New Preliminary Coastal Flood Maps

New Preliminary Coastal Flood Maps for Marathon & the Florida Keys

FEMA, Flood Insurance Rate Maps (FIRMs) are used to determine the minimum elevation required for new construction as well as to define construction methods required in certain zones (AE vs VE, and now “Coastal A”).

The Federal Emergency Management Agency (FEMA) on August 22, 2019 released Working Maps of the new FIRMs to City of Marathon staff. These maps, after a multi-year study of Monroe County’s coastal flood risks and an extensive vetting process, will eventually replace the current flood maps.  The new maps will be based upon the best and most recent available data as well as the most advanced possible modeling software.

While FEMA has emphasized that these are only Preliminary or Working  Maps, the City of Marathon, Monroe County, and other municipal jurisdictions want to make sure that all residents and business owners are aware of the potential for a change in flood risk (required flood elevations) for their property.  This will allow individuals to make informed decisions about maintenance or modification to existing structures on their property as well for making decisions concerning potential new construction.

To emphasize that flood risks are changing and to make sure property owners are aware that new FEMA FIRM maps will be adopted in the near future, the City of Marathon Building Department will be requiring Owner’s to sign a form with permits that acknowledges the issuance of these new DRAFT coastal flood maps and the fact that these maps may indicate a future change to the required elevation of a building currently in the permit process.  This is intended to help homeowners understand that what they are proposing to build today, under the existing flood maps, could become non-conforming after the new draft maps are formally adopted.  This could make their flood risk and insurance costs greater. Owners should think about designing their improvements to meet the proposed draft maps to assure they are addressing potential future risk.

As the DRAFT maps are rolled out, the City is considering its options to hire a consultant that would be charged with analyzing how flood risks are changing within its municipal boundaries based on the new DRAFT FIRMs and the best available science and technology.  If hired, the technical consultant would also be reviewing the maps and modeling conducted by FEMA and would be prepared to appeal any of the maps that do not appear to be correct.  

To view the City’s DRAFT FIRM maps, please click on the following link Preliminary Marathon coastal flood maps.  This link will open to an Index map of the Florida Keys which you can then utilize to navigate to individual specific maps concerning your area of the City.  In order to view other DRAFT FIRM maps outside of the City of Marathon, but within Monroe County, please click the following link HERE: DRAFT coastal flood maps.   This link will open a FEMA FIRM Draft Maps mapping tool.  Simply click in the FIRM Panel section where property is located to view the popup containing a link to the Draft Map (PDF).

IMPORTANT:  These maps don't show an additional difference in elevation due to a change in mapping standards between the old and new proposed flood maps (datum NGVD29 to datum NAVD88).  This means that all NGVD29 elevations (e.g., BFE, Lowest Floor Elevation) need to be converted to NAVD88.  While there is no set conversion factor, as it varies throughout Monroe County, on average there is -1.5 foot conversion factor. To account for this change, ON AVERAGE you should add +1.5-feet to any apparent increase. For example: If your building was in an AE-8 flood zone and is still shown in an AE-8 zone, then it actually experienced an increase of 1.5 feet.  Another example: If your building was in an AE-6 flood zone and is proposed to be in an AE-9 zone, the increase appears to be three-feet.  However, the actual increase would be 4.5’-feet.

To convert one vertical datum to another, visit https://vdatum.noaa.gov/vdatumweb/vdatumweb?a=094103020190826 or alternatively https://www.arcgis.com/home/item.html?id=4ffd84bc93ce4862bcd642bdb023668e .   For more information on vertical datums, read FEMA’s fact sheet at www.FEMA.gov/Media-Library/Assets/Documents/11535.

View current flood maps at FEMA Flood Map Service Center and search by property address.  

Map Review Process:

The public can email comments concerning the DRAFT coastal flood maps to DraftFloodMaps@ci.marathon.fl.us.  City staff will be documenting these comments and providing them informally to FEMA.

After draft maps are reviewed by City staff and comments are made to FEMA, PRELIMINARY maps will be issued by FEMA which the public will then have an opportunity to comment on officially through Community meetings.  Formal public comments or appeals of the preliminary maps can then be provided to FEMA only through local governments like the City of Marathon, other municipalities, or the County.

Once FEMA completes the review of all comments and appeals, they will publish the final Flood Insurance Rate Maps (FIRMs).  The FINAL FIRMs will most likely become effective sometime in 2021-2022.  As this happens, the City will formally adopt the maps by ordinance and the maps will then be used when reviewing applications for permits as the current maps are used today, in compliance with the City’s Floodplain Management Ordinance and the Florida Building Code.  For more information about the mapping process call 305-289 4111 or 289-4121.

The following diagram shows the tentative process timeline for the Draft Maps, Preliminary Maps, and Final Maps: