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<br />,3,
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<br />HMR 55A reproduction: CWCB Freedom oflnformation Act used at the request of the National Weather
<br />Service as a formality, A W A reviewed HMR 55A for additional information and concluded that insufficient
<br />information was given to reproduce the 1995 NWS Site Specific PMP Study values, A W A used storm data
<br />from 10 extreme Colorado storms,
<br />
<br />Evaluate the use of HMR 52 including storm centering, storm orientation, shape ratio, spatial distribution that
<br />compared the 29 storms to the Colorado storms (within/without curves), Tomlinson evaluated the HMR 52 -
<br />29 storms and believes that they are different than Colorado storms and HMR 52 should not be used in
<br />Colorado, He also believes that an evaluation ofk,factor use is appropriate, Tomlinson showed a radiating
<br />profile fan map; a 3,D map of inflow wind directions into the basin centroid, He showed the cross section
<br />from the northeast to the southwest. He also showed chart of upslope / down slope gradients, K,factors: storm
<br />inflow winds are down slope and k,factors are not justified for Cherry Creek basin, A W A evaluated the
<br />meteorological consistencies; storm orientation; went over storm physics for meeting participants,
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<br />AWA used only Colorado storms - 10 storms; basin average site,specific PMP rainfall is 24 hour = 14 inches;
<br />for 72 hours 15.4 inches, 24-hour rainfall is given because this is considered the main flood results from the
<br />main portion of the storm,
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<br />Presentation bv John Henz. HDR
<br />Mr, John Henz followed the Tomlinson presentation and he discussed: (I) Review the temporal
<br />characteristics of the key Colorado extreme storms (2) Development a storm mass curve (3) Identification of
<br />key meteorological relationships, ie, "physically possible", that is the intent of the PMP defmition,
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<br />Henz presented information about the relationship of rainfall pattern, cloud layer steering winds and inflow
<br />winds, The rainfall pattern sets up major axis along the direction of cloud layer winds = +/, 10 degrees
<br />Low,level winds are 40,90 degrees to right of the cloud layer winds, The major impact on storm rainfall
<br />pattem trans,positioning defines "physically possible" scenarios in Colorado,
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<br />Second presentation bv Ed Tomlinson. A W A
<br />A W A procedure: Transpose the 10 largest Colorado storms into the Cherry Creek basin then maximized the
<br />storms; adjust the rainfall amount for changes in atmospheric moisture; enveloping for rainfall timing;
<br />centered the storm; critically aligned; kept the pattern shape for each storm, Graphics and discussion used to
<br />depict this by A W A were:
<br />. Showed the ten events and their average rainfall depths,
<br />. Showed the isohyetal map of the Penrose / Pueblo storm,
<br />. Showed map of the trans, clipped to the basin,
<br />. Showed the isohyetal of the plum creek 1965 storm
<br />. Showed trans map of 1965 storm,
<br />. Described the maximization process for the Penrose storm,
<br />. Showed the mass curve and the enveloping curve for the combined 14 Colorado storms,
<br />. Showed the mass curve and enveloping curve for the June 16th and 17'h storms,
<br />. Described the comparisons of approach between NWS and A W A,
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<br />Questions {rom the I!roup:
<br />John LiOD , FEMA Region VIII - Mr, Liou asked why historical data is always used for PMP studies, and
<br />wondered if it is always the maximum? Historical data could be changed tomorrow if we get a big storm in
<br />this area, He also expressed concems over the PMP from the standpoint of the technical definition of PMP
<br />including the word, 'theoretical' in it. The main argument being that does the methodology employed by
<br />AWA and the National Weather Service of using historical storms encompassing the range of what is
<br />'theoretically' possible, The response by A W A was that the PMP methodology had employed an adjustment
<br />factor, which was meant to account for factors that go beyond that of the observed storms in place,
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<br />Flood Protection. Water Project Planning and Finance. Stream and Lake Protection
<br />Water Supply Protection. Conservation Planning
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