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<br />- 3,
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<br />Evaluate the use ofHMR 52 including storm centering, storm orientation, shape ratio, spatial distribution
<br />which compared the 29 storms to the Colorado storms (within/without curves), Tomlinson evaluated the
<br />HMR 52 - 29 storms and believes that they are different than Colorado storms and HMR 52 should not be
<br />used in Colorado, He also believes that an evaluation ofk-factor use is appropriate, Tomlinson showed a
<br />radiating profile fan map; a 3-D map of inflow wind directions into the basin centroid, He showed the croSS
<br />section from the northeast to the southwest. He also showed chart of upslope / down slope gradients, K,
<br />factors: storm inflow winds are down slope and k-factors are not justified for Cherry Creek basin, A W A
<br />evaluated the meteorological consistencies; storm orientation; went over storm physics for meeting
<br />participants,
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<br />A W A used only Colorado storms - 10 storms; basin average site,specific PMP rainfalI is 24 hour = 14 inches;
<br />for 72 hours 15.4 inches, 24,hour rainfalI is given because this is considered the main flood results from the
<br />main portion of the storm,
<br />
<br />Presentation bv John Henz, HDR
<br />Mr, John Henz folIowed 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 definition,
<br />
<br />Henz presented information about the relationship of rainfalI 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 rainfalI
<br />pattern trans,positioning defines "physicalIy possible" scenarios in Colorado,
<br />
<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 rainfalI amount for changes in atmospheric moisture; enveloping for rainfalI timing;
<br />centered the storm; criticalIy 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 rainfalI 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 17th storms,
<br />. Described the comparisons of approach between NWS and A W A.
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<br />Questions from the I!ronp:
<br />John Liou , 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 concerns over the PMP from the standpoint of the technical definition ofPMP
<br />including the word, 'theoretical' in it. The main argument being that does the methodology employed by
<br />A W A and the National Weather Service of using historical storms encompassing the range of what is
<br />'theoreticalIy' 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,
<br />
<br />John Henz, HDR - we maximize alI storms used in this study, He mentioned that not alI storms that are the
<br />'worst case' have been generated yet (ex: Big Thompson where surface dew points were extremely high),
<br />The point was that the PMP employed a maximization of surface dew points that have been observed in thea
<br />Flood Protection. Water Project Planning and Finance. Stream and Lake Protection
<br />Water Supply Protection. Conservation Planning
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