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<br />i~ c... <br /><= <br />CDS z: <br />~Q. - <br />"'0 <br />g~ c:r <br />ll'!!l - <br />!!1~ (0 <br />C- (0 <br /> 00 <br /> <br /> <br />United States Department of the Interior <br /> <br />U.S. GEOLOGICAL SURVEY <br />Box 25046 M.S. AI- i ~ <br />Denver Federal Center <br />Denver. Colorado 80225 <br /> <br />-"y. <br /> <br />IN RErLY REFER TO, <br /> <br />June 11, 1998 <br /> <br />Mr, William Miller, Project Manager <br />US Army Corps of Engineers, Omaha District <br />:Dog rams and Project Management Division <br />!!!i 5 North 17th Street <br />jt;1maha, NE 68102-4978 <br /><: <br />mear Mr, Miller: <br />C <br /> <br />Per your letter on the Cherry Creek Dam Safety Study to Mr:-Rel>er-I'MGGr-egor dated May 12, <br />1998, I am responding to your questions concerning paleoflood hydrology and risk analysis <br />(page 3), First, my paleoflood study was not done to justify reducing the Probable Maximum <br />Flood (PMF), rather it was done to provide the flood hydrometeorologists with additional <br />information about extreme flooding for streams draining the Palmer Divide, which includes <br />Cherry Creek, The enclosed manuscript "Regional Paleoflood Investigation to Assess <br />Topographic Effects of the Palmer Divide on Flooding in Eastern Colorado," which has just <br />received USGS Director's approval for submission to ASCE's Journal of Hydrologic Engineering, <br />may provide you with some additional information to assess some of the assumptions used to <br />estimate the magnitude and frequency of extreme flooding. Second, I rechecked with the Bureau <br />of Reclamation and they are now using risk assessments for dam safety, It is beyond the scope of <br />my responsibilities to recommend how you would conduct risk analysis for Cherry Creek Dam, <br />but the Bureau of Reclamation (contact Dan Levish at 303-445-3175 or Dean Ostenaa at 303- <br />445-3171) is willing to provide their paleoflood reports and become part of a dialog on this <br />important and complex issue, The level of detail in my study was not meant to be used directly <br />for a risk analysis for Cherry Creek, rather to demonstrate the feasibility and likely results a <br />detailed paleoflood investigation, I look forward to being part of technical discussion on <br />paleoflood studies risk analysis within the Corps of Engineers and to assess some of the <br />assumptions used to determine extreme flood potential such as the PMF, If you have any <br />questions, please call me at 303-236-6447, <br /> <br />wpJJ <br /> <br />Robert D, Jarrett, Ph,D. <br />Research Hydrologist <br /> <br />encl. <br /> <br />cc: D, Levish and D. Ostenaa, Bureau of Reclamation <br /> <br />/' <br />/ <br /> <br /> <br />\ <br />