100-year FloodA statistic that indicates the magnitude of flood which can be expected to occur on average with a frequency of once every 100 years at a given
point or reach on a river. The 100-year flood is usually developed from a statistical distribution that is based on historical floods.
This is also called a base flood.100-year Flood PlainThe flood plain that would be inundated in the event of a 100-year flood.Annual FloodIn hydrologic terms, the maximum discharge peak during a given water year (October 1 - September 30). Backwater FloodingHydrologic terms, upstream flooding caused by downstream conditions such as channel restriction and/or high flow in a downstream confluence stream.Base FloodIn hydrologic terms, the national standard for floodplain management is the base, or one percent chance flood. This flood has at least one chance in 100 of occurring in any given year. It is also called a 100 year flood.Closed Basin Lake FloodingFlooding that occurs on lakes with either no outlet or a relatively small one. Seasonal increases in rainfall cause the lake level to rise faster than it can drain. The water may stay at flood stage for weeks, months, or years.Coastal FloodingFlooding which occurs when water is driven onto land from an adjacent body of water. This generally occurs when there are significant storms, such as tropical and extratropical cyclones.Coastal/Lakeshore Flood AdvisoryMinor flooding is possible (i.e., over and above normal high tide levels. Coastal/Lakeshore Flood Advisories are issued using the Coastal/Lakeshore Hazard Message (CFW) product. Coastal/Lakeshore Flood WarningFlooding that will pose a serious threat to life and property is occurring, imminent or highly likely. Coastal/Lakeshore Flood Warnings are issued using the Coastal/Lakeshore Hazard Message (CFW) product.Coastal/Lakeshore Flood WatchFlooding with significant impacts is possible. Coastal/Lakeshore Flood Watches are issued using the Coastal/Lakeshore Hazard Message (CFW) product.Coastal/Lakeshore Flooding(i) (Oceanic) Coastal Flooding is the inundation of land areas caused by sea waters over and above normal tidal action. This flooding may impact the immediate oceanfront, gulfs, bays, back bays, sounds, and tidal portions of river mouths and inland tidal waterways. (ii) Lakeshore Flooding is the inundation of land areas adjacent to one of the Great Lakes caused by lake water exceeding normal levels. Lakeshore flooding impacts the immediate lakefront, bays, and the interfaces of lakes and connecting waterways, such as rivers.Daily Flood PeakIn hydrologic terms, the maximum mean daily discharge occuring in a stream during a given flood event.Direct Flood DamageIn hydrologic terms, the damage done to property, structures, goods, etc., by a flood as measured by the cost of replacement and repairs.Dry FloodproofingIn hydrologic terms, a dry floodproofed building is sealed against floodwaters. All areas below the flood protection level are made watertight. Walls are
coated with waterproofing compounds or plastic sheeting. Openings like doors windows, sewer lines and vents are closed, whether
permanently, with removable shields, or with sandbags. The flood protection level should be no more than 2 or 3 feet above the
top of the foundation because the buildings walls and floors cannot withstand the pressure of deeper water.E-3, Flood Stage ReportIn hydrologic terms, a form that a Service Hydrologist/ Hydrology Focal Point completes to document the dates in which forecast points are above
flood stage, as well as the crest dates and stages. Discussion of the flood event must also be included in the E-5, Monthly Report of
River and Flood conditions. An E-3 report is sent to Regional Headquarters, the appropriate RFC, as well as the Office of
Hydrology (OH). E-5, Monthly Report of River and Flood cIn hydrologic terms, a monthly narrative report covering flooding which occurred over the past month. Flood stage, flood crest and dates in which
flooding occurred is covered within this report for each data point which was in flood. If the flooding involved a forecast point, an
