Boulder, CO Environmental Rules: Flood Zones (2026)

Chapter 9-3 of the Land Use Code regulates flood-prone land through a stack of overlapping zones: the five-hundred-year floodplain, the one-hundred-year floodplain, the conveyance zone, and the high hazard zone, each with cumulative requirements. Section 9-3-3(a)(1) requires a floodplain development permit before any development occurs in the one-hundred-year floodplain, except for activities exempted under Section 9-3-6(a), such as maintenance work, small grade changes under six inches, or underground utilities that do not affect the floodway's capacity. R. Chapter 1. Construction standards in the one-hundred-year floodplain include anchoring requirements for manufactured homes with up to five tie-downs per side on units fifty feet or longer, flood-resistant construction materials, and elevation of the lowest floor to the flood protection elevation for new residential structures under Section 9-3-3(a)(17)(A).

The code specifically bars parking in any portion of the floodplain where flood depths exceed eighteen inches under Section 9-3-3(a)(8), and it requires hotels, motels, schools, daycare centers, and similar occupied uses in the Boulder Creek one-hundred-year floodplain to maintain a city-manager-approved flood warning system with twenty-four-hour monitoring under Section 9-3-3(a)(9). Rental properties in the one-hundred-year floodplain must post a flood-hazard warning sign at the entrance under Section 9-3-3(a)(10).