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Federal Emergency Management Agency Washington, D.C. 20472 SEP 27 2001 CERTIFIED MAIL RETURN RECEIPT REQUESTED IN REPLY REFER TO: Case No.: 00-08-342P The Honorable Marty Flaum Chairman, Adams County Board of Commissioners 450 South Fourth Avenue Brighton, CO 80601 Community: Adams County, CO Community No.: 080001 Panels Affected: 08001 C0390 G and 08001C0655 G Effective Date of J AN 2 3 2002 This Revision: 102-I-A-C Dear Mr. Flaum: This responds to a request that the Federal Emergency Management Agency (FEMA) revise the effective Flood Insurance Rate Map (FIRM) and Flood Insurance Study (FIS) report for Adams County, Colorado and Incorporated Areas, in accordance with Part 65 of the National Flood Insurance Program (NFIP) regulations. In a letter dated July 27,2000, Mr. Mark Mancini, P.E., Project Engineer, Public Works Department, City of Aurora, requested that FEMA revise the FIRM and FIS report to show the effects of construction over First Creek of the E-470 Tollway (E-470) crossing approximately 2,100 feet downstream and the Smith Way crossing approximately 1,700 feet downstream of Interstate Highway 70 (1-70); realignment of Gun Club Road; channelization along First Creek from approximately 700 feet downstream of E-470 to approximately 250 feet upstream of Smith Way; and placement of fill in the floodplain associated with a new overpass at 26th Avenue approximately 2,100 feet downstream of the Union Pacific Railroad. Six 10-foot by 6-foot concrete box culverts were installed under each of the E-470 and Smith Way crossings of First Creek. The twin 36-inch-diameter corrugated-metal pipe culverts that formerly existed at 26th Avenue were replaced by twin 36-inch-diameter reinforced-concrete pipe culverts. This request also included a new hydrologic analysis to reflect existing watershed conditions. This request follows up on a Conditional Letter of Map Revision issued on October 16, 1997. All data required to complete our review of this request were submitted with letters from l P.E., Design Director, MK Centennial Engineering, Inc., and Mr. Mancini. We have completed our review of the submitted data and the flood data shown on the effective FIRM and in the effective FIS report. We have revised the FIRM and FIS report to modify the elevations, floodplain boundary delineations, and zone designations of the flood having a I-percent chance of being equaled or exceeded in any given year (base flood) along First Creek. As a result of the modifications, Base Flood Elevations (BFEs) for First Creek were established from 26th Avenue to 1-70, and the width ofthe Special Flood Hazard Area (SFHA), the area that would be inundated by the base flood, increased