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I '!;, ,I i' :~ . :r , " . ,,~ J \;'~~'4..~~'J ~, - - ,II ____ ..;... ".- I I I I I I F:le: PMPtopic:s799summary.doc . 1 v124F-r July 21, 1999 1 . i This referred :to items done in Hydro 45 that were not needed for the antel:::edent study. The time constraints di~' not affect the quality of the study. Group agreed this was satisfactory answer.' ~ I 15. The region wi~hin which storms should have meteorologically homogeneous characteristics with ~orms that could occur over the Cherry Creek drainage basin is defined on p2 of the: study. The eastern most boundary of the region is 1 05.9 lL~grees West longitude. In! comparing this eastern limit with the 29 storms in derivillg th,e within/without stom! curves in HN!R .52, there is no overlap. This appears to be stating that any storms east of 105.9 degrees West are not to be considered to havle meteorologically homogeneous characteristics with the Cherry Creek drainage basin location. The only Colorado storm used in within/without curve~ derivation in HAt!R 52 (Hate, 1935) does not fall within this region. This indicates an inconsistency between this study ahd the site-specific PII,JP study. (Tomlinson) I Correct that the boundary is 104.3 degrees longitude. No consensus is reached by the group. The NWS will examine a way to verify this assumption , I v I 16. NWS HYDRO 15, dated January 1995, states on page 75, Finding 15 that "By logical deduction ahd extension, the conclusion is that a reasonable and piudent antecedent precipitation associated with a 3- to 5-day PMP event in the region of study would be 10-20 perqent of the PMP within a 31-day period centered on the day of maximum precipitation in the PMP storm for the region of study." Explicitly what caused the differente between this 10-20% and 32% provided in the Cherry Creek antecedent precipitaif.on study ? (Tomlinson) , We (USACE) will investigate the possiblity of and impacts from revising th'e antecedent snidy. ' 17. Often dam regulators u~ the 100-year event, e.g. rainfall or snowmelt, as th,e antecedent condition. What is the return frequency of the 32% PMP event for th,e Cherry Creek drainqge basin? If the PMP is seven times the 100-year rainfall, that should make the antecedent rainfall 32% of seven or 2.24 times the 100-year rainfail values. How does this compare to the antecedent rainfall usedfor other Corp Projects, in particular Cochise and Elephant Butte in New Mexico? (Tomlinson) The USACE ~delines state an antecedent flood of 50% of the PMF with a 5-day drawdown or: a half full flood control pool (which ever is more appropriate) is I I '. Topics iLI'21.JlIlyl~ ,Ttduriau Meeting . ~ ~;"~~~..Ib~~'~~~~;.+.~..: - . :.:;-.. 4 ---.......-