To provide communities with the information they need to enact and enforce floodplain management
ordinances or laws, FEMA conducts floodplain studies for communities throughout the United States
and publishes the results in Flood Insurance Studies (FISs) and Flood Insurance Rate Maps
(FIRMs). The FIS and FIRM for your community provide information about the names and locations of
flooding sources, sizes and frequencies of past floods, limits of the floodplain, also known
as the Special Flood Hazard Area (SFHA), and floodway, flood flow velocities, and
elevations of the 100-year flood throughout the SFHA. With this information, communities can manage
floodplain development and FEMA’s Federal Insurance Administration can establish accurate flood
The 100-year floodplain is the area of a community that is most at risk of flooding. Owners of
property in the 100-year floodplain are typically required by their mortgage lenders to purchase
flood insurance. Also, new development in the 100-year floodplain must
meet additional requirements. The most common
of these requirements is that homes must be elevated so that their lowest floor is above the
Flood Protection Elevation (FPE) — two feet above the elevation of the 100-year flood
(called the Regional Flood Elevation (RFE)).
The floodplain is divided into three districts: the floodway, the flood fringe, and the general
floodplain district. The floodway is the channel of a river or other watercourse and the portion of
the adjacent floodplain needed to carry the waters of the regional flood. Floodwaters are generally
deepest and swiftest in the floodway, and anything in this area is in the greatest danger during a
flood. Also, encroachment by development will potentially increase flood elevations significantly and
worsen flood conditions throughout the floodplain. For those reasons, all new development, except for
water-dependent structures (e.g., piers, wharves, etc.) and some open-space uses (e.g., recreational
facilities), is prohibited in the floodway. The flood fringe is the remaining portion of the
floodplain that lies outside of the floodway. Development in the flood fringe is generally allowed,
but required to meet certain elevation and dry-land access requirements. The general floodplain
district is the area of the floodplain in which detailed engineering studies have not been
completed. Development requiring a permit is restricted in the general floodplain district until an
engineering analysis is done to determine the exact boundaries of the floodplain and the floodway.
FEMA has a website where you can enter your address to find out whether your home or business is in
a 100-year floodplain. You can access this resource at
Flood Insurance Rate Maps (FIRMs) show the floodplain divided into zones. If your house in Dane County
is in a floodplain, chances are that it is in an A-Zone. As you can see in the table, there are
several specific types of A-Zones, but generally, the A-Zone is the part of the 100-year floodplain
that is inundated by floodwaters during the 100-year flood. If you live in an A-zone, you were probably
required by your mortgage lender to
purchase flood insurance.
You are also required to meet your community’s floodplain development ordinance. There is one other type
of zone in the 100-year floodplain: the V-Zone. The V-zone is the part of the 100-year floodplain
that is subject to wave action. Typically, V-Zones are found along the ocean or the shores of the Great
The remaining zones are not actually inside of the 100-year floodplain. If you live one of these zones
(B, C, D, or X), you are not required to purchase flood insurance. However, if you want to purchase flood
insurance, you can purchase a NFIP
Preferred Risk Policy at rates lower than
your neighbors in the 100-year floodplain. Remember, you don’t have to live in a floodplain to purchase
You can tell what zone you live in by visiting your local town hall or zoning office and examining your
community’s Flood Insurance Rate Map (FIRM).
Below, you will find an example of a Flood Insurance Rate Map (FIRM). The floodplain map forms the basis
for floodplain zoning and the floodplain zoning ordinance. A tutorial on how to read a FIRM may be found
on the FEMA website.
To find floodplain boundaries using approximate studies, use these steps:
Step 1: Find the correct map panel by using the map index.
Step 2: Locate the property on the index using landmarks such as roads.
Step 3: Locate the map panel number for the area around the property using the most recent
FBFW map or the most recent FIRM panel.
Step 4: Locate the property on the map using landmarks such as roads.
Step 5: Determine scale.
Step 6: Measure the distance from the SFHA boundary to the property boundaries or proposed development site.
If a project site is clearly out of the SFHA, then no floodplain regulations apply, but the project
should be reviewed for other considerations. However, if it cannot be easily determined whether or not
the property is in or out of the SFHA, the local official should request the applicant to provide an
engineering analysis as discussed below. In these cases, the applicant may need to hire a private
engineering firm to make the determination.
If a more exact determination of the SFHA boundary is needed, the hydraulic model from the original
flood study should be reviewed. Assistance in using this information is available from the DNR.
A case-by-case analysis is necessary if a proposed building site is determined to be within an
unnumbered A Zone (approximate study area). Unnumbered A Zones have not had a detailed engineering
study completed and do not have a determined RFE. Therefore, prior to issuing any land use permits in
an unnumbered A Zone, the local zoning official must follow a technical study process (case-by-case
engineering analysis) to determine an RFE for the property. Communities may require the developer to
perform the analysis. Once the analysis is completed, it must be submitted to the DNR for review and
approval. All approved case-by-case analyses must be filed with FEMA and the local community.
Standards for hydrologic and hydraulic studies may be found in s. NR 116.07, Wis. Admin. Code.
Exceptions may be allowed for structures that meet zoning district standards and do not change
existing grade after careful evaluation. These exceptions are:
Shore protection projects constructed in conformance with DNR guidance
Routine maintenance to existing streets, driveways, or parking lots where elevation and grade
Enlargements or ponds where the spoil material will be removed from the floodplain or spread out
thinly over the ground surface so as not to change the cross section
Park shelters associated with a recreational use that have no walls
Buried utilities where no earth cover rises above the original grade
If an analysis is required then it must indicate if the project is in the floodplain, if it is in
the floodway and if so, what the revised RFE will be. The analysis must also state what the lowest
floor elevation should be as well as the elevation at the top of the fill. All survey data and
computations leading to these conclusions must accompany the findings.
Based on the data provided, DNR will confirm the proposed RFE and determine whether or not a map
amendment will be necessary. Any and all map and floodplain zoning ordinance amendments must be
reviewed and approved by both the DNR and FEMA if FEMA-approved floodplain boundaries or elevations
are to be changed.
Revised: October 18, 2007