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Appendix C Glossary 0.2 Percent Annual Chance FloodâA flood that has Generally, the property is located on natural high a 0.2 percent chance of being equaled or exceeded in ground at or above the BFE or on fill placed prior to any given year; also known as a 500-year flood (FEMA, the effective date of the first NFIP map designating the 2003) property as within an SFHA. Limitations of map scale and development of topographic data more accurately 1 Percent Annual Chance FloodâA flood that has a reflecting the existing ground elevations at the time the 1 percent chance of being equaled or exceeded in any maps were prepared are the two most common bases given year; also known as a 100-year flood (FEMA, for amendment requests (FEMA, 2003) 2003) Approved ModelâA numerical computer model that 100-Year FloodâSee 1 percent annual chance flood has been accepted by FEMA for use in performing (FEMA, 2003) new or revised hydrologic or hydraulic analyses for National Flood Insurance Program (NFIP) purposes. 500-Year FloodâSee 0.2 percent annual chance flood All accepted models must meet the requirements set (FEMA, 2003) forth in Subparagraph 65.6(a)(6) of the NFIP regula- tions (FEMA, 2003) AccuracyâThe degree of correctness attained in a measurement. (FEMA, 2003) Approximate StudyâA flood hazard study that uses topographic data, typically without bathymetry or â¢ Horizontal AccuracyâThe positional accuracy bridge or culvert opening geometry, to conduct approx- of a dataset with respect to a specified horizontal datum imate hydrologic and hydraulic analyses. The analysis (Maune, 2007) results in the delineation of floodplain boundaries for â¢ Vertical AccuracyâThe positional accuracy the 1 percent annual chance (100-year) flood, but does of a dataset with respect to a specified vertical datum not include the determination of base flood elevations (Maune, 2007) (BFEs) or base flood depths (FEMA, 2003) AmendmentâA determination by the Federal Emer- BackwaterâWater backed up or retarded in its course gency Management Agency (FEMA) that a property compared to its normal or natural condition of flow has inadvertently been included in a Special Flood (FEMA, 2003) Hazard Area (SFHA) as shown on an effective Flood Insurance Rate Map (FIRM) and is not subject to Base FloodâA flood that has a 1 percent chance inundation by the 1 percent annual chance flood. of being equaled or exceeded in any given year, also 113
114 APPENDIX C referred to as the 100-year flood. The base flood is the Cooperating Technical PartnersâParticipating NFIP national standard used by the NFIP and all federal communities, regional agencies, and state agencies that agencies for the purposes of requiring the purchase are active participants in the FEMA Flood Hazard of flood insurance and regulating new development Mapping Program (FEMA, 2003) (<http://www.fema.gov/NFIPKeywords/>) Cross SectionâA line across a floodplain, developed Base Flood Elevation (BFE)âThe elevation of a from topographic data, at which a computation of flood having a 1 percent chance of being equaled or flood flow has been made to establish a potential flood exceeded in any given year (FEMA, 2003) elevation (<http://www.fema.gov/media/fhm/champ/ ot_chmp.htm>) BathymetryâThe measurement and study of water depths. Traditionally bathymetry has been expressed DatumâA common vertical or horizontal eleva- with contours and hydrography with spot depths tion reference point (<https://hazards.fema. (Maune, 2007) gov/femaportal/>) BenchmarkâA permanent monument established by â¢ Ellipsoidal DatumâA set of constants specify- any federal, state, or local agency, whose elevation and ing the coordinate system used for geodetic control, that description are well documented and referenced to the is, for calculating coordinates of points on the Earth; National Geodetic Vertical Datum of 1929 (NGVD also known as geodetic datum (<http://www.ngs. 29) or the North American Vertical Datum of 1988 noaa.gov/CORS-Proxy/Glossary/xml/NGS_Glossary. (NAVD 88) (FEMA, 2003) xml>) â¢ Orthometric DatumâThe reference surface BenefitsâPositive effects of an action. For FEMA from which orthometric heights are measured (i.e., flood hazard mitigation projects, benefits are defined NAVD 88 or NGVD 29) as avoided damages and losses (FEMA, 2001) â¢ Tidal DatumâA surface with a designed elevation from which heights or depths are reckoned, CalibrationâThe process of identifying and cor- defined by a certain phase of the tide. A tidal datum is recting for systematic errors in hardware, software, local, usually valid only for a restricted area about the or procedures; determining the systematic errors in tide gage used in defining the datum (Maune, 2007) a measuring device by comparing its measurements with the markings or measurements of a device that is Design StormâA rainfall event of specified size considered