E-3 must be filled out as well. If no flooding has occurred within the past month, a climatic summary of the past month can be
included as well as other interesting non-flood events, such as water supply, ice jams and the occurrence of drought. An E-5 report
is sent to Regional Headquarters, the appropriate RFC, as well as the Office of Hydrology (OH).E-7, Flood Damage ReportIn hydrologic terms, a report to be completed anytime there is reported flood damage or loss of life as a direct result of flooding. An E-7 report is sent
to Regional Headquarters, as well as the Office of Hydrology (OH).Exclusive Flood Control Storage CapacityIn hydrologic terms, the space in a reservoir reserved for the sole purpose of regulating flood inflows to abate flood damageFlash FloodA rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level, beginning within six hours of the causative event (e.g., intense rainfall, dam failure, ice jam). However, the actual time threshold may vary in different parts of the country. Ongoing flooding can intensify to flash flooding in cases where intense rainfall results in a rapid surge of rising flood waters. Flash Flood Guidance(FFG) Forecast guidance produced by the River Forecast Centers, often model output, specific to the potential for flash flooding (e.g., how much rainfall over a given area will be required to produce flash flooding).Flash Flood Statement(FFS) In hydrologic terms, a statement by the NWS which provides follow-up information on flash flood watches and warnings.Flash Flood TableIn hydrologic terms, a table of pre-computed forecast crest stage values for small streams for a variety of antecedent moisture conditions and rain
amounts. Soil moisture conditions are often represented by flash flood guidance values. In lieu of crest stages, categorical
representations of flooding, e.g., minor, moderate, etc. may be used on the tables.Flash Flood WarningIssued to inform the public, emergency management, and other cooperating agencies that flash flooding is in progress, imminent, or highly likely.Flash Flood WatchIssued to indicate current or developing hydrologic conditions that are favorable for flash flooding in and close to the watch area, but the occurrence is neither certain or imminent.FloodAny high flow, overflow, or inundation by water which causes or threatens damage.Flood CategoriesTerms defined for each forecast point which describe or categorize the severity of flood impacts in the corresponding river/stream reach. Each flood category is bounded by an upper and lower stage (see Example 1). The severity of flooding at a given stage is not necessarily the same at all locations along a river reach due to varying channel/bank characteristics or presence of levees on portions of the reach. Therefore, the upper and lower stages for a given flood category are usually associated with water levels corresponding to the most significant flood impacts somewhere in the reach. The flood categories used in the NWS are:
*Minor Flooding* - minimal or no property damage, but possibly some public threat.
*Moderate Flooding* - some inundation of structures and roads near stream. Some evacuations of people and/or transfer of property to higher elevations.
*Major Flooding* - extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations.
*Record Flooding* - flooding which equals or exceeds the highest stage or discharge at a given site during the period of record keeping.
Note: all three of the lower flood categories (minor, moderate, major) do not necessarily exist for a given forecast point. For example, at the level where a river reaches flood stage, it may be considered moderate flooding. However, at least one of these three flood categories must start at flood stage. Flood Control StorageIn hydrologic terms, storage of water in reservoirs to abate flood damageFlood CrestMaximum height of a flood wave as it passes a certain location.Flood Frequency CurveIn hydrologic terms,
(1) A graph showing the number of times per year on the average, plotted as abscissa, that floods of magnitude, indicated by the
ordinate, are equaled or exceeded.
