How to Read Flood Maps
FEMA’s flood maps are available online.
There are now two map formats available online:
- Copies of the traditional hard-to-read paper maps
- Enhanced digital maps with easy-to-recognize aerial photographs showing individual buildings
Online Paper Maps
FEMA’s online paper maps are scanned images of the large paper maps it no longer prints for distribution. These maps are more difficult to read and don’t have the detail enjoyed with the digital version.
However, if you need an official printout showing flood zones for a specific area, then checkout the "FIRMette" information. This tutorial shows how to read each type of map.
To understand flood maps, it’s helpful to know a couple of terms:
- D-FIRM: An enhanced digital version of the FIRMs.
- FIRM: Flood Insurance Rate Maps are large blueprint sized maps showing designated flood zones over a certain area.
- FIRMette: A small neighborhood sized FIRM map that can be printed on letter-sized paper (or larger). It’s a paper copy of a smaller user defined portion of a Flood Insurance Rate Map (FIRM), created online from your computer, with most of the relevant flood zone mapping information you’ll likely need for insurance or permitting purposes Elevation Certificates will likely be needed as well). A FIRMette qualifies as an official FEMA flood map document.
On the map the Z-Zone is shaded 0.02 PCT. X-Zones are areas where the elevation is higher than the minimum expected flood levels. Buildings in these zones aren’t subject to enhanced building codes to prevent flood damage, but flood insurance is available at a considerable discount.
The two shaded areas on the map show the only "X" and Shaded "X-Zones" within the city (except for Sunset Key).
The regulated floodplain (white) is known as the 100-year floodplain. The Shaded X-zone (dark grey) represents the 200 to 400-year floodplain, and the X-zone (teal) is the 500-year floodplain. So when someone talks about a 500-year flood, it’s not that such a flood only happens once in 500 years, but that flood waters reached the 500-year flood level; which has less than a 0.02% chance of happening during any year. So it’s possible to have two 500-year floods in just two or three years.
Base Flood Elevation (BFE)
In Key West, most buildings/lots are located within type "A" flood zones. These are zones more inland from the coastline, where a static rise in water levels can be expected.
Land close to the shoreline is usually located in type "V" flood zones. The "V" stands for "velocity," or breaking waves with a force that’s considerably more damaging. As a consequence, building standards are much higher within "V" zones.
V & A Zones
Type "V" and "A" zones appear on flood maps as "AE-#" and "VE-#. The "E" denotes this flood zone has an elevation level assigned to it, and is expressed as "AE-6" or "VE-9," with the trailing number indicating the Base Flood Elevation or BFE for that zone. That BFE number notes the height above sea level flood waters can be expected to rise at a minimum.
The BFE is a reference height for building elevations and flood insurance. A building below BFE is a building below the flood level for that site. Building codes require most new and Substantially Improved buildings be at a minimum height of BFE +1’.
Thus, a new or elevated building in an "AE-6" flood zone would need to be elevated to a minimum of seven feet above BFE. An Elevation Certificate is usually needed to determine the height of the land above sea level. If, for example, the land is determined to be four feet above sea level, then the building would need to be three feet above the ground.
The following images are examples of various flood map options for determining the flood zone for two buildings at the Wildlife facility at Indigenous Park near the White Street Pier.
FEMA Flood Maps - are the official standard for flood zone decisions. Begin your search here.
Locate the property on the FEMA map. If it’s clearly between any of the white flood zone lines, then you now know what zone it’s in and the elevation requirements.
In this example, the property appears to be in an "AE" zone, with an eight-foot elevation requirement (EL 8).
When a structure is close to a flood zone line, it can be difficult to determine from the old paper FIRMs in which zone a structure is located. When it’s a close call, use FEMA’s online digital flood maps.
In the example it’s very hard to discern where specific structures are when you get close to the zone lines (red circle). If any portion of a structure (not the property lot) touches a flood zone dividing line, then the entire structure is considered to be in the zone with the most restrictive requirements or greater required elevation.
How to Read Aerial Images
The aerial photos of houses don’t appear until you zoom-in to the neighborhood level. So if you’re not yet seeing the satellite view, keep zooming-in.
In this example, we can see a flood zone line (cyan colored) passes through the middle of one building (larger building in red circle). However, it’s not clear if the flood line is actually touching the smaller building to the left.
On the older FIRMs, the flood zone lines are very broad and aerial photos not very clear. However, on these new digital maps, the photos are very sharp and the flood zone lines very narrow, so it’s much easier to determine if a zone line actually touches a structure. When zoomed-in, it’s clear the flood line isn’t touching the smaller building.
Both building are in the "AE-8" flood zone (below the light blue line), as opposed to the "AE-7" zone above the line.