How to Identify a Floodplain

Floodplain maps show areas likely to flood.

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Shopping for a new house in a new community is challenging. There's so much to consider besides the house itself. Schools, community amenities and social structure--all should play a part in where we choose to live. One consideration that most people have no experience with, though, is finding out whether their prospective home is on a floodplain. Unless you've lived near a river or on a floodplain, you're probably not aware that floodplains have an effect on insurance rates, flood insurance--even whether you can buy insurance for your home at all. Know what to look for the next time you have to buy a home and you could save yourself some money.

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Instructions

Difficulty: Moderately Challenging

Things You’ll Need:

Floodplain maps
Atlas or source to find elevation

Step1

Understand how waterways work. Each creek, lake or river has a "watershed" area--a large area where water from rain and agriculture drain into that body of water. The floodplain is part of the watershed but is determined by land elevation, drainage patterns and water control measures like dams and dikes.

Step2

Find a flood insurance map. These are available from the FEMA website. Local insurance agents may have them and will be glad to share them with a potential customer. FEMA provides "community kits" consisting of detailed maps. The local public library or city may have one for emergency management planning. Some of these maps are rather old (the one above is almost thirty years old) and may not account for subsequent development and changes in the river but they're a good place to start.

Step3

This house, two miles from the river, flooded when the storm sewers were full Find out how close to the river your new home will be. Often, insurance companies consider anything within a few blocks of the river on a floodplain and offer coverage and rates accordingly. Your prospective home may be two blocks from the river but if it's on a hill behind a tall bluff, you can argue that you're not on a floodplain. On the other hand, if the city has an inadequate storm water system, you may not be safe anywhere, regardless of where the floodplain is.

Step4

Examine the land uses around your new home. The most common uses for floodplain land are parks and green spaces like cemetery parks. If your house is nestled in one of these ares, look carefully at the elevation of the house--even if it's been built up, you may be in for a perpetually soggy basement with all of its problems.

Step5

Look at the plant life. Floodplains tend to be hospitable for plants and trees that flourish in wet or boggy soil. Hackberry, river birches and silver maples are giveaways that the ground is moist, if not wet, most of the time. Species that tolerate wet soil can tolerate flooding from time to time.

Step6

Look at the "lay of the land" and your prospective home's closeness or proximity to the water. Floodplains can extend for quite a distance if the land stays the same elevation. If the land rises quickly, water will be pushed further down stream. Remember that water, a fluid, can run around bluffs and dunes if there's a lower way. Those closer to the headwaters of a creek or river tend to have more problems with "flash flooding"--flooding that comes with heavy rain, then runs off into the waterway. Those further downstream or where waterways merge experience flooding of longer duration. Each type of flooding helps determine the shape and size of the floodplain.

Step7

Decide how lucky you think you (and your new community) are. Hundred-year rains can flood any basement but avoiding floodplains will save you aggravation and money. Developers build on floodplains because they won't have to live there and customers love being near bodies of water. There are plenty of homes within sight of a body of water, though, that are not located on the floodplain. Check out the location before you lose your heart to that beautiful new home and you'll feel much more confident when the spring rains start next year.In addition to the floodplain, find out where the water table is. The water table is the depth to which you have to drill to find water for wells. If the table is high, you'll probably find very few neighbors with basements. It would be wiser not to insist on one yourself.

Tips & Warnings

Floodplains near the ocean tend to be better defined than floodplains near inland rivers and other bodies of water. Just look for sand. You'll generally find soil behind high dunes or bluffs. Building in this margin between sea and land is always a risky proposition. Check the history of the area to see what your odds are of being swamped by a Nor'easter or storm surge before buying.
Flood insurance generally covers structures only, not personal property or appliances. Even if you buy flood insurance, you're not guaranteed a full recovery from a disastrous flood.