(2) A similar graph but with recurrence intervals of floods plotted as abscissa.Flood Hazard Outlook (FHO)A high Level graphical depiction and key messages highlighting the potential threat of inland flood hazards (flash, urban, small stream and riverine) and their associated impacts (catastrophic, considerable, and limited) for the next seven days.Flood Inundation Mapping (FIM)In the context of the National Water Model (NWM) FIM, the expected maximum inundation extent over a particular period of time derived using the Height Above Nearest Drainage (HAND) method. Stage heights are interpolated from the NWM discharge values using synthetic rating curves, and are rounded to the nearest foot.Flood Loss Reduction MeasuresIn hydrologic terms, the strategy for reducing flood losses. There are four basic strategies. They are prevention, property protection, emergency
services, and structural projects. Each strategy incorporates different measures that are appropriate for different conditions. In
many communities, a different person may be responsible for each strategy.Flood of RecordIn hydrologic terms, the highest observed river stage or discharge at a given location during the period of record keeping. (Not necessarily the highest
known stage.)Flood PlainIn hydrologic terms, the portion of a river valley that has been inundated by the river during historic floods.Flood Potential Outlook(ESF on AFOS) (FPO for Acronym): In hydrologic terms, An NWS outlook that is issued to alert the public of potentially heavy rainfall that could send area rivers and streams into flood or
aggravate an existing flood.Flood PreventionIn hydrologic terms, measures that are taken in order to keep flood problems from getting worse. Planning, land acquisition, river channel maintenance,
wetlands protection, and other regulations all help modify development on floodplains and watersheds to reduce their susceptibility
to flood damage. Preventive measures are usually administered by the building, zoning, planning and/ or code enforcement offices
of the local government.Flood ProblemsIn hydrologic terms, problems and damages that occur during a flood as a result of human development and actions. Flood problems are a result from:
1) Inappropriate development in the floodplain (e.g., building too low, too close to the channel, or blocking flood flows);
Development in the watershed that increases flood flows and creates a larger floodplain, or;
3) A combination of the previous two. Flood ProfileIn hydrologic terms, a graph of elevation of the water surface of a river in flood, plotted as ordinate, against distance, measured in the downstream
direction, plotted as abscissa. A flood profile may be drawn to show elevation at a given time, crests during a particular flood, or to
show stages of concordant flowsFlood RoutingIn hydrologic terms, process of determining progressively the timing, shape, and amplitude of a flood wave as it moves downstream to successive points
along the riverFlood StageAn established gage height for a given location above which a rise in water surface level begins to create a hazard to lives, property, or commerce. The issuance of flood (or in some cases flash flood) warnings is linked to flood stage. Not necessarily the same as bankfull stage.Flood Statement (FLS)In hydrologic terms, a statement issued by the NWS to inform the public of flooding along major streams in which there is not a serious threat to life or
property. It may also follow a flood warning to give later information.Flood Warning(FLW) In hydrologic terms, a release by the NWS to inform the public of flooding along larger streams in which there is a serious threat to life or property. A
flood warning will usually contain river stage (level) forecasts.Flood WatchIssued to inform the public and cooperating agencies that current and developing hydrometeorological conditions are such that there is a threat of flooding, but the occurrence is neither certain nor imminent.Flood WaveIn hydrologic terms, a rise in streamflow to a crest and its subsequent recession caused by precipitation, snowmelt, dam failure, or reservoir releasesFlooded IceIn hydrologic terms, ice which has been flooded by melt water or river water and is heavily loaded by water and wet snow.FloodproofingIn hydrologic terms, the process of protecting a building from flood damage on site. Floodproofing can be divided into wet and dry floodproofing. In
areas subject to slow-moving, shallow flooding, buildings can be elevated, or barriers can be constructed to block the water’s
approach to the building. These techniques have the advantage of being less disruptive to the neighborhood. It must be noted that
during a flood, a floodproofed building may be isolated and without utilities and therefore unusable, even though it has not been
damaged.FloodwallIn hydrologic terms, a long, narrow concrete, or masonry embankment usually built to protect land from flooding. If built of earth the structure is usually
referred to as a levee. Floodwalls and levees confine streamflow within a specified area to prevent flooding. The term "dike" is used
to describe an embankment that blocks an area on a reservoir or lake rim that is lower than the top of the dam. FloodwayIn hydrologic terms,
(1) A part of the flood plain, otherwise leveed, reserved for emergency diversion of water during floods. A part of the flood plain
which, to facilitate the passage of floodwater, is kept clear of encumbrances.
