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<br />. <br /> <br />Introduction <br /> <br />The information in this report was developed at the request <br />of the Jefferson County Planning Department. Recent concern <br />has developed over the potential health hazard, should certain <br />radioactive mine tailings and other facilities located in <br />RaIson Creek, be washed out during a large flood. <br /> <br />The Colorado Water COnservation Board is the state agency <br />charged under Section 37-60-106(1), Colorado Revised Statutes <br />1973, to assist local governments in the prevention of flood <br />damages. Development of general floodplain information is <br />intended to assist county officials with land use planning <br />and with the evaluation of the flood hazard in their juris- <br />diction. <br /> <br />Section 30-30-102, CRS 1973, gives the Board of County <br />Commissioners the authorit~ for flood control purposes only, <br />to remove or cause to be removed any obstruction to the <br />channel of any natural stream which causes a flood hazard. <br /> <br />Purpose <br /> <br />. <br /> <br />This report was prepared to identify the depths, velocities, <br />and outline of the 100-year flood under existing conditions <br />on a short reach of Ralston Creek opposite the Schwartzwalder <br />Mine in Jefferson County, Colorado. <br /> <br />Rigorous application of detailed hydrologic and hydraulic <br />methods has not been made in determining the characteristics <br />of the 100-year flood. However, while the methods used to <br />delineate the floodplain are approximate, the level of detail <br />is compatible with the objective of determining which mine <br />facilities are presently exposed to potentially severe flood <br />damages. The information in this report can be refined by <br />field surveying several cross sections and routing the flood <br />through a mathematical model, such as computer program HEC-2. <br /> <br />Study Reach <br /> <br />The Schwartzwalder Mine is located on the south bank of <br />Ralston Creek, approximately 2~ miles upstream of Ralston <br />Reservoir. The study reach begins near the east line of <br />Section 25, Township 2 South, Range 71 West, 6th Principal <br />Meridian and extends approximately 3,920 feet upstream. <br /> <br />. <br /> <br />This reach of Ralston Creek falls from elevation 6,630 <br />feet to elevation 6,525 feet above mean sea level. The <br />average streambed slope is 141 feet per mile (0.0268 feet <br />per foot). <br /> <br />-1- <br />