Upper Goose Creek and Twomile Canyon Creek
Floodplain Mapping Update

The city has contracted with ICON Engineering to develop updated floodplain maps for Upper Goose Creek and Twomile Canyon Creek. Anderson Consulting Engineers is providing peer review of the engineering study.The Urban Drainage and Flood Control District (UDFCD) is a co-sponsor of this project and is also providing review. The following figure shows the study limits:

 Figure 1 - Study Area

Project Background

Floodplain mapping studies provide the basis for flood management by identifying the areas subject to flooding. This information is essential for determining areas where human safety is threatened and property damage is likely. Floodplain maps must be updated periodically to reflect changes in the floodplain resulting from land development, flood mitigation improvements, new study technologies and the impacts of major floods that may have occurred.

Upper Goose Creek and Twomile Canyon Creek were first studied by Greenhorne & O'Mara in 1987. The resulting Flood Hazard Area Delineation (FHAD) delineated the 100-year floodplain along these creeks.The Flood Insurance Study (FIS) and Flood Insurance Rate Map (FIRM) approved for these creeks were originally based on the 1987 FHAD and included a federally-regulated one foot rise floodway. In 1989, Love and Associates delineated the High Hazard Zone and City of Boulder Conveyance Zone (1/2 foot rise floodway).The delineations were based on the hydraulic models used in the 1987 FHAD.

In 1991, the city commissioned Love and Associates to restudy Twomile Canyon Creek. Based on that study, FEMA issued a Letter of Map Revision (LOMR) for Twomile Canyon Creek on April 5, 1994.The limit of the LOMR was between the confluence of Twomile Canyon Creek and Upper Goose Creek to just upstream of Linden Avenue. In 2004, McLaughlin Water Engineers, Ltd. updated flood mapping for Goose Creek to reflect channel improvements.The limits of the LOMR for this project extended from 30th Street to approximately 1,900 feet upstream of Folsom Street.

Project Materials

• Structures Affected by the Proposed 100-year Floodplain
• Structures Affected by the Proposed Conveyance Flood Zone
• Structures Affected by Proposed High Hazard Flood Zone
• Proposed 500-year Floodplain

The following project hydrology and field surveys have been conducted:

•  Hydrology Verification Report 
•  Field Documentation Memorandum
• Revised Hydraulic Report
  

Project Schedule and Next Steps

The anticipated next steps for this project include:

• Water Resources Advisory Board  – Monday, May 20, 2013 at 7 p.m.
• Planning Board – summer 2013
• City Council – fall 2013
• FEMA submittal – late 2013 and early 2014

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More Information

Find out if your property is located in a floodplain using the interactive floodplain map.

For property-specific information about the land development requirements for all floodplain zones, contact Planning & Development Services at 303-441-1880 or  This e-mail address is being protected from spambots. You need JavaScript enabled to view it .  

• Land Development Fact Sheet
•  Effects of Disclosure of Flood-Liability on Residential Property Values 

For more information, please contact This e-mail address is being protected from spambots. You need JavaScript enabled to view it , Engineering Project Manager, at 303-441-4232.

Last Updated on Tuesday, 14 May 2013 13:26