FAQs: Floodplains

What is a floodplain?

In general, a floodplain is the flat area located adjacent to the main stream channel. When stream banks overflow during or after a storm, the floodplain provides natural storage for the excess water. In Fairfax County, the 100-year frequency storm is used to determine the limits of the floodplain.

Are all floodplains the same?

No. There are three distinct kinds or categories of floodplains in Fairfax County, each of which carries different development restrictions. These three categories are:

  1. Minor Floodplain: drainage area greater than 70 acres but less than 360 acres.
  2. Major Floodplain: drainage area 360 acres or greater.
  3. Those which are designated as a floodplain by the National Flood Insurance Program.

For further information about defining floodplains, please see the Zoning Ordinance, Article 20, Definitions.

How can I determine if my property is in a floodplain?

If you are looking for a FEMA Special Flood Hazard Area specific to your property, maps are available through My Neighborhood. Follow these instructions to access the FEMA special flood hazard area maps.

For more information, contact the Stormwater Planning Division, 703-324-5500, TTY 711.

Who is responsible for regulating development in floodplains in Fairfax County?

The director of the Department of Public Works and Environmental Services is responsible for regulating development in floodplains. Land Development Services administers all the regulatory aspects of development in and adjacent to floodplains, including;

  • Granting written permission to work in a floodplain (which is required prior to disturbing a floodplain);
  • Approving the record plats which establish floodplain easements and reviewing; and
  • Approving the floodplain studies required to be submitted as part of the development process

For more information, call 703-324-1720, TTY 711.

How do I obtain permission to work in a floodplain?

Requests for permission to work in a floodplain should be submitted in writing to:

Director, Land Development Services
Department of Public Works and Environmental Services
12055 Government Center Parkway, Suite 444
Fairfax, Va. 22035-5504

If the response from Land Development Services indicates the work may be performed, that letter must be made a part of any construction plan.

How close can I build my house/addition to a floodplain?

For additions to residential structures that existed prior to Aug. 14, 1978: The Zoning Ordinance, Section 2-903.8 describes requirements and conditions that address additions to residential structures that existed prior to Aug. 14, 1978.

For new home construction or additions to houses built after Aug. 14, 1978, there are horizontal and vertical setback requirements. The horizontal setback requirement is 15 feet from the edge of the 100-year water surface. The vertical setback requirement is 18 inches between the computed 100-year water surface elevation and the lowest part of the lowest floor (including basements).

For further information, please contact Zoning Administration  at 703-222-1082, TTY 711.

Where can I find information about floodplain studies?

The Site and Addressing Center of Land Development Services provides this information. You may contact the Site and Addressing Center via email or call 703-222-0801, TTY 711. 
This information is also available by contacting the Stormwater Planning Division703-324-5500, TTY 711.


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