FLOOD04867

• County: Boulder
• Community: Boulder County and Incorporated Areas
• Stream Name: Lefthand Creek, St. Vrain Creek, Dry Creek No. 1
• Basin: South Platte
• Title: LOMR - Affected Panel 286F, 287F, 288F, 289F - Case No. 03-08-0580P
• Date: 10/7/2004
• Prepared For: FEMA
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

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Federal Emergency Management Agency
Washington, D.C. 20472

JUN 15 2004

CERTIFIED MAIL
RETURN RECEIPT REQUESTED

IN REPLY REFER TO:
Case No,: 03-08-0580P

The Honorable Paul Danish
Chainnan, Boulder County
Board of Commissioners
P,O, Box 471
Boulder, CO 80306

Community: Boulder County. CO
Community No,: 080023
Panels Affected: 08013C0286 F, 0287 F,
0288 F, and 0289 F
En:ective,Dateof OCT 07 200lt
ThIS RevlSlon:

."u,

l02-I-A-C

Dear Mr. Danish:

This responds to a request that the Department of Homeland Security's Federal Emergency Management
Agency (FEMA) revise the effective Flood Insurance Rate Map (FIRM) and Flood Insurance Study (FrS)
report for Boulder County, Colorado and Incorporated Areas, in accordance with Part 65 of the National
Flood Insurance Program (NFIP) regulations, In a letter dated August I, 2003, Mr, David
Hollingsworth, P,E" Storm Drainage Engineer, Public Works Division, Department of Community
Development, City of Longmont, requested that FEMA revise the FIRM and Frs report to show the effects
of channelization, placement of fill, and construction of a new bridge along Lefthand Creek and
construction of a new bridge across St. Vrain Creek, all associated with construction of Ken Pratt
Boulevard, This request also included an updated hydraulic analysis that incorporated more detailed
topographic data for the following streams:

. Lefthand Creek from the confluence with St. Vrain Creek in Boulder County to just upstream of
South Main Street (D.S, Highway 287) in the City of Longmont;
. St. Vrain Creek from approximately 160 feet upstream to approximately 7,200 feet upstream of
119th Street in Boulder County;
. Dry Creek No, I (Old Channel) from the confluence with St. Vrain Creek in Boulder County to
just upstream of Ken Pratt Boulevard in the City of Longmont; and
. Shallow flooding areas between Lefthand and St. Vrain Creeks from just upstream of Ken Pratt
Boulevard in Boulder County to just downstream of South Main Street in the City of Longmont.

All data required to complete our review of this request were submitted with letters from Mr, David C,
Webster, P.E., Water Resources Engineer, Floodplain Administrator, Transportation Department, Boulder
County; Mr. Mike Butters, P ,E" Carter & Burgess; and Mr. Hollingsworth.

The improved channel along Lefthand Creek includes a low-flow channel and a wider flood channel. Ken
Pratt Boulevard crosses Lefthand Creek approximately 1,200 feet upstream of the confluence with
St. Vrain Creek. The bridge span is 172 feet, which includes one pier and spill-through abutments, A
bench for an 8-foot-wide bike trail is included on the slope for the north abutment. Ken Pratt Boulevard

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