Public Works

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 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