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<br />western slope areas and is characterized by wide extremes resulting <br />from variations in topographic features. The greatest precipitation <br />is in the alpine zone above 11,000 feet in elevation, consisting <br />mainly of snowfall. At the lower basin elevations of 5,000 to 6,000 <br />feet, the climate is arid to semi-arid. <br /> <br />Thunderstorms typically develop from ~1,,'y to Octob€~r and are usually <br />of high intensity and short duration. Precipitation ranges hom 7 <br />inches annually in the desert valleys to 45 inches in the San Miguel <br />Mountains. <br /> <br />~1ajor flows are produced from early May to late ,June from snoV/melt <br />runoff, characterized by moderate peaks, large volumes and long flovl <br />durations. MSM Consultants, Inc., reports that the San Miguel River <br />at Naturita, Colorado recorded a flow of 7,100 cfs on April 15, 1942, <br />primarily due to snowmelt. The U.S. Geological Survey has recorded <br />a maximum flow of 6,690 cfs at Gaging Station 1171 located 1 mile up- <br />stream of Uravan immediately dwnstream of the confluence of Tabe- <br />guache Creek and the San Miguel. The average discharge at this <br />station is about 350 cfs. (See Figure 1 , Appendix) <br /> <br />3.2.2 Flood Insurance Administration Study: <br />Hydrology and Flood Flows <br /> <br />The flood flows calculated by MSM Consultants, Inc., for hydraulic <br />routing through the Uravan area were based on a statistical analysis <br />of actual stream gage data. It was concluded early in the study <br />that using a synthetic storm hydrograph based on rainfall alone would <br />not be adequate. Instead, a flood flow frequency analysis based on <br />actual basin gaging stations and peak separation of the mixed popu- <br />lation of snowmelt and rainfall runoff was used to calculate fr'equency <br />curves for various drainage areas. These curves are shown as Figure <br />3 in the Appendix to this report. <br /> <br />7 <br />