(2) The channel of a river or stream and those parts of
the flood plains adjoining the channel, which are reasonably required to carry and discharge the floodwater or floodflow of any
river or stream.Intangible Flood DamageIn hydrologic terms, estimates of the damage done by disruption of business, danger to health, shock, and loss of life and in general all costs not directly
measurable which require a large element of judgment for estimating.Lakeshore Flood AdvisorySee Coastal/Lakeshore Flood Advisory.Lakeshore Flood WatchSee: COASTAL/LAKESHORE FLOOD WATCHLakeshore FloodingSee COASTAL/LAKESHORE FLOODINGLowland FloodingIn hydrologic terms, inundation of low areas near the river, often rural, but may also occur in urban areas.Major FloodingA general term including extensive inundation and property damage. (Usually characterized by the evacuation of people and livestock and the closure of both primary and secondary roads.)Minor FloodingA general term indicating minimal or no property damage but possibly some public inconvenience.Moderate FloodingThe inundation of secondary roads; transfer to higher elevation necessary to save property -- some evacuation may be required.National Flood SummaryThis NWS daily product (abbreviated FLN) contains nationwide information on current flood conditions. It is issued by the Hydrometeorological Information Center of the Office of Hydrology.Partial-Duration Flood SeriesIn hydrologic terms, a list of all flood peaks that exceed a chosen base stage or discharge, regardless of the number of peaks occurring in a year.Rapid Onset Flooding (ROF)In the context of the National Water Model (NWM), rapid onset flooding refers to stream reaches that are forecast to at least double their flow within an hour, and meet or exceed their high water flow within six hours of this flow increase.River Flood StatementThis product is used by the local National Weather Service Forecast Office (NWFO) to update and expand the information in the River Flood Warning. This statement may be used in lieu of a warning if flooding is forecasted, imminent, or existing and it presents no threat to life or property. The statement will also be used to terminate a River Flood Warning.River Flood WarningThis is product is issued by the local National Weather Service Forecast Office (NWFO) when forecast points (those that have formal gaging sites and established flood stages) at specific communities or areas along rivers where flooding has been forecasted, is imminent, or is in progress. Flooding is defined as the inundation of normally dry areas as a result of increased water levels in an established water course. The flood warning is based on the RVF product from the River Forecast Center (RFC) in Minneapolis, Minnesota. The flood warning normally specifies crest information. It usually occurs 6 hours or later after the causative event and it is usually associated with widespread heavy rain and/or snow melt or ice jams.
It will contain the forecast point covered by the warning, the current stage (if it is available), and the established flood stage. It will also contain the forecasted crest from the River Forecast Center (RFC) in Minneapolis, Minnesota. From this forecasted crest, the NWFO will be able to determine which areas will be affected by the river flooding. This information will be included in the warning. Finally, the statement will include a site/event specific call to action.River FloodingThe rise of a river to an elevation such that the river overflows its natural banks causing or threatening damage.Small Stream FloodingIn hydrologic terms, flooding of small creeks, streams, or runs.Snowmelt FloodingIn hydrologic terms, flooding caused primarily by the melting of snow.Urban and Small Stream Flood AdvisoryThis advisory alerts the public to flooding which is generally only an inconvenience (not life-threatening) to those living in the affected area. Issued when heavy rain will cause flooding of streets and low-lying places in urban areas. Also used if small rural or urban streams are expected to reach or exceed bankfull. Some damage to homes or roads could occur.Urban and Small Stream FloodingFlooding of small streams, streets, and low-lying areas, such as railroad underpasses and urban storm drains. This type of flooding is mainly an inconvenience and is generally not life threatening nor is it significantly damaging to property.Urban Flash Flood GuidanceA specific type of flash flood guidance which estimates the average amount of rain needed over an urban area during a specified period of time to initiate flooding on small, ungaged streams in the urban area.Urban FloodingFlooding of streets, underpasses, low lying areas, or storm drains. This type of flooding is mainly an inconvenience and is generally
not life threatening. Wet FloodproofingIn hydrologic terms, an approach to floodproofing which usually is a last resort. Flood waters are intentionally allowed into the building to minimize
water pressure on the structure. Wet Floodproofing can include moving a few valueable items to a higher place or completely
rebuilding the floodable area. Wet floodproofing has an advantage over other approaches: no matter how little is done, flood
damage will be reduced. Thousands of dollars in damage can be avoided just by moving furniture and appliances out of the
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