The Federal Emergency Management Agency determines base flood elevations and publishes them in its Flood Insurance Rate Map, or FIRM, which designates special hazard areas and the risk premium zones for your community. Search by address on its Flood Map Service Center portal for the most up-to-date information.
Private insurance companies, in conjunction with the National Insurance Flood Insurance Program administered by FEMA, use the information found on FEMA's FIRM to set rates for flood insurance. Inversely, these companies use the map to deny coverage in some cases. Towns and communities also use this information to determine zoning areas for planned construction.
Base flood elevations, more specifically, are the water surface levels associated with FEMA's "100-year flood" designation, which ties the base elevation to a flood with a 1 percent chance of equaling or exceeding that level in any given year. Communities are grouped into flood zones by these base flood elevations. FEMA labels high-risk areas as Special Flood Hazard Areas, or SFHAs, because they run a 25 percent chance of flooding during a typical 30-year mortgage.
In addition, FEMA incorporates information about a community's width of drainage canals, water flow levels, drainage improvements and pumping stations into FIRM for more accurate zoning.