Floodplain Maps

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Floods are the most common natural disaster in the United States. To reduce the impact of flooding on communities, the Federal Emergency Management Agency (FEMA) requires communities to manage development in floodplains and publishes maps of floodplains.

These maps are used:

By the City to manage development through our Community Development Code (CDC) and
By lending institutions and companies that offer flood insurance under the National Flood Insurance Program.

FEMA requires local governments to manage floodplain development in order reduce flood damages and for property owners to be eligible for public flood insurance.

FEMA last updated the flood maps for all of Washington County in 2016, and the flood maps for Waible Creek were updated in 2018.

In 2019, the City and FEMA revised flood maps for Glencoe Swale in the northeast portion of Hillsboro, and these changes went into effect on April 25, 2019. View and print a copy of the approved Letter of Map Revision.

What is a floodplain?

The term “floodplain” is shorthand for the area that has at least 1% chance of flooding in any given year also known as the “100-year flood event." The City calls this area the Regulatory Floodplain in keeping with our CDC Regulatory Floodplain Overlay (RFO). FEMA calls this area the Special Flood Hazard Area, and there are a number of codes that provide managers with more information about the type of flooding or flood study; AE is the most common type of FEMA floodplain in Hillsboro.

Note that the outer floodplain boundary indicates an annual probability of flooding of at least 1%. The closer a property is to a waterway, the greater the likelihood of it flooding. Watch "The 100 Year Flood is Not What You Think It is (Maybe)" for a great explanation.

How do I determine if a structure or property is in the floodplain?

FEMA provides online access to flood maps here. However, it’s still a good idea to contact the City Floodplain Administrator, Rachel Marble, at 503-681-6155 or email our Community Development Department with the address to determine if the property is located in the floodplain.

The requirement to carry flood insurance is based on a property containing buildings that touch the floodplain. There is greater than a 1 in 4 chance that a home in the floodplain will be flooded during a 30-year mortgage, 27 times more likely than a fire.

Flooding can and does occur outside of the floodplain, although it is less likely. Flood insurance for buildings not in a mapped floodplain is much less expensive than policies for buildings that are in a floodplain, and worth having if you’ve had issues with water inundation from storms.

Conventional homeowners’ and renters’ insurance policies do not cover flood losses.

How might changes to floodplain maps affect me?

Certain areas of the City may be brought into the Regulatory Floodplain, and structures within the Regulatory Floodplain would be subject to the requirement to carry flood insurance.
Certain areas of the City may be removed from the Regulatory Floodplain, and structures in those areas may no longer be required to carry flood insurance. (It’s up to the mortgage lender, though.)
Rates on flood insurance premiums may change.

More about flood insurance

There are potentially discounted premiums for buildings that are “newly mapped” into the floodplain. Flood insurance is available for personal property as well as for structures. Flood insurance premiums can vary based on characteristics of the structure, such as its elevation.

Visit the National Flood Insurance Program's Food Smart website to learn more about insurance, premiums, and ways to lower rates. Flood insurance is available and advisable for buildings that are prone to flooding regardless of whether a lender requires it or whether the official FEMA maps show the property as within the regulatory floodplain.

Development and flood risk