Normally when people in New Orleans ask if an area floods they are talking about heavy rains causing water to pool in the streets until the city pumps can suck the water down the drains and into the Mississippi River, but since Hurricane Katrina caused the levees to fail and flood the city with water from Lake Pontchartrain, people include levee fail risk when they discuss flooding and debate whether the $14 billion dollar new levee system will save us all.
Protecting residents from the financial loss due to flooding, no matter whether it is from heavy rains or levee breaches, dates back to 1968 when Congress created the National Flood Insurance Program, giving the responsibility to the Federal Emergency Management Agency (FEMA) for producing Flood Insurance Rate Maps that show areas subject to flooding based on historic, meteorological, hydrologic, and hydraulic data. This article explains the various flood zones and provides step-by-step guidance on how to read a flood map and create your own for any location.
What’s In a Flood Map?
The Flood Map provides information that allows you to identify not only Special Flood Hazard Areas but the Base Flood Elevation at a specific site, as well as areas of undeveloped coastal barriers where flood insurance is not available.
Flood Maps provide a wealth of information, including:
- Common physical features, such as major highways, secondary roads, lakes, railroads, streams, and other waterways.
- Special Flood Hazard Areas.
- Base Flood Elevation.
- Flood Insurance Risk Zones.
- Areas subject to inundation by the 500-year flood.
100 Year Flood Zone Is Really a 26 % Chance
A 100-year flood is not a flood that occurs every 100 years, but one that has a 26 percent chance of occurring during a 30-year period, the length of many mortgages. The 100-year flood is a regulatory standard used by Federal agencies and most states, to administer floodplain management programs, and is used by the National Flood Insurance Program (NFIP) as the basis for insurance requirements nationwide. Special Flood Hazard Areas (SFHA) are those areas having at least a 1 percent chance of flooding during any one year. Flood Maps are easy to get and are found online at FEMA’s Map Service Center, http://www.msc.fema.gov.
How to Read a Flood Map
Step 1: Finding the Parish.
To discover the flood risk in your vicinity and use the Interactive Web Mapping Portal, first start with the general area such as the target property’s parish. Choose a Parish from the list below by clicking the link:
Step 2: Finding the Specific Location of the Property.
Let’s say we want flood zoning information on the Mercedes Benz Superdome in New Orleans, so we click on Orleans Parish, and when the map opens up, type in the target address in the box at the top left. The address for our target property, the Superdome, is 1500 Sugar Bowl Dr, New Orleans, LA 70112.
Step 3: Check Interactive Map Choices
Since the map is interactive, you can select a variety of options including satellite view, preliminary or effective map and panel or address view. Uncheck any pre-checked boxes in the panel on the left, and check Address Search Result, Flood Hazard Areas and select the radio button Google Hybrid as shown below:
Step 4: Identify the Flood Insurance Risk Zone and Base Flood Elevation.
Click the Identify icon at the top of the screen. It looks like a white (i) in a blue circle. If you hover over it, the function will pop up.
Then click on your target site to generate a pop-up box showing the Base Flood Elevation, Flood Zone, Panel Number.
The box details the flood map panel number, the Special Flood Hazard Area (SFHA) chance of increase or decrease, the Preliminary and Effective Flood Hazard Area (AE) and the Effective Base Flood Elevation (2 Feet).
Explanation of Flood Zone Designations
Zone A: This zone has a low risk of erosion and can experience breaking waves less than 1.5 feet. No base flood elevations are calculated.
Coastal Zone A: This zone is subject to erosion, fast and strong water movement, and wave heights of 1.5 to 3 feet during storm events. Base flood elevations are calculated for these zones and displayed on flood maps. Communities have the option of adopting more stringent building codes (up to V Zone standards) in this zone, which would give them points in the Community Rating System. This zone is relatively new, so it may not be applicable to your community’s current flood maps. On the new maps, the landward edge of the zone is marked by the LiMWA line (Line of Moderate Wave Action). An elevation certificate is required to accurately calculate insurance rates in this zone.
High Risk (Special Flood Hazard Area)
These zones make up the Special Flood Hazard Area and are in the 100-year-flood zone. They have at least a 1% chance of flooding each year and at least a 26% chance of flooding over the lifetime of a 30-year mortgage. Structures located in these zones with a federally-backed mortgage are required to purchase flood insurance. On a flood map these zones are referred to as the letters below or, collectively, as the 1% annual chance or 100-year-flood zone.
Zone AE or Zone A1-30: This zone has a low risk of erosion and can experience breaking waves less than 1.5 feet. Base flood elevations are calculated and displayed on flood maps. AE zones are present on newer maps; zones A1-30 are present on older maps. An elevation certificate is required to accurately calculate insurance rates in these zones.
Zones AH, AO, AR, A99: See FEMA’s Map Service Center definitions. The flood insurance rate zone that corresponds to areas of the 100-year floodplains that will be protected by a Federal flood protection system where construction has reached specified statutory milestones. No Base Flood Elevations or depths are shown within this zone. Mandatory flood insurance purchase requirements apply.
