Editing 100-year flood (section)

==Maps, elevations and flow rates==
For [[coastal flooding]] and lake flooding, a 100-year flood is generally expressed as a [[water level]] elevation or depth, and includes a combination of [[tide]], [[storm surge]], and [[wind wave|waves]].<ref>{{cite web|title=Coastal Flooding| url=https://www.floodsmart.gov/floodsmart/pages/coastal_flooding/cf_overview.jsp| website=FloodSmart|publisher=National Flood Insurance Program|access-date=7 March 2016|ref=NFIP coastal|archive-url=https://web.archive.org/web/20160308052549/https://www.floodsmart.gov/floodsmart/pages/coastal_flooding/cf_overview.jsp|archive-date=2016-03-08|url-status=dead}}</ref> 

For river systems, a 100-year flood can be expressed as a [[Discharge (hydrology)|flow rate]], from which the flood elevation is derived. The resulting area of inundation is referred to as the ''100-year floodplain''. Estimates of the 100-year flood flow rate and other streamflow statistics for any stream in the United States are available.<ref name="Ries">Ries, K.G., and others (2008) ''StreamStats: A water resources web application '' [http://pubs.usgs.gov/fs/2008/3067/ U.S. Geological Survey, Fact Sheet 2008-3067]  [http://water.usgs.gov/osw/streamstats/ Application home page] URL accessed 2015-07-12.</ref> 
A 100-year storm may or may not cause a 100-year flood, because of rainfall timing and location variations among different [[drainage basin]]s, and independent causes of floods, such as snow melt and ice dams.

In the UK, the [[Environment Agency]] publishes a comprehensive map of all areas at risk of a 100-year flood.<ref>{{cite web|url=http://maps.environment-agency.gov.uk/wiyby/wiybyController?x=460730.0&y=189442.0&topic=floodmap&ep=map&scale=9&location=OX10%200AJ&lang=_e&layerGroups=default&distance=&textonly=off|publisher=[[Environment Agency]]|title=Flood Map for Planning (Rivers and Sea)|access-date=25 August 2016|date=2016|archive-url=https://web.archive.org/web/20160916225532/http://maps.environment-agency.gov.uk/wiyby/wiybyController?x=460730.0&y=189442.0&topic=floodmap&ep=map&scale=9&location=OX10%200AJ&lang=_e&layerGroups=default&distance=&textonly=off|archive-date=2016-09-16|url-status=dead}}</ref> In the US, the [[Federal Emergency Management Agency]] publishes maps of the 100-year and 500-year floodplains.<ref name=femamap/>

Maps of the riverine or coastal 100-year floodplain may figure importantly in building permits, environmental regulations, and [[flood insurance]]. These analyses generally represent 20th-century climate and may underestimate the effects of [[climate change]].