causation

= = Flooding happens during heavy rains, when rivers overflow, when ocean waves come onshore, when snow melts too fast or when dams or levees break. Flooding may be only a few inches of water or it may cover a house to the rooftop. Floods that happen very quickly are called flashfloods. Flooding is the most common of all natural hazards. It can happen in every U.S. state and territory.


 * Important terms to know:**
 * Flood Watch or Flashflood Watch -- Flooding may happen soon. Stay tuned to the radio or television news for more information. If you hear a flashflood warning, talk to an adult immediately!
 * Flood Warning -- You may be asked to leave the area. A flood may be happening or will be very soon. Tell an adult if you hear a flood warning. If you have to leave the area, remember to bring your Disaster Supply Kit and make arrangements for your pets.
 * Flashflood Warning -- A flashflood is happening. Get to high ground right away. Tell an adult! by Andres lince

= =
 * why a flood is flood?**

=principal types and causes:= Riverine
 * Slow kinds: Runoff from sustained rainfall or rapid snow melt exceeding the capacity of a river's channel. Causes include heavy rains from[|monsoons], hurricanes and tropical depressions, foreign winds and warm rain affecting snow pack. Unexpected drainage obstructions such as [|landslides], [|ice], or [|debris] can cause slow flooding upstream of the obstruction.
 * Fast kinds: include flash floods resulting from convective precipitation (intense [|thunderstorms]) or sudden release from an upstream impoundment created behind a [|dam], [|landslide], or [|glacier].

Estuarine

 * Commonly caused by a combination of sea tidal surges caused by storm-force winds. A [|storm surge], from either a [|tropical cyclone] or an[|extratropical cyclone], falls within this category.

Coastal

 * Caused by severe sea storms, or as a result of another hazard (e.g. [|tsunami] or hurricane). A [|storm surge], from either a [|tropical cyclone] or an [|extratropical cyclone], falls within this category.

Catastrophic

 * Caused by a significant and unexpected event e.g. [|dam] breakage, or as a result of another hazard (e.g. [|earthquake] or volcanic eruption).

Muddy
A muddy flood is produced by an accumulation of runoff generated on cropland. Sediments are then detached by runoff and carried as suspended matter or bedload. Muddy runoff is more likely detected when it reaches inhabited areas. Muddy floods are therefore a hillslope process, and confusion with mudflows produced by mass movements should be avoided.
 * A [|muddy flood] is generated by run off on crop land.

Other
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 * Floods can occur if water accumulates across an impermeable surface (e.g. from rainfall) and cannot rapidly dissipate (i.e. gentle orientation or low evaporation).
 * A [|series of storms] moving over the same area.
 * [|Dam]-building [|beavers] can flood low-lying urban and rural areas, often causing significant damage. by andres lince