correct (Maune, 2007) and return frequency that is used to calculate runoff volume. It is assumed that the design storm for a Catchment AreaâAn area of land that is occupied by a given frequency will produce a simulated runoff peak drainage system consisting of a surface stream or a body and volume having the same return frequency. Thus, of impounded surface water, together with all tributary a 100-year design storm should produce a 100-year surface streams and bodies of impounded surface water runoff and volume (New York Department of Envi- that drains into a single outlet; also called drainage ronmental Conservation, 1992) basin or watershed (<http://water.usgs.gov/glossaries. html>) Detailed Study, CoastalâA coastal flood hazard study that uses transects and offshore bathymetry to conduct Coastal FloodingâFlooding that occurs along the detailed erosion, wave height, and wave runup analyses Great Lakes, the Atlantic and Pacific Oceans, and the and to prepare floodplain mapping. The analysis results Gulf of Mexico (FEMA, 2003) in the determination and publication of BFEs and designation of the coastal high-hazard areas (V zones) Confidence LevelâThe probability that errors are (FEMA, 2003) within a range of given values (Maune, 2007)
APPENDIX C 115 Detailed Study, RiverineâA riverine flood hazard cent grade of a building are certified relative to the base study that uses topographic data, channel bathymetry, flood elevation for the location of the building. Other and bridge or culvert opening geometry to conduct descriptive information is also provided to help identify detailed hydrologic and hydraulic analyses and flood- the flood risk to the building surveyed (Maune, 2007) plain mapping. The analysis results in the delineation of floodplain boundaries for the 1 percent annual chance FIRMetteâA full-scale section of a Flood Insur- (100-year) flood, determination of BFEs or flood depths, ance Rate Map created by users online by select- and normally, a regulatory floodway (FEMA, 2003) ing the desired area from a FIRM image. It also includes the map title block, north arrow, and scale Digital Elevation Model (DEM)âA file with Âterrain bar (<http://msc.fema.gov/webapp/wcs/stores/servlet/ elevations recorded for the intersection of a fine- FemaWelcomeView?storeId=10001&catalogId=10001 grained grid and organized by quadrangle as the digital &langId=-1>) equivalent of the elevation data on a topographic base map (FEMA, 2003) FloodâA general and temporary condition of partial or complete inundation of normally dry land areas from Digital Flood Insurance Rate Map (DFIRM)âA (1) the overflow of inland or tidal waters or (2) the Flood Insurance Rate Map that has been prepared unusual and rapid accumulation or runoff of surface as a digital product, which may involve converting an waters from any source (FEMA, 2003) existing manually produced FIRM to digital format or creating a product from new digital data sources using a Flood Hazard Mapping PartnerâCommunity offi- geographic information system (GIS) (FEMA, 2003) cials; regional agency officials; state agency officials; communities, regional agencies, and state agencies Digital Terrain Model (DTM)âA land surface rep- participating in the FEMA Cooperating Technical resented in digital form by an elevation grid or lists of Partners Program; other federal agencies; FEMA three-dimensional coordinates (FEMA, 2003) contractors; contractors of communities, regional agencies, and state agencies; community residents and DischargeâThe volume of water that passes a property owners; other program constituents, including given location within a given period of time. Usually the U.S. Congress; insurance lending, real estate, and expressed in cubic feet per second (<http://water.usgs. land development industries; and federal, state, and gov/Âglossaries.html>) local disaster and emergency response officials whose combined contribution with FEMA staff obtain and Drainage AreaâThe area upstream of a specific maintain accurate, up-to-date flood hazard information location, measured in a horizontal plane, that has a (FEMA, 2003) common outlet at the site for its surface runoff from precipitation that normally drains by gravity into a Flood Insurance Rate Map (FIRM)âThe insurance stream. Drainage areas include all closed basins, or and floodplain management map produced by FEMA noncontributing areas, within the area unless otherwise that identifies, based on detailed or approximate analy- specified (<http://water.usgs.gov/glossaries.html>) ses, the areas subject to flooding during a 1 percent annual chance (100-year) flood event in a community ElevationâThe distance of a point above the speci- and flood insurance risk zones. In areas studied by fied surface of constant potential; the distance is the detailed analyses, the FIRM shows BFEs to reflect direction of gravity between the point and the surface the elevations of the 1 percent annual chance flood. (<http://www.ngs.noaa.gov/CORS-Proxy/Glossary/ For many communities, when detailed analyses are xml/NGS_Glossary.xml>) performed, the FIRM also may show areas inundated by a 0.2 percent annual chance (500-year) flood and Elevation CertificateâA form on which the lowest regulatory floodway areas (FEMA, 2003) floor elevation, lowest adjacent grade, and highest adja-
