View source for Floods, Dams and Breaking Banks

[[File:MoM-atlas-floods-and-dams.png|thumb|right|400px|alt=An imagined river valley shows a dam and spillway, water spreading over a meadow, and a dry path on higher ground.|Containment, an outlet and an inundated floodplain appear together in this imagined landscape. Original illustration.]]
A flood covers ground that is ordinarily dry. A dam holds back water; a bank marks the side of a river channel; a spillway provides a designed route for water to leave a reservoir. These are different structures and events, even when everyday speech brings them together in the language of being overwhelmed.

This article concerns physical processes, cultural narratives and ordinary expressions. For recurring flows and tidal movement, see [[Currents, Tides and Undertows]].

== Background ==
Flooding has several forms. River flooding involves rising water in a river system; flash flooding develops rapidly; coastal flooding brings seawater onto normally dry land. Intense rainfall, snowmelt and the failure of a dam or levee can contribute to different flood situations. The cause, speed of onset, depth and direction of flow need not be the same.<ref>[https://www.weather.gov/ffc/flood_awareness_flooding US National Weather Service, ''Flooding and Related Phenomena''].</ref>

A spillway is a structure designed to pass water from a reservoir while protecting the dam. Some spillways are controlled by gates; others depend on their fixed shape. Water leaving a reservoir through its intended outlet is therefore a different event from an uncontrolled breach.<ref>[https://www.usbr.gov/library/glossary/ US Bureau of Reclamation, ''Glossary'', entries “spillway” and “service spillway”].</ref>

=== Floods, tides and tsunamis ===
These terms should not be treated as interchangeable. A flood describes inundation; a tide concerns a recurring change in sea level; a tsunami is a series of waves generated by a major displacement of water. NOAA notes that calling a tsunami a ''tidal wave'' is misleading because tides have little to do with its cause.<ref>[https://oceanservice.noaa.gov/facts/tsunami.html NOAA National Ocean Service, ''What is a tsunami?''].</ref>

== Comparing the images ==
{| class="wikitable"
! Image !! Feature brought into focus
|-
| Water rising slowly || A changing level and a diminishing margin before a boundary is crossed.
|-
| A sudden surge || Rapid arrival or acceleration.
|-
| A dam holding water back || Retention and the difference between upstream and downstream.
|-
| A gate being opened || A change in access through a controllable opening.
|-
| A bank being overtopped or breached || Water moves beyond its former channel, by different mechanisms.
|-
| Water receding || Ground becomes visible again, although its condition may have changed.
|}

These comparisons describe the imagery. A phrase about a flood does not, by itself, establish which physical arrangement a speaker has in mind.

== Examples in literature and culture ==
=== The Flood Tablet ===
The British Museum's account of Tablet XI of the ''Epic of Gilgamesh'' describes Gilgamesh meeting Utnapishtim, who had been warned of a divine plan to send a great flood. The museum places the tablet within the library collected by the Assyrian king Ashurbanipal.<ref>[https://www.britishmuseum.org/visit/object-trails/three-hours-museum British Museum, ''Three hours at the Museum'', object 19, “The Flood Tablet”].</ref>

This is a particular ancient narrative preserved in a particular textual tradition. It should be identified as such when comparing it with other flood stories.

=== Receding water in Genesis ===
Genesis 8 describes a sequence of diminishing water, emerging mountain tops and birds sent from the ark. The dove's return with an olive leaf supplies Noah with information about conditions beyond the vessel.<ref>[https://www.biblegateway.com/passage/?search=Genesis%208&version=KJV ''Genesis'' 8, King James Version].</ref>

'''Commentary:''' the story distinguishes surviving within a vessel from establishing that the surrounding ground is ready to inhabit. The end of the rain and the return to dry land are separate stages. Related images appear in [[Ships]], [[Rain]] and [[Rainbows]].

== Idioms ==
* '''Open the floodgates:''' allow something to occur in much greater numbers or quantity.<ref>[https://dictionary.cambridge.org/us/dictionary/english/open-the-floodgates Cambridge Dictionary, “open the floodgates”].</ref>
* '''A flood of messages:''' a large influx arriving together or in quick succession.
* '''A flood of memories:''' many recollections arriving with a sense of abundance or intensity.
* '''Stem the tide:''' check or reduce an advancing trend.
* '''Keep your head above water:''' manage to continue despite demands or difficulty.
* '''Be inundated with work:''' receive more work than can readily be dealt with.

The phrase ''open the floodgates'' describes an opening, whereas ''the dam burst'' describes a failure of containment. Preserving that difference makes comparisons more precise.

== Related pages ==
[[Currents, Tides and Undertows]] | [[Rivers and Civilisations]] | [[Rain]] | [[Oceans]] | [[Containers]] | [[Ships]] | [[Rainbows]]

== Sources ==
<references />

== Browse the library ==
[[Metaphor Atlas]] | [[Subject index]] | [[:Category:Water|Water]] | [[Idioms A-Z]]

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