Flood Hazard Mapping

 Flooding refers to the land being covered by water that is not normally covered or is not typically expected to be covered or inundated. Although low lying areas are typically more likely to be flooded, all areas of the United States are potentially subject to flooding under the right circumstances. Flooding can be the result of lakes, rivers, or streams overflowing their banks due to severe weather, dam failure, or sea level rising abnormally as the result of a tsunami, hurricane storm surge, or environmental changes. Wildfires can increase the potential for flooding. 

   House, levee and flooding. Oklahoma 2007.

Photo P.Brach, Courtesy FEMA

Flood hazard mapping is important to help prevent losses by identifying areas more subject to flooding. Flood hazard maps often depict the floodway (the maximum area that the flowing water body covers) and the floodplain (the area the relatively calm body of water covers). The floodplain most often depicted is referred to as the "hundred year floodplain". This does not mean that the area is flooded every hundred years, but that the is a .01 probability, or 1 percent chance, of the area being flooded in a given year.

  In the United states flood hazard mapping and floodplain management is a multiple agency effort. FEMA runs the NFIP - National Flood Insurance Program and is responsible for the production and distribution of flood hazard maps. The USGS maps the topography of river drainages and monitors water levels and conditions in rivers, streams and lakes. NOAA/NWS issues map based flood hazard watches, warnings and alerts. Other federal, state, or local agencies may be involved as well. Some useful resources are listed below. 

    To learn more about flood hazards in your area, contact the appropriate local, state or federal agency. If you plan to build, develop, or inhabit areas subject to flood hazards, consult a qualified professional regarding the hazard, your risk, and options for mitigation. The information on this site is only intended as an educational tool to help you get started. By using it you are subject to our terms of use.