Floodplains_Content Page_Mapping

Floodplain Mapping

The Federal Emergency Management Agency (FEMA) produces Flood Insurance Rate Maps (FIRMs) that show areas at risk to flooding. The FIRMs are based on engineering studies called Flood Insurance Studies (FIS). The FIRMs can be changed through Letters of Maps Change (LOMCs).

Using the maps

Flood Insurance Rate Maps (FIRMs) are maps of areas at risk to flooding also known as floodplains or Special Flood Hazard Areas (SFHA). Newer FIRMs use aerial photos as the base layer making it easier to determine if a structure or property is within a mapped floodplain. Effective FIRMs and Preliminary FIRMs are available on FEMA's Map Service Center. To learn more about using the maps visit FEMA's FIRM Tutorial and FIS Tutorial.

Mapping process

In the past, Flood Insurance Rate Maps were produced by FEMA and distributed on paper. In 2003, FEMA implemented a map modernization initiative to upgrade and distribute the maps in a digital format rather than on paper. The newer maps are called Digital Flood Insurance Rate Maps (DFIRMs). The DFIRMs show areas at risk to flooding overlain on aerial photos. In addition, the best available terrain data is used in the mapping process, which results in higher quality mapping products. Light Detection and Ranging (LiDAR) elevation data is used for all current and future DFIRM production in Wisconsin.

DFIRMs are available for download at FEMA's Map Service Center. The spatial data displayed on the DFIRMs is incorporated into FEMA's National Flood Hazard Layer which can be viewed on DNR's mapping application. In addition, engineering input models and flood insurance study text can be downloaded within the mapping application by identifying a reach in the Analysis Lines layer.

Risk MAP

FEMA implemented Risk MAP (Mapping, Assessment and Planning) in 2010, the next phase in floodplain mapping now that the map modernization phase is complete. Risk MAP is a new multi-year FEMA program using a watershed approach (vs. the countywide approach used previously).

The purpose of Risk MAP is to identify the risk at a location and mitigate that risk. This is done by creating some new products for the communities. These products include a new layer that shows the changes since last firm. Communities can use this to identify new areas of risk. There is also a series of raster datasets that shows the depth of the flood for various events. These show not just that there is flooding but the depth to be expected. The last set of products are HAZUS products. These are tables that show the possible financial risk for a given census block.

Mapping steps

The creation of new flood maps is a multi-step process.

  • Step 1-Discovery Meeting: FEMA staff and either FEMA's contractors and/or department staff meet with representatives from the communities chosen for remapping to gather information on local priorities and any available engineering and topographic data
  • Step 2-Data Development: Information and data gathered at the scoping meeting is reviewed for compliance with FEMA’s mapping standards. New engineering studies are done if funding available.
  • Step 3-Preliminary FIRMs: Preliminary FIRMs are created using the gathered data. The preliminary maps are made available to local officials and the public for review during an open house.
  • Step 4-Expanded Appeal Process: A 90-day appeal period set by the NFIP during which the public can submit comments (base map feature changes) and appeals (Special Flood Hazard Area/regulatory floodway changes) to the preliminary FIRMs. Community collects all comments and/or appeals and then forwards those on to the department for final evaluation. Changes are then made to the preliminary FIRMs to incorporate any valid comments and appeals.
  • Step 5-Final Map Creation: Once all changes are made to the preliminary FIRMs, the engineering data and maps are sent to FEMA for final map production. FEMA's Map Service Center is responsible for providing the final maps and the Flood Insurance Study to the affected communities.
  • Step 6-Letter of Final Determination and Ordinance Adoption: FEMA is responsible for notifying the communities of the effective date of the FIRMs. Each community that will have new FIRM panels is sent a Letter of Final Determination (LFD). The LFD notifies the community that it has six months to amend the current floodplain ordinance

A detailed flow chart outlines the mapping process, including a timeline.