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<br />File: PMPtopics799summary2.doc <br /> <br />July 22,1999 <br /> <br />105.9 degrees West are not to be considered to have meteorologically homogeneous <br />characteristics with the Cherry Creek drainage basin location. The only Colorado storm <br />used in withinlwithout curves derivation in HMR 52 (Hale, 1935) does not fall within this <br />region. This indicates an inconsistency between this study and the site-specific PMP study. <br />(Tomlinson) <br /> <br />The correct eastern boundary (for the Cherry Creek antecedent study) is 104.3 degrees <br />longitude. The group did not reach consensus. The NWS will examine a way to verify <br />this assumption. <br /> <br />16. NWS HYDRO 45, dated January 1995, states on page 75, Finding 15 that "By logical <br />deduction and extension, the conclusion is that a reasonable and prudent antecedent <br />precipitation associated with a 3- to 5-day PMP event in the region of study would be 10-20 <br />percent of the PMP within a 31-day period centered on the day of maximum precipitation in <br />the PMP storm for the region of study." Explicitly what caused the difference between this <br />10-20% and 32% provided in the Cherry Creek antecedent precipitation study? (Tomlinson) <br /> <br />USACE will investigate the possibility of revising the antecedent study and its potential <br />impacts. <br /> <br />17. Often dam regulators use the 100-year event, e.g. rainfall or snowmelt, as the antecedent <br />condition. What is the return frequency of the 32% PMP event for the Cherry Creek <br />drainage basin? If the PMP is seven times the 100-year rainfal~ that should make the <br />antecedent rainfall 32% of seven or 2.24 times the 100-year rainfall values. How does this <br />compare to the antecedent rainfall used for other Corp Projects, in particular Cochite and <br />Elephant Butte in New Mexico? (Tomlinson) <br /> <br />The USACE guidelines state an antecedent flood of 50% of the Probable Maximum <br />Flood (PMF) with a 5-day drawdown or a AaIf-'full flood control pool (which ever is <br />more appropriate) is used unless a site specific antecedent study provides other <br />information. Question was withdrawn. <br /> <br />18. Where should the boundary for orographic effects be placed? (Hammer) <br /> <br />This question will not impact the site specific Cherry Creek PMP study. The issue is <br />whether this boundary can be more accurately placed with additional study. <br /> <br />19. Determination of the average percentage of hail vs. the percentage of rainfall in a major <br />storm event should be done. Hail is almost always present in a major event Extracting the <br />hail values will reduce rainfall values and resulting runoff rates. (Greenwood Village <br />Meeting) <br /> <br />The group agreed that hail has no consequence on the final precipitation values and final <br /> <br />2 USACE reviewed its Engineer Regulation following the meeting. The Regulation states <br />full flood control pool rather than half-full flood control pool. <br />4 <br /> <br />Topics and summary of21 July 1999 Technical Meeting <br />