Zone V: This zone faces an additional hazard from erosion, fast and strong water movement, and waves that may be 3 feet or greater during storm events.
Zone VE or V1-V30: These zones face an additional hazard from storm waves, and can experience waves greater than 3 feet. Base flood elevations are calculated for these zones and displayed on flood maps. VE zones are present on newer maps; zones V1-30 are present on older maps. An elevation certificate is required to accurately calculate insurance rates in these zones.
Zone X (shaded) and Zone B: The area between the extent of the 100-year-flood (1% annual chance flood) and the 500-year-flood (0.2% annual chance flood). There is no base flood elevation calculated for these zones, so elevation certificates are not necessary. Flood insurance could be much cheaper in these zones because of the lower risk. These areas are not subject to the mandatory purchase of flood insurance.
Zone X (unshaded) and Zone C: The area outside of the extent of the 500-year-flood with minimal flood risk. If a structure is located in this zone, however, it does not mean that it is out of harm’s way. The risk determination is based on probability, and the probability of a flood reaching this area is low, but it is not impossible. There is no base flood elevation calculated for these zones, so elevation certificates are not necessary. Flood insurance could be as much as 50% cheaper in these zones because of the lower risk. These areas are not subject to the mandatory purchase of flood insurance.
Zone D: Areas classified as Zone D have not had a flood hazard analysis performed. These are often areas with very low population counts.
How To Make Your Own FIRMette, The FEMA Flood Map
If you need the actual Flood Map, one is available at the FEMA Flood Map Service Center, then enter the target property’s address.
and click the View Map icon as shown below.
The actual FEMA flood map is not in color as shown below. Click Make A Firmette
Drag the green viewer box over your target area, and click Create FIRMette Adobe PDF.
The final product is a FEMA flood map. This map is panel number 225 203 0160E, dated March 1, 1984, showing the Superdome is in Zone A1 but close to Zone B. Zone A1 is on the older maps and is the same as Zone AE on the newer maps.
It’s a Government Product, So Two Maps Are Better Than One
FEMA updates flood maps on a community-by-community basis so all maps are not exactly the same, differing in both format and content. The two basic paper formats used for flood maps are a Flat Flood Map and a Z-Fold Flood Map, but every flood map has several basic elements:
- Title box
- Standard symbols
Since the geographic coverage of a Flood Map may be quite large, FEMA divides an area into sections called panels and includes an index to indicate what areas are shown on each map. A Flat Flood Map consists of one or more 11″x17″ pages and a cover sheet that includes an index and a legend. A Z-Fold Flood Map is a one or more panels that is folded like a highway map and have a legend and index. While panels that make up a geographic area are considered one flood map and can include all of these jurisdictions: parishes, towns, townships, cities, incorporated areas and unincorporated areas have separate flood maps.
In addition to the two basic formats, flood maps also have several basic elements:
Title Block: Found on each Panel (or page), the title box contains the community name, the panel number (page number), date, and other information necessary to identify the flood map panel.
The Legend: Found on Z-fold flood maps, the legend provides information for identifying the risk zones and/or floodway on the flood map.
The Body: The body of a flood map displays the map contents. On an index, the body will usually only display primary features like major roads, corporate limits and other general landmarks that help to identify location. On a panel, the body will show more detail than what is shown on the index, including secondary roads, bridges, and flood hazard information.
Community Name: The title block displays name of the mapped community, the town, city, parish, and state. When the mapped community is a parish, the words “Unincorporated Areas” often appear below the parish name. This indicates that the incorporated areas in the parish area not covered by the flood map. When the flood map covers the entire geographic area of the parish, the words “Incorporated Areas” appear after the parish name.
Community Number: The Community Number is a six-digit identification number assigned to the mapped community. This number is also referred to as the community identification number (CID). You need to use the community identification number when you ask FEMA staff questions about a Flat Flood Map or a Z-fold Flood Map for an individual community and when your order a flood map from the Map Service Center.
Corporate Limit or Parish Line: The Corporate Limit or Parish Line identifies the jurisdictional limits of the community’s regulatory authority over land development and building construction. In some states, an incorporated community may exercise extraterritorial jurisdiction over land development and building construction in areas beyond its corporate limits. Where appropriate, these limits are shown and labeled on the index.
Panel Limit Line: This line reveals the extent of the area covered by each panel shown on the index.
Panel-not-Printed Notes: These notes identify the panels included in the flood map layout that are not printed and explain why they are not printed. For instance, when a panel covers an area of the community that falls entirely in one flood insurance risk zone, that panel may not be printed, and an explanatory note is added to the index. If all panels are printed this annotation is omitted.
Effective or Revised Date: This is the date the new or revised flood map becomes effective for flood insurance and floodplain management purposes. Partial revisions are common and the inside of the index will show the suffix of each panel to determine what has been revised. New parishwide indexes will have effective dates printed on each panel.
