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 depicted on a community's Flood Insurance Rate Map (FIRM). Each zone reflects the severity or type of flooding in the area.

FEMA has identified various flood risk zones throughout the United States. The following definitions are of those flood risk zones which are most common within the arid southwestern United States. For more information, please visit the FEMA Web site.

High Risk Zones

Zone A is any area with a 1% annual chance of flooding and a 26% chance of flooding over the life of a 30-year mortgage. Because detailed analyses are not performed for such areas no depths or Base Flood Elevations are shown within these zones. Mandatory flood insurance requirements apply.

Zones AE and A1-A30 are areas with a 1% annual chance of flooding and a 26% chance of flooding over the life of a 30-year mortgage. In most instances, Base Flood Elevations derived from detailed analyses are shown at selected intervals within these zones. Mandatory flood insurance requirements apply.

Zone AH is an area with a 1% annual chance of shallow flooding, usually in the form of a pond, with an average depth ranging from 1 to 3 feet. These areas have a 26% chance of flooding over the life of a 30-year mortgage. Base Flood Elevations derived from detailed analyses are shown at selected intervals within these zones. Mandatory flood insurance requirements apply.

Zone AO is a river or stream flood hazard areas, and an area with a 1% or greater chance of shallow flooding each year, usually in the form of sheet flow, with an average depth ranging from 1 to 3 feet. These areas have a 26% chance of flooding over the life of a 30-year mortgage. Average flood depths derived from detailed analyses are shown within these zones. Mandatory flood insurance requirements apply.

Moderate to Low Risk Zones

Zones B, C and X include areas outside the one-percent annual chance floodplain, areas of 1% annual chance sheet flow flooding where average depths are less than 1 foot, areas of 1% annual chance stream flooding where the contributing drainage area is less than 1 square mile, or areas protected from the 1% annual chance flood by levees. No Base Flood Elevations or depths are shown within this zone. Insurance purchase is not required in these zones.

Undetermined Risk Zone

Zone D is an area with possible but undetermined flood hazards. No flood hazard analysis has been conducted. Flood insurance rates are commensurate with the uncertainty of the flood risk.