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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />i <br /> <br />PREFACE <br /> <br />TABLE OF CONTENTS <br /> <br />Page No. <br /> <br />The purpose of this report is to provide Boulder County with <br />flood hazard area delineation maps whioh oan be used as a <br />tool in implementing flood plain zoning ordinanoes and other <br />land use oontrols. The overall study objeotive Was to reduoe <br />potential flood damages and unwise development in known flood <br />hazard areas. The study inoluded hydrologio investigations <br />of Boulder and Dry Creeks to determine the lOa-year reourrenoe <br />flood, and the delineation of the flood hazard areas on plan <br />and profile drawings provided by the Urban Drainage and Flood <br />Control Distriot. Various agenoies, inoluding the Corps of <br />Engineers, United States Geologioal Survey, Soil Conservation <br />Servioe, Urban Drainage Distriot and Boulder County Were oon- <br />taoted during the investigation. Information provided by these <br />agenoies has been inoorporated into the study. Teohnioal data <br />developed in this study is on file with the Urban Drainage and <br />Flood Control Distriot. <br /> <br />PREFACE <br /> <br />i <br /> <br />TABLE OF CONTENTS <br /> <br />i <br /> <br />LIST OF FIGURES AND TABLES <br /> <br />i <br /> <br />BOULDER CREEK FLOOD HAZARD AREA DELINEATION <br />Background Information <br />Hydrology <br />Hydraulics <br />Hazard Area Delineation <br /> <br />I <br />I <br />I <br />2 <br />2 <br /> <br />I <br />I <br />I <br /> <br />Hazard area limits are delineated for a total of 9.3 miles of <br />ohannel of both Boulder Creek and Dry Creek. This inoludes <br />3.1 miles of Boulder Creek, beginning at the Boulder-Weld <br />County line (County Line Street) and extending upstream to just <br />below North 107th Street. The remaining 6.2 miles are on the <br />Dry Creek ohannel beginning at its oonfluenoe with Boulder Creek <br />and extending upstream to Base Line Reservoir. <br /> <br />DRY CREEK FLOOD HAZARD AREA DELINEATION <br />Background Information <br />Hydrology <br />Hydraulics <br />Hazard Area Delineation <br /> <br />4 <br />4 <br />4 <br />4 <br />7 <br /> <br />DRAWINGS <br /> <br />Following Page 7 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />The peak disoharge on Boulder Creek approximates 11,000 ofs for <br />the entire reaoh. The main ohannel is insuffioient for oon- <br />veying the full 11,000 ofs for almost the entire length of the <br />reaoh studied. The resulting flood hazard area is broad and <br />averages about 3,000 feet in width. Initial mapping provided <br />by the Dis~riot was not suffioient to oover this broad width <br />and additional mapping was obtained. <br /> <br />Peak disoharge on Dry Creek is 1,000 ofs above Arapahoe Road <br />and 1,300 ofs below it. Unlike Boulder Creek, the delineated <br />flood hazard area is narrow and reasonably well defined. Only <br />below the Union paoifio Railroad bridge near the Dry Creek <br />mouth does it broaden out due to ground slopes whioh result in <br />shallow sheet flow. <br /> <br />LIST OF FIGURES <br /> <br />Figure <br /> <br />Title Page No. <br /> <br />I <br /> <br />IOO-year Flood Hydrograph, Boulder Creek 2 <br /> <br />2 <br /> <br />IOO-year Storm Hydrograph, Dry Creek above 5 <br />Arapahoe Road <br /> <br />3 <br /> <br />IOO-year Flood Hydrograph, Dry Creek at 5 <br />Boulder Creek <br /> <br />LIST OF TABLES <br /> <br />Table <br /> <br />Title Page No. <br /> <br />1 <br /> <br />IOO-year Flood Water Elevations, Boulder 3 <br />Creek <br /> <br />2 <br /> <br />IOO-year Flood Water Elevations, Dry Creek 6 <br /> <br />~ Le"nald Rice Consulting Water Englneers.lnc <br /> <br />- ~-_/- - ---- -- -- ~ ---~--- -- -- -- - --- ~ <br />