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<br />c. Based {)n statistical analysis of discharge records and regionaliza-
<br />tion studies, the annual probability of occurrence of a discharge of
<br />8,000 cubic feet per second at Morrison is four percent, whereas the one
<br />percent annual probability reflects a discharge potential of 44,000 cubic
<br />feet per second. A more extensive discussion of the hydrology of the
<br />Bear Cr~ek basin is provided in appendix III.
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<br />10. STORM OF RECORD
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<br />Since 1876, the twenty storms described briefly in the records
<br />demonstrate that the chief cause of floods on Bear Creek has been intense
<br />rainfall storms. Typically, these storms have centered in the 'area
<br />between Evergreen and Morrison and generally in the vicinity of Genesee
<br />Mountain north of Evergreen. The heaviest rainfall near Morrison
<br />occurred on 2,September 1938, and totaled 7.9 inches within a period of
<br />6 hours over a' 60-square mile area. The plains areas of the Denver
<br />metropolitan region are also ,subject 'to heavy precipitation. The maximum
<br />24-hour precipitation recorded at Denver was 6.53 inches in May 1876, ,
<br />and the 24-hour snowfall was 23 inches in April 1885. However,
<br />occasionally extremely heavy rainfall has occurred in the vicinity of
<br />metropolitan Denver. In 'the 'storm of May 1935, 24 inches of rain
<br />fell within 6 hours at Elbert, Colorado, about 45 air miles from Morrison.
<br />In June 1965, 14 inches of rain fell within a few hours at Larkspur,
<br />Colorado, about 34 air miles from Morrison.
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<br />11. FLOOD CHARACTERISTICS
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<br />The majority of floods on Bear Creek have been the flash floods
<br />typical of mountain streams. Flash floods are characterized by rapid
<br />concentration of runoff, sudden increase in discharge and stream stages
<br />and quick return to near normal discharge and stages. Observers normally
<br />describe such floods as a rapidly-moving wall of water with high, destructive
<br />velocities. However, because mountain snowmelt contributes the principal
<br />portion of streamflow volume, occasionally rapid snowmelt combined with
<br />storm rainfall causes high discharges of longer duration.
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<br />12. FLOODS OF RECORD
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<br />a. General. Since 1876, 22 floods have been recorded in the'Bear
<br />Creek basin. These have ranged from relatively minor to major floods
<br />causing considerable property damage and loss of life. ' Records show
<br />that 45 lives were lost to floods since 1876. Principal flood years
<br />were 1876,1878 (2),1885, 1886, 1893,1894,1896,1903, 1907, 1908,
<br />1921 (2), 1923, 1925, 1933, 1934, 1938, 1946, 1957 (2) and 1965. Flood
<br />histories demonstrate that the flood-prone season extends from May
<br />, through September, with July and August having the greatest flood
<br />frequency. However, the largest and most destructive flood of record
<br />occurred in September 1938.
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<br />b. Flood of 2 September 1938. The flood of 2 September 1938,
<br />resulted from an intense rainstorm centered over Genesee Mountain in
<br />the vicinity of Cold Spring Gulch and Mount Vernon Creek. An estimated
<br />7.9 inches of rain fell within 6 hours, causing peak discharges
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