Vantage Point: Is That Flood Information Correct?

At the annual conference of the Association of State Flood Plain Managers in June, one session I attended (“Why is my flood zone determination wrong?”) reminded me of the many problems we encounter when trying to find good flood data. Rather than air my own frustrations with FEMA’s Map Service Center (MSC,, I’ll focus on making sure we examine the data and use it correctly.

A feature many people rely upon from the MSC is the ability to look up an address to find the flood zone and relevant Flood Insurance Rate Map (FIRM). The brightly colored image bearing a red pin presumably indicating the requested address, however, should not be taken at face value. This imagery is the National Flood Hazard Layer (NFHL) and is not the same imagery as the Flood Insurance Rate Map (FIRM). This means that the angle of the base photography is not the same. Differences in angles of the plane mean that a building can appear to be “leaning” to the right on the NFHL but to the left in the FIRM, or vice versa. So I recommend comparing the two for a better idea of where the building’s foundation really is.

There is also the matter of geocoding, another human influence on what appears to be a straight forward flood zone determination. I have seen addresses displayed at the wrong end of the street and therefore in the wrong flood zone. I have seen addresses displayed on the wrong street. I have seen panel lines misdrawn on the NFHL so that the wrong panel information is reported. I always check the FIRM after finding what I consider general location on the NFHL. While it is possible to print out what the Map Service Center refers to as a FIRMette from either the NFHL or from the FIRM, it is only the extract from the regulatory FIRM that contains a paragraph stating that it is an official and legally acceptable depiction of the FIRM and the data shown on that FIRM. Check the text below the FIRM’s FIRMette title block for that notification. The lower right of the NFHL FIRMette informs us that data shown on that image derives from different sources.

The process of checking for any Letters of Map Change that might affect a site is considerably easier than it was before the MSC started providing a drop down list for each panel listing all of the Amendments, Revisions, and Revisions based on Fill affecting that panel. While this is light years of technological advancement beyond earlier “paper only” and heavily redacted Letter of Map Change (LOMC) copies that were so hard to find out even existed, much less obtain copies of, I must admit to being spoiled by the ease of viewing and obtaining digital copies of the FIRM and Flood Insurance Study Reports (FIS). This means that I find myself feeling irritated when confronted by a list of more than ten LOMCs for a single panel (we still call them “maps” and “panels” even though everything is digital these days rather than cartographic). Recognizing if a LOMC is pertinent by its listed Case Number is not particularly intuitive for anyone other than those who made the application for it. (I have commented to FEMA’s MSC contractors about better searching/listing options; time will tell if anyone will listen and improve this situation.)

Just because there is a LOMC listed for the property in which you are interested (hurray! jackpot!) doesn’t mean the diligence part is over. First, read the full header of the document, just below the Case Number and date issued. This tells us the kind of LOMC this is, and parenthetically also tells us either “(REMOVAL)” or less joyfully “(NON REMOVAL)”.This reminds us that the process of applying for LOMCs is just that—a process for review, and some reviews don’t go as well as we would like. Bur even when the header says “(REMOVAL)”, it does not necessarily mean that everything is cleared from the Special Flood Hazard Area and related regulations, restrictions, and requirements. Just below the determination section that tells us what has been removed by a successful LOMC application (parcel, part of a lot, structure) is additional information that could be important to the landowner. Here you may see that portions of the property remain in the 1% annual chance floodplain (when the LOMC has been for a specific building or described portion of a lot) or even that portions remain in the floodway. Both conditions affect planned land use, particularly the latter, as the floodway is meant to remain unobstructed by fill or structures so that it can accommodate the full volume of a 1% annual chance flood even when the flood fringes are no longer flood-worthy.

Bottom line? Check what data you rely upon and how you use it.

About the Author

Wendy Lathrop, PS, CFM, CFS

Wendy Lathrop is licensed as a Professional Land Surveyor in NJ, PA, DE, and MD, and has been involved since 1974 in surveying projects ranging from construction to boundary to environmental land use disputes. She is a Professional Planner in NJ, and a Certified Floodplain Manager through ASFPM.
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