116 APPENDIX C Flood Insurance Risk ZonesâThe areas, also referred health regulations, special-purpose ordinances, and to as flood insurance rate zones, shown on a FIRM that other applications of enforcement used by a community are used to determine flood insurance premium rates to manage development in its floodplain areas (FEMA, for properties in the community covered by the FIRM. 2003) The flood insurance risk zones include SFHAs (e.g., Zones A, A1-30, AE, V, V1-30, VE, V0) and areas FloodwayâThe regulatory area defined as the channel outside SFHAs (e.g., Zone X) (FEMA, 2003) of a stream plus any adjacent floodplain areas that must be kept free of encroachment so that the base flood Flood Insurance Study (FIS)âA compilation and discharge can be conveyed without increasing the BFEs presentation of flood risk data for specific watercourses, more than a specified amount (FEMA, 2003) lakes, and coastal flood hazard areas within a commu- nity. When a flood study is completed for the NFIP, FreeboardâA factor of safety usually expressed in feet the information and maps are assembled into an FIS. above a flood level for purposes of floodplain manage- The FIS report contains detailed flood elevation data ment. Freeboard tends to compensate for the many in flood profiles and data tables (<http://www.fema. unknown factors that could contribute to flood heights gov/plan/prevent/floodplain/nfipkeywords/fis.shtm>) greater than the height calculated for a selected size flood and floodway conditions, such as wave action, Flood Insurance Study ReportâA document, pre- bridge openings, and the hydrological effect of urban- pared and issued by FEMA, that presents the results ization of the watershed (44 CFR 59.1) of the detailed flood hazard assessment performed for a community. The primary components of the FIS report Geographic Information System (GIS)âA system of are text, data tables, photographs, and flood profiles computer hardware, software, and procedures designed (FEMA, 2003) to support the capture, management, manipulation, analysis, modeling, and display of spatially referenced Flood PeakâThe highest value of the stage or dis- data for solving complex planning and management charge attained by a flood; thus, peak stage or peak problems (FEMA, 2003) discharge (<http://water.usgs.gov/glossaries.html>) GeoidâThe equipotential (level) surface of the Earthâs Flood ProfileâA graph of elevation of the water gravity field, which on average coincides with mean sea s Â urface of a river in flood, plotted as ordinate, against level in the open undisturbed ocean. The geoid undu- distance, measured in the downstream direction, plotted lates up and down with local variations in the mass and as abscissa (<http://water.usgs.gov/glossaries.html>) density of the Earth (Maune, 2007) Flood StageâThe height of a water surface above an Global Positioning System (GPS)âA satellite-based established datum plane (FEMA, 2003) navigation and positioning system that enables horizontal and vertical positions to be determined (FEMA, 2003) FloodplainâAny land area that is susceptible to being inundated by water from any source (FEMA, 2003) HeightâThe distance, measured along a perpendicu- lar, between a point and a reference surface (e.g., height Floodplain ManagementâThe operation of a pro- of an airplane above the ground surface). The distance, gram of corrective and preventative measures for reduc- measured upward along a plumb line (line of force), ing flood damage, including emergency preparedness between a point and a reference surface of constant plans, floodcontrol works, and floodplain management geopotential. Elevation is preferred if the reference regulations (FEMA, 2003) surface is the geoid (Maune, 2007) Floodplain Management RegulationsâThe zoning â¢ Ellipsoid HeightâThe height above or below ordinances, subdivision regulations, building codes, the reference ellipsoid (i.e., the distance between a
APPENDIX C 117 point on the Earthâs surface and the ellipsoidal surface, LevelingâThe process of finding differences of eleva- as measured along the normal [perpendicular] to the tion (Maune, 2007) ellipsoid at the point and taken positive upward from the ellipsoid) (Maune, 2007) Light Detection and Ranging (lidar)âAn airborne â¢ Orthometric Height (Elevation)âThe height laser system that is used to acquire x, y, and z coordi- above the geoid as measured along the plumbline nates of terrain and terrain features that are both man- between the geoid and a point on the Earthâs surface, made and naturally occurring. LIDAR systems consist taken positive upward from the geoid (Maune, 2007) of an airborne GPS with attendant base station(s), inertial measuring unit, and light-emitting scanning Hydraulic AnalysisâAn engineering analysis of a laser (FEMA, 2003) flooding source carried out to provide estimates of the elevations of floods of selected recurrence intervals Limited Detailed StudyâA flood hazard study based (FEMA, 2003) on fewer surveyed cross sections than detailed studies. The analysis results in the delineation of floodplain Hydraulic ModelâA computer program that uses boundaries for the 1 percent annual chance (100-year) flood discharge values and floodplain characteristic flood and often base flood elevations (FEMA, 2006a) data to simulate flow conditions and determine flood elevations (FEMA, 2003) Map Modernization ProgramâA multiyear FEMA initiative (1) to provide a technology-based, cost- HydrographâA graph showing stage, flow, velocity, effective, long-term process for updating, maintaining, or other water properties with respect to time (FEMA, storing, and distributing the flood risk information 2003) portrayed on the flood maps; and (2) to use engineer- ing tools and analysis to update the flood maps so that Hydrologic AnalysisâAn engineering analysis of a they reflect physical changes that have occurred since flooding source carried out to establish peak flood dis- the original mapping (FEMA, 2006a) charges and their frequencies of occurrence (FEMA, 2003) MitigationâA sustained action taken to reduce or eliminate long-term risk to people and property from Inundation MapâA map depicting the spatial extent flood hazards and their effects. Mitigation distinguishes and depth of floodwaters in the vicinity of National actions that have a long-term impact from those that Weather Service river forecast locations (<http://www. are more closely associated with preparedness for, floodsafety.noaa.gov/inundation.shtml>) immediate response to, and short-term recovery from specific events (FEMA, 2003) Letter of Final DeterminationâThe letter in which FEMA announces its final determination regarding Monument or control monument (also called refer- flood hazard information, including (when appropri- ence mark)âA structure that marks the location of ate) proposed and proposed modified BFEs presented a corner or point determined by surveying; generally, on a new or revised FIRM, and FIS report. The Âletter any material, object, or collection of objects that indi- begins the compliance period and establishes the cates the ground location of a survey station or corner effective date for the new or revised FIRM and/or FIS (<http://www.ngs.noaa.gov/CORS-Proxy/Glossary/ report (FEMA, 2003) xml/NGS_Glossary.xml>) Letter of Map Change (LOMC)âA collective term National Flood Insurance Program (NFIP)âThe used to describe official amendments and revisions to federal program under which floodprone areas are FIRMs that are accomplished by an administrative identified and flood insurance is made available to the procedure and disseminated by letter (FEMA, 2003) owners of the property in participating communities (FEMA, 2003)
118 APPENDIX C OrthophotoâA photograph prepared from a perspec- Return PeriodâSee recurrence interval tive photograph by removing displacements of points caused by tilt, relief, and perspective (Maune, 2007) RevisionâA change to an effective NFIP map based on new or revised scientific or technical data (<http:// Peak FlowâThe maximum instantaneous discharge of www.fema.gov/plan/prevent/floodplain/nfipkeywords/ a stream or river at a given location; usually occuring at revision_maps.shtm>) or near the time of maximum stage (<http://water.usgs. gov/glossaries.html>) Riverine FloodingâThe overbank flooding of rivers and streams (FEMA, 2003) PhotogrammetryâThe science of deducing the physi- cal three-dimensional measurements of objects from RunoffâThat part of the precipitation that appears measurements on stereo photographs that photograph in surface streams (<http://water.usgs.gov/glossaries. an area from two different perspectives (Maune, 2007) html>) Q3 Flood Data ProductâA digital representation of Shallow FloodingâUnconfined flows over broad, certain features of the FIRM that is intended for use relatively low relief areas; intermittent flows in arid with desktop mapping and GIS technology. The Q3 regions that have not developed a system of well- flood data product is created by scanning the effective defined Âchannels; overbank flows that remain uncon- FIRM paper maps and digitizing selected features and fined; overland flow in urban areas; and flows collect- lines (FEMA, 2003) ing in depressions to form ponding areas. For NFIP purposes, shallow flooding conditions are defined as Recurrence IntervalâThe average interval of time flooding that is limited to 3.0 feet or less in depth where