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i Federal Emergency Management Agency Washington, D.C. 20472 CERTIFIED MAIL RETURN RECEIPT REQUESTED IN REPLY REFER TO: Case No.: 96-08-019P The Honorable Leslie Durgin Mayor, City of Boulder P.O. Box 791 Boulder, Colorado 80306 Community: City of Boulder, Colorado Community No.: 080024 Panels Affected: 08013C0395 F and 0415 F Effective Date of This Revision: J AN 16 1996 102-I-A-C Dear Mayor Durgin: This is in response to a request for a revision to the effective Flood InSurance Study (PIS) and National Flood Insurance Program (NFIP) map for your community. Specifically, this responds to a letter dated October 24, 1995, from Ms. Karen S. Medde, P .E., Civil Engineer I, Department of Public Works, City of Boulder, regarding the effective FIS report and Flood Insurance Rate Map (FIRM) for Boulder County, Colorado and Incorporated Areas. Ms. Medde requested that the Federal Emergency Management Agency (FEMA) revise the effective FIRM to show the effects of more detailed topographic information and the construction of channel improvements along Goose Creek, including a 1,440-foot trapezoidal grass-lined channel from Foothills Parkway to the Burlington Northern Railroad (BNRR) crossing, an 815-foot rectangular riprap-Iined channel from the BNRR crossing to 30th Street, five lO-foot by 8-foot reinforced concrete box (RCB) culverts under the BNRR crossing, and two 23-foot by 9-foot RCB culverts under 30th Street. This request follows up on a Conditional Letter of Map Revision, which was issued on January 10, 1990. All data required to complete our review of this request were submitted with Ms. Medde's October 24 letter and with letters dated November 1 and November 16, 1995, from Mr. Kent Barringer, P.E., Project Manager, Greenhorne & O'Mara, Inc. Because this Letter of Map Revision (LOMR) shows the effects of a publicly sponsored flood-control project that reduces 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, floodplain and floodway boundary delineations, and zone designations of a flood having a I-percent chance of being equaled or exceeded in any given year (base flood) along Goose Creek from Foothills Parkway to approximately 100 feet upstream of 28th Street. The trapezoidal channel downstream of the BNRR crossing, the culverts under the BNRR crossing, and the rectangular channel from the BNRR crossing to 30th Street have the capacity to contain the base flood discharge. However, a portion of the base flood discharge splits from the main channel of Goose Creek upstream of 30th Street and flows along the right overbank, creating an area of shallow flooding (average depth 1 foot) from just upstream of 30th Street to approximately 550 feet downstream of 30th Street.