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A Flood Insurance Rate Map (FIRM) is the official map of a community on which the Federal Emergency Management Agency (FEMA) has delineated both the special flood hazard areas and the flood risk premium zones. Communities are mapped by their respective flood control agencies or the U.S. Army Corps of Engineers. The Flood Control District is responsible for mapping and delineating Maricopa County.
Once floodplain delineation studies are completed on a local level, they are sent to FEMA for approval. This FEMA adoption process takes approximately six to nine months. In the interim period, the District uses this data as the "best available information" for floodplain management. Some delineation studies are not sent immediately to FEMA, during which time the District looks at options for reducing the floodplain.
On a FIRM, a Special Flood Hazard Area (SFHA) is noted with dark shading. An SFHA is an area with a one percent chance of being flooded in any given year, hence the property is in the 100-year floodplain. Any land area susceptible to being inundated by flood waters from any source is identified as a floodplain.
Elevation marks are found on all flood maps. These marks identify points where a ground elevation is established by survey. These elevations are usually expressed in feet. The maps also show the height of the flooding for a 100-year event in that particular area. If the elevation mark is higher than the height of the flooding, that spot is not in the floodplain.
Many of the flood maps produced since 1985 include both the floodplain and floodway information. The floodway is designated with an "FW" on the maps. No property or building should be located within the floodway. Many new maps also show simplified flood insurance risk zone designations.
Flood Zones
Flood zones are geographic areas that FEMA has defined according to varying levels of flood risk. These zones are shown on a FIRM and each zone reflects the potential severity of flooding in the area. Flood hazard area designations appear as dark and light tints. Dark tints indicate areas of increased flood hazard and light tints indicate areas of lesser flood hazard. FEMA produces countywide flood maps, which show flooding information for all of the geographic areas of a county, including towns and cities.
For a quick synopsis of the flood risk level of your property, go to the FEMA Web site.
High Risk Zones
Zone A floodplains are subject to inundation from a 100-year flood event. No base flood elevation or depths are shown in this zone, because no detailed hydraulic analysis has been performed. Mandatory flood insurance is required in this zone.
Zones AE and A1-A30 are subject to inundation by a 100-year flood. Base elevations are shown within these zones and mandatory flood insurance requirements apply.
Zone AH is subject to inundation by 100-year shallow flooding (usually areas of ponding) with average depths of between one and three feet. Base flood elevations are shown and mandatory flood insurance requirements apply.
Zone AO is subject to 100-year shallow flooding resulting from sheet flow on sloping terrain (average depths between one and three feet). Average flood depths are shown and mandatory flood insurance requirements apply.
Moderate to Low Risk Zones
Zones B, C and X are identified as having moderate or minimal hazard from flooding. These zones show the 100-year to 500-year floodplains, areas which have a one percent or less chance of being flooded in any given year. Buildings or other improvements in these zones could be flooded by severe, concentrated rainfall, in absence of adequate drainage systems. Flood insurance is available but not required.
Undetermined Risk Zone
Zone D is an unstudied area where flood hazards are undetermined but flooding is possible. Flood insurance is available but not required.
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