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",..... :,-' RECEIVED JAN 1 6 2002 COpy Review Comments Interim Report 1 Probable Maximum Precipitation (PMP) Site- Specific Study for Cherry Creek Reservoir Colorado Water Conservation Board (CWCA); RFP PDA-0133W-Cherry-Crk January 11,2002 Colorado Waler Conservation Board Task 1: Review ofNWS Site-Snecific PMP Studv fNWSSS) and Related Documents: . tn general, close attention should be paid to a rewrite of the information provided under this task. Much needed clarity could be achieved by checking the grannnar, adding references, and indicating just where in the material provided or reports discussed can one find support for the comments described. This made it not only difficult to understand the point being made and consumed a great deal. of time in trying to track down a particular comment, but also at times, I couldn't agree with a statement being made by A W A for lack of what could be some minor additional supporting data. Specific comments regarding Task 1 are: 1. Page 1, paragraph 2: Reference the NRC acceptarlce letter. 2. Page I, paragraph 3: Need references to each report referred to in this paragraph for clarity (HMR 55A, HMR52, NWSSS). The real question that A W A refers to here is not the criteria from HMR55A but with that found in HMR52 being applied to the Cherry Creek basin. What does the word "without" in the last sentence of this paragraph mean? If this is a typo, and one meant to use "with", than I don't feel that the National Weather Service (NWS) is in direct conflict with their own publication as A W A asserts. In fact, NWS took precautions in the development of their site-specific study to attempt to adjust the use ofHMR 52 techniques to make them applicable to the Cherry Creek basin. No doubt that if funding were made available, similar and further techniques as applied by NWS could be extended into the regions west of the Cherry Creek basin to address more orographic areas. 3. Page 1, paragraph 4: Need to really clarify what isbeing stated here. Is one increasing the nonorographic or orographic component or overall PMP value by 6 to 14%. Carl make a big difference. What is the reference to NOAA Climate Atlas? Is one referring to NOAA Atlas 2 for Colorado? 4. Pagel, paragraph 5: Indicate that your referring to storms used to describe the isohyetallabel determining process arid not that of developing storm sequences or isohetal pattern development. There are several rainfall distributions addressed in HMR52. 5. Page 2, paragraph 1: Should indicate where one obtained the 22% and 60% discussed in the paragraph. Need to clarify the statement that "A design PMP rainfall amount that is 60% bigger than the 'maximized' 1935 storm...". Where are you obtaining this information? What duration arid area size of the 1935 storm event are you referring to here? Every extreme storm that nature has produced Carl't provide the greatest precipitation for all durations and area sizes. This is a