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FLOOD11045
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Last modified
5/17/2010 12:51:13 PM
Creation date
11/30/2007 11:08:12 AM
Metadata
Fields
Template:
Floodplain Documents
County
Arapahoe
Douglas
Stream Name
Cherry Creek Reservoir
Basin
South Platte
Title
Probable Maximum Precipitation Study for Cherry Creek Reservoir - Technical Review - Final Report Technical Addendum
Date
8/1/2003
Prepared For
CWCB
Prepared By
Applied Weather Associates, LLC
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />6 <br /> <br />increments obtained through successive subtraction. The <br />incremental values were adjusted slightly for durational <br />consistency, as were the 6-hour accumulated values, and both are <br />presented in Table 4. <br /> <br />The final step was to create a suggested PMS hourly <br />chronology as shown in Table 5. The hourly amounts are based on <br />hourly percentage contributions to the 72-hour accumulated amount <br />obtained from the sample chronology prepared in PRHMR52. other <br />chronologies consistent with the accumulations and increments of <br />Table 4 are also permissible and might be hydrologically more <br />significant. <br /> <br />3. Comments <br /> <br />Comparisons were made between some of the results of this <br />study and other storm observations or study results. The <br />comparisons are contained in Table 6. In Table 6, the references <br />to Corps of Engineers (COE) and the Bureau of Reclamation (BUR) <br />mean, respectively: Part II. Report on storm of May 30-31, 1935 <br />(MR3-28A), Corps of Engineers, u.s. Army, Missouri River <br />Division, Kansas city District, 7 July 1945 and storm study <br />MR3-28A) (Zone A) May 30-31, 1935, storm Rainfall Centers <br />Northeast of Colorado Springs, Colorado (Cherry Creek storm), <br />Flood Section, u.s. Bureau of Reclamation, Denver, May 1985. <br />Other comparisons (NOAA Atlas 2) are with NOAA Atlas 2, <br />"Precipitation Frequency Atlas of the Western United states, <br />Volume III, Colorado, National Weather Service, National Oceanic <br />and Atmospheric Administration, u.s. Department of Commerce, <br />Silver Spring, Maryland, 1973. <br /> <br />For durations of 1- and 6-hours, the maximum point values <br />from this study are exceeded by the unmaximized ("observed") <br />point values from the May 30-31, 1935, storm in eastern Colorado <br />as well as by the among-storm, 10-mi2 values from Plates Ib and <br />lIb of HMR 55A. At 24 hours, the study's maximum point value <br />exceeds the unmaximized storm values, but it continues to be <br />exceeded by the 10-mi2 values out of HMR 55A. Such results are <br />acceptable and consistent with the hypothesis that if a PMS is to <br />occur at a storm area size near or at 386-mi2, it will produce <br />less than among-storm values of PMP at storm area sizes above and <br />below 386-mi2, with the percentage departure increasing, the <br />greater the difference between the given area size and 386-mi2. <br />Since at 386-mi2, the PMS of this study exceeds the unmaximized <br />1935 Storm by about a factor of 2, it is reasonable to believe <br />that the 1935 storm maximized near 10-mi2 or less. The maximum <br />point values at 6-, and 24-hours from this study exceed the <br />largest 100-year return period precipitation in the Cherry Creek <br />Drainage by roughly seven times. <br /> <br />The reduction of the basin (386-mi2) average depths of <br />within-storm PMP from the corresponding among-storm values out of <br />
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