Arlington County, VA Environmental Rules: Flood Zones (2026)

Arlington County Code § 48-47 establishes the Floodplain District as all land subject to inundation by the one percent annual chance (100-year) flood, delineated on FEMA's Flood Insurance Study and Flood Insurance Rate Map for Arlington County, FIRM panels 51013C 0017 through 0083, dated November 16, 2023, or the latest revision. The District splits into subdistricts with different rules. In the Floodway District, mapped within Zone AE, no fill, new construction, substantial improvement or other development can proceed unless a hydrologic and hydraulic analysis by a qualified professional engineer demonstrates the work will not raise the base flood water surface at all; a developer who wants to raise it anyway must first obtain Arlington County's endorsement for a Conditional Letter of Map Revision and FEMA approval.

In the balance of Zone AE, where the floodway has not been mapped, development can proceed only if its cumulative effect, combined with other existing and anticipated development, will not raise the base flood elevation more than one foot at any point. Zone A areas, where FEMA has approximated but not detailed the floodplain boundary, require the applicant to establish the base flood elevation itself using accepted hydrologic and hydraulic methods, with the lowest floor elevated to at least 18 inches above that figure once flood elevation data is applied.

Zone AO covers shallow flooding areas, where structures must be elevated to the flood depth shown on the FIRM, or two feet above the highest adjacent grade if no depth is listed. 2 percent annual chance of flooding, bar new emergency services, medical services, or government records storage except by special exception waiver. Unshaded X Zone and D Zone land, carrying minimal or undetermined flood hazard, fall outside the mapped floodplain altogether. The Floodplain Administrator in the Department of Environmental Services reviews all development in the District and requires a building permit under § 48-57 before any activity begins.