Preparing for a Flood

Become familiar with your community's flood risk

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 insurance rates.

The Floodplain

Diagram of a floodplain

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.

A chart of the odds of a flood over time

Learn Whether Your House is in a Floodplain

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 www.floodsmart.gov

Understanding Flood Zones

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 Lakes.

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 flood insurance.

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).

Explanation of flood zones graph.

Reading a 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.

Explanation of flood insurance rate map (FIRM) graph.

Locating a Project on a Floodplain Map

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.

Case-by-Case Analysis

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 are unchanged
  • 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.

The information provided above was adapted from Floodplain and Shoreland Zoning: A Guidebook for Local Officials (link to FloodplainShorelandZoningGuidebook.pdf), produced by the Wisconsin Department of Natural Resources.

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Revised: October 18, 2007