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Arapahoe County, CO Environmental Rules: Flood Zones (2026)

Significant Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified August 2026

FEMA flood zone rules in Arapahoe County, CO, also called floodplain regulations or special flood hazard area (SFHA) rules, determine flood insurance requirements and elevation standards for new construction.

Key Facts

Governing section: LDC § 4-3.5.D, Floodways
Floodway standard: County-adopted one-half-foot floodway requirement
Default rule: Fill and construction prohibited without no-rise certification
Undesignated floodways: No more than 0.5-ft base flood elevation rise
Governing map: FEMA FIS/FIRM dated April 11, 2024
Applies to: Unincorporated Arapahoe County only

FEMA Flood Zone Lookup

FEMA assigns every parcel in the U.S. a flood-hazard designation on its Flood Insurance Rate Maps (FIRMs). Zones starting with A or V are high-risk Special Flood Hazard Areas where federally backed mortgages require NFIP flood insurance. Zone X indicates moderate-to-minimal risk, where insurance is optional but often recommended. Your specific zone determines insurance cost, build elevation, and permit requirements in Arapahoe County, CO.

Zone	What it means	NFIP required?
A	High-risk flood area; 1% annual chance flood, no detailed analysis.	Yes
AE	High-risk; same as A but with established Base Flood Elevations.	Yes
AH	High-risk shallow flooding (1-3 ft), usually ponding.	Yes
AO	High-risk shallow flooding (1-3 ft) with sheet flow on sloping terrain.	Yes
V	High-risk coastal zone subject to wave action (no BFE).	Yes
VE	High-risk coastal zone with wave action and established BFEs.	Yes
X (shaded)	Moderate risk; between the 1% and 0.2% annual chance flood.	Recommended
X	Minimal risk; outside the 0.2% annual chance floodplain.	No

Look up Arapahoe County, CO on the FEMA flood map

FEMA maps update periodically; verify zone before buying flood insurance or building.

Summary

Unincorporated Arapahoe County bars new construction, fill and other development inside an adopted regulatory floodway under LDC § 4-3.5.D unless a Colorado-licensed engineer certifies no rise in flood levels or the county approves a Floodplain Modification Study, keeping mapped floodways clear for flood conveyance.

City-specific rules exist: Aurora, and Centennial have their own flood zones rules that differ from Arapahoe County's county-level regulations. If you live in one of those cities, check the city-specific page instead.

The floodway as defined in Section 7-2 is an extremely hazardous area due to the velocity of flood waters which carry debris, potential projectiles, and has erosion potential. Floodways are located within special flood hazard areas established in Section 4-3.4.B. The County has adopted a one-half foot floodway requirement. For special flood hazard areas which have a designated floodway, the following provisions apply: a. Development is prohibited, including fill, new construction, and other development within the adopted regulatory floodway unless certification by a Colorado registered professional engineer is provided demonstrating that encroachment shall not result in any increase in flood levels (no rise) during the occurrence of the base flood discharge, or otherwise alter the floodway in a manner which will constrict the channel or increase erosion potential unless a FEMA-approved CLOMR that addresses the 44 CFR Part 65, Section 12 requirements or a County-approved Floodplain Modification Study are obtained.

Source: Arapahoe County Floodplain ManagementView official code

Full Breakdown

D, Floodways, within the Floodplain Management chapter, which applies only to unincorporated Arapahoe County. Aurora, Centennial, Littleton and the county's other cities administer floodplain rules inside their own limits. B, using the FEMA Flood Insurance Study and Flood Insurance Rate Maps for Arapahoe County dated April 11, 2024, together with Urban Drainage and Flood Control District Flood Hazard Area Delineation studies. D bars fill, new construction and other development inside an adopted regulatory floodway outright unless a Colorado-registered professional engineer certifies the encroachment will cause no rise in flood levels during the base flood discharge and will not constrict the channel or increase erosion, or unless FEMA issues a Conditional Letter of Map Revision addressing 44 CFR Part 65 § 12, or the county approves a Floodplain Modification Study.

c still bars any encroachment that would raise the base flood elevation more than one-half foot until a floodway is mapped. C. The Floodplain Administrator, acting for the Board of County Commissioners, reviews these submittals and can require a map revision before permit approval.

Violations & Fines

Building or filling in a mapped floodway without the required no-rise engineering certification, CLOMR or Floodplain Modification Study is a violation the Floodplain Administrator can act on for the Board of County Commissioners; the county's regulations authorize whatever lawful action is necessary to prevent or remedy an unpermitted floodway encroachment, and no structure or land may be built, altered or converted in the floodplain without complying with these regulations.

Frequently Asked Questions

Can I build in a mapped Arapahoe County floodway?

Only if a Colorado-registered professional engineer certifies the project will cause no rise in flood levels during the base flood and will not constrict the channel, per LDC § 4-3.5.D.a, or the county approves a FEMA CLOMR or Floodplain Modification Study first.

Does this floodway ban apply in Aurora or Centennial?

No. LDC § 4-3.5.D governs only unincorporated Arapahoe County; the incorporated cities within the county's boundaries, including Aurora and Centennial, regulate floodplains inside their own city limits under their own codes.

What if my property's floodway hasn't been mapped yet?

Section 4-3.5.D.c still prohibits any encroachment that would raise the base flood elevation more than one-half foot in a special flood hazard area without a designated floodway, until the county maps one.

Sources & Official References

[1]Arapahoe County Ordinances & Resolutions

Other rules in Arapahoe County

Fence Regulations: Height LimitsSome Restrictions Erosion ControlSome Restrictions Flood Elevation RequirementsSome Restrictions Stormwater ManagementSome Restrictions Defensible SpaceSome Restrictions Vehicle Idling RestrictionsSome Restrictions Noise Ordinances: Decibel LimitsSome Restrictions Parking Rules: Commercial & Oversized VehiclesHeavy Restrictions Parking Rules: Loading ZonesSome Restrictions Fence Regulations: Retaining WallsSome Restrictions Fence Regulations: Fence Permit RequirementsSome Restrictions

All Arapahoe County rules

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Flood Zones in Cities Across Arapahoe County

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