FLOOD05107

• County: Boulder
• Community: Boulder
• Stream Name: Canyon Boulevard Overflow
• Basin: South Platte
• Title: LOMR - Affected Panel 395F - Case No. 95-08-129P
• Date: 6/14/1995
• Prepared For: Boulder
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

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Federal Emergency Management Agency
Washington, D.C. 20472

CERTIFIED MAIL
RETURN RECEIPT REQUESTED

IN REPLY REFER TO:
Case No.: 95-08-129P

The Honorable Leslie Durgin
Mayor, City of Boulder
P.O. Box 791
Boulder, Colorado 80306

Community: City of Boulder, Colorado
Community No.: 080024
Panel Affected: 08013C0395 F
Effective Date of
This Revision:

JUN 141995

102-I-A-C

Dear Mayor Durgin:

This is in response to a request for a revision to the effective Flood Insurance Study (FIS) and National
Flood Insurance Program (NFIP) map for your community. Specifically, this responds to a letter dated
March 20, 1995. from Mr. David J. Love, P.E., Love & Associates. Inc., regarding the effective FIS
report and Flood Insurance Rate Map (FIRM) for Boulder County. Colorado and Incorporated Areas.
Mr. Love requested that we revise the effective FIRM to reflect the results of more detailed hydraulic
analyses of Boulder Creek. including analyses of Canyon Boulevard Overflow and Boulder High School
Overflow as hydraulically disconnected flooding sources impacted by split flow from Boulder Creek. The
revised analyses incorporate the effects of overbank excavation between 17th Street and Broadway and
improvements to the bridges at Arapahoe A venue, 17th Street. and Broadway.

All data required to complete our review of this request were submitted with Mr. Love's March 20 letter
and with a letter dated March 31. 1995, from Mr. Ned Williams, Assistant Director of Public Works for
Utilities, City of Boulder. Because this Letter of Map Revision (LOMR) incorporates more detailed
information and reflects publicly sponsored channel improvements that reduce flooding to existing
development, fees were not assessed for the review.

We have completed our review of the submitted data and the flood data shown on the effective FIRM, and
have revised the FIRM to modify the elevations and floodplain boundary delineations of a flood having a
I-percent chance of being equaled or exceeded in any given year (base flood) along Boulder Creek, from
approximately 360 feet upstream of 19th Street to approximately 425 feet upstream of 6th Street. The
revised FIRM also shows base flood elevations (BFEs) and Special Flood Hazard Area (SFHA) delineations
for Canyon Boulevard Overflow, from approximately 230 feet upstream of 18th Street to just upstream of
6th Street, and for Boulder High School Overflow, from approximately 200 feet upstream of 18th Street
to just upstream of 15th Street. The floodplains for Canyon Boulevard Oyerflow and Boulder High School
Overflow represent split flow from Boulder Creek.

The hydraulic analyses performed for the effective FIRM did not consider the overflow areas to be
hydraulically disconnected from Boulder Creek. The SFHA shown for Boulder Creek on the effective
FIRM includes the areas identified in the revised analyses as Canyon Boulevard Overflow and Boulder High
School Overflow. To assess the impact of the revision, we will compare the reyised BFEs and SFHAs for
the main channel of Boulder Creek. Canyon Boulevard Overflow, and Boulder High School Overflow to
the BFEs and SFHA shown for Boulder Creek on the effective FIRM and on the Flood Profiles in the
effective FIS report. The revised analyses resulted in increases and decreases in the BFEs and SFHA along
the revised reach.