within which a given flood will be equaled or exceeded no defined channel exists (FEMA, 2003) once; also known as the return period (FEMA, 2003) Special Flood Hazard Area (SFHA)âThe area RedelineationâA data update method that involves delineated on an NFIP map as being subject to inun- no new analyses, but uses effective information and dation by the base flood. SFHAs are determined using new topographic data that are more up-to-date and/or statistical analyses of records of riverflow, storm tides, detailed than those used to produce the effective FIRM and rainfall; information obtained through consultation to redelineate floodplain boundaries (FEMA, 2003) with a community; floodplain topographic surveys; and hydrologic and hydraulic analyses (FEMA, 2003) Regression EquationâAn experimentally determin- able equation of a regression curve; that is, an approxi- Stillwater Flood Elevation (SWEL)âProjected mate, generally linear relation connecting two or more elevation that floodwaters would assume, referenced to quantities and derived from the correlation coefficient NGVD 29, NAVD 88, or other datum, in the absence (FEMA, 2003) of waves resulting from wind or seismic effects (FEMA, 2003) ResolutionâIn the context of gridded elevation data, resolution is synonymous with the horizontal post spac- Storm SurgeâThe rise in the water surface above ing; sometimes used to state the number of points in x normal water level on the open coast due to the action and y directions in a lattice (e.g., 1,201 Ã 1,201 mesh of wind stress and atmospheric pressure (<http://www. points in a U.S. Geological Survey [USGS] one-degree fema.gov/media/fhm/champ/ot_chmp.htm>) DEM) (Maune, 2007) Stream ReachâThe length of a channel for which RestudyâA revised study of flood hazards performed a single gage affords a satisfactory measure of the for a community that already has an effective FIRM stage and discharge (<http://water.usgs.gov/glossaries. (FEMA, 2003) html>)
APPENDIX C 119 StructureâFor floodplain management purposes, a â¢ Natural VariabilityâSometimes called Âaleatory walled and roofed building, including a gas or liquid uncertaintyâdeals with inherent variability in the storage tank that is principally above ground, as well as physical world; by assumption, this ârandomnessâ is a manufactured home. For flood insurance purposes, a irreducible. The word aleatory comes from the Latin walled and roofed building, other than a gas or Âliquid alea, meaning a die or gambling device. In the water storage tank, that is principally above ground and resources context, uncertainties related to natural vari- affixed to a permanent site, as well as a manufactured ability include things such as streamflow, assumed to be home on a permanent foundation (FEMA, 2003) a random process in time, or soil properties, assumed to be random in space. Natural variability is also TerrainâSee topography sometimes referred to as external, objective, random, or stochastic uncertainty. TopographyâThe form of the features of the actual surface of the Earth in a particular region, considered WatershedâSee catchment area collectively; also called terrain (Maune, 2007) Wave CrestâThe highest point on a ridge, deforma- Total StationâA tachymeter that senses angles and tion, or undulation of the water surface (<http://www. distances electronically. A tachymeter is a surveying fema.gov/media/fhm/champ/ot_chmp.htm>) instrument for the rapid determination of distance, usually together with the measurement of direction Wave EnvelopeâA combination of representa- and difference of elevation (<http://www.ngs.noaa.gov/ tive wave runup elevation and the wave crest profile CORS-Proxy/Glossary/xml/NGS_Glossary.xml>) determined by the wave results computed using the Wave Height Analysis for Flood Insurance Studies TransectâCross section taken perpendicular to the (WHAFIS) program (FEMA, 2003) shoreline to represent a segment of coast with similar characteristics (FEMA, 2003) Wave HeightâVertical distance between the wave crest and the wave trough (FEMA, 2003) UncertaintyâDegree to which an outcome is unknown or not established and is therefore in question (NRC, Wave RunupâRush of waves up a slope or structure 2000) (FEMA, 2003) â¢ Knowledge UncertaintyâSometimes called Wave SetupâThe increase in the stillwater surface epistemic uncertaintyâdeals with a lack of understand- near the shoreline, due to the presence of breaking ing of events and processes, or with a lack of data from waves (FEMA, 2003) which to draw inferences; by assumption, such lack of knowledge is reducible with further information. The Wind SetupâThe vertical rise in the stillwater level at word epistemic is derived from the Greek âto know.â the face of a structure or embankment caused by wind Knowledge uncertainty is also sometimes referred to as stresses on the surface of the water (FEMA, 2004) functional, internal, or subjective uncertainty.