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<br />The maximum annual peak discharge in 1957 at the paleoflood sites at Cimarron can be estimated for
<br />comparison with the maximum estimated paleoflood discharge. Only the streamflow-gaging station located
<br />in the headwaters (091260000) was in operation during 1957. The Cimarron River 1957 unit discharge is
<br />27 cubic feet per second per square mile and can be used to estimate the 1957 peak discharge at the
<br />paleoflood sites (average drainage area is 220 square miles). Using this unit discharge, the 1957 peak
<br />discharge at the downstream gages would have been about 5,900 cubic feet per second. That is a
<br />conservative estimate because it assumes equal snowpack throughout the basin and snowmelt runoff
<br />contributing from the entire basin. However, only the higher parts of the basin would contribute to
<br />snowmelt runoff, particulany in June. By using the maximum observed unit discharge for other gaged
<br />basins having about several hundred squares in central Colorado, the maximum unit discharge ranges
<br />from 15 to 20 cubic feet per second per square mile. Assuming this unit discharge at the downstream
<br />gaged sites lower value because drainage area is about three times larger having more non-contributing
<br />snowmelt runoff area), the 1957 peak discharge at Cimarron is estimated to ranging from 3,000 to 4,500
<br />cubic feet per second. This value is similar to the maximum paleoflood in the Cimarron River basin. We
<br />believe that the maximum paleoflood discharge (ranges from 3,000 to 4,000 cubic feet per second) on the
<br />Cimarron River probably correspond to the 1957 and/or 1984 runoff. Water year 1984 was another year
<br />that had near to record snowmelt runoff at many long-term streamflow-gaging stations in Colorado (Collins
<br />and others, 1991).
<br />
<br />METEOROLOGIC ANALYSIS
<br />
<br />The review of 1952 Cimarron 3SE rainfall data identified several other days of anonymously high and
<br />suspect rainfall (table 1). On August 10th, 2.25 inches of rainfall and on August 11th, 1.75 inclies of
<br />rainfall were reported (U.S. Department of Commerce, 1952, number 8). However, there was no rainfall
<br />runoff on August 11 th and a net peak rainfall runoff of only 42 cubic feet per second on August 11 th.
<br />Because the raingage was located about 3 miles upstream from the streamflow gage, it seems very
<br />unlikely that there would have been substantial attenuation of rainfall runoff.
<br />
<br />The mean annual precipitation for the Cimarron area is about 12 to 14 inches (Colorado Climate Center,
<br />1984), which is based on analysis of long-term data in the region. However, during several years in the
<br />1950s, the mean annual precipitation exceeded 30 inches compared to mean annual precipitation values
<br />typically ranging from 9 to 12 inches at raingages within 50 miles of Cimarron (eg., U.S. Department of
<br />Commerce, 1952). Quite often the Cimarron precipitation data were reported late and for most of 1951
<br />were not reported at all. This also suggests inconsistencies in measurement at Cimarron in the 1950s.
<br />
<br />The publiShed record of precipitation in Colorado for June 1952 provides additional insight into the
<br />validity of the June 3, 1952, Cimarron rainstorm. The Annual Summary of Climatological Data for Colorado
<br />(U.S. Department of Commerce, 1952, volume 13) includes a "Weather Summary and Severe Storms'
<br />summary. Smaller rainstorms that occurred elsewhere in Colorado during June 1952 and other months
<br />were noted in the Severe Storms summary, but the Cimarron rainstorm of June 1952 was not even.
<br />mentioned. The l00-year, l-hour rainfall for the Cimarron area is about 1.6 inches (Miller and others,
<br />1973). Thus, a rainstorm of 5.25 inches in 1.5 hours would be about 2 times greater than a l00-year
<br />event. That amount (5.25 inChes) is not much different from point-rainfall amounts of that duration in the
<br />1976 Big Thompson River basin (-12 inches in -6 hours) and several other notable large, flash-flood
<br />producing rainstorms in Colorado or the Rocky Mountain region (table 1). These extreme rainstorms
<br />include: 1921 near Pueblo, Colorado, 1935 Hale, 1938 Bear Creek near Monison, Colorado, 1948 Tucker
<br />Gulch near Golden, Colorado, 1964 Gibson Dam, Montana, 1965 Plum Creek, Colorado 1972 Rapid City,
<br />South Dakota, 1985 Cheyenne, Wyoming (Follansbee and Jones, 1922; Follansbee and Spiegel, 1937;
<br />Follansbee and Sawyer, 1948; Boner and Stermitz, 1967; Matthai, 1969; Snipes and others, 1974;
<br />Swartz and others, 1975; McCain and others, 1979; Druse and others, 1986). Rainstorms in Colorado
<br />with far less rainfall in that duration have prodUCed substantial rainfall runoff (greater than 100 cubic feet
<br />per second per square mile) including floods of 1991 in Virginia Canyon at Idaho Springs, 1991 in
<br />Stonewall Creek near Uvermore, and 1976 in Sweetwater Creek near Dotsero. Therefore, it seems very
<br />unlikely that a storm of this size (5.25 inches) occurring in the mountainous, sparsely vegetated parts of
<br />the Cimarron River basin would only produce a net rainfall runoff of only 70 cubic feet per second.
<br />
<br />Because of his interest in the accuracy and validity of the reported June 3, 1952 rainstorm, Henz (Henz
<br />Meteorological Services, Denver, Colorado, written commun., 1995) determined potential convective storm-
<br />genesis areas and storm tracks. His analysis was made without information of the actual Cimarron rain-
<br />gage location. He compiled available temperature, dew point, wind, cloud-cover, and radiosonde data for
<br />
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