How to Read a Flood Map
Flooding occurs when an area of land that is normally dry becomes inundated with water from rain, the ocean, a dam and other sources. You might wonder what the flood risks are in the location of your current home or a place you are considering moving to. The Federal Emergency Management Agency designates special flood hazard locations in communities, which are mapped by the Army Corps of Engineers. These areas are identified in flood maps, also known as flood insurance rate maps.
See the elevation reference marks on the flood map. These identify places where the elevation has been established by surveyors. Higher areas are generally less susceptible to flooding than lower areas.
Note the “Flood Hazard Area” designations on the map, appearing in dark and light tints. Darker tints show areas where there is increased flood hazard, and lighter areas show areas where there is a smaller flood hazard.
Look at the floodplain boundaries, which show the limits of 100-year and 500-year floodplains. The area of a 100-year floodplain has a 1 percent chance of flooding in any given year, and a 500-year floodplain has a 0.2 percent chance of flooding in any given year.
See different marked zones indicating high-risk areas, such as zone “A,” which has an annual 1 percent chance of flooding, and a 26 percent chance of flooding over the period of a 30-year mortgage; or zone “AH,” which is has an annual 1 percent chance of shallow flooding, typically in the form of a pond with an average depth of one to three feet.