Floodplain Remapping Project

Floodplain mapping updates reflect ongoing work by state and federal agencies to refine flood risk information for Boulder County’s waterways. These updates incorporate new studies, public review periods, and FEMA map revisions to ensure that floodplain regulations are based on the most accurate and current data available. Learn more on the Building, Safety and Inspection homepage.

Background

Following the 2013 Flood, the Colorado Water Conservation Board (CWCB) initiated a program to re-map the predicted 1% annual chance flood zone (100-year floodplain) of the most affected waterways (shown in the image below). The program was called the “Colorado Hazard Mapping Program,” or CHAMP. Draft map data and related flood studies for the CHAMP– studied reaches were adopted by the Board of County Commissioners (BOCC) through Docket Z-17-0001 and Docket Z-17-0002. In September 2019, FEMA released Preliminary Flood Insurance Rate Maps (FIRMs) for the same CHAMP reaches, refining the draft maps. The Preliminary FIRMs were adopted by the BOCC, replacing the draft map data via Docket Z-19-0001 to allow the county to base floodplain regulations on the best available data.

In 2020 and 2021, FEMA ran appeal periods, where anyone had the opportunity to appeal or comment on the Preliminary FIRMs. Following FEMA’s resolution of the appeals, revised Preliminary FIRMs were released in July 2023. Boulder County aligned the Boulder County Floodplain and Floodway with the revised Preliminary FIRMs through Docket Z-23-0001. On October 24, 2024, the revised Preliminary FIRMs became effective for flood insurance purposes.

Lefthand Creek Re-Study

Due to an appeal, the portion of Lefthand Creek between Geer Canyon and 49th Street was excluded from the 2024 FIRM update and is being re-studied by the Federal Emergency Management Agency (FEMA). Letters were sent to affected property owners in May 2025.

Please contact the Floodplain Management Team at FloodplainAdmin@bouldercounty.gov if you have with questions or to learn more about the floodplain mapping changes.

• Map: FEMA Draft Flood Risk Zones for Lefthand Creek

A virtual public meeting for the Lefthand Creek re-study was held on May 27, 2025. Affected property owners were invited to attend the meeting.

• View the video recording of the Lefthand Creek Floodplain Mapping Community Update.

Floodplain Remapping Stream Reaches for 2019-2020 Effort

Boulder County Floodplain Map

The interactive map linked in the sidebar, shows detailed flood risk zones and related FEMA map amendments that are currently regulated throughout unincorporated Boulder County as Floodplain Overlay Zoning District. This map will update as new FEMA maps become effective throughout Boulder County and as the Boulder County Board of County Commissioners (BOCC) adopts best available information.

The Boulder County and FEMA Regulatory Flood Risk Zones were updated on October 24, 2024 to reflect changes to the Floodplain Overlay District based on FEMA’s Physical Map Revision reflecting the Colorado Hazard Mapping Program (CHAMP) study. The zoning map amendments were adopted by the BOCC via Docket Z-23-0001.