Grand Junction, CO Environmental Rules: Flood Zones (2026)

The City of Grand Junction bases its floodplain regulations on the 2012 Flood Insurance Study for Mesa County and Incorporated Areas and the accompanying Flood Insurance Rate Maps, adopted under GJMC § 21.06.020. Before anyone constructs, maintains a use or structure, or otherwise develops or topographically alters land in the floodway or within a mapped area of special flood hazard, including for agricultural purposes, the Community Development Director must issue a Floodplain Development Permit under GJMC § 21.02.040(c)(2)(ii). Where FEMA has not mapped a regulatory floodway, GJMC § 21.06.020(c)(2) bars new construction, substantial improvement, or fill in Zones A1-30 and AE unless the applicant shows the project will not raise the base flood's water surface elevation more than one-half foot anywhere in the City; exceeding that threshold requires a Conditional Letter of Map Revision from FEMA.

Inside a mapped floodway, GJMC § 21.06.020(d) requires a Colorado-registered professional engineer's no-rise certificate showing the project will cause no increase in flood levels during the base flood discharge before any fill, new construction, or substantial improvement is allowed. New or substantially improved residential structures must have the lowest floor, including any basement, elevated at least one foot above the base flood elevation; nonresidential structures may instead be flood-proofed watertight below that elevation if a Colorado professional engineer certifies the design. Manufactured homes must be anchored with over-the-top or frame ties engineered to resist 4,800 pounds of force at each tie point.

The Director keeps records of lowest-floor and floodproofing elevations for every permitted project, and a permit's validity period runs for the length specified in the approved permit rather than a fixed term.