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<br />North St. Vrain & St. V rain Creeks <br />Floodplain Update <br /> <br />Town of Lyons <br /> <br />North St. Vrain & St. Vrain Creeks <br />Floodplain Update <br /> <br />Town of Lyons <br /> <br />TABLE OF CONTENTS <br /> <br />LIST OF TABLES AND FIGURE <br /> <br />Page <br /> <br />Table 1: <br /> <br />Summary of Culvert/Bridge Information <br /> <br />8 <br /> <br />LIST OF TABLES <br /> <br />iii <br /> <br />Table 2: <br /> <br />Historical Flood Peak Discharges and Stages, St. Vrain at Lyons <br /> <br />9 <br /> <br />PREFACE <br /> <br />iv <br /> <br />Table 3: <br /> <br />USGS Gaging Stations <br /> <br />23 <br /> <br />SECTION 1 - INTRODUCTION <br />1.1 Authorization <br />1.2 Background <br />1.3 Purpose and Scope <br />1.4 Acknowledgements <br />1.5 Related Flood Studies <br /> <br />1 <br />1 <br />1 <br />2 <br />4 <br />4 <br /> <br />Table 4: <br /> <br />Peak Discharges at Selected Locations <br /> <br />25 <br /> <br />Table 5: <br /> <br />Roughness Coefficients <br /> <br />26 <br /> <br />Table 6: <br /> <br />Flood Frequency-Elevation and Discharge Data <br /> <br />27 <br /> <br />Table 7: <br /> <br />North St. Vrain - St. Vrain Creek: Benchmark Information <br /> <br />30 <br /> <br />SECTION 2 - STUDY AREA DESCRIPTION <br />2.1 Drainage Basin Characteristics <br />2.2 Climate <br />2.3 Study Reach Description <br /> <br />6 <br />6 <br />6 <br />7 <br /> <br />Figure: <br /> <br />Lyons Benchmark Location Map <br /> <br />32 <br /> <br />Table 7 A: <br /> <br />BRW Benchmark Information <br /> <br />33 <br /> <br />SECTION 3 - HISTORY OF FLOODING <br /> <br />9 <br /> <br />APPENDICES <br /> <br />SECTION 4 - HYDROLOGIC AND HYDRAULIC DETERMINATIONS <br />4.1 Flood Characteristics <br />4.2 Hydrologic Analysis <br />4.3 Hydraulic Analysis <br /> <br />22 <br />22 <br />22 <br />24 <br /> <br />A. <br /> <br />Plate 1: Basin Map <br /> <br />B. <br /> <br />Plate 2: Index Map <br /> <br />SECTION 5 - INTERPRETATION AND USE OF REPORT DATA <br />5.1 Flooding Frequency and Discharge Table <br />5.2 10- and 50-Year Flood Events <br />5.3 100-Year Flood Event <br />5.4 SOD-Year Flood Event <br />5.5 Flooded Areas <br />5.6 Flood Elevations <br />5.7 Horizontal and Vertical Control Monumentation <br /> <br />28 <br />28 <br />28 <br />28 <br />28 <br />29 <br />29 <br />29 <br /> <br />c. <br /> <br />Plates 13 through 19: "North St. Vrain Creek Upstream of Lyons and St. Vrain Creek <br />Downstream of Lyons, Boulder County", Town of Lyons Floodplain Mapping, lOa-Year <br />and SOD-Year Floodplains <br /> <br />D. <br /> <br />Figure 1 through 6: Flood Profiles <br /> <br />E. <br /> <br />Technical Appendix (HEC-RAS Summary Printout Data with Computer Disks) <br /> <br />BIBLIOGRAPHY <br /> <br />34 <br /> <br />GLOSSARY <br /> <br />35 <br /> <br />Floodplain Information Report II <br />K:\356001004\FLOODPLAIN INFORMA nON REPORT.doc <br /> <br />June 1998 <br /> <br />Floodplain Information Report 1II <br />K:1356001004\FLOODPLAIN INFORMA nON REPORTdoc <br /> <br />June 1998 <br />