Where it rains, it can flood. But water runs downhill, so it is possible to anticipate the highest risk areas.
Local Flood Hazards: Where Will it Flood?
Special Flood Hazard Areas
Areas with a 1% or greater probability of flooding in any given year have been mapped by the Federal Emergency Management Agency (FEMA) for many rivers, streams, and lakes (also called the 100-year floodplain). Development activities within this “special flood hazard area” area require a floodplain development permit from the municipality. Flood insurance may be required for a mortgage. In addition to this regulated floodplain, some FEMA Flood Insurance Rate maps also show a floodway—high risk part of the floodplain that should be kept open to allow for the flow of water—and the moderate risk 0.2% probability (500-year) floodplain.
Flood hazards occur near every waterbody
Flash floods, which develop quickly, send torrents of water down streams and ditches and often cause extensive erosion damage. High runoff from developed areas can overwhelmed stormwater systems and flood urban areas, particularly in the fall when leaves clog the storm drains. Ice, debris, watershed development, or altered drainage patterns can result in flooding of areas that have not previously flooded or been mapped as high risk areas.
It is prudent to assume that any site near a river, stream, lake, wetland, or drainageway may be subject to flooding or erosion hazards. Soil characteristics and other analyses may provide additional clues about where these risks are highest.
Levees reduce — but do not eliminate — flood risks
Even though the design, construction, operation, and maintenance of the region’s levees may be exemplary, there is still a possibility that they will be overtopped or fail.
If it has flooded before, it can flood again
Mother Nature doesn’t look at the flood map and flood risks are increasing. Learn about past flooding from neighbors, historical societies, and local governments.