
| Profile | A graph that shows elevations of various flood events | |
| Public/Infrastructure Assistance | A disaster assistance grant that helps public agencies and nonprofit organizations finance repairs and reconstruction of public infrastructure | |
| Q3 Flood Data Product | A graphical representation of certain features of a FIRM in digital format | |
| Reconstruction | Building a new structure on the old foundation or slab of a structure that was destroyed, damaged, purposefully demolished or razed The term also applies when an existing structure is moved to a new site | |
| Recreational vehicle | A vehicle designed to be self propelled or permanently towable by a light duty truck that is designed for use as temporary living quarters for recreational, camping, travel, or seasonal use | |
| Rehabilitation | An improvement made to an existing structure which does not affect its external dimensions | |
| Restudy | A new Flood Insurance Study for all or part of a community that has already had a Flood Insurance Study | |
| Retrofitting | Retrofitting techniques include floodproofing, elevation, construction of small levees, and other modifications made to an existing building or its yard to protect it from flood damage | |
| Revision | A change to a floodplain map based on new data submitted to FEMA | |
| Riverine | Of or produced by a river. Riverine floodplains have readily identifiable channels. | |
| Roughness | A measure related to ground surface conditions that reflects changes in floodwater velocity due to ground friction | |
| Runoff | Rainfall and snowmelt that reaches a stream | |
| Sheet flow | Floodwater that spreads out over a large area and does not have defined channels at a somewhat uniform depth | |
| Special Flood Hazard Area | SFHA | Land areas at high risk for flooding. Also, the base floodplain displayed on FEMA maps. |
| Stafford Act | The Robert T. Stafford Disaster Relief and Emergency Assistance Act of 1988, as amended, which authorizes FEMA's current disaster assistance programs and the Hazard Mitigation Grant Program. The Disaster Mitigation Act of 2000 made extensive changes to the Stafford Act | |
| Stationing | Determining the distance along a stream | |
| Statutory authority | The powers granted to a local government by state law | |
| Storm drain system | The publicly owned facilities operated by the City of Henderson by which storm water is collected and/or conveyed | |
| Storm surge | Abnormal rise in sea level accompanying a hurricane or other intense storm, and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the storm. | |
| Stormwater detention | Storing stormwater runoff for release at a restricted rate after the storm subsides | |
| Stormwater management | Efforts to reduce the impact of increased runoff that results from new development | |
| Stormwater retention | Storing stormwater runoff for later use in irrigation or groundwater recharge, or to reduce pollution | |
| Structural flood control | Measures that control floodwaters by construction of barriers or storage areas or by modifying or redirecting channels | |
| Submit to rate | Process used when an insurance agent cannot complete the rate calculation for a flood insurance policy. The application is sent to the WYO Company or FEMA to be individually rated | |
| Substantial damage | 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 | Any reconstruction, rehabilitation, addition or other improvement to a structure, the total cost of which equals or exceeds 50 percent of the market value of the structure before the start of construction of the improvement. The definition of "substantial improvement" includes buildings that have incurred "substantial damage" regardless of the actual repair work performed | |
| Taking | Obtaining private property with or without compensating the owner. The term also includes reducing the value of private property to such an extent that the owner is deprived of all economic interest | |
| Thalweg | The bottom of a river channel | |
| Topographic map | Maps characterized by large-scale detail and quantitative representation of relief, usually using contour lines in modern mapping, but historically using a variety of methods. | |
| Transect | A survey of topographic conditions used in coastal flood studies | |
| Tsunami | A large wave caused by an underwater earthquake or volcano which can raise water levels as much as 15 feet | |
| Variance | A grant of relief by a community from the terms of a land use, zoning or building code regulation | |
| Velocity | The speed of moving water, a force that is measured in feet per second | |
| Wash | The dry bed of an intermittent stream | |
| Watershed | An area that drains into a lake, stream, or other body of water. Wave runup occurs when waves hit the shore and water is moving with such force that it keeps traveling inland | |
| Wave runup | The maximum vertical extent of wave uprush on a beach or structure above the still water level. | |
| Wet floodproof | Protecting a building from flood damage by using flood-resistant materials below the flood level and elevating things subject to flood damage above the flood level | |
| Write Your Own | WYO | An insurance company that has agreed to sell flood insurance policies on behalf of the NFIP |
| Zone A | The SHFA (except coastal V Zones) shown on a community's FIRM. There are five types of A Zones. | |
| Zone B | Area of moderate flood hazard, usually depicted on FIRMs as between the limits of the base and 500-year floods. B Zones are also used to designate base floodplains of little hazard, such as those with average depths of less than one foot | |
| Zone C | Area of minimal flood hazard, usually depicted on FlIRMs as above the 500-year flood level. B and C Zones may have flooding that does not meet the criteria to be mapped as a SFHA, especially ponding and local drainage problems | |
| Zone D | Area of undetermined but possible flood hazard | |
| Zone V | The SFHA subject to coastal high-hazard flooding. There are three types of V Zones. | |
| Zone X | Newer FIRMs show Zones B and C as Zone X |