List of Printed Panels: This list identifies those panels that are printed, but not necessarily revised. Partial revisions are common and the inside of the index will show the suffix of each panel to determine what has been revised. New parishwide indexes will have effective dates printed on each panel.
Map Repository Address: This is the address of the official community office where reference copies of the flood map and Flood Insurance Study report are stored and made available.
In addition to these items, there are 14 more elements that may be found on flood map panels:
- Area Not Included Label
- Base Flood Elevation
- Coastal Barrier Area
- Elevation Reference Marks
- Floodplain Boundary
- Hazard Area Designation
- Map Scale
- Panel Number
- River Mile Marker
- Stream Line
- Zone Designation
- Zone Division Line
- Flood Insurance Risk Zone Label
For more information on flood maps, read our article Flood Zoning For Dummies, and choose from over 150 articles on commercial real estate.
1-percent annual chance floodplain
This is the boundary of the flood that has a 1-percent chance of being equaled or exceeded in any given year. Also known as the 100-year floodplain.
1-percent annual chance water-surface elevation
The height, in relation to the National Geodetic Vertical Datum of 1929 (or other datum, where specified), of the flood having a 1-percent chance of being equaled or exceeded in any given flood year (also known as the 100-year flood or the base flood).
The flood having a 1-percent chance of being equaled or exceeded in any given year; also known as the base flood. The 1-percent annual chance flood, which is the standard used by most Federal and state agencies, is used by the National Flood Insurance Program (NFIP) as the standard for floodplain management and to determine the need for flood insurance. A structure located within a special flood hazard area shown on an NFIP map has a 26 percent chance of suffering flood damage during the term of a 30-year mortgage.
This is the boundary of the flood that has a 1-percent chance of being equaled or exceeded in any given year. Officially termed the 1-percent annual chance floodplain.
This is the boundary of the flood that has a 0.2-percent chance of being equaled or exceeded in any given year. Officially termed the 0.2-percent annual chance floodplain.
The effect of downstream flow on the water-surface profile.
Base Flood Elevation (BFE)
The height of the base flood, usually in feet, in relation to the National Geodetic Vertical Datum of 1929, the North American Vertical Datum of 1988, or other datum referenced in the Flood Insurance Study report, or depth of the base flood, usually in feet, above the ground surface.
Channel Bank Stations
Points that identify the extreme limits of the natural stream channel. These stations are typically assigned at locations along a cross section where a relatively flat area exists outside of the channel.
A location where two streams or rivers meet.
A line on a map joining points of equal altitude.
The depth of flow at which, for a given discharge at a given location, the total energy is the minimum value possible for flow to occur.
A fixed starting point of a scale.
Federal Emergency Management Agency (FEMA)
An independent agency of the Federal government, founded in 1979, which reports directly to the President. FEMA is responsible for identifying and mitigating natural and man-made hazards. The agency’s mission is: to reduce loss of life and property and protect our nation’s critical infrastructure from all types of hazards through a comprehensive, risk- based, emergency management program of mitigation, preparedness, response and recovery.
A general and temporary condition of partial or complete inundation of normally dry land areas. For flood insurance claim purposes, two or more structures must be inundated before flood damage will be covered.
Flood Boundary Floodway Map (FBFM)
A pre-Map Initiatives floodplain management map that delineates the 100-year (1% annual chance) and 500-year (0.2% annual chance) floodplains, floodway, and cross sections.
Flood Insurance Rate Map (FIRM)
A map on which the 100-year (1% annual chance) and 500-year (0.2% annual chance) floodplains, Base Flood Elevations, and risk premium zones (and floodway information on Map Initiatives FIRMs) are delineated to enable insurance agents to issue accurate flood insurance policies to homeowners in communities participating in the National Flood Insurance Program.
Flood Insurance Study (FIS)
An examination, evaluation, and determination of flood hazards and, if appropriate corresponding water-surface elevations. The resulting reports are used to develop Flood Insurance Rate Maps. Also know as a flood elevation study.
The operation of a program of corrective and preventative measures for mitigating flood damage, including, but not limited to, emergency preparedness plans, flood-control works, and floodplain management regulations. Floodway Channel of a stream plus any adjacent floodplain areas that must be kept free of encroachment so that the 100-year flood discharge can be conveyed without increasing the elevation of the 100-year flood by more than a specified amount (1 foot in most states).
Special Flood Hazard Area (SFHA)
Area inundated by the base (1-percent annual chance) flood, identified on the Flood Insurance Rate Map as Zones A, AE, AH, AO, AR, V, VE, or A99.
The height, in relation to the National Geodetic Vertical Datum of 1929 (or other datum, where specified) of floods of various magnitudes and frequencies in the identified floodplains of coastal or riverine areas.
Additional information can be found at: Federal Emergency Management Agency Map Service Center P.O. Box 1038 Jessup, Maryland 20794-1038 Telephone: (800) 358-9616 Fax: (800) 358-9620 http://www.msc.fema.gov