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What Goes into a Flood Map: Infographic


FEMA's Tom Pickering discusses flood maps with one of the people who attended an Open House on flood maps in Jefferson Parish. Jacqueline Chandler/FEMA

Helping homeowners and communities know their risk of being impacted by disasters stands as one of our top priorities at FEMA. When you know your risk, you can prepare for the worst, take steps to mitigate against hazards, and protect yourself, your family and your property.

Year to year, flooding is the most costly disaster in America. Flood maps play a vital role in helping us prepare for flooding by informing communities about the local flood risk. Flood maps help communities to incorporate flood risk into their planning. They’re also the basis for flood insurance rates through the National Flood Insurance Program, which FEMA administers at the direction of Congress. By law, you may be required to get flood insurance if you live in the highest risk areas. But flooding can happen anywhere -- about 20 percent of all the flood claims come from areas with lower risk. And you don’t have to live close to water to be at risk.

The process for developing and updating flood maps is a long one – and for good reason. It allows communities and property owners at all steps of the process to incorporate the best available data into each community’s flood maps. Projects typically take from 3-5 years to complete, but sometimes they can take longer.  Through the Risk MAP program, flood maps are developed using the best available science, analyzed by some of the leading engineering firms in the field. The mapping standards are published, vetted, have been peer reviewed, and are updated continuously to ensure they are aligned with current best practices.

The infographic below gives you an overview of all that goes into a flood map from beginning to end. The more that communities and homeowners know about this process, the better we can work together to make sure that we build safely and resiliently and are prepared for flooding and other natural disasters.

For full text of the infographic below, visit our document library.

What Goes into a Flood Map: Infographic

Last Updated: 
01/05/2018 - 09:53


Fantastically informative, thanks for this. That's a lot more steps than I thought there'd be.

Living out here in the west, the recent fire-storms have created a condition where flash floods coming off of the burned areas are now an issue. This is great that this information on flood risk areas is being updated and put out there for the public.

Recently affected by the Big Thompson River Flood of 2013, I have a concern about what happened and how it is viewed in floodplain revision. Our subdivision was served by a county bridge. The bridge had a low profile and it's span encroached on the river without flood conditions. The bridge is below the confluences of the North Fork and Mainstem Big Thompson and the community of Drake Colorado. Unfortunately the bridge clogged with debris routed the river toward the low angled wingwalls and into our properties of which our soil represents thousands of years of alluvial deposit without rocks. We lost the hillside that supported our access road and 3 of 5 homes are now perched on a cliff, one home was destroyed and one has 15' of land in front of a 20' cliff. Do flood mapping projects reflect on the detriment of man made structures (bridge) in a situation like this? If the bridge had been built to convey the flood or break away, the river may have stayed in it's channel. 11 dumptruck loads of debris was removed from the bridge (south end collapsed and further drove water into the subdivision) gravel and boulders were deposited on either side of the bridge and demonstrated how filled up the old channel was when compared to the new, un natural channel. The volume capability of the channel was completely shifted to the course of least resistance. The county intends to replace the bridge and I am concerned that per their report, FEMA will only match to replace the same bridge from a better bridge. What is the process to apply for and have hazard mitigation funds applied to improve safety for our community when the old bridge proved to be so detrimental. Does FEMA support break away bridge designs that will free the channel to convey flood waters rather than abuttment designs designed to withstand a greater than 100 year flood? Again, how does this kind of scenario play into the future of floodplain mapping? It has been 5 months and we still do not have access to our home as our subdivision access road was washed away. We park 1/4 mile away and hike in and out on rugged terrain with supplies. Our home is above the floodplain defined by the flood of 1976. This is a historic property that has been in the family for 3 generations, it will continue to be my home forever. I've been here for 2 historic floods but the results were quite different. In the flood of 76 our bridge collapsed and allowed the river to remain in it's channel.

where can a copy of the entire infograph be downloaded for printing?

This is a great tool for communities to use when communicating to their residents and business owners about the flood risk mapping process. The more tools we can put in their hands to help communicate important information about the process is important for the Program's success.

I am trying to buy a home, and found one that perfectly suits my needs, at a reasonable price. Then the lender informed me I needed flood insurance. The seller said the property was not in a flood zone when they purchased it, then overnight, it is in a zone "A". I had one quote at $7,000.00 a year, others won't quote without an elevation certificate, but I cannot spend $600.00 for a survey only to find out the insurance will beyond affordability. The flood map appears to have been drawn with a crayon or magic marker, and the boundary line is so wide it covers the house which is right on the boundary of the zone "A" flood zone. This ridiculous re-zoning is preventing persons such as myself from buying properties, and keeping sellers from selling their properties, and forcing some to let their property go into foreclosure because they can not afford the over blown insurance rates. Yes, it seems FEMA is creating emergencies.

We live in a 100 year floodplain I can't find any maps on 100 year flood plans and just find the website confusing. I found this information 3 years ago on a well detail map, the map I did find for my area was risk accessment not 100 year floodplain map. I checked and didn't see any revisions? I found non-government websites more informative. With better maps.

Unfortunately these flood maps are so out dated in our area (Santa Cruz Mountains, California) insurance companies are reaping the benefits by loan companies mandating flood insurance to home owners who live in areas with no flood history on record. The original maps used are based on 1920's data that was no more than a drive by survey of the area and not real flood potential data. Hopefully these efforts described here to update flood maps will happen sooner than later and alleviate the unnecessary financial burden placed on home owners in this area.

Make no mistake, this has nothing to do with new "Flood" risk areas. FEMA wants to recover the Billions of dollars it continually spends reimbursing people who live in costal areas every time a hurricane destroys their homes. How to do that? Simply add huge new areas to the phony "Flood-Plains" and force these folks to pay insurance to cover the fools who live on the costal marshes. This is just another TAX imposed by FEMA.

Which USGS vertical datum are you using, 1929 or 1988? The 1988 USGS datum is approximately 3.2 feet higher than the 1929 datum at my location, Laramie, WY