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<br />. <br /> <br />f <br /> <br /> <br />Federal Emergency Management Agency <br />Washington, D.C, 20472 <br /> <br />CERTIFIED MAIL <br />RETURN RECEIPT REQUESTED <br /> <br />IN REPLY REFER TO: <br />Case No.: 96.08.301P <br /> <br />The Honorable Ronald K. Stewart <br />Chairman, Board of County Commissioners <br />Boulder County <br />P,O. Box 471 <br />Boulder, Colorado 80306 <br /> <br />Community: Boulder County, Colorado <br />Community No,: 080023 <br />Panels Affected: 08013C0560 F and <br />08013C0576 G <br />Effective Date of <br />This Revision: <br />SEP 061996 <br /> <br />102-I-A-C <br /> <br />Dear Mr, Stewart: <br /> <br />This responds to a request for a revision to the effective Flood Insurance Study (PIS) and National Flood <br />Insurance Program (NFIP) map for your community, Specifically, this responds to a letter dated June 21, <br />1996, from Mr. Bill DeGroot, P.E., Chief, Floodplain Management Program, Urban Drainage and Flood <br />Control District, regarding the effective PIS report and Flood Insurance Rate Map (PIRM) for Boulder <br />County, Colorado and Incorporated Areas. Mr. DeGroot requested that the Federal Emergency Management <br />Agency (FEMA) revise the effective FIRM to show the effects of the construction of a new Burlington <br />Northern Railroad bridge along Coal Creek. This request follows up on a Conditional Letter of Map Revision, <br />which was issued on February 21, 1996. <br /> <br />All data required to complete our review of this request were submitted with Mr. DeGroot's June 21 letter. <br />Because this Letter of Map Revision (LOMR) shows the effects of a publicly sponsored flood-control project <br />that reduces flooding to existing development, fees were not assessed for the review. <br /> <br />We have completed our review of the submitted data and the flood data shown on the effective FIRM, and <br />have revised the FIRM to modi/}' the elevations and floodplain boundary delitteations of the flood having a <br />I-percent chance of being equaled or exceeded in any given year (base flood) along Coal Creek from <br />approximately 1,550 feet downstream of Empire Road to approximately 3,700 feet upstream of South 96th <br />Street. <br /> <br />In support of this request, Mr. DeGroot submitted HEC-2 hydraulic computer models of pre-project and <br />post-project conditions. The pre-project model represents the same conditions shown in the WSP2 computer <br />model used to develop the effective PIS report and FIRM, As a result of the differences between the two <br />models, the base flood elevations (BFEs) increased and decreased along the revised reach. The maximum <br />decrease in BFE, 2,1 feet, occurred at the Burlington Northern Railroad. The maximum increase in BFE, <br />1.9 feet, occurred approximately 150 feet upstream of Empire Road. <br /> <br />Mr. DeGroot also submitted a hydrologic analysis evaluating the effects of the construction of the Burlington <br />Northern Railroad bridge on the base flood discharges along Coal Creek, The discharges from that hydrologic <br />analysis were used in the post-project HEC-2 model submitted by Mr, DeGroot to develop the flood hazard <br />information used to revise the FIRM, <br />