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<br />FEDERAL EMERGENCY MANAGEMENT AGENCY <br />LETTER OF MAP REVISION <br /> <br />TWO-MILE CANYON CREEK <br />BOULDER, COLORADO <br /> <br />1.0 INTRODUCTION <br /> <br />1.1 Puroose of Study <br /> <br />This study was requested by the City of Boulder on January 22, 1991. Afte:r careful <br />review and evaluation of the existing regulatory Two-Mile Canyon Creek HEC-2 <br />model input and output files, it was evident that incomplete cross sections were <br />utilized in this study. The HEC-2 Water SUlface Profile Computer Program (HEC-2) <br />will automatically insert vertical extensions at the ends of the cross sections if the <br />input data does not provide the required vertical depth m~eded for conv(:yance. This <br />often produces unreasonable results. TIle existing study contains extensions at <br />several locations ranging from .01 feet to more than 6.00 feet. The purpose of this <br />re-study is to provide the necessary revisions to the existing analysis to produce a <br />more reasonable delineation of the l00-yellT floodplain limits for Two- l\1i1e Canyon <br />Creek. This re-analysis also includes detern:rination of thl~ floodway and the 10-, 50-, <br />100-, and 500-year water surface profiles. <br /> <br />1.2 Authority and Acknowledgments <br /> <br />The hydrologic and hydraulic analyses for the original sltudy were performl~d by the <br />U.S. Army Corps of Engineers (US ACE) for the Federal Emergency Management <br />Agency (FEMA) under Inter-Agency Agmements No. li\A.-H-15-72, Projt:ct Order <br />Nos. 2 and 3, Amendment No.1. This work was comple:ted in October 1975. <br /> <br />Revised hydrologic and hydraulic lUlalyses for Two..Mile Canyon Cre:ek were <br />performed by MSM/SP Group, for FEMA, under Contract No. EMW-C-0709. This <br />work was completed in April 1985 . <br /> <br />A revised hydraulic analysis for Two-Mile Canyon Crl~ek was completed in May <br />1987 by Greenhorne & Q'Mara, Inc. which was used as the basis for this re- <br />analysis. <br /> <br />1.3 Coordination <br /> <br />An initial coordination meeting for this revised study was held at the City of Boulder <br />on February 4, 1991. This meeting was at1ended by City of Boulder personnel and <br />representatives from Love & Associates, Inc. Public meetings were conducted on <br />August 7, 1991, March 9, 1992, and March 24, 1992. <br /> <br />2.0 AREA STUDIED <br /> <br />This re-analysis for Two-Mile Canyon Creek encompasses the reach extending from its <br />confluence with Goose Creek at 19th Street and. proceeding northwesterly approximately <br />2.0 miles upstream to just north of Linden Drive, as shown on the Vicinity Map (Figure I). <br />