Editing Floodplain (section)

==Flood control==
{{main|Flood control}}
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Excluding [[famines]] and [[epidemic]]s, some of the worst natural disasters in history<ref>{{Cite web|last1=development|first1=Jessica Karpilo holds a B. A. in Geography from the University of Denver She has written on the subjects of sustainable|last2=Karpilo|first2=maps our editorial process Jessica|title=What Are the 10 Deadliest Disasters in World History?|url=https://www.thoughtco.com/worlds-worst-disasters-1434989|access-date=2020-11-30|website=ThoughtCo|archive-date=2020-11-27|archive-url=https://web.archive.org/web/20201127013142/https://www.thoughtco.com/worlds-worst-disasters-1434989|url-status=live}}</ref> (measured by fatalities) have been river floods, particularly in the [[Yellow River]] in China – see [[list of deadliest floods]]. The worst of these, and the [[List of natural disasters by death toll#Ten deadliest natural disasters by highest estimated death toll excluding epidemics and famines|worst natural disaster]] (excluding famine and epidemics), was the [[1931 China floods]], estimated to have killed millions. This had been preceded by the [[1887 Yellow River flood]], which killed around one million people and is the second-worst natural disaster in history.

The extent of floodplain inundation depends partly on flood magnitude, defined by the [[return period]].

In the United States, the [[Fema|Federal Emergency Management Agency (FEMA)]] manages the [[National Flood Insurance Program]] (NFIP). The NFIP offers insurance to properties located within a flood-prone area, as defined by the [[Flood Insurance Rate Map]] (FIRM), which depicts various flood risks for a community. The FIRM typically focuses on the delineation of the 100-year flood inundation area, also known within the NFIP as the Special Flood Hazard Area.

Where a detailed study of a waterway has been done, the 100-year floodplain will also include the floodway, the critical portion of the floodplain which includes the [[stream channel]] and any adjacent areas that must be kept free of encroachments that might block flood flows or restrict storage of flood waters. Another commonly encountered term is the Special Flood Hazard Area, which is any area subject to inundation by a 100-year flood.<ref>{{cite web|url=https://www.law.cornell.edu/cfr/text/44/59.1|title=44 CFR 59.1 – Definitions.|website=LII / Legal Information Institute|access-date=2017-01-13|archive-date=2017-08-29|archive-url=https://web.archive.org/web/20170829162835/https://www.law.cornell.edu/cfr/text/44/59.1|url-status=live}}</ref> A problem is that any alteration of the watershed upstream of the point in question can potentially affect the ability of the watershed to handle water, and thus potentially affects the levels of the periodic floods. A large shopping center and parking lot, for example, may raise the levels of 5-year, 100-year, and other floods, but the maps are rarely adjusted and are frequently rendered obsolete by subsequent development.

In order for a flood-prone property to qualify for government-subsidized insurance, a local community must adopt an ordinance that protects the floodway and requires that new residential structures built in Special Flood Hazard Areas be elevated to at least the level of the 100-year flood. Commercial structures can be elevated or floodproofed to or above this level. In some areas without detailed study information, structures may be required to be elevated to at least two feet above the surrounding grade.<ref>{{cite web|url=https://www.law.cornell.edu/cfr/text/44/60.3|title=44 CFR 60.3 – Flood plain management criteria for flood-prone areas.|website=LII / Legal Information Institute|access-date=2017-01-13|archive-date=2017-08-29|archive-url=https://web.archive.org/web/20170829160732/https://www.law.cornell.edu/cfr/text/44/60.3|url-status=live}}</ref> Many State and local governments have, in addition, adopted floodplain construction regulations which are more restrictive than those mandated by the NFIP. The US government also sponsors flood hazard mitigation efforts to reduce flood impacts. [[California]]'s Hazard Mitigation Program is one funding source for mitigation projects. A number of whole towns such as [[English, Indiana]], have been completely relocated to remove them from the floodplain. Other smaller-scale mitigation efforts include acquiring and demolishing flood-prone buildings or flood-proofing them.

In some floodplains, such as the [[Inner Niger Delta]] of [[Mali]], annual flooding events are a natural part of the local ecology and [[rural economics|rural economy]], allowing for the raising of crops through [[recessional agriculture]]. However, in [[Bangladesh]], which occupies the [[Ganges Delta]], the advantages provided by the richness of the alluvial soil of the floodplain are severely offset by frequent floods brought on by [[cyclone]]s and annual [[monsoon]] rains. These [[extreme weather]] events cause severe economic disruption and loss of human life in the densely-populated region.
[[File:Flooding_of_Pampanga_River_after_Typhoon_Quinta_(Molave),_Santa_Rosa,_Nueva_Ecija.jpg|center|thumb|500x500px|Flooding of Pampanga River floodplain after [[Typhoon Molave (2020)|Typhoon Quinta]], 2020 (view from [[Santa Rosa, Nueva Ecija]] bridge).]]