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Flood stage is the
water level Water level, also known as gauge height or stage, is the elevation of the free surface of a sea, stream, lake or reservoir relative to a specified vertical datum.ISO 772: 1996. Hydrometric determinations – Vocabulary and symbols. See also * W ...
or
stage Stage or stages may refer to: Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly British theatre newspaper * Stag ...
at which the surface of a body of water has risen to a sufficient level to cause sufficient inundation of areas that are not normally covered by water, causing an inconvenience or a threat to life and property. When a body of water rises to this level, it is considered a
flood A flood is an overflow of water that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide Tides are the rise and fall of sea level Mean sea level (MSL) (often ...

flood
event. Flood stage does not apply to areal flooding. As areal flooding occurs, by definition, over areas not normally covered by water, the presence of any water at all constitutes a flood. Usually, moderate and major stages are not defined for areal
floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows int ...
s.


Definition

Flood stage is the water level, as read by a
stream gauge A stream gauge, streamgage or stream gauging station is a location used by hydrologists Hydrology (from Greek: ὕδωρ, "hýdōr" meaning "water" and wikt:λόγος, λόγος, "lógos" meaning "study") is the scientific study of the move ...
or
tide gauge A tide gauge is a device for measuring the change in sea level Mean sea level (MSL) (often shortened to sea level) is an average In colloquial, ordinary language, an average is a single number taken as representative of a list of numbers, ...

tide gauge
, for a body of water at a particular location, measured from the level at which a body of water threatens lives, property,
commerce Commerce is the exchange of goods and services, especially on a large scale. Etymology The English-language word ''commerce'' has been derived from the Latin word ''commercium'', from ''com'' ("together") and ''merx'' ("merchandise"). History ...

commerce
, or travel. The term "at flood stage" is commonly used to describe the point at which this occurs. "Gauge height" (also referred to as "stream stage", "stage of the ody of water, or simply "stage") is the level of the water surface above an established zero datum at a given location. The zero level can be
arbitrary Arbitrariness is the quality of being "determined by chance, whim, or impulse, and not by necessity, reason, or principle". It is also used to refer to a choice made without any specific criterion or restraint. Arbitrary decisions are not necessar ...
, but it is usually close to the bottom of the stream or river or at the average level of standing bodies of water. Stage was traditionally measured visually using a staff gauge, which is a fixed
ruler A ruler, sometimes called a rule or line gauge, is a device used in geometry Geometry (from the grc, γεωμετρία; ' "earth", ' "measurement") is, with , one of the oldest branches of . It is concerned with properties of spac ...

ruler
marked in 1/100 and 1/10
foot The foot (plural: feet) is an anatomical Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemis ...
intervals, however electronic sensors that transmit real-time information to the
Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a ''internetworking, network of networks'' that consist ...

Internet
are now used for many of these kinds of measurements. The flood stage measurements are given as a height above or below the zero level. Levels below zero are reported as a negative value. While usually the flood stage is set at the elevation of the floodplain, it can be higher (if there are no structures,
road A road is a wide way leading from one place to another, typically one with a specially prepared surface which vehicles and bikes can use. Roads consist of one or two roadway A carriageway (British English British English (BrE) is the ...

road
s, or
farm A farm (also called an agricultural Agriculture is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases i ...

farm
ing areas immediately on the floodplain) or lower (if there are structures such as
marina A marina (from Spanish Spanish may refer to: * Items from or related to Spain: **Spaniards, a nation and ethnic group indigenous to Spain **Spanish language **Spanish cuisine Other places * Spanish, Ontario, Canada * Spanish River (disambig ...

marina
s, lake houses, or docks low on the banks or shores of the body of water) depending on the location. Because flood stage is defined by impacts to people, as opposed to the natural topography of the area, flood stages are usually only calculated for bodies of water near communities. The flood stage can be listed for an entire community, in which case it is often set to the lowest
man-made Artificiality (the state of being artificial or man-made) is the state of being the product of intentional human manufacture, rather than occurring naturally through processes not involving or requiring human activity. Connotations Artificiality o ...
structure A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. ...

structure
or road in the area, the lowest farming field in the area, or the floodplain. It can also be set for a specific location ("flood stage is 12 feet on Maple Street at First Avenue" means that the specified intersection will begin to flood when the stage reaches ). In the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

