Laserfiche WebLink
<br />adopted, as mentioned earlier. Using this data set and the <br />methodology which the Corps described in their 1981 report, <br />a mean of 919 cfs, standard deviation of 0.459, and a <br />station skew of -0.356 were calculated. Weighting the <br />station skew with the WRC skew of -0,1 (Appendix 6), a value <br />of 8,314 cfs was calculated, Weiqhting the station skew with <br />the Corps value of 0.0 gave a value of 8,384 cfs. With a <br />value of 0.0 (for a normal distribution) adopted for the <br />skew, a value of 10,766 cfs was calculated for the peak 100- <br />year discharge. In a conversation with personnel from the <br />Omaha branch of the Corps, no concrete explanation for this <br />inconsistency could be given, as details of the 1981 <br />calculations were not readily available. possibilities <br />apparently range from differences in historic extension <br />methodology to uncertainties in the exact data set used, It <br />should be noted, however, that the peak 100-year discharge <br />adopted by the Corps in 1981 is within the 50 percent <br />confidence interval of these values, <br /> <br />Again, for the gage near Greeley, a reanalysis following the <br />strict guidelines of Bulletin #17B of the data now available <br />was performed on two sets of data. using a regional skew of - <br />0.1. <br /> <br />Station statistics were calculated using all of the <br />available data from 1903 through 1984. Using 65 data points <br />with a mean of 1024 cfs, standard deviation of 0.458, the <br />station skew was calculated to be -0.608. The station skew <br />was weighted with a regional skew of -0.1 to produce a <br />weighted skew of -0.532. This was used to calculate a 100- <br />year peak discharge of 7,832 cfs. <br /> <br />The data was then historically adjusted to consider the <br />estimated 1904 event of 18,000 cfs as the largest in 121 <br />years, and the station statistics were again computed. The <br />calculated skew of -0.459 was weighted with the regional <br />skew of -0.1, and the 100-year peak discharge was calculated <br />as 9,140 cfs. <br /> <br />Note that the original value calculated by the Corps in 1973 <br />lies only slightly outside the fifty percent confidence <br />interval of the value calculated using all of the data, but <br />well within the fifty percent confidence interval of the <br />historically extended value. <br /> <br />Near Ft. Collins <br /> <br />This gage was established in 1975 in north Ft. Collins. It <br />is approximately 2.5 miles upstream from the mouth of the <br />Dry Creek. As only 10 years of data are on record for this <br />gage, it was not considered in updating the earlier Corps <br />studies. <br /> <br />Page 10 <br />