How to Read A Flood Insurance Rate Map

How to Read A Flood Insurance Rate Map (FIRM)

Floodwaters can endanger both life and property. Thus, it is vital to know where flood hazards exist.

A FIRM, a Flood Insurance Rate Map, is the official map of a community on which FEMA, the Federal Emergency Management Agency, has delineated both the special flood hazard areas and the flood risk premium zones applicable to the community. Communities are mapped by the Army Corps of Engineers.

Special Flood Hazard Areas

Special Flood Hazard Areas, SFHA's, a darkly shaded area on a FIRM or Flood Hazard Boundary Map, FHBM, identifying 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.

What is a Flood?

A flood is a general and temporary condition of partial or complete inundation of normally dry land areas from one of the following four sources:

The overflow of inland or tidal waters.
The unusual and rapid accumulation or runoff of surface waters from any source.
Mudslides (i.e., mudflows) which are proximately caused by floods, as defined above, and are akin to a river of liquid and flowing mud on the surface of normally dry land area, as when earth is carried by a current of water and deposited along the path of the current.
The collapse or subsidence of land along the shore of a lake or other body of water as a result of erosion or undermining caused by waves or currents of water exceeding the cyclical levels which result in flood, as defined above.

Flood Maps

Flood Maps can be formatted by scale, types of jurisdictions included, or type of fold. Many of the Flood Maps produced since January 1985 include floodway and floodplain management information that was not shown on older versions of Flood Maps. Many new Flood Maps also present simplified flood insurance risk zone designations. The most common scales are one inch = 500 feet, one inch = 1,000 feet, and one inch = 2,000 feet. The jurisdictions covered may include partial or entire counties, divisions, parishes, or communities.

Two basic formats used are a "Flat Flood Map" and a "Z-fold Flood Map". A Flat Flood Map consists of a cover page, which includes an index, and one or more 11' x 17' pages. A Z-fold Flood Map, consists of panels similar to those found on highway maps; however, each panel, on a Z-fold, includes a legend. An index is an integral part of a Z-fold Flood Map consisting of more than one panel.

When a Flood Map cannot be presented on one page, it is produced on several pages. Those pages are known as panels. Panels depict the varying flood hazards throughout a community. Each panel includes a title box that contains the name of the community, the panel number, and other information. Z-fold Flood Maps also include legends. All panels, regardless of their format, include six items that also appear on the index. They are:

community name
community number
panel number/community panel number/map number
corporate limit or county boundary line
north arrow
effective or revised date

Special References on Maps

Elevation reference 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; for some communities, however, the elevations are shown in meters. Descriptions of the marks, including their elevations are provided; however, descriptions of locations appear in different places, depending on the format of the Flood Map.

Areas are identified which are located in the mapped area, but not located within the jurisdiction of the community; hence, that flood hazard information is not shown on the Flood Map.

A symbol identifies undeveloped coastal barriers in the Coastal Barrier Resources System established by the Coastal Barrier Resources Act of 1982 and the Coastal Barrier Improvement Act of 1990 and other related information. These areas are identified because as required by the 1982 and 1990 Acts new flood insurance coverage cannot be provided after specified dates for new or substantially improved structures on any Coastal Barrier in the system.

Flood Hazard Area designations appear as dark and light tints. Dark tints indicate areas of increased flood hazard; light tints indicate areas of lesser flood hazard.

Floodplain boundaries show the limits of the 100- and 500-year floodplains.

Most Flood Maps cover only one community. If that community is a county, flooding information is shown only for the areas under the jurisdiction of the county government. Thus, flooding information will not be listed for incorporated areas (e.g., towns and cities) on the Flood Maps produced for most counties. Separate Flood Maps are prepared for incorporated areas.

Recently, however, FEMA has produced countywide Flood Maps. These maps show flooding information for all of the geographic areas of a county, including the towns and cities.

How to Obtain FEMA Flood Maps

Copies of Flood Maps are made available by FEMA, for a nominal fee. To obtain a copy of the current flood map for a specific community, contact the

PO Box 1038
Jessup, MD 20794-1038

To facilitate your request, review the current Flood Map on file at the local community repository and obtain the panel number you will be needing. Or you may order the flood map index from the MSC to determine the panels you will need.

The MSC will also accept orders for maps and other NFIP materials on 1 (800) 358-9616.

(Information was taken from FEMA publication "Guide to Flood Maps," FEMA 258, May 1995, which can be ordered from the MSC using inventory #00108.)

Updated: 9/3/1998

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