United States
during flood events, the
National Weather Service The National Weather Service (NWS) is an agency Agency may refer to: * a governmental or other institution Institutions, according to Samuel P. Huntington, are "stable, valued, recurring patterns of behavior". Institutions can refer to m ...
will issue
flood warning A flood warning is closely linked to the task of flood forecasting. The distinction between the two is that the outcome of flood forecasting is a set of forecast time-profiles of channel flows or river levels at various locations, while "flood war ...
s that list the current and predicted stages for affected communities as well as the local flood stage. Current stage data is collected by the
USGS The United States Geological Survey, abbreviated USGS and formerly simply known as the Geological Survey, is a scientific agency Agency may refer to: * a governmental or other institution Institutions, according to Samuel P. Huntington, ...
using a network of gauges, over 9000 of which transmit real time data via
satellite In the context of spaceflight Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either human spaceflight, with or uncrewed spaceflight, without humans on board. Most spaceflight ...

satellite
,
radio Radio is the technology of signaling and telecommunication, communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device ...

radio
, or
telephone A telephone is a telecommunication Telecommunication is the transmission of information by various types of technologies over wire A wire is a single usually cylindrical A cylinder (from Greek Greek may refer to: Greece Anyt ...

telephone
. Many communities have inundation maps that provide information on which areas will flood at which stages.


Flood categories

In the United States, there are five levels of flooding.


Action Stage

* Rivers: typically at this level, the water surface is generally near or slightly above the top of its banks, but no man-made structures are flooded; typically any water overflowing is limited to small areas of
park A park is an area of natural, semi-natural or planted space set aside for human enjoyment and recreation Recreation is an activity of leisure Leisure has often been defined as a quality of experience or as free time. Free time is ...

park
land or
marshland A marsh is a that is dominated by rather than species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found at the edges of lakes and stre ...

marshland
. * Coastlines: at action stage, usually elevated
tide Tides are the rise and fall of sea level Mean sea level (MSL) (often shortened to sea level) is an average In colloquial, ordinary language, an average is a single number taken as representative of a list of numbers, usually the sum of ...

tide
s and minor inundation of low-lying
beach A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from Rock (geology), rock, such as sand, gravel, shingle beach, shingle, pebbles, etc., or biological so ...

beach
areas occurs.


Minor Flood Stage

* Rivers: minor flooding is expected at this level, slightly above flood stage. Few, if any,
building A building, or edifice, is a structure with a roof and walls standing more or less permanently in one place, such as a house or factory. Buildings come in a variety of sizes, shapes, and functions, and have been adapted throughout history for a ...

building
s are expected to be inundated, however, roads may be covered with water, parklands, and
lawn A lawn is an area of soil-covered land planted with grass Poaceae () or Gramineae () is a large and nearly ubiquitous family In , family (from la, familia) is a of people related either by (by recognized birth) or (by mar ...

lawn
s may be inundated and water may go under buildings on
stilts Stilts are poles, posts or pillars that allow a person or structure to stand at a height above the ground. In flood plain File:Flood plain 7991.JPG, Riparian vegetation on the floodplain of the Lynches River, close to Johnsonville, So ...
or higher elevations. * Coastlines: water will usually run all the way up to the
dune A dune is a landform A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the ...

dune
in
waves The United States Naval Reserve (Women's Reserve), better known as the WAVES (for Women Accepted for Volunteer Emergency Service), was the women's branch of the United States Naval Reserve The United States Navy Reserve (USNR), known as the U ...
during a minor flood. Overwash may occur on
shoreline A shore or a shoreline is the fringe of land Land is the solid surface of Earth that is not permanently submerged in water. Most but not all land is situated at elevations above sea level (variable over geologic time frames) and consis ...

shoreline
roads.
Lifeguard A lifeguard is a rescuer who supervises the safety and rescue of swimmers, surfers, and other water sports participants such as in a swimming pool, water park, beach, spa, river and lake. Lifeguards are trained in swimming and CPR/AED first ai ...
structures and beach
concession stand A concession stand (American English), snack kiosk or snack bar (British English, Irish English) is a place where patrons can purchase snacks or food at a movie theatre, cinema, amusement park, zoo, aquarium, circus, fair, stadium, beach, swimming ...
s will usually be flooded and may be damaged by
surf
surf
.


