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<br />Purpose ~nd Scope <br />The purpose or this report is to pro~ide the Town of La~e Ci~y and HinSCaie <br />County officials with d tocl for planning purposes and to regulate the land use <br />of areas within the flOOdplain of the Lake Fork of the Gunnison River and ~enson <br />Creek in order to minimize flood damages and dangers to both the property and <br />human life. The report contains information on historical floods in the study <br />reach, existing basin and channel parameters influencing the flood hazard, and <br />information related to the 10-, 50~, 100~ and 500~year frequency floods. <br /> <br />Mapping and Surve.1S <br />TOpO~NPhic "'.a~ping for this st'Jdy was prOVIded by the ColoradO '~~ter <br />C~nservation Board. The 1ap~lng was prepared in 1975 by Merrick and Co~pa~y <br />or Den'fer, Colorado. The!1'appingfurnishedisatascaleof 1":2CO' and <br />~n" contour interval ;s 5 '.eeL The datum is mean sea level. <br /> <br />The report presents flooded area maps delineating the extent of the 1OC~ <br />and 500-year floods, a one~foot rise floodway, water surface profiles, and <br />typical floodplain cross sections showing the water surface elevations for the <br />10~, 50-, 100., and 500~year floods. Supplemental information depicting the <br />backup data and calculations for the hydrologic and hydraulic analysis are <br />presented In the Technical Addendum. This information is useful for planning, <br />designing and implementing land use activities within the study area. <br /> <br />Sixteen cross-sections of the lake Fork of the Gunnison River an dfour <br />cress-sections of Henson Creek were surveyed oy the ColoradO Water Conservation <br />Board in August, 1982. Thesecross.sections, in adcitiontoothers required <br />for hydraulic accur~cy, are shown on the mapping and are designated by integer <br />numbers. The cross.sections defining the 8~ Street Bridge were revised from <br />construction plans to show the hydraulic effects of the proposed new bridge, <br />expected to be constructed by the end of 1986. <br /> <br />Colorado Water Conservation Board/Mr. Larry Lang <br />U.S. Geological Survey <br />Town of Lake Clty!~r. Scott Ross and Sheriff Burton smith <br />Lake City SilverWorld!Mr. Grant Huston <br />Mr. Ken Charles, Region IX Planning Commissioner <br /> <br />The 5 foot contour base maps have the following allowabletolera nee: 10-:; <br />of contours may have tolerances of t5 feet and 90% may have tolerances of <br />t2.5feet. The field surveys have an allowable tolerance of 0.5 feet. <br />Whenever differences exist between base map elevations and field surveys, the <br />field s'uneys shall govern. The Flood Profiles (Plates 9 through IS) are based <br />on field surveys. For further clarification of actual field elevations refer <br />to the Flooded Area Maps for locations and elevations of two USGS Benchmarks <br />Jnd several field-s~rveyed ground elevat:ons. USGS Benc~~~rk 8681, elevation <br />8675.36, is located at the northeast corner ot tne La~e CIty Hank HUllding. <br />USGS Benchmark 8663, elevation 8657.6, is located on the southwest corner of <br />the Elementary School playground. <br /> <br />Acknowledgements <br />We wish to acknowledge the assistance and cooperation of the agencies, <br />firms, organizations and individuals whi.char<olistedbejow. M,;.nyTown <br />and county officials and priyate cltizens provided much information that was <br />essentialtotheunderstandingofthefloodingproblemsinthestudyarea. <br />The efforts of all those who ccntributed ~o this st~dy are apprecia~ed. <br /> <br />Maps delineating the 100. and 500-year floods are available for review <br />at Lake City Town Kall and the Hinsdale County Court House. <br /> <br />Related FlOOd Studies <br />No co~parable fiood pialn studies of record have been prepared on <br />the Lake Fork of th" Gunn:son Rlver or Henson Creek in the reach covered by <br /> <br />this ~e~ort. <br /> <br />3 <br /> <br />4 <br />