Moderate Flood Stage

* Rivers: inundation of buildings usually begins at this stage. Roads are likely to be closed and some areas cut off. Some
evacuations Evacuation or Evacuate may refer to: * Casualty evacuation (CASEVAC), patient evacuation in combat situations * Casualty movement, the procedure for moving a casualty from its initial location to an ambulance * Emergency evacuation, removal of perso ...
may be necessary. * Coastlines: at moderate flood stage, usually water overtops the natural dune and begins flooding
coast The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean The ocean (also the or the world ocean) is the body of that covers approximately 70.8% of the surface of and contains 97% of . Anot ...

coast
al areas. Shoreline roadways and beaches will often be completely flooded out. High surf usually associated with this level of flooding may pound some oceanside structures like
pier Seaside pleasure pier in Brighton, England. The first seaside piers were built in England in the early 19th century.">England.html" ;"title="Brighton, England">Brighton, England. The first seaside piers were built in England in the early 19th ...

pier
s,
boardwalk A boardwalk (alternatively board walk, boarded path, or promenade An esplanade or promenade is a long, open, level area, usually next to a river or large body of water ( Lysefjord) in Norway Norway ( nb, ; nn, ; se, Norga; smj, ...

boardwalk
s, docks, and lifeguard stations apart.
Beach house Beach House is an American dream pop duo formed in Baltimore, Maryland Baltimore ( , locally: ) is the List of municipalities in Maryland, most populous city in the U.S. state of Maryland, as well as List of United States cities by populati ...

Beach house
s may be damaged by water and surf, especially if lacking stilts.


Major Flood Stage

* Rivers: significant to
catastrophic
catastrophic
, life-threatening flooding is usually expected at this stage. Extensive flooding with some low-lying areas completely inundated is likely. Structures may be completely submerged. Large-scale evacuations may be necessary. * Coastlines: Water surges over not only the dune, but also man-made
wall A wall is a structure and a surface that defines an area; carries a load; provides security Security is freedom from, or resilience against, potential Potential generally refers to a currently unrealized ability. The term is used in a wide ...

wall
s and roads. Large and destructive waves pound weak structures and severely damage well-built homes and businesses. Overwash occurs on high-level
seawall A seawall (or sea wall) is a form of coastal defence constructed where the sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers appro ...

seawall
s. If major flooding occurs at high tide, impacts may be felt well inland. If cities are at or below
sea level Mean sea level (MSL) (often shortened to sea level) is an average In colloquial, ordinary language, an average is a single number taken as representative of a list of numbers, usually the sum of the numbers divided by how many numbers are in th ...

sea level
, catastrophic flooding can inundate the entire city and cause millions or billions of dollars in damage (as occurred in
New Orleans New Orleans (,New Orleans
during
Hurricane Katrina Hurricane Katrina was a large and destructive List of Category 5 Atlantic hurricanes, Category 5 Atlantic hurricane that caused over 1,800 fatalities and $125 billion in damage in late August 2005, especially in the city of New Orleans and ...
).


Record Flood Stage

* Rivers: at this level, the river is at its highest that it has been since records began for the area where the stream gauge is located. This does not necessarily imply a major flood. Some areas may have never experienced major flooding, and thus record stage is in the moderate category. * Coastlines: Usually, record flooding at the coast is associated with
tropical cyclones A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation Atmospheric circulation is the large-scale movement of Atmosphere of Earth, air and together with oc ...
, but it may be associated with coastal storms,
Nor'easter A nor'easter (also northeaster; see below) is a synoptic-scale extratropical cyclone Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pres ...
s,
seiche A seiche ( ) is a standing wave In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related ...

seiche
s caused by
earthquakes An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth Earth is the third planet from the Sun and the only astronomical object known ...
, strong
thunderstorms A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning Lightning is a naturally occurring electrostatic discharge Electrostatic discharge (ESD) is the sudden fl ...

thunderstorms
, or
tsunamis A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquake An earthquake (also known as a quake, tre ...
. Destruction is often extensive and may extend a far distance inland.


References


External links


Advanced Hydrologic Prediction Service

U.S. National Streamflow Information Program
{{DEFAULTSORT:Flood Stage Hydrology